quaternary geology of the weeks and cote blanche island salt domes
DESCRIPTION
PDF file of Autin, W. J., and R. P. McCulloh, 1993, Quaternary Geology of the Weeks and Cote Blanche Island Salt Domes. Unpublished report by the Louisiana Geological Survey, Baton Rouge, LATRANSCRIPT
QUATERNARY GEOLOGY OF WEEKS AND COTE BLANCHE ISLANDS SALT DOMES
Whitney J. Autin Richard P. McCulloh
Louisiana Geological Survey Box G, University Station
Baton Rouge, Louisiana 70893
submitted to
Sandia National Laboratories Underground Storage Technology Division
Division 6257 Albuquerque, New Mexico 87185-5800
CONTRACT NUMBER 87-7671
FINAL REPORT
January 1993
CONTENTS
LIST OF TABLES .................................................. iii
LIST OF FIGURES ................................................. iv
ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. v
ABSTRACT ...................................................... vi
INTRODUCTION .................................................. 1 Previous Investigations ............................................. 4 Objectives ..................................................... 5 Methods ...................................................... 5
TOPOGRAPHY AND GEOMORPHOLOGY ................................. 5
STRATIGRAPHY .................................................. 13 General Stratigraphic Units .......................................... 13 Prairie Complex, Mt. Pleasant Bluff Alloformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 Surface Veneers Covering the Prairie Complex .............................. 25 Geometry of Stratigraphic Units ....................................... 28 Stratigraphic Comparison of Weeks and Cote Blanche Islands ..................... 30
STRUCTURE ..................................................... 31 General Salt Dome Structure. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 Geomorphic Evidence of Salt-Dome Uplift ................................. 33 Fracture Patterns in Quaternary Sediment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 Fracture Development by Tectonic and Pedogenic Mechanisms .................... 35
GEOLOGIC HISTORY ............................................... 37
IMPLICATIONS AND RECOMMENDATIONS ............................... 40 Implications for Salt-Dome Utilization .................................... 40 Recommendations for Additional Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40
REFERENCES .................................................... 42
APPENDIX! .................................................... A-I
APPENDIX II B-1
ii
LIST OF TABLFS Table Page
1. Field lithologic properties of surficial stratigraphic units at Weeks Island salt dome . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
2. Field lithologic properties of surficial stratigraphic units at Cote Blanche Island salt dome. . . . . . . . . . . . . . . . . . . . . . . . . . . . . • . . . . . . . 15
iii
LIST OF FIGURES .Eigms: Page
l. The Five Islands salt-dome chain has a northwest-southeast trend across south central Louisiana ...................................... 2
2. Weeks Island is a nearly circular dome with an irregularly dissected landscape surrounded by coastal marsh .......................... 3
3. Cote Blanche Island is a nearly-circular dome with an irregularly dissected landscape surrounded by coastal marsh to the north and Cote Blanche Bay to the south ................................... 7
4. Geomorphic components of a hillslope (adapted from Rube 1969) ................ 8
5. Ideal Five Islands salt dome illustrating the relation of salt island landform components to surficial stratigraphic units . . . . . . . . . . . . . . . . . . . .. 9
6. Geomorphic features of Weeks Island .... ' .............................. 10
7. Geomorphic features of Cote Blanche Island ............................. 12
8. Typical vertical profile of the Mt. Pleasant Bluff Alloformation from Weeks Island, core W4 ....................................... 17
9. Typical vertical profile of the Mt. Pleasant Bluff Alloformation from Cote Blanche Island, core CB 17 ................................. 18
10. Weeks Island cross section, N-S line along La. Hwy 83 ...................... 19
1l. Weeks Island cross section, N-S line along SPR pipeline right of way ............. 20
12. Weeks Island cross section, E-W line .................................. 21
13. Cote Blanche Island cross section, N-S line from Intracoastral Canal ferry to Cote Blanche Landing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22
14. Cote Blanche Island cross section, E-W line ............................. 23
15. Cote Blanche Island cross section, N-S line, west side of island ................. 24
iv
ACKNOWLEDGEMENTS
This investigation was partly supported by Sandia National Laboratories (contract 87-7671) through U.S. Department of Energy funding from the Strategic Petroleum Reserve Program. Thanks to Jim Neal of Sandia Laboratories for suggesting the project and maintaining a constant interest and support throughout the project. John Falis and Tim McCue of Carey Salt provided access to Cote Blanche Island. Marshal Jackson provided access to SPR sites at Weeks Island.
The Louisiana Geological Survey (LGS) provided much of the field support. Fred Kring of LGS provided invaluable assistance with the soil coring. The illustrations were prepared by David McCraw, Robert PaulselI, and Lisa Pond under the supervision of John Snead, LGS Cartographic Manager.
Technical reviews by Chacko John, Andres Asian, Jim Neal, and William Marsalis helped to improve the manuscript.
v
ABSTRACT
Weeks and Cote Blanche Islands, part of the Five Islands of south-central Louisiana, are piercementtype salt diapirs that have been uplifted from about 17 km deep. Both domes are nearly circular in plan, with maximum elevations of approximately 52 m and 30 m above mean sea level, respectively. Dissection has produced a terrain of gullies and steep slopes.
Surficial sediment cores from both islands reveal loess and silty colluvium overlying a buried soil developed in the late Pleistocene Mt. Pleasant Bluff Alloformation, part of the regionally extensive Prairie Complex. The loess represents a single genetic unit, whose thickness variations are chiefly related to slope erosion and sediment reworking. Around the perimeter of the islands, silty colluvium has accumulated at the toe-slope position. Geomorphic evidence of salt-induced uplift includes surface lineations, linear gullies, and excessively steep land surface topography coincident with steep topography on the top of the underlying salt.
Shear fractures with high-angle average dips occur in the Mt. Pleasant Bluff Alloformation. Fracture development is best expressed in clayey sediment but was also observed in sandy and loamy sediments. Apparent conjugate shear pairs observed in cores are believed to have developed from extensional stress associated with vertical uplift of the underlying salt. Additional data on the distribution of fractures in surficial sediment would help define possible relationships to shear zones in the underlying salt.
This study suggests a complex Quaternary geologic history for Weeks and Cote Blanche Islands. Deposition of the Mt. Pleasant Bluff Alloformation in a low-relief alluvial plain and concurrent middleto-late Wisconsinan soil development occurred prior to the latest emergence of the domes. The stratigraphy of loess and colluvial silt indicates the islands were emergent during late Wisconsinan loess deposition. The degree of dissection, distribution of colluvium, and shearing of Quaternary sediment reflect continued uplift after loess deposition. Engineering applications at these and other Gulf Coast salt domes should incorporate salt dome history into stability and subsidence analyses.
vi
INTRODUCTION
The Five Islands salt domes of south-central Louisiana have been important to the mineral and
economic resources of Louisiana for centuries. Early Indian cultures used the islands as a source of salt,
for lithic materials for stone tool manufacture, and for unique plants and animals. European settlers
colonized the islands and established plantations for agricultural production, and salt production was
initiated in 1862 during the Civil War. The 20th century has marked a period of intensive salt, sulphur,
and oil and gas exploration and production. Since 1982, Weeks Island has been the site of a U.S.
Strategic Petroleum Reserve (SPR) oil storage facility.
Weeks and Cote Blanche Islands are part of the Five Islands chain (figure 1). Weeks Island, located
in Iberia Parish, is an elevated mound, with uplifted late Wisconsinan Peoria Loess covering alluvial
deposits of the Prairie Complex. Elevations reach 52 m on Weeks Island, and the surrounding landscape
is Holocene coastal marsh at elevations near sea level (figure 2). Weeks Bay is directly adjacent to the
island's southwestern edge. Cote Blanche Island, located in St. Mary Parish, also is an elevated mound,
with uplifted late Wisconsinan Peoria Loess covering alluvial deposits of the Prairie Complex. Elevations
reach 30 m on Cote Blanche Island, and near-sea-level Holocene coastal marsh surrounds the island on
its east and west sides. To the north is the natural levee of Bayou Cypremort, with elevations of 1.5 to
3 m above sea level. The southern perimeter of Cote Blanche Island is prominently marked by Red
Bluff, a wave cut bluff on the shore of Cote Blanche Bay. Red Bluff exposes up to 12 m of the Prairie
Complex covered by Peoria Loess. Both islands have a network of small gullies that dissect the upland
landscapes. The gully networks are graded to colluvial aprons that accumulate wash sediment at the bases
of the islands.
I
31 ~ (;1 t-"
o;l " ~ rii: ., g, '" g) l'< Po
~ g. s· P' ., '" ., 15 ~ ~ '" ~ ~ ~ ::1 g Po ., g '" '" '" ~ ~ [
~ ~:
~
z
IM~H~~tt~t I "" , r I ~ '.' • ~ : II . It II '.'. I , 0 C
Figure 2. Weeks Island is a nearly circular dome with an irregularly dissected landscape surrounded by coastal marsh. A linear north-south ridge forms the Devil's Backbone near the center of the island. From USGS, Weeks, Louisiana, 7.S-min. topographic quadrangle map.
3
Previous Investigations
Veatch (1899) provided an excellent overview of the development of the Five Islands by European
settlers and a summary of 19th-century views on the geologic origin of the salt domes. Vaughan (1925)
reviewed the geology of the Five Islands and cited an extensive list of literature on early theories of salt
dome development. Barton (1930) conducted the first geophysical survey of Cote Blanche Island and
provided an initial definition of the geometry of the salt stock and its relation to surrounding clastic
sediment. Atwater and Forman (1959) discussed the relation of the geometry of the Weeks and Cote
Blanche Islands salt stocks to the surrounding structures and hydrocarbon production potential. Kupfer
(1974, 1976, 1990) mapped the internal salt structure inside the Five Island salt mines and related the
structure to the development of anomalous zones (shear zones). The shear zones were inferred to be
boundaries between salt spines that were differentially uplifted to form the salt islands. He cited
geomorphic evidence for the surface expression of shear zones over the islands. Seglund (1974)
described and mapped the Weeks Island collapse-fault system and illustrated how regional tectonism
controls diapirism of the Five Islands salt dome chain. Lewis (1976) mapped surface lineations on the
Five Islands from remotely sensed data and proposed a possible correlation with salt dome structure. The
U.S. Department of Agriculture (USDA 1952, 1978) mapped the surface soils of Cote Blanche and
Weeks Islands, respectively. Autin (1984) mapped the surficial geology of Jefferson Island and related
the distribution of surficial sediment to mass movement associated with the 1980 salt mine collapse.
Autin et al. (1986) characterized the surficial stratigraphy of Avery Island and related sediment
distribution to the geologic history of Quaternary salt-dome uplift. Acres International Corporation
(1987) characterized the geology of Weeks Island relevant to SPR development.
4
Objectives
This investigation of Weeks and Cote Blanche Islands is an effort to 1) define the characteristics of
the surficial geology of the islands, 2) infer relative relationships between landscape geomorphology,
stratigraphy and structure of surficial sediment, and structural properties of the salt domes, 3) evaluate
the geologic history of the islands, and 4) relate the findings of this investigation to engineering geology
and geologic risk.
Methods
This investigation was patterned after the approach applied in a previous investigation at Avery Island
(Autin et al. 1986). The field investigation entailed reconnaissance of the islands and gathering of
pertinent background information from technical representatives of Morton and Carey Salt Companies,
the Department of Energy (DOE), and appropriate DOE technical contractors. Thirty-six, shallow
borings (5.7 to 17.1 m) were drilled across both islands. Borings were located along linear cross sections
where logistically possible. Additional borings were located to assess sedimentary sequences beneath
selected landscape features. Cores were described in the field using a qualitative sedimento10gic
pedologic procedure modified from methods established by the Soil Survey Staff (1975) in an attempt to
document lithologic and soil-stratigraphic properties discernible from the cores. The positions of
stratigraphic contacts and soil horizon boundaries identified within the cores were estimated to lO-cm
precision.
TOPOGRAPHY AND GEOMORPHOWGY
In general, the landscapes of Weeks and Cote Blanche Islands are similar, both nearly circular to
elliptical uplifted mounds surrounded by coastal and deltaic landscapes. However, specific topographic
characteristics differ and may suggest stratigraphic and/or structural properties inherent to each dome.
5
Topographic features associated with the Weeks and Cote Blanche Islands salt domes were formed
by 1) diapiric uplift, 2) sediment erosion and deposition related to local drainage network development,
and 3) possible localized subsidence. Diapiric uplift elevated late Pleistocene sediment to elevations of
up to 52 m on Weeks Island and 30 m on Cote Blanche Island (figures 2 and 3). Erosion and dissection
formed small drainage networks on both islands, which produced gully fill deposits in the larger gullies
and colluvial aprons flanking the islands. Small, upland ponds frequently associated with local subsidence
(Autin et aI. 1986) are more common on Weeks Island than Cote Blanche Island.
Topographic landscape position is a variable affecting the sequence, characteristics, and thickness of
stratigraphic units in a vertical profile at a given field location. Nomenclature and classification of the
geomorphic landscape positions along topographic transects across Gulf Coast salt domes have yet to be
developed. For the purpose of standardized description and definition of salt-dome landscapes, the
geomorphic hillslope components as applied to erosional upland landscapes (figure 4, adapted from Rube
1969) are applied to the coring sites at Weeks and Cote Blanche Islands (appendixes I and ll). This
classification facilitates a direct comparison of stratigraphic properties between landscape settings.
General salt-dome landform components and their associated stratigraphic units are adapted from prior
geomorphic research on the Five Islands (figure 5) (Autin 1984, Autin et aI. 1986).
The highest topographic positions on Weeks Island are associated with the High Salt Island landform
component of the dome (figure 6). The base of the High Salt Island is marked by a pronounced increase
in topographic slope between 15 and 23 m elevations (figure 2). Previous investigators have named this
feature the "Devil'sBackbone" (Veatch 1899; Kupfer 1916, 1990; Acres International Corporation 1981),
a generally north-south trending ridge mostly underlain by loess-covered sandy deposits of the Prairie
Complex. The Middle Salt Island landform component occurs at intermediate elevations of 8 to 23 m,
and the Low Salt Island is a lower elevation landscape. Both landforms are underlain by mostly sandy,
but locally loamy loess-covered deposits of the Prairie Complex. The boundary between these landform
6
,. : ,., , . F--':
Figure 3.
~ ~-- ..... ,- .... -,
.•.. ' ...•...• ·(4;N'.:~J:'£'· ... - «-.--Q --c~~~::~:;~ -..
- ,.-
Cote Blanche Island is a nearly circular dome with an irregularly dissected landscape surrounded by coastal marsh to the north and Cote Blanche Bay to the south. The highest elevations and steepest slopes are in the northern part of the island. From USGS, Kemper and Marone Point, Louisiana, 7.5-min. topographic quadrangle maps.
7
Divide
. j ... /
..,....... ) .c - ... ~ ... ~ '------... ~ ... ----~ ... ~ --- ... ~
Su
Su - summit Sh - shoulder Bs - backslope Fs - foots lope Ts - toeslope
Figure 4. Geomorphic components of a hillslope (adapted from Ruhn 1969).
8
•
•
Figure 5.
LSI MSI
, , ,
HSI MSI
Mt. Pleasant Blut! Allotormatlon
Older PleIstocene Deposits
,
+"-t++++"'+++++++++
++++++++++++++-+-+++
++++++++++++++++++
+++++++++++++++f-+++
+++++++++1'+++++++++
++++++++++++++++++
++++++++++++++++++++++
++++++++++++++++++++++
T++++++++++++++t++++++
++++++++++++++++ ... +++++
+++++++++++++++++t+++++
++++++++++++++++++t++++
, , , + + •
+ + +
Overwash ColluvIum ~~~J Gully Fill
. . , .. - PeorIa Loess bilil,fl ~~~~ene
• • • + ...... 0 Salt + • •
Top ot Paleosol
, , , , , , , , +
• , +
• •• • •• , . .
+++++++++Tt-+ ... f."++++++"''''
LSI
Ideal Five Islands salt dome illustrating the relation of salt island landform components to suificial stratigraphic units. Peoria Loess and local gully fill sediment veneer Mt. Pleasant Bluff alluvium beneath the High Salt Island and Middle Salt Island. Holocene marsh and overwash colluvium also occur as veneer deposits beneath the Low Salt Island.
9
Figure 6.
.. -,;(~~~~~~~~ .. - .. -- .. -......... -.... - .....----- -- _..... ...... --.--- --_ .... - --_ ...... - --- -..... -:... ::: .... -- ..... -..... -:... ~--- ..... -..... -:... -..... ..... - .- ..... ....- ..... ..... ..... - ~ -- ..... - ..... -_ ..... - -- -_ ...... -..... - -- ...... - ..... -..... .--........... _- -.......... _..... - ..... ----- ..... ~-------- - --- --- - - ...... ~ - -- - - -~ - --- - - ..... ~
Middle Salt Island II1II Colluvial Apron
I ...... d Coastal Marsh
.'1/2 Core LocaHon
W4 W~ Line of Section
wa
- o Koomelers
Base: Weeks, LA USGS 1.5-mlnllle Quadrar:o:lle
2
Geomorphic features of Weeks Island. Core locations and section lines are identified.
10
components, and the High Salt Island may in part coincide with internal shear zones within the salt
(Kupfer 1976, Acres International Corporation 1987). Small ponds possibly formed by underlying salt
dissolution occur within the Low Salt Island. The lowest landscapes are aggradational gully fIlls in
tributaries and colluvial aprons surrounding the island.
The highest topographic positions on Cote Blanche Island are associated with the High Salt Island
landform component of the dome (figure 7). The base of the High Salt Island is marked by an increase
in topographic slope between 8- and 15-m elevations (figure 3). This feature occupies the majority of
the uplifted area of the mound and has an excessively steep slope on the north and northwest sides of the
island. The High Salt Island is north of the highest elevation of the salt stock, and the excessive slope
is roughly coincident with a pronounced salt overhang in the subsurface (Atwater and Forman 1959).
The Low Salt Island is best developed on the east side of the island and exists on the south side of the
island as two distinct nose slopes plunging towards West Cote Blanche Bay to form Red Bluff and Cote
Blanche Landing. These localities are wave-cut escarpments, where West Cote Blanche Bay is actively
eroding the Lower Salt Island. The High and Low Salt island landform components are underlain by
loess-covered clayey deposits of the Prairie Complex. Published literature does not mention shear zones
at Cote Blanche Island. Lineations were mapped by Lewis (1976), but the patterns produced by aerial
photograph interpretations were considered inconclusive.
Upland ponds and gullies on both landform components are few and small. The colluvial apron
discontinuously skirts the island and is best developed in between and adjacent to the nose slopes of the
southern part of the island.
11
~ ~ -- - - ....... --...... - -- ...... ...... - ...... -~
--- ...... _ ..... -- ....... -: .- -- - ...... -: ~--.---... -~-....... -....... ....... .... -~-........ --- -..... ...... - ....... - ...... - -- - ...... - ..... -__ ......... _ ....... __ ....... .A._ ....... __ _ ............ _....... _ .............. _ ....... --- .................. - -- -- ---...... -- ...... --
~ ---- -- ....... : ----- -- ....... : ...... --:::-- -- ............ - -------....... - ....... - --- -... - ....... - --_ .... ..;;.. -- ~ .... - -..;;..-
....... -- -..:: ....... ---- -....... -..::------ -....... - ...... -:..--...... ---_...... .......~ ............. ---....... ......._....... --~ ...... - -- --- - --- --- - -- --- - -_ ...... - - --
- ..... ~ --...... -- -- - ....... ---::... ...... --- ....... -- --- ....... -- --- ..... ---....... -,. ::0:. -,_ ..... -,_.- -- -- -- __ ~- ::;:.-- _~ -_~_~~_=~ -- -- - -- -- -- -- ....... - - --...... .......- -- - ...... - -- ....... - -- - ...... --- -- ..... _ ....... -- -- ............ - -- -- --...... -- ....... -- -- ..... -- ...... --- -- -- -...... -- ..... ---- ..... - ....... --- ..... --- ...... -.... ----
...... ::!:... - --- - -- - - .-..... - -- -- - - -...... -.-... ---- - -..... -..... ---- --- ...... -- .--...... ----:..----- -- - -...... - -- ...... ---- --- - -- ~ -=--~ -.......
....... - ..... -:- ..... -:.... - -- ---- ---- -- --- ..... --~ .-- ...... _~-__ ::o:. _~-....... _.. _ ....... - ...... ......- -- --~--- -_....... -- -- ....... ------ -----:!!::...------- ....... ~ -------- -- - --- ----...... -- --- ..... - --..... -
~-- --- ..... -:...---- ~ ~ -~
LANDFORMS
I". :'. :.:1 High Salt Island -= t~f(i-llOW Salt Island
E-=- Q Gully Fill
~ Coastal Marsh
1:"':::::.:::;1 Natural levee
.CB t9 Core location
CB CB
'....-!--tB 4
o KilOmEltecs
Une of Section
Base: Kerfll9f, LA and t.'.arooo Point. LA USGS 7 .5-rrirJJte Q..jaa~!ies
,
.... - --- -- ....... _-~- ~
-~-..... -:;' ~ ---- ....... _.
~
Figure 7. Geomorphic features of Cote Blanche Island. Core locations and section lines are identified.
12
I
, I' Ii
,
~ ,~ ,
STRATIGRAPHY
General Stratigraphic Units
The surficial sediment of Weeks and Cote Blanche Islands can be divided into stratigraphic units that
are useful for correlating sample sites, interpreting relative age relationships, and inferring surficial
depositional environments and processes. Criteria used to identify individual stratigraphic units include
lithology, soil development, landscape position, superposition, geometry of individual sediment bodies,
and cross-cutting relationships.
Surficial sediment of Weeks and Cote Blanche Islands can be classified into two broad categories:
1) sediment of the late Pleistocene Prairie Complex (Autin et al. 1991) and 2) various surficial sediment
veneeers that cover the Prairie Complex (Autin et al. 1986). Regionally, the Prairie Complex is an
informal geologic unit that consists of the constructional alluvial deposits associated with the aggradation
of the landscape mapped as the Prairie Terraces (Snead and McCulloh 1984). Deposits of the Prairie
Complex represent genetically associated relict alluvial, deltaic, and coastal depositional environments,
whose evolution spans late Illinoian to late Wisconsinan. In and around the Five Islands area, the Prairie
Complex consists of fluvial deposits of the Mississippi River. These deposits were characterized and
named the Mt. Pleasant Bluff Alloformation (Autin et al. 1988) at a locality north of Baton Rouge,
Louisiana. An alloformation is a stratigraphic unit defined primarily on the basis of its boundary
unconformities. Properties such as stratigraphic position, paleosol morphology, lithology, and lithofacies
geometry observed on Weeks and Cote Blanche Islands' correlate to the features characterized at the Mt.
Pleasant locality (Autin et al. 1988). Surface veneers that cover the Mt. Pleasant Bluff Alloformation
at Weeks and Cote Blanche Islands include Peoria Loess, a basal loess mixing zone, Holocene marsh
deposits, overwash colluvium, and gully fill sediment. These units were informally characterized at
Avery Island (Autin et al. 1986). The range in lithologic properties of each stratigraphic unit present at
Weeks and Cote Blanche Islands is summarized in tables 1 and 2, and typical vertical profiles are
13
-....
L [Or,
- ~o L
TABLE 1. Field lithologic properties of surficial stratigraphic units at Weeks Island salt dome.
UNIT
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION
PEORIA LOESS
PEORIA LOESS MIXING ZONE
GULLY FILL
OVERWASHCOLLUVIUM
HOLOCENE MARSH
HORIZON SEQUENCE
-Bt-C
A-Bt-BC-C
variable
A-Bw-Cg
A-Bw-C
-C
COLOR MATRIX
IOYRS/6 IOYR 6/8
lOYR4/4 7.SYR 4/4
lOYRS/4 IOYR 6/8
IOYR 3/2 lOYR6/4
IOYR 3/1 IOYR S/3
IOYR 211 lOYR 3/1
MOTTLES
IOYR 7.SYR 2.5YR
IOYR 6/3
TEXTURE
scI to s
sil
sil, I scI, sl
sil, 1, Is
sil
sicl muckyc
CONSISTENCE
friable
friable; grading to slightly plastic or sticky
friable, slightly plastic, or sticky
friable
friable
plastic
IJ
OTHER PROPERTmS
interbeds of loamy to sandy texture; Fe and Mn stain slickensides and shear fractures zones; pedogenic in clayey beds; zones of carbonate and/or oxide cementation
infilled root and worm casts
grass roots; charcoal; Fe and Mn stains; faint stratification; crudely fining upward texture sequences
grass roots; charcoal; faint stratification
wood, grass, and reed fragments
-r-",- .~~:;:~-;"~
TABLE 2. Field lithologic properties of surficial stratigraphic units at Cote Blanche Island salt dome.
UNIT HORIZON COLOR TEXTURE CONSISTENCE OTHER PROPERTIES SEQUENCE MATRIX MOTTLES
PRAIRIE COMPLEX, UNNAMEDLOWERFAC~ -C 10YR 2/1 sicl friable laJninated; charcoal, reeds, and
10YR 3/3 organic material; fibrous (gypsum?) crystals
PRAIRIE COMPLEX, MT. PLEASANT BLUFF -Bt-C 10YR6/6 5Y c to sicl firm interbeds of loamy to sandy ALLOFORMATION 10YR 6/8 2.SYR texture; Fe and Mn stain zones;
pedogenic slickensides and shear fractores; zones of carbonate and\or oxide cementation -VI
PEORIA LOESS A-Bt-BC-C 10YR4/4 10YR 6/3 sil friable; infilled root and worm casts; 7.5YR4/4 grading to perched water at or near
slightly plastic base of unit or sticky
PEORIA LOESS variable 10YR 6/6 lOYR 7/2 sil friable, tongues; oxide stains MIXING ZONE lOYR6/8 sicl slightly plastic, and concretions
or sticky
OVERWASH A-Bt-Cg 10YR 6/1 si1 friable grass roots; charcoal; faint COLLUVIUM 10YR6/2 stratification; oxide stains
and concretions
HOLOCENE -C SB 411 7.5YR4/4 c plastic wood and grass fragments MARSH 2.5Y 4/0
--I
-,
illustrated in figures 8 and 9. Individual core descriptions are provided in appendixes I and II. Cross
sections (figures 10 to 15) illustrate stratigraphic relationships between the units.
Prairie Complex, Mt. Pleasant Bluff Alloformation
Sediment sequences of the Mt. Pleasant Bluff Alloformation were identified at all core locations on
both Weeks and Cote Blanche Islands. At Weeks Island, the Mt. Pleasant Bluff sequence is typically a
yellowish brown to brownish yellow (lOYR 5/6 to 6/8) sandy clay loam grading downward to sand with
common loamy to clayey interbeds and laminations. A typical profile at Weeks Island (W4) is illustrated
by the columnar section of figure 8. Many sites have a paleosol at the top of the unit with a -Bt-C
horiwn sequence. The sandy clay loam B horizon of the paleosol generally has friable consistent and
blocky structure. Some sites have either a minimal B horizon thickness or only a C horiwn. The
paleosol has common iron and manganese mottles and stain zones. The buried soil would likely classify
as an Alfisol or Ultisol if it were a surface soil. Alfisols and Ultisols are forest soils identified by B
horizons developed by clay accumulation from overlying surface horizons. The C horizon properties are
variable depending on texture, but sequences normally grade to a sand that is water saturated beneath the
Middle and Low Salt Island. Clayey units have pedogenic slickensides and shear fractures. Local wnes
of carbonate and/or oxide nodules occur.
At Cote Blanche Island, the Mt. Pleasant Bluff alluvium is typically a 10YR 6/6 to 6/8 clay to silty
clay loam with iron and manganese mottles, stain zones, and concretions. A typical profile at Cote
Blanche Island (CB 17) is illustrated by the columnar section in figure 9. The paleosol at the top of the
unit has a -Bt-C horizon sequence, and the B horizon generally has firm consistent and blocky structure.
16
StraHgraphlc Horizon Depth, unit m
Fill
Peoria Loess
MIxIng zone
BC -2
C 8<2A
2A -3
2Bt
-4
2Cl -5
PraIrie Complex, -Mt. Pleasant Bluff
-6 Allo formaHon
2C2 -7
-8
2C3
WEEKS ISLAND W4 - 38.1 m elevation
Dark yellowIsh brown sill loam,blocky structure with clay films; friable roots, pores, and worm burrows
Figure 8. Typical vertical profile of the MI. Pleasant Bluff A1lofonnation from Weeks Island, core W4. Note the general fining upward nature of the alluvial sequence.
17
~I
_--J
COTE BLANCHE ISLAND CB 17 • 13.7m elevation
StraHgraphlc Unll Horizon Depth m
------~ -0
Btl '-1
Peoria Loess
BI2 -2 Mixing Zone Bt 8< 2Bt ------- 2Bt1
2B12 -3
2BC -4 Prairie Complex, Mt. Plea.ant Bluff AlioformaHon
2C1
2C2
2C3
2C4
2C5 ------3C1
Prairie Complex, Unnamed Lower Facie. 3C3
-5
-6
-7
-8
-9
-10
-11
-12
-13
-14
~:~: ~·tn~~I~\~~~':('~· Dark, yellowish brown , ,'I Ito, .(.: ". .' ~ sIft loam; blockV . ''-:/~ ~~~. :.:' . ''-: structure with clay ~Ims; , . ", ,\.1' "-.~,.< .. .,. I...... ...: ,;.;;; .' fri bl Is 5' -;-";; .:.t:.. : ..... ~.~:I./~.'~? a e; roo J pores, J .... '/, .1. .... , •• ,.:, .... and worm burrows
~'!'" .... ..!.~~--: t~·., .; .. :,:
~"; ':t..-=.-1I :"L-'it-~ Brownl.h yellow silty clay loam and clay;
yellowish red and very dark brown stains and concreHons; blocky structure with clay ~Ims; friable to ~rm; light gray tongues;
_ _ _ F:e_d~~e~,= !I,=~e~!!~e! __________ .
Light gray to greenish gray clay; brownish yellow, redl.h yellow, and very dark brown mollles, .taln., and concretions; firm; calcium carbonate nodule.; .111 Interbed.; pedogenic slickensldEis; shear fracture.
Dark brown to black silty clay loam; friable; lamlnaHons; $caHered charcoal, reeds, and organic material
Figure 9. Typical vertical profile of the Mt. Pleasant Bluff Allformation from Cote Blanche Island, core CB17. Note the clayey nature of the alluvial sequence.
18
HORIZONTAL DISTANCE (melers) NORTH SOUTH o~~~ml~I~I~I~lm~~~~~~~
ELEY ATION 18 -j--=:.=-...:.c:.---'::~"":":';'--=':":':"""':'::~..:..:i.=-":':'::"-':":'L:-=-=::":""""::""--=':""':;:::=:::==,=;t18 ELEY ATION (meters) SecHon (melers)
18
14
12
10
8
6
E -~ ",.1 Marsh
I\TI!!!m!l Overwash ~ Colluvium
!:~:~:~:;%~:::I Fill
MI. Pleasanl Blull Allolormatlon
Topol Paleosol
'
Clayey Facies ;:-:, Sandy facies
Shear Fractures
location
B
I@@i;il Peoria Loess
n~Ml MIxing Zone
~~------================~--~~---
14
12
10
Figure 10. Weeks Island cross section, N-S line along Louisiana Hwy 83 (vertical exageration = 100x).
19
HORIZONTAL DISTANCE (meters) NORTH SOUTH
ELEVATION ~-r-..J...._..J....-.l--T~~~11[42 ELEVATION (meters) " (meters)
40
34
30
28 28
~ 26 26
24
22 22
20 20
18
~ 18
Fill
16 16
~ -- Gully Fill
14 14 - Peoria Loess
12 12 - Mixing Zone
10 10
Mt. Pleasant Bluff Alloformallon 8
~ Top of
6 Paleosol 6 ,
I ~_I Clayey Facies 4 , Sandy Facies
2
Figure 11. Weeks Island cross section, N-S line along SPR pipeline right of way (vertical exaggeration = 100x).
20
HORIZONTAL DISTANCE (meters) WEST o ~ a ~ ~ l~l~lal~
EAST 1800 2~
ELEV ATI ON 42 t--.1...----'--...l...-----'---'--;:::========:;-t42 ELEVATION (meters) (meters)
40 ~:~:~:~:~:~:~:~:~ Fill 40
38
36
34
32
30
28
26
24
22
14
12
10
8 Section Location
6
4
2
~ ~ $I Gully Fill
111!1!!)!!11 r~~~~a 1;t¥!;i1iij ~~~g
Mt. Pleasant Bluff Alloformation
--«\ Top of \ \' Paleosol
'
Clayey Facies .;<.~ Sandy Facies
Shear Fractures
Figure 12. Weeks Island cross section, E-W line (vertical exaggeration = lOOx).
21
38
36
34
18
16
14
6
4
2
I -=-=-j
HORIZONTAL DISTANCE (meters) NORTH o 1000 2000
SOUTH 3000
ELEV ATIO N 32lr-....... -'--'--'----'----'-'---"--.J..-.......... --'--;::::::=::=::::;t (meters)
28
26
24
20
18
16
14
12
rnlwl11;1 ~~~~ene
I;tll;mtl r~~~sa
h£IIWfU ~~~:g
Section LocaHon
~
Mt. Pleasant Bluff AlioformaHon ---« Top of
- \ \' Paleosol
'
Clayey Facies ): :;. ~~:=~ Facies
Fractures
32 ELEVATION 30 (meters)
28
26
24
22
20
18
16
14
12
10
6
4
2
OMSL
·2
·10
·12
·14·-'---------------------'-·14
Figure 13. Cote Blanche Island cross section, N-S line from Intracoastal Canal ferry to Cote Blanche Landing (vertical exaggeration = 100x).
22
ELEVATION 32
(meters)
28
26
22
18
16
HORIZONTAL DISTANCE (meters) WEST
Section Locallon
Wind ---.. ~~
600 EAST
30
16
14
12
HIIIIJ Peoria Loess 10
IlI11MI Mixing Zone
MI. Pleasant Bluff 8 Alloformallon ~ Topof - \ \ ". Paleosol
'
Clayey Facies ~ :.~ Sandy Facies 4
Shear Fractures
2 2
Figure 14. Cote Blanche Island ClOSS section, E-W line (vertiCil I exaggeration = lOOx).
23
ELEVATION (meters)
--1
--I
-I
HORIZONTAL DISTANCE (meters) NORTH o 200 600 000 1000 1200
SOUTH
ELEVATION I. +_..I...._...I...._...I...._J.-_.l..-_.L...-_.L...-_L......_L......--''''---1r I. ELEVATION (meters) (meters)
14
12
10
8
• 4
2
MSlo
·2 Secllon Locallon
."""', 1m'" ® .. Mt. Pleasant Bluff Allolonnatlon .--<\ Top 01 \ "\. Paleosol
14
·2
Clayey Facies ; , Sandy Facies
Shear Fractures
~-L ________ -=======~============~~======~L~
Figure 15. Cote Blanche Island cross section, N-S line, west side of island (vertical exaggeration = lOOx).
24
The C horizon is variable in properties depending on texture. The buried soil would likely classify as
an Alfisol or Ultisol if it were a surface soil. Clay units have pedogenic slickensides, shear fractures,
oxide mottles, and concretions, but loamy to sandy units have oxide stains. The C horizon commonly
becomes laminated with depth and contains interbeds of loamy to sandy texture. Local wnes of carbonate
andlor oxide nodules occur.
An unnamed lower facies of the Prairie Complex was identified in the lower part of CB 17 at Cote
Blanche Island beneath the Mt. Pleasant Bluff Alloformation (figure 9). A 310-cm interval was cored,
but the base of the unit was not reached. The unnamed lower facies of the Prairie Complex is a black
to dark brown (IOYR 2/1 to IOYR 3/3), laminated silty clay loam, with scattered charcoal, reeds, and
organic material, and has a friable consistent. Scattered white fibrous crystals, possibly gypsum, occur
in the upper part of the unit.
Contrasting of Mt. Pleasant Bluff Alloformation lithologies reflects an overall sandy lithofacies at
Weeks Island and a clayey lithofacies at Cote Blanche Island. Sequences of sand and gravel grading
upward to loams and sandy loams with a paleosol at the top of the sequence indicate a probable meander
belt depositional environment at Weeks Island. Laminated clays with few silty and sandy interbeds
grading upward into a clayey paleosol indicates a likely backswamp depositional environment at Cote
Blanche Island.
Surface Veneers Covering the Prairie Complex
Deposits covering the Prairie Complex on Weeks and Cote Blanche Islands occur as veneers, whose
patterns reflect local landscape response to salt-dome uplift (figure 5). Veneer deposits include Peoria
Loess and its mixing zone, Holocene marsh deposits, overwash colluvium, and gully fill deposits.
On both islands, Peoria Loess is a dark, yellowish brown (IOYR 4/4) or dark brown (7.5YR 4/4) silt
loam with pale brown (IOYR 6/3) mottles at depth. Consistent is friable, grading to slightly plastic or
sticky at the base of the soil profile where wetness increases. Perched water occurs at or near the base
25
~1
of the unit, where the loess is underlain by clayey sediment. The B horizon has moderate blocky
structure, with clay films on peds and infilled root channels. The surface soil classifies as a Memphis
Silt Loam (Typic Hapludalf, an Alfisol with a well-drained soil profile), with an A-Bt-BC-C horizon
sequence (USDA 1978).
Peoria Loess was identified at Weeks Island at all sites except W2 and W16. The land surface at W2
is artificially cut down to the underlying mixing wne to provide a flat area for the SPR fill yard. At
W16, Holocene marsh deposits lie directly on the Mt. Pleasant Bluff alluvium. Otherwise, Peoria Loess
underlies the land surface, except where buried by artificial fill, overwash colluvium, or gully fill. The
maximum thickness cored on Weeks Island was 380 cm.
Peoria Loess was identified at Cote Blanche Island at all sites except at CB II, where Holocene marsh
underlies overwash colluvium, and at CB20, where overwash colluvium lies directly on the Mt. Pleasant
Bluff alluvium. Otherwise, Peoria Loess is the first unit beneath land surface, except where buried by
overwash colluvium. The maximum thickness cored on Cote Blanche Island was 300 cm.
The Peoria Loess mixing zone has the same approximate modal thickness on both islands. Weeks
Island thickness is typically near 50 cm and Cote Blanche Island thickness is typically near 30 cm.
However, lithologic and pedologic character vary considerably. At Weeks Island, the mixing wne is
normally a yellowish brown to brownish yellow (IOYR 5/4 to 6/8) silt loam, loam, sandy clay loam, or
sandy loam. The soil horizon has a weak blocky structure and friable, slightly plastic, or sticky
consistent. The specific nature of the mixed horizon varies depending on local mixing of individual
stratigraphic units but normally grades downward into sandy material below. At Cote Blanche Island,
the mixing zone is normally a brownish yellow (lOYR 6/6 to 6/8) silt loam or silty clay loam, with light
gray (lOYR 7/2) mottles and tongues into overlying and underlying horizons. Oxide stains and
concretions are common and locally abundant. The soil horizon has a weak blocky structure and friable,
26
slightly plastic, or sticky consistent. The specific nature of the mixed horizon is variable depending on
local mixing of individual units but normally grades downward into clayey material.
The Peoria Loess mixing zone was identified at Weeks Island at all sites, except W3 and W16. At
W3, Peoria Loess is between an overlying gully fill and the underlying Mt. Pleasant Bluff sequence. In
this core, the loess has an atypical lithology either because of wetuess and/or reworking in the gully. At
W16, the silty nature of the upper horizon of the Mt. Pleasant Bluff sequence beneath Holocene marsh
suggests that it may be loess influenced. The maximum mixing zone thickness cored on Weeks Island
was SO cm.
The Peoria Loess mixing zone was identified at Cote Blanche Island at all sites, except CBS, CB 11,
and CB20. At these sites, the overwash colluvium and Holocene marsh overlie Mt. Pleasant Bluff
alluvium. The maximum mixing zone thickness cored on Cote Blanche Island was SO cm.
The Holocene marsh sediment observed at Weeks Island is a very dark gray to black (10YR 2/1 to
3/1) silty clay loam to mucky clay with fibric to hemic reed, grass, and wood fragments. Organic matter
content was field estimated to be 10 to 40 percent. At Cote Blanche Island, marsh sediment consists of
a dark bluish gray (SB 411) clay, with dark brown (7.5YR 4/4) mottles in the upper oxidized part. A
dark gray (2.5Y 4/0) clay was found in the lower reduced part that contained wood and grass fragments.
The base of the marsh sequence is a greenish gray (SBG 6/1) silty clay loam that appears to be loess
derived. At both sites, the soil profile consists only of a C horizon. A 220 cm thickness of marsh
sediment was identified at Weeks Island at W16, beneath artificial fill and above Mt. Pleasant Bluff
alluvium. A 330 cm thickness was identified at Cote Blanche Island at CBll, beneath overwash
colluvium and above Mt. Pleasant Bluff alluvium.
Overwash colluvium was identified at Weeks Island at sites W12, W14, and WIS as the first unit
beneath land surface. The unit has a maximum observed thickness of 140 cm. The unit was identified
i at Cote Blanche Island at CBl, CBS, CBII, and CB20 as the first unit beneath land surface. The unit ,
27
has a maximum observed thickness of 340 cm. On both islands, overwash colluvium is a gray (10YR
6/1 to 6/2) or dark gray to brown (10YR 3/1 to 5/3) silt loam with friable consistent, faint stratification,
grass roots, charcoal, and oxide concretions and stains. The surface soil is mapped as the Frost Silt
Loam (USDA 1978), but its range in properties classify as a Glossaqualf (a poorly drained Alfisol, with
root casts tonguing down and crossing individual soil horizons), with A-Bt-Cg horizons and as an
Ochraquept (a poorly drained incipient soil, with a B horizon typified by weak soil structure and color
alteration) with A-Bw-C horizons.
Gully fill sequences are very dark, grayish brown to light, yellowish brown (lOYR 3/2 to 6/4) silt
loam to loamy sand. Vertical sequences are crudely fining upward in texture with faint stratification,
-i grass roots, oxide stains, charcoal, and friable consistent. A gully fill sequence was identified at Weeks
I
I
-, ,
Island at W3 and W7. Gully fill is the first deposit beneath the land surface where observed, but it
possibly could be covered by or interfingered with overwash colluvium locally on the island. Two
vertically stacked fill cycles are apparent at W7. The maximum observed thickness of an individual cycle
is 560 cm. The surface soil classifies as an Ochraquept, with A-Bw-Cg horizons. Overwash colluvium
and gully fill have similar lithologies. Facies differences are because of landscape position, sediment
body geometry, and profile thickness.
Geometry of Stratigraphic Units
On both islands, relief along the contact between the uplifted Prairie Complex and overlying veneer
deposits closely parallels the present land surface topography. Local variations in the thickness and
distribution of Peoria Loess and associated veneer deposits produce localized, minor variations from this
pattern.
The Weeks Island north-south cross section along Louisiana Highway 83 (figure 10) illustrates the
stratigraphy east of the areas, with previously defined or inferred shear zones. Although the Mt. Pleasant
~ Bluff Alloformation generally consists of sandy clay loam to sand (table 1, appendix I), clayey lithologies
~ 28
occur along the southern part of the transect along with shear fractures or possible shear fractures. Peoria
Loess appears thicker on the north side of the island, possibly a function of erosional reworking of the
loess. In general, the mixing zone thickness of about 50 cm is fairly consistent where identified.
The Weeks Island SPR pipeline right-of~way cross section (figure 11) illustrates stratigraphic relations
from the High Salt Island to the Low Salt Island landform component. The transect crosses a shear zone
identified by Acres International Corporation (1987) but not identified by Kupfer (1976). The paleosol
in the Mt. Pleasant Bluff Alloformation has a complete soil profile at the highest point in the cross section
(W4). In contrast, the paleosol has been eroded to remnants of C horizons beneath lower elevations.
The boundary between the High and Low Salt Island is marked by a thick (640 cm) gully fill. A distinct
topographic break (figures 2 and 6) and change in slope of the top of salt contours (Acres International
Corporation, 1987) occur near the gully fill. Peoria Loess has a relatively uniform thickness across the
transect (figure 11), except beneath the gully fill deposit. The mixing zone is illustrated as discontinuous
since it was not recognized beneath the gully fill sequence.
The Weeks Island east-west cross section (figure 12) crosses a series of shear zones inferred by both
Acres International Corporation (1987) and Kupfer (1976). The High, Middle, and Low Salt Island
landform components are represented in this transect. Limited site access prevented detailed defmition
of surficial features along this section. Mt. Pleasant Bluff sediment is generally sandy to loamy but have
thicker clayey sequences beneath the Low Salt Island (W3 and WIO). Paleosol profiles have been
severely eroded at W3 and W5 adjacent to or on shear zones. The shear zone beneath W3 is associated
with a steep change in slope of the land surface topography and the top of salt. Site W4, the highest
accessible location on the Devil's Backbone, has a complete paleosol profile. Peoria Loess is relatively
uniform in thickness, except beneath the gully fill deposit. The mixing zone ranges from 30 cm to 50
cm thick and was identified at all locations, except beneath the gully fill sequence.
29
On Cote Blanche Island, the Mt. Pleasant Bluff lithology is distinctly clayey relative to Weeks Island
because of facies variations. Weeks Island is within or near an ancestral Mississippi River meander belt;
whereas, Cote Blanche Island has uplifted, mostly backswamp deposits. Some sites at Cote Blanche
either grade to sand or have sandy interbeds. However, Barton (1930) affirmed the overall clayey nature
of its surficial cover.
The north-south section across Cote Blanche Island (figure 13) extends from the ferry landing on the
north side to the highest topographic elevation, then down to Cote Blanche Landing. Relief along the
contact between the Mt. Pleasant Bluff Alloformation and overlying veneer deposits closely parallels the
present land surface topography. Peoria Loess thickness decreases on steeper slopes and reaches a
maximum at the upper shoulder slope and lower back slope positions. Based on an assumed initially
uniform loess thickness across Cote Blanche Island, erosion and redistribution of loess appear to be the
likely cause of the thickness variations. Mixing zone thickness averages less than 50 cm and its pattern
follows Peoria Loess thickness trends. In general, loess mixed with clayey paleosols should produce a
thinner mixing zone than loess mixed with sandier paleosols (Schumacher et al. 1988). The east-west
section across Cote Blanche Island has similar patterns (figure 14).
The north-south section along the western part of Cote Blanche Island crosses the mouth of a linear
gully that produces a conspicuous lineation (figure 15). This lineation was not mentioned in previous
literature but was mapped by Lewis (1976). The top of the Mt. Pleasant Bluff Alloformation is slightly
lowered on the south side of the gully relative to the north side. Peoria Loess is thickest within the gully;
however, the mixing zone was not recognized beneath the loess where the loess was buried by colluvium
,--1 at CBl.
Stratigraphic Comparison of Weeks and Cote Blanche Islands
Although Weeks and Cote Blanche Islands have similar geomorphic properties, the surficial
=l stratigraphy illustrates differences in their geologic characteristics. Although both diapirs have uplifted I
30
the Mt. Pleasant Bluff Alloformation, Weeks Island has uplifted mostly sandy lithofacies, and Cote
Blanche Island has uplifted mostly clayey lithofacies. This difference has produced a thicker loess mixing
zone at Weeks Island and may be a factor in the higher topographic elevations and greater number of
solution ponds on Weeks Island. Reduced thickness of the Mt. Pleasant Bluff paleosol (interpreted to
reflect erosional stripping) and complex gully fill sequences coincide with an interpreted subsurface shear
zone on Weeks Island.
STRUCTURE
General Salt Dome Structure
The salt stock at Weeks Island has a nearly circular shape in plan view and reaches a subsea elevation
of -13 m in its shallowest portion (Stipe and Spillers 1960, 1962; Waguespack 1983). The top-of-salt
contours of Acres International Corporation (1987, figure 5.22) are in general agreement with previous
structure contour maps. The upper surface of the dome lacks cap rock and is extremely irregular. The
surface topography is also rugged, with nearly vertical slopes in places (Vaughan 1925) and 18-24 m of
relief (Van Lopik 1955). However, the surface topography shows little correspondence to the top of the
salt (Harris 1908). Vaughan (1925) attributed the rugged surface topography at Weeks Island partly to
dissection and partly to salt dissolution, with dissolution inferred from the variability of the dips of
surface strata on the island. No shear fractures or faults within the surface sediment at Weeks Island have
been described in the literature. The overall sandier lithofacies may mask recognition of such features.
Cote Blanche Island is characterized by a salt stock that reaches -91 m in its shallowest portion (Stipe
and Spillers 1960, 1962; Waguespack 1983). The upper surface of the salt appears to lack cap rock;
although, one of the borings reported by Barton (1930) on the east flank of the dome penetrated 8.5 m
of limestone above the salt at 500 m deep. The outline of the salt stock shows a NNW-SSE elongation
in the shallow subsurface with pronounced overhang to the north, but below 4,270 m the outline is nearly
31
circular (Atwater and Forman 1959). Below 3,660 m, the deep structure shows a few radial faults
restricted to the north flank of the dome (Atwater and Forman 1959).
Atwater and Forman (1959) infer the same overall style of salt uplift at Weeks and Cote Blanche
Islands. Below 3,660 m, the deep structure of the Weeks Island salt stock shows many radial faults. The
number, location, and stratigraphic position of unconformities within the subsurface sediment at Weeks
Island indicate differential movement of spines. Thickness distributions of the surrounding sediment
indicate shifting apexes of domal crests through time (Atwater and Forman 1959).
Surface and subsurface evidence indicates that the apexes of the domal crests of the Cote Blanche
structure have also shifted laterally through time. Barton (1930) inferred differential uplift of separate
salt spines from stratigraphic evidence of alluvium filling a sinkhole. The sediment interpreted as fill
corresponds to the clayey lithofacies of the Prairie Complex of this investigation. Barton (1930)
considered two areas of localized clay thickening as indicators of episodic solution and cavity fill
associated with two salt spines. Barton's (1930) cross section depicts an apparent truncation of gravel
and "gumbo" strata against the clay masses. Barton (1930) estimated the maximum thickness of the clay
at 137+ m, and inferred localized solution of 92+ m of salt accompanied by slumping. Atwater and
Forman (1959) also inferred differential uplift of discrete masses within the salt stock from deep-
subsurface, stratigraphic thickness data and speculated that late differential uplift in the northern part was
responsible for a density inversion that resulted in the pronounced overhang.
Surface faults at Cote Blanche Island have been mentioned only in connection with Red Bluff. Harris
(1908) considered the faults "noteworthy" (p. 85); Vaughan (1925) mentioned a fault at the west end,
downthrown to the northwest but gave no estimate of the displacement. Kupfer (1986) noted the presence
of small rollover growth faults with displacements of less than 60 cm. A reconnaissance of Red Bluff
during this investigation has indicated apparent conjugate shear fractures and faults with minor, cm-scale
displacements.
32
Geomorphic Evidence of Salt-Dome Uplift
Kupfer (1974, 1976, 1990) mapped the internal salt structure inside the Five Island salt mines and
related internal salt structure to the development of anomalous zones (shear zones). The shear ZOlles were
inferred to be boundaries between salt spines that were differentially uplifted to form the salt islands.
He cited geomorphic evidence for the surface expression of shear zones over the islands along trends
mapped within the underground mines. Lewis (1976) mapped surface lineations on the Five Islands from
remotely sensed data and proposed a possible correlation with salt dome structure. Autin et aI. (1986)
characterized the surficial stratigraphy of Avery Island and related shear fractures in cores and exposures
to diapiric uplift. The boundary between the High and Low Salt Island landform components near the
Devil's Backbone, the highest topographic position on Weeks Island, has been interpreted to be coincident
with internal shear zones within the salt (Kupfer 1976, Acres International Corporation 1987).
Fracture Patterns in Quaternary Sediment
The distribution of observed shear fractures in cores shows no conclusive relation to potential surface
lineaments discernible in the topography at either Weeks or Cote Blanche Island. The drilling programs
conducted for this investigation did not sample in the northwestern quadrant of either island. Slickensided
fractures, interpreted to be structural in origin, were logged where encountered. Pedogenic slickensides
on subangular blocky peds, interpreted to be associated with shrink-swell processes during soil evolution,
also were logged.
At Weeks Island, shear fractures were observed in cores in the southeastern quadrant of the island,
which includes two relatively straight ridges trending N 52 0 E and N 2 0 E that join at the southeastern
edge of the linear depression containing Sandy Bottom Pond (figure 2). The ridges are near core
localities where shears were identified, but the ridges were not cored. The most striking linear
topographic features at Weeks Island are the above-mentioned linear depression and the parallel ridge that
33
forms Devil's Backbone to the west. Both ridges have an average trend of N 17° E. The southern ends
-, of both features were cored, and neither core had shear fractures.
Fractures are typically 45° or higher angle. They are generally similar to but much less abundant
and less well developed than those at Cote Blanche Island, apparently because of the overall sandier
sediment at Weeks Island. Fractures are better developed in more clayey sediment and were observed
in clay to silt loam textures at Cote Blanche Island. Fracture surfaces show slickensides oriented parallel
to the dip of the fracture planes but tend to be less conspicuous than at Cote Blanche Island, except in
more clayey sediment. No suggestion of conjugate shear pairs was identified in: the Weeks Island cores.
Manganese oxide is present on fracture surfaces but is sparse in occurrence. At W16, powdery white
carbonate occurs as "veins" up to 1 cm thick along fracture surfaces in clayey sediment.
Cote Blanche Island lacks distinct surface topographic lineaments. Topographic ridges are not
typically straight, and apparently straight depressions are discontinuous. Two potential straight,
discontinuous lineaments trend N 74 ° W and N 40° E but occur in the unsampled northwestern quadrant
of the island (figures 3 and 7). However, the N 40° E feature extends near CB2, which cored sheared
sediment of the Prairie Complex. In general, sheared sediment was cored throughout the southern half
of Cote Blanche Island and was observed in outcrop at Red Bluff along the southern edge of the island.
In the northeast part of the island, cored sediment with shear fractures was identified only at CB12 (figure
13).
On Cote Blanche Island, most fractures are 45° or higher angle; though, some lower than 45° angles
were observed (for example at CB2). Fracture surfaces typically have slickensides oriented parallel to
the dip of the fracture planes. Shears occur in many places as apparent conjugate pairs. At CBI7, one
of the two apparent orientations of the conjugate pair is preferred. In the CBl5 core, some intersecting
shear fractures in the depth interval 420-485 cm could be verified as actual conjugate pairs because the
34
firm clay pieces separated easily without deformation, and visual inspection confirmed that some of the
opposite dipping shears have the same strike.
Fractures are better developed in clayey sediment but were observed in textures ranging from clay
to silt loam. At CBI8, fractures extend into the overlying loessal mixing zone and are expressed as
uneven, near-vertical parting surfaces, along which the sediment separated spontaneously into discrete
pieces on removal fro91 the core barrel. At CBI9, similar partings characterize the middle portion of
the loess interval. It appears that such partings characterize siltier sediment and are transitional with the
more typical shear fractures developed in more clayey sediment. Some fracture planes (for example at
CB2 and CB4) show a longitudinal fluting that is larger than but parallel to slickensides. The flute-like
ridges and swales occur in clay and are 1-2 cm wide with a maximum amplitude of about 1 cm.
Manganese oxide is generally present though sparse on fracture surfaces. At a few places, manganese
and iron oxides are heavily concentrated in densely fractured zones. Other mineralization types less
frequently associated with shear fractures are calcite, which occurs with manganese and iron oxides at
CB7, powdery carbonate at CB 17, possible gypsum in CB4, and a powdery crust of salt at CB2. These
features occur only in the more clayey sediment.
Fracture Development by Tectonic and Pedogenic Mechanisms
Shrink-swell slickensides were identified on subangular blocky peds and interpreted to have formed
by soil development. Pedogenic slickensides are commonly associated with Vertisols, a soil order
dominated by highly expansive shrink-swell clays (Buol et aI. 1973, Ahmad 1983). Slickenside
development in Vertisols is typified by high smectite content, commonly alkaline parent material, and
seasonal soil moisture deficiency.
Pedogenic slickensides are differentiated from tectonic shear fractures by the following criteria.
Pedogenic slickensides commonly are variable in scale, some only a few cm in length, others greater than
50 cm long (Blodgett 1991). The geometry of the larger scale pedogenic slickensides is typically
35
expressed as concave-upward bowls and/or dome structures (Buol et aI. 1973, Ahmad 1983), which are
"-I unlikely to produce preferred orientations. Criteria identified in clayey paleosols of Pliocene age in west
Texas and Mexico (Gustavson 1991) include 1) mulch or nutty soil structures, 2) near-vertical desiccation
cracks, 3) intersecting fractures with slickensides that bound smaller soil structural aggregates, 4)
manganese oxide or hydroxide filaments on fracture faces, and 5) calcium carbonate films or nodules.
Tectonic shear fractures are commonly several centimeters long, typically produce slickensided surfaces
(especially in clayey sediment), and may occur as conjugate pairs. Slickensides of obvious pedogenic
origin are smaller scale, with ragged, multi-oriented ped faces that terminate against each other. Over
salt domes, the orientation of conjugate pairs should reflect the effect of extension in the sediment above
the salt mass produced by vertical diapiric motion (Autin et aI. 1986). Tectonic shear fractures have been
identified in various soil textures (Autin et aI. 1986); whereas, pedogenic slickensides are common only
in clayey, high-shrink-swell soils (Buol et al. 1973, Ahmad 1983).
The distinction between large-scale pedogenic slickensides and tectonically induced shear fractures
is not simple, especially when working from core samples. For some applications, the three-dimensional
geometry of fracture patterns and statistically significant orientation data may be required to separate
fractures associated with tectonic and pedogenic processes.
The origin of fractures in surficial sediment above salt domes is complex; however, the distribution
is ubiquitous. The best criteria to distinguish tectonic shear fractures from fractures of other origins are
fracture pattern geometry, distribution of fractures across a dome, the stratigraphic unit and position
where fractures occur within a vertical sequence, and the physical properties of the lithofacies exhibiting
__ ~ fracture development. However, the systematic collection of such data is likely to be difficult.
36
GEOLOGIC IDSfORY
A definitive summary of the Quaternary geologic history of Weeks and Cote Blanche Islands has yet
to be synthesized. The generalized Quaternary geologic evolution of Avery Island (Autin et aI. 1986)
closely parallels that of Weeks and Cote Blanche Islands, so the results of this investigation can be
combined with results from Avery and Jefferson Islands (Autin 1984) to develop a general geologic
history applicable to the Five Islands. The relative sequence of events outlined in this section derives
from such an integration and provides a hypothesis for the geologic evolution of the Five Islands during
Quaternary time. Additional data are necessary to evaluate specific details of the proposed chronology.
The geologic development of the Five Islands began with the deposition of the Louann salt as part
of the Mesozoic sedimentary sequence of the Gulf Coast. Sedimentary loading during the Cenozoic
initiated the diapirism in south-central Louisiana probably during Eocene-Miocene time, according to the
crustal stress model of Nunn (1985). Whether individual spines developed at that time or whether the
salt was previously exposed through older paleosurfaces are questions that presently have not been
resolved.
The Geologic Map of Louisiana indicates different geologic ages for the surficial sediments of the
Five Islands (Snead and McCulloh 1984). However, Autin et aI. (1986) identified the Prairie Complex
beneath Peoria Loess at Avery Island in contrast to the Intermediate Terraces designation of the Geologic
Map of Louisiana (Snead and McCulloh 1984). This investigation confirms that the Prairie Complex
overlies the Weeks and Cote Blanche Island salt stocks to indicate late Pleistocene uplift of both domes.
Van Lopik (1955) recognized the surficial sediment of the Five Islands as uplifted remnants of the Prairie
Terrace to suggest the most recent uplift of the Five Islands chain of domes can be generally regarded
as late Quaternary.
Pre-Prairie Complex Quaternary sediment was deposited in the area; however, the relationship of
diapiric uplift to the older sediment is uncertain. The borings collected during this investigation did not
37
penetrate pre-Prairie Complex sediment. The Prairie Complex is generally considered Sangamonian to
late Wisconsinan in age (Autin et al. 1991). The features described in the Prairie Complex at Weeks and
Cote Blanche Islands indicate deposition on a low-to-moderate energy flood plain, with the coarse-grained
facies accumulating mostly in a meander belt environment and the finer grained facies accumulating
mostly in a low-energy flood basin environment. Regional stratigraphic relations indicate an ancestral
Mississippi River meander belt is preserved from the Marksville area, south through Opelousas and
Lafayette, and continuing to the vicinity of Jefferson, Avery, and Weeks islands (Autin et al. 1991). A
transition to backswamp deposition apparently occurs between Weeks and Cote Blanche Islands.
The Five Islands may have adjusted to more than one period of loading during the Quaternary and
also may have experienced periods of accelerated dissolution as the salt stocks interacted with aquifers.
The sandy Prairie Complex lithofacies at Weeks Island should favor the development of an active, high-
solute content dissolution plume, and the clayey lithofacies at Cote Blanche should slow salt stock
dissolution. Although previous topographic mounds may have been present, the latest uplift of the Five
Islands began sometime during the Wisconsinan, possibly contemporaneous with the latter part of Prairie
Complex deposition. Dissection of the islands was also initiated at this time, along with the infilling of
gullies with sediment. Paleosol properties at the top of the Mt. Pleasant Bluff Alloformation indicate that
the Prairie Complex experienced much of its pedogenic development prior to this time. Uplift after Mt.
Pleasant Bluff paleosol development is supported by the following lines of evidence: 1) a complete
paleosol profile has been uplifted onto the High Salt Island landform component of Weeks Island; 2)
the properties of the uplifted paleosol on Weeks and Cote Blanche Islands are comparable to features
identified on the Prairie Complex in areas unaffected by uplift (Autin et al. 1986, 1988, 1991); 3)
variations in paleosol properties across both domes are related to lithofacies variations in the Mt. Pleasant
Bluff Alloformation; and 4) many tectonic shear fractures in the Mt. Pleasant Bluff clayey lithofacies
d post-date paleosol development. '"1
38
Peoria Loess draped the landscapes of the Five Islands. Loess thickness, the development of well
drained Memphis soils, the inferred history of loess reworking and colluviation, and local thickness
variations of the loess deposit overlying the Prairie Complex suggest the islands were emergent during
the time of loess deposition. The deposition of Peoria Loess is generally considered a late Wisconsinan
event (Miller et aI. 1986, Otvos 1975). Uplift of the island continued during and after loess deposition.
Overwash colluvium accumulated along the perimeter of the island soon after loess deposition ceased.
Fracturing of the loess occurred during its pedogenic development. Reworking of loess from higher to
lower elevations resulted in the exposure of sandy facies of the Prairie Complex at Weeks Island on the
High and Middle Salt Island, accumulation of gully fill sediment, and the colluvial apron in the drainage
network and distal fringe of the islands.
Salt-dome uplift continued into the Holocene as Peoria Loess deposition ceased; salt dissolution also
was a continuing process. Deposition of overwash colluvium and gully fill sediment continued.
Holocene marsh deposits aggraded in low-lying areas along the edges of the island.
The Five Islands are still dynamic with respect to their geomorphic and tectonic processes. Dissection
of the higher parts of the landscape continues today, along with the accumulation of overwash colluvium
and gully fill sediment. Marsh sediment still accumulates along the fringes of the overwash colluvium.
The Five Islands are presently experiencing uplift, and the salt stocks are experiencing active dissolution
along their crests and upper flanks.
39
IMPLICATIONS AND RECOMMENDATIONS
Implications for Salt-Dome Utilization
Diapiric uplift of Weeks and Cote Blanche Islands has continued since the late Pleistocene, is
probably still active at present, and periods of tectonic and geomorphic instability are possible in the
future. The Five Islands have been actively uplifting since the deposition of the Mt. Pleasant Bluff
AIloformation, an aggradation sequence considered to have culminated sometime in the late Wisconsinan
(Autin et al. 1988, Autin et al. 1991). Study of Quaternary deposits overlying salt domes implies that
discrete periods of surface uplift, such as identified in this study and at Avery Island (Autin et al. 1986)
and periods of episodic subsidence such as identified at Jefferson Island (Autin 1984), can be considered
__ : common where Gulf Coast salt domes pierce surficial sediment. The degree and rate of landscape
modification by salt domes have important implications toward safe utilization of salt domes for mineral
resource extraction and engineering design of geostorage facilities.
Recommendations for Additional Investigations
The limited amount of conclusive data from the analysis of shear fractures at Weeks and Cote Blanche
Islands resulted from 1) restrictions on the distribution of core locations because of vehicle inaccessibility
and denial of permission to enter property of Morton Salt, Inc., 2) the limited number of exposures on
both islands, and 3) the coring process used in the investigation. The following suggestions could aid
in designing an investigation that can yield more substantial results.
If subsequent investigations of the surficial geology of Weeks Island are conducted, closely spaced
borings aligned in transects across surface lineations and across the surface expression of postulated shear
zones may yield more definitive results. Coring at natural or minimally disturbed locations also would
be more beneficial than localities heavily impacted by cut and fill associated with industrial development.
Existing exposures at Weeks and Cote Blanche Islands are minimal and yielded limited information
on shear fracture distributions. Exposures at an abandoned pit on Weeks Island, a small sinkhole that
40
developed on Weeks Island, an abandoned pit on Cote Blanche Island, and at Red Bluff on Cote Blanche
Island were visited in the reconnaissance phase of this investigation. Shear fractures were observed at
Red Bluff, but they are not abundant enough to warrant systematic orientation measurements. Additional
field descriptions of exposures in the gullies of Weeks Island also may yield insightful information on
shear fracture distributions. The orientation data reported by Autin et al. (1986) were based on an
excellent exposure that coincides with the position of a documented shear zone. It may be possible to
gather similar data on Weeks Island by placing backhoe trenches at carefully selected locations where
shear fractures have been identified by additional coring.
The small sinkhole that developed on Weeks Island in 1992 is analogous to the sinkholes that
developed on Avery Island in 1986. Although the development of such features have occurred naturally
on the Five Islands (Autin 1984, Autin et al. 1986), the proximity of these sinkholes to engineered
caverns and possible shear zones are a point of concern. It is possible that the creation of salt caverns
accelerates the tendency for the formation of natural collapse sinkhole structures if sufficient stress already
exists in the overburden. Additional data on the occurrence and distribution of subsidence and collapse
features at the Five Islands salt domes could explain the significance of this tendency and provide
information relevant to improved cavern development in salt domes.
41
i ~
REFERENCFS
Acres International Corporation 1987. Weeks Island Strategic Petroleum Reserve geologic site characterization report. Sandia National Laboratories. Contractor Report SAND87-7111.
Ahmad, N. 1983. Vertisols in Wilding, L. P., Smeck, N. E., and Hall, G. F. eds. Pedogenesis and Soil Taxonomy: II. The Soil Orders. Elsevier Science Publishers, Amsterdam, The Netherlands. p. 91-123.
Atwater, G. I., and Forman, M. J. 1959. Nature and growth of southern Louisiana salt domes and its effect on petroleum accumulation. American Association of Petroleum Geologists Bulletin. v. 43. no. 11. p. 2592-22.
Autin, W. J. 1984. Geologic significance of land subsidence at Jefferson Island, Louisiana. Gulf Coast Association of Geological Societies Transactions. v. 34. p. 293-309.
Autin, W. J., McCulloh, R. P., and Davison, A. T. 1986. Quaternary geology of Avery Island, Louisiana. Gulf Coast Association of Geological Societies Transactions. v. 36. p. 379-90.
Autin, W. J., Davison, A. T., Miller, B. J., Day, W. J., and Schumacher, B. A. 1988. Exposure ofIate Pleistocene meander-belt facies at Mt. Pleasant, Louisiana. Gulf Coast Association of Geological Societies Transactions. v. 38. p. 375-83.
Autin, W. J., Burns, S. A., Miller, B. J., Saucier, R. T., and Snead, J. I. 1991. Quaternary geology of the Lower Mississippi Valley in Morrison, R. B., ed. Quaternary non-glacial geology of the conterminous United States. Geological Society of America, Geology of North America. v. K-2. p. 547-82.
Barton, D. C. 1930. Late recent history of Cote Blanche salt dome, St. Mary Parish, Louisiana. American Association of Petroleum Geologists Bulletin. v. 20. no. 2. p. 179-85.
Blodgett, R. H. 1991. Distribution of Phanerozoic vertic paleosols-An independent test of paleoclimatic models. Geological Society of America Abstracts with Programs. v. 23. p. A343.
Buol, S. W., Hole, F. D., and McCracken, R. J. 1973. Soil Genesis and Classification. Iowa State University Press. Ames. 360 p.
Gustavson, T. C. 1991. Buried vertisols in lacustrine facies of the Pliocene Fort Hancock Formation, Hueco Bolson, west Texas and Chihuahua, Mexico. Geological Society of America Bulletin. v. 103. p.448-46O.
Harris, G. D. 1908. Rock salt: Its origin, geological occurrences and economic importance in the state of Louisiana. Report of 1907, Bulletin No.7. Baton Rouge. Louisiana State University, State Experiment Station, Geological Survey of Louisiana. 259 p.
Kupfer, D. H. 1963. Structure of salt in Gulf Coast salt domes. First Symposium on Salt, Northern Ohio Geological Society. Cleveland. p. 104-23.
42
Kupfer, D. H. 1974. Boundary shear zones in salt stocks. Fourth Symposium on Salt. Northern Ohio Geological Society. Cleveland. p. 215-25.
Kupfer, D. H. 1976. Shear zones inside Gulf Coast help to delineate spines of movement. American Association of Petroleum Geologists Bulletin. v. 60. no. 9. 1434-47.
Kupfer, D. H. 1986. Physiography of Louisiana Salt Domes (The Five Islands). Geological Society of America Centennial Field Guide-Southeastern Section. p. 431-434.
Kupfer, D. H. 1990. Anomalous features in the Five Islands salt stocks, Louisiana. Gulf Coast Association of Geological Societies Transactions. v. 40. p. 425-37.
Lewis, A. J. 1976. Detection of lineations over Louisiana salt domes using remotely-sensed data in Martinez, J. D. et al. An investigation of the utility of Gulf Coast salt domes for the storage or disposal of radioactive wastes. Louisiana State University Institute for Environmental Studies. p. 175-89.
Miller, B. J., Day, W. J., and Schumacher, B. A. 1986. Loess and loess-derived soils in the Lower Mississippi valley. American Society of Agronomy. Guidebook for soils-geomorphology tour. 144 p.
Otvos, Jr., E. G. 1975. Southern limits of Pleistocene loess, Mississippi valley. Southeastern Geology. v. 17. p. 27-38.
Nunn, J. A. 1985. State of stress in the northern Gulf Coast. Geology. v. 13. p. 429-32.
Rube, R. H. 1969. Quaternary Landscapes in Iowa. Iowa State University Press. Ames. 255 p.
Schumacher, B. A., Lewis, G. C., Miller, B. J., and Day, W. J. 1988. Basal mixing zones in loesses in Louisiana and Idaho. I. Identification and characterization. Soil Science Society of America Journal. v. 52. p. 753-58.
Seglund, J. A. 1974. Collapse-fault systems of Louisiana Gulf Coast. American Association of Petroleum Geologists Bulletin. v. 58. no. 12. p. 2389-97.
Snead, J. I., and McCulloh, R. P., compilers 1984. Geologic Map of Louisiana. Louisiana Geological Survey. Baton Rouge. scale 1 :500,000.
Soil Survey Staff. 1975. Soil Taxonomy. Soil Conservation Service. Agricultural Handbook 436. 754 p.
Stipe, J. C., and Spillers, J. P. eds. 1960. Salt Domes of South Louisiana. New Orleans Geological Society. Volume 1. 145 p.
Stipe,1. C., and Spillers, J. P. eds. 1962. Salt Domes of South Louisiana. New Orleans Geological Society. Volume 2. 107 p.
United States Department of Agriculture. 1978. Soil Survey of Iberia Parish, Louisiana. 67 p.
43
. 'I
United States Department of Agriculture. 1952. Soil Survey of St. Mary Parish, Louisiana. 45 p.
Van Lopik, J. R. 1955. Recent geology and geomorphic history of central coastal Louisiana: Trafficability and navigability of delta-type coasts, trafficability and navigability of Louisiana coastal marshes. Technical Report No.7. project no. N7 ONR 35608, Task Order NR 388 002 of the Office of Naval Research. Baton Rouge. Louisiana State University. 88 p.
Vaughan, F. E. 1925. The Five Islands, Louisiana. American Association of Petroleum Geologists Bulletin. v. 9. no. 4. p. 756-97.
Veatch, A. C. 1899. The Five Islands, Louisiana in Harris, G. D., and Veatch, A. C. eds. A preliminary report on the geology of Louisiana. Louisiana State University Experiment Station. Geology and Agriculture. pt. 5. Special Report no. 3. p. 209-62.
Waguespack, S. J. ed. 1983. Salt Domes of South Louisiana. New Orleans Geological Society. Volume 3. 142 p.
44
APPENDIX I
CORE DESCRIPTIONS FROM WEEKS ISLAND
, i ,
-,
WI -- Weeks Island, Louisiana; core is from an artificial flat on the shoulder slope of the island; elevation is 32.0 m (lOS ft); slope is 0 - I per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 200 em
-- 0 - 200 cm -- Light olive brown (2.5Y S/4) silt loam; friable consistent; soil clasts; gravel; organic matter; abrupt boundary.
PEORIA LOESS - 200 - 300 em
BC -- 200 - 240 cm -- Dark brown (7.SYR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; common pores; root traces; gradual boundary.
C -- 240 - 300 cm -- Dark brown (7.SYR 4/4) silt loam; friable consistent; common pores; root traces; clear boundary.
PEORIA LOESS MIXING ZONE - 300 - 330 em
C&2C -- 300 - 330 cm -- Yellowish brown (lOYR S16) loamy sand; very friable consistent; common pores; very pale brown (lOYR 7/3) worm casts filled-with sand; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 330 - 970 em
2Cl -- 330 - 460 cm -- Reddish yellow (SYR 6/6) sandy loam; very friable consistent; very pale brown (lOYR 7/3) sand stringers; clear boundary.
2C2 -- 460 - SSO cm -- Very pale brown (lOYR 7/4) medium sand; loose consistent; clear boundary.
2C3 -- SSO - 800 cm -- Yellowish red (SYR S16) sandy loam; very friable consistent; scattered very dark brown (lOYR 2/2) stains; clear boundary.
2C4 -- 800 - 970 cm -- Yellowish red (SYR S16) medium to coarse sand; very friable consistent; scattered very dark brown (lOYR 212) stains.
A-2
W2 -- Weeks Island, Louisiana; core is from an artificial flat on the back slope of the island; elevation is 21.3 m (70 ft); slope is 0 - 1 per cent; approximately 3 m of natural soil removed from site; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 30 em
-- 0 - 30 cm -- Pale yellow (5Y 7/3) sandy clay loam; friable consistent; soil clasts; gravel; charcoal; abrupt boundary.
PEORIA LOESS MIXING ZONE - 30 - 50 em
C&2Bt -- 30 - 50 cm --Reddish yellow (7.5YR 6/6) sandy clay loam; weak, fine, angular blocky structure; friable consistent; common pores; shear fractures; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 50 - 680 em
2Btl -- 50 - 110 cm -- Reddish yellow (7.5YR 6/6) sandy clay loam with common, medium, distinct brownish yellow (lOYR 6/8) mottles; weak, medium, subangular blocky structure; friable consistent; clay films on ped surfaces; common pores; clear boundary.
2Bt2 -- 110 - 150 cm -- Very pale brown (10YR 7/4) loamy sand with common, medium, distinct brownish yellow (lOYR 6/8) mottles; weak, medium, subangular blocky structure; friable consistent; clay films on ped surfaces; common pores; gradual boundary.
2Bt3 -- 150 - 170 cm -- Light gray (5Y 7/2) clay loam with common, coarse, distinct brownish yellow (lOYR 6/8) mottles; moderate, medium, subangular blocky structure; friable consistent; clay films on ped surfaces; red (lOR 4/8) stains; shear fractures at 170 cm; gradual boundary.
2BC -- 170 - 220 cm -- Light gray (5Y 7/2) sandy clay loam with common, coarse, distinct brownish yellow (10YR 6/8) mottles; friable consistent; red (2.5YR 5/8) stains; shear fractures from 170 to 220 cm; gradual boundary.
2Cl --. 220 - 360 em -- Pale yellow (2.5Y 7/3) sandy loam with common, coarse, distinct light yellowish brown (lOYR 6/4) mottles; very friable consistent; strong brown (7.5YR 5/8) stains; clear boundary.
2C2 -- 360 - 500 em -- Reddish yellow (7.5YR 6/8) loamy sand; very friable consistent; gradual boundary.
2C3 -- 500 - 680 em -- Very pale brown (10YR 7/3) fine to medium sand; loose consistent.
A-3
W3 --Weeks Island, Louisiana; core is from the toe slope in a gully; elevation is 12.2 m (40 ft); slope is 0 - 1 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 10 em
-- 0 - 10 cm -- Crushed oyster shells; abrupt boundary.
GULLY FILL -- 10 - 200 em
A -- 10 - 40 cm -- Light brownish gray (10YR 6/2) loamy sand; weak, fine, granular structure; friable consistent; gradual boundary.
Bw -- 40 - 120 cm -- Dark yellowish brown (lOYR 3/4) sandy loam; weak, fine, angular blocky structure; friable consistent; common pores; few burrows; clear boundary.
C -- 120 - 200 cm -- Light yellowish brown (IOYR 6/4) loamy sand with few, medium, distinct dark yellowish brown (IOYR 4/4) mottles; friable consistent; very dark brown (IOYR 2/2) and brownish yellow (IOYR 6/8) stains; clear boundary.
PEORIA LOESS - 200 - 360 em
2Bt -- 200 - 360 cm --Dark yellowish brown (IOYR 4/4) silt loam with common, coarse, distinct light brownish gray (10YR 6/2) mottles; friable consistent; common pores; very dark brown (10YR 2/2) and light gray (IOYR 7/2) root traces; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 360 - 680 em
3Cl -- 360 - 480 cm -- Yellowish brown (IOYR 5/6) sandy clay loam with common, medium, distinct light yellowish brown (IOYR 6/4) mottles; weak, fine, angular blocky structure; very friable consistent; very dark brown (10YR 2/2) stains; water saturated; clear boundary.
3C2 -- 480 - 980 cm -- Light yellowish brown (IOYR 6/4) medium sand; loose consistent; interbeds of coarse sand; water saturated.
A-4
W4 --Weeks Island, Louisiana; core is from the upper shoulder slope near the summit of the island; elevation is 3S.1 m (125 ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 10 em
-- 0 - 10 cm -- Gravel fill.
PEORIA LOESS - 10 - 240 em
Btl -- 10 - 50 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, medium, subangular blocky structure; firm consistent; few roots and pores; clay films on ped surfaces; horizon is artificially packed; clear boundary.
BIZ -- 50 - 130 cm -- Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common pores and worm burrows; clay films on ped surfaces; diffuse boundary.
BC -- 130 - 240 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; common pores; discontinuous clay films on ped surfaces; gradual boundary.
PEORIA LOESS MIXING ZONE - 240 - 290 em
C&2A -- 240 - 290 cm -- Yellowish brown (10YR 514) loam; weak, fine, angular blocky structure; very friable consistent; few pores; scattered gravel; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 290 - 850 em
2A -- 290 - 320 cm -- Yellowish brown (lOYR 516) medium sand; loose consistent; clear boundary.
2Bt -- 320 - 420 cm -- Yellowish red (5YR 5/S) sandy clay loam; weak, medium, angular blocky structure; friable consistent; scattered gravel; gradual boundary.
2C 1 -- 420 - 550 cm -- Yellowish red (5YR 5/S) sandy loam; very friable consistent; scattered gravel; very dark brown (10YR 2/2) stains; gradual boundary.
2C2 -- 550 - SOO cm -- Yellowish red (5YR 5/8) loamy sand; very friable consistent; scattered gravel; very dark brown (lOYR 2/2) stains; gradual boundary.
2C3 -- SOO - S50 cm -- Reddish yellow (7.5YR 7/8) medium sand; loose consistent; scattered gravel; very dark brown (lOYR 2/2) stains.
A-5
W5 --Weeks Island, Louisiana; core is from the back slope of the island; elevation is 21.3 m (70 ft); slope is 3 - 5 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL - 0 - 300 em
-- 0 - 300 cm -- Brownish yellow (IOYR 6/8) sand; loose consistent; silty clay loam layers; rock and shell fragments; clear boundary.
PEORIA LOESS - 300 - 580 em
Bt -- 300 - 380 cm -- Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common pores; worm burrows; clay films on ped surfaces; gradual boundary.
C -- 380 - 580 cm -- Dark yellowish brown (IOYR 4/4) silt loam; weak, fine, subangular blocky structure; friable consistent; common pores and worm burrows; clear boundary.
PEORIA LOESS MIXING ZONE - 580 - 610 em
C&2C -- 580 - 610 cm -- Yellowish brown (IOYR 5/4) loam; very friable consistent; clear boundary. .
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 610 - 1190 em
2CI -- 610 -740 cm -- Very pale brown (IOYR 7/4) medium sand; loose consistent: gradual boundary.
2C2 --740 - 900 cm -- Strong brown (7.5YR 5/8) loamy sand; loose consistent: abrupt boundary.
2C3 -- 900 - 910 cm -- Light gray (5Y 7/2) silty clay loam with common, medium, distinct reddish yellow (7.5YR 6/8) mottles; firm consistent; pedogenic slickensides; abrupt boundary.
2C4 -- 910 - 1010 cm -- Reddish yellow (7.5YR 6/6) silt loam; very friable consistent; strong brown (7.5YR 5/8) and brownish yellow (IOYR 6/8) stains on laminations; clear boundary.
2C5 -- 1010 - 1190 cm -- Yellowish red (5YR 5/8) coarse sand; loose consistent; scattered gravel.
A-6
W6 -- Weeks Island, Louisiana; core is from the back slope of the island; elevation is 25.9 m (85 ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 260 em
A -- 0 - 20 cm -- Dark brown (IOYR 4/3) silt loam with common, fine, distinct brownish yellow (IOYR 6/6) mottles; moderate, medium, subangular blocky structure; friable consistent; common roots; horizon is disturbed and packed; abrupt boundary.
Btl -- 20 - 70 cm -- Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, sub angular blocky structure; friable consistent; few roots and pores; worm burrows; dark brown (IOYR 3/3) clay films on ped surfaces; clear boundary.
Bt2 -- 70 - 120 cm --Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common pores and worm burrows; gradual boundary.
C -- 120 - 260 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; common pores; few worm burrows; clear boundary.
PEORIA LOESS MIXING ZONE - 260 - 320 em
C&2C -- 260 - 320 cm -- Yellowish brown (lOYR 5/4) loam; friable consistent; common pores; root traces; worm burrows; abrupt boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 320 - 830 em
2Cl -- 320 - 500 cm -- Brownish yellow (IOYR 6/6) medium sand; loose consistent; clear boundary.
2C2 -- 500 - 830 cm -- Strong brown (7.5YR 5/8) loamy sand; loose consistent; very dark brown (lOYR 2/2) and brownish yellow (lOYR 6/8) stains.
A-7
W7 --Weeks Island, Louisiana; core is from the back slope of the island; elevation is 13.7 m (45 ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
GULLY FILL I - 0 - 80 em
Ap -- 0 - lO cm --Dark brown (lOYR 3/3) silt loam; weak, fine, granular structure; friable consistent; grass roots; charcoal fragments; fireclay brick; gradual boundary.
Bw -- 10 - 60 cm -- (10YR 5/3) silt loam with few, fme, faint (lOYR 312) mottles; weak, thin, platy structure; friable consistent; few roots; yellowish brown (10YR 5/8) and strong brown (7.5YR 5/8) stains; abrupt boundary.
C -- 60 - 80 cm -- Dark brown (lOYR 3/3) silt loam; friable consistent; brownish yellow (10YR 6/8) stains; laminations of fine sand; charcoal fragments; fireclay brick; gradual boundary.
GULLY FILL IT - 80 - 640 em
2Bwl -- 80 - 330 cm -- Dark brown (10YR 3/3) silt loam with common, fine, distinct (lOYR 7/1) mottles; weak, fine, angular blocky structure; friable consistent; worm burrows; common pores with clay films; brownish yellow (10YR 6/8) and reddish yellow (7.5YR 6/8) stains; gradual boundary.
2Bw2 -- 330 - 500 cm -- (10YR 3/2) silt loam with common, fine, distinct (10YR 7/1) mottles; weak, fine, angular blocky structure; friable consistent; worm burrows; common pores; brownish yellow (lOYR 6/8) stains; gradual boundary.
2Cl -- 500 - 590 cm -- light brownish gray (10YR 612) loam with common, fine, distinct brownish yellow (lOYR 6/6) mottles; friable consistent; very dark brown (lOYR 2/2) and brownish yellow (10YR 6/8) stains; basal medium sand bed; clear boundary.
2C2 -- 590 - 640 cm -- (lOYR 3/2) silt loam with common, fine, faint dark yellowish brown (10YR 3/4) mottles; friable consistent; gradual boundary.
PEORIA WESS - 640 - 810 em
3Bt -- 640 - 660 cm -- Dark yellowish brown (lOYR 4/6) silt loam with common, fme, distinct dark brown (lOYR 3/3) mottles; weak, fine, angular blocky structure; friable consistent; gradual boundary.
3BC -- 660 - 810 cm -- dark yellowish brown (lOYR 4/4) silt loam; weak, fine, subangular blocky structure; friable consistent; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALWFORMATION - 810 - 950 em
4Cl -- 8lO - 850 cm -- yellowish brown (10YR 516) loamy sand; loose consistent; scattered gravel; gradual boundary.
A-8
4C2 -- 850 - 950 em -- yellowish red (5YR 5/8) loamy sand; very friable consistent; scattered gravel.
A-9
, - ,
W8 --Weeks Island, Louisiana; core is from the foot slope of the island; elevation is 13.7 m (4S ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 280 em
A -- 0 - 20 cm -- Dark brown (lOYR 3/3) silt loam; weak, fine, granular structure; friable consistent; common roots; charcoal fragments; clear boundary.
Btl-- 20 - 60 cm -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, sub angular blocky structure; friable consistent; few roots; common pores; dark brown (10YR 3/3) clay films on ped surfaces; gradual boundary.
Bt2 -- 60 - 120 cm --Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few pores; dark brown (10YR 3/3) clay films on ped surfaces; gradual boundary.
BC -- 120 - 2S0 cm -- Dark yellowish brown (IOYR 4/4) silt loam with common, coarse, distinct light yellowish brown (lOYR 6/4) mottles; weak, fine, angular blocky structure; very friable consistent; common pores; clear boundary.
C -- 2S0 - 280 cm -- Yellowish brown (10YR S16) silt loam with common, fine, faint light yellowish brown (10YR 6/4) mottles; slightly plastic consistent; gradual boundary.
PEORIA LOESS MIXING ZONE - 280 - 310 em
C&2B -- 280 - 310 cm -- Yellowish brown (10YR S16) loam with few, medium, distinct light brownish gray (lOYR 6/2) mottles; slightly plastic consistent; very dark brown (IOYR 2/2) stains and concretions; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 310 - 580 em
2Cl -- 310 - 360 cm -- Pale yellow (2.SY 7/4) sandy clay loam; slightly plastic consistent; brownish yellow (10YR 6/8) stains; yellowish red (SYR S/8) concretions; clear boundary.
2C2 -- 360 - S80 cm -- Light gray (lOYR 7/1) medium sand; loose consistent; yellowish brown (lOYR S/8), strong brown (7.SYR S/8), and yellowish red (SYR S/8) stains; silt loam bed at base; water saturated.
A-IO
W9 -- Weeks Island, Louisiana; core is from the foot slope of the island; elevation is 10.7 m (35 ft); slope is 3 - 5 per cent; site on cut surface of road; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 30 em
-- 0 - 30 cm --Very dark grayish brown (10YR 3/2) silt loam; firm consistent; shell fragments; gravel; charcoal fragments; abrupt boundary.
PEORIA LOESS - 30 - 100 em
BC -- 30 - 100 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; common pores; roots; clear boundary.
PEORIA LOESS MIXING ZONE - 100 - 180 em
C&2Bt -- 100 - 180 cm -- Brownish yellow (lOYR 6/6) silt loam; weak, fine, angular blocky structure; friable consistent; very dark brown (10YR 2/2) stains and concretions; yellowish red (5YR 5/8) stains; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 180 - 820 em
2Bt -- 180 - 240 cm -- Yellow (2.5Y 7/6) sandy clay loam with common, medium, prominent strong brown (7.5YR 5/8) mottles; moderate, medium, angular blocky structure; friable consistent; clay films on ped surfaces; very dark brown (lOYR 2/2) stains and concretions; clear boundary.
2C1 -- 240 - 520 cm -- Pale yellow (2.5Y 7/3) clay loam with common, medium, prominent brownish yellow (lOYR 6/8) mottles; weak, medium, angular blocky structure; slightly plastic consistent; red (2.5YR 4/8) stains; pedogenic slickensides; shear fractures from 330 to 360 cm; clay, silty clay loam, and sand interbeds; gradual boundary.
2C2 -- 520 - 720 cm -- Light gray (2.5Y 7/2) sandy clay loam with few, coarse, prominent brownish yellow (10YR 6/8) mottles; slightly plastic consistent; laminations; silty clay loam, loamy sand, and sand interbeds; clear boundary.
2C3 -- 720 - 820 cm -- Light gray (2.5Y 7/2) loamy sand; loose consistent; brownish yellow (lOYR 6/8) stains; water saturated.
A-ll
WlO --Weeks Island, Louisiana; core is from the foot slope of the island; elevation is 12.2 m (40 ft); slope is 1 - 3 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 240 em
Ap -- 0 - 10 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, subangular blocky structure; firm consistent; common roots; clear boundary.
Bt -- 10 - 60 cm -- Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; common pores; dark grayish brown (lOYR 4/2) silt loam films on ped surfaces and in pores; clear boundary.
Cl -- 60 - ISO cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, medium, crumb structure; friable consistent; common pores and worm burrows; gradual boundary.
C2 -- ISO - 240 cm -- Yellowish brown (10YR S/4) silt loam; weak, fine, crumb structure; slightly plastic consistent; common pores and worm burrows; gradual boundary.
PEORIA LOESS MIXING ZONE - 240 - 280 em
C&2B -- 240 - 2S0 cm -- Yellowish brown (10YR S/6) loam; weak, medium, angular blocky structure; slightly plastic consistent; few root traces; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 280 - 860 em
2Bt -- 2S0 - 310 cm -- Brownish yellow (10YR 6/6) loam; weak, fine, angular blocky structure; slightly plastic consistent; dark yellowish brown (10YR 4/4) silt loam fills in root traces; gradual boundary.
2BC -- 310 - 360 cm -- Yellowish brown (lOYR SIS) loam with few, medium, prominent red (2.SYR 4/S) mottles; slightly plastic consistent; grayish brown (2.SY SI2) stains at base; clear boundary.
2Cl -- 360 - 680 cm -- Light gray (SY 7/1) loam; slightly plastic consistent; yellowish brown (10YR SIS), strong brown (7.5YR SIS), and yellowish red (SYR SIS) stains; laminations; sandy clay loam interbeds; clear boundary.
2C2 -- 6S0 - 730 cm -- Light gray (SY 7/1) sandy clay loam; plastic consistent; abrupt boundary.
2C3 --730 - S60 cm -- Light gray (IOYR 7/2) medium sand; loose consistent; sandy clay loam interbeds; water saturated.
A-12
Wll --Weeks Island, Louisiana; core is from a foot slope along a nose slope of the island; elevation is 15.2 m (50 ft); slope is 3 - 5 per cent; drilled by R. P. Mc Culloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 270 em
Ap -- 0 - 30 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, angular blocky structure; firm consistent; few roots and pores; clear boundary.
Bt -- 30 - 120 cm -- Dark yellowish brown (10YR 4/4) silt loan}; moderate, medium, subangular blocky structure; friable consistent; common pores and worm burrows; clay films on ped surfaces; gradual boundary.
BC -- 120 - 220 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; common pores and worm burrows; gradual boundary.
C -- 220 - 270 em -- Dark yellowish brown (lOYR 4/4) silt loam; friable consistent; few pores and worm burrows; clear boundary.
PEORIA LOESS MIXING ZONE - 270 - 320 em
C&2C -- 270 - 320 cm -- Yellowish brown (lOYR 5/4) silt loam; very friable consistent; fine sand fills in worm burrows and root traces; abrupt boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 320 - 860 em
2Cl -- 320 - 430 cm -- Light yellowish brown (10YR 6/4) medium sand; loose consistent; clear boundary.
2C2 -- 430 - 600 -- Pale brown (lOYR 6/3) loam with common, coarse, distinct yellowish brown (lOYR 5/8) mottles; friable consistent; few very dark brown (lOYR 2/2) stains; abrupt boundary.
2C3 -- 600 - 860 cm -- Light gray (5Y 711) coarse sand; loose consistent; brownish yellow (lOYR 6/8) stains; sandy clay loam interbeds; water saturated.
A-13
W12 -- Weeks Island, Louisiana; core is from a foot slope along a nose slope of the island; elevation is 12.2 m (40 ft); slope is 3 - 5 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
OVERW ASH COLLUVIUM - 0 - 140 em
Ap -- 0 - 70 cm --Brown (lOYR 5/3) silt loam; friable consistent; grass roots; brownish yellow (lOYR 6/8) stains; laminations; shell fragments; clear boundary.
Bw -- 70 - 140 cm -- Dark brown (lOYR 4/3) silt loam; weak, fine, crumb structure; friable consistent; common roots; laminations at base of unit; clear boundary.
PEORIA LOESS - 140 - 400 em
2A -- 140 - 160 cm -- Very dark gray (lOYR 3/1) silt loam; weak, fine, granular structure; friable consistent; few roots; buried mollie horizon; gradual boundary.
2Bt -- 160 - 270 cm --Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common pores and worm burrows; clay films on ped surfaces; gradual boundary.
2BC -- 270 - 400 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, medium, angular blocky structure; friable consistent; common pores and worm burrows; clay films in pores; gradual boundary.
PEORIA LOESS MIXING ZONE -- 400 - 460 em
2C&3C -- 400 - 460 cm -- Yellowish brown (lOYR 5/4) loam; very friable consistent; fine sand fills in root traces; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 460 - 670 em
3C -- 460 - 670 cm -- Light yellowish brown (10YR 6/4) medium sand; loose consistent; water saturated.
A-14
W13 --Weeks Island, Louisiana; core is from a foot slope along a nose slope of the island; elevation is 12.2 m (40 ft); slope is 1 - 3 per cent; drilled by W.J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 30 em
-- 0 - 30 cm -- Dark brown (IOYR 3/3) silt loam; friable consistent; grass roots; scattered shells; clear boundary.
PEORIA LOESS - 30 - 410 em
A -- 30 - 60 cm -- Very dark grayish brown (IOYR 3/2) silt loam; weak, fine, granular structure; friable consistent; scattered charcoal fragments; mollic horizon; clear boundary.
E -- 60 - 80 cm -- Light brownish gray (10YR 6/2) silt loam; moderate, medium, granular structure; friable consistent; common pores and worm burrows; gradual boundary.
Btl -- 80 - 110 cm -- Dark yellowish brown (10YR 4/4) silt loam with common, fine, distinct brownish yellow (IOYR 6/8) mottles; moderate, medium, subangular blocky structure; friable consistent; common pores and worm burrows; very dark gray (lOYR 3/1) silt loam films on ped surfaces and in root traces; gradual boundary.
BtZ -- 110 - 200 cm -- Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common pores and worm burrows; clay films on ped surfaces, root traces, and pores; gradual boundary.
BC -- 200 - 350 cm -- Dark yellowish brown (IOYR 4/4) silt loam with common, medium, distinct light brownish gray (10YR 6/2) mottles; weak, medium, angular blocky structure; friable consistent; common pores and worm burrows; clay films in root traces and pores; very dark brown (10YR 2/2) stains; clear boundary.
C -- 350 - 410 cm -- Dark yellowish brown (IOYR 4/4) silt loam with common, medium, distinct light brownish gray (IOYR 6/2) mottles; slightly plastic consistent; very dark brown (IOYR 2/2) stains; gradual boundary.
PEORIA LOESS MIXING ZONE -- 410 - 450 em
C&2C -- 410 - 450 cm -- Light yellowish brown (IOYR 6/4) silt loam with common, medium, distinct gray (10YR 6/1) mottles; slightly plastic consistent; very dark brown (IOYR 2/2) stains; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 450 - 730 em
2Cl -- 450 - 480 cm -- Light gray (2.5Y 7/2) sandy clay loam with common, fine, prominent brownish yellow (IOYR 6/8) mottles; slightly plastic consistent; very dark brown (IOYR 2/2) stains; yellowish red (5YR 5/8) stains at base; abrupt boundary.
A-15
2C2 -- 480 - 730 em --Brownish yellow (lOYR 6/6) medium sand; loose consistent; yellowish red (SYR 5/8) stains; sandy clay loam interbeds; water saturated.
A-16
W14 --Weeks Island, Louisiana; core is from the lower foot slope of the island; elevation is 6.1 m (20 ft); slope is 1 - 3 per cent; drilled by W. J. Autin and F. K. Kring; described by W. 1. Autin and R. P. McCulloh.
OVERW ASH COLLUVIUM -- 0 - 50 em
Ap -- 0 - 20 cm --Dark gray (lOYR 4/1) silt loam; friable consistent; few grass roots; clear boundary.
Bw -- 20 - 50 cm -- Very dark grayish brown (lOYR 3/2) silt loam; weak, fine, granular structure; friable consistent; common roots; gradual boundary.
PEORIA LOESS - 50 - 330 em
2Bt -- 50 - 140 cm -- Light gray (10YR 7/2) silt loam with common, medium, distinct yellowish brown (lOYR 516) mottles; moderate, medium, subangular blocky structure; friable consistent; very dark brown (lOYR 2/2) stains and concretions; clay fIlms on ped surfaces; gradual boundary.
2BC -- 140 - 200 cm -- Dark yellowish brown (10YR 4/4) silt loam with common, fine, distinct light gray (lOYR 7/2) mottles; friable consistent; very dark brown (lOYR 2/2) stains; light gray (10YR 7/2) silt loam fIlms in root traces; clear boundary.
2C -- 200 - 330 cm -- Yellowish brown (lOYR 5/4) silt loam; plastic consistent; gradual boundary.
PEORIA LOESS MIXING ZONE - 330 - 400 em
2C&3C -- 330 - 400 cm -- Brownish yellow (lOYR 6/6) sandy clay loam with few coarse, distinct very pale brown (lOYR 7/3) mottles; slightly plastic consistent; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 400 - 670 em
3Cl -- 400 - 440 cm -- Light gray (lOYR 711) sandy clay loam with common, fine, distinct yellowish brown (lOYR 5/8) mottles; firm consistent; strong brown (7.5YR 5/8) stains; very dark brown (lOYR 2/2) concretions; clear boundary.
3C2 -- 440 - 590 cm -- Light gray (2.5Y 7/2) sandy clay loam with few, coarse, distinct yellowish brown (lOYR 5/8) mottles; slightly plastic consistent; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains and concretions; clear boundary.
3C3 -- 590 - 670 cm -- Light gray (2.5Y 7/2) sandy loam; very friable consistent; water saturated.
A-17
d , =-1
W1S -- Weeks Island, Louisiana; core is from the colluvial apron on the toe slope of the island; elevation is 1.S m (S ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
OVERW ASH COLLUVIUM - 0 - 50 em
Ap -- 0 - 10 cm --Very dark gray (10YR 3/1) silt loam; weak, medium, granular structure; friable consistent; common grass roots; mollic horizon; gradual boundary.
Bw -- 10 - SO cm -- Very dark gray (10YR 3/1) silt loam; weak, fine, angular blocky structure; friable consistent; common roots and worm burrows; yellowish red (SYR S/8) stains; gradual boundary.
PEORIA LOFSS - 50 - 330 em
2Btl -- SO - 130 cm -- Gray (2.5Y S/O) silt loam with common, medium, prominent yellowish red (SYR S/8) mottles; moderate, medium, subangular blocky structure; friable consistent; very dark brown (10YR 2/2) and yellowish red (SYR S/8) stains and concretions; very dark gray (1OYR 3/1) krotovina; clay films on ped surfaces; gradual boundary.
2Bt2 -- 130 - 200 cm -- Yellowish brown (lOYR S/8) silt loam with common, medium, prominent gray (2.SY 6/0) mottles; weak, fine, subangular blocky structure; very friable consistent; yellowish red (SYR S/8) stains; very dark gray (10YR 3/1) root traces; clay films on ped surfaces; gradual boundary.
2Cl -- 200 - 240 cm -- Yellowish brown (lOYR S/8) silt loam with common, medium, prominent gray (2.SY 6/0) mottles; plastic consistent; very dark gray (10YR 3/1) root traces; gradual boundary.
2C2 -- 240 - 330 cm -- Brownish yellow (10YR 6/8) silt loam; plastic consistent; very dark gray (1OYR 3/1) root traces; gradual boundary.
PEORIA LOESS MIXING ZONE - 330 - 350 em
2C&3C -- 330 - 3S0 cm -- Brownish yellow (1OYR 6/8) loam; slightly plastic consistent; very dark brown (10YR 2/2) stains; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 350 - 570 em
3C1 -- 3S0 - SOO cm -- Light gray (2.5Y 7/2) sandy clay loam with common, fine, distinct yellowish brown (1OYR S/8) mottles; slightly plastic consistent; yellowish red (SYR S/8) stains and concretions; very dark brown (10YR 2/2) concretions; clear boundary.
3C2 -- SOO - S70 cm -- Very pale brown (lOYR 7/3) loamy sand with common, coarse, distinct yellowish brown (10YR S/6) mottles; slightly plastic consistent; water saturated.
A-I8
I W16 -- Weeks Island, Louisiana; core is from the colluvial apron on the lower toe slope of the island; elevation is 1.5 m (5 ft); slope is 0 - 1 per cent; drilled by W. I. Autin and F. K. Kring;
I, described by W. I. Autin and R. P. McCulloh.
I FILL--0-80em I
-- 0 - 80 cm -- Dark gray (lOYR 4/1) silt loam; friable consistent; shell bed at top of unit; scattered fireclay brick fragments; charcoal fragments; abrupt boundary.
HOLOCENE MARSH - 80 - 310 em
Cl -- 80 - 130 cm -- Very dark gray (lOYR 3/1) silty clay loam; sticky consistent; fibric grass, reed-sedge, root, and wood fragments comprise 10 to 20 per cent of unit by volume; abrupt boundary.
-- 130 - 250 cm -- No recovery; probably part of marsh sequence.
C2 -- 250 - 310 cm -- Black (lOYR 2/1) clayey muck; very sticky consistent; hemic reedsedge and wood fragments comprise 30 to 40 per cent of unit by volume; abrupt boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -310 - 980 em
2Cl -- 310 - 420 cm -- Greenish gray (5GY 6/1) silt loam with common, coarse, distinct olive (5Y 4/4) mottles; plastic consistent; unit maybe loess influenced; diffuse boundary.
2C2 -- 420 - 660 cm -- Yellow (lOYR 7/8) silty clay loam with common, medium, prominent light yellowish brown (2.5Y 6/4) mottles; plastic consistent; few root traces; very dark brown (10YR 2/2) and yellowish red (5YR 5/8) stains and concretions; diffuse boundary.
2C3 -- 660 - 820 cm -- Strong brown (7.5YR 5/8) silt loam with common, coarse, prominent light gray (5Y 7/2) mottles; friable consistent; light gray (5Y 7/2) tongues; very dark brown (lOYR 2/2) and yellowish red (5YR 5/8) stains and concretions; diffuse boundary.
2C4 -- 820 - 980 cm -- Light gray (5Y 7/2) clay with common, medium, prominent yellowish red (5YR 5/8) mottles; plastic consistent; very dark brown (lOYR 2/2) and yellowish red (5YR 5/8) stains and concretions; shear fractures at 920 cm; powdery CaC03 on fractures and at 970 cm.
A-19
I I I'
! i
, , I
APPENDIX II
CORE DESCRIPTIONS FROM COTE BLANCHE ISLAND
i i \
CB 1 -- Cote Blanche Island, Louisiana; core is from the colluvial apron on the middle toe slope of the island; elevation is 4.6 m (15 ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
OVERW ASH COLLUVIUM - 0 - 230 em
Ap -- 0 - 30 cm -- Gray (lOYR 5/1) silt loam; friable consistent; gravel and shells; road fill; abrupt boundary.
Btg -- 30 - 160 em -- Gray (lOYR 6/1) silt loam with few, fine, distinct yellowish brown (10YR 5/4) mottles; weak, medium, subangular blocky structure; friable consistent; clay films on peds; faint laminations; very dark brown (10YR 2/2) and yellowish brown (10YR 5/8) stains and concretions; gradual boundary.
Bwg -- 160 - 230 cm -- Gray (10YR 6/1) silt loam; weak, fine, subangular blocky structure; friable consistent, some parts of the horizon are plastic; faint laminations; very dark brown (lOYR 2/2) and dark yellowish brown (IOYR 4/6) stains and concretions; clear boundary.
PEORIA LOESS - 230 - 450 em
2Bt -- 230 - 370 cm -- Yellowish brown (lOYR 5/6) silt loam with common, coarse, distinct gray (10YR 6/1) mottles; weak, medium, angular blocky structure; friable consistent; discontinuous films on peds; very dark brown (lOYR 2/2) and dark yellowish brown (lOYR 4/6) stains and concretions; gradual boundary.
2C -- 370 - 450 cm -- Yellowish brown (lOYR 5/6) silt loam with common, medium, distinct gray (IOYR 6/1) mottles; sticky consistent; very dark brown (lOYR 2/2) and dark yellowish brown (lOYR 4/6) stains and concretions; clear boundary .
. i PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 450 - 850 em
3Bt -- 450 - 620 cm -- Brownish yellow (lOYR 6/6) silty clay loam with common, medium, distinct light gray (2.5Y 7/2) mottles; weak, fine, angular blocky structure; plastic consistent; gray (lOYR 6/1; 10YR 5/1) root and worm fills; very dark brown (lOYR 2/2) concretions; clear boundary.
3C I -- 620 - 670 cm -- Yellow (IOYR 7/6) sandy clay loam; sticky consistent; brownish yellow (lOYR 6/8) stains; very dark brown (lOYR 2/2) concretions; clear boundary.
3C2 -- 670 - 730 em -- Light gray (5Y 7/2) clay; plastic consistent; laminated; red (2.5YR 4/8) and brownish yellow (lOYR 6/8) beds; very dark brown (lOYR 2/2) concretions; clear boundary.
3C3 -- 730 - 780 cm -- Yellowish brown (lOYR 5/6) coarse sand; loose consistent; reworked very dark brown (IOYR 2/2) concretions; clear boundary.
3C4 --780 - 850 cm -- Yellow (lOYR 7/6) sandy clay loam; sticky consistent; brownish yellow I (IOYR 6/8) stains; very dark brown (IOYR 2/2) concretions.
"-I
B-2
I
I , ,
CB2 -- Cote Blanche Island, Louisiana; core is from the back slope of the island; elevation is 13.7 m (4S ft); slope is 1 - 3 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA WESS - 0 - 80 em
Ap -- 0 - 10 cm -- Brown (1OYR 4/3) silt loam; weak, fine, angular blocky structure; friable consistent; common roots; worm burrows; clear boundary.
Bt -- 10 - SO cm -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common roots; films on peds; gradual boundary.
PEORIA WESS MIXING ZONE - 80 - 130 em
Bt&2E -- SO - 130 cm --Brownish yellow (lOYR 6/6) silt loam with few, medium, faint very pale brown (1OYR 7/4) mottles; moderate, medium, subangular blocky structure; friable consistent; very pale brown (1OYR 7/4) films on peds; few very dark brown (lOYR 2/2) stains; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALWFORMATION -- 130 - 980 em
2Btl -- 130 - 170 cm --Brownish yellow (lOYR 6/6) silty clay loam with common, medium, prominent light gray (2.5Y 7/2) mottles; moderate, medium, subangular blocky structure; friable consistent; brownish yellow (1OYR 6/6) films on peds; light gray (2.SY 7/2) tongues; few red (2.SYR S/6) stains; gradual boundary.
2BtZ -- 170 - 290 cm -- Red (2.SYR S/6) clay with common, coarse, prominent light gray (2.SY 7/2) mottles; moderate, medium, angular blocky structure; plastic consistent; modern roots on peds; light gray (2.SY 7/2) tongues; very dark brown (10YR 2/2) stains; pedogenic slickensides; diffuse boundary.
2Cl -- 290 - 470 cm -- Light yellowish brown (2.SY 6/3) clay; plastic consistent; faint laminations; very dark brown (1OYR 2/2), yellowish brown (1OYR SIS), strong brown (7.5YR S/8), and red (2.5YR S/6) stains; pedogenic slickensides; diffuse boundary.
2C2 -- 470 - SOO cm -- Light olive gray (5Y 6/2) clay; plastic consistent; very dark brown (1OYR 212), brownish yellow (1OYR 6/S), and red (2.SYR S/6) stains; silty clay loam beds; NaCI crust at 730 cm; shear fractures with Mn stains; gradual boundary.
3Bt -- SOO - 8S0 cm -- Pale olive (5Y 6/3) clay with common, coarse, prominent light brown (7.5YR 6/4) mottles; moderate, medium, angular blocky structure; plastic consistent; strong brown (7.5YR S/8), yellowish red (SYR S/8), and red (2.5YR S/8) stains; films and stains on peds and root traces; shear fractures; clear boundary.
3C -- 880 - 980 cm -- Pale yellow (2.5Y 7/3) fine sand, very friable consistent; loamy sand beds; few yellowish red (5YR S/8) stains on root traces.
B-3
CB3 -- Cote Blanche Island, Louisiana; core is from the upper shoulder slope of the island; elevation is 24.4 m (SO ft); slope is 3 - S per cent; drilled hy R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 200 em
Ap -- 0 - lO cm -- Dark grayish brown (lOYR 4/2) silt loam; weak, fine, granular structure; friable consistent; common roots; shell fragments; clear boundary.
Bt -- 10 - 120 -- Yellowish brown (lOYR S/4) silt loam; weak, fine, angular blocky structure; friable consistent; few roots; discontinuous clay films; diffuse boundary.
BC -- 120 - 200 --Dark yellowish brown (lOYR 4/6) silt loam with few, medium, faint light yellowish brown (lOYR 6/4) mottles; weak, fme, angular blocky structure; slightly plastic consistent; few roots; gradual boundary.
PEORIA LOESS MIXING ZONE - 200 - 240 em
C&2B -- 200 - 240 cm -- Brownish yellow (IOYR 6/S) silt loam with common, medium, faint light yellowish brown (lOYR 6/4) mottles; friable consistent; few very dark brown (IOYR 2/2) stains and concretions; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 240 - 850 em
2Bt -- 240 - 3lO cm -- Brownish yellow (lOYR 6/S) clay with common, medium, prominent red (2.SYR 4/S) mottles; moderate, medium, angular blocky structure; firm consistent; clay films on peds; few very dark brown (lOYR 212) stains and concretions; clear boundary.
2BC -- 310 - 3S0 cm -- Yellow (lOYR 7/S) sandy clay loam with common, coarse, prominent red (2.SYR 4/S) mottles; weak, fine, angular blocky structure; friable consistent; red (2.SYR 4/6, 2.SYR 4/S) stains; light gray (IOYR 7/2) sandy tongues; light gray (2.SY 7/2) clay zones; faint laminations; gradual boundary.
2CI -- 3S0 - 710 -- Light gray (SY 7/2) clay; plastic consistent; brownish yellow (IOYR 6/S) and very dark brown (IOYR 2/2) stains; yellowish red (SYR 4/6) concretions at 620 cm, 3 - 4 cm diameter; shear fractures; sandy clay loam zones; reddish yellow (SYR S/4) clay beds; gradual boundary.
2C2 -- 710 - 7S0 cm -- Olive yellow (2.5Y 6/8) clay with common, medium, prominent dark yellowish brown (lOYR 4/4) mottles; weak, fine, angular blocky structure, firm consistent; strong brown (7.SYR S/8) stains on root traces; diffuse boundary.
2C3 -- 7S0 - 840 cm -- Light olive gray (SY 612) clay; firm consistent; yellowish brown (IOYR ~ SIS) and strong brown (7.SYR SIS) stains; some stains on root traces; shear fractures; clear boundary .
• ~~ 2C4 -- S40 - 8S0 cm -- Light yellowish brown (IOYR 6/4) sandy loam with few, coarse distinct .j light olive gray (SY 6/2) mottles; very friable consistent; brownish yellow (lOYR 6/8) stains.
B-4
CB4 -- Cote Blanche Island, Louisiana; core is from the edge of the summit of the island; elevation is 27.4 m (90 ft); slope is 3 - 5 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 180 em
Ap -- 0 - 10 cm -- Brown (10YR 4/3) silt loam; weak, fine, granular structure; friable consistent; common roots; shell fragments; clear boundary.
Btl -- 10 - 90 cm --Dark yellowish brown (1OYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common roots; clay films on peds; gradual boundary.
Bt2 -- 90 - 180 cm -- Dark yellowish brown (lOYR 4/4) silt loam with common, medium, distinct pale brown (10YR 6/3) mottles; moderate, medium, subangular blocky structure; friable consistent; clay films and pale brown (1OYR 6/3) silt films on peds; gradual boundary.
PEORIA LOESS MIXING ZONE - 180 - 200 em
Bt&2Bt -- 180 - 200 cm -- Brownish yellow (10YR 6/6) silty clay loam; moderate, medium, subangular blocky structure; friable consistent; red (2.5YR 4/8) stains; very dark brown (lOYR 2/2) stains and concretions; clay films and pale brown (10YR 6/3) silt films on peds; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 200 - 790 em
2Btl -- 200 - 330 cm -- Brownish yellow (lOYR 6/6) clay with common, fine prominent red (2.5YR 516) mottles; moderate, medium, angular blocky structure; firm consistent; clay films on peds; very dark brown (lOYR 2/2) stains; light gray (10YR 7/2) silt loam tongues; clear boundary.
2Bt2 -- 330 - 390 cm -- Red (2.5YR 516) clay with common, medium, prominent brownish yellow (lOYR 6/6) mottles; moderate, medium, angular blocky structure; firm consistent; brownish yellow (lOYR 6/6) clay films on peds; very dark brown (lOYR 2/2) stains; shear fractures; gradual boundary.
2Cl -- 390 - 500 cm -- Light gray (5Y 712) clay with common, medium, prominent reddish brown (5YR 5/4) mottles; firm consistent; very dark brown (lOYR 2/2) stains on root traces and pedogenic slickensides; shear fractures; faint laminations, some are silty; diffuse boundary.
2C2 -- 500 - 790 cm -- Light gray (5Y 7/2) clay; firm consistent; very dark brown (lOYR 2/2), reddish brown (5YR 5/4), and red (2.5YR 516) stains; heavy stained zone at 730 - 750 cm with white powdery gypsum; abundant shear fractures.
B-5
CBS -- Cote Blanche Island, Louisiana; core is from the upper shoulder slope of the island; elevation is 21.3 m (70 ft); slope is 3 - S per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
--, FILL -- 0 - 10 ern
-- 0 - 10 cm -- Very dark grayish brown (10YR 3/2) silt loam; friable consistent; common roots; dark yellowish brown (10YR 4/6) soil clasts; clear boundary.
PEORIA LOESS - 10 - 210 em
A -- 10 - 30 cm -- Dark grayish brown (10YR 4/2) silt loam; weak, fine, granular structure; friable consistent; common roots; gradual boundary.
Bt -- 30 - 170 cm -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; clay films on peds; clear boundary.
BC -- 170 - 210 cm -- Dark yellowish brown (10YR 4/4) silt loam with common, medium, faint pale brown (1OYR 6/3) mottles; weak, fine, angular blocky structure; slightly plastic and sticky consistent; clear boundary.
PEORIA LOESS MIXING ZONE - 210 - 260 em
C&2E -- 210 - 260 cm --Brownish yellow (lOYR 6/6) silt loam with few, medium, distinct pale brown (10YR 6/3) mottles; moderate, fine, angular blocky structure; friable consistent; very dark brown (10YR 2/2) stains and concretions; dark yellowish brown (lOYR 4/4) stains on root traces; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 260 - 910 em
2Btl-- 260 - 3S0 cm -- Brownish yellow (lOYR 6/6) clay with common, fine, prominent red (2.SYR S/8) mottles; moderate, medium, angular blocky structure; firm consistent; clay films on peds; few very dark brown (10YR 2/2) concretions; light gray (lOYR 7/2) silt loam tongues; diffuse boundary.
2Bt2 -- 3S0 - 400 cm -- Red (2.SYR S/6) clay with common, fine, prominent pale yellow (2.5Y 7/3) mottles; weak, fine, angular blocky structure; firm consistent; clay films on peds; few very dark brown (10YR 2/2) stains; diffuse boundary .
. ; 2Cl -- 400 - 600 cm -- Light gray (SY 7/2) clay with common, coarse, prominent strong brown (7.5YR S/8) mottles; plastic consistent; very dark brown (10YR 2/2), brownish yellow (1OYR 6/8), and reddish yellow (7.SYR 6/8) stains, heavy at base; few shear fractures; clear boundary . .
- , -J 2C2 -- 600 - 7S0 cm -- Light olive gray (SY 6/2) clay with common, coarse, prominent
yellowish brown (1OYR S/6) mottles; plastic consistent; very dark brown (1OYR 2/2) stains; thin !-i laminations of silt and fine sand; gradual boundary.
j B~
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2C3 --750 - 860 em -- Yellowish red (5YR 516) sandy clay loam; friable consistent; very dark brown (lOYR 2/2) stains; laminations; loamy sand and light gray (5Y 7/2) clay beds; clear boundary.
B-7
CB5 -- Cote Blanche Island, Louisiana -- CONTINUED.
-I
~ 2C4 -- 860 - 910 cm -- Light gray (5Y 7/2) clay; plastic consistent; very dark brown (IOYR 2/2), brownish yellow (IOYR 6/8), reddish yellow (7.5YR 6/8), yellowish red (5YR 5/6), and red (2.5YR 5/6) stains; cemented wne of CaCO, at base of unit, core barrel refused to penetrate.
B-8
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CB6 -- Cote Blanche Island, Louisiana; core is from the edge of the summit of the island; elevation is 25.9 m (85 ft); slope is 1 - 3 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 10 em
-- 0 - 10 cm -- Very dark grayish brown (10YR 3/2) loam; friable consistent; common roots; shell fragments; abrupt boundary.
PEORIA LOESS - 10 - 300 em
A -- 10 - 30 cm -- Dark grayish brown (IOYR 4/2) silt loam with few, fine, faint light brownish gray (10YR 6/2) mottles; friable consistent; horizon packed by traffic; few roots; clear boundary.
Btl -- 30 - 120 cm -- Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; clay films on peds and in pores; diffuse boundary.
Bt2 -- 120 - 230 cm -- Dark yellowish brown (IOYR 4/4) silt loam with few, coarse, distinct light yellowish brown (10YR 6/4) mottles; moderate, medium, subangular blocky structure; friable consistent; clay films on peds; gradual boundary.
BC -- 230 - 300 cm -- Brownish yellow (IOYR 6/6) silt loam; weak, fine, angular blocky structure; slightly plastic consistent; very dark brown (10YR 2/2) stains and concretions; light gray (10YR 7/2) tongues; gradual boundary.
PEORIA LOESS MIXING ZONE - 300 - 340 em
C&2Bt -- 300 - 340 cm -- Brownish yellow (lOYR 6/6) silty clay loam; moderate, fine, angular blocky structure; slightly plastic consistent; very dark brown (IOYR 2/2) stains and concretions; discontinuous clay films on peds; light gray (IOYR 7/2) silt loam tongues; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATlON - 340 - 760 em
2Bt -- 340 - 510 cm -- Brownish yellow (IOYR 6/6) clay with common, medium, distinct light gray (10YR 7/2) mottles; moderate, fine, angular blocky structure; firm consistent; very dark brown (IOYR 2/2) and yellowish red (5YR 5/8) stains and concretions; clay films on peds; light gray (IOYR 7/2) silt loam tongues; gradual boundary.
2Cl -- 510 - 640 cm -- Light gray (5Y 7/2) clay; plastic consistent; very dark brown (IOYR 2/2) stains and concretions; yellowish red (5YR 5/8) stains; laminations; red (2.5YR 5/6) clay beds; strong brown (7.5YR 5/8) calcareous cemented zones at 580 and 640 cm; clear boundary.
2C2 -- 640 - 720 em -- Light gray (5Y 7/2) clay; plastic consistent; few brownish yellow (10YR 6/8) stains; laminations; shear fractures; clear boundary.
B-9
1
___ I
2C3 -- 720 - 760 em -- Light gray (5Y 7/2) clay; plastic consistent; very dark brown (lOYR 2/2) and reddish yellow (7.5YR 6/8) stains and concretions; light brown (7.5YR 6/4) clay bed at base.
B-lO
CB7 -- Cote Blanche Island, Louisiana; core is from the upper shoulder slope of the island; elevation is 21.3 m (70 ft); slope is 1 - 3 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA WESS - 0 - 160 em
Ap -- 0 - 10 cm -- Grayish brown (10YR 5/2) silt loam; friable coosistent; common roots; yellowish red (5YR 5/8) staios; clear boundary.
Btl -- 10 - 110 cm -- Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable coosistent; few roots; clay filros on peds; gradual boundary.
Bt2 -- 110 - 160 cm --Dark yellowish brown (lOYR 4/4) silt loam with common, medium, distinct very pale brown (10YR 7/3) mottles; weak, fine, subangular blocky structure; friable coosistent; clay films on peds; very pale brown (10YR 7/3) root traces; gradual boundary.
PEORIA WESS MIXING ZONE - 160 - 220 em
BC&2Bt -- 160 - 220 cm -- Brownish yellow (10YR 6/8) silt loam with common, medium, distinct very pale brown (10YR 7/3) mottles; weak, fine, angular blocky structure; slightly plastic coosistent; very dark brown (10YR 2/2) stains and concretioos; discontinuous clay filros on peds; light gray (10YR 7/2) tongues; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALWFORMATION -- 220 - 920 em
2Btl -- 220 - 290 cm -- Brownish yellow (lOYR 6/8) clay with few, fine, prominent red (2.5YR 5/8) mottles; moderate, fine, angular blocky structure; firm coosistent; very dark brown (10YR 2/2) staios on root traces; clay filros on peds; light gray (10YR 7/2) tongues; gradual boundary.
2Bt2 -- 290 - 320 cm -- Light gray (5Y 7/2) clay with many, medium, prominent red (2.5YR 5/8) mottles; firm coosistent; clay filros on peds; gradual boundary.
2Cl -- 320 - 350 cm -- Light gray (5Y 7/2) clay with few, medium, prominent strong brown (7.5YR 5/8) mottles; firm coosistent; strong brown (7.5YR 5/8) staios on root traces; clear boundary.
2C2 -- 350 - 400 cm -- Light gray (2.5Y 7/2) sandy clay loam with common, coarse, prominent brownish yellow (lOYR 6/8) mottles; slightly plastic coosistent; strong brown (7.5YR 5/8) stains; medium sand beds; clear boundary.
2C3 -- 400 - 430 cm -- Light gray (5Y 7/2) clay with common, coarse, prominent brownish yellow (10YR 6/8) mottles; plastic consistent; brownish yellow (10YR 6/8) stains on laminations; abrupt boundary.
2C4 -- 430 - 630 cm -- Red (2.5YR 5/6) clay; plastic consistent; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains on laminatioos; light gray (2.5Y 7/2) laminated clay interbeds; very dark brown (lOYR 2/2) and yellowish red (5YR 5/8) calcareous concretions; abrupt boundary.
B-ll
- ,
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2C5 -- 630 - 840 cm -- Gray (5Y 611) clay; firm consistent; yellowish red (5YR 5/8) stains; very dark brown (lOYR 2/2) stains along shear fractures; laminations; red (2.5YR 5/6) clay beds; clear boundary.
B-12
CB7 -- Cote Blanche Island, Louisiana -- CONTINUED.
2C6 -- 840 - 920 cm -- Gray (5Y 6/1) clay; firm consistent; very dark brown (10YR 2/2) and yellowish red (5YR 5/8) stains and calcareous concretions; laminations; red (2.5YR 516) clay beds.
B-13
"--...,
CB8 -- Cote Blanche Island, Louisiana; core is from a flat on a foot slope of a nose slope on the south edge of the island; elevation is 3.0 m (10 ft); slope is 0 - 1 per cent; drilled by W. J. Autin and F. K. Kring; described by W. 1. Autin and R. P. McCulloh.
FILL-O-20em
-- 0 - 20 cm -- Very dark grayish brown (10YR 3/2) silt loam; friable consistent; common roots; abundant shell fragments; road fill; abrupt boundary.
OVERW ASH COLLUVIUM - 20 - 50 em
Bw -- 20 - SO -- Brown (10YR S/3) silt loam; weak, fine, angular blocky structure; common roots; charcoal; faint laminated wnes; very dark brown (10YR 2/2) and yellowish red (SYR S/8) stains at base; fragment of metal at base; abrupt boundary.
PEORIA LOESS -- 50 - 220 em
2Btl -- SO - 120 cm -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, sub angular blocky structure; friable consistent; few roots; films on peds; gradual boundary.
2Bt2 -- 120 - 180 cm -- Dark yellowish brown (10YR 4/4) silt loam with common, medium, distinct pale brown (10YR 6/3) mottles; moderate, medium, subangular blocky structure; friable consistent; pale brown (10YR 6/3) root traces; films on peds; gradual boundary.
2C -- 180 - 220 cm --Dark yellowish brown (10YR 4/4) silt loam with common, medium, distinct pale brown (IOYR 6/3) mottles; sticky consistent; pale brown (10YR 6/3) root traces; very dark brown (IOYR 2/2) stains; clear boundary.
PEORIA LOESS MIXING ZONE - 220 - 240 em
2C&3E -- 220 - 240 cm -- Brownish yellow (10YR 6/6) silt loam with common, medium, distinct pale brown (10YR 6/3) mottles; slightly plastic consistent; pale brown (10YR 6/3) root traces; very dark brown (IOYR 2/2) stains; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 240 - 1040 em
3Bt -- 240 - 340 cm -- Brownish yellow (10YR 6/6) clay with few, medium, distinct light gray (lOYR 7/2) mottles; weak, fine, angular blocky structure; firm consistent; strong brown (7.SYR S/8) stains; very dark brown (lOYR 2/2) concretions; discontinuous clay films on peds; light gray (IOYR 7/2) tongues; gradual boundary.
3BC -- 340 - 420 cm -- Brownish yellow (lOYR 6/6) clay; weak, fine, angular blocky structure; firm consistent; very dark brown (10YR 2/2) stains on root traces; bluish gray (SB 6/1) stains around modern roots; light gray (IOYR 7/2) tongues; shear fractures; gradual boundary.
3Cl -- 420 - S70 em -- Pinkish gray (SYR 7/2) sandy clay loam with common, fine, prominent light gray (2.SY 7/2) mottles; friable consistent; yellowish red (SYR 5/8) and very dark brown (lOYR
B-14
2/2) stains; faint laminations; clay loam and loam interbeds; light gray (5Y 7/2) clay bed at 450 em; abrupt boundary.
B-15
CBS -- Cote Blanche Island, Louisiana -- CONTINUED.
070 " 3C2 -- 570 - 630 cm -- Light olive gray (SY 6/2) silty clay loam with common, coarse, distinct yellow (2.5Y 7/S) mottles; slightly plastic consistent; brownish yellow (10YR 6/S) and yellow (2.5Y 7/S) stains; clear boundary.
3C3 -- 630 - 770 cm -- Light reddish brown (2.SYR 6/4) sandy clay loam with common, coarse, prominent light gray (2.SY 7/2) mottles; friable consistent; red (2.5YR 516), strong brown (7.5YR 5/S), and very dark brown (10YR 2/2) stains; laminated; clay, loam, and loamy sand interbeds; clear boundary.
3C4 -- 770 - 930 cm -- Gray (SY 6/1) clay with common, coarse, prominent strong brown (7.5YR 5/S) mottles; plastic consistent; laminations; bed of light reddish brown (2.5YR 6/4) clay at S70 - 900 cm; cemented yellowish red (5YR 5/S) calcareous wnes; clear boundary.
3CS -- 930 - 990 cm -- Brown (7.5YR 5/4) sandy loam; friable consistent; laminated; abrupt boundary.
3C6 -- 990 - 1040 cm -- Olive yellow (2.SY 6/S) clay; firm consistent; yellowish red (5YR 5/S) stains on root traces; yellowish red (SYR SIS) and strong brown (7.SYR 5/S) calcareous cemented nodule layers.
B-16
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CB9 -- Cote Blanche Island, Louisiana; core is from the lower back slope of a nose slope on the island; elevation is 9.1 m (30 ft); slope is 1-3 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS -- 0 - 240 em
Ap -- 0 - 20 cm --Dark grayish brown (IOYR 4/2) silt loam; hard consistent; brick, shell and charcoal fragments; packed and disturbed horizon; abrupt boundary.
Bt -- 20 - 200 cm -- Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; films in pores and on peds; gradual boundary.
BC -- 200 - 240 cm -- Dark yellowish brown (lOYR 4/4) silt loam; weak, fine, angular blocky structure; sticky consistent; few very dark brown (lOYR 2/2) stains; clear boundary.
PEORIA LOESS MIXING ZONE - 240 - 320 em
C&2Bt -- 240 - 320 cm -- Brownish yellow (lOYR 6/6) silt loam with weak, medium, subangular blocky structure; slightly sticky consistent; few strong brown (7.5YR 5/8) stains; very dark brown (lOYR 2/2) stains and concretions; diffuse boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 320 - 860 em
2Bt -- 320 - 400 cm -- Brownish yellow (lOYR 6/8) silty clay loam with common, fme, distinct light gray (lOYR 7/2) mottles; moderate, medium, angular blocky structure; firm consistent; strong brown (7.5YR 5/8) stains; very dark brown (IOYR 2/2) stains and concretions; clay films on peds; gradual boundary.
2CI -- 400 - 500 cm -- Light gray (5Y 7/2) clay with common, coarse, prominent brownish yellow (lOYR 6/8) mottles; plastic consistent; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; pedogenic slickensides; clear boundary.
2C2 -- 500 - 550 cm -- Light gray (2.5Y 7/2) clay loam; friable consistent; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; faint laminations; sand and loamy sand interbeds; clear boundary.
2C3 -- 550 - 660 cm -- Light gray (5Y 712) clay with common, coarse, prominent yellowish red (5YR 5/8) mottles; plastic consistent; very dark brown (lOYR 2/2), strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; pedogenic slickensides; clear boundary.
2C4 -- 660 - 700 cm -- Light gray (2.5Y 7/2) sandy loam with common, coarse, distinct olive yellow (2.5Y 6/6) mottles; very friable consistent; clear boundary.
2C5 -- 700 - 730 cm -- Light gray (5Y 7/2) clay with common, fine, distinct olive yellow (2.5Y 6/6) mottles; plastic consistent; yellowish red (5YR 5/8) stains and concretions; laminations; red (2.5YR 5/6) clay beds; clear boundary.
B-17
2C6 -- 730 - 750 cm -- Light gray (5Y 712) clay loam with common, fine, distinct olive yellow (2.5Y 6/6) mottles; very friable consistent; laminations; clear boundary.
B-18
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CB9 -- Cote Blanche Island, Louisiana -- CONTINUED.
2C7 -- 750 - 860 cm -- Light gray (5Y 7/2) clay with common, coarse, prominent yellowish red (5YR 5/8) mottles; plastic consistent; very dark brown (lOYR 2/2) stains; red (2.5YR 4/6) laminated clay bed; pedogenic slickensides; shear fractures.
B-19
CBIO -- Cote Blanche Island, Louisiana; core is from the back slope of the island; elevation is 12.2 m (40 ft); slope is I - 3 per cent; drilled by W. J. Autin and F. K. Kring; described by W. 1. Autin and R. P. McCulloh.
PEORIA LOESS -- 0 - 250 em
Ap -- 0 - 20 cm -- Grayish brown (IOYR 5/2) silt loam; weak, thin, platy structure; friable consistent; few roots; horizon packed by traffic; upper 5 cm are road fill; clear boundary.
Btl -- 20 - 90 cm --Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; clay films on ped faces; gradual boundary.
Bt2 -- 90 - 190 cm -- Dark yellowish brown (10YR 4/4) silt loam with few, medium, distinct very pale brown (IOYR 7/3) mottles; moderate, medium, subangular blocky structure; friable consistent; very pale brown (IOYR 7/3) silt loam fills of root traces and worm burrows; gradual boundary.
BC -- 190 - 250 cm -- Light yellowish brown (IOYR 6/4) silt loam with few, fine, faint very pale brown (IOYR 7/3) mottles; weak, fine, angular blocky structure; sticky consistent; few very pale brown (10YR 7/3) silt loam tongues; gradual boundary.
PEORIA LOESS MIXING ZONE - 250 - 290 em
C&2Bt -- 250 - 290 cm -- Yellow (IOYR 7/6) silt loam with few, medium, distinct light gray (lOYR 7/2) mottles; weak, fine, angular blocky structure; sticky consistent; very dark brown (lOYR 2/2) concretions; few very pale brown (10YR 7/3) silt loam tongues; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 290 - 850 em
2Btl-- 290 - 320 cm -- Yellow (IOYR 7/6) silty clay loam with few, medium, distinct light gray (lOYR 7/2) mottles; weak, fine, angular blocky structure; slightly plastic consistent; very dark brown (10YR 2/2) concretions; discontinuous clay films; gradual boundary.
2Bt2 -- 320 - 380 cm -- Yellow (lOYR 7/8) clay with common, fine, distinct light gray (10YR 7/2) mottles; weak, medium, angular blocky structure; firm consistent; yellowish red (5YR 5/8) stains; discontinuous clay films; gradual boundary.
2Bt3 -- 380 - 430 cm -- Yellow (IOYR 7/8) clay with common, coarse, distinct light gray (lOYR 7/2) mottles; moderate, medium, angular blocky structure; firm consistent; yellowish red (5YR 5/8) stains; clay films on ped surfaces; gradual boundary.
2BC -- 430 - 490 cm -- Light gray (2.5Y 7/2) silt loam with common, medium, prominent strong brown (7.5YR 5/8) mottles; moderate, medium, angular blocky structure; friable consistent; brownish yellow (lOYR 6/8) stains; clear boundary.
B-20
I
2CI -- 490 - S80 cm - Light gray (SY 7/2) clay; firm consistent; very dark brown (IOYR 2/2), yellowish brown (IOYR S/8), and yellowish red (SYR S/8) stains, and heavy (2.SY S/6) stains and concretion zone at base of unit; silt loam interbeds; abrupt boundary.
2C2 -- 580 - 660 cm -- Light gray (5Y 7/2) clay; firm consistent; very dark brown (lOYR 2/2), yellowish brown (IOYR 5/8), and strong brown (7.5YR 5/8) stains; concretion zone at top of unit; silt loam interbeds; diffuse boundary.
B-21
CB10 -- Cote Blanche Island, Louisiana -- CONTINUED.
= 2C3 -- 660 - 740 cm -- Light gray (2.SY 7/2) clay with common, coarse, prominent reddish yellow (7.SYR 6/S) mottles; firm consistent; yellowish red (SYR SIS) stains; shear fractures; clear boundary.
2C4 -- 740 - SOO cm -- Light reddish brown (SYR 6/4) clay; firm consistent; very dark brown (lOYR 2/2) stains; light gray (2.SY 7/2) tongues; shear fractures; clear boundary.
2CS -- SOO - SSO cm -- Light gray (2.5Y 7/2) clay with common, coarse, prominent brownish yellow (lOYR 6/S) mottles; firm consistent; very dark brown (lOYR 2/2) stains; shear fractures.
B-22
CBll -- Cote Blanche Island, Louisiana; core is from the colluvial apron on the lower toe slope of the island; elevation is I.S m (S ft); slope is 0 - 1 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
FILL -- 0 - 10 em
-- 0 - 20 cm -- Very dark grayish brown (10YR 3/2) silt loam; friable consistent; abundant shells; road fill; abrupt boundary.
OVERW ASH COLLUVIUM - 20 - 340 em
A -- 20 - 40 cm --Dark gray (SY 4/1) silt loam; friable consistent; few roots; packed by traffic; abrupt boundary.
Bw -- 40 - 120 cm -- Light yellowish brown (IOYR 6/4) silt loam with many, medium, distinct brown (IOYR 4/3) mottles; weak, fine, angular blocky structure; friable consistent; abundant very dark brown (lOYR 2/2) stains and concretions; clear boundary.
Cgl -- 120 - 220 cm -- Light brownish gray (IOYR 6/2) silt loam with common, coarse, distinct dark yellowish brown (IOYR 4/4) mottles; sticky consistent; common very dark brown (lOYR 2/2) stains and concretions; gradual boundary.
Cg2 -- 220 - 340 cm -- Gray (IOYR 6/1) silty clay loam; slightly plastic consistent; strong brown (7.SYR S/8) and yellowish red (SYR S/8) stains; very dark brown (10YR 212) stains and concretions; silt loam interbeds; clear boundary.
HOLOCENE MARSH - 340 - 670 em
2Cgl -- 340 - 410 cm -- Dark bluish gray (SB 4/1) clay with common, medium, distinct dark yellowish brown (IOYR 4/4) mottles; plastic consistent; few roots; diffuse boundary.
2Cg2 -- 410 - S60 cm -- Dark gray (2.SY 4/0) clay; plastic consistent; abundant roots, grass, and wood fragments; wood sample from 490 cm; laminated silty clay loam bed at SIO to S20 cm; abrupt boundary.
2Cg3 -- S60 - 600 cm -- Greenish gray (SBG 6/1) silty clay loanl; slightly plastic consistent; clear boundary.
2Cg&3Bt -- 600 - 670 cm -- Olive yellow (2.SY 6/8) silty clay loam with common, medium, prominent gray (SY 6/1) mottles; slightly plastic consistent; wood fragments, wood sample from 660 cm; brownish yellow (IOYR 6/8) stains; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 670 - 980 em
3Bt -- 670 - 700 cm -- Brownish yellow (lOYR 6/8) clay with common, fine, distinct light gray (IOYR 7/2) mottles; moderate, medium, angular blocky structure; firm consistent; clay films on ped
B-23
faces; very dark brown (lOYR 2/2) stains and concretions; light gray (lOYR 7/2) tongues; gradual boundary.
~ 3Cl -- 700 - 790 cm -- Light brownish gray (2.5Y 6/2) clay with common, fine, prominent brownish yellow (lOYR 6/8) mottles; firm consistent; very dark brown (lOYR 2/2) stains and concretions; light gray (lOYR 7/2) tongues; pedogenic slickensides; shear fractures; gradual boundary.
_1
,\ B-24
CBll -- Cote Blanche Island, Louisiana -- CONTINUED.
3C2 -- 790 - 890 cm -- Light gray (2.5Y 7/2) silty clay loam; fIrm consistent; very dark brown (lOYR 2/2) stains and concretions; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; gradual boundary.
3C3 -- 890 - 960 cm - Yellow (2.5YR 7/6) clay; firm consistent; very dark brown (IOYR 2/2) stains and concretions; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; sandy clay loam and silt loam interbeds; clear boundary.
3C4 -- 960 - 980 em -- Light gray (5Y 712) clay; firm consistent; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; laminations; yellow (2.5Y 7/6) interbed.
B-25
I _
CB12 -- Cote Blanche Island, Louisiana; core is from the lower back slope of the island; elevation is 7.6 m (25 ft); slope is 1 - 3 per cent; drilled by W. 1. Autin and F. K. Kring; described by W. 1. Autin and R. P. McCulloh.
PEORIA WESS -- 0 - 270 em
Ap -- 0 - 10 cm -- Dark grayish brown (10YR 4/2) silt loam; weak, fine, angular blocky structure; friable consistent; common roots; clear boundary.
Bw -- 10 - 40 cm -- Dark yellowish brown (1OYR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; few roots; clear boundary.
Btl -- 40 - 80 -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; clay ftIms on ped surfaces; gradual boundary.
Bt2 -- 80 - 210 -- Dark yellowish brown (10YR 4/4) silt loam with common, medium, distinct very pale brown (10YR 7/3) mottles; moderate, medium, subangular blocky structure; friable consistent; very pale brown (10YR 7/3) root traces; clay ftIms on ped surfaces; gradual boundary.
BC -- 210 - 270 -- Light yellowish brown (10YR 6/4) silt loam with common, coarse, faint very pale brown (10YR 7/3) mottles; weak, fine, angular blocky structure; sticky consistent; very pale brown (10YR 7/3) root traces; gradual boundary.
PEORIA WESS MIXING ZONE - 270 - 340 em
C&2Bt -- 270 - 340 cm -- Brownish yellow (10YR 6/6) silt loam with common, medium, distinct light gray (10YR 7/2) mottles; moderate, medium, angular blocky structure; friable consistent; clay films on ped surfaces; very dark brown (10YR 2/2) concretions; very pale brown (1OYR 7/3) root traces; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALWFORMATION -- 340 - 850 em
2Bt -- 340 - 380 cm -- Brownish yellow (1OYR 6/S) clay with common, fine, prominent red (2.5YR 4/S) mottles; weak, fine, angular blocky structure; firm consistent; clay films on peds; very dark brown (1OYR 2/2) stains on root traces; light gray (10YR 7/2) silt loam tongues; gradual boundary.
2Cl -- 3S0 - 470 cm -- Light gray (5Y 7/2) clay with common, medium, prominent red (2.5YR 4/S) mottles; firm consistent; heavy ,red (2.5YR 4/S) stains at top of unit; diffuse boundary.
2C2 -- 470 - 5S0 cm -- Light olive gray (5Y 6/2) silty clay loam with common, coarse, prominent light reddish brown (5YR 6/3) mottles; slightly plastic consistent; yellowish red (5YR SIS) stains at base of unit; silt loam interbeds; diffuse boundary.
2C3 -- 580 - 620 cm -- Light reddish brown (5YR 6/3) clay; firm consistent; laminations; light _I gray (5Y 7/2) interbeds; clear boundary. c-~i
B-26
I I i Ii
I , ;j
2C4 -- 620 - 700 cm -- Brownish yellow (lOYR 6/8) silty clay loam with common, medium, distinct strong brown (7.SYR S/8) mottles; slightly plastic consistent; yellowish red (SYR S/8) stains; light gray (2.SY 7/0) tongues; diffuse boundary.
2CS -- 700 - 770 cm -- Brownish yellow (lOYR 6/8) clay; firm consistent; light gray (2.SY 7/0) tongues; diffuse boundary.
B-27
CB12 -- Cote Blanche Island, Louisiana -- CONTINUED.
~ 2C6 --770 - 850 cm -- Strong brown (7.5YR 5/8) clay with common, fine, distinct red (2.5YR 516) mottles; firm consistent; light gray (2.5Y 7/2) interbeds; shear fractures.
B-28
i
CB 13 -- Cote Blanche Island, Louisiana; core is from the middle back slope of the island; elevation is 16.8 m (55 ft); slope is 3 - 5 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh; description generalized due to poor recovery.
PEORIA LOESS - 0 - 220 em
A -- 0 - 10 cm -- Very dark grayish brown (lOYR 3/2) silt loam; weak, fine, granular structure; friable consistent; common roots; clear boundary.
B -- 10 - 60 cm -- Dark yellowish brown (10YR 4/4) silt loam; weak, fine, angular blocky structure; friable consistent; few roots; clear boundary.
C -- 60 - 220 cm -- Light yellowish brown (10YR 6/4) silt loam with few, medium, faint very pale brown (lOYR 7/3) mottles; sticky consistent; clear boundary.
PEORIA LOESS MIXING ZONE - 220 - 250 em
C&2B -- 220 - 2S0 cm -- Brownish yellow (1OYR 6/6) silty clay loam; slightly plastic consistent; very dark brown (1OYR 2/2) stains; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 250 - 790 em
2Bt -- 2S0 - 310 cm -- Brownish yellow (lOYR 6/6) clay with common, fme, prominent red (2.5YR 4/6) mottles; moderate, medium, angular blocky structure; firm consistent; light gray (1OYR 7/2) silt loam tongues; gradual boundary.
2C1 -- 310 - 410 cm -- Light gray (SY 7/1) clay with common, coarse, prominent red (2.5YR 4/6) mottles; firm consistent; faint laminations; clear boundary.
2C2 -- 410 - 790 cm -- Light gray (SY 7/2) clay with common, coarse, prominent brownish yellow (10YR 6/8) mottles; firm consistent; very dark brown (10YR 2/2), yellowish red (5YR S/8), and red (2.SYR 4/8) stains; silt loam interbed at 660 to 680 cm.
B-29
I
I
CB14 -- Cote Blanche Island, Louisiana; core is from the upper shoulder slope of the island; elevation is 22.9 m (75 ft); slope is 3 - 5 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 250 em
Ap -- 0 - 10 cm -- Very dark grayish brown (10YR 3/2) silt loam; weak, fine, granular structure; friable consistent; common roots; shell fragments; abrupt boundary.
Btl -- 10 - 60 -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common roots; clay films on ped surfaces; gradual boundary.
Ba -- 60 - 130 -- Dark yellowish brown (1OYR 4/4) silt loam with few, medium, distinct very pale brown (10YR 7/3) mottles; moderate, medium, sub angular blocky structure; friable consistent; very pale brown (1OYR 7/3) root traces; clay films on ped surfaces; gradual boundary.
Bt3 -- 130 - 210 -- Dark yellowish brown (10YR 4/4) silt loam with common, medium, distinct very pale brown (10YR 7/3) mottles; moderate, medium, subangular blocky structure; friable consistent; very pale brown (1OYR 7/3) root traces; clay films on ped surfaces; very dark brown (10YR 2/2) stains; gradual boundary.
BC -- 210 - 250 -- Light yellowish brown (10YR 6/4) silt loam with common, medium, faint very pale brown (lOYR 7/3) mottles; weak, fine, angular blocky structure; sticky consistent; very pale brown (10YR 7/3) root traces; very dark brown (10YR 2/2) stains; gradual boundary.
PEORIA LOESS MIXING ZONE - 250 - 320 em
BC&2Bt -- 250 - 320 cm -- Brownish yellow (10YR 6/8) silt loam with common, medium, distinct light gray (10YR 712) mottles; weak, fine, angular blocky structure; friable consistent; yellowish red (5YR 5/8) stains; very dark brown (1OYR 2/2) concretions; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 320 - 910 em
2Bt -- 340 - 370 cm -- Brownish yellow (lOYR 6/8) silty clay loam with common, fme, distinct light gray (10YR 7/2) mottles; weak, fine, angular blocky structure; firm consistent; clay films on peds; yellowish red (5YR 5/8) stains; very dark brown (lOYR 2/2) stains on root traces; gradual boundary.
2Cl -- 370 - 470 cm -- Light gray (2.5Y 7/2) clay with common, medium, prominent red (2.5YR 4/8) mottles; firm consistent; pedogenic slickensides; diffuse boundary.
2C2 -- 470 - 570 cm -- Light gray (2.5Y 7/2) sandy clay loam with few, fine, prominent yellow (1OYR 7/8) mottles; firm consistent; brownish yellow (lOYR 6/8) stains at base of unit; clear boundary.
2C3 -- 570 - 910 cm -- Pale yellow (2.5Y 8/3) fine to medium sand; loose consistent; brownish yellow (1OYR 6/8) stains; sandy loam and loamy sand interbeds.
B-30
I CBI5 -- Cote Blanche Island, Louisiana; core is from the upper shoulder slope of the island; elevation is 24.4 m (80 ft); slope is I - 3 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA WESS - 0 - 250 em
Ap -- 0 - 10 cm -- Very dark grayish brown (lOYR 3/2) silt loam; weak, fine, granular structure; friable consistent; common roots; clear boundary.
Bt -- 10 - 160 -- Dark yellowish brown (IOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; clay films on ped surfaces; gradual boundary.
BC -- 160 - 220 -- Dark yellowish brown (IOYR 4/4) silt loam with common, medium, faint very pale brown (IOYR 7/3) mottles; weak, medium, angular blocky structure; friable consistent; very pale brown (IOYR 7/3) root traces; gradual boundary.
PEORIA WESS MIXING ZONE -- 220 - 250 em
C&2B -- 250 - 270 cm -- Brownish yellow (IOYR 6/6) silt loam with common, medium, distinct light gray (IOYR 7/2) mottles; weak, fine, angular blocky structure; friable consistent; very dark brown (IOYR 2/2) stains and concretions; light gray (IOYR 712) tongues; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 250 - 760 em
2Btl -- 250 - 320 cm -- Brownish yellow (IOYR 6/8) silty clay loam with common, medium, distinct light gray (IOYR 7/2) mottles; weak, medium, angular blocky structure; firm consistent; clay films on peds; light gray (IOYR 7/2) tongues; clear boundary.
2BtZ -- 320 - 380 cm -- Brownish yellow (IOYR 6/8) clay with common, fine, prominent red (2.5YR 4/8) mottles; moderate, medium, angular blocky structure; firm consistent; clay films on peds; light gray (IOYR 7/2) tongues; very dark brown (IOYR 2/2) stains on root traces; pedogenic slickensides; clear boundary.
2Bt3 -- 380 - 420 cm -- Reddish brown (5YR 5/4) clay with common, coarse, prominent light gray (5Y 7/2) mottles; moderate, medium, angular blocky structure; firm consistent; yellowish red (5YR 5/8) and strong brown (7.5YR 5/8) stains; discontinuous clay films; very dark brown (lOYR 2/2) stains and concretions; pedogenic slickensides; clear boundary.
2CI -- 420 - 490 cm -- Light gray (5Y 7/2) clay; firm consistent; shear fractures with modern roots on surfaces; gradual boundary.
2C2 -- 490 - 520 cm -- Light gray (5Y 712) silty clay; firm consistent; brownish yellow (IOYR 6/8) stains; gradual boundary.
2C3 -- 520 - 590 cm -- Light gray (5Y 712) clay with common, coarse, prominent brownish yellow (IOYR 6/8) mottles;; firm consistent; pedogenic slickensides; clear boundary.
B-3 I
_I
2C4 -- S90 - 760 -- Light gray (SY 7/2) clay with common, coarse, prominent brownish yellow (lOYR 6/8) mottles; firm consistent; heavy very dark brown (IOYR 2/2) stains; strong brown (7.SYR S/8) and yellowish red (SYR S/8) stains and concretions; pedogenic slickensides; silty clay and silt loam interbeds.
B-32
CB16 -- Cote Blanche Island, Louisiana; core is from the summit of the island; elevation is 29.6 m (97 ft); slope is 0 - 1 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and
!, R. P. McCulloh. I'
. :j
PEORIA LOFSS - 0 - 230 em
Ap -- 0 - 10 cm --Dark grayish brown (10YR 4/2) silt loam; weak, fine, angular blocky structure; friable consistent; common roots; clear boundary.
Btl -- 10 - 100 -- Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; clay films on ped surfaces; gradual boundary.
Bt2 -- 100 - 230 -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; clay films on ped surfaces; gradual boundary.
PEORIA LOESS MIXING ZONE - 230 - 310 em
Bt&2Bt -- 230 - 310 cm -- Brownish yellow (IOYR 6/6) silt loam; moderate, medium, subangular blocky structure; friable consistent; very dark brown (lOYR 2/2) and yellowish red (SYR S/8) stains and concretions; clay films on ped surfaces; gradual boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 310 - 1710 em
2Btl -- 310 - 3S0 cm --Brownish yellow (IOYR 6/6) silty clay loam; moderate, medium, subangular blocky structure; firm consistent; clay films on peds; yellowish red (SYR S/8) stains and concretions; brecciated fragments of Peoria Loess in crack fill at 340 to 3S0 cm; clear boundary.
2Bt2 -- 3S0 - 480 cm -- Brownish yellow (10YR 6/8) clay with few, medium, prominent light gray (SY 7/2) mottles; moderate, fine, angular blocky structure; firm consistent; red (2.SYR 4/6) stains; very dark brown (IOYR 2/2) stains on root traces; pedogenic slickensides; clear boundary.
2Cl -- 480 - 640 cm -- Light gray (SY 712) clay with common, coarse, distinct brownish yellow (lOYR 6/8) mottles; firm consistent; yellowish red (SYR S/8) stains; pedogenic slickensides; gradual boundary.
2C2 -- 640 - 740 cm -- Reddish yellow (7.SYR 6/6) loam; friable consistent; very dark brown (10YR 2/2) stains; light gray (SY 7/2) clay interbeds; brecciated soil fragments from 680 to 720 cm; abrupt boundary.
2C3 -- 740 - 800 cm -- Light gray (SY 7/2) clay; firm consistent; brownish yellow (IOYR 6/8), very dark brown (lOYR 2/2), strong brown (7.5YR S/8), and yellowish red (SYR S/8) stains; laminations of fme sand and silt loam; gradual boundary.
2C4 -- 800 - 980 cm -- Light gray (SY 712) silty clay loam; friable consistent; brownish yellow (10YR 6/8) stains; brecciated soil fragments throughout horizon; gradual boundary.
B-33
2C5 -- 980 - 1350 cm -- Light brown (7.5YR 6/4) sandy loam; very friable consistent; brownish yellow (IOYR 6/8) and light gray (5Y 7/2) beds of loam and silt loam; calcareous below 1280 cm; clear boundary.
2C6 -- 1350 - 1610 cm -- Greenish gray (5GY 5/1) clay; plastic consistent; light gray (5Y 7/2), 1 ~. strong brown (7.5YR 5/8), and yellowish red (5YR 5/8) stains; laminated CaCO, rock at 1470 cm;
red (2.5YR 5/6) laminated clay beds at 1530 cm and 1580 cm; horizon is calcareous; abrupt boundary.
B-34 ___ I
CB16 -- Cote Blanche Island, Louisiana -- CONTINUED.
2C7 -- 1610 - 1660 cm -- Gray (5Y 5/1) coarse sand; loose consistent; horizon is calcareous; abrupt boundary.
2C8 -- 1660 - 1710 cm -- Dark greenish gray (5GY 411) clay; very plastic; strong brown (7.5YR 5/8) and yellowish red (5YR 5/8) stains; laminations; horizon is calcareous.
B-35
CB 17 -- Cote Blanche Island, Louisiana; core is from a shoulder slope of a nose slope on the southwestern side of the island; elevation is 13.7 m (4S ft); slope is 1 - 3 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
I ~ PEORIA LOESS -- 0 - 220 em
, "j , , !
-,
Ap -- 0 - 10 cm -- Dark grayish brown (lOYR 4/2) silt loam; weak, fine, granular structure; friable consistent; common roots; clear boundary.
Btl -- 10 - ISO -- Dark yellowish brown (lOYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; common roots, pores, and worm burrows; clay films on ped surfaces; gradual boundary.
Bt2 -- ISO - 220 -- Dark yellowish brown (10YR 4/4) silt loam with common, medium, distinct light yellowish brown (10YR 6/4); moderate, medium, subangular blocky structure; friable consistent; common roots, pores, and worm burrows; clay films on ped surfaces and in pores; clear boundary.
PEORIA LOESS MIXING ZONE - 220 - 250 em
Bt&2Bt -- 220 - 2S0 cm -- Brownish yellow (lOYR 6/6) silt loam with common, coarse, distinct light gray (10YR 7/2) mottles; moderate, fine, angular blocky structure; friable consistent; clay films on ped surfaces; very dark brown (10YR 2/2) stains in root traces; light gray (lOYR 7/2) tongues; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 250 - 1150 em
2Btl -- 2S0 - 290 cm -- Brownish yellow (10YR 6/6) silty clay loam; weak, fine, angular blocky structure; friable consistent; clay films on peds; very dark brown (10YR 2/2) and yellowish red (SYR SIS) stains and concretions; light gray (10YR 7/2) tongues; clear boundary.
2Bt2 -- 290 - 390 cm -- Brownish yellow (10YR 6/6) clay; weak, fine, angular blocky structure; firm consistent; clay films on peds; very dark brown (lOYR 2/2) and yellowish red (SYR SIS) stains and concretions; light gray (10YR 7/2) tongues; pedogenic slickensides; clear boundary.
2BC -- 390 - 420 cm -- Brownish yellow (10YR 6/6) clay with common, fine, prominent red (2.SYR 4/S) mottles; weak, fine, angular blocky structure; firm consistent; pedogenic slickensides; shear fractures; clear boundary.
2Cl -- 420 - 610 cm -- Light gray (SY 7/2) clay with abundant, coarse, prominent brownish yellow (IOYR 6/6) mottles; firm consistent; very dark brown (lOYR 2/2) stains; CaCO' nodules at S60 cm; abundant shear fractures; diffuse boundary.
2C2 -- 610 - 910 cm -- Light gray (SY 7/2) clay with abundant, coarse, prominent reddish yellow (7.5YR 6/S) mottles; firm consistent; very dark brown (10YR 2/2) and red (2.SYR 4/S) stains; abundant shear fractures; silt interbeds; diffuse boundary.
B-36
2C3 -- 910 - 1080 cm -- Light gray (5Y 7/2) clay; firm consistent; abundant shear fractures with very dark brown (10YR 2/2) and reddish yellow (7.5YR 6/8) stained surfaces; clear boundary.
2C4 -- 1080 - H20 cm -- Gray (5Y 5/1) clay with common, fine, distinct greenish gray (5BG 5/1) mottles; firm consistent; abrupt boundary.
B-37
CB17 -- Cote Blanche Island, Louisiana -- CONTINUED.
oc! 2C5 -- 1120 - 1150 cm -- Greenish gray (5BG 5/1) clay; firm consistent; scattered white fibrous crystals; abrupt boundary.
OJ .. I
PRAIRIE COMPLEX, UNNAMED WWER FACIES - 1150 - 1460 em
3CI -- 1150 - 1190 cm -- Dark gray (IOYR 4/1) silty clay loam; friable consistent; laminations; scattered organic material; scattered white fibrous crystals; clear boundary.
3C2 -- 1190 - 1240 cm -- Black (lOYR 2/1) silty clay loam; friable consistent; scattered charcoal, reeds, and organic material; diffuse boundary.
3C3 -- 1240 - 1460 cm -- Dark brown (IOYR 3/3) silty clay loam; friable consistent; laminations; scattered charcoal, reeds, and organic material on laminae.
B-38
I 1
CBlS -- Cote Blanche Island, Louisiana; core is from an upper back slope of a nose slope on the southwestern side of the island; elevation is 10.7 m (35 ft); slope is 1 - 3 per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS - 0 - 210 em
A -- 0 - 10 cm -- Grayish brown (IOYR 5/2) silt loam; weak, fine, granular structure; friable consistent; common roots; abrupt boundary.
Bt -- 10 - SO -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few pores; clay films on ped surfaces; gradual boundary.
Btx -- SO - 210 cm -- Dark yellowish brown (10YR 4/4) silt loam; moderate, medium, angular blocky structure; firm consistent; few pores; very pale brown (IOYR 7/3) silt films on ped surfaces; very dark brown (10YR 2/2) stains and concretions at base of unit; clear boundary.
PEORIA LOESS MlXING WNE - 210 - 230 em
Bt&2Bt -- 210 - 230 cm -- Yellow (10YR 7/6) silt loam; moderate, medium, angular blocky structure; firm consistent; very pale brown (IOYR 7/3) silt films on ped surfaces; very dark brown (10YR 2/2) stains and concretions; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION - 230 - 1100 em
2Bt -- 230 - 310 cm -- Brownish yellow (lOYR 6/6) clay; weak, fine, angular blocky structure; firm consistent; clay films and very dark brown (IOYR 2/2) stains on ped surfaces; pedogenic slickensides; clear boundary.
2Cl -- 310 - 340 cm -- Yellowish red (5YR 516) clay with common, fine, prominent olive yellow (2.5Y 6/6) mottles; firm consistent; pedogenic slickensides; shear fractures; clear boundary.
2C2 -- 340 - 650 cm -- Light gray (5Y 7/2) clay with common, coarse, prominent yellowish brown (IOYR 516) mottles; friable consistent; laminations; interbeds of silt, silt loam, and fine sand; shear fractures in clay beds; clear boundary.
2C3 -- 650 - 750 cm -- Pale yellow (5Y 7/3) loamy sand; very friable consistent; brownish yellow (10YR 6/S) and very dark brown (IOYR 2/2) stains; laminations; clay rip clasts; gradual boundary.
2C4 --750 - 1100 cm -- Pale yellow (2.5Y 7/4) fine sand; loose consistent; yellow (10YR 7/S) stains.
B-39
CB19 -- Cote Blanche Island, Louisiana; core is from a local summit on the southwestern side of the island; elevation is 29.0 m (95 ft); slope is 1 - 3 per cent; drilled by R. P. McCulloh and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
PEORIA LOESS -- 0 - 250 em
A -- 0 - 20 cm -- Yellowish brown (10YR 5/4) silt loam; weak, fine, granular structure; friable consistent; common roots; clear boundary.
Bt -- 20 - 210 -- Dark yellowish brown (1OYR 4/4) silt loam; moderate, medium, subangular blocky structure; friable consistent; few roots; common root traces, pores, and worm burrows; clay films on ped surfaces; gradual boundary.
BC -- 210 - 250 -- Yellowish brown (10YR 5/4) silt loam with common, medium, faint light yellowish brown (10YR 6/4) mottles; moderate, medium, subangular blocky structure; friable consistent; clay films in root traces; clear boundary.
PEORIA LOESS MIXING ZONE - 250 - 270 em
Ct&2Bt -- 250 - 270 cm -- Brownish yellow (lOYR 6/6) silt loam with common, coarse, distinct light gray (lOYR 7/2) mottles; moderate, fine, angular blocky structure; friable consistent; very dark brown (1OYR 2/2) stains and concretions; yellowish brown (1OYR 5/4) clay films on ped surfaces and in root traces; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 270 - 1280 em
2Bt -- 270 - 320 cm --Brownish yellow (lOYR 6/6) clay; weak, fine, angular blocky structure; firm consistent; clay films on peds; very dark brown (1OYR 2/2) stains on root traces; pedogenic slickensides; clear boundary.
2Bg -- 320 - 410 cm -- Light gray (5Y 7/2) clay with common, coarse, prominent yellowish brown (1OYR 5/6) mottles; weak, medium, angular blocky structure; firm consistent; very dark brown (10YR 2/2) and yellowish brown (10YR 5/8) stains; pedogenic slickensides; shear fractures; powdery CaCO' at base; clear boundary.
2Cl -- 410 - 580 cm -- Light gray (5Y 7/2) clay; firm consistent; very dark brown (1OYR 2/2), yellowish brown (1OYR 5/8), strong brown (7.SYR 5/8), and yellowish red (SYR 5/8) stains; shear fractures; laminations; interbeds of silt, silt loam, and fine sand; abrupt boundary.
2C2 -- 580 - 700 cm -- Red (2.5YR 5/8) clay; firm consistent; very dark brown (1OYR 212), strong brown (7.5YR 5/8), and yellowish red (5YR 5/8) stains and concretions; shear fractures; interbeds of light gray (SY 712) clay; clear boundary.
2C3 -- 700 - 780 cm -- Light yellowish brown (2.5Y 6/3) sandy loam; friable consistent; very dark brown (10YR 2/2), strong brown (7.5YR 5/8), and yellowish red (5YR 5/8) stains and
'I concretions; interbeds of light gray (SY 7/2) clay; CaCQ3 nodules at 760 to 770 cm; clear boundary. =l
B-40
2C4 -- 7S0 - 12S0 cm --Light gray (5Y 7/2) clay; firm consistent; very dark brown (1OYR 2/2), yellowish brown (1OYR SIS), strong brown (7.5YR SIS), and yellowish red (5YR SIS) stains; shear fractures from SSO to 1020 cm; interbeds of loamy sand from 1030 to 1090 cm.
B-41
CB20 -- Cote Blanche Island, Louisiana; core is from the colluvial apron on the upper toe slope of the island; elevation is 1.5 m (5 ft); slope is 0 - [ per cent; drilled by W. J. Autin and F. K. Kring; described by W. J. Autin and R. P. McCulloh.
OVERW ASH COLLUVIUM - 0 - 120 em
A -- 0 - [0 cm -- Dark grayish brown (IOYR 4/2) silt loam with common, fine, distinct dark yellowish brown (IOYR 3/6) mottles; weak, fine, granular structure; friable consistent; common roots; clear boundary.
Bwg -- 10 - 60 cm -- Gray ([OYR 5/[) silt loam with common, fine, distinct brown ([OYR 4/3) mottles; weak, fine, angular blocky structure; friable consistent; common roots; very dark brown ([OYR 2/2) stains; gradual boundary.
Cg-- 60 - [20 cm -- Gray (IOYR 5/[) silt loam; friable consistent; brownish yellow (lOYR 6/8) and very dark brown (lOYR 2/2) stains; clear boundary.
PRAIRIE COMPLEX, MT. PLEASANT BLUFF ALLOFORMATION -- 120 - 970 em
2Bt -- [20 - [50 cm -- Light brownish gray (2.5Y 612) silt loam with common, medium, distinct brownish yellow ([OYR 6/6) mottles; weak, medium, angular blocky structure; friable consistent; clay films on peds; brownish yellow (lOYR 6/8) stains; very dark brown (IOYR 2/2) concretions; gradual boundary.
2C[ -- [50 - 250 cm -- Light brownish gray (2.5Y 6/2) silt loam with few, fine, distinct brownish yellow (IOYR 6/6) mottles; friable consistent; few very dark brown ([OYR 2/2) concretions; gradual boundary.
2C2 -- 250 - 360 cm -- Light brownish gray (2.5Y 6/2) silt loam with common, coarse, distinct brownish yellow (IOYR 6/6) mottles; friable consistent; abundant very dark brown ([OYR 2/2) and brownish yellow ([OYR 6/8) stains; gradual boundary.
2C3 -- 360 - 390 cm -- Light brownish gray (2.5Y 6/2) silt loam; friable consistent; few very dark brown (lOYR 212) and brownish yellow ([OYR 6/8) stains; gradual boundary.
2C4 -- 390 - 580 cm -- Light gray (5Y 7/2) clay with common, fine, distinct yellowish brown (IOYR 5/6) mottles; plastic consistent; very dark brown (lOYR 2/2) and brownish yellow ([OYR 6/8) stains; abrupt boundary.
2C5 -- 580 - 760 cm -- Greenish gray (5BG S/[) clay with common, medium, distinct olive (5Y 4/4) mottles; plastic consistent; scattered reeds and wood fragments; clear boundary.
- , 2C6 -- 760 - 820 cm -- Greenish gray (5BG 5/[) sandy clay loam with few, medium, distinct -, olive (5Y 4/4) mottles; friable consistent; interbeds of clay and fine sand; clear boundary.
r 1 2C7 -- 820 - 970 cm -- Greenish gray (5GY 5/[) silty clay loam; slightly plastic consistent; ,I scattered organic matter.
B-42