Bureau of Mines Report of Investigations/l985 

Reducing Hazards in Underground Coal Mines 

Through the Recognition and Delineation 

of Coalbed Discontinuities Caused 

by Ancient Channel Processes 

By Carla A. Kertis 

UNITED STATES DEPARTMENT OF THE rn INTERIOR C 
UNITED STATES DEPARTMENT OF THE INTERIOR 

Donald Paul Hodel, Secretary 

BUREAU OF MINES 

Robert C. Horton, Director 
. 

Kertis, Carla A 

Reducing hazards in underground coal mines through the recognition 

and delineation of coalbed discontinuities caused by ancient channel 

processes. 

(Report of investigations ; 8987) 

Bibliography: p. 21-23. 

Supt. of Docs. no.: I 28.23: 8987. 

1. Coal-Geology -Pennsylvania-Indiana County. 2. Coal-GeologyPennsylvania-Armstrong County. 3. River channels. 4. Coal mines and 

mining-Pennsylvania-Indiana County-Safety measures. 5. Coal mines 

and mining-Pennsy lvania-Armstrong County -Sa€ety measures. I. Title. 

11. Series: Report of investigations (United States. Bureau of Mines) ; 

8987. 

TN23.U43 [TN805.P4] 622s [622'.334] 85-600080 

* 
CONTENTS 

Page 

Abstract ...................................................................... Introduction .................................................................. Acknowledgments ............................................................... Study area and data base ...................................................... Stratigraphy ................................................................ Structural setting .......................................................... Problems associated with fluvio-deltaic channel discontinuities ............... Patterns of coal distribution ................................................. Upper Freeport Coalbed ...................................................... Lower Freeport Coalbed ...................................................... Lower Kittanning Coalbed .................................................... Sandstone distribution ........................................................ Relationship between coal and sandstone thicknesses ........................... Effects of channels on peat deposits .......................................... Splits ...................................................................... Thinning of coalbeds over topographic highs ................................. Abnormally thick peat accumulations ......................................... Coal quality ................................................................ Effects of structural controls on channels .................................... Prediction of coalbed discontinuities in advance of mining .................... Summary and conclusions ....................................................... References .................................................................... 

ILLUSTRATIONS 

1 . Physiographic setting of study area ...................................... 2 . Seven-and-one-half-minute quadrangles comprising study area .............. 3 . Base map of study area ................................................... 4 . Typical gamma-ray log response for various lithologies and corresponding 

facies .................................................................. 5 . Generalized stratigraphic column of units in study area .................. 6 . Structural contour map of study area drawn on top of Upper Freeport 

Coalbed ................................................................. 7 . Isopach map of Upper Freeport Coalbed .................................... 8 . Isopach map of Lower Freeport Coalbed .................................... 9 . Isopach map of Lower Kittanning Coalbed .................................. 10 . Sandstone isolith map of Brush Creek marine unit to Upper Freeport 

Coalbed interval ........................................................ 11 . Sandstone isolith map of Upper Freeport Coalbed to Lower Freeport Coalbed 

interval ................................................................ 12 . Sandstone isolith map of Lower Freeport Coalbed to Lower Kittanning 

Coalbed interval ........................................................ 13 . Cross section depicting scouring of Upper Freeport Coalbed by a channel .. 14 . Cross section depicting scouring of Lower Freeport and Lower Kittanning 

Coalbeds by channels .................................................... 15 . Two ways splitting is induced in a coalbed ............................... 16 . Cross section of splits in Lower Freeport Coalbed ........................ 17 . Cross section illustrating thinning of Lower Kittanning Coalbed over a 

natural levee ........................................................... 18 . Cross section showing anomalous thickness of Upper Freeport Coalbed 

adjacent to a channel deposit ........................................... 19 . Map of increased sulfur content in Lower Kittanning Coalbed with approach 

to a sandstone-filled channel ........................................... 
UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT 

cm centimeter m meter 

f t foot mi mile 

g/cm3 gram per cubic centimeter 

km kilometer 

lb/f t3 pound per cubic foot 

percent 

square kilometer 

square mile 
REDUCING HAZARDS IN UNDERGROUND COAL MINES THROUGH THE RECOGNITION 

AND DELINEATION OF COALBED DISCONTINUITIES 

CAUSED BY ANCIENT CHANNEL PROCESSES 

By Car la A. Kertis ' 

ABSTRACT 

Because coalbed discontinuities often pose serious economic and safety 

problems in underground coal mines, criteria were documented for the 

recognition and prediction of discontinuities in advance of mining. 

Pennsylvanian strata in Indiana and Armstrong Counties, PA, were deposited as part of fluvio-deltaic complexes with channel-phase sandstones 

as the predominant type of coalbed discontinuity. Coalbed isopach maps 

constructed for this study delineated numerous want areas (areas of no 

coal) with elongate to linear geometries. A comparison of coalbed isopach and corresponding sandstone isolith maps of the study area revealed 

many examples of a thick-sandstone, thin-subjacent-coalbed relationship. 

Nearly 60 pct of the want areas in the study area were found to lie subjacent to thick (> 20 ft [6 m]) sandstone accumulations. In addition to 

erosion of the coalbed, channels may contribute to coalbed splitting, 

coalbed thinning over paleotopographic highs, abnormal coalbed thicknesses, and deterioration of coal quality. If these features are considered, then approximately 80 pct of all interruptions in the economic 

coalbeds in this area result from channel activity. By using the criteria developed in this study and described in this Bureau of Mines report, the occurrence of coalbed discontinuities may be predicted and anticipated in advance of mining. 

~eolo~ist, Pittsburgh Research Center, Bureau of Mines, Pittsburgh, PA. 
INTRODUCTION 

Exploratory drilling, mine development, 

and methane drainage are severely hampered by coalbed discontinuities. Since 

discontinuities result in absence or 

thinning of the coalbed, the coal reserves and production potential of a mine 

property may be overestimated if an undetected discontinuity lies within its 

boundaries. Discontinuities encountered 

during mine development inhibit the extension of mine entries and may cause the 

abandonment of some sections (11).2 A 

coalbed gas reservoir may be coeartmentalized by discontinuities, thereby precluding effective methane drainage (15, - 

- 26). In certain geologic settings, a 

coalbed discontinuity may behave as a gas 

reservoir and emit methane into mine 

workings that intercept it (31). Water, 

or water and gas, may accumu~te in mine 

entries in the proximity of discontinuities. In addition, roof stability and 

coal quality commonly deteriorate in the 

proximity of a coalbed discontinuity 

(16) 

Coalbed discontinuities are varied in 

geometry and genesis. The term "coalbed 

inhibited (11). Channel-bank slumping, 

although genetically different from 

faulting, produces similar offsets in the 

coalbed (35). Both faulting and slumping 

discontinxties are variable in the 

amount of vertical displacement they 

cause and lateral extent (5). 

Clastic dikes are irregularly shaped 

bodies that cut across coalbeds. These 

structures are filled with brecciated 

clastic material and are believed to result from differential compaction (5, 32) 

or collapse into tensional cracks (n. 

Clas tic dike discontinuities are generally less than 5 ft (1,5 m) wide and extend 

up to several thousand feet laterally. 

Because clastic dikes serve as barriers 

to migration of methane gas, large unexpected gas emissions may be experienced 

as a mining machine cuts through the dike 

and encounters virgin coal on the other 

side. Additionally, clastic dikes often 

give rise to serious roof control problems (7). 

LOC~~ topographic variations in the 

peat swamp may result in thinning or absence of the coalbed over high areas. 

discontinuity" refers to any physical Structural highs that developed contemfeature or process that results in poraneously with peat deposition may also 

the interruption of coalbed continuity. produce discontinuous coalbeds (12). 

Therefore, coalbed discontinuities may However, in comparison to the Kscontiresult from nondeposition or erosional nuities mentioned above, the most deleteprocesses, from sedimentation processes, rious coalbed discontinuities are more 

or from structural activity. Some fea- commonly the result of scouring by antures that lie parallel to bedding planes cient fluvio-deltaic channels. The coalwithin the coalbed may be considered dis- bearing strata in Indiana and Armstrong 

continuities. Partings, or binders, in 

coalbeds consist mainly of minerals and 

must be separated during preparation of 

the mined coal to preserve high coal 

quality and are therefore one type of 

discontinuity. 

Various features that cut across bedding planes, such as faults, slumps, and 

clastic dikes, are more commonly recognized as coalbed discontinuties. Faulting may offset the coalbed to such a degree that successful mine development is 

2~nderlined numbers in parentheses refer to items in the list of references at 

the end of this report. 

Counties, PA, were deposited as part of 

fluvio-deltaic complexes that prograded 

across the study area to the northwest 

and south (2-4, 6, 8-10). Channels cut -- - -- 

erratic courses over the alluvial and 

delta plain and commonly scoured out peat 

accumulations and underlying deposits as 

well. The fluvio-deltaic channels, which 

subsequently filled with sand and, locally, finer grained sediments, are the predominant type of coalbed discontinuity 

found in the study area. 

The study area, located in western 

Pennsylvania, has a long history of commercial coal production and remains active with both surface and underground 
mine development (27). The recoverable 

coal resources in Indiana and Armstrong 

Counties are estimated to be over 3.3 

billion short tons (3 billion metric 

tons) (22). - Mining is expected to continue to be a leading industry in this 

area and may intensify in the future to 

exploit the abundant coal reserves. 

Therefore, the ability to recognize coalbed discontinuities and predict their occurrence would be especially beneficial 

to the mining industry in this area. 

The project described in this report 

was undertaken to delineate coalbed discontinuities associated with channel deposits and to document criteria for their 

recognition and rediction. "- lU acconi 

plish this, isopach maps of several of 

the economic coalbeds in the area--the 

Upper Freeport, the Lower Freeport, and 

the Lower JCi t tanning--were constructed, 

and want areas were delineated. Comparison of these maps with sandstone isolith 

maps of the area showed a relationship 

between thick sandstone and thin or no 

subjacent coal in many cases. In light 

of this relationship, if the major 

channel-phase sandstones of an area can 

be delineated, then areas likely to be 

plagued by channel discontinuities can 

also be discerned and predicted. Once 

these discontinuities have been located, 

main entry systems, longwall panels, 

shafts, and slopes can be positioned to 

avoid the hazards associated with coalbed 

discontinuities. 

ACKNOWLEDGMENTS 

The author gratefully acknowledges 

the personnel of the Rochester & Pittsburgh Coal Co., Indiana, PA, and the 

Pennsylvania Geological Survey, Pittsburgh, PA, for providing drill-hole data 

and other technical information. Innumerable valuable suggestions were furnished by the reviewers of the manuscript 

for this report: William A. Bragonier, 

manager of exploration, and Gary D. Ball, 

geologist, of the Rochester & Pittsburgh Coal Co.; James M. Madar, project 

geologist, of Consolidation Coal Co., 

Pittsburgh, PA; Dr. David K. Brezinski, 

State stratigrapher-sedimentologist, of 

the Maryland Geological Survey, Baltimore, MD; Dr. David W. Houseknecht, associate professor, of the University of 

Missouri, Columbia, MO; Maurice Deul, 

visiting professor, of the University 

of Pittsburgh, Pittsburgh, PA; and Dr. 

Eugene G. Williams, professor, of the 

Pennsylvania State University, University 

Park, PA. 

STUDY AREA AND DATA BASE 

The area chosen for this project lies 

in the Appalachian Plateau physiographic 

province of western Pennsylvania and 

straddles the Allegheny Mountain and 

Pittsburgh Plateau sections (fig. 1). 

Eight 7-112' quadrangles from Indiana and 

Armstrong Counties and a small part of 

Westmoreland County constituted the study 

area, which encompassed approximately 450 

mi2 (1,170 km2). The quadrangles studied 

were Whitesburg, Avonmore, Elderton, McIntyre, Ernest, Indiana, Clymer, and 

Brush Valley (fig. 2). 

Data from coal-exploration drill holes 

and wireline log data from gas wells were 

used in this study. A total of 636 data 

points, including 403 core descriptions 

and 233 electric logs (fig. 3), was collected from coal companies, the Pennsylvania Geological Survey, and the Petroleum Information Corp. Midland, TX. 

All of the geophysical-log (gas well) 

data points represent gamma-ray logs. In 

addition to the gamma-ray logs, bulkdensity logs were run in 20 of the 

holes. 

Coals, sandstones, and limestones are 

defined by sharp deflections to the left 

on gamma-ray logs (fig. 4). Unfortunately, this similarity in log response makes 

coalbeds virtually indistinguishable from 

thin sandstone or limestone beds on 

gamma-ray logs. Bulk-density logs, when 

available, confirm the presence of coals. 
/ Whitesburg 

2 Avonmore 

3 Elderton Westmoreland 

4 Mclntyre 

5 Ernest 

6 Indiana Scale, mi 

7 Clymer 

8 Brush Valley 

FIGURE 2. - Seven-and-one-half-minute quadrangles comprising study area. 

A bulk density of less than 2.0 g/cm3 

(124 lb/ft3) was interpreted as coal. In 

this study, the geophysical logs were 

used to determine the presence or absence 

of coal, not to estimate coal thickness. 

However, sandstone thicknesses were estimated from the geophysical logs. 

STRAT I GRAPHY 

The geologic interval examined in this 

study was restricted to the coal-bearing 

strata of the Pennsylvanian System (fig. 

5). In Indiana and Armstrong Counties, 

the Pennsylvanian rocks are predominantly 

g 

Upper Kittanning Coalbed occurs in minable thicknesses at some locations, but 

production from these areas is limited 

(1). Because of their regional extent 

and economic viability, the Upper and 

Lower Freeport and the Lower Kittanning 

Coalbeds were the focal point of this 

study . The Conemaugh Group immediately overlies the Allegheny Group and consists of 

a series of sandstones and shales punctuated by several calcareous marine horizons (28, - - 30). Because coalbeds in the 

Conemaugh Group are thin and laterally 

discontinuous, they have not been intensively worked in the study area and were 

not included in this study. 

The uppermost Pennsylvanian strata exposed in the study area belong to the 

Monongahela Group, a sequence of shale, 

sandstone, limestone, and coal (30). The 

Monongahela is restricted to 14-mi2 (35 

km2) of exposure in the southwestern portion of the study area along the axis of 

the Elders Ridge syncline (29). - The base 
Town or city - 

-@F U.S route 

-@- State route 

CountCoreho

Geoph

FIGURE 3. - Base map of study area. (Lines A-A', B-B', etc., 
(30). but ow 

s essetav ed out GU5. Geeaed statgapc cou

(v): For these reasons, the Pittsburgh of units in study area. 

~Glbed is not included in this study. 

STRUCTUKAL SETTING 

Deformation of the strata in Indiana 

and Armstrong Counties occurred during 

the late Paleozoic Allegheny orogeny. 

Compressional forces from the southeast 

produced relatively tight folds east of 

the Allegheny ~ront and~successively more 

gentle folds across the Appalachian Plateau physiographic province to the west 

(24, - - 30). In most of the folded Plateau 

region, limbs of major anticlines are 

broken by east-dipping thrust faults in 

Lower Devonian strata (13). . . The structure of Pennsylvanian roxs in the study 

area is characterized by gently folded 

strata that form relatively open, subparallel anticlines and synclines. The fold 

axes generally trend northeast-southwest 

and are about 2 to 5 mi (3 to 8 km) apart 

(27). A structural contour map of the 

area, drawn on the top of the Upper Freeport Coalbed, is shown in figure 6. 

LEGEND ----- AXIS of major fold 

-600- Structural contour line 

(Contour interval = I00 ft) 

0 - 4 8 

Scale, mi 

FIGURE 6. - Structural contour map of study 

area drawn on top of Upper Freeport Coalbed. 
Major faults are absent within the These faults are largely intraformational 

study area. However, minor faults (with and extend from the roof through the 

displacement less than 10 ft 13 m]) are coalbed and the floor. Striking parallel 

relatively common. Thrust faults have to the trend of local structures, these 

been observed in the Lucerne No. 6 Mine faults are a consequence of local strucin the Indiana quadrangle (21) and in the tural adjustment to the tectonic forces 

Lucerne No. 8 and Jane ~inz in the Mc- of the Allegheny orogeny or result from 

Intyre and Elderton quadrangles (27). differential compaction or slumping (27). - 

PROBLEMS ASSOCIATED WITH FLUVIO-DELTAIC CHANNEL DISCONTINUITIES 

Channel sandstones pose a host of problems in underground coal mines. Areas 

where the coalbed has been removed or 

thinned by scouring are an impediment to 

mining both because of the loss of economic coaibed tiiickness and because more 

roof rock must be removed to maintain 

proper entry height. 

The presence of channel sandstone discontinuities in some cases adversely affects coal quality. In the Hartshorne 

Coalbed in eastern Oklahoma, a decrease 

in the free-swelling index (FSI) with approach to a distributary-channel sandstone has been documented (14). The 

sulfur content of a coalbed near a channel may also increase to well above the 

average level for the coalbed (14, 19). - - 

Infiltration of ground water and sulfurbearing solutions from the sandstone has 

been suggested as a possible means for 

the deterioration of coal quality adjacent to channel sandstone discontinuities 

(19). The opposite is true in the Illinois basin, where the sulfur content of 

the coal is lowest immediately adjacent 

reasons for roof control problems are (1) 

slickensided surfaces between adjacent 

cross-bed sets, (2) slickensided contacts between sandstone and shale as a 

result of differential compaction, and 

(3) prominent joints (9). Spalling of 

rock along slickensides or joint planes 

can produce spectacular roof falls, especially in the zone adjacent to a channel where the strata coarsen from shale 

to sandstone. Areas of roof instability as a result of differential cow 

paction near a sandstone channel have 

been noted in mines in Cambria County, PA 

(20), and wes t-central Illinois ( 19). If 

tG channel-f ill sandstone is masxve and 

does not break easily, longwall chocks 

may be pinned beneath a cantilever beam 

produced by flexure of the sandstone. 

A rise in the floor elevation of the 

coalbed is commonly known as a roll. 

Rolls are often coupled with areas where 

the coal has been scoured out by a channel. Rolls may occur on either flank of 

a channel-phase sandstone and are the result of peat accumulation over natural 

to the channels (23). This anomaly is levees adjacent to the channel (19) or 

attributed to thh unique depositional differential compaction (14). ~zause 

setting of strata in that basin. The ash they create irregular roof and floor topcontent of a coalbed may also increase in 

the proximity of a channel-phase sandstone as a result of increased clastic 

deposition in the peat swamp during episodes of flooding. The resultant overbank deposits may become thick enough to 

form partings or splits in the coalbed. 

This has been documented in Illinois, 

where splitting of the Herrin No. 6 Coalbed becomes more pronounced with approach 

to the Anvil Rock Sandstone (25). 

Severe roof stability prxlems have - - 

been encountered as mining approaches 

channel-phase sandstones. Several features that have been recognized as 

ography through locally variable dips and 

may impound water, rolls are a hindrance 

to safe and economical coal production. 

Additionally, they sometimes inhibit the 

movement of mining machinery. 

Like many other sandstones, channelphase sandstones may serve as aquifers 

and reservoir rocks. Therefore, water 

and/or gas may accumulate in a channel 

sandstone and subsequently be released 

into adjacent mine workings. Water commonly accumulates along the irregular 

bottom of the sandstone, where it is 

trapped by underlying layers of impervious shale. Severe water accumulation 
problems may occur where the channel 

sandstone is intersected by underground 

workings. If the water is saline, as in 

west-central Illinois, mining equipment 

may be corroded (25). Roof bolting, 

which is especially necessary in the unstable area adjacent to the channel-fill 

sandstone, may aggravate water problems 

because the aquifer may be tapped, resulting in increased seepage (19). 

Ground water from the sandstone may react 

with pyrite in the coalbed and adjacent 

strata to produce acid drainage. Environmental laws require that this water 

meet minimum standards of pH and mineral 

content before being discharged into surf ace streams (i7 j. Tne handling and 

treatment of acn mine water add to the 

operating costs of the mine. 

Similarly, methane-gas-emission problems multiply in the proximity of 

channel-phase sandstones. In eastern 

Oklahoma, where natural gas is produced 

from Hartshorne distributary-channel 

sandstones that are in direct contact 

with the Hartshorne Coalbed, investigators concluded that gas-emission problems 

could be anticipated in any mine workings 

that advance toward these sandstones 

(g). In a mine in northern West Virginia, abnormally high methane emissions 

adjacent to a channel-phase sandstone 

were documented (2). The presence of 

channel discontinuities increases the 

likelihood of a methane ignition not only 

because of increased emissions, but also 

because the sudden thinning or absence of 

the coalbed may cause mining machinery to 

generate sparks as the cutting bits 

strike the roof rock. 

In some cases, the coalbed may thicken 

substantially immediately proximate to 

the channel. Some coalbeds have been 

known to double or triple in thickness 

(2). This thickening may be the consequence of (1) increased peat deposition 

contiguous to the channel, stimulated by j-ane more lcapid subsidence of 1 3 - ~rie aeriser 

sandstone (relative to the density of 

peat); (2) slumping of the coalbed over 

itself; or (3) an increasing number of 

partings as the channel is approached. 

However, any possible economic advantage 

gained through thickening of the coalbed 

is lost if the coalbed has been eroded by 

channel activity. Additionally, all of 

the previously described problems associated with channel-phase sandstones 

are likely to be more prominent in the 

area immediately adjacent to the channel 

deposit. 

PATTERNS OF COAL DISTRIBUTION 

To delineate areas of discontinuous 

coal, isopach maps of the Upper Freeport, 

Lower Freeport, and Lower Kittanning 

Coalbeds were constructed (figs. 7-9). A 

contour interval of 6 in (15 cm) was used 

so that any subtle changes in coalbed 

thickness that might impend with approach 

to a coalbed discontinuity could be discerned. (The contour maps constructed 

for this study were not computergenerated. Even spacing of contour lines 

was used to arbitrarily eliminate the effects of irregularities in channel 

shape.) Areas of thin, split, or no coal 

were closely scrutinized for clues leading to interpretations of the genesis of 

these discontinuities. 

UPPER FREEPORT COALBED 

The Indiana quadrangle and the southern 

half of the Ernest quadrangle are underlain by thick accumulations of Upper 

Freeport coal (60 to 92 in [150 to 230 

cm]). Two anomalously thick tracts of 

coal are present in the western Brush 

Valley quadrangle and in the western 

Avonmore quadrangle (fig. 7). Numerous 

small, pod-shaped want areas (< 2 mi2 

[ < 5 km2] in size) occur throughout the 

study area. Extensive areas of no coal 

are found in the Clymer and Brush Valley 

quadrangles (fig. 7). Although no study 

has specifically addressed the absence 

of the Upper Freeport Coalbed in these 
OUFC Outcropof Upper Freeport Coalbed 

Corehole data point 

Geophysical-lq data point 

( Onlv ueaence or absence of ?he coolbed has been 

deteimined from geophysical lqa Absence of the coolbed Is indicated by Om.) 

FIGURE 
OLFC Omrapof Lower heeport Coalbed ,,c- Co

Conhole data point (C

lin

Geophyrical-log data point (Only presence or absence of the coalbed has been Lo

determined from geop~sicologs. Absence of the 

coalbed Is indicated by Ow.) 

FIGURE 8. - lsopo
OLKC Outcmp of Lower Kittanning Coalbed 

. Corehole data point 

ophysiml-log data point Only presence or absence of the cwlbed has been ' F" 

determined from geoph siwl logs Absence ofthe coalbed is indicated by&*.) 

FIGU

OUFC Outcrop of Upper Freepart Caalbed 

Corehole data point 

Geophysical-log data point 

@

FIGURE 11. - Sandstone isolith m
OLFC Outcrop of Lower Freeport Coalbed /go' Sandston

Corehole data point (Contour 

lines ind

Geophysical-log data point 

FIGURE 12. - Sandstone isolith map of Lower Fre
quadrangles, inferences in the literature relatively thin and is only locally 

indicate nondeposition of the coal over greater than 60 in (150 cm) thick. 

growing structural highs, such as the 

Chestnut Ridge, Nolo, and Laurel Hill LOWER KITTANNING COALBED 

anticlines (18, - - 34). 

LOWER FREEPORT COALBED 

Lying an average of 80 ft (24 m) below 

the Upper Freeport Coalbed, the Lower 

Freeport Coalbed is the most laterally 

discontinuous of the three coalbeds analyzed in this study. Want areas in the 

Lower Freeport Coalbed typically possess 

a shoestring geometry (fig. 8). Unlike 

the Upper Freeport and Lower Kittan- 

---- f---lL LI~LI~ b~d~~eds, the LOWCL ---- u-nnn KLCC~O~~ IS 

The Lower Kittanning Coalbed occurs an 

average of 200 ft (60 m) below the Upper 

Freeport Coalbed. Of the three coalbeds 

examined in this study, the Lower Kittanning is the most laterally persistent; 

fewer discontinuities have been identified in this coalbed than in the overlying Upper and Lower Freeport Coalbeds. 

The thickest accumulations of the Lower 

Kittanning Coalbed (> 72 in [> 180 cm]) 

occur in the Indiana and Brush Valley 

quadrangles (fig. 9). 

SANDSTONE DISTRIBUTION 

Sandstone isolith maps with a contour 

interval of 10 ft (3 m) were drawn for 

three intervals, one immediately suprajacent to each of the three economic 

coalbeds (figs. 10-12). These intervals 

were (1) the Brush Creek marine horizon 

to the Upper Freeport Coalbed, (2) the 

Upper Freeport Coalbed to the Lower Freeport Coalbed, and (3) the Lower Freeport 

Coalbed to the Lower Kittanning Coalbed. 

These divisions were chosen because they 

are easily recognized by their delimiting 

marker beds. These intervals are not of 

equal thickness, nor do they individually 

maintain uniform thicknesses across the 

study area. However, the thickness of 

each interval tends to increase where 

thick sands tone is present. 

As revealed by the sandstone isolith 

maps and numerous cross sections, sandstone bodies in all three intervals display a shoestring geometry (1-2 mi [2-4 

km] wide, tens of miles long). These 

units were interpreted as channel-phase 

sandstones that interfinger laterally 

with alluvial plain and interdistributary 

bay deposits. Several major channels 

(> 40 ft [> 12 m] thick) and numerous minor ancillary channels constitute the 

sandstone strata in each interval. A few 

crevasse splay deposits, recognized by 

their coarsening upward character and 

lobate geometry, were delineated. Examples can be seen in the Brush Creek to 

Upper Freeport interval in the eastern 

McIntyre quadrangle (center of figure 10) 

and in the Lower Freeport to Lower Kittanning interval in the central Elderton 

and central Indiana quadrangles (figure 

12, north-central and east-central portions). Many of the channel sandstones 

with numerous bifurcations can be traced 

the length of the study area. In many 

cases, these sandstone channels trend 

north-south to northeast-southwest and 

lie subparallel to local structures. 

RELATIONSHIP BETWEEN COAL AND SANDSTONE THICKNESSES 

Through comparison of the coalbed isopach and corresponding sandstone isolith 

maps, a relationship between coal and 

sands tone thicknesses was clearly perceived. The coalbed isopachs indicated 

41 want areas in the study area. Of 

these, 24 (59 pct) are located subjacent 

to thick (> 20 ft [> 6 m]) sandstone accumulations. Generally, these want areas 

display elongate to linear geometries and 

appear to be related to channel-phase 

sandstone systems. These discontinuities 

are most probably the result of (1) erosional scouring by channels that breached 

their levees and issued across marshswamp environments during episodes of 

flooding or (2) scouring of buried semiconsolidated peat deposits by younger 
y 

of this phenomenon are exhibited in the 

northern Indiana and central Brush Valley 

quadrangles, and along the border between 

the McIntyre and Avonmore quadrangles. 

(Compare figures 8 and 11.) 

The Lower Kittanning Coalbed, although 

the most persistent coalbed in the study 

area, is not immune to the erosive effects of channels. Notable examples of 

channel scouring of the Lower Kittanning 

Coalbed are evident in the west-central 

Indiana, east-central Whitesburg, and 

central Brush Valley quadrangles. (Compare figures 9 and 12.) The cross section in figure 14 illustrates that erosion by a channel has removed a portion 

of the Lower Kittanning Coalbed in the 

central Brush Valley quadrangle. This 

cross section shows that the Lower Freeport Coalbed also has been removed by 

channel scouring in the same area. The 

sandstone isolith maps suggest vertical 

stacking of channel-phase sandstones at 

this location. (Compare figures 11 and 

12. ) 

O Sandstone Undercloy 

KEY 1 

Shale Cool 

Sandy shale 

0 3,000 

Scale, ft 

FIGURE 14. - Cross section depicting scouring of 

Lower Freeport and Lower Kittanning Coalbeds by 

channels. (For location, see line B-B' in figure 3.) 

Ancient fluvio-deltaic channels cannot 

always be detected by delineating shoestring sandstone deposits. In certain 

geologic settings, a fluvio-deltaic channel may fill with clay rather than sand 

(1). Therefore, it is reasonable to assume that some coalbed discontinuities 

that do not lie in areas of thick sandstone accumulations may be attributed to 

clay-filled, abandoned channels. Several 
p

in thinning or absence of coalbeds. In 

addition, some instances of deterioration 

of coal quality result when sulfur

Topographic highs produced by the formation of natural levees adjacent to 

bearing solutions percolate through permeable sandstone-filled channels. 

SPLITS 

Splits in a coalbed are generated when 

detrital material is introduced into a 

peat swamp by overbank flooding or by 

crevasse splays (fig. 15). Coalbed partings generated by crevasse splays tend to 

be areally restricted, coarsening upward 

sequences that occur on one side of the 

channel (fig. 15). Crevasse splays are 

generally singular events; therefore, 

they produce one fairly thick split in a 

coalbed. Overbank flooding creates thinner, finer grained, laterally persistent 

coalbed partings. Because flooding 

events occur repeatedly and affect widespread areas, numerous coalbed partings 

resulting from overbank flooding may be 

found on both sides of the channel (fig, 

15). 

KEY 

Sandstone Coal 

I3 Sandy shale .=I Shale 

FIGURE 15. - Two ways splitting is induced in a 

coalbed. A, Overbank flooding; 8, crevasse splay. 
Freeport Coalbed. (For location, see line C-C' 

in figure 3.) 

D 

KEY 

Sandstone FZZ Limestone 

H Shale E Cool 

E2 Sondy shale B Underclay 

O~ 500 

Scale, ft 

FIGURE 17. - Cross section illustrating thinning 

of Lower Kittanning Coalbed over a natural levee. 

(For location, see line D-D' in figure 3.) 

g wtsad eatve to cotguous 

deposits may generate abnormally thick 

peat accumulations. As the sand accumulates, sediments under the channel body 

compact differentially. This is reflected at the surface as differential subsidence. ~eposition in contemporaneous peat 

swamps immediately adjacent to the channel keeps pace with this "subsidence," 

thus producing thick accretions of peat. 

Pods of unusually thick coal may also be 

the consequence of flooding events that 

piled up peat along the banks of the 

channel (27) or sedimentary slumping. 

Two trGts of anomalously thick Upper 

Freeport coal are present in the western 

Avonmore and western Brush Valley quadrangles (fig. 7). Both of these thickcoal areas adjoin channel-phase sandstones. Figure 18 depicts the increased 

thickness of the coalbed in the Brush 

Valley quadrangle. The advantages of 

mining these thick coal deposits are 

quickly offset by the previously mentioned economic and safety problems attendant to channel discontinuities. This 
overlies the Lower Kittanning Coalbed. 

In its active phase, this channel scoured 

out portions of the peat precursor of the 

coalbed. Where the Lower Kittanning 

Coalbed is overlain by the channel sandstone, the sulfur content of the coalbed 

generally varies from 3 to greater than 6 

pct (fig. 19). Where the sandstone channel is absent, the sulfur content of the 

coalbed averages 2.50 pct or less. The 

iso-sulfur contour lines lie subparallel 

to the trend' of the channel-phase sandstone, implying that there is some influence by the channel. 

Ash content of the coalbeds does not 

display the strong correspondence to 

channel deposits as does sulfur content. 

Shaded orea reDresents 

map locatlon w~th~n 

study area dep~cted 

in figure 2 

0 4.000 8,000 L I I 

Scale, ft 

FIGURE 19. - Map of increased sulfur content 

in Lower Kittanning Coalbed with approach to a 

sandstone-fi l led channel. 

In some coreholes adjacent to channels, a 

higher coalbed ash content was indicated. 

However, no distinct correlation could be 

discerned. 

EFFECTS OF STRUCTURAL CONTROLS ON CHANNELS 

As mentioned previously, structural over the Chestnut Ridge and Nolo antifolds growing contemporaneously with peat clines. Subtle effects of structural 

deposition may have produced extensive controls are also expressed by channelwant areas in the Upper Freeport Coalbed phase sandstones. Several areas of 
stacked sandstone zones that tend to coincide with structurally low areas have 

been recognized in Conemaugh Group strata 

(18). In this study, comparison of the 

three sandstone isolith maps and the 

structural contour map of the study area 

revealed some relationships between the 

positions of many of the sandstone-filled 

channels and structural (paleotopographic) lows. 

Comparison of the sandstone isolith 

maps (figs. 10-12) reveals that some 

sandstone channels are vertically juxtaposed in successive horizons. Several 

areas of sandstone stacking coincide with 

PREDICTION OF COALBED DISCONTI 

The serious hazards that accompany 

coalbed discontinuities may severely 

hamper mine development. All mine personnel involved in planning and development should be aware of the existence of 

coalbed discontinuities and the problems 

they create in underground coal mines. 

The results of this study showed that 

in the portion of the northern Appalachian basin in which the data were collected, coalbed discontinuities are most commonly the result of scouring by ancient 

fluvio-deltaic channels. In many cases, 

these channels are not randomly oriented, 

but tend to lie subparallel to local 

flexures; in some cases, they are preferentially located along synclinal axes. 

With these points in mind, several steps 

should be taken when a prospective mine 

property is evaluated with respect to 

coalbed discontinuities. These steps are 

as follows: 

1. Build a data base for the area. 

By including information from gas-well 

geophysical logs, the data base will be 

greatly enhanced at a fraction of the 

cost of drilling exploratory coreholes. 

2. Construct a structure map of the 

area, paying particular attention to the 

traces of anticlinal and synclinal axes. 

3. Delineate ancient channels through 

the construction of sandstone isolith maps. (In western Pennsylvania, 

the channels may tend to be vertically 

stacked and often will coincide with 

structurally low areas.) 

and lie subparallel to the synclines 

(structural and topographic lows) in the 

area. In some cases, sandstone channels 

in all three intervals are vertically 

stacked in the synclines (along the axis 

of the Elders Ridge syncline, on the 

western flank of the Brush Valley syncline, and along the northern portion of 

the axis of the Latrobe syncline). The 

superposition of sandstone-filled channels and their correspondence to local 

structural trends imply that folds were 

growing during the time of sedimentation 

and that they exerted some control on the 

location of channel courses. 

.NUITIES IN ADVANCE OF MINING 

4. After the channel deposits have 

been delineated, mine development should 

be planned for areas where channels are 

absent. If it is impossible to avoid 

zones where there is a high probability 

of encountering channels, mine layouts 

should be designed to intersect the channel trend at an angle which most alleviates the hazardous conditions that may 

be induced by the presence of the channel. In this portion of the Appalachian 

basin, channels tend to follow strike. 

Therefore, by orienting headings at a 

suitable angle with respect to strike, 

the number of mine entries hampered by 

the adverse conditions created by fluviodeltaic channel discontinuities could be 

limited. 

Using the criteria developed in this 

study for the recognition of coalbed discontinuities, areas likely to be affected 

by the problems associated with discontinuities can be predicted well in advance of mine development. Channel deposits can be traced for several miles, 

and, because of their vertically stacked 

arrangement in this portion of the Appalachian basin, problem areas can also be 

predicted deeper in the section. By anticipating the occurrence of coalbed discontinuities, and planning mine development accordingly, the safety and economic 

hazards discontinuities create in underground coal mines may be minimized or 

avoided. 
SUMMARY AND CONCLUSIONS 

Sandstone-filled channels are the predominant coalbed discontinuity in the 

studied portion of Indiana and Armstrong 

Counties. Of the 41 want areas in the 

study area, 24 (59 pct) lie subjacent to 

thick sandstone accumulations. However, 

if areas of split coal adjacent to channels and areas of thin coal over natural 

levee deposits are also included, then 

approximately 80 pct of all interruptions 

in the economic coalbeds in this area result from channel activity. 

Serious safety hazards and economic 

risks are created in underground coal 

mines by sandstone-filled channels. An 

obvious economic disadvantage results 

when the coalbed has been removed by 

channel scouring. Other economic disadvantages engendered by channels are 

splitting of the coalbed and deterioration of coal quality in the proximity of 

the channel. Significant safety hazards 

correlated with channel-sandstone discontinuities include roof-rock instability, 

water accumulation problems, and dangers 

associated with methane emissions. 

The use of inexpensive gas-well 

geophysical logs can assist in the 

delineation of sandstone-filled channels. 

Prospective mine properties may be evaluated with respect to coalbed discontinuities without the drilling of numerous costly exploratory boreholes. 

Because fluvio-deltaic channels in the 

northern Appalachian basin possess shoestring geometries, their trends and occurrence may be predicted well in advance 

of mine development with an adequate data 

base. Recognition of the various features associated with channels--coalbed 

thinning over levee deposits, splitting 

of the coalbed, diminished coal quality, 

and rolls in the coalbed--will aid in 

the prediction of coalbed discontinuities 

caused by channel scouring before the 

actual want areas are encountered. Once 

the location of a channel deposit is ascertained, the direction of mine headings 

can be planned to avoid the unfavorable 

mining conditions that accompany channel 

discontinuities. 

If sufficient data are available, the 

methods described in this report can be 

applied to other coal-bearing areas and 

basins to predict the occurrence of channel discontinuities. 

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*U.S. GPO: 1985-505-019/20,114