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Sequence Stratigraphy, Distribution and Preservation of Organic Carbon, and Reservoir Properties of the Middle Devonian

Marcellus Shale, of the Central Appalachian Basin; Northern West Virginia and Southwestern Pennsylvania

Roy Sexton Department of Geology and Geography, West Virginia University, Morgantown, WV 26506

Abstract

A transgressive – regressive (T-R) sequence stratigraphic study of the Marcellus Shale interval, using 250

geophysical logs and four cored sections in northern West Virginia and southwestern Pennsylvania, indicates that

the Union Springs and Oatka Creek members of the Marcellus Formation and the Levanna Member of the

Skaneateles Formation define three third-order stratigraphic sequences (i.e., MSS1, MSS2, SKS). The MSS1

stratigraphic sequence encompasses the Union Springs Member of the Marcellus Formation and extends from a

gamma-ray inflection point and/or bulk density base line shift located near the top of the Onondaga Formation to

either an erosional surface at the base of the Cherry Valley Member of the Marcellus Formation, or a gamma-ray

minimum and/or bulk density maximum within the Cherry Valley Member (or stratigraphic equivalent). The MSS2

stratigraphic sequence encompasses the Oatka Creek Member of the Marcellus Formation and extends from the

upper boundary of the MSS1 stratigraphic sequence to either an erosional surface at the base of the Stafford

Member of the Skaneateles Formation, or a gamma-ray minimum and/or bulk density maximum within the Stafford

Member (or stratigraphic equivalent). The SKS stratigraphic sequence encompasses the Levanna Member of the

Skaneateles Formation and extends from the upper boundary of the MSS2 stratigraphic sequence to a gamma-ray

minimum and/or bulk density maximum within a limestone or calcareous grey shale interval overlying the Levanna

Member.

Physical core descriptions and geochemical data (i.e. TOC, x-ray diffraction, and x-ray fluorescence

spectroscopy) provide support for the placement of stratigraphic surfaces and aid in interpretation of depositional

conditions. Specific geochemical proxies for terrigenous sedimentation include the concentrations of calcium,

aluminum, zirconium and silica; the ratio of titanium to aluminum and silica to aluminum; and total clay volume.

Geochemical proxies for paleo-redox states include the concentrations of manganese, molybdenum, and barium; the

ratios of molybdenum to aluminum, barium to aluminum, and thorium to uranium; the degree of pyritization (DOP);

and the depletion of sulfur isotope 34S relative to 32S (δ34S).

Interpretation of depositional conditions of the study interval, utilizing integrated geophysical logs, core

descriptions and geochemical data, suggests a dynamic environment characterized by varying relative sea-level,

oxygen concentration, and sedimentation rates. Organic-rich shale units within the study interval were deposited

under anoxic or possibly euxinic conditions initiated by relative sea-level rise. A significant portion of the silica within

black shale intervals is likely biogenic and/or eolian sourced. Limestone beds and calcareous grey shale intervals

were deposited under dysoxic/oxic conditions initiated by relative sea-level fall. Terrigenous input increases moving

upward stratigraphically from the MSS1 through the SKS stratigraphic sequences and into overlying grey shale

intervals. During periods of relative sea-level fall, carbonate production outpaced terrigenous sedimentation,

resulting in deposition of concentrated skeletal beds. Gravity driven sediment flows and winnowing processes are

interpreted to have commonly introduced oxygenated waters to the basin, resulting in diagenetic fronts and

concentration of heavier mineral grains (titanium).

Variations in the thickness of the MSS1, MSS2, and SKS stratigraphic sequences are controlled by sediment

input originating near the structural front east of the basin and the paleo-topography of underlying strata. The MSS2

and SKS sequences display infilling of paleo-topographic lows in the underlying sequences, suggesting increased

deposition by sediment driven gravity flows. Areas of rapidly increasing thickness of the MSS1, MSS2, and SKS

stratigraphic sequences in the eastern portion of the study area are associated with the distal portions of fluvial

sediment sources located on the basin margins.

Sequence Stratigraphy

Study Area

The study area in northern West Virginia and southwestern Pennsylvania is

highlighted in green. Locations of wells used in the study are indicated by

black circles. Cored wells used in the study are located in southwestern

Pennsylvania, northern West Virginia, and eastern West Virginia. The exact

locations of cored wells are proprietary. The study covers approximately

13,600 square miles (35, 200 square km).

Paleogeography during the Middle Devonian (385 Ma). Study area is outlined

by a red oval. The Appalachian basin was bound by the (1.) Cincinnati arch to

the west, the (2.) Acadian mountains to the east and the (3.) Rheic ocean to

the south. (Modified from Blakey, Ron:

http://jan.ucc.nau.edu/~rcb7/namD385.jpg)

Simplified stratigraphy of the current study. Includes approximate distribution

of the MSS1, MSS2, and SKS stratigraphic sequences compared with the

stratigraphy of the study interval.

Geochemical Analysis

Sequence stratigraphic framework of Eifelian and Givetian strata within the Appalachian basin. Includes relative sea-

level curve (Modified from Brett et al., 2011) Comparison of base level change with T-R events,

maximum regressive surfaces (MRS) and maximum

flooding surfaces (MFS) (Modified from Embry, 2002).

Type logs in southwestern Pennsylvania (Pa-1) and northern West Virginia (WV-1). Maximum regressive surfaces are identified by high density values and high clay or carbonate

volumes as well as low gamma-ray and resistivity values. The correlation track contains gamma-ray and caliper logs. The gamma-ray log is scaled 0-200 API units and wraps twice,

first when the gamma-ray exceeds 200 API (light green shading) and again when it exceeds 400 API (red shading). The caliper log is scaled 6-16 inches. The porosity track contains

neutron porosity, density porosity, bulk density, and photo electric (PE) logs. The neutron and density porosity logs are scaled 45-(-15) %, the bulk density log is scaled 2-3 g/cm3,

and the PE log is scaled 0-10 barns/electron. The resistivity track contains the deep, medium, and shallow resistivity logs which are scaled .2-2000 ohms (logarithmic). The clay

volume track contains a measurement of clay volume calculated from the corrected gamma-ray log and is scaled from 0-1 in percent decimal form. The carbonate track contains a

measurement of carbonate (Ca) concentration which is scaled from 0-50 percent.

Type logs in southwestern Pennsylvania (Pa-1) and northern West Virginia (WV-1). Maximum flooding surfaces are identified by low density values, and locally low clay or carbonate

volumes (depending on location) as well as high gamma-ray and resistivity values. The correlation track contains gamma-ray and caliper logs. The gamma-ray log is scaled 0-200

API units and wraps twice, first when the gamma-ray exceeds 200 API (light green shading) and again when it exceeds 400 API (red shading). The caliper log is scaled 6-16 inches.

The porosity track contains neutron porosity, density porosity, bulk density, and photo electric (PE) logs. The neutron and density porosity logs are scaled 45-(-15) %, the bulk

density log is scaled 2-3 g/cm3, and the PE log is scaled 0-10 barns/electron. The resistivity track contains the deep, medium, and shallow resistivity logs which are scaled .2-2000

ohms (logarithmic). The clay volume track contains a measurement of clay volume calculated from the corrected gamma-ray log and is scaled from 0-1 in percent decimal form. The

carbonate track contains a measurement of carbonate (Ca) concentration which is scaled from 0-50 percent.

Northern West Virginia WV-1

Southwestern Pennsylvania Pa-1 Northern West Virginia WV-1

Southwestern Pennsylvania Pa-1


Defined stratigraphic sequences in southwestern Pennsylvania (Pa-1) and northern West Virginia (WV-1). Stratigraphic sequences include: MSS1; MSS2; and SKS. Transgressive

system tracts are highlighted in blue and regressive system tracts are highlighted in gold.

Aluminum (Al) terrigenous sedimentation

Titanium / Aluminum (Ti/Al) heavier mineral grains

Silica (Si) vs. Zirconium (Zr) biogenic and/or eolian silica

Silica / Aluminum (Si/Al) biogenic and/or eolian silica

Manganese (Mn) oxic/dysoxic

Barium/ Aluminum (Ba) oxic/dysoxic

Molybdenum (Mo) and Molybdenum / Aluminum (Mo/Al)

anoxic/euxinic conditions

Degree of Pyritization (DOP)

Depletion of sulfur isotope 34S relative to 32S (δ34S)

Thorium / Uranium (Th/U)

Indicators of bulk sedimentation and paleo-redox conditions (Modified from Sageman et al.,

2003).

Type logs in southwestern Pennsylvania (Pa-1) and northern West Virginia (WV-1). Track 1 contains gamma-ray and caliper logs. The gamma-ray log is scaled 0-200 API units and wraps twice, first when

the gamma-ray exceeds 200 API (light green shading) and again when it exceeds 400 API (red shading). The caliper log is scaled 6-16 inches. Track 2 contains calcium (Ca) concentration which is scaled 0-

50%. Track 3 contains aluminum (Al) concentration and total organic carbon (TOC). The Al concentration is scaled 0-15% and TOC is scaled 0-25 weight percent (w%). Track 4 contains Zirconium (Zr)

concentration and silica (Si) concentration. The Zr concentration is scaled 0-150 ppm and the Si concentration is scaled 0-35%. Track 5 contains a ratio of titanium (Ti) to Al (Ti/Al) which is scaled 0-(0.20).

Track 6 contains a ratio of Si to Al (Si/Al) which is scaled 0-10. Track 7 contains a measurement of total clay which is scaled 0-65 w%.




the gamma-ray exceeds 200 API (light green shading) and again when it exceeds 400 API (red shading). The caliper log is scaled 6-16 inches. Track 2 contains manganese (Mn) concentration which is

scaled 0-1000 ppm. Track 3 contains molybdenum (Mo) concentration and the ratio of Mo to aluminum (Al) (Mo/Al). The Mo concentration is scaled 0-250 ppm and Mo/Al is scaled 0-(0.015) (Pa-1); 0-(.02)

(WV-1). Track 4 contains barium (Ba) concentration and the ratio of Ba to Al (Ba/Al). The Ba concentration is scaled 0-2000 ppm and Ba/Al is scaled 0-(0.4). Track 5 contains total organic carbon (TOC) and

degree of pyritization (DOP). TOC is scaled 0-15 weight percent (w%) (Pa-1); 0-20 w% (WV-1) and DOP is scaled 0-3 (Pa-1); 0-2 (WV-1). Track 6 in Pa-1 contains the depletion of sulfur isotope 34S

compared to 32S (δ34S) which is scaled (-35)-0 (‰) S(V-CDT) (sulfur isotopic differences relative to a reference sample expressed in the Vienna Canyon Diablo Troilite scale). Track 7 contains the spectral

gamma-ray log and includes concentrations of uranium, thorium, and potassium. The uranium concentration is scaled 0-100 parts per million (ppm), thorium is scaled 0-25 ppm, and potassium is scaled 0-

10 %. Track 7 contains the ratio of thorium to uranium and is scaled 0.01-100 (logarithmic).


the gamma-ray exceeds 200 API (light green shading) and again when it exceeds 400 API (red shading). The caliper log is scaled 6-16 inches. Track 2 contains manganese (Mn) concentration which is

scaled 0-1000 ppm. Track 3 contains the ratio of Ba to Al (Ba/Al) which is scaled 0-(0.4) (Pa-1); 0-(.2) (WV-1). Track 4 contains a ratio of titanium (Ti) to Al (Ti/Al) which is scaled 0-(0.2). Track 5 contains a

ratio of Si to Al (Si/Al) which is scaled 0-10.


Stratigraphy

Stratigraphy of study interval adapted from New

York (Modified from Brett et al., 2011)

Isopach map of the MSS1 stratigraphic sequence. The MSS1

stratigraphic sequence decreases in thickness from a maximum of 165

feet (50.3m) in the east and 86 feet (26.2m) in the north to a minimum

of 12 feet (3.7m) in the southwest. A trend of decreased MSS1

thickness, oriented southwest to northeast, is evident in southwestern

Pennsylvania (indicated by dashed red line).

Isopach map of the SKS stratigraphic sequence. The SKS stratigraphic

sequence decreases in thickness from a maximum of 99 feet (30.2m) in

the east and 151 feet (46m) in the northeast to a minimum of 13 feet

(4m) in the southwest. A trend of decreased SKS thickness, oriented

southwest to northeast, is evident in southwestern Pennsylvania

(indicated by dashed red line).

Isopach map of the gross MSS1, MSS2, and SKS stratigraphic

sequence. The gross thickness of the MSS1, MSS2, and SKS

stratigraphic sequences decreases from a maximum of 470 feet (143m)

in the east to a minimum of 52 feet (15.8m) in the west. A trend of

decreased gross thickness, oriented southwest to northeast, is evident

in southwestern Pennsylvania (indicated by dashed red line).

Isopach map of the MSS2 stratigraphic sequence. The MSS2

stratigraphic sequence decreases in thickness from a maximum of 180

feet (54.9m) in the east to a minimum of 16 feet (4.9m) in the west and

8 feet (2.4m) in the southwest. A trend of increased MSS2 thickness,

oriented southwest to northeast, is evident in southwestern

Pennsylvania (indicated by dashed red line).

Isopach Maps

Northeast to southwest cross section datumed on the upper boundary of the SKS stratigraphic sequence. Observe the

thinning of the MSS1, MSS2, and SKS stratigraphic sequences to the southwest.

Pronounced thinning to the southwest

Condensation in distal portion of basin

Removal of strata related to Taghanic

unconformity

Northeast to southwest cross section datumed on the upper boundary of the SKS stratigraphic sequence.

Observe the thinning of the MSS1, MSS2, and SKS stratigraphic sequences to the southwest.

Thinning to the southwest

Increased sediment input

Dilution of organic material

West to east cross section datumed on the upper boundary of the SKS stratigraphic sequence. Observe the

variations in thickness of the MSS1, MSS2, and SKS stratigraphic sequences.

Variations in thickness

Infilling of paleo-topographic

lows

Basement faulting

West to east cross section datumed on the upper boundary of the SKS stratigraphic sequence. Observe the

rapid, westward thinning of the MSS1, MSS2, and SKS stratigraphic sequences in the eastern portion of the

cross section.

Pronounced thinning to west

Condensation in distal portion of basin

Removal of strata related to Taghanic

unconformity

Stratigraphic Cross Sections

Conclusions Characterization of the study interval using a transgressive – regressive sequence stratigraphic model combined with analysis of geochemical, lithologic, sedimentologic, and paleontologic properties lead

to the following conclusions:

Significant stratigraphic surfaces can be identified on common wireline logs, allowing for construction of a basin-wide sequence stratigraphic framework.

Reservoir properties, including mineralogic composition and total organic carbon (TOC) concentration, vary in a predictable manner based on their spatial and temporal relation to specific sequence

stratigraphic system tracts and surfaces.

Relative sea-level change was the dominant factor in controlling sedimentologic properties and paleo-redox states.

Organic-rich black shale intervals were deposited under periods of anoxic/euxinic conditions during relative sea-level rise.

A significant portion of the silica within black shale intervals is interpreted to be biogenic and/or eolian sourced.

Skeletal concentrations and calcareous grey shale intervals were deposited during dysoxic/oxic conditions initiated by relative sea-level fall.

Gravity driven sediment flows and winnowing processes are interpreted to have commonly introduced oxygenated waters to the basin resulting in diagenetic fronts and concentration of heavier

mineral grains (titanium).

Variations in the thickness of the MSS1, MSS2, and SKS stratigraphic sequences are generally controlled by sediment input originating near the structural front located east of the basin and the

paleo-topography of underlying strata.

Isolated areas of rapidly increasing thickness of the MSS1, MSS2, and SKS stratigraphic sequences are associated with the distal portions of fluvial sediment sources located on the basin margins.

250 wireline logs

Two strike lines (I, II)

Two dip lines (III, IV)

Acknowledgments

Dr. Tim Carr; Dr. Richard Smosna; Randy Blood

West Virginia University & EQT Production

References Brett, C. E., G. C. Baird, A. J. Bartholomew, M. K. DeSantis, and C. A. V. Straeten, 2011, Sequence stratigraphy and a revised sea-level curve for the Middle Devonian of eastern North America:

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 304, p. 21-53.

Embry, A. F., 2002, Transgressive-regressive (T-R) sequence stratigraphy: Gulf Coast SEPM Conference Proceedings, p. 151-172.

Lash, G. G., and T. Engelder, 2011, Thickness trends and sequence stratigraphy of the Middle Devonian Marcellus Formation, Appalachian Basin: Implications for Acadian foreland basin development:

AAPG Bulletin v. 95, p. 61-103.

Sageman, B. B., A. E. Murphy, J. P. Werne, C. A. V. Straeten, D. J. Hollander, and T. W. Lyons, 2003, A tale of shales: the relative role of production, decomposition, and dilution in the accumulation of

organic-rich strata, Middle – Upper Devonian, Appalachian basin: Chemical Geology, v. 195, p. 229-273.

Ver Straeten, C. A., C. E. Brett, and B. B. Sageman, 2011, Mudrock sequence stratigraphy: A multi-proxy (sedimentological, paleobiological and geochemical) approach, Devonian Appalachian Basin:

Palaeogeography, Palaeoclimatology, Palaeoecology, v. 304, p. 54-73.

Werne, J., B. Sageman, T. Lyons, and D. Hollander, 2002, An integrated assessment of a "type euxinic" deposit: Evidence for multiple controls on black shale deposition in the middle Devonian Oatka

Creek formation: American Journal of Science, v. 302, p. 110-143.

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