International Journal of Coal Geology, 8 (1987) 305-314 305 Elsevier Science Publishers B.V., Amsterdam P Printed in The Netherlands

Earlier Sediment Differential Compaction in Gibson County, Indiana

DONALD L. EGGERT

Indiana Geological Survey, 611 N. Walnut Grove, Bloomington, IN 47401, U.S.A.

(Received and accepted for publication May 21, 1987)

ABSTRACT

Eggert, D.L., 1987. Earlier sediment differential compaction in Gibson County, Indiana. Int. J. Coal Geol., 8: 305-314.

A thick wedge of nonmarine gray shale extends from the Galatia Channel and overlies the Springfield Coal Member of the Petersburg Formation (Pennsylvania) in western Gibson Coun- try, but mainly marine black shales overlie the Springfield in the eastern part of the county. The sulfur content of the Springfield coal is lower beneath this wedge of nonmarine gray shale than beneath the marine shales. Fine-grained, compacted bay and overbank deposits form the western delta platform of the coal. Less compacted deposits of fluvial channel sandstone make up the eastern delta platform. Differential compaction of the delta platform of the Springfield coal con- trolled gray-shale distribution and determined the sulfur content of the coal.

INTRODUCTION

The Springfield Coal Member of the Petersburg Formation is a major bitu- minous coal seam of North America and the second most extensive coalbed in the Illinois Basin. It is generally a high-sulfur coal. Coal from the Illinois Basin competes with coal from other basins and other energy sources for a market. The chemical and physical properties of coal determine its use, and transpor- tation and production costs determine the price consumers pay for it. Harper (1981) found that coal mines in the Illinois Basin meet competition by mining thick high-quality coal and by using highly mechanized mining. High-tech- nology mining provides only short-term advantages because this kind of min- ing can also be used in many other coal basins. The coal industry in the Illinois Basin can best meet competition by mining the better quality and thicker coals.

The exploration geologist's role is to find marketable and minable coal. Effi- cient coal exploration and development require knowledge of depositional environments, sedimentology, and stratigraphy. This knowledge can be used in the Illinois Basin to find thick low-sulfur coal. Research has found that low-

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sulfur coal, less than 2.5% total sulfur, lies beneath nonmarine gray shales adjacent to sandstone-filled fluvial channels contemporaneous with peat dep- osition of the coal.

The Galatia and Leslie Cemetery Channels, contemporaneous with peat deposition of the Springfield coal, are present in Gibson County. The smaller Leslie Cemetery Channel has only modest low-sulfur reserves. The larger Gal- atia Channel, however, has more than 80 square miles (207 km e) of thick, nonmarine gray shale overlying the Springfield in western Gibson County. The Springfield coal in this area is thicker than normal and is believed to be a low- sulfur coal. In contrast, the gray shale is absent or limited in extent adjacent to the Galatia Channel in eastern Gibson County. The purpose of this report is to describe the controlling mechanism for the deposition of nonmarine gray shale associated with the Springfield coal in Gibson County.

PREVIOUS RESEARCH

Our knowledge of coal deposition in the Illinois Basin began to emerge when Ashley (1899, 1920) found significant variations in seam thickness and asso- ciations of the roofs of nonmarine gray shale with coals of lower sulfur content. Later workers have substantiated the relationship between low-sulfur coal and gray-shale roofs. These later researchers found that the areas of gray-shale roof and thick coal are adjacent in many places to fluvial channels contempora- neous with peat deposition of the coal seam ( Gluskoter and Simon, 1968; Hop- kins, 1968; Gluskoter and Hopkins, 1970; and Johnson, 1972).

The Springfield Coal Member has been singled out for sedimentologic, stra- tigraphic, and depositional-environmental study. Eggert et al. (1983) reviewed previous studies and described the deltaic origin of the Springfield coal. This coal formed on a delta platform consisting of bay-fill, prodeltaic, and fluvial- channel deposits. During peat deposition major and minor fluvial channels ( Fig. 1 ) traversed the delta plain. Channel position was determined by subsid- ence induced by compaction of earlier sediments. Some channels were aban- doned before deposition of the Springfield peat. Peat deposition was time transgressive in that peat was deposited first adjacent to contemporaneous channels and later above former bays. Pre-Springfield deltaic sediments and mud-dominated areas of the Springfield delta platform adjacent to channels contemporaneous with peat deposition compacted and subsided during peat deposition. These sinking areas allowed thick peat to be deposited and also thick Springfield coal to be formed as a result of burial, compaction, and coal- ification. Areas of gray-shale roof areas overlie some but not all near-channel areas. Previous studies have not considered why gray shales are not uniformly distributed along contemporaneous channels.

Studies of the Springfield coal in Gibson County recognized prodeltaic shale, bay-fill sequences of coarsening-upward shales and sandstones, and fluvial

307 CHANNELS

Contemporaneous; cool absent

I ~ Contemporaneous; cool split

I - ~ Erosional; cool absent

1

25 Miles~#~ I I I I

I I I

i

i

N

!

E:.i i~ P""'~extent of

Springfield Coal Member

W,n,,ow ,." Channel

C h o n n e l ~ ~ ,' ~ ~"x Leslie , ~ r Evansville," .~)~ \Cemetery

! Channel '., , , ~. ~ - ~ . "-,~,~

• ~ . . . . . . , ._. : ,~o ~ ~ . . . / - J --"

Fig. 1. Extent of the Springfield Coal Member in southeastern Illinois, southwestern Indiana, and western Kentucky.

channels of fining-upward sandstone (Eggert, 1982a, b, 1984; Eggert et al., 1983; Eggert and Adams, 1984). Four named paleochannels affected the Springfield coal: the Francisco Channel (Eggert, 1984), the Galatia Channel ( Hopkins et al., 1979 ), the Leslie Cemetery Channel (Eggert, 1982a), and the Winslow-Henderson Channel ( Eggert, 1984).

The Francisco Channel predates the Springfield peat and is contempora- neous with the constructional phase of the delta platform. This fluvial-channel system is a series of parallel meandering fining-upward sandstone-filled chan- nels that are rarely more than 75 feet (23 m) thick. This channel complex trends from northwest to southeast in eastern Gibson County.

308

The major Galatia Channel is younger than the Francisco Channel and trends from east to west across the county. In places the Galatia Channel has eroded the Houchin Creek coal and Francisco Channel sediments. The Galatia Chan- nel is a fining-upward sand body that may exceed 125 feet ( 38 m ) in thickness, and it splits into two channels in northeastern Gibson County. The Leslie Cemetery Channel is somewhat younger than the Galatia Channel. This chan- nel is represented by shale, siltstone, and sandstone of the Folsomville Member that split the Springfield coal into two seams separated by 65 feet (20 m) of Folsomville sediments (Eggert, 1982b, 1984).

Eggert (1984) found that the youngest paleochannel system affecting the Springfield coal in Gibson County is the Winslow-Henderson Channel. This channel is younger than the Springfield coal and has eroded the coal in south- eastern Gibson County. This channel is represented by a sand body more than 100 feet (30 m) thick, and it trends from south to northeast.

Eggert (1984) believes that differential compaction of pre-Springfield del- taic sediments determined the courses of the fluvial channels in this county and that this compaction combined with the compaction of the delta platform determined the coal thickness. Others have suspected the importance of dif- ferential compaction in coal and deltaic sedimentation. Brown (1975) found that differential compaction determined channel locations in Pennsylvanian deltaic deposits in Texas. Ashley (1907), Wier (1952, 1955), Stanley (1952), Friedman (1956, 1960), and Hutchison (1960) all found differential compac- tion to be a major controlling mechanism for coal deposition in Indiana. Hac- quebard and Donaldson (1969) considered differential compaction an important control for coal deposition in Nova Scotia, Canada. This mechanism controlled the thickness of Cretaceous coal in Utah ( Spieker, 1929) and con- trolled Tertiary Fort Union deposition in northwestern Colorado ( Beaumont, 1979).

METHODS

Gibson County is a good place to study the strata of the gray-shale roof strata associated with contemporaneous channels. It covers a 500-square-mile (1,250 km 2) area in the southeastern part of the Illinois Basin. Since the 1930's more than 7,300 holes have been drilled for petroleum exploration, and most of these holes have geophysical logs that indicate the presence of the Springfield coal.

Geophysical and some coal-drilling records of the interval from the Houchin Creek Coal Member to the Bucktown Coal Member were examined; maps showing thickness of the Springfield to Houchin Creek coals interval, the Bucktown to Springfield coals interval, the fluvial sandstone associated with the Springfield coal, the Springfield coal, and the Springfield to Alum Cave Limestone Member interval were prepared.

309

Ft 0

8 m ~ 7

Fig. 2. Diagrammatic cross section showing stratigraphic relationships between the Springfield Coal Member and associated sediments: 1 =Houchin Creek Coal Member; 2=sandstone-filled Francisco Channels; 3 = Springfield Coal Member; 4 = Folsomville Member = the Leslie Cemetery Channel; 5=sandstone-filled Galatia Channel; 6=Dykersburg Shale Member; 7=Alum Cave Limestone Member; 8 = Bucktown Coal Member.

STRATIGRAPHY

Peppers (1970) and Kosanke (1973) found that the Springfield coal of the Illinois Basin and the Middle Kit tanning and Princess No. 7 coals of the Appa- lachian Basin were similar in age. The age of the rocks in the interval from the Houchin Creek coal to the Bucktown coal, which includes the Springfield, cor- relates with some sediments of the Alleghenian Series in the Appalachian Basin, the Westphalian D Stage in Western Europe, and the Muscovian in the Union of Soviet Socialist Republics.

The term "Dykersburg Shale Member" (Fig. 2 ) was introduced by Hopkins (1968) for the wedge of nonmarine sandy gray shale above the Springfield coal adjacent to the Galatia Channel in southeastern Illinois. This unit is traceable from Illinois into western Gibson County, and its extent and thickness are defined by the increasing interval thickness between the Alum Cave Limestone or the Bucktown coal to the Springfield coal (Figs. 3 and 4). In Indiana, a shale considered equivalent to the Dykersburg shale and referred to informally as Dykersburg in this study, is stratigraphically below the Alum Cave Lime- stone Member of the Dugger Formation.

RESULTS

Mapped stratigraphic relationships provide major insight into the Spring- field coal and its roof in Gibson County. The interval between the Houchin Creek and Springfield coals represents the delta platform of the Springfield coal and is mappable except where it is absent because of erosion by the Galatia Channel. Prodeltaic shale, upward-coarsening shale and sandstone bayfill, and upward-fining fluvial sandstone platform deposits range from less than 40 feet (12 m) to more than 120 feet (37 m) in thickness (Fig. 5).

310

E X P L A N A T I O N

: ~ . : c ~ Galatia Channel

. . . . . Dykersbur 9 Shale Member 0 20 It lhlck

- Dykersburg Shale Member more than 20 ft thick

10 , 0 20 Miles ( ~ l

JEFFERSON

WAYNE

HAMILTON

s: -/I

A J

J EDWARDS

I

i / "" I

- ~ ~ w H i T E

J ~A,~AT,N ~"~," . D

]

KNOX ~,1

/ " ~ "-'1 ~1 WABASH ~ - J . . . . . . . .

"¢O"

h - - - - ' L _ _ _

L _ _ _ _ Y -

l l I I N

WILLIAMSON I Southern v

Fig. 3. Extent of the Dykersburg Shale Member in southeastern Illinois and Gibson County, Indi- ana (southeastern Illinois from Hopkins, 1968).

R 1 0 W GJq 1

Fig. 4. Interval thickness between the Alum Cave Limestone and Springfield Coal Members in Gibson County, Indiana.

311

Fig. 5. Interval thickness between the Springfield Coal and the Houchin Creek Coal Members in Gibson County, Indiana.

EXPLANATION

~------~. Leslie Cemetery Chanr

~ Springfield Coal Membq

~ < 3.5ft

~ - I 3.5-5.5ft

5.5 - 7.5 ft

~ > 7.5 ft /~

5 0 [ I l I I I

Fig. 6. Thickness of the Springfield Coal Member in Gibson County, Indiana.

312

R 1 4

c

;~ 5 Miles • I

% 1: Fig. 7. Thickness of the sandstone underlying the Springfield Coal Member in Gibson County, Indiana.

The thickness of the Springfield coal is variable (Fig. 6). The Springfield was never deposited along the axis of the Galatia Channel, and it is split in many places along the axis flanks. The Winslow-Henderson Channel has eroded the Springfield coal in southeastern Gibson County. Springfield coal, more than 5.5 feet (1.8 m) thick, parallels the Galatia and Leslie Cemetery Chan- nels. This coal thins distally from these channels, particularly over the sand- filled Francisco Channel complex. Extensive Dykersburg shale, as indicated by the thickening interval between the Springfield coal and the Alum Cave limestone, is present in western Gibson County. The Alum Cave limestone pinches out over the gray shale wedge. The Bucktown coal to Springfield coal interval thickens toward the channel; in this area the Dykersburg shale may exceed 90 feet (27 m) in thickness. In the eastern half of the county a thicker Alum Cave to Springfield interval above and parallel to the Leslie Cemetery Channel reflects thicker marine deposition above the former channel margins (Eggert and Maples, in prep). Only limited areas of gray shale extend from the Galatia channel in this eastern area.

DISCUSSION AND CONCLUSIONS

The roof rock of the Springfield coal adjacent to the Galatia Channel in Gibson County is thick gray shale of the Dykersburg in the west and mostly

313

black fissile shale in the east. Therefore, Springfield coal is probably lower in sulfur in the western part of the county than in the eastern part.

The eastern and western areas have different platform compositions. The eastern delta platform consists largely of sand-filled Francisco channels and clays and sand of restricted overbank and bay areas (Fig. 7 ). Pre-platform and platform compaction helped determine the location of the Galatia Channel and encouraged thick peat deposition adjacent to the channel. The sand-domi- nated platform did not compact significantly; there was no adequate subsid- ence for thick Dykersburg to develop.

The western delta platform consists primarily of mud, silt, and clay over- bank and bay-fill deposits. Compaction of earlier sediments induced subsid- ence that determined the course of the Galatia Channel and provided a habitat that was favorable for thick peat deposition. Compaction of the fine-grained bay-fill and overbank sediments within the delta platform provided additional subsidence that allowed thick Dykersburg shale to accumulate.

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