Bureau of Mines Report of Investigations/l979 

Geology of the Lower Kittanning 

Coalbed and Related Mining 

and Methane Emission Problems 

in Cambria County, Pa. 

UNITED STATES DEPARTMENT OF THE INTERIOR 
Report of Investigations 8354 

Geology of the Lower Kittanning 

Coalbed and Related Mining 

and Methane Emission Problems 

in Cambria County, Pa. 

By A. T. Iannacchione and D. G. Puglio 

UNITED STATES DEPARTMENT OF THE INTERIOR 

Cecil D. Andrus, Secretary 

BUREAU OF MINES 

Roger A. Markle, Director 
CONTENTS 

Page 

Abstract ................................................................ Introduction ............................................................ Acknowledgments . ......................................................... Regional geology ........................................................ Geology of the Lower Kittanning coalbed ................................. Stratigraphy ....................................................... Structure .......................................................... Mining problems related to geology of the Lower Kittanning coalbed ...... Occurrence of 'bants" .............................................. Types of unstable roof ............................................. Methane emission ........................................................ Summary and conclusions ................................................. References .............................................................. 

ILLUSTRATIONS 

Location of study area ............................................. Location of important geographic features of northern Cambria 

County. Pa ....................................................... Physiographic divisions in the area around Canibria County .......... Generalized stratigraphic column of exposed rocks in the Allegheny 

Mountain section of Appalachian Plateau Pruvince ................. Generalized stratigraphic column of the Kittanning Formation ....... Clay parting in the Lower Kittanning coalbed ....................... Panel diagram of the interval from the bottom of the Lower 

Kittanning coalbed to the top of the Upper Kittanning coalbed .... Percent sandstone map of the interval from the top of the Lower 

Kittanning coalbed to the bottom of the Middle Kittanning 

coal group ....................................................... Isopach map of the interval from the top of the Lower Kittanning 

coalbed to the bottom of the Middle Kittanning coal group ........ Structure contours on the base of the Lower Kittanning coalbed ..... Location and cross-sectional view of three displacement faults 

encountered in the Barnes and Tucker No . 20 mine ................. Rose diagrams of bedrock joints of each of the nine quadrangles 

of the study area ................................................ Rose diagrams of cleat orientations in eight of the nine 

7-112-minute quadrangles ......................................... Mined-out-area map of mines in the Lower Kittanning coalbed. 

showing "want" areas ............................................. Isopach map of the Lower Worthington Sandstone ..................... Map showing the correlation of the thick Lower Worthington Sandstone with "wants" in the Lower Kittanning coalbed ............... Isopach map of the Lower Kittanning coalbed ........................ Stratigraphic sections ofthe Lower Kittanning coal group and 

location of cross sections ....................................... Stratigraphic sections of the Lower Kittanning coal group .......... 
ILLUSTRATIONS --C ontinued 

Page 

20. Generalized cross section of characteristic unstable roof associated with sandstone channels................................... 21 

21, Map showing the high-roof-instability areas related to the 

stratigraphic position of the Lower Worthington Sandstone and 

the Middle Kittanning coalbed............................,....... 22 

22. Generalized cross section of characteristic unstable roof associated with thinning of the interval between the top of the 

Lower Kittanning coalbed and the bottom of the Middle Kittanning 

coalbed...................................................... 23 

23. "Cutter" occurring parallel to the rib ............................. 25 

24. Isopach map of the overburden above the Luwer Kittanning coalbed... 26 

TABLE 

1. Average methane emissions during coal production and depth of six 

active deep mines in Lawer Kittanning coalbed.................... 27 
GEOLOGY OF TtIE LOWER KITTANNING COALBED AND RELATED 

hilNlNG AND METHANE EMISSION PROBLEMS 

IN CAMBRIA COUNTY, PA. 

A. T. lannacchione 1 and D. G. Pugl io 1 

ABSTRACT 

The Bureau of Mines established geologic factors affecting the mining of 

the Lower Kittanning coalbed to aid in coalbed minability studies and examined 

the occurrence of "wants" (places where coal is missing) and types of unstable 

roof rock strata. Trends established from mapping, including prediction of 

areas of high methane emissions, were extrapolated to unmined areas. 

'Vants" in the coalbed are of two types: Erosional and depositional. 

Erosional features occur where north-south-trending sand-filled channels cut 

into the coalbed. Variations in depositional environments have caused the 

coalbed to "split" into several thinner units. 

Slickensides, commonly indicative of unstable roof, are adjacent to and 

on the underside of sandstone channels; they were caused by differential c&- 

pact ion and by soft sediment sliding along the contact between the sandstone 

and adjacent shale. The frequency of unstable roof also increases where the 

interval between the Middle and Lower Kittanning coalbed is less than 30 feet. 

The zones of weakness at the contacts above and below the Middle Kittanning 

coalbed are the controlling factors for unstable roof in these strata. 

Methane emissions from the coalbed are controlled primarily by depth, 

fracture permeability, and rank of coal. Local geologic factors are coalbed 

thickness, associated rock strata, structure, and proximity to outcrop. 

INTRODUCTION 

The Lower Kittanning coalbed in Cambria County, Pa., has a long mining 

history and is currently being explored to define deeper reserves. As these 

deeper reserves are explored, geologic factors that affect mining in unmined 

coal need to be examined to aid in mine planning. With the accumulation of 

large amounts of exploration drilling data over the last century, it is now 

possible to analyze geologic trends in actively mined areas and to project 

these trends into unmined areas. Delineation of "want" trends where the coal 

l~eologist, Pittsburgh Mining and Safety Research Center, Bureau of Mines, 

Pittsburgh, Pa. 
is missing and prediction of areas of high roof instability and high methane 

emissions are the main topics of concern in this Bureau of Mines study. ' 

Cambria County is in west-central Pennsylvania (fig. 1). It lies near 

the eastern edge of the Allegheny Plateau Province and is near the northeastern 

edge of the Appalachian coalfield, which extends from southern New York to 

northern Alabama. Major towns , rivers , and the nine 7-1/2-minute topographic 

quadrangles that make up the study area are shown in figure 2. 

In Cambria County the Lower Kittanning is a low- to medium-volatile bituminous coal which has been used for coke making and steam generation. It is 

generally very friable and ranges in thickness from 0 to 117 inches, averaging 

36 to 60 inches. Overburden thickness ranges from zero at the outcrop to 

1,100 feet. Mining is presently most active in the deepest synclines, where 

most of the remaining reserves lie under 600 feet of overburden. 

When the Lower Kittanning coalbed was first mined, it was common practice 

to mine from outcrop into the surrounding hillsides, always staying abwe 

drainage. "Wants" and unstable roof were encountered, but methane gas was not 

the major problem that it is today. Little exploration coring was done, and 

coal was mined until thin coal, bad roof, or excessive water problems made it 

uneconomical to continue. 

The methane problem increased as deeper coal reserves were mined, and the 

gas is now generally considered a major mining hazard of this area. In a 

recent survey, Irani (5J2 compiled a list of the 35 counties in the United 

States with the highest gas emissions from active mines. Cambria County ranks 

ninth (methane emissions totaled 10.3 MMcfd in 1975) among those counties. 

This ranking is largely controlled by the Lower Kittanning coalbed because it 

accounts for the greatest amount of tonnage of the four coalbeds presently 

being mined in this county and also because it is stratigraphically the lowest 

minable coalbed in the local geologic section. 

ACKNOWLEDGMENTS 

The authors thank the following companies and their officials for their 

cooperation in collecting data: Barnes and Tucker Mining Co., Bethlehem 

Mining Co. , Eastern Associated Coal Corp. , and Clearfield Bituminous Coal Co. 

The authors also thank Norman K. Flint, Department of Earth and Planetary 

Sciences, University of Pittsburgh, Pittsburgh, Pa., for his suggestions 

regarding preparation of the manuscript. 

REGIONAL GEOLOGY 

Cambria County lies physiographically within the A'llegheny Mountains 

section of the Appalachian Plateau Prwince (fig. 3). The Allegheny Front, 

which forms the border between the Appalachian Plateau Prwince and the Valley 

'underlined numbers in parentheses refer to items in the list of references at 

the end of this report. 
/ 

I-- 

NEW YORK -- 

I 1 PENNSYLVANIA I r 

-yI PEN;+?LVANIA / i -- 

WEST VIRGINIA MARYLAND 0 20 - 

Scale, miles 

FIGURE 1. - Location of study area. 

* 7-ID-minute quadrangle names 

FIGURE 2. - Location of important geo

northern Cambria County, 
Pittsburgh n~ PA~PIPI n 

SOMERSET COUNTY I BEDFORD COUNTY \ 

0 - 10 

APPALACHIAN PLATEAU VALLEY AND RIDGE Scale, miles 

PROVINCE PROVINCE 

FIGURE 3. - Physiographic divisions in the area around Cambria County. 

and Ridge Province, generally coincides with the eastern border of Cambria 

County. Directly west of the Allegheny Front, open folds having flank dips of 

1" to 20" characterize the Allegheny Mountain Province. 

Predominantly Pennsylvanian sediments are exposed in the Allegheny Mountain section. A generalized geologic column of exposed rocks in the Allegheny 

Mountain section is shown in figure 4. 

The Allegheny Group (the group containing the Lower Kittanning coa lbed) 

includes all rocks from the base of the Brookville coal to the top of the 

Upper Freeport coal. The Allegheny Group, comprised ofthe Clarion, Kittanning, 

and Freeport Formations, is composed of sandstone, shale, limestone, clay stone, 

and coalbeds (5). 

The local geologic setting directly reflects the regional geology. The 

stratigraphic section of interest is the Kittanning Formation, which includes 

the Lower Kittanning coalbed. The formation varies in thickness within the 

area of investigation in two ways: (1) It shows a regional thinning to the 

northwest, and (2) localized channel scour-and-fill phenomena have thinned, 
thickened, or removed sections of the 

geologic column. The formation has a 

maximum thickness of 130 feet and a 

minimum thickness of 85 feet. 

Sy s tern 

Pennsylvanian 

Mississippian 

Devonian 

. 

Figure 5 is a generalized stratigraphic column describing the lithology 

from the Lower Kittanning to the Upper 

Kittanning coalbed (the Kittanning 

Formation) . The more important stratigraphic markers include the Lower, 

Middle , and Upper Ki ttanning coa lbeds 

and their underclays , the Lower and 

Upper Worthington Sandst one, and the 

Johnstown Limestone. In any particular location one or more of the members may be absent. 

Rock unit 

Monongahela Group 

Conemaugh Group 

Allegheny Group 

Pottsville Group 

Mauch Chunk Formation 

Loyalhanna Formation 

Pocono Formation 

Catskill Formation 

Jennings Formation Recognition of a coalbed is partially dependent on recognizing key 

rock units. The Lower Kittanning coal 

group is recognized as lying between 

FIGURE 4. - Generalized stratigraphic col- the Kittanning Sands tone and ,-he werumn of exposed rocks in the lying Lower Worthington Sandstone. We 

Allegheny Mountain section of chose to refer to the horizon containAppalachian Plateau Province. ing the Lower Kittanning coalbed as 

part of the Lower Kittanning coal group, 

owing to the inconsistent character of the interval. The lower coalbed as a 

rule is the thicker, more persistent coal. For this reason local usage refers 

to the lower coalbed in the Lower Kittanning coal group as the Lower Kittanning coalbed, and to the upper coalbed as the Lower Kittanning "ridert1 coal. 

Another stratigraphic problem in this interval is distinguishing the 

Lower Kittanning "ridert' coal from the Middle Kittanning coal group where the 

Lower Worthington Sandstone is missing. The lowest member of the Middle 

Kittanning coal group has a thick underclay, whereas the Lower Kittanning 

"rider" coalbed generally has none. In correlating the Middle Kittanning coal 

group throughout the area, the first coalbed above the Lower Kittanning coalbed with a well-developed underclay is considered the Middle Kittanning. It 

has been suggested by Spieker (l6) in his studies of the Cretaceous of Utah 

and by Weller (20) in his studies of the Pennsylvanian of Illinois that coalbeds representiz a regression of the sea have sharp lower contacts of sandstone, siltstone, or shale, whereas transgression of the sea produces varying 

thickness of claystone beneath a coal. 

Local structures include folds , faults , joints, and cleats in the coal. 

The folds , joints, and cleats generally appear to have a genetic relationship 

with the Allegheny Front, based on the fact that the fold axes, nonsystematic 

joints, and butt cleats are parallel to the trend of the Allegheny Front, 

while the systematic joints and face cleats are perpendicular to it. 
Upper Kittanning coalbed (thick, continuous coal) 

Upper Kittanning Underclay (plastic claystone) 

Johnstown Limestone (grading horizontally and vertically into 

limy shale 1 LEGEND 

coal 

Upper Worthington (channel sandstone, where sandstone is ..: ::!:! :.. 

Sandstone missing or tabular, shale and siltstone Sandstone 

dominate interval ) Sandy shale 

Middle Kittanning (lower bench most continuous, upper "rider" 

coal group coals discontinuous and grade laterally 

into carbonaceous shale 1 Shale 

Middle Kittanning Underclay (claystone) 

Limestone 

Limy shale 

Lower Worthington (channel sandstone, where sandstone is 

Sandstone missing or tabular, shale, siltstone, and claystone 

claystone dominate interval 

Lower Kittanning (thick, continuoy: lobvfr bench with shale 

coal group partings, upper rider coal separated from 

lower bench by 10 to 15 ft of shale ond sandstone) 

FIGURE 5. - Generalized stratigraphic column of the Kittanning Formation. 

No faults were described in this area by earlier geologists; however, the 

present writers observed several faults with a maximum of 5 feet of vertical 

displacement in the Barnes and Tucker No. 20 mine. 

GEOLOGY OF THE LOWER KITTANNING COALBED 

The Lower Kittanning coalbed is the highest grade, most persistent, and 

economically the most important coalbed in Cambria County. Its thickness 

ranges from zero to as much as 8 feet. Generally, the coal is clean and 

bright, occurring as a single bench with few partings; in some localities clay 

partings separate the coal into two benches (fig. 6). I 

Stratigraphy 

Recognition of the Kittanning Formation in the field was accomplished 

through the use of key rock units. ~aage (2) identified key rock units 

as the Lower Kittanning coal group, Lower Worthington Sandstone, Middle 

Kittanning coal group, Upper Worthington Sandstone, Johnstown Limestone, and 

Upper Kittanning coal group. 
FIGURE 6. - Clay porting in she Lower Kittanning coolbed. 

Figure 7 is a panel diagram showing a three-dimensional view of Lithologic facies in the Kittanning Formation. Several key rock units are recognized in every section; however, no one section contains all. key units 

identified by Waage (19). - 

The Lower Kittanning coalbed is very persistent (fig. 7) even though it 

may be split by as many as three visible partings. InnnedFateZy belcrw the 

Lower Kittanning coalbed and overlying the Kittanning Sandstone and shale 

members of the Clarion Formation is the Lower Kittanning Underclay. 

The strata immediately overlying the Lower Kittanning coalbed generally 

consist of dark gray and gray shale, some siltst me, and thin tabular sandstone. Abundant siderite nodules in layers parallel to the bedding occur in 

the siltstone and shale. 

The "-riderf' coal, or its stratigraphic equivalent, is observed in most 

seci:ions where the Lower Worthington Sandstone is not well developed. This 

car1 be seen in the northwestern Cresson, south-central Colver , and east-central 

Hastings quadrangles of figure 7. This condition, as Williams (2l) suggested, 

indicates that the "rider" coal was once present over most of the area, but 

was cut out by channel erosion. 

The Lower Worthington Sandstone occupies the interval between the Lower 

and Middle Kittanning coal groups. A good exposure can be found along Chest 

Creek in an abandoned strip mine 2 miles north of Patton, Pa. Where the sandstone is not developed, shales, which grade horizontally and vertically into 

sandy to silty gray shales, commonly occupy the section. 

The. Lower Worthington Sandstone is found in the western Ebensburg, eastern Carrolltown, western Ashville , southern Coalport, and southern Hastings 

quadrangles (fig. 7). In the southern Hastings and northeastern Carrolltown 

quadrangles the Upper and Lower Worthington Sandstones are combined to form 

one thick sandstone unit. Recognition of the Lower Worthington Sandstone is 

also accomplished by the construction of a percent sandstone map (fig. 8) of 

the interval between the Lower Kittanning coalbed and the lowest coal in the 

Middle Kittanning coal group. 

The percent sandstone map shows the Lower Worthington Sandstone to be a 

linear body with sharp lateral boundaries. The geometry of the sandstone 

bodies is generally troughlike. These features were produced by high-energy 

streams eroding into semilithified to lithified sediments. Periodically, 

with sediment overload of streams and channel abandonment, sands, shales, and 

clay filled in channel cuts. " Theref ore, undersides of the ancient stream 

channe 1s represent disconformable surf aces. 

The Middle Kittanning coal group lies from 20 to 60 feet abwe the Lower 

Kittanning coalbed (fig. 9). This interval tends to be thin where the section 

is composed mainly of shale, as in northern Nanty Glo, southern Colver, western Carrollt own, and western and southern Ebensburg quadrangles, and thick 

where the Lower Worthington Sandstone is present in the section as in eastern 

Carrolltown, Coalport, and Ashville quadrangles (fig. 7). Trends of this 

interval were projected where the Middle Kittanning coal group is eroded. The 

coals of this group are erratic in thickness, splitting into as many as three 

benches of coal in some places. 

The Upper Worthington Sandstone overlies the Middle Kittanning coal group. 

In some places the sandstone extends downward through the strata of this coal 

group, thereby replacing them. This can be seen in portions of southern 

Hastings, northern Carrolltown, and southwestern Coalport quadrangles (fig. 7). 

Where channel-type sandstone is not present, the interval contains shale, 

siltstone, and thin tabular bodies of sandstone. Variations in the thickness 

and lithologic character of the interval occur over very short lateral 

distances. 
I 

I CLEARFIELD 

INDIANA COUNTY 

COUNTY - - - 

I CAMBRIA 

LEGEND 

a0 to IOpct n25 to 50pct 0 A 20 000 

HlOto25pct m>50pct Scale, ft 

FIGURE 8. - Percent sandstone map of the interval from the top of tne Lower 

Kittanning coalbed to the bottom of the hliddle Kittanning coal 

group. 
The Johns town Limestone 

typically rests on shale and 

grades laterally into limy 

shale. This limestone has 

proven to be very persistent, 

being especially thick in 

the southern half of the 

study area (fig. 7). It is 

a dark-gray , fine -grained, 

yellowish-weathering, argillaceous limestone which 

breaks with a smooth, concoidal fracture. Generally, 

the limestone occurs as a 

lenticular body; however, it 

may occur as nodules within 

thicker sections of the 

Upper Kittanning Claystone. 

The interval above the 

Johnstown Limestone is occupied by the Upper Kittanning 

Underclay, or the Upper 

Kittanning coal group, as in 

the northern Ebensburg quadrangle (fig. 7). This underclay has comnercial value as 

a refractory clay in the 

northeastern Carrolltown 

quadrangle. 

Resting on top of the 

LEGEND Upper Kittanning Underclay 

10to 20ft mm]40to 50ft 0 - 2900~ and/or Johnstown Limestone 

m20 to 3oft m50 to 6oft Scale, ft is the Upper Kittanning coal 

m30 to 40ft mz60ft (fig. 7). It is generally a 

thick, continuous c oalbed 

FIGURE 9. - lsopach map of the interval from the top of lying approximately 110 feet 

the Lower Kittanning coal bed to the bottom above the top of the Lower 

of the Middle Kittanning coal group. Kittanning coalbed. 

Structure 

The most pronounced fold in the area (fig. 10) is the Nittany arch, the 

northwest limb of which crosses the southeastern corner of the study area in 

Blair and Cambria Counties. The northwestern limb of this arch forms a cuestalike feature which has been named the Allegheny Front. Ten miles to the west 

of this structure lies the Laurel Hill anticline. This fold plunges to the 

northeast and is flanked to the east by the Ebensburg anticline and the west 

by the Nolo anticline. The narrow Bradley and Wilmore synclines lieenechelon 

to one another between the Laurel Hill anticline and the Allegheny Front. The 
LEGEND Od 

/ Structure contour, 1Wt interval Scale, ft 

FIGURE 10. - Structure contours on the base of the 

Lower Ki ttanning coal bed. 

Section A-A'- Strike and dip of fault 

Section B-Bf- Strike and dip of fault 

N 77O W, 400 NE 

Location of 

cross sections in mine 

FIGURE 11. - Location and cross-sect

displacement faults encou

and Tucker No. 20 mine. 
spoon-shaped Johnstawn syncline plunges to the southwest in the southwestern 

portion of the area, while the broader Barnesboro syncline parallels the western boundary of Cambria County. 

The structure map shows distinctive changes in the fold along a northwestsoutheast belt from the southeast corner to the northwest corner of the study 

area. Generally, greater amplitudes and closer spacing of folds occur to the 

south of this diagonal. A structural culmination along the Barnesboro syncline and a saddle in the Laurel Hill anticline occur along this belt. The 

Johnstown syncline and Ebensburg anticline die out directly to the south of 

the belt, and the Wilmore and Bradley synclines occur en echelon directly 

along the belt. Finally, the amplitude of the Nittany arch increases to the 

southwest. Perhaps the differing degrees of compressional forces exerted on 

either side of this belt are associated with a deep strike-slip fault, a 

byproduct of the bending in the Allegheny Front in central Pennsylvania. 

No major faulting was recognized in the study area, but several minor displacement faults in the Barnes and Tucker No. 20 mine (fig. 11) were observed 

along the eastern flank of the Laurel Hill anticline. Upon first observation, 

the faults appeared to be interconnected and of tectonic origin, based on the 

presence of highly polished, slickensided fault planes, but closer observation 

shows the initial observation to be in error. First, the strike and dip of 

all three faults are different (EW 30' S, N 77' W, 40" NE, and N 40" SE). 

Second, the fault plane flattens out directly into the bedding plane above the 

coalbed (c-c', fig. 11). Finally, the bedding shows reverse drag along the 

fault plane (B-B' , fig. 11). All of these features probably result from softsediment slumping and are not necessarily due totectonic forces. Williams (22) 

described similar features in the interval abwe the Lower Kittanning coalbed 

in Clearfield County. He referred to them as rotational slumps, indicating 

that their origin is connected with slumping of semilithified blocks of sediment into paleotopographic low areas. 

Joint directions measured in mine roofs, strip mine highwalls, and widespread outcrops within each of the nine quadrangles were plotted on rose diagrams and are illustrated in figure 12. Joint traces are widely spaced and 

show many inconsistent orientations. 

Cleat measurements were taken in deep mines, in strip mines, and at 

different coal outcrops (fig. 13), using the method devised by Diamond (3). 

The mean face cleat, the principal cleat perpendicular to structural trends, 

ranges in direction from N 8Z0 W to N 54O W. Mean butt cleat directions range 

from N 10' E to N 45' E and parallel the structural trends in the area. The 

face cleats were probably formed as extension fractures during structural 

deformation, and the butt cleats as released fractures during erosion and 

uplift (14). - 
LI-' '4 '-I-' 

2 measurements 1 2 measurements 1 2 measurements I 

2 measurements 4 meas'urements 2 measzements 

BARNESBORO 

1 17 readings 

COLVER CARROLLTOWN ASHVILLE 

95 readings 162 readings 70 readings 

4 + measurements 

I 

HASTINGS 

37 readings 

8 measurements 

+I 

COALPORT 

I I I readings 

4 measurements 

-1 I NANTY GLO I EBENSBURG 1 CRESSON I 1 203 readings 1 550 readings 138 readings 

016,000 

Scale, fT 

No readings 

I BARNESBORO I HASTINGS 

Butt 

205 

W readings measurements 

525 I readings meaGiements 1 

COLVER CARROLLTOWN 

I . .I - ~ltt cleat 

Face cleat 

Face cleat 

'650 

I E 

82O 4487 

W 

20 

readings measurements 

103 A 

readings measukments 

NANTY GLO EBENSBURG 

FIGURE 12. - Rose diagrams of bedrock ioints of each of FIGURE 13. - Rose diagrarrs of cleat o

the nine quadrangles of the study area. of the nine 7-l/2-minute 
MINING PROBLEMS RELATED TO GEOLOGY OF THE LOWER KITTANNING COALBED 

Certain geologic factors control the conditions that lead to problems in 

mining the Lower Kittanning coalbed. These factors are associated with the 

sedimentary environment of deposition and the diagenesis of these sediments 

into their present lithified state. Two principal geologic factors affecting 

mining are 'kants" and the nature of roof -rock strata. Some preliminary work 

was done on the geology of the Lower Kittanning coalbed (lo), but this study 

is more detailed and of broader scope. 

Occurrence of "Wants " 

The term "wants" refers to the localized thinning or disappearance of 

coal. The two types of "wants" encountered are erosional and depositional in 

origin. The depositional and postdepositional environments in the coalforming swamp were the controlling factors in the distribution and frequency 

of these "wants .'I The mechanism for their formation follows: Local removal 

of an incipient coalbed takes place when streams erode channels into underlying sediments. These channels are the sites of both erosion and deposition 

of sediments. The coarser grains settle out of suspension and may eventually 

fill the channel; the clay- and silt-size sediments are generally deposited in 

low-energy environments as werbank deposits in interdistributory bays or as 

delta-front deposits. It is possible, however, for a channel to be filled 

with silt and clay. 

The type of "want" encountered must be determined be£ ore potential "wants" 

in unmined areas can be delineated. Figure 14 shows all the mines that have 

worked the Lower Kittanning coalbed in the area studied. Four major "want" 

areas can be identified from the mine maps; however, all are inaccessible for 

inmine inspect ion. 

The first "want" area is encountered in three mines (15, 17, and 32, 

fig. 14); this Y-shaped "want" is between 3,000 to 5,000 feet in width. The 

second "want" area extends wer a 12-mile, north-south direction in parts of 

mines 8, 9, 10, 24, and 42 (fig. 14) ; it meanders slightly with widths ranging 

from 100 to 3,000 feet. A third, north-south-trending "want" area occurs in 

mines 25, 29, and 46 (fig . 14) ; the northern extent of this "want" is not 

defined. Finally, a fourth small isolated "want" area is encountered in 

mine 49 (fig . 14) . 

It has already been shown that the Lower Worthington Sandstone is located 

stratigraphically between the Middle and Lower Kittanning coal groups. Figure 15 shows the thickness and trends of the linear, wedge-shaped sandstone 

bodies. In comparing the first three '%rantf1 areas described earlier (fig. 14) 

with the thick sandstone areas of figure 15, there is a correlation of "wants" 

with thick sandstone. A north-south trend is shown in both figures. Furthermore, figure 15 provides important information on sandstone trends in unmined 

coal, indicating that these three "want" areas are part of the same distributary system and can possibly be connected. 
LEGEND 

/ Barnes and Tucker No. 14 

2- d Tudrer No.15 

3 Barnes and Tucker No.20 

4 Barnes and Tucker No.24-B 

5 hhy No. 6 

6 Bear Rock 

7 Berwhd-White No. 2 

8 Bethlehem No. 3 1 

9 Bethlehem No. 32 

/o BetNeh No. 33 

// Bsthlah No. 77 

/2 Beunier Puritan 

N Big Bend Nonpareil 

/4 Baker No. 2 

/5 Bkrboker No. I0 

16 Carrolltown- Victor No. 9 

/7 Carolltown - Victor No. I0 

/8 CBC - Seldom Seen 

/9 Commercial No. 2 

a Commercial No. 5 

2/Connnondd~ 

22 Cymbria 

29 Dafsh No. I 

P)Eastern Associated-Colm 

P5 Eastern Associated -Som#n Wo 

S Hastings No. 2 

27 Heisley No. 2 

&? Hertzog 

29 Hughes No. 2 

30 HW Z - Bans Creek No. 2 

3/ Imperial Cardiff No. l 

32 Lanark No. l 

33 Laurel Run No. 2 

34 Lilly No. 3 

35 Lilly New Slope 

36 Lincoln 

37 Link 

38 Spongier No.4 

39 Miller Run No. I 

40 Navy Smokeless 

4/ Pennsylvania - Cresson No. 9 

42 Pennsylvania - Ehrenfeld No. 3 

43 Pennsylvania - Pardee No. 36 

44 Pine Valley No. I 

45 Reilly No. I 

46 Sonman Shaft 

47 Springfield No, land 3 

48 Springfield No.4 

49 Sterling No. I 

50 Sterling No. 3,4 and 5 

I 

I 

I I CLEARFIELD COUNTY 

5 / Sterling No. 9 

52 Warren No. I0 

53 Webster-Nanty Glo No. 14 

54 W H Piper- Sonman No. 2 

55 WJ Holtz 

Scale, ft 

FIGURE 14. - Mined-out-area rriap of mines in the Lower Kittanning coalbed, showing "want" 

areas. 
LEGEND 

ooto~oft m20to30ft 

m10 to 20ft 30 to 40ft 

m > 40ft 

0 

Scale, ft 

I 

I 

I I CLEARFIELCOUNTY 

CAMBRIA 

COUNTY 

bi.1 

I WNTY GLO I EBENs~RG 

Coalbed thickness less than 28 in 

Areas where erosional-type "wants" h

occurring. In these areas the Lower W

greater than 20 ft thick and the interv

coalbed is less than loft thick 

FIGURE 15. - lsopach map of the Lower Worthington FIGURE 16. - Map showing the co

Sandstone. Lower Worthington Sa

in the Lower Kittann
Correlation of sandstone-filled channels with "wants" is further improved 

by constructing a map (fig. 16) showing areas of thin coal in relation to the 

Lower IJorthington Sandstone where it is at least 20 feet thick and within 

10 feet of the underlying Lower Kittanning coalbed. The 28-inch line (fig.16) 

was arbitrarily selected to indicate possible '%ant" areas because the 

continuous-mining machines used in this area have a lower limit of 28 inches. 

It is believed that "wants," indicated by the 28-inch line and associated with 

areas where the Lower Worthington Sandstone i s a t least 20 feet thick and 

within 10 feet of the underlying coalbed, are of the erosional type. 

There may be a "want" in the north-south-trending area of Lower Worthington Sandstone in the Carrolltown quadrangle (fig. 16). Although all the cores 

from that area show a minable thickness of coal (fig. 17), two show a thick 

sandstone directly on top of the coalbed. In areas adjacent to those from 

where these cores came, it is possible that this sandstone extends down into 

the coalbed to reduce its thickness or perhaps even cut it out completely. 

Another type of "want" is one in which a minable coalbed splits into several thinner coalbeds which are not mined individually or together because of 

the excessive intervening rock. Often the total thickness of the split coal 

is less than that of the total undivided coalbed. This is referred to as a 

depositional "want" or "split." Moore (l3) explained the origin of splits as 

follows : 

Splits are due to the fact that while the vegetal matter is 

being laid down in the swamp there are periods when clay or sand is 

brought in by water from the surrounding lands and carried out over 

the vegetal matter. 

The Lower Kittanning coalbed, generally 4 feet thick (fig. 17), splits 

into as many as three coal units within 25 feet of section in the northeastern 

portion of the study area (figs. 18-19). This "want" area (less than28 inches 

of coal, fig. 17) is considered to be depositional in origin based on the 

stratigraphic cross sections (figs. 18-19). 

Types of Unstable Roof 

Roof-rock strata affect the physical condition of the roof and type of 

support needed to maintain a good roof in a coal mine. Observation of many 

roof falls and areas of unstable roof in the five underground mines led the 

authors to identify five types of unstable roof related to the geologic conditions. They are characterized as follows: 

1. Slickensided disconformities on the underside ofthe channel sandstones. 

2. Randomly oriented slickensided slip planes resulting from slumping as 

the sediments were undergoing consolidation. Commonly found in black shales 

above the coalbed. 

3. Slickensided slip planes caused by differential cumpaction of sandstone and adjacent shale. 

4. Abrupt lateral pinchouts or wedges of strata (generally thin sandstone pinchouts), 
LEGEND 

0 to 14 in 28 to 42 in 0 L - 24000 j 

14 to 28 in > 42 in Scale, f t 

FIGURE 17. - lsopach map of the Lower Kittanning coal bed (including shale partings less than 1 foot in thickness). 
Upper coal or "rider" coal 

LEGEND 

I(D Bony coal s~dy shak 

.., ; Sandstone Claystone 

LEGEND 

-1 

rm ~ony coal Key 

Sandstone 

Shale 

Sandy shale 

FIGURE 18. - Stratigraphic sectionsof the Lower Kittanning FIGURE 19. - Stratigraphic sectionsof 

coal group and location of cross sections. coal group. 
5. Abrupt lithologic boundaries between clays, shales, siltstones , sandstones, and coal, causing planes of weakness. 

Of the five types of unstable roof, areas with slickensided surfaces on 

the underside and adjacent to the Lower Worthington Sandstone and abrupt lithologic boundaries of the Middle Kittanning coalbed can be identified, with the 

aid of core log data, in advance of mining. 

Slickensided fractures are commonly present adjacent to and on the underside ofthe thick channel sandstone abovetheLower Kittanning coalbed (fig. 20). 

These fractures are caused by differential compaction and by soft-sediment 

sliding along and adjacent to the contact between the sand-filled channels and 

the shale that underlies the sandstone. 

The s lickensided surfaces are planes of weakness. When unsupported, shales , clays, and thin "rider" coals beneath and adjacent to channel sandstones easily 

separate and fall into mine rooms (12). The underside of such a channel represents a disconformable surface. The closer the underside of the channel sandstone is to the top of the coalbed, the greater the chance of roof failure. 

Figure 21 shows areas where the interval from the top of the Lower Kittanning 

LEGEND 

coal # Shale z L 151cale, ft 

3 / Sandstone Sa"dy shale 0 15 

Horizontal 

FIGURE 20. - Generalized cross section of characteristic unstable roof associated with 

sandstone channels. 
LEGEND 

Areas where roof falls, related to sandstone channels less than 

20 ft above the coalbed, have a high probability of occurring 

Areas where roof fallsi related to an interval of less than 30ft ... .. 

between the Lower and Middle Kittanning coalbeds, have a high 

probability of occurring 

FIGURE 21. - Map showing the high-roof-instability areas related to the 

stratigraphic position of the Lower Worthington Sandstone 

and the Middle Kittanning coal bed. 
coalbed to the bottom of the Lower Worthington Sandstone is less than 30 feet. 

Roof instability increases greatly in such areas. 

Another type of roof instability is associated with the abrupt lithologic 

boundaries of the Middle Kittanning coalbed (fig. 22). Benedict (1) noted 

this characteristic in the Bethlehem No. 32 mine: 

According to the experience of mine operators, when the thickness of this unit is less than 20 feet, the bond between the overlying coal and its associated underclay of ten fails, thus causing 

the entire stratigraphic unit to fall into the mining area below. 

Benedict mapped the interval from the Lower Kittanning coalbed to the 

next highest coalbed, because a thick "rider" coalbed occurs locally between 

the Middle and Lower Kittanning coalbeds on ~ethlehem's property. However, 

regionally this coalbed is discontinuous and very thin, unlike the regionally 

persistent Middle Kittanning coalbed (fig. 7). 

Wherever the Middle Kittanning coalbed is less than 30 feet above the 

Lower Kittanning coalbed, the frequency of roof falls is increased. In one 

area of the Colver mine, where the interval is less than 30 feet, more than 

half of the existing roof falls extended upward to the top of the Middle 

Kittanning coalbed. 

The increase in this type of roof instability is related to the sharp 

lithologic contacts between the Middle Kittanning coalbed and the shale above 

and the underclay below this coalbed. These contacts represent planes of 

structural weakness. In this thin interval, void of channel sandstones , alternating lithologies are generally gradational, unlike the coal-shale and coalunderclay contacts. Figure 21 shows areas where the interval is less than 

LEGEND 

coal Shale 

.:>:....:, ;.;, Sandstone Claystone 

Sandy shale 

0 15 

Horizontal 

30 feet, indicating areas 

where this type of unstable 

roof will increase in frequency. This type of unstable roof is common in mines 

in eastern NantyG10,western 

Ebensburg , eastern Colver , and western Carrolltown 

quadrangles (fig . 2 1) . 

Unstable roof strata 

described above may occur 

when supporting coal is first 

remwed. Also wer long 

periods of time, moist mine 

air, moving through fractures and s lickens ided planes 

in the roof, weakens contact FIGURE 22. - Generalized cross section of characteristic bonds between lithologies. unstable roof associated with thinning of the interval shales and especially clay- between the top of the Lower Kittanning coalbed and stones soften and become 

the bottom of the Middle Kittanning coalbed. 
1 

difficult to support, so that same roof falls may occur in the later stages of 

mining. Unstable roof associated with slickensides resulting from slumping 

and abrupt lateral pinchouts of strata were found to be local in extent and 

extremely difficult to predict in unmined areas. 

So far we have discussed unstable roof problems associated with geologic 

conditions. However, not all unstable roof can be related to geologic in£ luences . An example of this is an elongated roof fall occurring parallel to the 

rib, commonly referred to as a "cutter." The origin of "cutters" is unclear. 

They generally occur parallel to the ribs (fig. 23) but are also found to cut 

across entries . There are no bedding disturbances or s lickensided surfaces 

associated with a "cutter." One of the more probable explanations for their 

occurrence could be abnormally high horizontal stress forces in the rock 

strata. "Cutters" are among the many roof failure conditions observed that 

need to be investigated in much greater detail. 

METHANE EMISSION 

Methane is always present in coal and can constitute a serious safety 

hazard in coal mining. Several other gases are associated in far less amounts 

with methane in coal. These include hydrogen, water vapor, nitrogen, carbon 

dioxide, and helium (z). Gas content of a coalbed is primarily influenced by 

depth and rank. During mining, methane emission from a coalbed is controlled 

by porosity, permeability, and gas pressure. 

The most easily documented geologic factor influencing methane content of 

coal is depth. Generally at greater depths and therefore higher pressures, a 

greater volume of gas is held within the coal. Also, since the gas at greater 

depths is contained under higher pressure, it is released in larger volumes 

during mining (2). Figure 24 is an isopach map of the overburden above the 

Lower itt tanning coalbed. It is expected that in the deeper parts of the 

study area, the gas content of the coalbed will increase. This is partly substantiated by work done by Puglio (IS) in nearby Indiana County. A sample of 

the Lower Kittanning coalbed taken from a depth of 623 feet contained only 

about 1 cm3 /g (32 ft3 /ton) of methane, while a sample taken £ran a depth of 

1,060 feet contained about 11 cm3/g (352 ft3/ton). 

A second geologic factor influencing the methane content of coal is rank. 

Kim (g), in comparing actual gas contents of coals with different ranks and 

depths, considered rank as an aid in estimating methane content of bituminous 

coals. Stach (17) stated that in the different coalification stages large 

amounts of methane are generated in the medium-volatile to anthracite range. 

Additionally, Joubert (5) showed that increased moisture content in coal 

reduces its capacity to absorb methane. Because the Lower Kittanning coalbed 

in the study area is a low- to medium-volatile bituminous coal (high rank, 

low moisture content), it contains more methane gas than lower rank coals. 
-. . .* W"' -. . 

I %a' 

FIGURE 23. - "Cutter" occurring parallel to the rib. 
!8m0 to 200 ft 600 to 800 ft 0 

200 to 400 ft C-C-20,000 

EZl800 to 1,000 ft 

a 400 to 600 ft Scale, ft 

m 1,000 to 1,200 ft 

INDIANA 1 

COUNTY I 

FIGURE 24. - lsopach map of the overburden above the Lower Kittanning coalbed. 

CLEARFIELD 

COUNTY 
Possibly the best indicator of the high methane content of this coalbed 

is the high methane emissions encountered in deeper mines. As shownintable 1, 

the average methane emissions from mines within the study area increase substantially with depth. 

TABLE 1. - Average methane emission duringcoalproductionandde~th 

of six active deep mines in Lower Kittanning coalbed 

Geologic factors influencing methane emissions from a coalbed during mining are porosity, permeability, and gas pressure. Porosity measurements are 

difficult to make, but porosity is believed to depend on characteristic moisture content (6) and rank (2). Although by definition primary permeability 

is through the solid coal microstructure, secondary permeability (permeability 

along cleat fracture planes or fracture permeability) is higher. Fracture 

permeability is one of the controlling factors in migration and retention of 

methane in a coalbed. 

Coal mine 

Eastern Associated, Colver.. .... Bethlehem No. 31................ 

Barnes and Tucker No. 24B.. ..... Barnes and Tucker No. 20........ 

Bethlehem No. 33................ 

Bethlehem No. 32................ 

Directional permeability of coal is dependent on orientation and density 

of the cleat fracture. Kissell (2) showed gas emissions from the Pittsburgh 

coalbed in Greene County, Pa., to be 2.5 to 10 times higher where horizontal 

degasification holes were drilled perpendicular to face cleat than emissions 

with the holes perpendicular to the butt cleat. Because of the friable nature 

of the Lower Kittanning coalbed in the study area and several different clustering~ of face and butt cleat orientations (fig. 13), it is expected that the 

fracture permeability will vary in different directions but not as much as 

that of the more b locky coalbeds . 

Only a small percentage of the coal lying deeper than 700 feet has been 

mined. More than 80 percent of the remaining minable reserves lie deeper than 

600 feet in Ebensburg , eastern Carrolltown, western Ashville , and northwestern 

Cresson quadrangles (fig. 24). Mining in these areas can be expected to 

encounter very high methane emissions, whereas comparatively low methane emissions can be expected in mining the remaining reserves close to the outcrop in 

eastern Ashville quadrangle and northern Cresson quadrangle. Direct determination (11) of methane content of coal cores from exploration drill holes will 

greatlyaid in calculating the methane content in the unmined areas of the 

coalbed. 

Average me thane 

emission (1976), 

MMc f d 

400,000 

212,000 

274,000 

2 ,643,000 

2,695,000 

3,101,000 

More localized geologic factors influencing methane emissions are coalbed 

thickness (fig. 17), presence of other coalbeds above the coalbed presently 

being mined (fig. 7), porous sandstone lying between source rocks (fig. 7), 

structure, and proximity to outcrop (fig. 24). 

Average depth, 

feet 

3 00 

350 

400 

500 

650 

7 00 
SUMMARY AND CONCLUSIONS 

Using data gathered from core logs, mine maps, and geologic mine surveys, 

the geology of the Lower Kittanning coalbed was investigated and its influence 

on mining was determined. The important characteristics of the stratigraphy 

of the coalbed follow: 

1. The Lower Kittanning coal group is made up of all the coalbeds 

between the Kittanning Sandstone and Lwer Worthington Sandstone. 

2. The Lower Kittanning coal group is generally composed of a thin upper 

coal (Lower Kittanning "rider" coal) and a thick lower coal (Lower Kittanning 

coalbed). 

3. The lower coal of the Middle Kittanning coal group is distinguished 

from the Lower Kittanning "rider" coal by the presence of a thick underclay 

below the former and a carbonaceous shale, siltstone, or sandstone below the 

latter. 

4. The Middle Kittanning coal group lies 20 to 60 feet above the Lower 

Kittanning coalbed, is erratic in thickness, and splits into many thin benches 

of coal through the area. 

Important depositional variations that were examined and that influence 

coal extraction follow: 

1. The Lower Worthington Sandstone is a sand-filled channel deposit, 

ranging in thickness from 0 to 60 feet. Locally it erodes through key marker 

units. 

2. The Lower Worthington Sandstone is generally present in the interval 

between the Lower and Middle Kittanning coal groups. A thickening of this 

interval is associated with the presence of the Lower Worthington Sandstone. 

3. Wherever the Lower to Middle Kittanning interval is less than 30 feet 

thick, there is generally no channel-type sandstone present. Instead, this 

interval is composed of thin tabular sandstones and shales that grade vertically and horizontally into sandy and silty gray shales. 

4. The most distinctive horizontal breaks or zones of weakness between 

lithologies occur between the rocks above and below a coalbed and also at the 

bottom of sandstone channels. 

5. 'Vants" are either erosional or depositional in nature. Erosion is 

accomplished by distributary channels cutting into the coalbed and washing it 

away. Variations in deposition influence the development of "wants" in the 

form of splits or thinning of the coalbed. 
Conclusions drawn from this investigation are-- 

1. "Wants," located by coal isopach and mine maps, show a high correlation with areas where the bottom of the Lower Worthington Sandstone comes 

within 10 feet of the top of the Lower Kittanning coalbed. Therefore, the 

occurrence of "wants" can be predicted in advance of mining if sufficient 

exploration data are available. 

2. Roof rock instability can be linked with the close position of either 

a channel sandstoneor the Middle Kittanning coalbed above the Lower Kittanning 

coalbed. This cbndition can be used in predicting areas of unstable roof in 

unmined coal and can aid in designing an effective roof-bolting plan. 

3. High mithane emissions in the Lower Kittanning coalbed are influenced 

by relatively great depths, high rank, and good fracture permeability. 

4. The already serious problem of high methane emissions will become 

even greater in future extraction of the deeper areas of coal. 

A long mining history and an active exploration program to delineate deep 

reserves characterizes the area under investigation, As these deeper reserves 

are exploited, an understanding of geologic factors affecting mining in the 

virgin coal will aid in planning more productive mines with better hazard 

evasion. 
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