preservation and recognition of middle and early

QUATERNARY RESEARCH 47, 147–154 (1997)ARTICLE NO. QR961864

Preservation and Recognition of Middle and Early Pleistocene Loessin the Driftless Area, Wisconsin

PETER M. JACOBS

Department of Physics, Astronomy, and Geology, Valdosta State University, Valdosta, Georgia 31698

JAMES C. KNOX

Department of Geography, University of Wisconsin, Madison, Wisconsin 53706

AND

JOSEPH A. MASON

Department of Geography, Northern Illinois University, Dekalb, Illinois 60115

Received July 8, 1996

throughout the valley; locally as many as six to seven unitsAn exceptional stratigraphic and pedologic record of Pleistocene are present. The Mississippi Valley loess stratigraphic record

environmental conditions occurs at the Kieler Site in the Driftless extends throughout much of the middle Pleistocene, but noArea of southwestern Wisconsin. Peoria, Roxana, Loveland, and early Pleistocene loess has been recognized. Rare occur-pre-Loveland loesses overlie weathered bedrock residuum. The rences of middle Pleistocene loesses older than the Illinoianpre-Loveland unit previously has been included as part of the Glaciation and complete absence of early Pleistocene loessesresiduum at other Driftless Area sites. Early and middle Pleisto-

is enigmatic. We address this issue and hypothesize fromcene loesses in the Mississippi Valley are normally absent at moststratigraphic information gleaned from the Kieler sectionslocalities. Rather than nondeposition, we suggest the apparentthat at least some pre-Illinoian loesses are not recognizedabsence of pre-Illinoian loess units is due in part to erosion, butbecause they are strongly weathered and integrated with re-also to weathering that renders loesses unrecognizable so they aresiduum.classified as ‘‘residuum.’’ q 1997 University of Washington.

STRATIGRAPHY AND PALEOPEDOLOGYINTRODUCTION AT THE KIELER SITE

Several 8- to 9-m-thick stratigraphic sections containingThe Driftless Area of the Upper Mississippi Valley is ahilly, stream-dissected region of southwestern Wisconsin multiple loess deposits and buried soils were exposed during

recent highway construction near Kieler, Grant County, Wis-and northwestern Illinois that was not over-ridden by glacierice during the Quaternary Period. This region experienced consin in the East 1/2 of Section 9, T1N, R2W, 4th principal

meridian (latitude 42734* N, longitude 90736* W). The Kielervery severe erosion during the Quaternary that was acceler-ated by periglacial climatic conditions when glacier ice epi- Site is characterized by four loess units overlying bedrock

residuum developed on shale of the Maquoketa Formationsodically abutted one or more sides of the Driftless Area(Fig. 1). Here we present stratigraphic and pedologic data (Ordovician) on the higher ridge-crest elevations or non-

cherty dolomite of the upper Galena Formation at slightlyfrom the Kieler Site, located in the extreme southwesterncorner of the Driftless Area (Fig. 1). The site is on an upland lower elevations.

Multiple stratigraphic sections were measured, described,divide about 4.5 km east and about 100 m above the presentfloodplain of the Mississippi River. The site has preserved and sampled at the Kieler Site. Additional cores were ex-

tracted with a Giddings hydraulic probe on the adjacent un-evidence of four Quaternary loess units and four buried soilsand represents one of the best Quaternary eolian records for disturbed upland. One core was sampled in detail for charac-

terization purposes. Pedologic descriptions generally followthe Driftless Area.The record of pre-Illinoian loess deposits in the Missis- standard terminology, including describing mottling patterns

as redox features (Table 1) (Soil Survey Staff, 1992, 1993).sippi Valley is very fragmentary (Follmer, in press; Jacobsand Knox, 1994; Leigh and Knox, 1994; Autin et al., 1991). We also used Follmer’s (1995) klumpen terminology to de-

scribe mesoscale pedogenic fabric. Grain size was deter-Generally, there are three loess units found repeatedly

147 0033-5894/97 $25.00Copyright q 1997 by the University of Washington.

All rights of reproduction in any form reserved.

AID QR 1864 / a606$$$$61 03-11-97 07:09:36 qral AP: QR

148 JACOBS, KNOX, AND MASON

cherty bedrock units tends to be thick because erosion-resis-tant stonelines form as surface lags and protect the residuumfrom excessive erosion. Because the Rountree Formationshown in Figure 2 developed from weathering of shale anddolomite, its color is grayish brown rather than more typicaldark-brown to reddish-brown colors observed where the re-siduum has developed only from carbonates. The age of Unit1 at the Kieler Site is unknown, but based on stratigraphicrelationships it probably is at least of middle Pleistoceneage and possibly is much older. Long-term pedogenesis isindicated by strong, very fine and fine blocky structure andhigh clay content throughout the unit. Most ped faces arelustrous, but we could not confidently separate clay filmsfrom shrink–swell surfaces.

Pre-Illinoian silt (unit 2). The oldest loess at the KielerSite appears to be contained in a strongly weathered zoneresting on top of the Rountree Formation residuum. Thiszone has been previously recognized due to its notable siltcontent, but was included as an upper member of theRountree Formation (Knox and Maher, 1974; Knox et al.,1990). Unit 2 is pedologically continuous with the residuumof Unit 1. The boundary between the units is largely ob-scured, but the units are discernable upon detailed morpho-logical description and particle-size analysis. The well-orga-nized pedogenic fabric of Unit 2 differs from Unit 1 inhaving a browner color and pervasive clay films coating thefine subangular to angular blocky structure. On average, Unit2 contains 23% more silt than Unit 1 (Fig. 2). The high clay

FIG. 1. Map of the Driftless Area in the Upper Mississippi Valleycontent of Unit 2 relative to other buried soils in midwesternshowing location of Kieler sections relative to the Mississippi River andloess units is probably due to a variety of reasons, includingother sites mentioned in the text.eolian accretion, particle-size reduction associated withstrong weathering, and long-term pedogenic mixing with theclayey residuum beneath. High-resolution Coulter Counter

mined at whole phi intervals, combining wet sieving for the analyses showed skewness toward finer silt fractions, similarsand fraction, Coulter Counter analyses for the silt fraction to a stratigraphically equivalent pre-Illinoian loess at the(Milligan and Krank, 1991), and hydrometer analyses for Oil City Site in the central Driftless Area (Fig. 1). There,the clay fraction (Gee and Bauder, 1986). Dithionite soluble micromorphological examinations showed nearly completeiron oxyhydroxides were determined following the method weathering of silt-size mica grains to clay domains, indicat-of Olsen and Ellis (1982), and calcite and dolomite percent- ing strong interglacial weathering (Jacobs and Knox, 1994).ages in the õ74 mm fraction were determined by gasometric The silt is the key to understanding the origin of Unit 2. Weevolution in a Chittick apparatus (Machette, 1986). Clay believe the only reasonable interpretation for the origin ofminerals of the õ2 mm fraction were identified by X-ray the silt in a pedologically distinct, clast-free, silty clay uplanddiffraction using CuKa radiation on magnesium saturated unit is eolian. We suggest that the silt is related to a pre-and ethylene glycol solvated smears on glass slides. Illinoian ice advance in the midcontinent.

Unit 2 is pre-Illinoian in age, based on stratigraphic posi-Residuum (unit 1). Strongly weathered, clay-rich sedi-ment resting on Paleozoic bedrock is known as the Rountree tion beneath the Loveland loess (Illinoian) and the degree

of soil development; no finite ages are available. The best ageFormation in the Driftless Area (Knox et al., 1990). TheRountree Formation is referred to as ‘‘residuum,’’ but may control on pre-Wisconsinan deposits in the Driftless Area is

at the Oil City Site, where five pre-Wisconsinan units alloriginate from both weathering of shale and dolomite bed-rock and long-term eolian accretion (Frolking et al., 1983; possess normal remanent magnetism (Jacobs and Knox,

1994). Although long-distance correlation is tenuous, UnitSimonson, 1995). At the Kieler Site the Rountree Formationis usually õ1.5 m thick, typical of many sites elsewhere in 2 at Kieler is in the same stratigraphic position and displays

similar pedogenic characteristics as Unit 4 at Oil City, sug-the Driftless Area where the underlying bedrock is shale,sandstone, or chert-free carbonates. Residuum evolving from gesting to us that Unit 2 is middle Pleistocene in age. In

AID QR 1864 / a606$$$$62 03-11-97 07:09:36 qral AP: QR

149EARLY AND MIDDLE PLEISTOCENE LOESS IN WISCONSIN

TABLE 1Pedologic Description of a Representative Kieler Section

Depth Clay Redox and other LowerHorizon (cm) Moist Munsell color Texturea Structureb Consistencec filmsd featurese boundary f

Ap 0-28 10YR 3/2 sil 1f gr mfr — — asBE 28-33 10YR 4/3 sil 1m sbk mfr v1f pf — cBt1 33-67 10YR 4/4 sicl 2m sbk mfr 2d pf — cBt2 67-85 10YR 4/4 sicl 2m-c sbk mfr 2f pf — cBCt1 85-112 10YR 4/4 sicl 1c sbk mfr vld pf — cBCt2 112-130 10YR 5/4 sicl 1c sbk mfr vld pf — gBCt3 130-174 10YR 5/3 sil 1vc sbk mfr vld pf — cBCt4 174-220 10YR 5/3 sil 1vc sbk mfr vld po fld 10YR 6/6,6/8 cC1 220-290 10YR 6/3 sil 0 m mfr vld po c2d 10YR 5/6, 4/6 gC2 290-410 10YR 6/2 sil 0 m mfr — f3p 10-7.5YR 5/6, 4/6 a2BC 410-442 10YR 4/3 sil 0 m mfr — — c2A1 442-456 10YR 4/4 sil 1m gr mvfr — — c2A2 456-474 10YR 4/4 sil 1m pl, 1f sbk mfr — c3p 7.5YR 6/8, silans c3A3 474-488 10YR 4/3 sil 1m sbk, 1f gr mfr — silans c3Bt1 488-516 7.5YR 4/4 sicl 3f-m sbk mfr-fi 3p pf — g3Bt2 516-556 7.5YR 5/4 sicl 3m sbk mfr 3p pf — g3Bt3 556-606 10YR 4/4 sicl 2m-c abk mfr 2p pf — c4Bt1 606-661 7.5YR 4/3 sic 3-2f sbk mfi 3p pf — c5Bt2 661-704 2.5Y 6/2 c 3f-vf sbk mvfi ? c1-2p 10YR-5YR 4/4 c5Bt3 704-776 2.5Y 5/3 c 3f abk, sbk mvfi ? c2p 10YR 2/1(Mn) c5Bt4 776-806 10YR 6/2 c 3f abk, sbk mvfi ? ml-3p 10YR 7/8, 6/8 c6R 806/ Ordovician dolomite

a sil, silt loam; sicl, silty clay loam; sic, silty clay; c, clay.b Grade: 1, weak; 2, moderate; 3, strong. Size: vf, very fine; f, fine; m, medium; c, coarse; vc, very coarse. Kind: gr, granular; pl, platy; sbk, subangular

blocky; abk, angular blocky.c moist (m): vfr, very friable; fr, friable; fi, firm; vfi, very firm.d Amount: v1, very few; 1, few; 2, common; 3, many. Distinctness: f, faint; d, distinct; p, prominent. Location: pf, ped face; po, pores.e Quantity: f, few; c, common; m, many. Size: 1, õ5 mm; 2, 5–15 mm; 3, ú15 mm. Contrast: f, faint; d, distinct; p, prominent.f a, abrupt; c, clear; g, gradual.

contrast, Unit 2 at the Kieler Site is notably different from dale Geosol. The brown A horizon displays strong klumpenthe pre-Loveland silt (Wyalusing Formation) reported by which separates readily into moderate to weak, fine andLeigh and Knox (1994) for the CR3 Site in the lower Wis- medium granular structure (Fig. 3). The sand peak in Figureconsin River Valley (Fig. 1). The Wyalusing Formation at 2 is caused by ferromanganese concretions in the A horizonthe CR3 Site is typically a brown (10YR 4/3 to 10YR 4/4) that formed in association with oxidation of organic mattersilt loam and has a very weak pedogenic fabric, resembling following burial. An E horizon with lighter colors and weakcambic-B to cumulic-A and -E horizon morphology. These to moderate blocky structure and coated with common siltcharacteristics stand in sharp contrast to the strong pedogenic coats (silans) was observed in many sections, but not infabric of Unit 2 at the Kieler Site, suggesting that the silt at the core extracted for characterization. The argillic horizonCR3 is younger than the pre-Loveland silt at the Kieler Site encompasses the bulk of the Loveland Silt and is subdividedand that the two silt units have a different sedimentological into three subhorizons on the basis of coarsening structurehistory. and fewer and thinner clay films with depth. The lower

boundary of the Loveland Silt and Sangamon Geosol is clearLoveland silt (unit 3). The Kieler exposures contain ex-and easily recognized by a change in color and soil structure.ceptionally well-preserved sections of the Loveland Silt and

Unit 3 is loess that was probably derived from an Illinoiana well-drained Sangamon Geosol (Figs. 3 and 4). The siltyvalley train in the Mississippi Valley. The Illinoian age isclay loam unit is noncalcareous. The solum of the Sangamoninferred from the completeness of the Wisconsinan strati-Geosol encompasses the entire thickness of the unit andgraphic section and correlation of pedogenic characteristicscontains a complete uneroded sequence of genetic horizons.with those of the Sangamon Geosol in its type area in IllinoisThe former Sangamon A horizon is preserved almost per-(Follmer, 1983). Rodbell and Forman (1995) used thermolu-fectly, except for minor color loss and overprinting withminescence age estimates for Loveland Loess units in theweak subangular blocky structure following burial and pedo-

genesis associated with development of the overlying Farm- central Mississippi Valley of western Tennessee to suggest

AID QR 1864 / a606$$$$62 03-11-97 07:09:36 qral AP: QR


FIG. 2. Stratigraphy and laboratory data for a representative Kieler section. (A) Grain-size distribution of õ2 mm fraction, (B) carbonate content,(C) dithionite extractable Fe content, and (D) DI ratio, the ratio of the diffraction intensity (counts per second) of the 1.0 nm peak divided by the 0.72nm peak. Degree of pedogenic development indicated by density of shading.

FIG. 3. Photograph of Dalsing Farm Section showing truncated Peoria Silt, Roxana Silt (dark tone, in part), and Loveland Silt with SangamonGeosol. Note thin layers of Roxana Silt sheared over basal Peoria Silt. Downslope is to right. Spade is about 1 m long.

AID QR 1864 / a606$$1864 03-11-97 07:09:36 qral AP: QR


and drier than middle Holocene climates of the region andmay have approximated climate conditions of the moderncentral Great Plains. Zhu and Baker (1995) also describepollen zones suggesting expansion of grassland into centralIllinois during parts of the Sangamonian. Curry and Follmer(1992) suggested that the fossil evidence for grassland usedby King and Saunders (1986) may have only reflected localvegetation around intermittent wetlands rather than a re-gional pattern.

On the well-drained upland at the Kieler Site, a thickSangamon A horizon with well-preserved granular structuresuggests that this Sangamon profile supported grassland dur-ing at least part of its evolution (Fig. 4). In addition, X-raydiffractograms of clay minerals in the Sangamon A horizonshowed a peak between 0.7 and 1.0 nm, indicative of inter-stratified kaolinite and expandable minerals. The interstrati-fication is consistent with the suggestion of Hughes et al.(1993) that K/E interstratification is commonly associatedwith SiO2-extracting plants (grasses). The timing, duration,and extent of grassland is not certain, but abundant sprucecharcoal in the overlying Roxana Silt suggests that borealforest vegetation developed in the region by at least 55,000yr B.P. (Leigh and Knox, 1993). Because the mollic charac-teristics are so well preserved and transgress into the Farm-dale Geosol, we feel confident that grassland existed at thissite in the early Wisconsinan prior to the establishment ofboreal forest, but we are uncertain about the regional signifi-cance of this observation at a single site. Nevertheless, earlyWisconsinan grassland in Wisconsin is consistent with a risein grass pollen and other prairie species at the beginning ofthe glacial–interglacial transition at Pittsburg Basin in Illi-nois (Curry and Follmer, 1992; Zhu and Baker, 1995).

FIG. 4. Photograph of Dalsing Farm Section showing Roxana Silt thrust Roxana silt (unit 4). The Roxana Silt is a noncalcareous,into basal Peoria Silt and the composite Farmdale-Sangamon Geosol. The dark-brown silt loam in which the Farmdale Geosol islighter tones at the bottom of the photo correspond with the red and blocky

formed. The Roxana is pedogenically organized in its lowerstructured 3Bt horizon, while the darker tones are associated with the 2BCpart as A horizons (moderate to strong klumpen) superim-horizon of the Roxana Silt and the 2A and 3A horizons. Note the bumpy

surface texture corresponding with granular structure. Decimal scale in feet. posed on the Sangamon Geosol, whereas the upper part ofthe unit is typically massive and shows some B horizoncharacteristics of blockiness and weak klumpen. CoulterCounter distributions across the lithologic discontinuity andthat the Loveland Loess there is divisible into three parts.

The oldest part was found to be about 170,000 { 14,000 yr into the Sangamon A horizon are skewed toward the finersilt sizes characteristic of the Roxana Silt (Leigh, 1994). Theold, while the younger two parts had ages between 120,000

and 70,000 yr B.P. However, we observed no stratigraphic skewness suggests that pedologic mixing of Units 3 and 4outpaced sedimentation. Our data support previous interpre-or pedologic discontinuities that would suggest more than

one episode of deposition within the Loveland. Unit 2 may tations of the mixing and inverted solum relationship whichindicate that environmental conditions became cooler andcorrelate with the lower part of the Loveland described by

Rodbell and Forman (1995). less conducive to soil formation as deposition of the RoxanaSilt progressed (Follmer, 1983; Leigh, 1994).Previous pedologically based interpretations of the Sanga-

monian paleoenvironment have suggested that forest domi- A finite age for the loess-derived Roxana Silt at Kielerhas not been determined, but the age is assumed to fallnated upland environments (Ruhe, 1974; Follmer, 1983;

Curry and Follmer, 1992). However, fossil pollen and fauna within the 55,000 to 27,000 yr B.P. age range established byLeigh and Knox (1993). Hogan and Beatty (1963) reported afrom south-central Illinois suggest periods with grassland

vegetation during the Sangamonian. King and Saunders radiocarbon age of 29,400 { 700 yr B.P. for spruce charcoalcollected in Roxana sediment from a nearby roadcut in 1959.(1986) concluded that the Sangamonian climate was warmer

AID QR 1864 / a606$$$$62 03-11-97 07:09:36 qral AP: QR


Peoria silt (unit 5). The Peoria Silt is a loess-derived may account for the apparent paucity of older loesses. First,early middle and early Pleistocene loesses were never depos-silt loam with silty clay loam textures in the solum of the

modern soil. Colors vary according to oxidation–reduction ited. Second, they were deposited but have been eroded fromthe landscape. Third, they were deposited and have beenstatus of zones within the unit. Zones beneath the well-

drained solum of the modern soil are (1) mottled, oxidized, sufficiently weathered and reworked that they are not readilyrecognizable as loesses in the modern record.and leached, (2) mottled, oxidized, and unleached, and (3)

mottled, reduced and bleached, and unleached (terminology Nondeposition. The only evidence suggesting earlymodified from Hallberg et al., 1978). The Peoria Silt is Pleistocene loesses were never deposited is negative evi-uniformly nearly sand-free and silty, with coarse silt (16– dence; that is, because no early Pleistocene loesses have been62 mm) reaching a maximum near the center of the unit. A found, perhaps they were never deposited. Saucier (1994, p.radiocarbon age of about 24,000 yr B.P. for snail shells 134) suggests older loesses were not deposited in the Lowerlocated 25 cm above the base of the Peoria Silt at another Mississippi Valley because the valley was small and geomet-Driftless Area locality 30 km northwest of Kieler indicates rically not conducive to loess deflation. For the Upper Mis-that the basal age of the Peoria Silt here closely approximates sissippi Valley, however, a nondeposition hypothesis is dif-the regionally average basal age of about 25,000 yr B.P. ficult to accept given the evidence of multiple Pliocene and(McKay, 1979; Leigh and Knox, 1994). early Pleistocene (i.e., ú790,000 yr B.P.) glaciations in the

Intense frost action and severe mass wasting probably midcontinent (Knox and Attig, 1988; Richmond and Fuller-characterized much of late Wisconsinan time in the Driftless ton, 1986). Major dust sources associated with outwashArea. Figure 1 shows that late Wisconsinan glaciers nearly plains and valley trains must have existed, and it seemsencircled the Driftless Area, except for the southern sector. improbable to us that loess was not deposited.The presence of nearby glaciers created a periglacial climate

Evidence for erosion. The scattered occurrence of multi-in the Driftless Area, as indicated by large ice wedge castsple pre-Illinoian silts of probable loessial origin suggestsnear Sparta in the central Driftless Area. Periglacial climaticthese units once covered the landscape, but they have sinceconditions probably greatly accelerated hillslope erosion bybeen eroded from all but a few protected localities. Themass wasting. There is evidence of mass wasting duringfrequency of occurrence of pre-Illinoian units is low; never-Peoria Silt deposition in parts of the Kieler exposures (Fig.theless, they exist and provide a proof of middle Pleistocene3 and 4). Here one or more thin layers of Roxana Silt haveloess deposition and reworking. Examples of some of thebeen carried downslope over the basal increment of Peorianotable sites and the number of pre-Illinoian silts includeSilt, with movement occurring on discrete shear surfaces.the Oil City Site in Wisconsin with three units (Jacobs andWe interpret this as evidence of either plug-like solifluctionKnox, 1994), the Pancake Hollow Site in Illinois with four(Mackay, 1981) or more rapid active-layer detachment slidesunits (Hajic, 1989), the Maryville Site in Illinois with three(Lewkowicz, 1992), both of which are associated with failureunits (McKay, 1989), and Crowleys Ridge in Arkansas withof thawing ice-rich soil above permafrost. Mass movementone or two units, depending on stratigraphic interpretationon such low slope gradients seems unlikely in the absence(Autin et al., 1991, p. 569–571). The absence of pre-Illi-of permafrost. Leigh and Knox (1994) estimated that thenoian units in other areas in the Mississippi Valley suggestsaverage annual sediment loss during periglacial climatic con-that erosion has removed them. Furthermore, at the Oil Cityditions between about 20,000 and 12,000 yr B.P. in a smalland Pancake Hollow sites there is clear evidence that somewatershed 7 km northeast of the Kieler Site was approxi-units have been reworked, supporting claims for erosion ofmately double the modern agriculturally accelerated rate.middle Pleistocene loess. While age control is always tenu-ous and often lacking, there is no evidence that any of the

THE PROBLEM OF MISSING EARLY MIDDLE AND units at the aforementioned sites are early Pleistocene in age,EARLY PLEISTOCENE LOESSES leaving open the question of erosion of early Pleistocene

loesses.With no known examples, erosion of early PleistoceneThe record of pre-Illinoian loesses and reworked loess

deposits in the Mississippi Valley is fragmentary. Leigh and loess units can only be inferred from other known geologicphenomena. For example, Knox and Attig (1988) reportedKnox (1994) and Follmer (in press) summarize the occur-

rence frequency of loess units in the Mississippi River Valley that proglacial silt beds older than 790,000 yr B.P. occur onand below a bedrock strath along the lower Wisconsin Riverand report that a maximum of six or seven loess or loess-

derived silt units have been found. The frequency of occur- Valley. The position of the silt beds 135–150 m below theadjacent uplands implies that considerable landscape en-rence decreases with increasing age. None of the loess units

are reported to be older than 790,000 yr B.P. and only the trenchment occurred before their deposition. However, theirposition 50–55 m above the adjacent bedrock valley floor,oldest sections known, such as Oil City (Jacobs and Knox,

1994) and Pancake Hollow (Hajic, 1989), possibly extend which is covered with younger Pleistocene alluvium, alsoindicates that either re-excavation or additional entrench-to the early middle Pleistocene. Three possible explanations

AID QR 1864 / a606$$$$63 03-11-97 07:09:36 qral AP: QR


ment occurred after 790,000 yr B.P. Other evidence indicates ering, eolian accretion, and pedogenesis have reduced silt-size grains to clay and also organized the fabric. We hypothe-that valleys were re-excavated as recently as the last intergla-

ciation. Illinoian and older lacustrine, colluvial, and alluvial size that the silty clay Unit 2 and similar units elsewhere inthe region are largely the derivative of pre-Illinoian loessfills present in relict cutoff valley meanders in the Driftless

Area (Knox and Leigh, 1990) are absent in alluvial fills deposits that have been highly weathered, mixed with andpedogenically welded to the Rountree Formation clayey re-underlying present-day valleys (Knox, 1982). The major pro-

portion of alluvial fills in modern river valleys resulted from siduum. The Kieler Site stratigraphy is particularly signifi-cant because it is here that we can distinguish the unitsmassive aggradation during the late Wisconsinan glaciation

in response to greatly accelerated hillslope erosion, interpre- morphologically. Here, the setting is an upland divide thatwould not receive colluvial influx, and it is underlain byted to be a result of periglacial climatic conditions (Knox,

1982). Evidence of entrenchment is not positive evidence shale with low silt content.that early Pleistocene loesses were ever present and doesnot necessarily indicate regional upland erosion, but it does CONCLUSIONprovide inferential evidence that major erosional episodes,

The Kieler Site has special significance because it includescapable of removing early Pleistocene loess deposits, oc-exceptionally well-preserved sections of the Loveland Siltcurred in the region during the Pleistocene.(loess) and the Sangamon Geosol. The Sangamon A horizonEvidence for weathering. Stratigraphic evidence fromis preserved nearly perfectly and has mollic characteristicsthe Kieler Site, along with previous observations of thethat suggest former grassland conditions, at least locally, lateRountree Formation residuum, provide the basis for a weath-in the evolution of the soil. The environmental associationering hypothesis. In the following section we offer theseis consistent with fossil fauna and fossil pollen evidence ofdata and an hypothesis which suggests that the apparentSangamonian and early Wisconsinan environmental condi-absence of older loesses is partially due to their extensivelytions in the type area of south-central Illinois (King andweathered condition. This weathering has resulted in loss ofSaunders, 1986; Zhu and Baker, 1995).their primary loessial characteristics. While this hypothesis

We propose that the apparent lack of pre-Illinoian loessesis based on data from the Driftless Area, we believe it appliesin the Upper and Middle Mississippi Valley is due in partto other Upper Mississippi Valley regions as well.to erosion, but also reflects the fact that old loesses arecommonly weathered beyond recognition and classified as

KIELER SITE PRE-LOVELAND SILT AND THE ‘‘residuum.’’ The Kieler Site stratigraphy provides a veryROUNTREE FORMATION RESIDUUM good example of an intermediate step in the conversion of

loess to residuum, since the mesoscale pedogenic fabrics areIf early middle and early Pleistocene loess deposits were still distinct. The strongly weathered but discernable Unit 2

once present in the region, it is reasonable to expect residual at Kieler, combined with previous observations of the siltytraces of their former occurrence. We believe the pre-Love- clay residuum of the upper part of the Rountree Formation,land Unit 2 silty clay at the Kieler Site represents remnants supports the idea that older, pre-Illinoian loesses once wereof an older loess. A silty clay has been identified in the upper present but that weathering and mixing with clayey residuumRountree Formation residuum, but has been categorized as has obscured their recognition. Thus, the paucity of pre-a mixed zone because of morphological similarity with the Illinoian loess units in the Driftless Area is a likely conse-underlying residuum (Knox and Maher, 1974; Knox et al., quence of widespread Pleistocene erosion and intense inter-1990). Oxygen-isotope analyses by Frolking et al. (1983) of glacial weathering that, in essence, turns old loesses intothe 1–10 mm quartz fraction in the Rountree Formation ‘‘residuum.’’residuum at the type locality showed that the silty uppermixed unit has isotopic values more similar to the surficial ACKNOWLEDGMENTloess than to the underlying clayey residuum and dolomite.Knox and Maher (1974) postulated that the silty clay mixed This research was supported in part by National Science Foundation

Grants EAR-8904352 and EAR-8707504 to J. C. Knox, University of Wis-zone resulted from the influence of mass-wasting processesconsin, Madison.that mixed overlying loess, possibly of pre-Wisconsinan age,

with the residuum. However, at the Kieler Site, the siltyREFERENCESupper phase, although merged with the residuum at the mac-

roscale, has different mesoscale fabric than the underlyingAutin, W. J., Burns, S. F., Miller, B. J., Saucier, R. T., and Snead, J. I.clayey phase. This relationship implies long-term ground-

(1991). Quaternary geology of the Lower Mississippi Valley. In ‘‘Quater-surface stability for the two units and suggests that the silt is nary Nonglacial Geology: Conterminous U.S.’’ (R. B. Morrison, Ed.),not due solely to mixing by Wisconsinan or pre-Wisconsinan pp. 547–582. Geological Society of America, Boulder, CO.mass-wasting processes. Rather, it suggests that the unit may Curry, B. B., and Follmer, L. R. (1992). The last interglacial-glacial transi-

tion in Illinois: 123-25 ka. In ‘‘The Last Interglacial-Glacial Transition inonce have had a higher silt content, but that long-term weath-

AID QR 1864 / a606$$$$63 03-11-97 07:09:36 qral AP: QR


North America’’ (P. U. Clark and P. D. Lea, Eds.), pp. 71–78. Geological Attig, Eds.), pp. 64–67. Wisconsin Geological and Natural History Sur-vey Information Circular 67.Society of America Special Paper 270.

Leigh, D. S. (1994). Roxana silt of the Upper Mississippi Valley: Lithology,Follmer, L. R. (in press). Loess studies in central United States: Evolutionsource, and paleoenvironment. Geological Society of America Bulletinof concepts. Engineering Geology.106, 430–442.Follmer, L. R. (1995). Klumpen—a mesoscale level of classification for

Leigh, D. S., and Knox, J. C. (1993). AMS radiocarbon age of the Uppersoil structure: Rationale. INQUA/ISSS Paleopedology CommissionMississippi Valley Roxana Silt. Quaternary Research 39, 282–289.Newsletter No. 11, Part 2, 4–7.

Leigh, D. S., and Knox, J. C. (1994). Loess of the upper Mississippi ValleyFollmer, L. R. (1983). Sangamonian and Wisconsinan pedogenesis in theDriftless Area. Quaternary Research 42, 30–40.Midwestern United States. In ‘‘Late Quaternary Environments of the

United States’’ (H. E. Wright, Jr., Ed.), Vol. 1, ‘‘The Late Pleistocene’’ Lewkowicz, A. G. (1992). Factors influencing the distribution and initiation(S. C. Porter, Ed.), pp. 138–144. Univ. of Minnesota Press, Minneapolis. of active-layer detachment slides on Ellesmere Island, Arctic Canada. In

‘‘Periglacial Geomorphology’’ (J. C. Dixon and A. D. Abrahams, Eds.),Frolking, T. A., Jackson, M. L., and Knox, J. C. (1983). Origin of red claypp. 224–250. Wiley, New York.over dolomite in the loess-covered Wisconsin Driftless Area uplands.

Soil Science Society of America Journal 47, 817–820. McKay, E. D. (1979). Wisconsinan loess stratigraphy of Illinois. In ‘‘Wis-consinan, Sangamonian, and Illinoian Stratigraphy in Central Illinois,’’Gee, G. W., and Bauder, J. W. (1986). Particle-size analysis. In ‘‘Methodspp. 95–108. Illinois State Geological Survey Guidebook 13.of Soil Analysis’’ (A. Klute, Ed.), Part 1, 2nd ed. pp. 383–411. American

Society of Agronomy, Madison, WI. McKay, E. D. (1989). Illinoian and older loesses and tills at the MaryvilleSection. In ‘‘Quaternary Records of Southwestern Illinois and AdjacentHallberg, G. R., Fenton, T. E., and Miller, G. A. (1978). Standard weather-Missouri,’’ pp. 21–30. Illinois State Geological Survey Guidebook 23.ing zone terminology for the description of Quaternary sediments in Iowa.

In ‘‘Standard procedures for evaluation of Quaternary materials in Iowa’’ Machette, M. (1986). Calcium and magnesium carbonates. In ‘‘Field and(G. R. Hallberg, Ed.), pp. 75–109. Iowa Geological Survey Technical Laboratory Procedures Used in a Soil Chronosequence Study’’ (M. J.Information Series 8. Singer and P. Janitzky, Eds.), pp. 30–33. U.S. Geological Survey Bulletin

1648.Hajic, E. R. (1989). Pre-Wisconsinan loesses and paleosols at Pancake Hol-low, west-central Illinois. In ‘‘Quaternary Records of Southwestern Illi- Mackay, J. R. (1981). Active layer slope movement in a continuous perma-nois and Adjacent Missouri,’’ pp. 91–98. Illinois State Geological Survey frost environment, Garry Island, Northwest Territories, Canada. CanadianGuidebook 23. Journal of Earth Sciences 18, 1666–1680.

Hogan, J. D., and Beatty, M. T. (1963). Age and properties of Peorian loess Milligan, T. G., and Kranck, K. (1991). Electroresistance particle size ana-and buried paleosols in southwestern Wisconsin. Soil Science Society of lyzers. In ‘‘Principles and Applications of Particle Size Analysis’’ (J.America Proceedings 27, 345–350. P. M. Syvitski, Ed.), pp. 109–118. Cambridge Univ. Press, Cambridge.

Hughes, R. E., Moore, D. M., and Reynolds, R. C., Jr. (1993). The nature, Olsen, R. V., and Ellis, R., Jr. (1982). Iron. In ‘‘Methods of Soil Analysis’’detection, occurrence, and origin of kaolinite/smectite. In ‘‘Kaolin Gene- (A. L. Page, R. H. Miller, and D. R. Keeney, Eds.), Part 2, pp. 301–312.sis and Utilization’’ (H. H. Murray, W. M. Bundy, and C. C. Harvey, American Society of Agronomy, Madison, WI.Eds.), pp. 291–323. The Clay Minerals Society, Boulder. Richmond, G. M., and Fullerton, D. S. (1986). Summation of Quaternary

glaciations in the United States of America. In ‘‘Quaternary GlaciationsJacobs, P. M., and Knox, J. C. (1994). Provenance and pedology of a long-in the Northern Hemisphere’’ (V. Sibrava, D. Q. Bowen, and G. M. Rich-term Pleistocene depositional sequence in Wisconsin’s Driftless Area.mond, Eds.), Quaternary Science Reviews 5, 183–196.Catena 22, 49–68.

Rodbell, D. T., and Forman, S. L. (1995). Loess and paleosol stratigraphy,King, J. E., and Saunders, J. J. (1986). Geochelone in Illinois and the Illi-and thermoluminescence age estimates of Mississippi Valley loess innoian–Sangamonian vegetation of the type region. Quaternary Researchwestern Tennessee. Geological Society of America, Abstracts with Pro-25, 89–99.gram 27, A-170.Knox, J. C. (1982). Quaternary history of the Kickapoo and lower Wiscon-

Ruhe, R. V. (1974). Sangamon paleosols and Quaternary environments insin River valleys, Wisconsin. In ‘‘Quaternary History of the DriftlessMidwestern United States. In ‘‘Quaternary Environments’’ (W. C. Maha-Area,’’ pp. 1–65. Wisconsin Geological and Natural History Surveyney, Ed.), pp. 153–167. York University Press, Toronto.Field Trip Guidebook 5.

Saucier, R. T. (1994). ‘‘Geomorphology and Quaternary Geologic HistoryKnox, J. C., and Attig, J. W. (1988). Geology of the pre-Illinoian sedimentof the Lower Mississippi Valley.’’ U.S. Army Corps of Engineers, Vicks-in the Bridgeport terrace, lower Wisconsin River valley, Wisconsin. Jour-burg.nal of Geology 96, 505–513.

Simonson, R. W. (1995). Airborne dust and its significance to soils. Ge-Knox, J. C., and Leigh, D. S. (1990). ‘‘Valley trenching at the Driftlessoderma 65, 1–43.Area Boice Site.’’ pp. F26–F31. Geological Society of America, North

Central Section Field Trip Guidebook. Soil Survey Staff (1992). ‘‘Keys to Soil Taxonomy, 5th ed.: USDA-SCS.’’United States Government Printing Office, Washington, DC.Knox, J. C., and Maher, L. J. (1974). ‘‘Late Quaternary Environments of

the Driftless Area: Southwestern Wisconsin.’’ pp. 24–43. American Qua- Soil Survey Staff (1993). ‘‘Soil Survey Manual (revised): USDA-SCS.’’ternary Association Guidebook, Field Trip 2, Wisconsin Geological and United States Government Printing Office, Washington, DC.Natural History Survey. Zhu, H., and Baker, R. G. (1995). Vegetation and climate of the last glacial-

interglacial cycle in southern Illinois, USA. Journal of PaleolimnologyKnox, J. C., Leigh, D. S., and Frolking, T. A. (1990). Rountree Formation(New). In ‘‘Geology of Sauk County Wisconsin’’ (L. Clayton and J. W. 14, 337–354.

AID QR 1864 / a606$$$$64 03-11-97 07:09:36 qral AP: QR

preservation and recognition of middle and early

Documents