Principal Oil and Gas Plays in the Appalachian Basin 

(Province 131)

Middle Eocene Intrusive Igneous Rocks of the 

Central Appalachian Valley and Ridge Province 

Setting, Chemistry, and Implications for Crustal 

Structure

U.S. GEOLOGICAL SURVEY BULLETIN 1839-I, J

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I. Principal Oil and Gas Plays in the Appalachian Basin 

(Province 131)

By WALLACE de WITT, Jr.

J. Middle Eocene Intrusive Igneous Rocks of the 

Central Appalachian Valley and Ridge ProvinceSetting, Chemistry, and Implications for Crustal 

Structure

By C. SCOTT SOUTHWORTH, KAREN J. GRAY, and 

JOHN F. SUTTER

U.S. GEOLOGICAL SURVEY BULLETIN 1839-1, J 

EVOLUTION OF SEDIMENTARY BASINS-APPALACHIAN BASIN
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director

Any use of trade, product, or firm names

in this publication is for descriptive purposes only

and does not imply endorsement by the U.S. Government.

UNITED STATES GOVERNMENT PRINTING OFFICE: 1993

For sale by

U.S. Geological Survey, Map Distribution, 

Box 25286, MS 306, Federal Center, 

Denver, CO 80225

Library of Congress Cataloging in Publication Data

de Witt, Wallace, Jr. 1920-

Principal oil and gas plays in the Appalachian Basin (Province 131) / by Wallace 

de Witt, Jr. Middle Eocene intrusive igneous rocks of the central Appalachian Valley and Ridge province setting, chemistry, and implications for 

crustal structure / by C. Scott Southworth, Karen J. Gray, and John F. 

S utter.

p. cm. (U.S. Geological Survey bulletin ; 1839-l-J)

Includes bibliographical references.

Supt. of Docs, no.: I 19.3:18391-)

1. Petroleum Geology Appalachian Basin. 2. Natural gas GeologyAppalachian Basin. 3. Geology, Stratigraphic Eocene. 4. Rocks, 

Igneous Virginia. 5. Rocks, Igneous West Virginia. I. Southworth, 

C. Scott. Middle Eocene intrusive igneous rocks of the central Appalachian Valley and Ridge province setting, chemistry, and implications for 

crustral structure. 1992. II. Gray, Karen. III. Sutter, John F. IV. 

Title. V. Title: Middle Eocene intrusive igneous rocks of the central 

Appalachian Valley and Ridge province setting, chemistry, and implications for crustral structure. VI. Series.

QE75.B9 no. 1839-l-J

[TN870.5]

557.3 s-dc20 92-20025

[553.2'8'09755] CIP
Chapter I

Principal Oil and Gas Plays in the Appalachian Basin 

(Province 131)

By WALLACE deWITT, Jr.

A discussion of the six remaining principal oil 

and gas plays in reference to the stratigraphic and 

structural framework of the Appalachian basin, and 

a general description of oil and gas productivity of 

individual plays

U.S. GEOLOGICAL SURVEY BULLETIN 1839 

EVOLUTION OF SEDIMENTARY BASINS-APPALACHIAN BASIN

CONTENTS

Abstract II 

Introduction II

Basin Size II

Structure 13

Source Beds 13

Thermal Maturation 110

Oil and Gas Migration 110

Depositional History 112 

Definition of the Principal Plays 115 

Details of the Principal Plays 116

Upper Devonian Sandstone Play 116

Lower Devonian Oriskany Play 119

Lower Silurian Sandstone Play 122

Ordovician Carbonate Shelf Play 126

Upper Cambrian and Lower Ordovician Knox Carbonate Shelf Play 129

Rome Trough Play 132 

Virtually Exhausted Plays 134 

References Cited 135

FIGURES

1,2. Maps showing:

1. The surface extent of the Appalachian basin 12

2. Locations of some structural features and places mentioned in the text 14

3. Generalized geologic map of the Appalachian basin 16

4. Penetration chart showing age and position of source beds, reservoir rocks, and 

principal oil and gas plays in the Appalachian basin 17

5. Schematic cross section athwart the Appalachian basin 110 

6-13. Maps showing:

6. The structure on top of the autochthonous Precambrian basement complex 

under the Appalachian basin 111

7. Conodont color alteration index isograds in the Appalachian basin 112

8. The Upper Devonian sandstone play 117

9. The Lower Devonian Oriskany play 120

10. The Lower Silurian sandstone play 123

11. The Ordovician carbonate shelf play 127

12. The Upper Cambrian and Lower Ordovician Knox carbonate shelf 

play 130

13. The Rome trough play 133

TABLE

1. The relative stratigraphic position of rock units mentioned in the text 18

Contents III

EVOLUTION OF SEDIMENTARY BASINS-APPALACHIAN BASIN

Principal Oil and Gas Plays in the Appalachian Basin 

(Province 131)

By Wallace de Witt, Jr.

Abstract

The Appalachian basin is an elongate, asymmetric 

foreland basin that is about 230,000 square miles in area. It 

is more than 1,000 miles long and as much as 350 miles 

wide. More than 550,000 cubic miles of Paleozoic rock 

ranging in age from Early Cambrian to Early Permian fill the 

basin. The basin lies south and east of the cratonic 

platform and west of a series of erogenic highlands that 

were major sources for much of the basin-filling siliciclastic sediment. Large tectonic fan-delta complexes, which 

contain abundant coarse-grained siliciclastic reservoir 

rocks of shallow neritic to fluvial depositional environments, are concentrated mainly on the eastern side of the 

basin. Carbonate rocks are more abundant in the western 

part of the Appalachian basin. Finer grained turbiditic 

siltstone and sandstone are associated as prodelta reservoirs for gas and oil. Karstic carbonate reservoir rocks are 

associated with unconformities in the major carbonate 

strata. Reefs are of lesser importance as reservoirs. Extensive marine shale source rocks rich in organic detritus 

blanketed large segments of the basin during parts of the 

Ordovician and Devonian Periods. Coals and canneloid 

shales in the Mississippian and Pennsylvanian terrestrial 

rocks may have been source beds for oil and gas reservoired in late Paleozoic rocks. Thermal maturation 

increased in intensity eastward across the basin with 

increasing depth of burial of specific strata. Oil and 

associated gas occur mainly in the western part of the 

basin. Nonassociated dry gas occurs in the central and 

eastern parts of the basin, where maturation temperatures 

are too high for the existence of oil. Thick sequences of 

shale, mudrock, or massive carbonate rock appear to be 

the better reservoir-sealing strata in the basin.

As defined for the national assessment of undiscovered recoverable oil and gas resources, a play is a group of 

rocks and its contained hydrocarbons having the same 

general stratigraphy, structure and tectonic history,

Manuscript approved for publication May 1, 1992.

source rocks, degree of thermal maturation, and types of 

reservoir rocks, traps, and seals. Because of the great areal 

extent and thick stratigraphic sequence of the Appalachian basin, plays tend to be less well delineated in this 

basin than plays in some smaller basins with thinner 

stratigraphic sequences.

In descending stratigraphic order, the major oil and 

gas plays in the Appalachian basin are the Upper Devonian 

sandstone play, the Lower Devonian Oriskany play, the 

Lower Silurian sandstone play, the Ordovician carbonate 

shelf play, the Upper Cambrian and Lower Ordovician 

Knox carbonate shelf play, and the Rome trough play.

INTRODUCTION

During much of the Paleozoic Era, the Appalachian 

basin was an elongate active foreland basin west of a series 

of orogenic source areas that were generated by continental 

collision between the North American continental plate and 

several other continental plates or associated island arcs. 

During the Cambrian and Early Ordovician, the eastern 

margin of the North American plate was passive, and Early 

and Middle Cambrian extensional tectonics associated with 

the opening of an ancestral Atlantic Ocean were dominant. 

Sediments from cratonic sources accumulated in nearshore 

shallow-water environments in rift and postrift sequences. 

In the Middle Ordovician and continuing to the close of the 

Paleozoic Era, the continental margin was active, and most 

of the clastic detritus filling the foreland basin was derived 

from eastern orogenic source areas.

Basin Size

The Appalachian basin of the petroleum industry, 

Province 131 (Dolton and others, 1981; U.S. Geological 

Survey and Minerals Management Service, 1988), and as 

used in this report (fig. 1) includes all or parts of 10 States

Principal Oil and Gas Plays in the Appalachian Basin 11
50 100 150 200 MILES 78° 74°

0 50 100 150 200 250 300 KILOMETERS

42'

40

34°

Figure 1. The surface extent of the Appalachian basin.

and the United States' segments of Lakes Erie and Ontario. 

The basin includes about 230,000 mi2 of the Eastern United 

States from the Canadian border south to central Alabama. 

In its present thrust-faulted configuration, the asymmetric 

Appalachian basin is 75 to 350 mi wide and more than 

1,000 mi long. Its most extensive subdivision, the Appalachian Plateaus segment, covers about 135,000 mi2 (fig. 2) 

from Lakes Erie and Ontario south to central Alabama,

where the Plateaus segment melds with the Black Warrior 

basin to the west and southwest. The Appalachian Plateaus 

segment of the basin includes much of the Appalachian 

Mountains as well as small parts of the Great Lakes plains 

or the Eastern Interior lowlands. It lies along the eastern 

flank of the Cincinnati arch and is bordered on the east by 

the Allegheny Front, a conspicuous east-facing escarpment 

that extends from New York to Alabama. The Valley and

12 Evolution of Sedimentary Basins Appalachian Basin
Ridge segment of the basin abuts the Appalachian Plateaus 

segment on the east. It covers an area of about 45,000 mi2 

from eastern New York to central Alabama, where Mesozoic and Tertiary coastal plain rocks cover the southplunging Paleozoic rocks of the Valley and Ridge. Overthrusted metamorphic and igneous rocks of the Blue Ridge 

and Piedmont border the Valley and Ridge on the east.

The Appalachian basin is filled by more than 550,000 

mi3 of Paleozoic sedimentary rock ranging in age from 

latest Precambrian to Early Permian (fig. 3); source beds 

and reservoir rocks are widespread (fig. 4, table 1). Gas and 

oil have been found and exploited in some parts of the basin 

in rocks from all periods of the Paleozoic except the 

Permian.

Structure

The Appalachian basin is asymmetric in cross section 

(fig. 5). Cambrian rocks on the west flank of the basin dip 

gently eastward from about 2,000 to 5,000 ft below sea 

level along the flank of the Cincinnati arch to more than 

50,000 ft below sea level in the eastern buried segment 

beneath the Blue Ridge (fig. 6). In contrast to the generally 

gently dipping rocks exposed on the Appalachian Plateaus, 

Paleozoic strata of the Valley and Ridge segment of the 

basin have been greatly thrust faulted, folded, and telescoped by erogenic events that occurred mainly during the 

Alleghany orogeny, at the close of the Paleozoic Era. 

During this orogeny, metamorphic rocks of the Blue Ridge 

and Piedmont were thrust more than 150 mi westward over 

a wedge of Paleozoic Valley and Ridge sedimentary rocks 

as much as 20,000 ft thick (Harris and others, 1981). As a 

result of thrusting, the easternmost segment of the Appalachian basin is hidden beneath the Blue Ridge and contiguous Piedmont province. The extent of the eastern buried or 

hidden segment of the basin is known only from a few deep 

reflection seismic profiles and a scattering of fensters in the 

Blue Ridge of eastern Tennessee and adjacent North Carolina. It is not well defined. Harris and others (1981) 

suggested that the eastern segment may be as large in area 

as the Valley and Ridge segment. If so, the Appalachian 

basin, including its eastern buried segment, would underlie 

more than 230,000 mi2 of the Eastern United States.

Thrust faulting and associated folds produced by 

duplication of parts of the stratigraphic sequence are not 

restricted to the Valley and Ridge and the eastern buried 

segments of the Appalachian basin. Thrusts extend westward in a major thrust-fault system under the eastern and 

central parts of the Appalachian Plateaus. Decollements 

follow several zones of shale or evaporitic rocks in the 

Cambrian to Devonian sequence. Anticlines commonly 

formed where thrust faults ramped steeply across sequences 

of resistant, more brittle beds between decollement levels or

where thrusts splayed into thick sequences of middle to 

upper Paleozoic clastic strata. The area of the Appalachian 

basin underlain by thrust faults is termed the Eastern 

Overthrust belt by the petroleum industry as an analog of its 

western counterpart in the western cordillera. The western 

boundary of the Eastern Overthrust belt is the western limit 

of Alleghanian thrusting. Because bordering thrust faults do 

not crop out, the western boundary of the Eastern Overthrust belt is totally in the subsurface. At places such as the 

Burning Springs anticline of northern West Virginia or 

along the Bass Islands trend of Chautauqua County in 

western New York, the western boundary of the overthrust 

belt is sharply defined. Elsewhere, the terminal faults are 

not easily located, and the west edge of the belt is not as 

clearly delineated.

The Eastern Overthrust belt is an important element 

in the Appalachian basin because of the belt's structural 

traps and associated zones of fracture porosity. Many oil 

and gas fields in the central and eastern parts of the 

Appalachian Plateaus occur because zones of fracture 

porosity form the reservoirs. Gas fields in the Oriskany 

Sandstone from central New York to eastern West Virginia 

are good examples of anticlinal fault traps in which fractures are the dominant type of porosity in the sandstone. 

Secondary porosity developed extensively within the Eastern Overthrust belt because fracture porosity is dominant in 

the eastern part of the Appalachian Plateaus segment and 

the adjacent Valley and Ridge segment of the basin, 

particularly in the "cleaner" siliciclastic reservoir rocks. In 

contrast, original intergranular porosity, commonly modified by interstratal solution of chemically unstable minerals 

to develop some secondary porosity, is dominant in stratigraphic traps in the relatively undeformed rocks in the 

western part of the Appalachian Plateaus.

Source Beds

Two sequences of dark-gray, dark-brown, and black 

marine shale, rich in organic matter, have been documented 

as major source beds of oil and gas in the Appalachian 

basin. The younger sequence, which ranges in age from 

Middle Devonian to Early Mississippian, is extensive 

beneath the Appalachian Plateaus from New York to 

Alabama. The Devonian shale source-bed sequence 

includes many black shales from the Lower Devonian 

Mandata Formation to the Lower Mississippian Sunbury 

Shale (Roen and de Witt, 1984). Adjacent to its pinchout in 

southern Tennessee (Conant and Swanson, 1961, p. 

21-42), the Devonian source-bed sequence consists of one 

or two beds of black shale in about 30 ft of the Upper 

Devonian Chattanooga Shale. The black shale thickens to 

the north and northeast where it interfingers and merges into 

an eastward-thickening sequence of lighter gray, coarser 

grained siliciclastic rocks in West Virginia, Pennsylvania,

Principal Oil and Gas Plays in the Appalachian Basin 13
0 50 100 150 200 MILES

0 50 100 150 200 250 300 KILOMETERS

42°

"Approximate eastern edge of the 

Eastern Overthrust belt

Figure 2A. Locations of some structural features mentioned in the text. A-A', approximate line of section shown in 

figure 5.

and central New York. In New York, the black Devonian for the oil and gas derived from adjacent black Devonian

source-bed sequence includes at least five extensive discrete source rocks.

black shales intercalated in several thousand feet of gray or The older source-bed sequence, which is Middle to

greenish-gray mudrock, shale, siltstone, and sandstone. early Late Ordovician in age, consists largely of brownishThe more porous rocks in the gray siliciclastic sequence in black to black marine shale with small amounts of gray

New York, Pennsylvania, and West Virginia are reservoirs shale, siltstone, or intercalated nodular argillaceous lime14 Evolution of Sedimentary Basins Appalachian Basin
EXPLANATION 

KENTUCKY

1 Boyd County

2 Cumberland County

3 Estill County

4 Johnson County

5 Lee County

6 Wolfe County

7 Powell County

TENNESSSEE

8 Hancock County

9

10

11

12

13

14

15

16

17

18

19

20

21

22

16,

NEW YORK

Cattaraugus County 

Cayuga County 

Chautauqua County 

Erie County 

Oswego County 

Schuyler County 

Seneca County 

Utica

Seneca Lake 

Wayne-Dundee field 

Blue Tail Rooster field 

Bass Islands trend 

Allegany field 

Lake Shore field

INDIANA

Ashtabula County 

Brown County 

Carroll County 

Coshocton County 

Guernsey County

	PENNSYLVANIA

41 Bedford County

42 Centre County

43 Clinton County

44 McKean County

45 Tioga County

46 Erie

47 Pittsburgh

48 Titusville

49 Chestnut Ridge anticline

50 Broadtop basin

51 Bradford fields

52 Devils Elbow field

53 Leidy field

54 Punxsutawney-Driftwood field

55 Somerset County

	VIRGINIA

SOUTH

CAROLINA

30

31

32

33 Columbus

34 Conesville

35 Findlay

36 Lancaster

37 Lima

38 North Salem field

39 Lima-Findlay field

40 East Canton field

57

58 Ben Hur field

WEST VIRGINIA

59 Jackson County

60 Kanawha County 

Mineral County 

Mingo County 

Wood County 

Charleston 

Elk-Poca gas field 

Burning Springs anticline

61

62

63

64

65

66

50

I

100 150 200 MILES

50 100 150 200 250 300 KILOMETERS

Figure 2B. Locations of places mentioned in the text.

Principal Oil and Gas Plays in the Appalachian Basin 15
76°

50 100 150

I I

200 MILES

I

78°

0 50 100 150 200 250 300 KILOMETERS

84'

42°

36°

EXPLANATION

Gulf Coastal Plain Mesozoic and Tertiary rocks

Permian, Pennsylvanian, and 

Mississippian rocks

Devonian and Silurian rocks 

Ordovician and Cambrian rocks

Blue Ridge, Reading Prong, 

Hudson Highlands, Green 

Mountains, and Adirondack 

Mountains metamorphic 

and igneous rocks

Figure 3. Generalized geology of the Appalachian basin.

stone. The sequence is best developed in the northern part 

of the basin and in the Valley and Ridge segment from New 

York to Alabama. The sequence has been termed the "Utica 

facies" for exposures near Utica in east-central New York 

(Wallace and Roen, 1988). The facies includes the Athens 

Shale in Alabama, the Blockhouse Shale in Tennessee, the 

Paperville Shale in southwestern Virginia, the Antes Shale 

in Pennsylvania, the Utica Shale in northern Ohio, and the

Point Pleasant Formation in southwestern Ohio. Utica 

source beds range in thickness from a feather edge to as 

much as 600 ft in the Appalachian Plateaus and thicken 

eastward into the black slate of the Martinsburg Formation 

in the Valley and Ridge of eastern Pennsylvania. The "Utica 

facies" is present across the northern part of the basin and in 

the adjacent part of the Michigan basin. Cole and others 

(1987) have analyzed the characteristics of the "Utica

16 Evolution of Sedimentary Basins Appalachian Basin
Era

t:

CO 

0.

0

O 

N

O

LU

 1

rf

System

Permian 

(part)

Pennsylvanian

Mississippian

Devonian

Silurian

Ordovician

Series

Lower

undivided

Upper

Lower

Upper

Middle

Lower

Upper

Lower

Upper

Middle

Lower

Upper

Middle

Lower

Source beds 

Reservoir rocks

s r' # 

s r' 

sr' *

sr' * 

r' *

R' * 

S R' *

_R * # 

b Rf #

s r #

R, Rf #

r # 

r *

R, Rf * -&

r * 

S r #

s R * * 

Rf 

S

r #

r 

R * #

R # r *

r * * 

s

r?

Principal oil 

and gas plays

Virtually 

exhausted

Upper Devonian 

sandstone

Lower Devonian 

Oriskany

Lower Silurian 

sandstone

Ordovician

carbonate 

shelf

Upper Cambrian and 

Lower Ordovician

Knox carbonate 

shelf

Rome trough

 7 

EXPLANATION

S Major source bed 

s Minor source bed 

R Major reservoir 

Rf Major fractureporosity reservoir 

r Minor reservoir 

' Virtually depleted 

reservoir

 & Mainly gas

 Oil and gas

 Mainly oil

Figure 4. Age and position of source beds, reservoir rocks, and principal oil and gas plays in the 

Appalachian basin.

Principal Oil and Gas Plays in the Appalachian Basin 17
Table 1. The relative stratigraphic position of rock units mentioned in the text

[Other Paleozoic units and erosional hiatuses are not shown on this chart]

CD 

UJ

Icc

<

Q_ 

U

0

N 

O 

UJ

_i 

< 

Q_

E

CD

to 

C/D

Mississippian

Devonian

c

_CD

3

c/5

Ordovician

Cambrian

w

_CD

CD 

C/3

CD 

D. 

Q.

=3

CD 

0

CD 

D. 

D.

=3

CD 

 D 

T3

^

CD

O

_J

CD 

D. 

Q.

D

CD 

T3 

T3'^

CD

O

_l

CD 

D. 

Q.

D

Middle

CD

O

_l

CD 

D. 

D.

13

CD

-c

"C

i

CD

O

_l

Principal oil 

and gas plays

Upper Devonian , 

sandstone play

Oriskany play

Lower Silurian 

sandstone play

Ordovician 

carbonate shelf 

play

Knox carbonate 

shelf play

Rome trough play

New York

1 * 

Dunkirk Bradford zone 

Rhinestreet sandstones 

Middlesex

Geneseo

Geneseo 

Marcellus Shale

Ohondaga 

Limestone

Oriskany Sandstone

Rochester Shale

^Medina Sand 

Whirlpool Sandstone

Utica Shale

fUrica Shale 

Trenton Group

Black River Group

Beekmantown Group

Beekmantown Group

Beekmantown Group 

"Theresa"

Pennsylvania

Mauch Chunk 

Formation 

(part)

Big Injun sand 

Squaw sand

Sunbury Shale 

Berea Sandstone

Venango zone 

sandstones

Dunkirk Bradford zone 

Rhinestreet sandstones 

Middlesex 

Burket ; 

Geneseo

Geneseo 

Marcellus Shale

Qnondaga 

Limestone Huntersville Needmore

Chert Shale 

Oriskany Sandstone 

Mandata Formation

Rochester Shale

Keefer Sandstone

Medina Sand 

Tuscarora Sandstone 

I Whirlpool Sandstone

Antes Shale

Trenton Group 

Black River Group

Beekmantown Group

Beekmantown Group

Gatesburg Formation !

\ Pleasant Hill Limestone) /

V Waynesboro Formation /

\ basal sand / 

V __^ ? 1

Maryland

Mauch Chunk 

Formation 

(part)

Bradford zone 

sandstones !

Burket

Marcellus Shale

HuntersvHIe Needmore

Chert Shale 

jOriskany Sandstone 

Mandata Formation

Rochester Shale

Tuscarora Sandstone

Antes Shale

Beekmantown Group

Beekmantown Group

Gatesburg Formation

West Virginia

Pennington 

Group

Ravencliff Member of the 

Hinton Formation

Keener sand 

Big Injun sand 

Squaw sand 

Weir sand 

Sunbury Shale 

Berea Sandstone

Cleveland Venango zone 

Huron sandstones

Dunkirk Bradford zone 

Rhinestreeti sandstones 

Middlesex 

Burket 

Geneseo

Geneseo 

Marcellus Shale

Onondaga 

Limestone Huntersville Needmore

Chert Shale 

Oriskany Sandstone 

Mandata Formation

Keefer Sandstone

Clinton Tuscarora 

sand Sandstone

Antes Shale

Trenton Group

Beekmantown Group

Beekmantown Group

Gatesburg Copper Ridge 

Formation Dolomite

\ Conasauga Group / 

V Rome Formation /

\ Rome Formation / 

\ basal sand /

18 Evolution of Sedimentary Basins Appalachian Basin

B1839-1 

TABLE 1
Virginia

Pennington 

Group

Ravencliff Member of the 

Hinton Formation

i/Veir sand 

Sunbury Shale Chattanooga Shale 

Berea Sandstone

Cleveland 

 luron

Ihinestreet 

Vlillboro Shale Chattanooga Shale

/larcellus Shale Millboro Shale

)nondaga 

.imestone Huntersville Needmofe

Chert Shale 

Qriskany Sandstone

Rochester Shale

Keefer Sandstone

Tuscarora Clinch 

Quartzite Sandstone

Paperville Shale

Beekmantown GroupX

Beekmantown Group

Gatesburg Copper Ridge 

Formation Dolomite

Ohio

Keener sand 

Big Injun sand 

Squaw sand 

Weir sand 

Sunbury Shale 

Berea Sandstone

Cleveland Venango zone 

Huron sandstones

Rhinestreet 

Middlesex

Geneseo

Geneseo 

Marcellus Shale

Columbus Limestone

Oriskany Sandstone

Clinton Cabot Head Formation 

sand Medina sand

Point Pleasant 

Utica Shale Formation

Trenton Limestone 

Black River Limestone 

Wells Creek Formation

Beekmantown Group 

Rose Run Sandstone

Copper Ridge Trempealeau 

Dolomite Formation

Kentucky

Pennington 

Group

Big Injun sand 

Weir sand

Fort Payne Formation 

Sunbury Shale Chattanooga Shale 

Berea Sandstone

Cleveland Chattanooga 

Huron Shale

Rhinestreet

Marcellus Shale

Corniferous lihne

Oriskany Sandstone 

Corniferous time

Corniferous lime

Corniferous lime

Big Six sand ]

 ClinchiSandstone 5

upper Sunnybrook sand j 

Wells Creek Dolomite !

Rose Run Sandstone ( 

Copper Ridge Dolomite

\. Conasauga Group / 

\v Rome Formation / / 

\ -base! sand / / nW

Tennessee

Pennington 

Formation

Fort Payne Formation 

Chattanooga Shale

Cleveland Cnattanooga 

Huron Shale

Rhinestreet

Marcellus Shale

Clinch Sandstone

Blockhouse Shale

0. 3 

o

0

X

0

c ^

Q. 

3 

O

O

x Copper Ridge Dolomite o '- '.-..-..>

5

Alabama

Pennington 

Formation

Fort Payne Formation 

Chattanooga Shale

Chattanooga 

Shale

Athens Shale

Copper Ridge Dolomite

|

]/ 

*Devontan gas-s 

Cleveland = Cleveland 

Huron = Huron 

itfirfc Dunkirfc Rhnle Memher nf

/? Rhinestreet = Rhinestreet Shale Member o 

' Middlesex = Middlesex Shale Membe 

Burket = Btirket Shale Memb 

Geneseo = Geneseo Shale Member

hale source-bed sequence \ 

Member of the Ohio Shale 

Vlember of the Ohio Shale ! 

the Perrysburg Formation I 

f the West Falls Formation ' 

r of the Sonyea Formation 

er of the Harrell Formation 

ofthe Genesee Formation

Principal Oil and Gas Plays in the Appalachian Basin 19
A'

Appalachian basin

Eastern Overthrust belt

Cincinnati 

arch

Appalachian Plateaus Valley and Ridge Blue Ridge Piedmont

Allochthonous metamorphic 

and igneous rocks

~,\ ^- M^S''~ VvV ^7''\VjVi.!'^T^r--v-^trough sedir v'-v 'V'^''^V"'v |'"-\VI^ N ~"'\S/V'--'-^''A .-» V^vT,x 7? r~=:

x * v ^ x ~ * v ~^."-/ - ^ ^^v^ ^ ^ v . x^. \^7 . » _ ^ > -~ f ^ ^ _ _ ^^^^^..^-yv^ixo ^""^^-^r i * \^' \ / \ ' ^ 

v^'Autochthpnous'Precambrian1 basement complex y\-V( ''^ 'J\'t ^^T^^r^^!!^f:~:^~:?^^^:B«^-_._^^ ^^==:;^c^//'--T-" i"-7

50.000 FEET

Figure 5. The Paleozoic sedimentary rock sequence from the Cincinnati arch eastward to the west flank of the Blue Ridge 

and extending eastward in the subsurface beneath the Blue Ridge and adjacent Piedmont. Approximate line of section 

A-A' shown on figure 2A. No horizontal scale.

fades" as a source bed in Ohio. Other marine shales that 

may have some potential as source beds include the Middle 

and Upper Cambrian Conasauga Group, the Middle Ordovician Wells Creek Formation, the Lower Silurian Cabot 

Head Shale, the Middle Silurian Rochester Shale, and the 

Lower Devonian Mandata Shale.

Possible source beds in Mississippian and Pennsylvanian rocks include the many coal beds and associated 

canneloid shales in the Appalachian Plateaus, the Lower 

Mississippian coals of Virginia's Valley coal fields, and the 

anthracite of the eastern Pennsylvania anthracite fields. The 

abundance of natural gas in many coal beds of the Appalachians attests to the ability of the coals to generate methane 

gas in quantity.

Thermal Maturation

General eastward thickening of the basin's Paleozoic 

sequence is the result of nearly continuous deposition in the 

central and eastern parts of the basin. Westward thinning of 

major siliciclastic delta sequences and several episodes of 

nondeposition and subaerial erosion in the western part of 

the basin thin the Paleozoic sequence along the flank of the 

Cincinnati arch. Consequently, the degree of thermal maturation of source rocks, which is dependent largely upon 

thickness of sediment, depth of burial, and existing thermal 

gradient, increases from west to east across the basin (fig. 

7). Epstein and others (1977) noted that levels of thermal 

maturation in the basin determined from analysis of conodont color alteration data were controlled mainly by depth 

of burial and showed little effect of tectonism in much of the 

Appalachian basin. The conodont color alteration index 

(CAI) isograds depicted by Epstein and others (1977) 

intersect and cross the main structural trends. This pattern 

of intersection indicates that the maturation pattern was 

established in the basin generally before the Alleghanian

thrusting. Oil and associated gas occur in fields and pools in 

the relatively low level of thermal maturation in the western 

part of the basin, whereas only nonassociated dry gas occurs 

in the more mature rocks of the Valley and Ridge of 

Pennsylvania and adjacent States. Although data are generally lacking, maturation levels in the buried eastern 

segment of the basin appear to be sufficiently low to contain 

nonassociated dry gas in eastern Tennessee and possibly in 

contiguous North Carolina and Virginia. However, farther 

to the east, where the Paleozoic sedimentary rocks underlie 

the eastern side of the Blue Ridge and inner Piedmont, 

source beds are overmature, and dry gas is probably not 

present in commercially producible volumes.

Oil and Gas Migration

Data delineating the time of oil and gas migration are 

very scant for the Appalachian basin. Cole and others 

(1987) suggested that an increased thermal gradient associated with the Alleghany orogeny at the close of the 

Paleozoic Era was responsible for generation of oil and gas 

in the Ordovician rocks of eastern Ohio and contiguous 

Pennsylvania. Because of their shallower depth of burial, 

Devonian black shale and younger source rocks passed into 

and through the oil-generation zone (window) farther to the 

east in Pennsylvania and central West Virginia. Thrusting 

during the Alleghany orogeny developed structural traps 

with extensive zones of fracture porosity at the propitious 

interval for recently generated hydrocarbons to migrate into 

these newly formed structural traps.

Migration of hydrocarbons from more deeply buried 

source beds (for example, from shale in the Conasauga 

Group in the Rome trough) may have occurred earlier, prior 

to the Alleghany orogeny, when the shale reached oilgeneration temperature beneath the thick sedimentary fill in

110 Evolution of Sedimentary Basins Appalachian Basin
50 100 150 200 MILES

0 50 100 150 200 250 300 KILOMETERS

42

34° EXPLANATION

Trend of the crest of the

Cincinnati arch 

Normal faults bounding the

Rome trough Ticks on

downthrown side

Figure 6. The structure on the top of the autochthonous Precambrian basement complex under the Appalachian basin. 

Datum is mean sea level. Contour interval 10,000 ft (with 2,000- and 5,000-ft intervals shown locally). Rome trough faults 

shown by ticks on the downthrown side. Modified from Harris (1975).

the trough. Also, the thinned crust beneath that extensional rocks in much of the basin. The scant data available for

feature might have produced a greater thermal gradient, times of hydrocarbon generation and migration in the

which would have accelerated maturation. These are spec- Appalachian basin clearly indicate the need for more

ulative concepts because data are lacking for the deeper detailed research on these subjects.

Principal Oil and Gas Plays in the Appalachian Basin 111
50 100 150 200 MILES 78°

50 100 150 200 250 300 KILOMETERS

84

42

34°

Figure 7. Conodont color alteration index isograds in the Appalachian basin. Isograds 2.5 'O' and 2.5 'M' mark the eastern 

limits of oil occurrence in the Ordovician amd Mississippian rocks, respectively. Isograd 4.5 marks the eastern limit for 

the recovery of nonassociated dry gas in the basin. Modified from Harris and others (1978).

Depositional History

A general discussion of the burial history of Paleozoic 

rocks in the Appalachian basin requires consideration of the 

basin's large size and the fact that the southern part may 

have been undergoing subaerial erosion concurrently with 

subsidence and the accumulation of thousands of feet of

deltaic sediments in the northern part. Such differences in 

deposition and erosion occurred in the basin during the Late 

Devonian.

An episode of extensional tectonics in the Late 

Proterozoic opened a rift basin early during the creation of 

the proto-Atlantic Ocean, lapetus. Early Cambrian seas 

flooded the rift and expanded westward onto the edge of the

112 Evolution of Sedimentary Basins Appalachian Basin
North American craton. A sheet of sandy sediment accumulated along the edge of the transgressing sea as detritus 

was swept eastward and southward from the craton. The 

Rome trough (fig. 6), whose rift phase occurred in the 

Middle Cambrian, contains Cambrian rocks from the time 

of rifting and postdating the rifting (Ryder, 1989). As much 

as 8,000 ft of siliciclastic mud, silt, sand, and some 

intercalated carbonate sediment accumulated in the trough 

in parts of West Virginia and Pennsylvania. Dark shale and 

associated argillaceous limestone rich in organic matter are 

most probably the source beds for oil and gas found in the 

western part of the trough in Kentucky and for dry gas in 

contiguous West Virginia. Because of the great depth of 

burial of both source beds and reservoir rocks to the 

northeast, much of the Rome trough's 23,000 mi3 of fill 

remains to be explored and evaluated.

During the Late Cambrian and the Early Ordovician, 

a broad shelf of shallow-marine carbonate sediment blanketed a large part of the basin except for its eastern deeper 

water segment. About 7,500 ft of shallow-water to supratidal sediment accumulated in the central part of the basin. 

A brief episode of uplift and erosion near the close of the 

Early Ordovician exposed the shelf strata and developed 

local zones of karstic porosity in the carbonate rocks, or 

concentrated residual quartzose sandstones along the unconformable surface leached into the carbonate strata. At a later 

date, oil and gas migrated into the porous sandstones or the 

residual karstic hills mainly in central and eastern Ohio or in 

the Cumberland saddle (fig 2.) of southern Kentucky and 

adjacent north-central Tennessee. Potential source beds 

include some of the Middle Ordovician shales that cap and 

seal the porous carbonate reservoir rock.

Along the Findlay segment of the Cincinnati arch in 

northwestern Ohio, the Trenton and Black River Limestones of Middle Ordovician age were extensively dolomitized to form the reservoir rock of the giant Lima-Findlay oil 

and gas field. Although not strictly a part of the Appalachian basin, local porous zones of dolomitized limestone 

project from the Lima-Findlay area downdip into central 

Ohio, where some oil and gas has been found in the Trenton 

Limestone.

During the Middle Ordovician, the eastern margin of 

the North American continent shifted from passive to 

active. A foreland trough formed in the eastern and central 

part of the basin apparently as a result of compressional 

tectonics associated with active plate collision to the east. 

Siliciclastic sediment from eastern orogenic source areas 

accumulated east of the basin's carbonate shelf. During the 

Middle and Late Ordovician and Early Silurian, an extensive wedge of deltaic clastic sediment from eastern sources 

prograded westward across the foreland trough and spread 

onto the adjacent cratonic platform. A basal blanket of 

black mud covered much of the eastern half of the basin 

from New York to Alabama. This black mud, the "Utica 

fades" (Wallace and Roen, 1988) also spread westward

across the northern part of the basin and into the Michigan 

basin by way of the Chatham sag north of the Findlay arch. 

The "Utica fades," which is the older of the two principal 

source-rock sequences in the Appalachian basin, is as much 

as 600 ft thick. It supplied gas to the Trenton Limestone in 

northeastern New York and oil and gas to the Trenton and 

older limestones in the Valley and Ridge of southwest 

Virginia and to the Ordovician carbonate reservoir rocks in 

the nearby Cumberland saddle of southern Kentucky and 

contiguous Tennessee. Cole and others (1987) suggested 

that the source of oil from the Late Cambrian Trempealeau 

Formation, a Copper Ridge Dolomite equivalent, in central 

Ohio may have been the black "Utica fades" to the east, 

where it lay deeper in the basin.

Widespread, dominantly marine transgressive Lower 

Silurian sandstones in the northern part of the basin are 

reservoirs for oil and associated gas in Ohio and locally in 

Kentucky and Pennsylvania. They contain nonassociated 

dry gas in New York, Pennsylvania, and West Virginia. 

The sandstones are the upper part of the thick and extensive 

siliciclastic deposits of the Queenston delta that filled the 

northern part of the foreland trough during the Late Ordovician. The basal Silurian sandstones change from marine to 

terrestrial, thicken, and become coarser grained eastward. 

They thicken from a feather edge in central Ohio to more 

than 700 ft in the Valley and Ridge in northern Virginia.

Continued transgression of the shallow epicontinental 

sea flooded all but the eastern part of the foreland trough 

during the Middle Silurian. The Bloomsburg delta, a small 

mass of red siliciclastic sediment built above sea level in 

eastern Pennsylvania, and some of its flanking sandstones 

spread southward into Virginia and adjacent West Virginia. 

A marine carbonate shelf with small fringing reefs occupied 

the western segment of the basin. Local exposure of the 

carbonate strata produced small zones of karstic, enhanced 

porosity near the top of the carbonate sequence. During the 

Late Silurian, restricted circulation of the shallow sea 

within the basin produced a superhaline environment, and 

evaporitic sediment accumulated widely from New York to 

central West Virginia and westward to the Michigan basin 

by way of northern Ohio and the Chatham sag (fig. 2). A 

scattering of oil and gas pools has been found in the 

carbonate platform rocks, mainly in Ohio. However, counterparts of the coeval, prolific oil- and gas-filled reefs of the 

Michigan basin have not been found in the Appalachian 

basin, although the Silurian carbonate sequence has been 

penetrated by many thousands of wells from Lake Erie 

south to the Ohio River.

During the Early Devonian, much of the central part 

of the basin was covered by a shallow sea that had a 

prograding shoreline on the east and a low coastal plain on 

the west. Carbonate muds accumulated along the shore of 

the western coastal plain, and carbonate sands were deposited on higher energy depositional sites to the east. On the 

eastern side of the sea, carbonate sediments intertongued

Principal Oil and Gas Plays in the Appalachian Basin 113
with siliciclastic detritus from adjacent source areas. The 

abundantly fossiliferous Oriskany Sandstone was spread as 

a marine shallow-water, high-energy blanket of quartz sand 

from eastern New York to eastern Ohio and southwest to 

south-central Virginia in both the Valley and Ridge and the 

Appalachian Plateaus. It ranges in thickness from a feather 

edge in Ohio to more than 300 ft in central Maryland 

(Oliver and others, 1971). The Oriskany is one of the 

principal gas sands of the Appalachian basin. It produced 

gas and a little associated oil from stratigraphic traps in 

Ohio and western West Virginia, whereas it produced dry 

gas in abundance from zones of fracture porosity associated 

with structural traps downdip in the basin in the Eastern 

Overthrust belt from central New York to east-central West 

Virginia in both the Appalachian Plateaus and the Valley 

and Ridge.

Probably as a result of increasing orogenesis at the 

onset of the Acadian orogeny, the sea deepened in the 

foreland trough in the Middle Devonian. The vast Catskill 

delta, a tectonic delta complex (Friedman and Johnson, 

1966) composed of siliciclastic detritus from eastern orogenic sources, prograded westward into the foreland trough. 

West of the growing delta, an anoxic environment in the 

deepening sea preserved much of the terrestrial organic 

detritus swept into the sea from eastern sources as well as 

much of the locally abundant marine organic matter. Beds 

of black mud charged with large amounts of organic matter 

blanketed the central and western parts of the basin at 

different times during the Middle and Late Devonian and 

Early Mississippian. Upon lithification, these muds formed 

the younger of the two principal source-bed sequences for 

hydrocarbons in the Appalachian basin. These black shales 

are generally called the Devonian shale sequence or the 

Devonian gas-shale sequence. Extensive Devonian black 

shales were not confined to the Appalachian basin. At times 

the black sediment spread through the Chatham sag across 

the crest of the submerged Cincinnati arch or through the 

Cumberland saddle into the Michigan or the Illinois basin.

The Devonian and Mississippian black shale 

sequence is the main source for oil and gas in middle and 

late Paleozoic reservoir strata in the basin. The black shales 

are nonconventional reservoirs. Where extensively fractured, as along the Rome trough, the shales are both source 

beds and reservoir rocks. Because their contained organic 

matter adsorbs much of the indigenously generated gas, the 

Devonian and Mississippian black shales are estimated to 

contain a large, nonconventional gas resource of about 840 

trillion cubic feet (Charpentier and others, 1982), most of 

which is unrecoverable by existing extraction techniques.

Middle to Late Devonian erosion cut deeply into the 

rocks in the western part of the basin and formed a series of 

karstic porous zones in Ordovician, Silurian, and Devonian 

carbonate rocks beneath a Devonian unconformity from 

Ohio south to Tennessee. During the early part of the 

present century in eastern Kentucky, prolific oil fields were

discovered in the Corniferous lime (drillers' term), a local 

designation for the Middle Silurian to Lower Devonian 

carbonate rock sequence.

During the Middle and Late Devonian, the vast 

Catskill tectonic delta-fan complex prograded into and filled 

much of the northern half of the foreland trough with a 

sequence of siliciclastic sediment that ranged from coarse 

conglomeratic sands in the east to fine-grained mud and 

clay in the west. In places, as much as 12,000 ft of 

quartzose clastic sediment accumulated in the eastern part 

of the basin. To the west, prodelta turbiditic silts, shallow 

marine sheet sands, bars, and beach sands were deposited 

by the prograding Catskill delta. Many of the beds of silt or 

sand became reservoir rocks for oil and gas generated in the 

adjacent and interfingering black shale sequences. The 

Upper Devonian sandstones of the Venango and Bradford 

sequences of western Pennsylvania and adjacent New York 

and West Virginia are the principal oil reservoirs in the 

basin. More than half the oil recovered in the Appalachians 

has been produced from the Upper Devonian sandstones, 

particularly from the giant Bradford field astride the Pennsylvania-New York State line.

From the Late Devonian into the Early Permian, the 

Appalachian foreland basin was largely filled by siliciclastic 

detritus, largely from eastern orogenic source areas, with 

the exception of a period of flooding and accumulation of 

shallow-water carbonate sediment during the Late Mississippian. The carbonate sediment was deposited in the 

southern and western part of the basin and interfingered to 

the northeast and east into red beds of the terrestrial Mauch 

Chunk delta. At times some clastic detritus was eroded from 

the cratonic shield to the north and northwest of the 

Appalachian foreland trough and was swept southward into 

the northwestern part of the trough. Although locally 

important as reservoir rock, the amount of siliciclastic 

sediment from cratonic sources is trifling in comparison to 

the vast amount of clastic material derived from eastern 

orogenic source areas.

In the western part of the basin, several deltaic 

shallow-marine sandstones of Early Mississippian age have 

been and are reservoirs for oil and gas whose source was the 

black shales of the Devonian and Lower Mississippian 

shale-gas sequence. The Berea Sandstone, having sediment 

source areas both on the craton and in the orogenic 

highlands to the east (Pepper and others, 1954), is the most 

extensive of these siliciclastic reservoir rocks. The younger 

Keener, Big Injun, Squaw, and Weir sequence produced 

large volumes of oil and gas in parts of eastern Kentucky, 

southern Ohio, and northern West Virginia during the past 

century. During the Early Mississippian, much of the 

eastern part of the foreland trough was filled with coarsegrained terrestrial deltaic deposits. Coal beds are present 

locally in the sequence in the Valley and Ridge of Maryland, Pennsylvania, Virginia, and West Virginia. Marine 

sandstones extending westward into the basin from the

114 Evolution of Sedimentary Basins Appalachian Basin
Early Mississippian deltas produced much nonassociated 

dry gas in western Pennsylvania and contiguous West 

Virginia. Farther to the west, oil and associated gas accumulated in the porous shallow-water sandstones. Although 

these petroliferous reservoir sandstones have long been in a 

mature stage of exploration and have been drilled extensively, they contained important oil and gas fields during 

the past century, when the petroleum industry developed in 

the Appalachian basin.

Although the southwestern segment of the Appalachian basin was inundated in the Early Mississippian, the 

last major flooding of the Appalachian foreland trough by 

the Paleozoic epicontinental sea occurred mainly in the 

early part of the Late Mississippian. A broad northeastwardthinning wedge of shallow-marine to locally supratidal 

carbonate sediments blanketed the western and southern 

parts of the basin. Evaporitic sediments, including halite, 

accumulated in partly isolated subbasins. The carbonate 

strata thin and intertongue with red siliciclastic rocks of the 

Mauch Chunk delta in the northeastern and eastern segment 

of the basin. The Mississippian carbonate strata are more 

than 3,500 ft thick in the Greendale syncline in the Valley 

and Ridge of southwest Virginia and thin to a feather edge 

in the Broadtop basin in south-central Pennsylvania. Dolomitized zones with enhanced porosity and permeability, 

especially in the lower part of the Mississippian carbonate 

sequence, produced both oil and gas in parts of West 

Virginia, eastern Kentucky, and adjacent Tennessee. Other 

reservoirs in the carbonate sequence include vugular porosity in biostromes or small bioherms (Milici and others, 

1979).

During the Late Mississippian, great volumes of 

terrestrial siliciclastic sediment from eastern orogenic 

source areas prograded into and filled the northern and 

central parts of the foreland basin. The Mauch Chunk 

deltaic sequence of red beds is more than 6,000 ft thick in 

eastern Pennsylvania (Wood and others, 1969, p. 65-70). 

The continental rocks of the delta grade laterally into and 

intertongue with sequences of marine rocks to the southwest 

along the central part of the basin in the Pennington 

Formation. The formation contains a mixture of siliciclastic 

and carbonate rocks, many of which were deposited in 

shallow-marine to coastal-swamp environments. Local coal 

beds and coaly shale as well as dark-gray to black marine 

shale or mudrock may have been source beds for some of 

the oil and gas trapped in the more porous rocks of the 

Pennington Formation. Several quartzose channel, bar, and 

beach sandstones in the Pennington form stratigraphic traps 

for both oil and gas, mainly in the central and west-central 

parts of the basin. Of the channel-filling sandstones, the 

Ravencliff Member of the Hinton Formation of West 

Virginia is probably the most extensive gas reservoir in the 

Upper Mississippian rocks of the basin.

To the south in Alabama, much of the middle and 

upper part of the Mississippian sequence is dominated by

shale and mudrock. Dolomite, limestone, and sandstone are 

interbedded in the sequence, although the finer grained 

siliciclastic rocks make up much of the sequence. Some of 

these shaly rocks may have been source beds for gas and oil 

trapped in porous strata to the west in the Black Warrior 

basin.

Coal-bearing sequences of dominantly siliciclastic 

deltaic rock derived largely from eastern orogenic source 

areas filled the Appalachian foreland basin during the 

Pennsylvanian and Early Permian. Locally, in eastern 

Pennsylvania and southwestern Virginia, these strata are 

more than 5,000 ft thick, and in central Alabama they are 

about 9,500 ft thick (Wanless, 1975). In general, the 

coal-bearing rocks thin to the west, and several relatively 

thin sequences of marine limestone, mudrock, and chert 

from the midcontinent extend eastward into the basin's 

Pennsylvanian rocks, particularly in Ohio. Most of the 

carbonate rocks in the Appalachian basin are, however, 

lacustrine limestones. Coals in the basin range from highvolatile bituminous to anthracite. Bituminous coals underlie 

the Appalachian Plateaus in the western and central parts of 

the basin, whereas anthracite occurs in the folded and 

faulted Valley and Ridge rocks in eastern Pennsylvania. 

Black canneloid and carbonaceous shales are locally abundant in these upper Paleozoic rocks. Both the coals and 

black shales were probably source beds for gas and oil in 

stratigraphic traps in the coarser grained sandstones and 

conglomerates of the Pennsylvanian strata. Some hydrocarbons in Pennsylvanian reservoirs may have been derived 

from the Devonian and Lower Mississippian black shale 

sequence. Data are lacking, so the genesis of oils trapped in 

the Pennsylvanian rocks cannot be resolved at present.

Locally, channel-filling, beach, and bar sandstones of 

Pennsylvanian age have produced oil or gas or both in 

eastern Kentucky, southeastern Ohio, southwestern Pennsylvania, and West Virginia. Although by present standards 

the volume of oil and gas from the Appalachian basin's 

Pennsylvanian rocks is relatively small, it was economically 

important during the nascent stages of the petroleum industry, from 1860 to 1890, and was responsible for much 

drilling and exploration in the vicinity of the Burning 

Springs anticline of north-central West Virginia and adjacent southeastern Ohio during and just after the Civil War. 

Consistent with the general pattern of increasing thermal 

maturation eastward across the Appalachian basin, oil and 

associated gas commonly occur in the western part of the 

basin, whereas nonassociated dry gas is present farther to 

the east.

DEFINITION OF THE PRINCIPAL PLAYS

The procedure for assessing the undiscovered recoverable oil and gas resources in the Appalachian basin 

requires subdividing the basin's rocks into a series of

Principal Oil and Gas Plays in the Appalachian Basin 115
individual oil and gas plays. An assessment was made for 

each play after the geometry of the plays was delineated and 

their geologic attributes were defined and documented. The 

total analysis of all plays yields the required evaluation of 

the basin's undiscovered recoverable resources of gas and 

oil.

A play is a sequence of rocks and its contained 

hydrocarbons having the same general stratigraphy, structure and tectonic history, source rocks, general degree of 

thermal maturation, and types of reservoir rocks, traps, and 

seals. A play is a discrete entity both geologically and 

geographically. It differs in some of its characteristics from 

adjacent plays. With sufficient data available, plays of 

small geographic extent may be rigorously defined and their 

resources estimated to a high degree of accuracy. Conversely, a play of large geographic extent, for example, a 

play involving a basin of several hundred thousand square 

miles in area, will be less well defined, particularly if data 

are relatively scant in a large segment of the play's extent. 

The principal plays of the Appalachian basin are categorized as being extensive.

In this report, some plays are named for the principal 

reservoir rock or stratigraphic unit. However, a play will 

contain other units source beds, reservoirs, or seals that 

may be of different age than the play's named unit. In the 

Appalachian basin, the principal plays consist of generally 

extensive, well-known stratigraphic units or sequences of 

units whose geometries are clearly defined. Most Appalachian basin plays contain coarse-grained siliciclastic reservoir rocks that underlie all or parts of several States and 

range from areas of extensive drilling and exploration in the 

Appalachian Plateaus to the little-drilled area of the Valley 

and Ridge. Facies relations within the siliciclastic reservoirs 

are moderately well documented from drill cuttings, core 

samples, and electric logs. Areas of low permeability and 

low porosity produced by diagenesis are reasonably well 

known. Regional and local structural features in the mainly 

unfaulted western segment of the basin have been mapped 

on many different stratigraphic units, whereas to the east in 

the overthrusted areas many deeply buried features may be 

defined only from seismic profiles. Consequently, it is 

necessary to select plays, the boundaries of which are 

clearly defined lithologically and are readily identifiable in 

seismic sections, in order to establish their subsurface 

extent in the Eastern Overthrust belt. To evaluate plays 

containing karstic carbonate and siliciclastic sandstone reservoir strata associated with unconformities of regional or 

local extent requires the knowledge of their stratigraphic 

position, lithology, thickness, volume of rock removed 

during known erosional intervals, and the paleotopography 

of existing unconformities. Many of these data are available 

from outcrop studies on the basin's periphery and to a 

considerably smaller extent from sample studies, cores, and 

the analysis of suites of wire-line geophysical logs. Karstic 

carbonate oil and gas reservoirs are found mainly in the

western segment of the basin, where extensive unconformities formed in rocks along and adjacent to the Cincinnati 

arch.

The principal plays defined in the present assessment 

of the Appalachian basin's undiscovered recoverable oil and 

gas resources are, in descending stratigraphic order, the 

Upper Devonian sandstone play, the Lower Devonian 

Oriskany play, the Lower Silurian sandstone play, the 

Ordovician carbonate shelf play, the Upper Cambrian and 

Lower Ordovician Knox carbonate shelf play, and the 

Rome trough play.

DETAILS OF THE PRINCIPAL PLAYS

Upper Devonian Sandstone Play

The Upper Devonian sandstone play underlies about 

33,000 mi2 of Maryland, New York, Ohio, Pennsylvania, 

and West Virginia (fig. 8). The play consists of a 15,000- 

mi2 western area (Area 1, fig. 8) generally producing oil 

and associated gas, and an eastern 13,000-mi2 area (Area 2, 

fig. 8) containing nonassociated dry gas. The play consists 

of a 600- to 4,000-ft eastward-thickening sequence of 

deep-water to shallow-marine to terrestrial delta-plain 

rocks shale, mudrock, siltstone, sandstone, and conglomerate within the vast Catskill tectonic fan-delta complex 

(Friedman, 1988), which occupied much of the northern 

part of the Appalachian foreland basin during the Late 

Devonian. Sources of siliciclastic sediment lay to the east in 

orogenic highlands elevated during continental-plate collision in the Acadian orogeny. Clastic detritus was transported westward along the paleoslope into the subsiding 

foreland trough. Rates of sedimentation exceeded subsidence, and the Catskill delta prograded west across the 

trough so that its mud and silt blanketed the eastern edge of 

the cratonic platform in Ohio. The Upper Devonian sandstone play lies within the marine clastic sequence in the 

Catskill delta.

Reservoir Rocks

In the Upper Devonian sandstone play, reservoir 

rocks range from very tight, low-permeability, lowporosity, distal- to proximal-turbidite siltstones in the lower 

part to highly porous, high-permeability, pebbly, beach or 

offshore-bar sandstones in the upper part. The siliciclastic 

rocks generally increase in grain size upward so that in 

west-central Pennsylvania gas-bearing silty turbidites of the 

Bradford zone in the lower part of the play are overlain by 

oil-productive sandstones in the Venango zone in the upper 

part of the play. Similarly, the beach and nearshore bar 

sands grade westward into equivalent-age tight, largely 

nonproductive siltstones in eastern Ohio. Although the 

Upper Devonian sandstone play may be several thousand

116 Evolution of Sedimentary Basins Appalachian Basin
50 100 150 200 MILES

_______I________

50 100 150 200 250 300 KILOMETERS

76°

78° 74°

44°

Lake Onfanc^/

YORK

84'

42'

V

./ ~\

36°

34°

/ ^

1 NEW

f JERSEY

X

ALABAMA

EXPLANATION

Area 1 Oil and associated gas 

Area 2 Nonassociated dry gas

Figure 8. The upper Devonian sandstone play. The play consists of a 15,000-mi2 western area (Area 1) and a 13,000-mi2 

eastern area (Area 2).

feet thick, only about 10 to 15 percent of the play at a given 

locality is reservoir rock; much of the sequence is composed 

of siltstone, silty mudrock, or shale. Porosity ranges from 

about 25 percent in the coarse-grained pebbly beach and bar 

sandstones to less than 4 percent in the fine-grained distal 

turbiditic siltstones. Permeability ranges from several darcies locally in conglomeratic sandstones (Dickey, 1941) to 

less than 10 |xD in unfractured siltstone. In the finer 

textured reservoir rock, fracture porosity is an important 

factor for gas productivity, particularly to the east in the 

segment of the play within the buried western part of the 

Eastern Overthrust belt.

Principal Oil and Gas Plays in the Appalachian Basin 117
Traps and Seals

In the western part of the play, traps are mainly 

stratigraphic in the form of permeability barriers or are 

stratigraphic traps modified by small-amplitude anticlines 

or domes. Some original porosity may be preserved in the 

coarser grained pebbly sandstone; however, much of the 

porosity is secondarily developed during diagenesis by 

dissolution of chemically unstable mineral grains and by 

modification of clay coatings and cements in the original 

pores. Some of the coarser grained oil sands contain 

saltwater, which underlies oil in low-amplitude folds.

Source Beds

Source beds for oil and gas in the Upper Devonian 

sandstone play are the dark-gray, dark-brown, and black 

Middle and Upper Devonian and Lower Mississippian 

shales that underlie, are intercalated in, or overlie the 

coarse-grained rocks of the play. Because of greater depth 

of burial to the east, maturation levels in the source rocks 

range from immature (conodont alteration index 1.5) in 

central Ohio to mature (CAI 2 to 2.2) in eastern Ohio, 

western Pennsylvania, and contiguous West Virginia to 

overmature (CAI 4.5 to 5) in the Valley and Ridge of 

eastern Pennsylvania, eastern Tennessee, and central Virginia (Harris and others, 1978). Some data indicate that the 

source shales contain an admixture of marine kerogens, 

type II, and terrestrial kerogens, type III. The increase in 

the amount of terrestrial kerogens to the east, and also the 

increase in the degree of thermal maturation, indicates that 

the source rocks are progressively more gas prone eastward 

across the play. Some oil is present in the source beds in the 

central part of the basin from northwestern Pennsylvania 

south to southeastern Kentucky. The shales produce oil 

locally from fracture porosity in southeastern Ohio and 

adjacent West Virginia. Newberry (1860) suggested that the 

black Devonian shales were the source for oils in Pennsylvania's Upper Devonian oil sand reservoirs. Claypool's 

(G.E. Claypool, written commun., 1978) geochemical 

analyses of the black shales and oil from the Bradford oil 

sands confirmed Newberry's suggestion.

Timing and Migration

Data on the time of generation and migration of oil in 

the Upper Devonian sandstone play are scant. Cole and 

others (1987) suggested that maximum maturation and 

attendant migration took place at the close of the Paleozoic 

during the Alleghany orogeny, when the maximum burial 

depth of strata in the basin was coupled with a pulse of 

increased temperature accompanying the orogeny. Oliver 

(1986) suggested that hot brines squeezed from thick 

sequences of shale beneath the Appalachian megathrust 

fault system during the orogeny may have been part of the 

migration mechanism for displacing hydrocarbons from

source beds to cooler reservoir rock. Hearn and Sutler

(1985) presented evidence that during the Pennsylvanian 

and Permian, brines reacting with siliciclastic detritus in 

some carbonate rocks of the Valley and Ridge formed 

potassic feldspars at relatively low temperatures. These data 

suggest that warm to hot fluids migrated into the rocks of 

the Appalachian basin at about the time suggested by Oliver

(1986) and Cole and others (1987).

Depth of Occurrence

In the shallow, western, oil-producing part of the 

play, oil and gas occur at depths of 450 to 1,000 ft in 

western New York, from 1,600 to 2,500 ft in southeastern 

Ohio, from 695 to 3,900 ft in western Pennsylvania, and 

from 2,600 to 3,900 ft in central West Virginia. In the 

eastern, nonassociated dry-gas segment of the play, the 

upper reservoirs of dry gas underlie the deepest oil-bearing 

sands of the oil play. Reservoirs of nonassociated dry gas 

have been found to depths of 5,000 ft under the eastern part 

of the Appalachian Plateaus in central Pennsylvania and to 

more than 6,500 ft under the eastern part of the plateaus of 

northeastern West Virginia.

Exploration Status

The western, oil-productive segment of the Upper 

Devonian sandstone play has been largely explored and 

exploited. Drilling began in the play in 1859 with Drake's 

well at Titusville, Pa., and spread to the south in the 1860's. 

The area of the play was considerably extended into New 

York by the discovery of the Bradford and Allegany fields 

in the 1870's. At several times, parts of the play were 

redrilled when deeper sands were found to contain oil. 

Exploration spread southward into northern West Virginia, 

where many local oil-bearing sandstones were found in this 

part of the play. Most of the major oil pools had been 

discovered and delineated by 1910. More than half of the 3 

billion barrels of oil and gas liquids produced in the 

Appalachian basin have come from the Upper Devonian 

sandstone play. The introduction of secondary recovery 

methods, principally by waterflooding, recovered a large 

volume of oil that was unobtainable by primary recovery 

techniques, particularly in the sands of the giant Bradford 

field. In the oil-productive part of the play, the number of 

wells in a single pool ranges from one to several hundred. 

In the early drilling campaigns, drilling density was commonly excessively high, as several wells were drilled on a 

1-acre lease. Consequently, reservoir pressure was soon 

dissipated, and much of the original oil was not recovered. 

Deeper drilling for nonassociated gas in the western part of 

the play began in the 1880's as the market for gas to fuel 

steel and glass manufacturing developed in the Pittsburgh 

area, and pipelines were laid to exploit newly discovered 

gas pools and fields at considerable distances from these 

major markets. After exploiting the gas sands in the less

118 Evolution of Sedimentary Basins Appalachian Basin
deeply buried western segment of the Upper Devonian 

sandstone play, drilling for gas spread slowly to the east and 

southeast into the more deeply buried low-permeability 

reservoir rocks in the nonassociated dry-gas segment of the 

play. At present, drilling is concentrated mainly in the 

eastern segment of the basin under the eastern and central 

parts of the Appalachian Plateaus from north-central Pennsylvania southwest to east-central West Virginia. Many 

low-permeability siltstone or fine-grained turbiditic sandstone reservoir rocks are stacked in this part of the play. 

Hydraulic fracturing stimulation techniques in areas of 

fracture porosity have developed gas production in parts of 

the play that were heretofore believed to be dry. These 

newly developed stimulation techniques have extended the 

potentially productive part of the dry-gas play almost to the 

western edge of the Valley and Ridge in northeastern West 

Virginia and in central Pennsylvania. Pool size data are very 

sparse for nonassociated-gas pools and fields of this play. 

Production ranges from single well pools with cumulative 

production of several million cubic feet of gas to multiwell 

fields producing from as many as eight zones and having a 

cumulative production exceeding 1 billion cubic feet of dry 

gas. At present, the eastern limit of the play appears to be 

the Allegheny Front at the west edge of the Valley and 

Ridge. The few wells drilled to the Lower Devonian 

Oriskany Sandstone or to older stratigraphic units in the 

Valley and Ridge did not encounter commercially exploitable volumes of gas in the Upper Devonian sandstones. 

Much of the Valley and Ridge contiguous with the play area 

is in a terrestrial red-bed sequence that has maturation levels 

equivalent to CAI4 to 4.5, which precludes the presence of 

oil and suggests only a small possibility for nonassociated 

gas in commercially exploitable amounts.

Lower Devonian Oriskany Play

The Lower Devonian Oriskany play underlies about 

88,000 mi2 of the northern part of the basin in a triangular 

area from eastern New York to northern Ohio and south to 

eastern Kentucky. It includes much of the northern half of 

the Appalachian Plateaus and parts of the adjacent Valley 

and Ridge of Pennsylvania, Maryland, Virginia, and West 

Virginia (fig. 9). The play is dominantly a siliciclastic 

sandstone reservoir play except in parts of West Virginia, 

Maryland, and Pennsylvania where beds of fractured chert 

in the overlying Huntersville Chert have been included in 

evaluating fracture porosity zones of the Oriskany play. The 

Oriskany is an abundantly fossiliferous, siliciclastic, 

marine, sheet sandstone that is more than 350 ft thick near 

its depositional center in western Maryland and adjacent 

West Virginia. The sandstone thins to a feather edge to the 

north, west, and southwest. Within the sheet of sandstone 

are areas of considerable areal extent in which the Oriskany 

was either not deposited or was scoured away before

younger rocks were deposited. The southern edges of the 

areas of the Oriskany are permeability barriers that locally 

trapped gas during its migration northwestward up the 

regional dip. The very fossiliferous Oriskany Sandstone has 

been tightly cemented by secondary calcite at many places. 

Locally, the sandstone has been cemented by silica.

The Oriskany play is subdivided into two segments. 

The western and smaller segment (Area 1, fig. 9) is gas 

dominated with some associated oil at a few widely spaced 

localities in New York, Ohio, and West Virginia. The 

eastern and larger segment (Areas 2 and 3, fig. 9) contains 

nonassociated dry gas.

Reservoir Rocks

In the western segment of the Oriskany play, gas and 

oil accumulated in a highly porous, extremely permeable 

open-textured quartz sandstone reservoir. Although much 

of the sandstone is relatively fine grained, even at the edges 

of the Oriskany Sandstone, some coarse-grained sand, 

granules, and small pebbles are present. Permeability barriers, such as decrease of grain size and abundance of 

secondary calcite cement, commonly limit the size of 

reservoirs. Saline water is generally present downdip from 

gas or oil. Porosities in the reservoirs range from less than 

10 percent to as much as 25 percent. Because many of the 

Oriskany reservoirs in the western segment of the play were 

drilled by cable tools and few, if any, cores were cut in the 

more productive zones, high permeabilities in this segment 

of the play are indicated only by scant data. Lockett (1937) 

noted that wells 1 mi apart quickly registered a change in 

reservoir pressure if one of the two were shut in or was 

produced at full capacity with no back pressure to restrict 

the gas flow. Such quick response to pressure change in the 

reservoir indicates a very permeable reservoir.

To the east and deeper into the basin, the initial 

intergranular porosity has been largely obliterated by diagenesis and secondary cementation of the reservoir rock. 

Solution of chemically unstable minerals in the framework 

may have locally enhanced porosity, but the general effect 

decreased both porosity and permeability. However, within 

the Eastern Overthrust belt, secondary porosity increased as 

a result of the development of zones of fracture porosity 

associated with imbricate and splay faults rising from a zone 

of decollement in the upper part of the subjacent Silurian 

sequence. Fracture porosity is commonly localized along 

anticlinal folds produced by thrust duplication of parts of 

the stratigraphic section. Some intergranular porosity is 

necessary for continuing production from Oriskany wells, 

even where the sandstone has been fractured (Sanders, 

1982).

Traps and Seals

Stratigraphic traps formed from a decrease of permeability and porosity dominate the western segment of the

Principal Oil and Gas Plays in the Appalachian Basin 119
50 100 150 200 MILES

50 100 150 200 250 300 KILOMETERS

42

36°

34° ALABAMA

EXPLANATION

Area 1 Area of stratigraphic traps. 

Structural effects locally 

important

Area 2 Structural traps with associated zones of fracture 

porosity. Anticlinal accumulations dominant

Area 3 Oriskany Sandstone present. 

Scant drilling to Lower 

Devonian rocks

Oriskany Sandstone absent. 

Locally the play includes 

the Huntersville Chert in 

eastern West Virginia and 

adjacent Pennsylvania

Figure 9. The Lower Devonian Oriskany play. Area 1 is gas dominated with some associated oil. Areas 2 and 3 contain 

nonassociated dry gas.

Oriskany play. Locally, small-scale folds and faults may 

slightly modify traps. In this segment of the play, saltwater 

lies downdip to the east of oil or gas, and the sandstone is 

tight and dry updip to the west or northwest. The giant 

Elk-Poca field near Charleston in central West Virginia, 

which has produced almost a trillion cubic feet of gas, is a 

typical stratigraphic trap that has a well-defined gas-water 

contact on its eastern side.

To the east, in the dry-gas segment of the Oriskany 

play, stratigraphic traps become less important as intergranular porosity decreases, and structural traps with associated 

fracture porosity dominate in the Eastern Overthrust belt. 

All of the eastern dry-gas part of the play lies within the 

overthrust belt. Seismic data and drilling show that structural features in the Oriskany beneath major anticlines in the 

eastern half of the Appalachian Plateaus and in the Valley

I20 Evolution of Sedimentary Basins Appalachian Basin
and Ridge are complex because of numerous fault blocks 

(Gwinn, 1964). Some blocks may contain saltwater, 

whereas adjacent blocks are dry. Small, pop-block anticlinal fault traps are not uncommon in the bottom of larger 

synclines. Such small structural traps are not apparent in the 

surface geology and must be located by detailed reflection 

seismic profiles.

In the western segment of the Oriskany play, the 

Columbus Limestone or equivalent Onondaga Limestone 

generally overlies the Oriskany and forms a tight seal to 

Oriskany reservoirs. In West Virginia, the Huntersville 

Chert, a sequence of brittle bedded chert with some intercalated limestone or shale, which is a siliciclastic facies of 

the Onondaga, overlies the Oriskany Sandstone. Where the 

chert is extensively fractured, it may contain gas that is in 

equilibrium with gas in the underlying Oriskany. A 

sequence of Devonian shale, mudrock, and siltstone several 

thousand feet thick overlies the Huntersville and effectively 

seals the Oriskany and Huntersville reservoirs.

To the east, in the dry-gas segment of the Oriskany 

play, the Huntersville Chert is present above the Oriskany 

under much of the Appalachian Plateaus in West Virginia 

and adjacent southern Pennsylvania. Eastward into the 

Valley and Ridge, the Huntersville grades laterally into the 

Needmore Shale, which, with the younger Devonian shales, 

is an adequate seal for the Oriskany reservoirs in that part of 

the play.

Source Beds

The Middle Devonian to Lower Mississippian shale 

sequence contains at least eight regionally extensive darkbrown to black shales, which contain as much as 10 percent 

organic matter by weight. They appear to have been source 

beds for much of the oil and gas trapped in Upper Silurian 

to Pennsylvanian rocks of the basin, including strata of the 

Oriskany play. The Marcellus Shale, which closely overlies 

the Oriskany Sandstone and Huntersville Chert sequence, is 

the logical source bed for these reservoirs. However, 

younger Devonian black shales the Geneseo Shale Member of the Genesee Formation, the Burket Shale Member of 

the Harrell Formation, the Middlesex Shale Member of the 

Sonyea Formation, the Rhinestreet Shale Member of the 

West Falls Formation, the Dunkirk Shale Member of the 

Perrysburg Formation, and the Huron Member of the Ohio 

Shale may also have been source beds for some gas in the 

Oriskany Sandstone.

Timing and Migration

Sparse data suggest that gas migrated into the Oriskany Sandstone reservoirs during or just after the Alleghany 

orogeny during the closing phases of Paleozoic tectonism. 

The existence of several different sites of residual hydrocarbons within quartz grains or pores in the Oriskany 

Sandstone of eastern West Virginia, as noted by Bruner and

Heald (1989), indicates that discrete pulses of migrating 

hydrocarbons had passed through the Oriskany in the 

Eastern Overthrust segment of the nonassociated dry-gas 

part of the play. Formation of extensive zones of fracture 

porosity in the otherwise well-cemented Oriskany during 

the Alleghany orogeny at about the peak of gas generation 

and migration would have assured the widespread occurrence of Oriskany gas pools associated with large and small 

anticlines within the area of the Eastern Overthrust belt in 

the central Appalachians.

Depth of Occurrence

In the western segment of the play, which contains oil 

and gas, gas occurs in the Oriskany Sandstone at a drilling 

depth of 1,600 ft in Ashtabula County in northeastern Ohio, 

about 1,950 ft near Conesville in southern Coshocton 

County in central Ohio, and about 4,600 ft in the Elk-Poca 

field near Charleston, W. Va. In the eastern segment of the 

play, which contains dry gas, many fields occupy the crests 

of anticlines, and drilling depths range from about 1,800 ft 

at the Wayne-Dundee field in Schuyler County, N.Y., to 

more than 8,500 ft along the Allegheny Front in northeastern Mineral County, W. Va. To the east in the Valley and 

Ridge, the top of the Oriskany Sandstone in synclines may 

exceed 10,000 ft in drilling depth, whereas the Oriskany 

may crop out on the sides of adjacent anticlines.

Exploration Status

The western oil and gas segment of the Oriskany play 

has been thoroughly explored, particularly in Ohio, where 

the Oriskany Sandstone has been penetrated by thousands of 

wells drilled to the basal Silurian Clinton sands. In contrast, 

considerable areas in the eastern dry-gas segment of the 

play remain largely unexplored, although most of the large 

anticlines under the northern part of the Appalachian 

Plateaus have been explored and their contained Oriskany 

pools and fields converted to gas storage.

Drilling for hydrocarbons in the Oriskany Sandstone 

began about 1899 in northeastern Ohio, where the sand was 

originally called the Jefferson gas rock or the Austinberg 

gas sand in Ashtabula County. Both oil and gas were found. 

In the early 1920's, drilling for Oriskany gas began in 

east-central Ohio near Cambridge in Guernsey County, 

where several large stratigraphic trap fields were quickly 

delineated. Drilling spread southward near the edge of the 

sheet of Oriskany Sandstone. By 1930, the first wells were 

drilled in the giant Elk-Poca field near Charleston, W. Va. 

Many wells in stratigraphic traps in the western segment of 

the Oriskany play had initial open flows in the 1-MMCF 

(million cubic feet) to 10-MMCF range. Pools ranged from 

a single well to the 160,000-acre Elk-Poca field (Cardwell 

and Avary, 1982), which produced more than 960 BCF 

(billion cubic feet) of gas before being converted largely to 

gas storage. A scattering of relatively small oil fields was

Principal Oil and Gas Plays in the Appalachian Basin 121
found in the Oriskany, mainly in Ohio. The largest of the oil 

fields, the North Salem field in Guernsey County, which 

lies downdip from two small gas fields, was discovered in 

1926. Some of the wells produced for more than 20 years. 

In general, oil is a rarity in the Oriskany play.

Drilling also began in the eastern dry-gas segment of 

the play in the Eastern Overthrust belt in 1930 with the 

discovery of the Wayne-Dundee field in Schuyler County in 

central New York and the Tioga field on the Sabinsville 

anticline in Tioga County in north-central Pennsylvania. 

Drilling spread quickly along the larger anticlines in the part 

of the Appalachian Plateaus where Oriskany wells had 

initial open flows in the 1 to 60 MMCF range. By the early 

1950's, many Oriskany gas fields had been found in 

anticlinal traps from southern New York to northeastern 

West Virginia. As drilling sought deeper Oriskany pools 

eastward in the basin, the effective economic drilling depth 

by cable tools was reached, and in the late 1950's rotary 

drilling rigs were introduced to explore Oriskany Sandstone 

targets unreachable by cable tool rigs. From that time, most 

drilling for Oriskany gas in the dry-gas segment of the play 

has been by rotary methods. The use of wire-line electric 

well logging equipment and refinements in Common Depth 

Point (CDP) reflection seismic profiles enabled geologists 

and geophysicists to enhance their subsurface maps and to 

resolve many of the small-scale structural complexities in 

anticlinal Oriskany fault traps.

Analysis of detailed seismic profiles and deep exploratory drilling in the eastern part of the Appalachian Plateaus 

and in the adjacent Valley and Ridge led to revision of many 

ideas in Appalachian tectonics and the development of the 

concept of a basinwide megathrust system in which the 

gas-productive Oriskany anticlines are only a small part of 

a complex of decollements, imbricates, duplexes, and splay 

faults. By the late 1970's, most of the more obvious 

anticlines in the Appalachian Plateaus had been explored, 

and some Oriskany pools had been defined in the Valley 

and Ridge of southern Pennsylvania and adjacent Maryland 

and West Virginia. At present, exploration for Oriskany gas 

continues in the eastern part of the Appalachian Plateaus 

and in the adjacent part of the Valley and Ridge from 

northeastern Pennsylvania to west-central Virginia.

In the Appalachian Plateaus, field sizes range in 

ultimate production from about 5 to 960 BCF in West 

Virginia (Cardwell and Avary, 1982) to large, complex 

fields such as the Leidy field in Clinton County, Pa., with 

a cumulative production of more than 160 BCF and the 

Punxsutawney-Driftwood field with a cumulative production greater than 383 BCF (Harper, 1984). Fields in the 

Valley and Ridge tend to be smaller in ultimate yield and 

are usually in the 5- to 30-BCF range. Along the eastern side 

of the dry-gas play, thermal maturation of the Oriskany and 

associated rocks is in the range of CAI 4.0 to 4.5, which 

approaches the limit for commercially exploitable volumes 

of gas in the Oriskany play. However, an area of more than

32,000 mi2 in the eastern part of the Oriskany play where 

drilling depths are in the 8,000- to 12,000-ft range and 

anticlinal structures are complex remains little explored. 

The size and extent of zones of fracture porosity within 

structures will control the volume of gas available to a 

specific well. The area can be classed as a high-risk drilling 

area.

Lower Silurian Sandstone Play

The Lower Silurian sandstone play underlies about 

117,500 mi2 in the northern half of the Appalachian 

Plateaus and the adjacent Valley and Ridge (fig. 10). The 

play is bordered on the north and east by outcrops of several 

Lower Silurian sandstones except where Lake Erie intervenes. The western boundary of the play is defined in the 

subsurface at the depositional termination of several Lower 

or lower Middle Silurian sandstones in Ohio and Kentucky. 

The southern boundary is arbitrarily chosen at the feather 

edge of the Clinch Sandstone in Tennessee.

The Lower Silurian sandstone play includes several 

of the more quartzose marine sandstones in the vast Late 

Ordovician and Early Silurian Queenston delta. These 

sandstones include the sandstones of the Medina Group of 

western New York and northwestern Pennsylvania; the 

Tuscarora Sandstone of Pennsylvania, Maryland, northern 

Virginia, and contiguous West Virginia; the Clinton sands 

of Ohio and western West Virginia; the Middle Silurian 

Keefer Sandstone and equivalent Big Six sand, mainly in 

eastern Kentucky; and the Clinch Sandstone of southern 

Virginia, southeastern Kentucky, and northeastern Tennessee.

The Lower Silurian sandstone play may be subdivided into four general segments. A western shallow-oil and 

associated-gas segment occupies much of east-central Ohio 

(Area 1, fig. 10), whereas an eastern deeper nonassociated 

dry-gas segment extends from New York south to eastern 

Tennessee (Areas 2 and 3, fig. 10). The dry-gas segment 

may be subdivided into a western section under the Appalachian Plateaus in which gas has been produced from 

Lower Silurian reservoirs (Area 2), a speculative eastern 

section, mainly in the Valley and Ridge (Area 3, fig. 10), in 

which gas has not been found to date in commercially 

exploitable quantity except in the vicinity of the Devils 

Elbow field in Centre County, Pa., and the area of KeeferBig Six sand of northwestern West Virginia and adjacent 

Kentucky (Area 4, fig. 10).

Reservoir Rocks

Reservoir rocks of the Lower Silurian sandstone play 

are dominantly quartzose sandstones and siltstones, which 

accumulated in a variety of shallow-marine to delta-plain 

environments associated with the large Queenston tectonic 

fan-delta complex in the northern half of the Appalachian

122 Evolution of Sedimentary Basins Appalachian Basin
50 100 150 200 MILES

50 100 150 200 250 300 KILOMETERS

42°

36°

34° ALABAMA

EXPLANATION

Area 1 Oil and gas in Clinton sands

of Ohio and the Medina sand 

of Pennsylvania. Stratigraphic 

traps predominate

Area 2 Nonassociated dry gas in the 

Clinton sands of Ohio, the 

Medina sand of New York 

and Pennsylvania, and the 

Tuscarora Sandstone of 

Pennsylvania and eastern 

West Virginia

Area 3 Deep dry-gas play. Basal

Silurian sands are present, 

but few drilling data are 

available

Area 4 Mainly a gas play. Keefer 

Sandstone and Big Six 

sand.

Figure 10. The Lower Silurian sandstone play. This play consists of two main segments. Areal is a western shallow-oil and 

associated gas segment. The second main segment comprises Areas 2 and 3, which are a deeper, nonassociated dry-gas 

segment. Area 4 is a separate unit of sands slightly younger than those of Area 1.

basin. Sheet sands, offshore bars, and beach sands, marine 

and terrestrial channel-filling sands, and crevasse-splay and 

point-bar sands are found within the play. Marine reservoir 

rocks predominate in the west, whereas fluvial reservoirs 

typical of delta-plain accumulation predominate to the east. 

In the western segment, the grain size of reservoir siliciclastics, which has been only moderately altered by diagenesis, ranges from fine sand to medium silt. Porosity ranges 

from 10 to 25 percent, and permeability is commonly 

greater than 1 mD. Near Charleston, W. Va., the gasproductive part of the Tuscarora Sandstone has porosity 

ranging from 3 to 12 percent, horizontal permeability from 

less than 0.10 to 750 mD, and vertical permeability from 

less than 0.10 to 240 mD (Bruner and Heald, 1982). To the

Principal Oil and Gas Plays in the Appalachian Basin 123
east, in the dry-gas segment of the play, grain size 

increases, and locally some coarse sand and granules are 

present. Diagenesis and cementation have modified much 

of the original porosity and developed considerable secondary porosity by solution of chemically unstable mineral 

grains (Laughrey and Harper, 1986). The reservoir rocks in 

the dry-gas segment of the play are much tighter, with 

porosity ranging from less than 2 to 12 percent and 

permeability in the range of 0.2 to 0.01 mD. Although the 

basal Silurian sandstone reservoirs are generally considered 

dry-gas sands, nonproducible saline water commonly fills a 

large percent of the pore space in the finer grained sandstone and siltstone.

Traps and Seals

Most of the traps in the western and central parts 

(Areas 1 and 2, fig. 10) of the Lower Silurian sandstone 

play are stratigraphic barriers to permeability or stratigraphic traps with slight structural modification. The pinchout of effective porosity and permeability associated with 

depositional changes along channels, bars, and beaches is 

the most common type of trap. In the eastern part of the 

play, which includes the Eastern Overthrust belt, thrusting 

and folding involve the basal Silurian rocks. Structural traps 

with zones of closely spaced fracture porosity become 

dominant. Both regional joint systems and tectonically 

induced fractures are traps. The regional joints are commonly open and are more important in trapping gas than the 

fractures are (Wescott, 1982).

Throughout the play area, the Lower Silurian sandstones are overlain by a sequence of soft, silty clay shale 

and mudrock with small amounts of interbedded sandstone, 

siltstone, and limestone. Commonly the shale appears to be 

an adequate seal in most of the play. At many localities in 

the western part of the play, several sheets of marine 

sandstone are separated by beds of silty shale. Although 

many of the sandstones may produce gas or oil or both, 

scant production data suggest that natural vertical communication does not exist between adjacent reservoirs. In most 

of the western, oil and associated-gas segment of the play, 

hundreds of feet of massive dolomite and dolomitic limestone overlie the basal Silurian siliciclastic rocks and form 

a regionally extensive seal for this part of the play from 

Lake Erie south to eastern Kentucky and adjacent West 

Virginia.

Source Beds

Data on source rocks for hydrocarbons reservoired in 

the Lower Silurian sandstone play are scant and somewhat 

conflicting. The several sandstones in the western part of 

the play grade westward and intertongue with a sequence of 

gray and greenish-gray marine shale, the Cabot Head Shale 

of Ontario (Knight, 1982). The Lower Silurian sandstones 

are overlain by grayish-red to very dark gray marine shale in

the Valley and Ridge in Pennsylvania and adjacent States. 

The dark, very fossiliferous Rochester Shale, as much as 50 

ft thick, lies stratigraphically close above the Keefer Sandstone from Pennsylvania to central West Virginia. Presumably, some of these marine shales may have been sources 

for some hydrocarbons found in the Lower Silurian siliciclastic reservoir rocks.

The brownish-black to black Middle to Upper Ordovician black shale facies, the "Utica fades" and lithologic 

equivalents, also contributed hydrocarbons to the Lower 

Silurian sandstone play (Cole and others, 1987; Laughrey, 

1989). Laughrey (1989) also found traces of hydrocarbons 

from Middle Ordovician carbonate source rocks in some 

Lower Silurian reservoir rocks in western Pennsylvania. 

These data suggest several sources for oil and gas.

Timing and Migration

Cole and others (1987) suggested that the maximum 

generation of oil and gas from Ordovician and Devonian 

source beds was during the latest Pennsylvanian and Permian. This time interval corresponds to part of the Alleghany orogeny when structural traps and much fracture 

porosity were developed in the rocks of the Eastern Overthrust belt. Consequently, many traps were available for 

early filling, as recently generated hydrocarbons moved 

from the deeper parts of the Appalachian basin westward 

into areas of lower pressure and cooler strata. Gas that 

migrated into the reservoir at an early time may have 

blocked later cementation of the strata.

Depth of Occurrence

The upper reservoirs in the oil and associated-gas 

segment of the play lie at drilling depths of about 2,500 ft 

near Cleveland in northern Ohio, 1,800 ft east of Columbus 

in central Ohio, and 3,200 ft in southern Ohio. Eastern 

regional dip brings the upper reservoirs along the east edge 

of the segment to drilling depths of about 3,100 ft near Erie 

in northwestern Pennsylvania and to more than 6,000 ft 

along the Ohio River in southeastern Ohio. Reservoir sands 

in the nonassociated dry-gas segment of the play occur at 

drilling depths of about 1,800 to 1,900 ft in central New 

York, 10,000 ft in the Devils Elbow field of Centre County, 

Pa., 12,500 ft near the top of the Chestnut Ridge anticline 

in southwestern Pennsylvania, and 6,500 to 7,200 ft in the 

vicinity of Charleston in central West Virginia. Within the 

Eastern Overthrust belt, drilling depths to targets within the 

Lower Silurian sandstone play will vary greatly, depending 

upon the position of the targets in relation to structures in a 

specific thrust sheet.

Exploration Status

Much of the oil and associated-gas segment of the 

Lower Silurian sandstone play has been well explored by

124 Evolution of Sedimentary Basins Appalachian Basin
tens of thousands of wells, and some parts have undergone 

several drilling campaigns since exploitation began in the 

middle 1880's. Cable-tool wells were closely spaced in 

much of the shallower part of the play, and since the 

introduction of rotary drilling and hydraulic stimulation 

techniques, much infill drilling has further increased the 

drilling density. In contrast, much of the eastern dry-gas 

segment of the play remains unexplored. In the Valley and 

Ridge, for example, less than 500 wells have penetrated the 

Tuscarora and Clinch Sandstones in an area of about 45,000 

mi2 .

Drilling for gas and oil in the Lower Silurian Clinton 

sands began in central Ohio in the 1880's and spread rather 

rapidly to northern and southern Ohio. The Cleveland gas 

field along Lake Erie's south shore was drilled during 

World War I. Although the initial yield of oil from Clinton 

wells was not large (the greatest well flow prior to hydraulic 

treatment was 550 barrels per day; Cottingham, 1951), 

Clinton wells are noted for their long productivity. Drilling 

for gas in the Lower Silurian play began in Erie County, 

N.Y., in the 1850's and spread eastward to Seneca County 

in central New York by 1885. Although several fields were 

developed for dry gas, the low permeability of these 

shallow sandstones inhibited extensive drilling in western 

New York. Gas fields were found widely in Ohio in the oil 

and associated-gas area during the 70 years following the 

drilling of the first Clinton gas wells near Lancaster in the 

1880's. During the 1930's, several exhausted Clinton gas 

fields were converted to gas storage to augment local gas 

supplies during periods of peak demand. With the introduction of gas from the Gulf Coast and other sources by 

pipeline in the late 1940's, more than a dozen gas storage 

fields were developed in the Clinton sands of northern and 

central Ohio. At about the same time, several old Medina 

gas fields in New York were also converted to gas storage.

By 1950, geologists and drillers had demonstrated 

that a large area of Ohio's eastern counties and adjacent 

Pennsylvania was underlain by low-permeability, tight 

Clinton sand, Medina sand, or Whirlpool Sandstone that 

contained small amounts of oil or gas in almost every test 

well. However, these wells could not be stimulated to 

commercial productivity by "shooting" techniques employing nitroglycerin or other explosives. Although the sandstones had adequate porosity, in the range of 5 to 15 

percent, which is sufficient to contain considerable gas or 

oil, the permeability was too low to permit adequate flow of 

hydrocarbons to the well bore for successful commercial 

exploitation.

The introduction of well stimulation by hydraulic 

fracturing techniques in the Appalachian basin in the mid 

1950's drastically altered the Clinton-Medina production 

history, particularly in the tighter reservoir sands in eastern 

Ohio. Commonly, wells having small initial yield were 

stimulated into productive wells by hydraulic fracturing. 

Gas production rates increased from a few thousand cubic

feet to several million cubic feet per day. Oil production 

increased from a small trace of oil to more than 100 barrels 

per day after stimulation. The East Canton field of Stark and 

Carroll Counties, Ohio, one of Ohio's better Clinton oil 

fields, has produced more than 50 million barrels of oil 

from the tight sand area, which was considered a dry area 

before the introduction of hydraulic-fracturing stimulation. 

At present, exploratory drilling in the oil and associated-gas 

segment of the Lower Silurian sandstone play is mainly 

along the east edge of the play from northwestern Pennsylvania southwest to Washington County, Ohio, along the 

Ohio River. In general, the volume of gas recovered from 

the Clinton sands in this area decreases downdip, from 

north to south.

Well stimulation by hydraulic fracturing also revitalized exploration for nonassociated dry gas in the eastern 

segment of the play. Reservoir rocks with 4 to 6 percent 

porosity and 0.01 to 0.2 mD permeability (Laughrey and 

Harper, 1986) responded well to hydraulic stimulation by 

both foam and gas. A large area from central New York 

through western Pennsylvania to central West Virginia has 

been explored in some detail during the past 30 years. Infill 

and stepout drilling have extended and amalgamated many 

of the older Medina gas fields in Chautauqua and Erie 

Counties, N.Y. The area is shown as one large field, the 

Lake Shore field, covering Chautauqua County and parts of 

adjacent Cattaraugus and Erie Counties (New York State 

Department of Environmental Conservation, 1986). Similar 

enlargement and consolidation of older fields have taken 

place in northwestern Pennsylvania and contiguous Ohio. A 

scattering of deep gas wells has been drilled in the play from 

north-central Pennsylvania to southern West Virginia. The 

large nonflammable component in Lower Silurian gas is of 

concern to explorationists drilling in the central and eastern 

parts of the nonassociated dry-gas segment of the play. In 

Devils Elbow Tuscarora Sandstone field, Centre County, 

Pa., only 35 percent of the well's gas from the Tuscarora 

Sandstone was flammable. The remaining 65 percent was 

largely nitrogen (Harper, 1981, p. 53). In contrast, in 

south-central West Virginia the carbon dioxide content of 

gas from the Tuscarora ranges between 12 and 80 percent 

(Patchen, 1968). Separating the gas stream into its several 

components and selling them individually may be an 

alternative to abandoning a well because it has a large 

percent of nonflammable gas.

The potential for finding additional undiscovered oil 

is low because much of the known oil-productive area has 

been well explored. Obviously, some additional volume of 

oil will be discovered by infill and wildcat wells. However, 

the amount will not be large, considering the initial yield of 

recently drilled Clinton wells, mainly in the tighter sands 

along the east side of the oil and associated-gas segment of 

the play. Initial yields range from 1 to 10 barrels per day in 

this area, with the majority near the lower end of the range.

Principal Oil and Gas Plays in the Appalachian Basin 125
The potential for the natural gas resource is considerably better, although the greatest part of the resource will 

be found in the nonassociated dry-gas segment of the play. 

The unexplored part of the play is large, and many 

anticlines are available, particularly in the Valley and 

Ridge. Inhibiting factors for natural gas recovery include 

decreased porosity and permeability with greater depth of 

burial, restriction of porosity to zones of fractures in a 

dominantly impermeable rock, and increasing degree of 

thermal maturation eastward with depth, as shown by 

greater CAI numbers, to an economic extraction limit of 

about CAI 4.5 to 5 on the east side of the Valley and Ridge 

or locally under the west edge of the Blue Ridge thrust 

sheet.

Ordovician Carbonate Shelf Play

The Ordovician carbonate shelf play includes carbonate rocks of Middle and Late Ordovician age throughout the 

Appalachian basin. The rocks of the play underlie the 

Queenston delta siliciclastic rocks in the northern part of the 

basin and grade laterally into siliciclastic rocks to the 

southeast in the Valley and Ridge from New York to 

Alabama. The play is underlain by dominantly dolomitic 

rocks of the Knox play beneath the Middle Ordovician 

Knox unconformity except in an area from central Pennsylvania to northern Virginia, where deposition was continuous from Early to Middle Ordovician and the unconformity 

does not exist. The Ordovician carbonate shelf play underlies about 176,000 mi2 of the Appalachian basin (fig. 11).

In the western part of the basin, particularly along the 

east side of the Cincinnati arch and in the Cumberland 

saddle, the play is largely stratigraphic. To the east and 

deeper in the basin, in the Valley and Ridge of southwest 

Virginia and adjacent Tennessee, the play is structural, and 

fracture porosity is dominant. East and southeast of Lake 

Ontario (Area 3, fig. 11), the upper part of the Trenton 

Limestone contains a nonconventional shale-gas play 

(Orton, 1899) in which gas is derived from the overlying 

black Utica Shale source beds. Recent drilling in central 

New York has disclosed dolomitized carbonate rocks associated with subtle structural traps in the Ordovician carbonate shelf play (Rothman, 1989). Although the rocks of the 

play range in thickness from less than 500 ft to more than 

1,500 ft (Miller, 1975), only a small percent are of reservoir 

quality at any specific locality.

Similar to other plays in the basin, the Ordovician 

carbonate shelf play may be subdivided into a western oil 

and associated-gas play of about 6,900 mi2 lying west of the 

2.5 CAI isograd and a larger nonassociated dry-gas play of 

169,100 mi2 to the east between the 2.5 and 4.5 CAI 

isograds (fig. 11).

Harris and others (1978) suggested that the CAI 

isograd pattern was developed largely before the thrusting

and folding of the Alleghany orogeny. Consequently, the 

isograds cross the present structural grain of the Appalachian basin at an acute angle, particularly in the southern 

Appalachians, which is the only part of the play where oil 

is found in the Valley and Ridge. In contrast, to the north, 

the Valley and Ridge rocks all lie in the more mature 

dry-gas segment of the play.

Reservoir Rocks

Reservoir rocks of the Ordovician carbonate shelf 

play are dominantly fossiliferous calcarenites that are commonly associated with small disconformities. Porosity is 

enhanced locally by karstification or fracturing. In part of 

Ohio and in central New York, dolomitization appears to 

have enhanced porosity in the carbonate sequence. Reefal 

or karstic reservoirs in the play commonly have good 

porosity and permeability. Consequently, they form oil or 

gas reservoirs that quickly decline to small-volume stripper 

oil wells or are drowned by encroaching saltwater.

In the Valley and Ridge of southwest Virginia, 

carbonate rocks have been shattered and fractured in zones 

associated with thrust faults. Some of the oil in the Rose 

Hill and Ben Hur fields of Lee County, Va., may have been 

indigenous to the carbonate rocks and may have been 

released to newly formed fracture porosity reservoirs during 

an episode of thrusting.

In the nonconventional shale-gas area of eastern New 

York, beds of black shale in the Trenton Limestone appear 

to be both source and reservoir, as is the case with the 

younger Devonian gas shales. The interbedded limestone 

appears to act as an impermeable seal or a porous reservoir.

Traps and Seals

Except for areas of fracture porosity in structural 

traps, traps in the Ordovician carbonate shelf play are 

stratigraphic or are stratigraphic modified by small-scale 

structural features. Porosity and permeability decreasing to 

impermeability both horizontally and vertically seal hydrocarbons in these reservoirs. Commonly, sequences of interbedded shale and dense limestone are effective seals in 

much of the play area. Locally in the Cumberland saddle, 

gravity separation was effective, and saltwater underlies oil 

or gas. In this area, sudden release of reservoir pressure 

during drilling may permit rapid encroachment of saltwater, 

which can flood the well before recovery of much of the 

reservoir's contained hydrocarbons.

In the Rose Hill field of southwest Virginia, oil in the 

play was trapped beneath the Pine Mountain thrust sheet 

(Miller and Fuller, 1954). However, the seal was shattered 

in the vicinity of fensters in the thrust plate, and drilling 

near oil seeps in and adjacent to the fensters led to the 

discovery and development of the field.

In the shale-gas area of northeastern New York, beds 

of Trenton limestone appear to function as seals rather than

126 Evolution of Sedimentary Basins Appalachian Basin
50 100 150 200 MILES

50 100 150 200 250 300 KILOMETERS

42

40'

36°

34° ALABAM

38

EXPLANATION

Area 1 Oil and associated gas in 

central Ohio

Area 2 Oil and associated gas in 

the Cumberland saddle 

and the Valley and Ridge 

of southwestern Virginia 

and adjacent Tennessee

Area 3 Shale gas in the Utica

Shale and Trenton Limestone sequence

Area 4 Gas with some associated

oil in permeability traps in 

local disconformities or 

bioherms

Area 5 Subtle structural traps in 

central New York

Figure 11 . The Ordovician carbonate shelf play. The play is divided into a western oil and associated-gas segment of about 

6,900 mi2 lying west of the CAI 2.5 isograd and a larger nonassociated dry-gas segment of 169,100 mi to the east between 

the 2.5 and 4.5 CAI isograds.

reservoirs. In this area the beds of shale and limestone are 

fractured, and the seals are incomplete. The fracturing 

occurred possibly during isostatic rebound from loading by 

Pleistocene continental glaciers. Gas seeps to the surface at 

many places, and drilling near conspicuous seeps led to the 

earliest discovery of pools and fields in this part of New 

York.

Source Beds

Black shales of the "Utica fades," rich in organic 

matter, are the logical source beds for oil and gas reservoired in the carbonate rocks of the Ordovician carbonate 

shelf play. In the Valley and Ridge, the black source beds, 

the Antes Shale of Pennsylvania and Maryland, the Paperville Shale of Virginia, the Blockhouse Shale of Tennessee,

Principal Oil and Gas Plays in the Appalachian Basin I27
and the Athens Shale of Alabama, interfinger westward 

with carbonate rocks. Continued subsidence of the basin 

brought the black shales structurally deeper than their 

carbonate-rock equivalents. Hydrocarbons generated by 

thermal maturation migrated updip, possibly assisted by 

gravity-driven brines, into the areas of reefal and karstic 

reservoir rocks under the Appalachian Plateaus, particularly 

in the Cumberland saddle area. The Utica Shale and its 

lithologic equivalent, the Point Pleasant Formation of Ohio, 

overlie the Ordovician carbonate shelf play from New York 

to northwestern Ohio. Cole and others (1987) and Wallace 

and Roen (1988) have discussed the petroleum potential of 

the regionally extensive "Utica fades" and consider it one 

of the major source rocks of the basin. In the western part 

of the basin along the flank of the Cincinnati arch, CAI 

isograds, which are in the 1.5 to 2.0 range, indicate that the 

source beds are capable of yielding oil and gas, whereas to 

the east, the isograd range of 2.5 to 4.5 suggests that the 

source beds released oil earlier and have since generated 

large amounts of dry gas.

In the southwestern part of the basin, because of 

extensive Middle Devonian erosion, the Upper Devonian 

and Lower Mississippian black Chattanooga Shale lies upon 

the lower part of the Upper Ordovician carbonate sequence. 

In this area along the east flank of the Cincinnati arch, the 

Chattanooga Shale may have been the primary source of oil 

and gas in the Ordovician carbonate shelf play.

Timing and Migration

Cole and others (1987) suggested that migration of 

hydrocarbons from eastern source beds to western reservoir 

rocks in the Ordovician carbonate shelf play probably 

occurred in the Late Pennsylvanian and Permian during the 

onset of the Alleghany orogeny. Migration of hydrocarbons 

at this time would have made oil and gas readily available 

to fill structural traps generated by tectonic activity in the 

Eastern Overthrust belt segment of the play during the 

orogeny. Early arrival of hydrocarbons would have filled 

the fracture porosity systems with oil or gas and prevented 

their later cementation by calcite or other minerals.

Depth of Occurrence

In the Cumberland saddle and along the east flank of 

the Cincinnati arch from Ohio to Tennessee, oil and gas 

occur at depths ranging from less than 100 ft to more than 

3,000 ft in the Ordovician carbonate shelf play. In the 

shale-gas fields of northeastern New York, drilling depths 

to the gas productive zone range from 500 ft in the north to 

more than 2,600 ft in the south. Gas has recently been found 

at about 7,500 ft in subtle traps in the play adjacent to the 

south end of Seneca Lake (Rothman, 1989). Oil and gas 

occur at depths of 1,000 to 2,000 ft in structural traps in the 

Rose Hill and Ben Hur fields of Lee County in Virginia's 

Valley and Ridge. Noncommercial amounts of gas have

been found in the Valley and Ridge and the eastern part of 

the Appalachian Plateaus in structural traps in the nonassociated dry-gas segment of the play at depths as great as 

5,000 ft. The porous zones containing the gas are near the 

crest of anticlinal traps, whereas the depth to the top of the 

play in adjacent synclines might be several times greater.

Exploration Status

Much of the western oil and associated-gas segment 

of the Ordovician carbonate shelf play has been relatively 

well explored, particularly along the east flank of the 

Cincinnati arch and the Cumberland saddle, where oil wells 

were first drilled in the late 1820's (Jillson, 1947). Much of 

the remainder of this segment of the play has been little 

explored, with the exception of the oil fields in Lee County, 

Va., which have produced about 300,000 barrels of oil 

mainly from fractured Trenton Limestone reservoirs during 

the past half century. Scant drilling has been done in the 

more deeply buried dry-gas segment of the play from 

central New York to central Alabama.

The first recorded occurrence of oil from the Ordovician carbonate shelf play was in March 1829 in the 

Cumberland saddle when Emerson and Stockton's salt well 

on Little Renox Creek, near Burkesville, Cumberland 

County, Ky., blew in and produced about 2,500 barrels of 

oil per day for about a week (Jillson, 1947). By 1860 

Stockton's well, known locally as the Old American well, 

had produced more than 50,000 barrels of oil from the 

upper Sunnybrook sand (Jillson, 1947). A small number of 

wells drilled just after the Civil War from central Kentucky 

to northern Alabama found oil in the Ordovician carbonate 

reservoirs and began a series of local drilling campaigns in 

the Cumberland saddle and along the eastern flank of the 

Cincinnati arch of Kentucky and Tennessee that has continued sporadically to the present.

In the early 1880's, drilling to the Trenton Limestone 

on the crest of the Cincinnati arch at Findlay, Ohio, opened 

the giant Lima-Findlay oil field, which produced more than 

390 million barrels of oil in the Ohio segment of the field 

(Cottingham, 1951). The excitement produced by large oil 

wells in the Lima-Findlay field induced considerable drilling down the eastern flank of the Cincinnati arch and into 

the western part of the Appalachian basin in central Ohio. 

Because the dolomitic and karstic reservoir facies in the 

Trenton Limestone of northwestern Ohio is absent in central 

Ohio, few of these test wells found even small amounts of 

oil or gas, and none was successful. Recently, however, 

with the drilling of many wells to the Trempealeau Formation and Rose Run Sandstone in the underlying Upper 

Cambrian and Lower Ordovician Knox play, gas has been 

found in the Ordovician carbonate shelf play in central Ohio 

north of Columbus (Wickstrom and Gray, 1985). Data on 

the reservoir characteristics are scant.

128 Evolution of Sedimentary Basins Appalachian Basin
Having observed many local gas seeps and having 

been encouraged by stories of fortunes being made from oil 

and gas wells in the Trenton Limestone near Lima and 

Findlay in western Ohio during the 1890's, citizens of 

Oswego and adjacent counties in northeastern New York 

began drilling for gas in the area between Lake Ontario and 

the Adirondack Mountains (Orton, 1899). During the next 

two decades, several large gas fields were developed in the 

Trenton Limestone. Orton (1899) demonstrated that much 

Trenton gas in this part of New York came from nonconventional gas-shale reservoirs rather than from conventional 

carbonate reservoir rock. Production histories and well 

characteristics for the Trenton gas pools in northeastern 

New York are similar in many respects to the Devonian gas 

shales of the central Appalachians. Well cuttings from one 

Trenton gas field that were studied recently by A.M. Van 

Tyne (oral commun., 1990) showed that some of the black 

shale beds reported in the Trenton Limestone are actually 

porous zones of fossiliferous limestone. Interbedded 

impermeable limestones seal the gas-filled zones. Consequently, Orton's shale-gas play (area 3) has aspects of both 

a nonconventional shale-gas play and a conventional 

stratigraphic-trap play. Most of the Trenton gas fields in 

northeastern New York have been long abandoned. However, as recently as 1966, the Blue Tail Rooster field in 

Cayuga County, N.Y., produced gas from the Trenton 

Limestone. More recently, deep drilling to the Trenton and 

Black River Limestones of the play in the Finger Lakes area 

of central New York has encountered gas in dolomitized 

zones associated with subtle structural traps (Rothman, 

1989). As yet, data are not available to identify the extent of 

the area where such traps may exist.

Butts (1927, p. 10) noted oil seeps in the vicinity of 

fensters in the Pine Mountain thrust sheet in the Valley and 

Ridge of Lee County, Va. Drilling began in the area of the 

Rose Hill oil field in 1942. Several small oil pools have 

been found in which zones of fracture porosity are associated with structural traps beneath the Pine Mountain thrust 

sheet near Rose Hill and Ben Hur in Lee County. Although 

the initial yield of some wells was spectacular, most wells 

rather quickly passed into stripper-well status. Water 

encroachment has been a problem in the area. To date, 

Virginia's oil production, almost exclusively from the 

Ordovician carbonate shelf play, has amounted to about 

300,000 barrels. The petroleum geology of the Rose Hill 

area has been discussed in considerable detail by Miller and 

Brosge (1954, p. 205-227) and Miller and Fuller (1954).

The potential of the Ordovician carbonate shelf play 

is difficult to assess because many of the older well and pool 

data were never recorded or have been lost. Much of the 

area under the Appalachian Plateaus and the Valley and 

Ridge, excepting the Cumberland saddle and Lee County, 

Va., has been sparsely explored. Much of the oil in the 

Cumberland saddle and along the flank of the Cincinnati 

arch occurs in relatively small isolated pools. Since 1860

the Middle and Upper Ordovician rocks in this area have 

produced about 10 million barrels of oil (Bond and others, 

1971), but much of the oil came from the Cincinnati arch 

area west of the Appalachian basin. Oil production from 

Virginia's Valley and Ridge is about 300,000 barrels, only 

about one-third of the minimum 1-million-barrel field-size 

cutoff established for play analysis evaluation in the U.S. 

National assessment (U.S. Geological Survey and U.S. 

Minerals Management Service, 1988, p. 27^16). Data for 

gas production are scant, particularly for the Trenton gas 

shales of New York. The main problems in attempting to 

assess the hydrocarbon potential of the Ordovician carbonate shelf play are the absence of well and pool data both old 

and new, the lack of deep drilling to the Trenton and Black 

River rocks in much of the area, and the unavailability of 

regional seismic data for evaluation of areas of subtle 

subsurface traps in the play.

Upper Cambrian and Lower Ordovician Knox 

Carbonate Shelf Play

The Knox play includes a sequence of subtidal to 

supratidal dolomite, dolomitic limestone, and limestone 

with small amounts of intercalated quartz sand and silt, 

chert, shale, and anhydrite. Dolomite is the dominant 

lithology of the sequence, which is generally several thousands of feet thick. Rocks of the Knox play underlie more 

than 176,500 mi2 of the Appalachian basin from New York 

to Alabama and from the eastern flank of the Cincinnati 

arch east to the 4.5 CAI isograd in the Valley and Ridge or 

locally under the western edge of the Blue Ridge (fig. 12). 

The play is mainly a karstic-reservoir stratigraphic trap 

except for some structural traps in the Valley and Ridge of 

Tennessee and Virginia. At places along the Middle Ordovician unconformity at the top of the Knox play, some fineto coarse-grained reservoir sandstones have formed where 

solution has dissolved the carbonate rock and enhanced the 

porosity and permeability of the siliciclastic residue. 

Nomenclature of rocks within the Knox play is complicated 

because different names have been applied to a specific 

stratigraphic unit in different parts of the basin (Harris, 

1975). In general, the play contains all the strata below the 

Middle Ordovician unconformity to the base of the Copper 

Ridge Dolomite of the Knox Group of eastern Tennessee (or 

its stratigraphic equivalents).

The Knox play is herein subdivided into a relatively 

shallow western oil and associated-gas play about 41,000 

mi2 in extent and a deep eastern dry-gas play between the 

2.5 and 4.5 CAI isograds in an area of about 163,900 mi2 

(fig. 12). In the oil and gas segment and along the west side 

of the dry-gas segment, stratigraphic traps or combination 

traps are dominant. To the east in most of the nonassociated 

dry-gas segment of the play, structural traps with zones of 

fracture porosity are paramount.

Principal Oil and Gas Plays in the Appalachian Basin 129
50 100 150 200 MILES

50 100 150 200 250 300 KILOMETERS

84'

42'

36°

34°

38'

 Area 6

ALABAM

EXPLANATION

Area 1 Oil and associated gas in

the Trempealeau Formation

Area 2 Oil and associated gas in

the Beekmantown Group in 

the Cumberland saddle

Area 3 Oil in fracture porosity in

the Beekmantown Group in 

Lee County, Virginia

Area 4 Nonassociated dry gas in 

the Gatesburg Formation

Area 5 Mostly gas and some associated oil in the Rose Run 

Sandstone

Area 6 Gas, karstic reservoir rocks 

of the upper Knox

Area 7 Gas in fault traps with

fracture porosity, upper 

Knox

Figure 12. The Upper Cambrian and Lower Ordovician Knox carbonate shelf play. The play is divided into a relatively 

shallow western oil and associated-gas segment of about 41,000 mi2 and a deep eastern dry-gas segment between the 2.5 

and 4.5 CAI isograds in an area of about 163,900 mi2 .

Reservoir Rocks

In the oil and gas segment of the play, karstic 

erosional hills of Upper Cambrian dolomite with paleotopographic relief of as much as 150 ft lie directly below the 

Middle Ordovician unconformity (Dolly and Busch, 1972). 

They are the most important Knox play reservoirs in Ohio. 

The vugular open-textured dolomite in these residual hills

has produced about 40 million barrels of oil in Morrow and 

contiguous counties in central Ohio. To the south, similar 

karstic reservoirs are associated with the Middle Ordovician 

unconformity in the Cumberland saddle of southern Kentucky and adjacent Tennessee. A major siliciclastic reservoir, the Rose Run Sandstone, extends south from northeastern Ohio at Lake Erie to Brown County along the Ohio

130 Evolution of Sedimentary Basins Appalachian Basin
River in southwestern Ohio (Janssens, 1973, p. 26, fig. 16). 

The best development of productive Rose Run Sandstone is 

in Coshocton County in east-central Ohio (Atha, 1981; 

Coogan and Maki, 1988). Downdip to the east and south, 

the Rose Run is tightly bound by carbonate cements. 

Reservoirs are a combination of calcareous siliciclastic and 

sandy carbonate strata in the western part of the nonassociated dry-gas segment of the Knox play. To the east, 

structural traps with associated fracture porosity become 

dominant.

Traps and Seals

In the western part of the play, karstic solutional 

stratigraphic traps predominate. Some are a combination of 

stratigraphic trap modified by small-scale folding. Structural traps predominate to the east. Fracture porosity 

becomes progressively important eastward into the thicker 

broken formation zones in faulted sequences of the play in 

the Valley and Ridge, and locally beneath the Blue Ridge.

Shaly residuum, calcareous shale, and massive 

impermeable carbonate rocks in the lower part of the 

Ordovician carbonate shelf play are seals for the Knox play, 

particularly in central and north-central Ohio. Locally, the 

seal is incomplete, and Knox oil appears to have leaked into 

the basal units of the overlying play. In the Eastern 

Overthrust belt, thrust-faulted sequences of carbonate and 

fine-grained siliciclastic strata in the Rome Formation and 

Conasauga Group in the hanging-wall block of thrusts form 

seals for Knox traps in the footwall block.

Source Beds

The identification of source beds for oil and gas 

trapped in the Knox play is somewhat enigmatic. The 

greenish-gray to gray shale of the Wells Creek Formation at 

the base of the Ordovician carbonate shelf play from central 

Ohio to central Tennessee is low in organic carbon and does 

not appear to be an adequate source rock. Data from Cole 

and others (1987) strongly suggest that the Middle to Upper 

Ordovician black shale, the "Utica fades" of Wallace and 

Roen (1988), is the main source rock for Knox oil and gas 

in central Ohio. In the Cumberland saddle and southward 

along the eastern side of the Nashville dome in Tennessee, 

the Upper Devonian Chattanooga Shale is a possible source 

for oil and gas in the upper part of the Knox play. Laughrey 

(1989) suggested that Black River Group carbonates may 

have generated some oil and gas in Medina sand reservoirs. 

Because the Black River carbonate rocks make up the lower 

part of the Ordovician carbonate shelf play, they may also 

have contributed some hydrocarbons to Knox reservoirs just 

beneath the Middle Ordovician unconformity. Older shales 

below the Knox play do not appear to be good source rocks 

except possibly for some dark-gray to grayish-black shaly 

rocks in the western part of the Rome trough.

Timing and Migration

Cole and others (1987) suggested that oil generation 

and migration most probably occurred in the western part of 

the play during the late Paleozoic Era. However, a sufficient thickness of post-Ordovician sediments had accumulated at many places in the eastern part of the basin to have 

permitted some gas and oil generation earlier in the era from 

the more deeply buried source beds such as the "Utica 

fades." If it is assumed that migration of fluids began 

before and continued during the formation of structural 

traps during the Alleghany orogeny, an early filling of 

porous zones in the traps would be assured.

Depth of Occurrence

Gas and oil occur in the Lower Ordovician part of the 

Knox play in the Cumberland saddle area at drilling depths 

ranging from 1,300 to 1,700 ft. In central Ohio, the Upper 

Cambrian Copper Ridge Dolomite and its equivalent, the 

Trempealeau Formation, contain oil at depths of 2,850 to 

3,550 ft. In eastern Ohio, the Rose Run Sandstone contains 

gas and oil at depths ranging from 6,000 to 7,200 ft. Dry 

gas occurs in the play locally at greater depths under 

Pennsylvania's segment of the Appalachian Plateaus to a 

maximum depth of 9,920 ft in McKean County in northwestern Pennsylvania. Gas with a considerable hydrogen 

sulfide content was found at 8,870 ft in a well drilled on the 

crest of the Shellsburg dome in the Valley and Ridge of 

western Bedford County, Pa. (Fettke, 1953). The top of the 

Knox play was found at a depth of 20,850 ft in the Amoco 

Producing Company's No. 1 Leonard Svets well in the 

Appalachian Plateaus of Somerset County, Pa. In southwest 

Virginia, oil occurs in the upper part of the Knox play at 

depths of 3,700 to 3,900 ft near Rose Hill, and gas was 

found in a faulted anticlinal trap at about 7,575 ft in the 

upper part of the Knox in Hancock County, Tenn.

Exploration Status

Drilling for oil in the Knox play began in the 

Cumberland saddle in the decades following the Civil War. 

Several fields were developed in the Lower Ordovician part 

of the play in both Kentucky and Tennessee, mainly as a 

result of drilling through the strata of the younger Ordovician carbonate shelf play and into the Knox play close to the 

Middle Ordovician unconformity. Most of the Knox fields 

in the Cumberland saddle were found by random drilling. 

Consequently, several vigorous drilling campaigns, interspersed with long periods of relative inactivity, have been 

conducted in the area during the past 100 years. At present, 

drilling in the play continues in the saddle area and outward 

northeast and east in Kentucky and east to southeast in 

Tennessee. Drilling has spread eastward across the Appalachian Plateaus and locally into the Valley and Ridge.

Principal Oil and Gas Plays in the Appalachian Basin 131
In the 75 years following the opening of the giant 

Lima-Findlay field in the Trenton Limestone of northwestern Ohio, only a scattering of wells was drilled to the Knox 

rocks in the western half of Ohio. This drilling resulted in 

the discovery of oil in five small fields in north-central Ohio 

(Dolly and Busch, 1972; Janssens, 1973, p. 26, fig. 16). In 

1961, however, a boom quickly developed in Morrow 

County, where oil was found in Cambrian karstic paleotopographic reservoirs beneath the Middle Ordovician unconformity. Erosion had removed all the Lower Ordovician 

sequence in the Knox section, and significantly porous 

reservoirs had developed in a hilly topography beneath the 

erosion surface. Many prolific wells were found in Morrow 

County, which has produced about 40 million barrels of oil 

to date. Drilling continues in Morrow County but at a 

subdued rate.

Expectation of extending major discoveries along the 

unconformity to the northeast and southwest of Morrow 

County was not realized. Only a few small fields were 

found in the play in northern Ohio, where structure seems to 

be more important than in central Ohio (Janssens, 1973, p. 

26, fig. 16; Coogan and Maki, 1988). Several gas wells 

were found in the sandy Gatesburg Formation, the equivalent of the Copper Ridge Dolomite of Late Cambrian age, in 

northwestern Pennsylvania. The presence of considerable 

saltwater in the Gatesburg gas-bearing zone apparently 

inhibited additional exploratory drilling in the northwestern 

part of Pennsylvania.

A scattering of very deep wells has penetrated the 

Knox play in the eastern part of the Appalachian Plateaus 

and in the Valley and Ridge from New York to Alabama. 

Only in southwest Virginia and adjacent east Tennessee 

have oil and gas been found in the Valley and Ridge part of 

the Knox play, although noncommercial amounts of gas 

have been encountered locally deep in the play. Most of the 

central and eastern parts of the Knox carbonate shelf play 

remains unexplored.

Rome Trough Play

The Rome trough play is a combination structuralstratigraphic trap play involving the Lower and Middle 

Cambrian sedimentary rocks that fill part of a complex 

graben, the Rome trough of McGuire and Ho well (1963) or 

the Eastern Interior aulacogen of Harris (1978). The rocks 

of the Rome trough play underlie an area of about 40,300 

mi2 and fill part of the aulacogen from east-central Kentucky into southwestern Pennsylvania (fig. 13). Faults that 

formed the graben appear to have been initiated during a 

period of extensional tectonics associated with the opening 

of lapetus, the ancestral Atlantic Ocean, during the Late 

Proterozoic. Reactivation of the Late Proterozoic normal 

faults was greatest during the Middle Cambrian when as 

much as 8,000 to 12,000 ft of pre-Knox sediments accumulated in the deeper parts of the Rome trough (Ryder, 

1989). Subsidence of the trough recurred but on a lesser 

scale at other times during the Paleozoic Era (Harris, 1978), 

and stratigraphic units as young as the Lower Devonian 

Oriskany Sandstone show some thickening along the axis of 

the Rome trough.

Reservoir Rocks

Most of the reservoir rocks in the Rome trough are 

sandstones and sandy carbonate rocks (Ryder, 1989). The 

Lower and Middle Cambrian sequence contains considerable sandstone and quartzose siltstone; however, in much of 

the coarser grained siliciclastic rock the pores are tightly 

filled with carbonate or siliceous cement. Some beds are 

sufficiently porous and permeable to contain gas and 

saltwater. In the Sand Hill well (Hope Natural Gas Company No. 9634, Power Oil Company, Walker District, 

Wood County, W. Va.) in the Rome trough sequence, 

small, noncommercial volumes of gas were encountered in 

the basal Cambrian sandstone within 8 ft of the Precambrian 

basement complex.

Source Beds

Dark-grayish-black to black shales and grayish-black 

limestones of the Conasauga Group appear to be source 

beds in the Rome trough play of Kentucky and western 

West Virginia. In Mingo County in western West Virginia, 

grayish-black to very dark gray shale in the lower part of the 

play has gas-generating potential (Donaldson and others, 

1975). However, the coarser grained siliciclastic reservoir 

rocks are not well developed in the play in Mingo County. 

Data on the geochemistry of the source rocks of the Rome 

Trough play are unavailable.

Timing and Migration

Very scant time and temperature data suggest that the 

Rome trough rocks in northern West Virginia and adjacent 

Pennsylvania probably passed through the oil generation 

zone and well into the hotter, nonassociated dry-gas zone 

during the Late Mississippian and Pennsylvanian. To the 

west, in eastern Kentucky, source beds may not have begun 

oil generation until the Permian, and migration within the 

trough may have occurred shortly thereafter.

Depth of Occurrence

The top of the Rome trough sequence dips eastward 

from a drilling depth of about 6,000 ft along the flank of the 

Cincinnati arch in east-central Kentucky to about 25,000 ft 

in southwest Pennsylvania. Oil and gas occur at depths of 

5,800 to 7,500 ft in eastern Kentucky, whereas nonassociated dry gas has been produced briefly from a depth of 

14,350 ft in Exxon Company's No. 1 Walter McCoy well in 

Jackson County, W. Va. (Patchen, 1977).

132 Evolution of Sedimentary Basins Appalachian Basin
0 50 100 150 200 MILES

0 50 100 150 200 250 300 KILOMETERS

84'

36°

34° ALABAMA

EXPLANATION

Area 1 Oil and associated gas 

Area 2 Nonassociated dry gas 

Area 3 Area probably greater than 

CAI 4.5. Noncommercial amounts of nonassociated dry gas 

possible

 L Normal faults bounding the

Rome trough Ticks on the 

downthrown side

Figure 13. The Rome trough play. The play underlies an area of about 40,300 mi2 .

Exploration Status

The more than 40,000 mi2 of the Rome trough play 

have had little exploration except in eastern Kentucky. 

Interest in drilling to the thick section of mainly Middle 

Cambrian rocks in the Rome trough was generated by 

Woodward's (1961) paper on a preliminary study of the 

subsurface of part of the Appalachian Plateaus and the 

suggested presence of a fault-bordered deep basin in eastern

Kentucky and northwestern West Virginia. Several widely 

spaced deep wells drilled in eastern Kentucky in the late 

1950's and early 1960's encountered small amounts of gas, 

oil, or saltwater at a number of places in the Rome trough 

rocks (McGuire and Howell, 1963; Sutton, 1981). Sufficient data accumulated to show that the Rome trough was a 

large graben of considerable complexity (Silberman, 1981; 

Sutton, 1981). One small oil pool, Marity, was found in the 

trough in Boyd County in northeastern Kentucky.

Principal Oil and Gas Plays in the Appalachian Basin 133
In the mid-1970's, Exxon extended exploration east 

along the Rome trough into western and central West 

Virginia. It drilled six deep wells, which entered Precambrian basement rocks at depths of 13,266 to 20,222 ft after 

penetrating 5,000 to 8,000 ft of Rome trough rocks. Small 

amounts of dry gas were found in several wells. The Exxon 

No. 1 Walter McCoy well in Jackson County produced gas 

at a rate of 5 million cubic feet per day for a short time 

before the daily yield decreased to 1 million cubic feet per 

day and saltwater encroached to spoil the well. The well 

was shut in after producing dry gas for about 6 months 

(Patchen, 1977). In the mid-1980's, wells drilled to the 

Rome trough play in Johnson County, Ky., found gas and 

a small amount of oil.

To date, all oil or gas pools in the Rome trough play 

have been small. However, because the play is deep in 

eastern Kentucky and deeper in West Virginia and Pennsylvania, relatively few exploratory wells have been drilled 

into the trough. Encouraging data include the production of 

some oil and gas, as well as the presence of both source 

beds and reservoir rocks, within the complex graben fill in 

the Rome trough play. Offsetting these favorable factors are 

the increasing depth to target zones eastward in the play, the 

great cost per well in most of the play, and the probable 

excessively high degree of thermal maturation in the deeper 

parts of the play in western and central Pennsylvania.

VIRTUALLY EXHAUSTED PLAYS

In addition to the principal plays discussed, several 

regionally extensive and many local plays are present in the 

younger Paleozoic rocks in the Devonian, Mississippian, 

and Pennsylvanian sequences in Kentucky, Ohio, Pennsylvania, and West Virginia. The probability of finding large 

volumes of gas or oil in these plays is remote because they 

occupy the extensively drilled western segment, where 

more than half of the 750,000 wells in the basin were 

drilled. Many of the plays in these younger Paleozoic rocks 

were essentially drilled up by 1920, and their contained 

hydrocarbons have been extracted to the limits of economic 

production. Secondary recovery techniques have produced 

additional amounts of oil from siliciclastic reservoir rocks in 

several of these plays, particularly from the Berea, Weir, 

and Big Injun sands in the Lower Mississippian sequence. 

Pools of oil or gas remaining to be discovered in these plays 

will be small and will fall below the lower cutoff of 1 

million barrels of oil or 6 billion cubic feet of gas specified 

for inclusion in pool evaluation by play-analysis methodology for the U.S. Geological Survey and U.S. Minerals 

Management Service's national assessment (1988, p. 

27^-6) of undiscovered conventional oil and gas resources. 

In consideration of these factors, the pools were accorded 

only a small portion of the oil and gas resources estimated 

for the Appalachian basin.

Unfortunately for resource assessment, production 

data for most of these plays are scant because many were 

discovered and extensively exploited between 1859 and 

1890, which was when the first major drilling campaigns 

began in the basin. Regulations on drilling were almost 

nonexistent during those times, and very few volumetric 

data remain from this hectic period of exploration and 

development. In West Virginia, for example, channel 

filling and sheet sandstones of Pennsylvanian age produced 

more than 28 million barrels of oil (Cardwell and Avary, 

1982). The Lower Mississippian Keener, Big Injun, 

Squaw, and Weir sands in the same State produced more 

than 175 million barrels of oil, and the basal Mississippian 

Berea Sandstone (de Witt, 1970) produced more than 68 

million barrels of oil in West Virginia (Cardwell and Avary, 

1982) during this same time interval. Data for natural gas 

from these sands for the period 1859-95 in West Virginia 

are not available. Sparse production records from States 

contiguous to West Virginia are insufficient to permit 

assessment of oil and gas recovered from the shallow plays 

during the early period of drilling in the Appalachian basin. 

For plays in several States, production data, even to the 

present decade, are inadequate for definitive pool-size 

analysis and play analysis.

The siliciclastic sands and carbonate reservoir rocks 

in the shallow plays of the basin have been so thoroughly 

perforated in their nonproductive parts by wells drilled to 

test older and deeper plays that the younger Paleozoic plays 

are mainly in a terminal stage of primary exploitation. An 

example of a single-State play that has been of great 

importance in the past but is nearly completely explored at 

present is the Silurian and Devonian Corniferous karstic 

play of east-central Kentucky. The play contains karstic 

carbonate reservoir rocks of Middle to Late Silurian and 

Early Devonian ages. The larger fields in the Corniferous 

were drilled and delineated mainly just after World War I. 

Many wells produced oil prolifically, and a hectic drilling 

campaign developed as the Corniferous reservoirs were 

explored. Corniferous pools in the four-county area of 

Estill, Lee, Powell, and Wolfe Counties produced more 

than 90 million barrels of oil by primary and secondary 

recovery methods between 1918 and 1970 (Ray, 1971, p. 

1266). A more recent example of a single-State carbonatereservoir play is the Fort Payne play of northeastern 

Tennessee. In the decade from 1969 to 1979, more than 8 

million barrels of oil were produced from the Fort Payne 

Formation in eastern Tennessee (Milici and others, 1979). 

Although a modest drilling campaign continues to the 

present in the Fort Payne, much of the main productive area 

was explored during the 1970's, and only small parts of the 

play remain relatively sparsely drilled (Milici and others, 

1979). Although some oil pools remain to be found in the 

Fort Payne play, undoubtedly they will be small in size and 

in volume.

134 Evolution of Sedimentary Basins Appalachian Basin
All possibilities of finding additional oil or gas from 

the late Paleozoic plays have not been exhausted, particularly in the more deeply buried parts of the plays in southern 

West Virginia and contiguous parts of Kentucky and Virginia. Undoubtedly, small amounts of oil and gas will be 

found in the late Paleozoic plays but in decreasing volumes 

as the undrilled parts of the basin shrink in size. A 

considerable amount of the undiscovered resources in these 

younger plays will be found fortuitously in wells drilled to 

explore more deeply buried strata in the Paleozoic 

sequence.

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adjoining areas, Pennsylvania: United States Geological Sur- of Petroleum Geologists Bulletin, v. 45, no. 10, p.

vey Professional Paper 602, 150 p. 1634-1655.

Principal Oil and Gas Plays in the Appalachian Basin 137

Chapter J

Middle Eocene Intrusive Igneous Rocks of the 

Central Appalachian Valley and Ridge ProvinceSetting, Chemistry, and Implications for Crustal 

Structure

By C. SCOTT SOUTHWORTH, KAREN J. GRAY, and 

JOHN F. SUTTER

A summary of the distribution, chemistry, and 

radiometric age dates of middle Eocene intrusive 

igneous rocks in the Valley and Ridge province 

of Virginia and West Virginia

U.S. GEOLOGICAL SURVEY BULLETIN 1839 

EVOLUTION OF SEDIMENTARY BASINS-APPALACHIAN BASIN

CONTENTS

Abstract Jl

Introduction Jl

Eocene Intrusive Igneous Rocks J6

Models of Emplacement J9

Geochemical Models J9

Previous Tectonic Models J14

Proposed Tectonic Model J15 

Summary J17 

Acknowledgments J17 

References Cited J21

FIGURES

1. Regional map of the Appalachian basin J2

2. Generalized geologic map of the Shenandoah Valley and Valley and Ridge 

province of the central Appalachian foreland fold and thrust belt J3

3. Index map of Late Jurassic and middle Eocene intrusive igneous rocks showing 

radiometric age data by K-Ar and 40Ar/ 39Ar methods J4

4. 40Ar/ 39Ar age spectrum data for Late Jurassic mica pyroxenite dike J4

5. Index map of intrusive igneous rocks of this study J6

6. Plot showing classification of the middle Eocene intrusive igneous rocks on the 

basis of silica content versus Na2O + K2O J7

7. AFM projection showing basaltic to trachytic-rhyolitic composition of samples

in table 3 J12 

8-14. Photographs showing:

8. Trimble Knob, a basalt diatreme intruded in Devonian Millboro 

Shale J13

9. A peridotite porphyry dike in Silurian Tuscarora Quartzite that has 

weathered to saprolite J13

10. A sill of explosion breccia in Ordovician Beekmantown Dolomite, 

Hightown, Va., quarry J13

11. Columnar-jointed basalt east of Hightown, Va. J13

12. The northwest face of the abandoned Virginia Department of Highways 

and Transportation quarry in Hightown, Va. J14

13. Trachybasalt sill in vertical beds of Devonian Millboro Shale J14

14. Trachybasalt sill in shale beds of the Devonian Brallier Shale J15

15. Hf/3-Th-Ta ternary diagram for tectonic setting of basalts J16

16. Light and heavy rare-earth-element plots of select mafic and felsic rock 

suites J18

17. Sketch map showing structural features interpreted in this region J19

18. A, Diagram showing the proposed tectonic model of the Late Jurassic and 

middle Eocene intrusive rocks. B, Schematic block diagram illustrating the 

possible relationship of basement fracture zones to Alleghanian structures and 

Late Jurassic and middle Eocene igneous activity. C, Equal-area stereographic 

projections of poles to strikes of near-vertical dikes and sills J20

Contents III
TABLES

1. K-Ar and 40Ar/39Ar ages for intrusive igneous rocks in the central Appalachian 

Valley and Ridge province J5

2. 40Ar/39Ar age spectrum data for biotite in a Late Jurassic mica pyroxenite dike J5

3. Bulk rock analysis by optical spectroscopy for dikes, sills, and plugs J8

4. Trace-element analyses for dikes, sills, and plugs J10

5. Variations in structure, tectonics, and stress fields of the central Appalachian 

region from Late Proterozoic to present time J21

IV Contents
EVOLUTION OF SEDIMENTARY BASINS-APPALACHIAN BASIN

Middle Eocene Intrusive Igneous Rocks of the 

Central Appalachian Valley and Ridge ProvinceSetting, Chemistry, and Implications for Crustal 

Structure

By C. Scott Southworth, Karen J. Gray, and John F. Sutter

Abstract

Middle Eocene basalt and rhyolite dikes, sills, plugs, 

and diatremes intrude allochthonous Paleozoic sedimentary rocks of the Valley and Ridge province of the central 

Appalachian basin. Two main areas of silicic igneous rocks 

surrounded by basaltic rocks are found in Pendleton 

County, W. Va., and Highland County, Va. A bimodal 

distribution in this suite with alkaline trends is shown on 

projection diagrams to be a mafic group (basaltpicrobasalt-basanite) and a felsic group (trachytetrachydacite-rhyolite). Major-element and trace-element 

geochemistry of 52 samples (24 basalt, 18 trachydacite and 

rhyolite, and 10 intermediate), 25 consistent radiometric 

(11) and paleomagnetic (14) dates of middle Eocene age 

(about 48 Ma), diatremes, and minor contact metamorphism support a mode of rapid emplacement through a 

deep-seated fracture system. A Hf/3-Th-Ta ternary diagram 

shows that the nepheline-normative basalts lie in the field 

of alkaline within-plate basalts associated with slow intraplate extension. The low levels of the lithophile elements 

K, Rb, and Cs in the felsic rocks indicate a mantle origin 

with little or no crustal contamination.

A K-Ar and an 40Ar/ 39Ar date (about 148 Ma) of Late 

Jurassic age and geochemical data indicate that not all of 

the igneous rocks in Pendleton County, W. Va., are 

Eocene. Late Jurassic alkalic dikes were emplaced along a 

cross-strike basement fracture zone during Mesozoic 

extension. A change in regional strike of the alkalic dikes 

indicates a variation in stress across this zone. Northwesttrending middle Eocene intrusive rocks in Pendleton 

County, W. Va., are parallel to dikes of Late Jurassic 

extension. However, northeast-trending middle Eocene 

rocks in Highland County, Va., suggest that a local variaManuscript approved for publication May 1, 1992.

tion of the stress field may have reactivated an existing 

fabric of structural weakness. Consistent radiometric 

dates of middle Eocene age support the interpretation that 

the igneous activity was the result of a change in stress 

associated with a major reorganization of global plate 

motion from 53.5 to 37.5 Ma.

Structural discontinuities in the allochthonous Paleozoic country rock are used to interpret the general 

orientation of crustal structures that were conduits for the 

igneous rocks. The proposed tectonic model is extensional reactivation of two basement fracture zones: a 

strike-parallel growth fault of Late Proterozoic to early 

Paleozoic age and a cross-strike basement fault. Continental extension may have been the result of changes in 

motion of the North American plate.

INTRODUCTION

Mesozoic and Cenozoic igneous rocks that intruded 

allochthonous folded and thrust-faulted Paleozoic sedimentary rocks of the central Appalachian Valley and Ridge 

province provide evidence of tectonic and igneous activity 

long after the occurrence of the Alleghanian orogeny. Late 

Jurassic dikes are attributed to Mesozoic extension. Geochemistry of the middle Eocene igneous rocks shows that 

they are associated with an extensional tectonic environment (Gray and Diecchio, 1983; Gray and Gottfried, 1986). 

However, no structural setting for the tectonic model of the 

Eocene igneous rocks has been proposed. Geologic mapping, geochemical analyses, radiometric dating, compilation of known exposures, and published paleomagnetic data 

of the igneous rocks have provided insight into this problem. Mesozoic and Cenozoic intrusive igneous rocks are 

spatially associated with both surface and subsurface PaleIntrusive Igneous Rocks of the Valley and Ridge Province J1
85'

35'

200 KILOMETERS

____ EXPLANATION

____ Appalachian basin 

® Kimberlites 

N^ Dikes (Jurassic)

Dikes, sills, plugs, and diatremes (Middle Eocene)

Figure 1. Regional map of the Appalachian basin (shaded) 

showing the distribution of late Paleozoic to Cretaceous 

kimberlites along the basin axis, Early Jurassic diabase dike 

swarms in the Appalachian Piedmont and Blue Ridge, Late 

Jurassic alkalic dikes in the eastern portion of the basin in 

the Shenandoah Valley, Va., and the middle Eocene dikes, 

sills, plugs, and diatremes in the central Appalachian 

Valley and Ridge province (in the box). The box delimits 

the area of figure 5. Modified from Dennison (1983) and 

Ragland and others (1983).

ozoic structures. If the conduits for the igneous rocks were 

reactivated crustal fractures, then the relationship of basement fractures to structures in the allochthonous rocks could 

be investigated in this region of "thin-skinned" deformation.

Three general suites of intrusive igneous rocks are 

found in the Appalachian basin: (1) Mississippian to Cretaceous kimberlites, (2) Late Jurassic alkalic dikes, and (3) 

Eocene dikes, sills, plugs, and diatremes of mafic to felsic 

composition (fig. 1). This paper discusses mainly the 

Eocene intrusive rocks in the Valley and Ridge province of 

the central Appalachians; however, a general review of the 

other intrusive rocks and their structural settings follows.

Kimberlites occur in the Appalachian basin (Parrish 

and Lavin, 1982), and two localities are found in the Valley 

and Ridge province: Clear Spring, Md. (de Witt and Perry, 

1977; Kappler and others, 1986), and Mt. Horeb, Va. 

(Sears and Gilbert, 1973, 1975) (fig. 1). No isotopic ages 

are available for these two kimberlites; however, the other 

kimberlites show a decrease in apparent age from Mississippian to Permian northward across Tennessee to Cretaceous in New York (Parrish and Lavin, 1982). Two models 

for the origin of kimberlites in the Appalachian Plateaus 

province have been proposed. Parrish and Lavin's (1982, 

1983) tectonic model for the kimberlites in Pennsylvania 

and New York invokes a crustal zone of weakness at the 

intersection of cross-strike faults with strike-parallel growth 

faults. The growth faults are believed to be extensional 

structures related to the Early Cambrian Rome trough and 

the Ordovician Martinsburg trough. Dennison's (1983) 

keel-line model invokes isostatic reactivation of fractures 

parallel to the axis of the basin.

A group of north west-trending, near-vertical, Late 

Jurassic dikes occurs in central Virginia (Johnson and 

Milton, 1955; King, 1961, 1971; De Boer and Snider, 

1979), where they cross the Blue Ridge anticlinorium into 

the Shenandoah Valley (Dennison and Johnson, 1971) (fig. 

2). These dikes are an unusual suite of alkalic rocks that 

include nepheline syenite, teschenite, and picrite (Johnson 

and others, 1971). A teschenite dike and a nepheline syenite 

dike in Ordovician carbonate rocks in the Shenandoah 

Valley north of Staunton, Va. (fig. 3, samples 1 and 2), 

yielded potassium-argon (K-Ar) ages of about 155 Ma 

(Zartman and others, 1967; Marvin, 1968; and Johnson and 

others, 1971) by use of the new decay constants and 

isotopic abundance ratios for K-Ar (Steiger and Jager, 

1977). Table 1 provides the recalculated data of all published K-Ar ages in this area, and the sample locations are 

shown in figure 3. Biotite from a mica pyroxenite dike in 

Pendleton County, W. Va. (fig. 3, sample 3), yields an 

40Ar/ 39Ar plateau age of 147 Ma (table 2 and fig. 4). 

Contrary to what has been published on recent maps of the 

area (Manspeizer and others, 1989), this dike appears to 

mark the known western limit of this Late Jurassic event. 

The variation in trend of the Late Jurassic dikes in the 

Shenandoah Valley (fig. 2) probably represents a change in 

the stress field of the basement during emplacement. In 

general, the northwest trend of the dikes suggests a 

northeast-oriented axis of greatest tension or least compresFigure2. Generalized geologic map of the Shenandoah ^ 

Valley and Valley and Ridge province of the central 

Appalachian foreland fold and thrust belt showing the 

Late Jurassic alkalic dikes and middle Eocene intrusive 

igneous rocks. Generalized geology after Milici and 

others (1963) and Cardwell and others (1968). Cross 

section modified from Woodward and others (1985); 

vertical lines in cross section are schematic dikes.

|2 Evolution of Sedimentary Basins Appalachian Basin
I WILLS MOUNTAIN ANTICLINORIUM^ I BRQAJPTQP SYNpUNQRJU.M__J_ 

*£

S

QAPTQP SYNpUNt 78°45'

A

KILOMETERS 

SEA LEVEL

10-

^^1 Mississippian rocks 

D Devonian rocks 

S I Silurian rocks 

O | Ordovician rocks 

 Cambrian rocks 

'B ' A Proterozoic rocks

EXPLANATION

Contact

Anticline Showing crestline and direction of plunge where known

Syncline Showing trough line

Overturned syncline Showing trace of axial surface and direction of dip of limbs

Thrust fault Sawteeth on upper plate

Igneous dike

Igneous sill, plug, or diatreme

Intrusive Igneous Rocks of the Valley and Ridge Province J3
79°15'

38°30'-A

Figure 3. Late Jurassic and middle Eocene intrusive igneous rocks from the Great Valley to the Appalachian Plateaus 

structural front. Radiometric age data by K-Ar and 40Ar/39Ar methods are listed for the numbered samples in table 1.

200

150

100

50

Plateau age = 147.0 ± 0.7 Ma 

K-Ar age = 149.2 ± 1.7 Ma

10 20 30 40 50 60 70 

ArK RELEASED (PERCENT)

80 90 100

Figure 4. 40Ar/ 39Ar age spectrum data for Late Jurassic mica 

pyroxenite dike. (See table 1, sample 3, and fig. 3, sample 

3.)

sion; this interpreted orientation of the stress ellipse is 

coaxial with Alleghanian deformation.

Mica pyroxenite dikes, similar to the dated Late 

Jurassic dike, occur near Martinsburg, W. Va. (Mann, 

1955; Donaldson and others, 1964), and Front Royal, Va. 

(Young and Bailey, 1955). These dikes are undated, as is a 

kimberlite near Mt. Horeb, Va. (Sears and Gilbert, 1973, 

1975).

Intrusive rocks that range in composition from basalt 

to rhyolite occur as dikes, sills, plugs, and diatremes in the 

western portion of the Valley and Ridge province near the 

Appalachian Plateaus structural front (fig. 2). These intrusive rocks were long thought to be Mesozoic (Darton and 

Diller, 1890; Johnson and Milton, 1955; and Zartman and 

others, 1967). However, in an attempt to date the Devonian 

Tioga Ash Bed (Johnson and others, 1971; Dennison, 

1975), Fullagar and Bottino (1969) dated an andesite sill 

(fig. 3, sample 6), which was Eocene. Eleven K-Ar and 

40Ar/ 39Ar dates and paleomagnetic data of 14 samples show 

a consistent age of middle Eocene for the igneous rocks in 

this region. These are the youngest igneous rocks in the 

Eastern United States and recently have been called the 

Shenandoah igneous province (McHone, 1988; Vogt, 

1991). Previous workers (Zartman and others, 1967; Fullagar and Bottino, 1969; Dennison and Johnson, 1971;

|4 Evolution of Sedimentary Basins Appalachian Basin
Table 1. K-Ar and 40Ar/ 39Ar ages for intrusive rocks in the central Appalachian Valley and Ridge Province 

[B, biotite; H, hornblende; WR, whole rock; Do., ditto]

Sa(see' e Rock unit 

fig. 3) or *yPe

Geochemical 

sample

Mineral »»±' K ,%)

tables 3 

and 4)

40Ar (moles/ Apparent 

gram x 10~9 ) age* (Ma) Reference

Late Jurassic

1 . . . Nepheline sy

do. .........

enite dike

2 ... - - Teschenite dike . . . . .

3

do. .........

do. .........

do. .........

lite dike .

B .....

H .....

B .....

H .....

WR ..

WR ..

B.....

............................... ....... 148 + 7 ......

... 2

... 2,

... 6

.56 

56

.10

0.666 ....

.677 .....

1.644 ....

... 157 +

... 156 +

... 155 +

... 143.8 =

. . . 146.2 :

. . . 149.2 :

8

5

10 . . . . .

h

(-

H

1 8

1 7

1 7

. . Zartman and others (1967).

.. Do.

.. Do.

. . This work; supersedes Core

and others (1974) and Ressetar 

and Martin (1980). 

.. Do.

.. Do.

Middle Eocene

4

5

6

7

8

9

10

11

13

. . Tephrite basa

do. .........

. . Basalt dike. .

. . Basalt dike..

. . Trachydacite

do. .........

. . Basalt dike. .

mite dike.

dike/sill .

dike

WR...

B .....

B .....

B ..... 

WR ...

WR...

WR ... 

WR ..

WR...

WR ..

WR...

46

.. 38 .........

31

, . . 29, 52 . . . . 

... 36, 51 ....

.. 49 ........

.. 18........

.. 21,47 ....

... 6

... 1.

... 1. 

... 1.

... 3.

... 3.

.34

'66 

19

.24 

06

78

71

.532 ..... 

.0470 ....

.0903 ....

.0998 .... 

.0881 ....

.284 .....

292

. . . 48 + 1

44

... 48.1 +

. . . 48.4 +

. . . 47.7 ± 

... 35.0 +

... 43.1 +

... 45.8 ± 

... 47.3 +

. . . 42.8 +

... 44.8 +

... 47.1 ..

1

1

0 

0

0 

0

0

0

1

3

.6....

5

1

.6....

8

5

6

. . Wampler and Dooley (1975).

. . Hunt (1974).

. . Fullagar and Bottino (1969).

.. Do.

. . This work; supersedes Core 

and others (1974) and Ressetar 

and Martin (1980). 

.. Do.

.. Do.

.. Do. 

.. Do.

.. Do.

.. Do.

. . Ressetar and Martin (1980).

* All apparent ages have been recalculated on the basis of decay constants and isotopic abundance ratios for potassium and argon recommended by 

Steiger and Jager (1977). The conversion tables published by Dalrymple (1979) were used in the recalculations.

Table 2. 40Ar/ 39Ar age spectrum data for biotite in a Late Jurassic mica pyroxenite dike

[Sample 3, fig. 3 and table 1; / = 0.004833]

Temperature (°C)

600...............

800...............

900...............

1,025...............

1,100...............

1,400...............

Total gas .......

40Ar/ 39Ar 

(measured)

28.67

18.83

18.26

18.17

18.55

18.60

19 25

36Ar/ 39Ar 

(measured)

39ArK 40ArR 

(% of total) (% of total)

0.03676 6.88 62.2 

.00400 30.73 93.7 

.00236 12.81 96.2 

.00247 14.76 96.0 

.00302 11.85 95.2 

.00368 22.98 94.2 

.00563 100 91.4 

Plateau (800°C-1,400°C) age = 

Conventional K-Ar age =

Age1 

(Ma)

148.9±2.2 

147.7±1.2 

147.0±1.1 

146.0±1.1 

147.7±1.1 

146.6±1.2 

147.2 

147.0±0.7 

149.2±1.7

1 Biotite mineral separate of >99% purity was irradiated together with neutron flux monitor DY-8C-71 

(Sutler and Smith, 1979) in the Central Thimble Facility of the U.S. Geological Survey TRIGA reactor (GSTR) 

at the Federal Center in Denver, Colo. (Dalrymple and others, 1981). Corrections for argon isotopes produced 

during irradiation are those suggested by Dalrymple and others (1981) for the Central Thimble. Decay constants 

and isotopic abundance ratios are those recommended by Steiger and Jager (1977). The definition of an age 

"plateau" is that proposed by Fleck and others (1977), and the error in age (1 sigma) has been calculated by use 

of the equation suggested by Dalrymple and others (1981).

Rader and others, 1986) attribute this igneous activity to the 

38th parallel lineament of Heyl (1972).

One purpose of this investigation is to reexamine the 

geochemical data base of the intrusive rocks in the Highland 

County, Va., and Pendleton County, W. Va., region and to

add to isotopic evidence in support of a new interpretation 

of the tectonic environment. Minor-element geochemical 

data suggest a tectonic environment of continental extension 

(Gray and Diecchio, 1983; Gray and Gottfried, 1986). 

Surface and inferred subsurface structures in the allochthoIntrusive Igneous Rocks of the Valley and Ridge Province J5
79°15'

38°30' -

EXPLANATION 

K-Ar/ 40Ar/ 39Ar date 

Paleomagnetic date 

Both K-Ar and paleomagnetic date

Figure 5. Intrusive igneous rocks in the study area. Numbers refer to geochemical data in tables 3 and 4. Data originally 

compiled on 1:24,000-scale topographic maps.

nous Paleozoic host rocks are used to support this tectonic 

model of emplacement. Since the distribution of Late 

Jurassic and middle Eocene intrusive rocks in this region 

has been unclear (Rader and others, 1986; Manspeizer and 

others, 1989), we define the respective areas of igneous 

activity by showing the location of samples with radiometric and paleomagnetic data. Trace-element geochemical 

signatures of the Jurassic and Eocene rock suites appear to 

be different (Gray and Gottfried, 1986); therefore, this 

method is used to show that both Late Jurassic and middle 

Eocene rocks spatially overlap.

EOCENE INTRUSIVE IGNEOUS ROCKS

Eocene intrusive igneous rocks of mafic and felsic 

composition (Fullagar and Bottino, 1969; Hunt, 1974;

Lovlie and Opdyke, 1974; Wampler and Dooley, 1975; 

Ressetar and Martin, 1980) occur in the Valley and Ridge 

province as dikes, sills, plugs, and diatremes (fig. 5). K-Ar 

and 40Ar/ 39Ar dates (table 1 and fig. 3) and paleomagnetic 

data (Lovlie and Opdyke, 1974; Ressetar and Martin, 1980) 

suggest that most of the igneous rocks in this region are 

Eocene. Geochemical data of dated samples from sites in 

figure 5 and from table 1 are shown in tables 3 and 4. In 

general, K-Ar dates suggest that the Eocene igneous activity 

was short lived (probably not more than a few million 

years). These Eocene intrusive rocks represent the youngest 

known igneous activity in the Eastern United States.

The igneous rocks were first recognized by Rogers 

(1884) and have been studied by Darton and Diller (1890), 

Darton (1894, 1899), Darton and Keith (1898), Butts

|6 Evolution of Sedimentary Basins Appalachian Basin
£ 8

i 

^

95 7

LLJ

°~ 5 03 J

2

4

3

2

1

Basaltic 

Trachyandesite

Trachyte

 30

20* 29® 39 

15* !* 

 33 

 32 26

Trachydacite 31

 37

 40

 9

Rhyolite

43

J» 28 ' 

36®

27*

Picrobasalt

044 

 17

®49 

148

 16

046 

>25

Basalt

Basaltic 

Andesite

Andesite

Dacite

40 45 50 55 60 65 70 75

SiO, (WEIGHT PERCENT)

Figure 6. Classification of the middle Eocene intrusive igneous rocks on the basis of silica content versus Na2O + K2O 

(after Le Bas and others, 1986). Circles denote dated samples. Sample numbers from figure 5 and table 3.

(1933), Johnson and Milton (1955), Garner (1956), 

Core (1971), Johnson and others (1971), Sutler (1976), 

Gray and Diecchio (1983; unpub. data, 1992), Rader and 

others (1986), and Gray and Gottfried (1986). Field mapping suggests that the igneous activity was restricted to 

portions of Highland County, Va., and Pendleton County, 

W. Va. The distribution of known igneous rocks is partly 

due to good exposures in agricultural valleys underlain by 

carbonate and shale rocks and to extensive mapping in the 

adjacent areas (Garner, 1951; Kapnicky, 1956; Duncan and 

others, 1969; Kettren, 1970; Lesure, 1982).

On the basis of major-element geochemistry, the 

igneous rocks can be classified after LeBas and others 

(1986) (fig. 6, table 3). This classification shows a primarily bimodal distribution on the basis of silica content vs. 

Na2O + K2O (fig. 6). The mafic rocks (SiO2 of 42 to 52 

weight percent) occur within the basalt (9), picrobasalt (2),

and basanite (8) fields, while the felsic rocks (SiO2 of 64 to 

71 weight percent) cluster within the trachyte-trachydacite 

(15) and rhyolite (2) fields. Nine samples are intermediate 

in composition (fig. 7). Seven samples from diatremes 

include picrobasalt (2), basalt (4), and one andesite that are 

altered and contaminated by country rock; therefore, the 

geochemical data are provided at the end of the table and are 

not further analyzed.

The mafic rocks are widely distributed and surround 

two areas of silicic activity in Highland County, Va., and 

Pendleton Co., W. Va. The easternmost outcrop of Eocene 

age (48 ± 1 Ma; K-Ar whole-rock age recalculated by use of 

new constants) is Mole Hill, an olivine-spinel basalt plug 

intruded into Ordovician carbonate rocks of the Shenandoah 

Valley (Wampler and Dooley, 1975) (fig. 3 and table 1, 

sample 4). The basalts are predominantly very fine grained 

and are dark gray (N 3) to black (N I). Several dikes and

Intrusive Igneous Rocks of the Valley and Ridge Province |7
Table 3. Bulk rock analysis by optical spectroscopy for dikes, sills, and plugs

[Performed in the laboratories of the U.S. Geological Survey. H. Smith, analyst. Six altered and contaminated samples at the end of the table are from 

indicates Eocene age determined by: A, K-Ar and 40Ar/ 39Ar; B, paleomagnetic data (Lovlie and Opdyke, 1974; Ressetar and Martin, 1980); and C, both

Picrobasalt

SiO, .........

A1263 ........

Fe2O3 ........

FeO .........

MgO. ........

CaO .........

Na,O ........

K,6 .........

H,O+ ........

H.CT ........

TiO2 .........

p n

MnO. ........

CO2 .........

Total ....

SiO2 .........

A12O3 ........

Fe,O3 ........

FeO .........

MgO. ........

CaO .........

Na^O ........

K26 .........

H2O+ ........

H2O~ ........

TiO, .........

P205 .........

MnO. ........

CO, .........

Total ....

1*

42.6 

12.6 

5.8 

4.6 

9.4

13.3

2.2 

.54 

3.2 

1.8

2.5 

1.1 

.13 

.07 

99.84

16*

43.3 

16.4 

6.6 

3.8 

4.3

11.3 

2.0 

1.3 

3.4 

2.8

1.8 

.75 

.19 

.87 

98.81

27

41.6 

13.3 

4.9 

6.7

7.4

13.5 

1.5 

1.1 

1.0

1.8

2.3 

.35 

.17 

4.9 

100.52

17

43.4 

15.9 

9.0 

4.0 

5.6

7.7 

2.7 

1.4 

3.0 

2.6

2.9 

1.1 

.21 

.26 

99.77

13

43.0 

16.4 

5.3 

7.9 

6.7

10.9 

2.8 

.75 

1.3 

.51

2.9 

.52 

.20 

.02 

99.20

25

42.3 

13.2 

4.8 

6.0 

9.7

11.7 

1.6 

.80 

1.9 

1.7

1.8 

.39 

.18 

4.5 

100.57

28

43.3 

14.9 

5.6 

7.6 

6.4

10.8 

1.9

1.7 

2.7 

1.3

2.7 

.55 

.20 

.05 

99.70

44

45.5 

17.3 

4.9 

7.5 

5.1

10.1

3.2 

1.3 

.93 

.67

2.9 

.63 

.22 

.13 

100.38

34B

41.0 

14.6

5.3 

8.3 

8.0

11.4 

2.6 

1.4 

1.9 

1.0

3.2 

.41 

.19 

.37 

99.67

Basalt

46A

45.6 

14.9 

3.4 

7.2 

10.0

12.4 

2.2 

.70 

.73 

.47

1.5 

.36 

.19 

.1 

99.75

Tephrite Basanite

36C

44.4 

14.1 

3.5 

8.2 

10.1

12.2 

2.3 

1.1 

1.2 

.55

2.2 

.47 

.19 

.12 

100.63

38C

41. 

14. 

7. 

6. 

8.

11. 

3.

1. 

1.

2. 

100.

,5 

,8 

.0

,4 

,7

.6 

,0

,54 

,8 

,4

,7 

,38 

19 

13

.14

41

43.2 

15.6 

3.7 

9.4 

8.8

11.4 

2.1

1.5 

1.4 

.55

2.7 

.55 

.19 

.1 

101.19

42

43.4 

16.1 

5.8 

7.6 

6.4

11.1

2.2 

1.7 

1.9 

.92

2.8 

.58 

.21 

.3 

101.01

43

44.0 

13.2 

4.6 

7.5 

11.8

13.0 

1.9 

1.1 

.54

.32

2.2 

.48 

.18 

.04 

100.86

Trachybasalt

48 49C

46.8 47, 

14.4 13. 

9.05 4. 

4.18 7. 

5.52 6.

8.00 8. 

2.88 3. 

1.19 1. 

3.63 3. 

1.55

2.86 2. 

.78 

.24 

.16 

101.24 100.

.8 

,8 

,38 

,77 

,80

,28 

18 

,30

,25 

,77

41 

64 

20 

,26 

69

50B

45.4 

13.5 

5.21 

6.11 

7.34

10.45 

1.97 

.98 

4.84 

2.01

2.10 

.64 

.20 

.26 

101.01

51C

47.4 

13.0 

2.85 

8.38 

9.73

11.83 

2.33 

1.04 

.96

.25

2.10 

.46 

.18 

.12 

100.63

8

49.0 

17.8 

5.0

4.1

2.2

8.9 

4.1 

1.7 

.80 

1.0

1.9 

1.0 

.19 

.92 

98.61

19B

48.3 

20.4 

4.3 

4.2 

2.1

5.7 

4.4 

.80 

2.6

2.4

1.5 

1.1

.42 

.44 

98.66

diatreme breccias are porphyritic basalt with large olivine 

and augite phenocrysts. The basalts are nepheline normative. The trachydacite and rhyelites are predominantly 

aphanitic and medium to light gray (TV 5 to TV 7) and weather 

to yellowish gray (5F8/1). However, some felsic rocks are 

porphyritic with phenocrysts of feldspar, biotite, and (or) 

hornblende.

Outcrops of the igneous rocks are discontinuous, and 

exposures range in width from less than 1 m to over 100 m. 

Mafic rocks are generally resistant to erosion and form 

topographic knobs (fig. 8) and ridges, whereas felsic rocks 

are more likely to be deeply weathered to saprolite (fig. 9). 

The igneous rocks crop out at elevations ranging from 548 

m in valley bottoms to 1,329 m on ridges. Exposed contacts 

of the igneous rocks with Ordovician to Devonian sedimentary rocks show little contact metamorphism. Diatremes and

volcanic breccias indicate rapid and forceful emplacement. 

Breccia zones as much as 2 m thick in carbonate rock (fig. 

10) suggest volatile exchange of CO2 by gas fluidization 

during intrusion (Johnson and others, 1971). The Ugly 

Mountain diatreme in Pendleton County, W. Va., is one of 

several large diatremes that shows layered breccia composed predominantly of the Paleozoic host rock. Columnarjointed aphanitic basalt (fig. 11) and volcanic glass suggest 

near-surface emplacement.

Some Eocene dikes have orientations that parallel the 

northwest trend of Late Jurassic dikes, so relationships 

between age and strike (Core and others, 1974) are tenuous. 

Eocene dikes and sills trend both northwest and northeast. 

The conjugate trends suggest that either (1) the stress field 

changed, (2) two stress fields were active, or (3) the 

intrusions were emplaced along near-surface fractures not

J8 Evolution of Sedimentary Basins Appalachian Basin
diatremes; the seventh sample is a basalt dike. All analyses are in weight percent. Sample localities are shown in fig. 5. Letter adjacent to sample no. 

A and B. Samples with an asterisk (*) have geochemical signatures of Late Jurassic igneous rocks]

Trachyte-Trachydacite

12

67.5

16.2

3.0

.28

.24

.63

6.0

4.0

.70

.50

.16

.04

.07

<.01

99.32

14

65.8

17.9

2.2

.28

.26

1.6

6.0

3.7

.87

.63

.30

.13

.03

<.01

99.70

15 20 21A 26 29C

65.7 64.0 67.0 65.4 65.2

17.5 18.2 16.6 17.2 16.8

2.8 3.6 2.4 3.0 1.1

1.1 .66 .96 .16 2.0

.58 .14 .18 .16 .19

1.8 .90 .88 1.2 1.5

6.2 5.0 5.7 5.1 4.1

3.5 4.7 3.8 4.0 5.6

.54 1.6 .96 1.3 2.6

.56 .55 .24 .67 .34

.36 .04 .04 .30 .20

.15 .08 .06 .09 .06

.13 .04 .03 .11 .18

.09 <.01 .01 .01 .25

101.01 99.51 98.86 98.70 100.12

30

65.6

18.1

1.2

.36

.24

1.4

5.7

4.4

.88

.62

.47

.11

.05

.04

99.17

31C

66

18

1

1

4

4

1

1

100

.8

.5

.4

.29

.21

.0

.6

.2

.9

.20

.19

.07

.02

.011

.39

32B

64.1

17.6

2.9

.60

.40

2.0

5.3

3.7

.9

1.5

.38

.13

.04

.03

99.58

33B

64.8

19.3

1.8

.20

.09

1.6

5.3

4.0

1.5

.92

.50

<.01

.04

.02

100.08

Diatreme Breccias

Basaltic Trachyandesite Trachyandesite

7

52.4

17.4

7.7

1.8

2.2

5.7

4.5

1.9

1.2

1.8

1.8

.45

.17

.01

99.03

10

50.3

16.5

8.4

1.9

2.2

6.7

4.2

1.8

1.5

1.9

2.0

.47

.32

.43

98.62

11 35 45 5B 69

49.0 52.5 51.7 53.3 54.1 68

16.2 18.7 17.5 18.0 15.4 16

7.2 4.3 6.4 4.3 5.7 1

1.8 2.2 3.6 1.2 1.5

1.7 1.3 2.6 1.2 1.8

6.9 5.7 7.9 5.7 5.8

3.8 4.4 4.4 4.2 4.3 6

1.9 2.0 1.9 1.9 2.4 3

1.8 1.3 .6 1.6 1.2

3.2 4.0 1.0 3.6 2.8

1.9 1.8 1.6 1.7 1.3

.46 .81 .93 .73 .34

.19 .08 .17 .06 .13

2.6 1.9 .6 1.3 2.2

98.65 100.99 100.90 98.79 98.97 98

Rhyolite

40

.6 68.

.3 16.

.6 1.

.08 <.

.21

.66

.0 6.

.9 5.

.60

.60

.16

.04

.02

.01

.78 99.

Picrobasalt

9

3

4

01

10

39

3

1

5

47

18

05

06

02

78

4

38.3

11.8

11.3

.12

8.3

12.0

.72

.86

3.8

6.0

1.6

.38

.26

4.8

100.22

23

34.8

11.4

9.1

.72

5.6

18.0

.81

.72

2.9

3.8

1.5

.37

.23

9.8

99.75

2*

40.0

19.9

9.7

1.1

3.8

3.0

<.01

.80

8.1

8.9

3.2

2.1

.06

.01

100.67

37

61.2

17.0

4.1

.48

1.4

2.5

4.9

3.0

1.6

3.1

.79

.23

.10

.03

100.43

39

65.8

16.8

2.3

.16

.23

1.4

5.6

4.0

.7

1.6

.35

.11

.02

.02

99.09

47C

66.4

16.9

2.35

.98

.02

1.18

4.90

4.38

1.04

.47

.15

.08

.26

.41

99.52

52C

67.1

17.0

.97

1.81

.37

1.35

4.62

4.26

1.21

.47

.29

.15

.20

.24

100.04

: Altered and Contaminated

Basalt

3

37.5

10.3

1.5

1.0

4.8

17.7

.80

2.9

3.0

3.4

.26

.09

.08

15.7

99.03

ISA

44.3

17.9

7.1

6.1

3.7

3.0

2.5

1.6

4.4

4.6

2.3

.72

.22

.44

98.88

22

43.0

15.4

5.3

7.5

4.9

7.9

3.1

1.4

1.2

2.0

2.0

.79

.19

6.3

100.98

Andesite

24*

53.7

12.6

3.0

1.3

3.3

9.0

1.9

2.9

2.1

2.6

.54

.19

.10

6.4

99.63

related to the trend of the basement fracture conduit. The 

intrusive rocks undoubtedly utilized preexisting Alleghanian fractures. Longitudinal joints, cross joints, and 

oblique fracture sets provided conduits for dikes (figs. 9 and 

12), while bedding surfaces provided conduits for sills 

(figs. 10, 13, and 14).

Minor mineralization is associated with some dikes 

(Mitchell and Freeland, 1986). Sulfide minerals occur in a 

trachybasalt dike near the Ugly Mountain, W. Va., diatreme (fig. 5, sample 19). Local residents report that 

drilling of the diatreme in the late 1960's yielded shows of 

gold and uranium. Herbert and Young (1956) speculated 

that dikes provided the hydrothermal fluids for sulfide 

mineralization near Timberville, Va. Brucite marble, containing 17 percent brucite, has been recognized recently in 

the Hightown, Va., quarry at the contact of an Eocene

trachydacite dike with dolomite of the Lower Ordovician 

Beekmantown Group (Giannini and others, 1987) (fig. 12).

MODELS OF EMPLACEMENT

Geochemical Models

Trace-element geochemistry of 46 samples is provided in table 4. Both the major-element and stable traceelement geochemistry indicate alkaline trends (tables 3 and 

4). The Zr abundance is 600 ppm in sample 33 (table 4), a 

level which is considered to be the lower boundary for 

peralkaline rocks. A Hf/3-Th-Ta ternary diagram (fig. 15) 

shows that the basalts lie in the field of alkaline within-plate 

basalts; the tectonic environment associated with this rock

Intrusive Igneous Rocks of the Valley and Ridge Province J9
Table 4. Trace-element analysis for dikes, sills, and plugs

[Work performed in the laboratories of the U.S. Geological Survey. R. Johnson, analyst. All samples analyzed by INAA except Sr, Nb, and Y, which 

Eocene age determined by: A, K-Ar and 40Ar/ 39Ar; B, paleomagnetic data (Lovlie and Opdyke, 1974; Ressetar and Martin, 1980); and C, both A and

Picrobasalt

1* 27 13

Tephrite Basanite

28 34B 36C 38C 41 42 43

Large Cations

Rb . . . . 

Ba . . . . 

Sr..... 

Cs ....

23. 

4,475 

1,190 

32.

.2 

,2

1

19.1 

,760

772 

.36

18 

429 

692 

.30

28.6 30 24 

430 509 340 

770 642.8 619.8 

.36 <.4 <2.0

60 

470 

608.7 

3.6

34 

363 

638. 

<.

5 

7

30 

403 

804.4 

.8

29 

361

.31

High- Valence Cations

Th .... 

U .....

Zr..... 

Hf . . . .

Nb . . . . 

Ta .... 

Th/U .. 

Zr/Hf . .

5. 

1. 

155

3, 

76 

5. 

4. 

43.

.21 

,12

,50

,31 

.58 

,56

2.07 

2.5 

61 

2.93 

27 

1.62 

.84 

20.75

2.99 

.95 

135

4.21 

38 

2.38 

3.152 

32.03

2.62 2.8 2.7 

<2 .6 <2.0 

175 140 

4.22 4.1 3.5 

33 32.8 30.1 

2.12 2.44 2.06 

4.7 

41.48 34.1

2.4 

<3.0 

120 

3.8 

25.9 

1.97

31.6

2. 

<4. 

195 

4. 

33. 

2.

46.

7 

0

2 

2

27 

4

2.6 

<3.0 

190 

4.4 

28.9 

2.26

34.2

2.17 

.64 

128 

3.53

1.84 

3.4 

36.2

Ferromagnesian Elements

Co .... 

Zn .... 

Cr. . . . .

Sc. . . . .

27. 

108 

486

35.

,5 

,2

50.4 

76 

236 

32.8

44.9 

93 

43.1 

25.1

40.0 48.6 52.8 

98 91 96 

26.2 21.1 381.0 

22.0 31.90 30.70

65.5 

110 

294 

38

55. 

Ill 

209 

30.

8 

70

41.4 

109

22.5 

22.50

55.7 

94.4 

627 

34.3

Rare Earth Elements

La .... 

Ce ....

Nd . . . . 

Sm . . . . 

Eu . . . . 

Gd . . . . 

Tb .... 

Tm . . . . 

Yb . . . . 

Lu .... 

Y .....

47. 

96. 

47 

8. 

2. 

8.

<.

1.

22

16*

,4 

,2

9

,57 

1 

,92 

,2 

64 

240

17

20.7 

38.3 

21 

4.97 

1.55 

6.1 

.66 

.25 

1.80 

.248 

17

Basalt

25

27.2 

53.2 

29 

7.04 

1.97 

6.8 

.885 

.35 

1.92 

.39 

26

44

21.0 28 27 

52.0 53 49 

28.0 29 27 

6.0 7.4 6.3 

2.10 2.22 1.81 

7.8 7.3 5.8 

.90 .98 .78 

.33 .38 .34 

2.04 2.2 1.8 

.30 .31 .27 

21 24.1 22.4

Trachybasalt

46A 8 19B

22 

44 

20 

6.1 

1.85 

5.5 

.85 

.24 

1.7 

.25 

19.6

26 

49 

27 

6.

2.

7.

1.

27.

8 

16 

4 

84 

31 

9 

30 

2

27 

50 

29 

6.9 

2.20 

6.8 

.85 

.42 

2.2 

.32 

23.8

23.5 

45.3 

28.5 

6.50 

1.72 

5.9 

.72 

.29 

1.74 

.242

Basaltic Trachyandesite

7 10 11 35 45

Large Cations

Rb . . . . 

Ba . . . .

Sr.....

Cs ....

174 

3,890 

1,900 

50.5

1

32.1 

,580 

772 

.50

20 

570 

684

.42

19

449 

1,049 

<.7

17 41.8 20.5 

385 782 709 

547.2 1,190 1,090 

<.9 .34 .83

25 

870 

1,030 

1.28

35 

800 

946 

.33

38 

681 

806

.34

41 

657

2.3

42 

773 

1080.8

.7

High-Valence Cations

Th .... 

U .....

Zr. . . . .

Hf . . . . 

Nb .... 

Ta .... 

Th/U .. 

Zr/Hf . .

16.8 

2.7 

241 

5.14 

122 

6.30 

6.24 

46.92

4.26 

1.2 

171 

4.55 

55 

2.86 

3.47 

37.64

2.85 

<3 

112 

2.97 

38 

2.09

41.75

3.7 

<3.0 

260 

5.1 

31.7 

2.78

50.9

3.5 5.50 6.28 

<2.0 1.50 1.5 

150 277 257 

2.5 6.93 5.57 

30.4 51 70 

1.51 3.42 3.84 

3.67 4.105 

60.0 40.00 46.12

5.90 

1.15 

261 

7.09

52 

3.75 

5.13 

36.87

4.82 

1.68 

265 

6.36 

50 

3.10 

3.01 

41.74

4.72 

1.22 

256 

6.09 

45 

3.03 

3.88 

42.02

5.3 

1.2 

250 

6.6

3.65 

4.4 

37.9

5.7 

1.9 

336 

7.7 

42.7 

4.25 

3.0 

43.6

Ferromagnesian Elements

Co .... 

Zn .... 

Cr. . . . .

Sc. . . . .

41.0 

86 

313 

21.1

25.8 

80 

3.0 

13.69

46.8 

78 

380 

26.2

28.9 

107 

36.4 

17.50

52.5 11.77 18.5 

89 94 11.8 

378.0 5.4 4.5 

36.70 9.02 8.48

18.1 

97

4.3 

12.48

27.1 

96.5 

3.8 

13.76

22.3 

78 

3.93 

12.18

6.2 

94 

1.6

5.74

17.7 

126 

1.0 

10.30

Rare Earth Elements

La .... 

Ce . . . .

Nd . . . . 

Sm . . . . 

Eu . . . . 

Gd . . . . 

Tb .... 

Tm . . . . 

Yb . . . . 

Lu .... 

Y .....

128 

174 

61 

10.8 

2.80 

7.2 

1.19 

<.2 

3.0 

.41 

26

41.3 

77.7 

42 

9.11 

2.68 

8.8 

1.12 

<.5 

2.48 

.36 

36

26.4 

48.9 

25.9 

5.58 

1.61 

5.7 

.71 

.32 

1.61 

.24 

22

35 

66 

35 

8.3 

2.66 

8.3 

1.09 

.37 

2.7 

.40 

23.4

29 50.6 46.8 

44 96.4 93.4 

21 46.4 44.7 

4.8 10.35 9.98 

1.53 2.97 2.54 

6.1 8.7 9.2 

.84 1.20 1.16 

.46 .389 <.l 

2.7 3.16 2.50 

.46 .459 .318 

27.9 31 36

61.7 

101.6 

55 

11.0 

3.04 

9.2 

1.20 

.55 

3.25 

.456 

32

57.3 

95.7 

48.4 

10.25 

2.91 

9.3 

1.20 

.45 

3.14 

.465 

43

42.3 

83.5 

42 

8.41 

2.51 

7.5 

.95 

.34 

2.32 

.343 

27

46 

91 

47 

9.4 

2.97 

9.2 

1.18 

.42 

2.8 

.37

54 

107 

54 

9.9 

3.16 

9.5 

9.5 

.65 

2.9 

.41 

23.1
were analyzed by XRF. All analyses are in parts per million. No trace-element data are available for samples 47-52. Letter adjacent to sample no. indicates 

B. Samples with an asterisk (*) have geochemical signatures of Late Jurassic igneous rocks]

29C 30 31C 32B 33B

Trachyte-Trachydacite

37 39 12 14 15 20 21A 26

Large Cations Continued

114 

1,100

1.2

96 

1,290 1 

369.8 

<.3

92 70 

,030 3,050 2 

198.1 

<.2 .4

80.5 

,,890 

433.3 

<.4

64 90 99.3 75 78 

1,017 1,200 1,300 1,550 1,690 

492.9 347.7 145 595 591 

.4 .2 .276 .154 .170

68 

1,680 1 

319 

.530

80 

,280 

239 

.254

91.9 

1,430 

330 

.152

High- Valence Cations Continued

8.9 

2.6 

402 

9.3

4.56

3.42 

43.2

14.2 

3.6 

586 

13.2 

83.0 

6.08 

3.9 

44.4

16.9 12.6 

3.1 2.4 

490 463 

11.9 11.7 

81.9 

6.33 5.23 

5.45 5.25 

41.3 39.6

14.95 

3.9 

601 

13.15 

78.6 

6.02 

3.6 

45.7

10.9 14.4 14.1 9.07 8.67 

2.8 2.8 2.24 1.8 2.19 

408 505 369 575 546 

9.0 12.5 10.3 13.5 12.9 

79.9 79.9 111 65 58 

5.31 5.99 7.19 4.36 4.30 

3.9 5.1 6.31 4.70 3.96 

45.3 40.4 35,91 42.74 42.44

23.1 

5.25 

346 

10.82 

170 

10.25 

4.39 

31.98

22.2 

4.8 

330 

10.48 

160 

9.90 

4.65 

31.16

15.8 

5.1 

459 

12.43 

114 

7.21 

3.12 

36.88

Ferromagnesian Elements Continued

.6 

86 

<3.0 

.96

.6

31 

<8.0 

.8

.7 1.0 

85 160 

<9.0 <9.0 

1.13 1.22

.6

138 

<10.0 

1.52

1.1 .2 .75 .501 1.62 

95 61 81 74 78 

<10.00 <10 2.33 .90 2.71 

2.01 .82 .271 .766 .94

6.12 

26.2 

1.08 

.378

2.62 

14.5 

1.6 

.316

5.77 

87.8 

2.1

.722

Rare Earth Elements Continued

65 

107

48 

7.2 

1.81

3.2 

.47

86 

150 

59 

10.0 

2.60 

8.2 

1.27 

.37 

3.9 

.50 

34.5

139 92 

188 153 

89 70 

14.6 11.4 

3.00 3.15 

10.2 9.3 

1.82 1.51 

<.30 .54 

4.3 3.9 

.57 .53 

41.5

70 

117 

49

7.8 

2.37 

6.3 

.97 

<.30 

2.8 

.41 

26.5

83 128 22.2 74.2 64.7 

130 139 109 107 116.5 

62 108 15.9 46.2 41.2 

9.6 17.1 3.63 7.80 7.56 

2.93 4.16 1.63 2.27 2.08 

6.3 13.1 4.4 4.75 5.4 

1.01 1.88 .51 .764 .83 

<.30 .73 <.08 <.08 .39 

3.1 4.7 3.71 2.44 2.91 

.44 .62 .444 .338 .455 

31.4 37.6 22 26 28

86.8 

144 

41 

8.0 

1.89 

9.1 

1.01 

<.l 

4.65 

.654 

41

104.9 

170 

50.0 

8.70 

1.58 

9.0 

.98 

<.l 

3.99 

.610 

40

75.4 

131 

38.8 

7.10 

1.78 

6.3 

.87 

<.09 

3.58 

.491 

32

Diatreme Breccias: Altered and Contaminated

Trachyandesite

5B 6

Rhyolite

9 40

Picrobasalt Basalt

4 23 2* 3 ISA 22

Andesite

24*

Large Cations Continued

34.1 

2,190 

961

.28

50 

840 

553 

.55

102.5 

1,340 1, 

155 

.30

100 

170 

73.3 

.3

16 17.2 20 159 

480 381 2,110 2,695 

278 300 305 1,940 

.28 .58 1.59 34.75

33 

1,660

338 

1.52

29.4 

691 

961

.45

146 

385 

269 

3.16

High- Valence Cations Continued

5.22 

1.69 

264 

6.33 

55 

3.61 

3.08 

41.77

6.30 

1.65 

241 

6.60 

58 

3.92 

3.78 

35.70

15.38 

2.81 

349 

10.65 

122 

7.61 

5.47 

32.78

17.6 

3.5 

534 

13.6 

136.8 

9.38 

5.03 

39.2

2.73 2.34 10.1 5.80 

.52 <2 2.42 2.00 

163 83 173 316 

2.55 2.50 4.22 7.15 

31 26 175 28 

1.56 1.45 8.8 2.26 

5.28 - 4.13 2.60 

64.17 33.01 40.96 43.54

10.19 

1.74 

190 

4.49

71 

3.25 

5.51 

40.24

4.88 

1.07 

170 

4.40 

46 

2.66 

4.54 

38.69

35.7 

7.5 

264 

10.9 

289 

15.5 

4.79 

24.11

Ferromagnesian Elements Continued

3.84 

34.5 

1.9 

5.56

15.3 

80.6 

2.6 

9.32

.39 

37.7 

1.99 

.33

5.7 

17 

<9.0 

.32

51.4 35.2 30.4 2.5 

80 61 108 52.6 

527 276 323 11.55 

26.9 23.4 30.6 2.02

21.3 

91.9 

3.4 

11.56

34.2 

91.0 

20.3 

14.09

8.43 

107 

43.9 

8.06

Rare Earth Elements Continued

46.0 

89.5 

42.1 

9.65 

2.94 

9.1 

1.14 

<.9 

2.80 

.402 

30

42.9 

100

44.7 

9.32 

2.37 

7.7 

1.01 

.401 

2.90 

.420 

28

56.4 

152.3 

32.6 

6.10 

1.89 

6.6 

.716 

<.09 

3.38 

.471 

29

73 

147 

54 

9.0 

2.40 

8.9 

1.41 

.78 

5.8 

.81 

51.5

23.3 21.7 84.1 34.4 

41.7 40.6 135 59.8 

19.5 20.6 70 22.4 

4.70 4.67 13.7 4.03 

1.44 1.40 3.28 1.11 

4.9 4.3 12.1 3.30 

.733 .625 1.09 4.41 

<.4 <.4 <.2 .15 

1.46 1.41 1.66 1.60 

.243 .24 .25 .251 

20 17 34 9

58.5 

94.5 

39 

7.97 

2.26 

9.2 

1.00 

.330 

2.37 

.32 

33

45.0 

78.6 

36 

7.62 

2.25 

6.7 

.85 

<.l 

1.89 

.27 

21

90.2 

82 

51 

11.3 

1.64 

12.7 

1.69 

<.2 

5.5 

.84 

85
(Fe2O3+FeO)

(Na2O+K2O)

M (MgO)

Figure 7. AFM projection showing basaltic to trachytic-rhyolitic composition of samples in table 3. Sample localities 

shown in figure 5. Circles denote dated samples.

type is slow intraplate extension (Wood, 1980). Several 

samples (1, 2, 16, and 24) fall outside of the boundary for 

alkaline within-plate basalts. Although these samples have 

not been dated, they have geochemical signatures similar to 

those of the Late Jurassic rocks (Gray and Gottfried, 1986). 

The Late Jurassic suite shows an unusual enrichment in Nb, 

Ta, U, and Th, and this enrichment pulls them out of the 

normal alkaline field because the diagram uses two of these 

elements. The low abundance levels of lithophile elements 

K, Rb, and Cs in the felsic rocks indicate a mantle origin 

with little or no crustal contamination. On a logarithmic plot 

of Th versus Ta, the Eocene mafic and felsic rocks show a 

remarkable linearity, which suggests that they are cogenetic 

(Gray and Diecchio, 1983; unpub. data, 1992; Gray and 

Gottfried, 1986). This correlation supports conclusions 

made by Hall (1975) on the basis of major-element chemistry. The light rare earth elements (REE's) are enriched and

the heavy REE's are depleted, so the REE plots (fig. 16) 

have a steep slope that is similar to those associated with 

continental rifting (Condie, 1976).

Considered as a whole, the trace-element geochemistry of the Eocene igneous rocks suggests a mantle source, 

extensional tectonics, a common source for both the mafic 

and felsic rocks, and little crustal assimilation. These 

factors can best be explained by a mode of rapid emplacement through a deep-seated fracture zone. Such a fracture 

zone would allow magma to rise rapidly without assimilating continental crust. The existence of diatremes and 

volcanic breccia and the fact that there is little contact 

metamorphism support a model in which emplacement was 

rapid and explosive. The close spatial association of Late 

Jurassic and Eocene igneous rocks in this region indicates 

that such a fracture zone could have been a zone of crustal 

weakness in the Mesozoic that was reactivated in the

J12 Evolution of Sedimentary Basins Appalachian Basin
Figure 8. Trimble Knob, a basalt diatreme intruded in 

Devonian Millboro Shale. View is to the north toward 

Monterey, Va.; relief is approximately 73 m. (Sample 8, 

fig. 3 and table 1, and samples 36 and 51, fig. 5 and tables 

3 and 4.)

Figure 10. A sill of explosion breccia in Ordovician Beekmantown Dolomite, Hightown, Va., quarry. Rounded 

clasts of dolomite as much as 7 mm in diameter are due to 

corrosion by CO2 gas fluidization. View is to the east. 

(Sample 3; fig. 5 and tables 3 and 4.)

Figure 9. A peridotite porphyry (Garner, 1956) dike in 

Silurian Tuscarora Quartzite has weathered to saprolite. 

View to the north along Route 33 in West Virginia. (Sample 

2, fig. 5 and tables 3 and 4.) Possibly a Late Jurassic dike.

Figure 11. Columnar-jointed basalt east of Hightown, Va., 

suggests near-surface emplacement. (Sample 34, fig. 5 and 

tables 3 and 4.) Paleomagnetic coreholes are visible to the 

right of the hammer (Lovlie and Opdyke, 1974; Ressetar 

and Martin, 1980).

Intrusive Igneous Rocks of the Valley and Ridge Province J13
Figure 12. The northwest face of the abandoned Virginia 

Department of Highways and Transportation quarry in 

Hightown, Va. Near-vertical, branching basalt (B) dikes 

crosscut an older basaltic trachyandesite (A) sill in the 70° 

southeast-dipping Ordovician Beekmantown Dolomite; 

breccia (C) is shown in figure 10. Brucite marble (Giannini 

and others, 1987) occurs here as an alteration product. 

Width of basalt dikes is approximately 1 m. (Samples 3, 5, 

29, 35, and 52, fig. 5 and tables 3 and 4.)

Cenozoic. Differentiation of the magma probably occurred 

at great depth, where the fractionation could have occurred 

without melting or assimilating crustal rocks. The felsic 

rocks are generally not rich in phenocrysts, and therefore a 

shallow magma chamber probably did not exist for a long 

period of time before emplacement.

Figure 13. Trachybasalt sill in vertical beds of Devonian 

Millboro Shale. The concordant intrusion is not offset by a 

fault; displacement by branching is similar to the exposure in figure 12. View is to the northeast, just south of 

Sugar Grove, W. Va. (Sample 19, fig. 5 and tables 3 and 4.)

Previous Tectonic Models

Tectonic models proposed for the origin of the 

Jurassic and Eocene intrusive rocks invoke either regional 

cross-strike structures (fig. 17), hotspots, or a combination 

of both. Zartman and others (1967), Fullagar and Bottino 

(1969), Dennison and Johnson (1971), King (1971), Heyl 

(1972), and Rader and others (1986) attribute the igneous 

activity to a structural lineament along the 38th parallel 

(Heyl, 1972) (fig. 17). However, geologic data are insufficient to extend the 38th parallel lineament east of the 

Irving-Paint Creek fault zone in Kentucky (fig. 17). Sutler 

(1976) suggested the transcurrent Cornwall-Kelvin fracture 

zone as the conduit of magma. Sykes (1978) and Metcalf 

(1982) proposed that the igneous activity was due to the

J14 Evolution of Sedimentary Basins Appalachian Basin
Figure 14. Trachybasalt sill in shale beds of the Devonian 

Brallier Shale. View is to the southwest, just south of Sugar 

Grove, W. Va. Note paleomagnetic coreholes (Ressetar 

and Martin, 1980) near the center. (Sample 8, fig. 3 and 

table 1, and sample 49, fig. 5 and table 3.)

westward extension of the offshore Norfolk fracture zone 

onto the continent (fig. 17). McHone and others (1987) 

suggested that the extension of the Kane fracture zone onto 

the continent was the conduit for the Eocene intrusive rocks 

and the Bermuda seamount. Core and others (1974) suggested that the 38th parallel structure passed over a hotspot. 

De Boer and Snider (1979) also proposed a hotspot model. 

Dennison and Johnson (1971) suggested that the 

70-milligal negative Bouguer gravity anomaly in this region 

signified an area of maximum domal uplift that was due to 

isostatic rebound. They also postulated that the thermal 

springs to the south were heated by a slow-cooling, Eocene 

felsic pluton. Perry and others (1979) later determined that 

there was no connection between the exposed Eocene 

igneous rocks and the thermal springs. Bollinger and 

Gilbert (1974) recognized an apparent low heat flow and an 

earthquake shadow zone in this region.

Proposed Tectonic Model

The relationship between structures in the basement 

and structures in the allochthonous cover rocks of the 

Valley and Ridge province becomes important in formulating a tectonic model for the intrusive rocks. Indirect 

basement involvement on the overlying structures is 

believed to be that of normal faults in the basement that 

extend into and through potential zones of decollement to 

initiate tectonic ramps (Jacobeen and Kanes, 1974; 

Wiltschko and Eastman, 1983; and Shumaker, 1986). The 

basement faults would control the location of the tectonic

ramps of the duplex structures of Cambrian to Ordovician 

rocks and resultant anticlinoria of Silurian to Devonian 

rocks (fig. 2, cross section). The vertical correlation of 

northeast-trending surface structures to basement faults is 

problematic because of tectonic transport of the Alleghanian 

orogeny. Cross-strike structures that parallel the direction of 

tectonic transport may, however, overlie a northwesttrending subsurface fault (Wheeler, 1986). The coincidence 

of some surface and inferred subsurface structures in this 

region suggests a tectonic model of reactivated cross-strike 

and strike-parallel basement faults (fig. 18). Extensional 

growth faults of Late Proterozoic to early Paleozoic age 

may have been reactivated by compressional tectonics of 

the late Paleozoic Alleghanian orogeny and by extensional 

tectonics of the Mesozoic and early Cenozoic eras.

Reactivated growth faults in the central Appalachians 

are well documented (Root, 1978; Shumaker, 1986). 

Jacobeen and Kanes (1974), using seismic reflection data, 

interpreted a down-to-the-southeast normal fault in basement rocks beneath the Wills Mountain anticline to the 

north of this study area. Ryder (1988) interprets similar 

normal faults beneath the Appalachian Plateaus structural 

front in this study area as continental margin rifted during 

the Cambrian. It has also been suggested that reactivated 

growth faults in the Appalachians are causally related to 

kimberlite intrusions (Parrish and Lavin, 1983) and areas of 

seismicity (Bollinger and Wheeler, 1983).

Northwest-trending transform faults of the Cambrian 

Rome trough, interpreted from regional gravity data (Kane, 

1983; Rice, 1983), border this region (fig. 17, nos. 6 and 

7). Lateral changes in duplex blocks of Cambrian and 

Ordovician carbonate rocks (Wilson and Shumaker, 1988) 

occur across the zone of the Eocene igneous rocks (fig. 17, 

no. 10). The differences in shortening of the duplex blocks 

across this zone (Wilson and Shumaker, 1988) may be 

represented by northwest-trending lineaments of the Appalachian Plateaus province (Gwinn, 1964; Rodgers, 1970; 

Kulander and Dean, 1978; and Wheeler, 1986). The Bartow 

lineament (Wheeler, 1986; fig. 17, nos. 5 and 8) is believed 

to be the lateral boundary of the Browns Mountain and 

Elkins Valley allochthonous blocks that underwent differentia] tectonic transport in the Alleghanian orogeny 

(Kulander and Dean, 1978). Stratigraphic studies suggest 

that the Bartow lineament controlled sedimentation during 

much of Middle and Late Devonian time at the Appalachian 

Plateaus structural front (Wheeler, 1986). Yielding and 

Dennison (1986) report that tectonic activity along the 

eastern end of the 38th parallel lineament (fig. 17, no. 9) is 

indicated by lithologic variations in Upper Devonian to 

Upper Mississippian rocks on the plateau of West Virginia.

Sykes (1978) and Metcalf (1982) place the continental extension of the Jurassic Norfolk fracture zone (fig. 17, 

no. 4) near the area where the unusual alkalic suite of Late 

Jurassic dikes changes regional strike. Down-to-thenortheast basement faulting, and both uplift and subsidence

Intrusive Igneous Rocks of the Valley and Ridge Province J15
Hf/3

Mid-ocean 

ridge 

basalt

Destructive

plate-margin

basalt

Alkaline

within-plate

basalt

 Sample 1 

Sample 16« Sample 24 'Sample 2

Enriched mid-ocean 

ridge and tholeiitic 

within-plate 

basalt

Figure 15. Hf/3-Th-Ta ternary diagram for tectonic setting of basalts (after Wood, 1980) showing the field of samples in the 

Valley and Ridge province.

during the Eocene, has been interpreted from stratigraphy in 

the Coastal Plain where the Norfolk fracture zone projects 

on land (Cederstrom, 1945; Powars and others, 1987).

The drainage divides of seven tributaries of the 

Potomac and James Rivers are found across this zone of 

intrusive rocks (fig. 17). These highlands form a linear zone 

of headwaters that equally divide over 100 km of longitudinal drainage. The divides of the Jackson River and South 

Branch Potomac River coincide with a structural culmination of the Wills Mountain anticline at Hightown, Va. This 

structural culmination is near the duplex boundary suggested by Wilson and Shumaker (1988) and is in the center 

of the Eocene activity. The 100-km-long region of high 

topography is the structural culmination of the Wills Mountain anticline and the fold belt on the plateau.

We propose that an extensionally reactivated crossstrike basement fracture and a strike-parallel growth fault 

near the Appalachian Plateaus structural front are the deep 

fracture conduits for the Eocene igneous rocks (fig. ISA, 

B). The near-perpendicular trends of the basement fracture 

zones may define part of a rift and (or) transform fault 

system that borders basement blocks. Northwest-trending 

Late Jurassic dikes were emplaced along a cross-strike 

basement fracture zone that extends into Pendleton County, 

W. Va. Some middle Eocene intrusive rocks were emplaced 

along the same cross-strike basement fracture zone. 

Northeast-trending intrusive rocks in Highland County, 

Va., are parallel to inferred growth faults. The conjugate 

trend of dikes presents a mechanical problem of two 

stress-field directions. Northeast- and northwest-trending

J16 Evolution of Sedimentary Basins Appalachian Basin
middle Eocene rocks suggest that a local variation of a 

consistent stress-field orientation may have reactivated an 

existing fabric of structural weakness (fig. 18C).

The orientation of the stress and strain ellipse for this 

region is interpreted to have varied throughout geologic 

time (table 5). Northwest-oriented least compressive stress 

(0-3) prevailed during Late Proterozoic and early Mesozoic 

rifting (table 5). The interpreted orientation of the stress and 

strain ellipse of the Late Paleozoic Alleghanian orogeny 

(northwest-oriented o^) is coaxial to Late Jurassic extension 

(northeast-oriented a3) (table 5). Conjugate trends of middle Eocene intrusive rocks (fig. 18) suggest that both stress 

regimes were active. The occurrence of two nearly perpendicular stress fields is mechanically impossible, and a 

change in stress field is unlikely over short periods of 

geological time. However, a north-south-oriented maximum 

compressive stress (o^) that bisects the acute angle of the 

conjugate dike trend could account for the two orientations.

Data from well breakouts and Cenozoic fault orientations show that the Eastern United States is characterized 

by northeast to east-northeast compressional stress (Zoback 

and Zoback, 1989). Relaxation of this stress orientation can 

account for the northeast trend of middle Eocene rocks. The 

"Atlantic coastal stress province" shows northwest-oriented 

maximum compression, but these data are eliminated 

(Zoback and Zoback, 1989) because they are inconsistent 

with the rest of the region.

The cause of continental extension of this region 

during the middle Eocene is interpreted to be the result of a 

change in plate tectonic motion. Manspeizer and others 

(1989) and Vogt (1991) suggest that plate-kinematic reorganizations caused the middle Eocene igneous activity and 

the formation of the Bermuda Rise. Over 56 events worldwide indicate a major reorganization of global plate motion 

from 53.5 to 37.5 Ma (Rona and Richardson, 1978). A 

specific event of plate reorganization, Chron 19, occurred at 

44 Ma (McGowran, 1989). The main, edifice-building 

phase of Bermuda volcanism (45-33 Ma), the formation of 

the Bermuda Rise (45-40 Ma), and reorganization of the 

Pacific plate motion are thought to be related to the Middle 

Eocene intrusive rocks (Vogt, 1991). The range of radiometric ages of 48 to 35 Ma for igneous rocks in this region 

suggests a causal relationship. The apparent offset of 

northwest-trending vertical dikes by low-angle thrust faults 

has been observed at several exposures by the lead author, 

Donaldson and others (1964), and Johnson and others 

(1971).

SUMMARY

The central Appalachian basin has experienced at 

least three episodes of igneous activity since the late

Paleozoic Alleghanian orogeny. Late Paleozoic to Cretaceous kimberlite dikes and plugs intruded along the basinal 

axis. Hypothetical crustal fractures along the basin axis 

were perhaps reactivated because of isostatic rebound (Dennison, 1983). Late Jurassic dikes intruded rocks of the 

Shenandoah Valley and the Valley and Ridge province. 

This unusual suite of alkalic igneous rocks, and the more 

extensive, Early Jurassic mafic dike swarms of the Appalachian Piedmont and Blue Ridge, is the result of Mesozoic 

continental extension related to the opening of the Atlantic 

Ocean. Finally, middle Eocene basalt and rhyolite dikes, 

sills, plugs, and diatremes were intruded into the Paleozoic 

rocks of the Valley and Ridge province. Geochemical data 

suggest that the source of magma was upper mantle to lower 

crust and related to continental extension. The Eocene 

igneous activity was short lived, areally restricted, and 

sometimes explosive; no evidence of extrusive flows is 

preserved. Radiometric data show that the region of the 

youngest igneous rocks in the Eastern United States also 

experienced igneous activity in the Late Jurassic.

The tectonic model proposed here for the origin of the 

middle Eocene intrusive rocks is the extensional reactivation of basement fracture zones. The northwest-trending 

basement fracture zone may be inferred from structural 

discontinuities in the overlying allochthonous rocks of 

Paleozoic age. An apparent change in stress field marked by 

the change in orientation of Late Jurassic dikes may 

delineate the cross-strike basement fracture zone. The 

western limit of Late Jurassic activity occurs in the area of 

Eocene rocks in Pendleton County, W. Va. Strike-parallel 

growth faults of Late Proterozoic to Early Cambrian age 

may have provided the fracture conduit for northeasttrending Eocene intrusive rocks in Highland County, Va. 

Conjugate trends of middle Eocene rocks suggest that a 

local variation of a consistent stress field may have reactivated existing fabrics of structural weakness. The cause of 

middle Eocene continental extension is interpreted to be the 

result of a change in plate motion that is recognized 

worldwide.

ACKNOWLEDGMENTS

The authors wish to thank D.L. Core for 40Ar/ 39Ar 

data in table 2. Technical reviews by William C. Burton, 

Albert J. Froelich, and J. Gregory McHone (Wesleyan 

University) greatly improved the text. We would like to 

thank the landowners of Highland County, Va., and Pendleton, County, W. Va., for providing access to exposures.

Intrusive Igneous Rocks of the Valley and Ridge Province J17
1000

'100

10

100

1

1000

100

1 T

Trachybasalt (nos. 8, 19)

and 

Trachyandesite (no. 5)

1000

La Ce Nd Sm Eu Gd Tb Yb Lu

%Si02 %MgO

* 43.0 6.7

I I

La Ce Nd Sm Eu Gd Tb

= 100

Trachydacite

%Si02 %MgO

*67.0 0.18

66.8 0.21

64.1 0.40

--65.4 0.16

| " 64^8 0 09

La Ce Nd Sm Eu Gd Tb Yb Lu

I I I I T I I T

Picrobasalt (nos. 1, 25)

and 

basalt (nos. 16, 17, 27)

%SiU, %MgU

4.3 

6.7 

9.7 

7.4 

9.4

La Ce Nd Sm Eu Gd Tb

RARE EARTH ELEMENT

Yb Lu

Figure 16. Light and heavy rare-earth-element (REE) 

plots of select mafic and felsic rock suites. (Sample 

localities shown on fig. 5.)

Figure 17. Structural features interpreted in the 

study region. Inset shows the previous tectonic 

model of the eastward projection of the 38th parallel 

lineament (Heyl, 1972) and the westward projection 

of the Norfolk fracture zone by Sykes (1978).

La Ce Nd Sm Eu Gd Tb

RARE EARTH ELEMENT

Yb Lu

J18 Evolution of Sedimentary Basins Appalachian Basin
38°45' [ 

Plugs and diatremes

Igneous dikes and sills

Drainage divides of the Potomac and James Rivers

Fault

EXPLANATION

 Structural lineament (reference; age) 

©Gwinn, 1964; Pennsylvanian 

@Rodgers, 1970; Pennsylvanian 

®Heyl, 1972; Precambrian 

@Sykes, 1978; Jurassic 

©Kulander and Dean, 1978; Pennsylvanian 

©Kane, 1983; Cambrian 

©Rice, 1983; Cambrian 

©Wheeler, 1986; Devonian

©Yielding and Dennison, 1986; Devonian to Mississippian 

@ Wilson and Shumaker, 1988; Pennsylvanian

Intrusive Igneous Rocks of the Valley and Ridge Province J19
79°15'

EXPLANATION

- Current stress field ' Mafic # Diatreme breccias

- Zone boundary (^) Felsic v Dike

Elkins Valley 

allochthonous block

Dikes in Shenandoah Valley, Virginia

B

Pendleton County, West Virginia

Figure 18. A, Proposed tectonic model of the Late Jurassic and middle Eocene 

intrusive rocks. The northwest-trending zone is a cross-strike basement fault that 

was active in Late Jurassic and middle Eocene time. The northeast-trending zone is 

a strike-parallel growth fault of Late Proterozoic to Cambrian age that extended in 

middle Eocene. B, Schematic block diagram illustrates the possible relationship of 

basement fracture zones to Alleghanian structures and Late Jurassic and middle 

Eocene igneous activity. Schematic diagram is parallel to the northwest-trending 

zone. C, Equal-area stereographic projections (lower hemisphere) of poles to 

strikes of near-vertical dikes and sills. Highland County, Va.: N = 43; contour 

percent = 30, 20,10, and 5. Pendleton County, W. Va.: N = 47; contour percent = 

20, 15, 10, 6, and 4; = 2 percent.

J20 Evolution of Sedimentary Basins Appalachian Basin
Table 5. Variations in structure, tectonics, and stress fields of the central Appalachian region from Late Proterozoic to 

present time

[Oj, direction of maximum compressive stress; O3 , direction of least compressive stress; x, axis of greatest principal strain; r, axis of least principal strain]

Geologic age Geologic feature Geologic event Tectonic regime

Interpreted elipse 

orientations

Stress Strain

Tertiary to Holocene High-angle thrust faults Spreading Mid-Atlantic Ridge Compression

Middle Eocene Dikes, sills, and 

diatremes

Late Jurassic

Early Jurassic

Permian to 

Pennsylvanian

Dikes

Grabens, dikes, 

and sills

Folds and low-angle 

thrust faults

Change in plate tectonic motion Extension

Continental rifting to form the Extension 

Atlantic Ocean

Continental rifting to form the Extension 

Atlantic Ocean

Continent-to-continent collision Compression 

of the Alleghanian orogeny

IN

A

Early Cambrian to Grabens and normal Continental rifting to form the Extension 

Late Proterozoic faults lapetus Ocean

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microearthquake survey of the Hot Springs, Virginia area: 

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Bollinger, G.A., and Wheeler, R.L., 1983, The Giles County, 

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1063-1065.

Butts, Charles, 1933, Geologic map of the Appalachian Valley of 

Virginia: Virginia Geological Survey Bulletin 42, 56 p., 1 pi.

Cardwell, D.H., Erwin, R.B., and Woodward, H.P., 1968, 

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Core, D.L., 1971, Potassium-argon dating of igneous rocks in 

Pendleton County, West Virginia: Columbus, Ohio, Ohio 

State University, unpub. senior thesis, 22 p.

Core, D.L., Sutler, J.F., and Fleck, R.J., 1974, K/Ar ages of 

igneous rocks from eastern West Virginia and western Virginia [abs.]: Eos, Transactions of the American Geophysical 

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Dalrymple, G.B., 1979, Critical tables for conversion of K-Ar 

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Dalrymple, G.B., Brent, G., Alexander, B.C., Jr., Lanphere, 

M.A., and Kraker, G.P., 1981, Irradiation of samples for 

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J22 Evolution of Sedimentary Basins Appalachian Basin
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J24 Evolution of Sedimentary Basins Appalachian Basin
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