Stratigraphic Framework of Cambrian and 

Ordovician Rocks in the Central Appalachian 

Basin from Medina County, Ohio, through 

Southwestern and South-Central Pennsylvania to 

Hampshire County, West Virginia

U.S. GEOLOGICAL SURVEY BULLETIN 1839-K

Chapter K

Stratigraphic Framework of Cambrian and 

Ordovician Rocks in the Central Appalachian Basin 

from Medina County, Ohio, through Southwestern 

and South-Central Pennsylvania to Hampshire 

County, West Virginia

By ROBERT T. RYDER, ANITA G. HARRIS, and 

JOHN E. REPETSKI

Stratigraphic framework of the Cambrian and Ordovician 

sequence in part of the central Appalachian basin and the 

structure of underlying block-faulted basement rocks

U.S. GEOLOGICAL SURVEY BULLETIN 1839 

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

MANUEL LUJAN, Jr., 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: 1992

For sale by

Book and Open-File Report Sales 

U.S. Geological Survey 

Federal Center, Box 25286 

Denver, CO 80225

Library of Congress Cataloging in Publication Data

Ryder, Robert T.

Stratigraphic framework of Cambrian and Ordovician rocks in the central 

Appalachian Basin from Medina County, Ohio, through southwestern and 

south-central Pennsylvania to Hampshire County, West Virginia / by 

Robert T. Ryder, Anita C. Harris, and John E. Repetski.

p. cm. (Evolution of sedimentary basins Appalachian Basin ; ch. K) (U.S. 

Geological Survey bulletin ; 1839-K)

Includes bibliographical references.

Supt. of Docs, no.: I 19.3:1839-K

1. Geology, Stratigraphic Cambrian. 2. Geology, Stratigraphic Ordovician. 

3. Geology Appalachian Basin. I. Harris, Anita G. II. Repetski, John E. 

III. Title. IV. Series. V. Series: U.S. Geological Survey bulletin ; 1839-K.

QE75.B9 no. 1839-K

557.3 s-dc20

[551.7'23'0974] 92-25091

CIP
CONTENTS

Abstract Kl

Introduction K2

Drill-Hole Control for Section K5

Basement Structure K7

Thickness Changes in the Cambrian and Ordovician Sequence K9

Stratigraphic Framework K10

Basal Sandstone Unit and Tomstown Dolomite (Lower Cambrian) K10

Waynesboro Formation (Lower and Middle Cambrian) K10

Pleasant Hill Limestone, Warrior Formation, and Elbrook Formation (Middle

and Upper Cambrian) Kll 

Gatesburg Formation (Upper Cambrian) K13 

Beekmantown Group (Lower and Lower Middle Ordovician) K14 

Knox Unconformity K16

Loysburg Formation and Black River Group (Middle Ordovician) K17 

Trenton Group (Middle and Upper Ordovician) K20 

Reedsville Shale and Bald Eagle Formation (Upper Ordovician) K23 

Juniata Formation and Queenston Shale (Upper Ordovician) K24 

Tuscarora Sandstone and "Clinton" Sandstone and Shale (Lower Silurian) K24

Summary and Conclusions K25

References Cited K27

PLATE

1. Restored Stratigraphic section C-C' from Medina County, Ohio, through southwestern and south-central Pennsylvania to Hampshire County, W. Va., showing 

the Cambrian and Ordovician sequence [In pocket]

FIGURES

1. Map showing the tectonics of Ohio, Pennsylvania, West Virginia, and adjoining 

States showing the Appalachian basin, section C-C', selected drill holes, and 

selected counties K3

2. Chart showing correlation of Middle Proterozoic, Cambrian, and Ordovician rocks 

along section C-C' and in adjoining Franklin County, Pa. K4

TABLES

1. Drill holes used in section C-C' K6

2. Conodonts from the Amoco No. 1 Svetz drill hole, Somerset County, Pa. K7

Contents III

EVOLUTION OF SEDIMENTARY BASINS-APPALACHIAN BASIN

Stratigraphic Framework of Cambrian and 

Ordovician Rocks in the Central Appalachian Basin 

from Medina County, Ohio, through Southwestern 

and South-Central Pennsylvania to Hampshire 

County, West Virginia

By Robert T. Ryder, Anita G. Harris, and John E. Repetski

Abstract

A 275-mi-long restored stratigraphic cross section from Medina 

County, Ohio, through southwestern 

and south-central Pennsylvania to 

Hampshire County, W. Va., provides 

new details on Cambrian and Ordovician stratigraphy in the central Appalachian basin and the structure of 

underlying Precambrian basement 

rocks. From west to east, the major 

structural elements of the blockfaulted basement in this section are 

(1) the relatively stable, slightly 

extended craton, which includes the 

Wooster arch, (2) the fault-controlled 

Ohio-West Virginia hinge zone, 

which separates the craton from the 

adjoining Rome trough, (3) the Rome 

trough, which consists of an eastfacing asymmetric graben and an 

overlying sag basin, and (4) a positive 

fault block, named here the Southcentral Pennsylvania arch, which borders the eastern margin of the graben 

part of the Rome trough. Pre-Middle 

Ordovician structural relief on Precambrian basement rocks across the

Manuscript approved for publication June 

11, 1992.

down-to-the-west normal fault that 

separates the Rome trough and the 

adjoining South-central Pennsylvania 

arch amounted to between 6,000 and 

7,000 ft.

The restored cross section 

shows eastward thickening of the 

Cambrian and Ordovician sequence 

from about 3,000 ft near the crest of 

the Wooster arch at the western end 

of the section to about 5,150 ft at the 

Ohio-West Virginia hinge zone adjoining the western margin of the 

Rome trough to about 19,800 ft near 

the depositional axis of the Rome 

trough. East of the Rome trough, at 

the adjoining western edge of the 

South-central Pennsylvania arch, the 

Cambrian and Ordovician sequence 

thins abruptly to about 13,500 ft and 

then thins gradually eastward across 

the arch to about 12,700 ft near the 

Allegheny structural front and to 

about 10,150 ft at the eastern end of 

the restored section.

In general, the Cambrian and 

Ordovician sequence along this section consists of four major lithofacies 

that are predominantly shallow 

marine to peritidal in origin. In 

ascending Stratigraphic order, the 

lithofacies are identified by the following descriptive names: (1) sandstone, shale, limestone, and dolomite

unit, (2) dolomite and sandstone unit, 

(3) limestone and black shale unit, 

and (4) shale and sandstone unit. Each 

of these units and their associated 

subunits thicken from west to east 

across the restored section to a maximum near the depositional axis of 

the Rome trough and then thin eastward to the end of the section.

The sandstone, shale, limestone, and dolomite unit is largely 

confined to the asymmetric graben 

that marks the initial phase of the 

Rome trough. This unit is Early and 

Middle Cambrian in age and consists, 

in ascending order, of a basal sandstone unit (undrilled but probably 

present), the Tomstown Dolomite 

(undrilled but probably present), the 

Waynesboro Formation, and the 

Pleasant Hill Limestone and its equivalent lower one-third of the Elbrook 

Formation at the eastern end of the 

section.

The dolomite and sandstone 

unit forms the core of the Cambrian 

and Ordovician sequence. In the 

Rome trough and on the adjoining 

South-central Pennsylvania arch, this 

unit consists, in ascending order, of 

the Middle and Upper Cambrian Warrior Formation and the equivalent 

upper two-thirds of the Elbrook Formation at the eastern end of the secCambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K1
tion, the Upper Cambrian Gatesburg Formation, and the 

Lower Ordovician and Middle Ordovician (Whiterockian 

and Chazyan) Beekmantown Group. West of the OhioWest Virginia hinge zone, the dolomite and sandstone 

unit consists, in ascending order, of the Conasauga Formation of Janssens (1973), the Krysik sandstone of driller's 

usage, the B zone of Calvert (1964), the Knox Dolomite 

and the associated Rose Run Sandstone Member, and the 

Wells Creek Formation. The widespread Knox unconformity is located at the base of the Wells Creek Formation and 

at or near the top of the adjoining Beekmantown Group, 

except near the depositional axis of the Rome trough, 

where the unconformity seems to be absent.

The limestone and black shale unit is the thinnest of 

the four lithofacies. In ascending order, this unit consists 

of the Middle Ordovician (Chazyan) Loysburg Formation, 

the Middle Ordovician (Blackriveran and Rocklandian) 

Black River Group, and the Middle and Upper Ordovician 

(Rocklandian through lowermost Edenian) Trenton 

Group. West of the Ohio-West Virginia hinge zone, the 

Loysburg Formation and the Black River Group combine 

to form the Black River Limestone, and the Trenton Group 

is replaced by the Trenton Limestone and the overlying 

Utica Shale.

The shale and sandstone unit consists of (1) a lower 

shale unit, the Upper Ordovician (Edenian and Maysvillian) Reedsville Shale; (2) a middle argillaceous sandstone 

between the depositional axis of the Rome trough and the 

eastern end of the section, the Upper Ordovician (upper 

Maysvillian and lower Richmondian) Bald Eagle Formation 

and its equivalent Oswego Sandstone; and (3) an upper 

silty red shale containing local sandstone beds, the Upper 

Ordovician (Richmondian) Juniata Formation and its 

equivalent Queenston Shale.

INTRODUCTION

Oil and gas exploration in the Ohio, Pennsylvania, 

and West Virginia parts of the Appalachian basin, from the 

late 1950's to the middle 1980's, resulted in the drilling of 

a modest number of holes into Cambrian strata and (or) 

Precambrian basement rocks (Calvert, 1963; Wagner, 

1966, 1976; Oil and Gas Journal, 1973; Weaver and others, 

1974; Cardwell, 1977; Maslowski, 1986). On the basis of 

geophysical and lithologic logs from these drill holes and 

paleontologic data from one of these holes, we have drawn 

a 275-mi-long restored stratigraphic cross section through 

the Cambrian and Ordovician sequence from Medina 

County, Ohio, through southwestern and south-central 

Pennsylvania to Hampshire County, W. Va. (section C-C' , 

fig. 1). The stratigraphic framework of the Cambrian and 

Ordovician sequence along this cross section and, to a lesser 

extent, the structure of the underlying block-faulted basement rocks are the main topics of this paper.

Cross section C-C' is the third in a series of restored 

stratigraphic cross sections drawn by the senior author to 

show the stratigraphic framework of Cambrian and OrdoFigure 1. Tectonics of Ohio, Pennsylvania, West Virginia, and adjoining States showing the Appalachian 

basin, section C-C', selected drill holes, and selected 

counties. Lines of sections E-E' and D-D' (Ryder, 1992, 

1991) and A-A' (R.T. Ryder, unpub. data) are also 

identified on the map. Base from Wallace and de Witt 

(1975). Major tectonic and geologic features are from 

Cooper (1945), Calver and Hobbs (1963), Swingle and 

others (1966), Rodgers (1970), Wallace and de Witt 

(1975), Root and Hoskins (1977), Berg and others (1980), 

Shumaker and others (1985), and Coogan and Maki 

(1988a). Recent studies (for example, Wickstrom, 1990) 

indicate that the structure of the Cincinnati and Findlay 

arches is more complex than shown in this figure and 

by Wallace and de Witt (1975). Numbered drill holes in 

section C-C' are identified in table 1. Selected counties 

are identified as follows: Maryland W, Washington. 

Ohio C, Columbiana; Ha, Harrison; M, Medina; N, 

Noble; S, Stark. Pennsylvania B, Bedford; Bl, Blair; C, 

Centre; F, Franklin; H, Huntingdon; L, Lycoming; Me, 

Mercer; So, Somerset. West Virginia H, Hancock; 

Hd, Hardy; Hm, Hampshire; Mn, Mingo; P, Pendleton; W, Wood.

vician rocks across the Appalachian basin from Pennsylvania to Tennessee. Previously completed section E-E' 

(Ryder, 1992) and section D-D' (Ryder, 1991) are identified in figure 1. The stratigraphic framework of the Cambrian and Ordovician sequence presented in sections C-C' , 

D-D', and E-E' is probably the most comprehensive to 

date, in terms of both its detail and its regional perspective. 

Much of what can be considered "new" information in 

section C-C centers around (1) the lithology of littlestudied Cambrian, Lower Ordovician, and lower Middle 

Ordovician strata in the deep subsurface of the Rome trough 

and adjoining thrust-faulted terrane east of the Allegheny 

structural front and (2) their correlation with previously 

described outcrop or subsurface sequences. Conodont species recovered from a 21,460-ft-deep drill hole in Somerset 

County, Pa. (No. 5, fig. 1), also constitute new data. They 

are used to constrain the position of the Lower OrdovicianMiddle Ordovician boundary in the Rome trough. Implications of the sedimentary record concerning the early Paleozoic evolution of the Appalachian basin and the eastern 

continental margin of North America are not discussed 

here.

The stratigraphic nomenclature used in section C-C' 

follows existing nomenclature wherever possible, but, in 

certain places, modifications and additions are recommended. Stratigraphic investigations of the Cambrian and 

(or) Ordovician that were particularly applicable to this 

investigation include (1) Calvert (1963, 1964), Janssens 

(1973), Stith (1979, 1986), Wickstrom and others (1985), 

and Wickstrom and Gray (1988) in Ohio, (2) Knowles 

(1966), Wagner (1966, 1976), and Berg and others (1983) 

in Pennsylvania, and (3) Wagner (1966, 1976) in West 

Virginia. Information relating to compressional structures 

that cross section C-C' was provided by Jacobeen and

K2 Evolution of Sedimentary Basins Appalachian Basin
85° 80° 75°

40°

35°

r

Ohio-West Virginia 

hinge zone

40th parallel

25 50 75 100 MILES

100 150 KILOMETERS

 * A_ Thrust fault Sawteeth on 

upper plate

Transverse fault

Normal fault (in subsurface) 

Only segments crossing section 

C-C'are shown; bar and ball 

on relative downthrown side

3o Present location of drill hole used to construct section C-C' (this report). Number refers 

to drill hole described in table 1.

 Present location of drill hole used to construct sections E-E' (Ryder, 1992), D-D' 

(Ryder, 1991), and A-A' (R.T. Ryder, unpub. data).

cf ~~ gt Present location of drill hole restored along the dashed line to approximately original 

position prior to westward tectonic transport. These projected positions are shown in 

section C-C'. Number refers to drill hole as described in table 1 .

* "^ Present location of drill hole restored along the dashed line to approximately original 

position prior to westward tectonic transport. These projected positions are shown in 

sections F-Pand D-D'.

Kanes (1975), Berg and others (1980), Shumaker and 

others (1985), and Kulander and Dean (1986).

European chronostratigraphic units (for example, 

Tremadocian through Ashgillian Series) commonly do not 

apply to the cratonal and platformal Ordovician rocks of 

North America (Ross and others, 1984). Therefore, in this 

paper, we apply North American chronostratigraphic units

used by Barnes and others (1981) and Ross and others 

(1982) rather than the European chronostratigraphic units 

used by Palmer (1983), Berg and others (1983), and the 

COSUNA charts (for example, see Patchen and others, 

1984). Our correlation chart (fig. 2) subdivides the Ordovician System into the Lower, Middle, and Upper North 

American Series of Barnes and others (1981) and the

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K3
Tectonic provinces in Ohio, West Virginia, and Pennsylvania 

___(along section C-C") East of C-C'

O OJ^T- £ o^o .. <D «^ Jr E <uei 

5E 1

*lorth American 

:ime-stratigraphic 

units (modified 

after Barnes and 

others, 1981; 

toss and others, 

1982; Palmer. 1983)

Relatively 

stable 

craton

Series Stage

Ohio-West

Virginia 

hinge zone

Rome 

trough

Allegheny

structural front

and adjoining

Valley and Ridge

province

Carbaugh-Marsh Creek

:ault block and adjoining

North Mountain fault

block, southeastern

Franklin Co., Pa.

(Root, 1968; Berg and

others 1983)

438 '

448-

478-

Bellefonte-p.

Dolomite ?<rQT^^L505-

523-

540-

570-

Queenston 

Shale

Juniata 

Formation

Juniata 

Formation

Juniata 

Formation

Bald Eagle Formation

Bald Eagle Formation 

(Oswego Sandstone)

Reedsville 

Shale

Reedsville 

Shale

Reedsville 

Shale Reedsville 

Shale

Utica Shale

Trenton Limestone

_a marker of Stith 11979)

Antes Shale

Coburn 

Limestone

Antes Shale

Coburn 

Limestone

a marker pmarke

Rose Run 

Sandstone

Beekmantown 

Group

Beekmantown 

Group

Dolomite

ofJanssens

(1973)

B zone of Calvert (1964)

Krvsik ss. of driller's usage

Upper sandy 

member

Mines Dolomite Member

Upper sandy 

member

Middle 

dolomite 

member

Rome Formation 

ofJanssens(1973)

900-

Mount Simon 

Sandstone

Antes Shale

Martinsburg 

Formation

Coburn Limestone

-Bentonite R

Bentonite No. 0-,

)( M )( II H M H H\

Nittany 

Dolomite

Larke Dolomite

Mines Dolomite Member

Upper sandy 

member

Ore Hill 

Limestone Member

Lower sandy 

member

Unnamed Is. mbr.

Rockdale

Run 

Formation

Stonehenge Limestone 

IStoufferstown Membei

Shadygrove 

Formation

Zullinger 

Formation

Unnamed 

dolomite 

member

Pleasant Hill 

_ Limestone _

Elbrook 

Formation

Waynesboro 

Formation

Waynesboro 

Formation

Tomstown 

Formation

Antietam Formation

Harpers Formation

Metamorphic and igneous rocks of 

Grenville erogenic belt

Weverton Formation

atoctin Formation

K4

EXPLANATION 

" " " " " " Metabentonite 

Evolution of Sedimentary Basins Appalachian Basin

Hiatus
respective Ibexian, Whiterockian and Mohawkian combined, and Cincinnatian Series of Ross and others (1982). 

In addition, the Canadian Series of Barnes and others 

(1981) because of its well-established usage in North 

America is shown in our correlation chart as being equivalent to the Ibexian Series of Ross and others (1982). By 

equating the Ibexian (Canadian) Series with the Lower 

Ordovician Series, the Whiterockian and Mohawkian Series 

combined with the Middle Ordovician Series, and the 

Cincinnatian Series with the Upper Ordovician Series, we 

are in agreement with many Ordovician specialists in North 

America such as Miller (1984), Repetski (1985), Sweet and 

Bergstrom (1986), and Shaw and others (1990).

The Blackriveran through Gamachian Stages of the 

Ordovician listed in our correlation chart (fig. 2) follow 

those defined by Barnes and others (1981) and Ross and 

others (1982). The Chazyan as used by Barnes and others 

(1981) is retained in this paper as a formal stage because of 

its long-time usage in North America. In contrast, Ross and 

others (1982) recognized the Chazyan as a chronostratigraphic unit of historical interest rather than as a formal 

stage of the Ordovician System.

DRILL-HOLE CONTROL FOR SECTION

Section C-Cf , the subject of this paper, is shown on 

plate 1. Nine drill holes ranging from 11 to 76 mi apart and 

from 6,676 to 21,460 ft in total depth constitute the control 

for the section (table 1). In the Ohio part of section C-C' , 

one drill hole and probably a second penetrated the entire 

sedimentary cover and bottomed in crystalline basement 

rocks of Proterozoic age. However, no drill holes reached 

basement rocks in the Pennsylvania and West Virginia parts 

of the section.

Stratigraphic correlations between drill holes are 

based primarily on geophysical logs, whereas lithofacies 

patterns between drill holes are based on lithologic logs 

described by the Geological Sample Log Company (Pittsburgh, Pa.) (table 1). Section C-C has been restored to a 

horizontal datum located at the base of a widespread, 60- to 

90-ft-thick, micritic limestone in the middle of the LoysFigure 2. Correlation of Middle Proterozoic, Cambrian, 

and Ordovician rocks along section C-C and in adjoining Franklin County, Pa. Absolute age (in Ma) is taken 

from the geologic time scale compiled by Palmer 

(1983). The time scale is nonlinear. North American 

chronostratigraphic units are modified after Barnes and 

others (1981), Ross and others (1982), and Palmer 

(1983). Series and Stage names: BR, Blackriveran; Ca, 

Canadian; C, Chazyan; E, Edenian; Ga, Gamachian; K, 

Kirkfieldian; M, Maysvillian; R, Rocklandian; Ri, Richmondian; S, Shermanian; WR, Whiterockian. Group 

name: BRG, Black River Group. Formation names: LF, 

Loysburg Formation; LHL, Linden Hall Limestone; SL, 

Snyder Limestone.

burg Formation in Pennsylvania and adjoining northernmost 

West Virginia (pi. 1). In the Ohio part of the section, the 

micritic limestone datum is located at the base of the Black 

River Limestone or, in local oil industry terminology, the 

base of the Gull River Formation. At the eastern end of 

section C-C', in Hampshire County, W. Va., the datum 

horizon has been removed by pre-Black River Group 

erosion. This micritic limestone was chosen as the datum 

horizon for section C-C' because it appears to be the most 

widespread and easily recognizable subsurface marker unit 

in the Cambrian-Ordovician sequence of the central Appalachian basin. Metabentonite beds in the Black River 

Limestone (Group) and Trenton Group are good marker 

units, but they cannot be traced with as much confidence as 

the micritic limestone unit. In addition, the shallow marine 

origin of the micritic limestone datum (Ryder, in press) and 

its proximity to the widespread Knox unconformity (pi. 1) 

permit the restoration of the pre-unconformity structural 

configuration of the Rome trough and adjoining structural 

elements. The Kerr-McGee No. 1 Schellsburg (KMS), 

Kerr-McGee No. 1 Martin (KMM), Arco No. 1 Steele 

(ARS), and Shell Oil No. 1 Duckworth (SD) drill holes 

(Nos. 6, 7, 8, and 9, fig. 1, pi. 1, table 1), located at or east 

of the Allegheny structural front, have been moved in this 

study southeastward of their present-day locations to 

account for westward tectonic transport along frontal imbricate thrust faults (Knowles, 1966; Wagner, 1966; Jacobeen 

and Kanes, 1975; Berg and others, 1983; Shumaker and 

others, 1985; Kulander and Dean, 1986). Southeastward 

palinspastic restoration of allochthonous strata in the KMS, 

KMM, ARS, and SD drill holes amounted to about 4, 10, 

22, and 20 mi, respectively (pi. 1, fig. 1).

Of the nine drill holes used in section C-C', drilled 

thicknesses of Stratigraphic units were corrected for dip only 

in the ARS drill hole. In this drill hole, the drilled 

thicknesses of units were corrected for a 30° dip that 

approximates nearby surface dips recorded by Knowles 

(1966). In addition to the 30° dip correction, about 450 ft of 

duplication by a thrust fault was required to reconcile the 

drilled thickness of the upper sandy member of the Gatesburg Formation in the ARS drill hole with the nearby 

surface section measured by Knowles (1966). About 700 ft 

of thrust-fault duplication was removed from the Reedsville 

Shale in the SD drill hole. Thicknesses of Upper Ordovician 

and Lower Silurian strata that crop out near the KMM drill 

hole were taken from an unpublished section measured by 

Wallace de Witt, Jr. (unpub. data, 1969) (pi. 1). Lithology 

and thicknesses of Ordovician and Lower Silurian strata in 

the vicinity of the ARS drill hole were obtained from 

measured outcrop sections by Thompson (1963) and 

Knowles (1966) and from the geologic map by Knowles 

(1966).

Scattered macrofossils collected from outcrops near 

the KMM and ARS drill holes in Bedford County, Pa. 

(Thompson, 1963; Knowles, 1966; Spelman, 1966; WalCambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K5
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K6 Evolution of Sedimentary Basins Appalachian Basin
Table 2. Conodonts from the Amoco No. 1 Svetz drill hole, Somerset County, Pa.

[100- to 200-g cuttings taken at 100-ft intervals between 15,000 and 21,000 ft were processed for conodonts; only the productive samples are listed. Well 

collar at 2,480-ft elevation; total depth 21,460 ft. Conodont color alteration index (CAI) is a measure of organic maturation (Epstein and others, 1977)]

Sample 

interval (ft)

uses

collection no. Conodonts Age CAI

Coburn Limestone

15,400-15,500..... 10750-CO 1 P (dichognathiform) element of Phragmodus Middle Ordovician, no older than early 5

sp. indet. or Plectodina sp. indet. Chazyan [no older than the Phragmoldus tangshanensis Zone (=P. preflexuosus Zone of Sweet and Berg-

__________________________________________________strom (1986)]________________ 

____________________________________Trenton Group___________________________________ 

15,700-15,800..... 10751-CO 1 P (dichognathiform) element of Phragmodus do. 5

sp. indet. or Plectodina sp. indet.

______________________1 M element, unassigned._______________________________________ 

_______________________________Trenton and Black River Groups______________________________ 

15,800-15,900..... 10752-CO 1 P (dichognathiform) element of Phragmodus do. 5 

_______________________sp. indet. or Plectodina sp. indet._________________________________ 

__________________________________Loysburg Formation__________________________________ 

16,500-16,600..... 10753-CO 1 M element, unassigned. do. 5

1 indeterminate fragment.

16,600-16,700..... 10754-CO 1 robust hyaline ramiform fragment. do. 5 

16,900-17,000..... 10755-CO______________do.________________________do.____________5_ 

__________________________________Beekmantown Group__________________________________ 

17,000-17,100..... 10756-CO 1 Pb element of Curtognathus sp. indet. do. 5 

17,100-17,200..... 10757-CO 1 Pb element of Curtognathus sp. indet. do. 5

1 robust hyaline ramiform fragment.

17,700-17,800..... 10758-CO 1 indeterminate fragment. do. 5 

17,800-17,900..... 10759-CO 1 M element of Phragmodus sp. indet. Middle Ordovician, interval of P. 5

1 fragment of Multioistodusl sp. tangshanensis 2&ne-Cahabagnathus

1 indeterminate fragments. friendsvillensis Zone.

18,000-18,100..... 10759-CO 1 indeterminate fragment. do. 5 

18,100-18,200..... 10760-CO 1 P (dichognathiform) element of Phragmodus do. 5

sp. indet.

18,200-18,300..... 10760-CO 2 indeterminate fragments. do. 5 

18,400-18,500..... 10760-CO 1 indeterminate hyaline fragment. do. 5 

19,900-20,000..... 10760-CO 1 poorly preserved panderodontacean? ele- Middle(?) Ordovician, probably down- 5

ment. hole contamination.

1 hyaline coniform fragment.

lace deWitt, Jr., unpub. data, 1969), and conodonts 

recovered from cuttings from the Amoco No. 1 Svetz (AS) 

drill hole (No. 5, fig. 1, pi. 1, tables 1, 2) provided specific 

ages for several stratigraphic units in section C-C'. Additional age assignments for units in section C-C' were 

determined by projecting paleontologically dated horizons 

from (1) adjoining drill holes, (2) thrust-faulted strata that 

crop out along the eastern margin of the basin, and (3) 

gently warped strata that crop out along the western margin 

of the basin.

BASEMENT STRUCTURE

Basement rocks in Pennsylvania and adjoining Ohio 

and West Virginia consist largely of metamorphic rocks of 

Grenville age (1.0 Ga; Grenvillian) (Bass, 1959, 1960;

Lapham, 1975). We know from several published seismic 

lines showing basement faults having normal displacement 

(Beardsley and Cable, 1983; Henderson and Timm, 1985) 

and from isopach maps showing abrupt thickness changes in 

drilled Cambrian and Lower Ordovician rocks (Wagner, 

1976; Harris, 1978) that the Middle Proterozoic basement 

rocks of western Pennsylvania have been disrupted by 

extensional tectonics. However, details of the basement 

structure here are poorly understood because (1) drill holes 

have not yet penetrated the sedimentary cover, (2) magnetic 

and gravity data have not been calibrated to known 

basement rock types and structures, and (3) very few 

seismic data have been published. Most interpretations cite 

the northeast-trending, fault-controlled Rome trough as the 

dominant tectonic element of western Pennsylvania basement structure (Wagner, 1976; Harris, 1978; Beardsley and 

Cable, 1983; Harper, 1989). One exception is the interpreCambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K7
tation by Shumaker (1986), who suggested that the trend of 

the Rome trough changes abruptly in southwestern Pennsylvania from northeast to easterly, subparallel to and south 

of his 40th parallel lineament (fig. 1) and the colinear Lat 

40°N fault zone of Root and Hoskins (1977) (fig. 1).

We favor the interpretations of Wagner (1976), Harris (1978), Beardsley and Cable (1983), and Harper (1989) 

and thus extend the Rome trough northeastward into southwestern Pennsylvania approximately normal to section 

C-C' (fig. 1, pi. 1). Our interpretations of the faults 

accompanying the Rome trough in the vicinity of section 

C-C' are based on limited data and, for this reason, are 

shown as 30- to 80-mi-long, incomplete segments on figure 

1. Undoubtedly, these structures will be modified as multifold seismic records in the area are published and as holes 

in and adjacent to the Rome trough are drilled to Middle 

Proterozoic basement.

The abnormally wide Rome trough in southwestern 

Pennsylvania (fig. 1) probably resulted from the northeastward merger of the Rome trough in West Virginia with an 

adjoining unnamed graben between the Central and Eastern 

West Virginia arches (horst blocks) of Kulander and Dean 

(1976, 1986) (Ryder, 1992). The northwestern side of the 

Rome trough, where it intersects section C-C' (fig. 1), is 

bounded by a down-to-the-southeast normal fault (Harper, 

1989). Harper (1989) suggested that this border fault is 

offset in a right-lateral sense by the northwest-trending 

Pittsburgh-Washington lineament (40th parallel lineament 

of Shumaker (1986)) (fig. 1). The border fault, described 

here, coincides with the Ohio-West Virginia hinge zone of 

Ryder (1992) and the Middle Cambrian hinge of Read 

(1989). Before the deposition of the datum horizon in 

Middle Ordovician time, the structural relief on Proterozoic 

basement rocks across this hinge zone is estimated to have 

been on the order of 2,000 ft (pi. 1).

The down-to-the-northwest normal fault that bounds 

the eastern side of the Rome trough, where it intersects 

section C-C' (fig. 1), is interpreted here to be the northward 

continuation of the western border fault of the Eastern West 

Virginia arch (horst) of Kulander and Dean (1976, 1986) 

(Ryder, 1992). Also, this down-to-the-northwest normal 

fault is closely aligned with the New York-Alabama lineament of King and Zietz (1978) that defines the down-tothe-southeast fault proposed by Ryder (1992) on the eastern 

side of the Central West Virginia arch (horst) of Kulander 

and Dean (1976, 1986). The AS drill hole (fig. 1, pi. 1), 

located on the downthrown northwestern side of the fault, 

drilled about 650 ft into Upper Cambrian rocks before 

reaching a total depth of 21,460 ft. Judging from the 

abnormally thick Ordovician sequence in the AS drill hole 

and from nearby proprietary seismic data, we estimate that 

an additional 8,000 to 10,000 ft of undrilled Cambrian 

strata underlie the AS drill hole (pi. 1). The drilling depth to 

Middle Proterozoic basement rocks may be greater here 

than anywhere else in the Rome trough. Before the deposition of the datum horizon in Middle Ordovician time, the 

structural relief on Proterozoic basement rocks between the 

eastern edge of the Rome trough and the adjoining positive 

fault block is estimated to have been 6,000 to 7,000 ft (pi. 

1). At the same time, structural relief of 12,000 to 14,000 

ft may have existed between the eastern edge of the Rome 

trough and the positive basement block west of the OhioWest Virginia hinge zone (pi. 1).

Relatively thin Middle and Upper Cambrian strata 

encountered in the ARS and SD drill holes, in comparison 

with the estimated thickness of these strata in the Rome 

trough, suggest that the positive fault block adjoining the 

eastern edge of the Rome trough along section C-C' has not 

been broken by major basement-involved normal faults (pi. 

1). This positive fault block, here named the South-central 

Pennsylvania arch (fig. 1, pi. 1), is contiguous with the 

Eastern West Virginia arch (horst) defined by Kulander and 

Dean (1976, 1986) (Ryder, 1992).

Neither the Rome trough nor the adjoining horst 

blocks along section C-C' stand out on the aeromagnetic 

maps of King and Zietz (1978) and Zietz and others (1980), 

as they seem to do along section E-E' (fig. 1), where 

positive and negative magnetic anomalies coincide with 

major positive and negative basement-involved fault 

blocks, respectively (Ryder, 1992). In contrast, the magnetic anomalies near section C-C' and near section D-D' 

about 50 mi to the south (fig. 1) seem to require structural 

interpretations that are opposite to those in section E-E'. 

That is, positive magnetic anomalies near sections C-C' 

and D-D' coincide with negative fault blocks, whereas 

negative anomalies coincide with positive fault blocks.

For example, the Rome trough in southwestern Pennsylvania and adjoining West Virginia where the AS, 

Occidental No. 1 Burley, and Phillips No. A-l Finch drill 

holes (fig. 1) suggest a minimum drilling depth of 20,000 ft 

to Proterozoic basement rocks is characterized by moderate to high magnetic intensities (King and Zietz, 1978; Zietz 

and others, 1980). However, structurally higher blocks that 

adjoin the Rome trough, where the Humble No. 1 Minesinger (HM) (No. 4, fig. 1, pi. 1, table 1), KMS, KMM, 

and ARS holes have been drilled, are characterized by 

lower magnetic intensities. These interpretations suggest 

that major lithologic and (or) structural differences exist 

between the Middle Proterozoic basement rocks of central 

West Virginia and southwestern Pennsylvania. Mafic rocks 

that formed before or during the initial phases of Rome 

trough rifting may be one reason why higher magnetic 

intensities accompany the tectonically negative areas of 

southwestern Pennsylvania and adjoining West Virginia.

Near Pittsburgh, Pa. (fig. 1), the aeromagnetic maps 

of Popenoe and others (1964), King and Zietz (1978), and 

Zietz and others (1980) show a conspicuous narrowing of 

northwest-trending contours. The magnetic gradient normal 

to this magnetic trend slopes steeply to the northeast. This 

magnetic trend, first described by Beck and Mattick (1964),

K8 Evolution of Sedimentary Basins Appalachian Basin
is nearly coincident with a line that marks the terminations 

of northeast-trending fold axes (Wagner and Lytle, 1976) 

and is aligned with the Lat 40°N fault zone of Root and 

Hoskins (1977) (fig. 1). Shumaker (1986) identified the 

magnetic trend as the 40th parallel lineament (fig. 1), which 

marks the southern end of a well-defined, northeasttrending, low-intensity magnetic anomaly that Culotta and 

others (1990) have defined as the Amish anomaly. They 

interpreted this low-intensity magnetic anomaly to be the 

result of Grenvillian compressional tectonics.

Rifting that created the Rome trough and associated 

basement-involved structures occurred largely in the Middle 

Cambrian (Read, 1989). Later tectonic events may have 

reactivated these Middle Cambrian structures, as Harper 

(1989) has proposed in western Pennsylvania, but the 

restoration of section C-C' to a horizontal datum in the 

lower part of the Middle Ordovician sequence has removed 

the later offsets. According to Beardsley and Cable (1983), 

block faulting of the basement beneath part of West 

Virginia may have been controlled by normal dip-slip 

motion along preexisting thrust faults of Middle Proterozoic 

(Grenvillian) age.

West of the Ohio-West Virginia hinge zone in eastern 

Ohio, the Middle Proterozoic basement rocks are undoubtedly broken by numerous normal faults (Sanford and others, 

1985; Ahmad and Smith, 1988), but, in general, they have 

offset basement rocks far less than those faults east of the 

hinge zone. A northwest-trending basement arch called the 

Wooster arch by Coogan and Maki (1988a, b) crosses the 

western end of section C-C' (fig. 1). Moreover, Shumaker 

(1986) suggested that an unnamed, low-relief arch (monoclinal flexure), located several miles southwest of and 

subparallel to section C-C', is underlain by a basementinvolved normal fault (fig. 1).

THICKNESS CHANGES IN THE CAMBRIAN 

AND ORDOVICIAN SEQUENCE

Section C-C' shows a sixfold to sevenfold increase in 

thickness of the Cambrian and Ordovician sequence 

between the relatively stable craton of Ohio and the eastern 

side of the Rome trough in southwestern Pennsylvania (pi. 

1). East of the Rome trough, on the adjoining South-central 

Pennsylvania arch, the Cambrian and Ordovician sequence 

along section C-C' decreases in thickness from about 

one-half to two-thirds of the thickness in the Rome trough 

(pi. 1). This magnitude of thickening and thinning is based 

on (1) the 3,000-ft-thick Cambrian and Ordovician 

sequence that was penetrated in the Wiser Oil No. A-l 

Smith (WS) drill hole (No. 1, fig. 1, pi. 1, table 1) at the 

western end of the section, (2) the 9,500-ft-thick uppermost 

Cambrian and Ordovician sequence penetrated in the AS 

drill hole and the estimated 10,300 ft of undrilled Cambrian 

strata beneath it, (3) the 8,200-ft-thick uppermost Cambrian

and Ordovician sequence penetrated in the KMS drill hole 

near the Allegheny structural front and the estimated 4,500 

ft of undrilled Cambrian strata beneath it, and (4) the 

10,500-ft-thick Cambrian and Ordovician sequence east of 

the Allegheny structural front that consists of 4,500 ft of 

dip- and fault-corrected drilled strata in the ARS drill hole, 

5,100 ft of outcrop section stratigraphically above the ARS 

drill hole, and an estimated 900 ft of undrilled Lower and 

Middle Cambrian strata beneath the ARS drill hole (pi. 1).

In the Rome trough segment of section C-C', the 

thickness of the Cambrian strata is estimated to represent 

about 55 percent of the total Cambrian and Ordovician 

sequence, whereas, on the positive fault blocks adjoining 

the Rome trough, the thickness of the Cambrian strata is 

estimated to represent 25 and 40 percent of the sequence 

(pi. 1). Although we have no corroborating drill-hole data, 

we speculate that most of the thickening of the Cambrian 

strata in the Rome trough segment of section C-C' occurred 

in the Middle Cambrian (pi. 1). The proposed down-to-theeast normal fault that marks the Ohio-West Virginia hinge 

zone is the approximate western limit of Lower and Middle 

Cambrian strata along section C-C'. In contrast, Lower and 

Middle Cambrian strata extend eastward beyond the eastern 

margin of the Rome trough to the eastern end of section 

C-C' (pi. 1). Documentation for the assigned ages in this 

section is presented in the following discussion of the 

stratigraphic framework.

Lower and Middle Ordovician strata also markedly 

increase in thickness in the Rome trough segment of section 

C-C'. However, this thickening is much better documented 

than the thickening of the Cambrian strata. Combined 

Lower and Middle Ordovician strata shown on section C-C' 

expand eastward from about 1,050 ft in the WS drill hole to 

about 5,800 ft in the AS drill hole and then thin to about 

3,300 ft in the ARS drill hole (pi. 1).

Upper Ordovician strata in section C-C' show the 

same differential thickening as underlying strata, but the 

depocenter has shifted from the Rome trough to the Allegheny structural front (pi. 1). Drilled thicknesses of these 

strata increase from about 1,150 ft in the WS drill hole to a 

maximum of about 3,625 ft in the KMS drill hole (pi. 1). 

East and south of the KMS drill hole, the Upper Ordovician 

strata in section C-C' thin to between 2,500 and 3,000 ft in 

the KMM, ARS, and SD drill holes and contiguous outcrop 

sections.

Most of the observed thickness patterns in section 

C-C' are depositional, but they also have been influenced 

by several unconformities that truncate strata overlying the 

positive fault blocks adjoining the Rome trough. The most 

significant of these unconformities is the Knox unconformity (Beardsley and Cable, 1983; Coogan and Maki, 1988a; 

Mussman and others, 1988), which truncates progressively 

older lower Middle Ordovician, Lower Ordovician, and 

Upper Cambrian strata from about 40 mi east of the 

Ohio-West Virginia hinge zone to the western end of

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K9
section C-C' (pi. 1). In Medina County, Ohio, at the 

western end of section C-C' , Lower Ordovician rocks have 

been completely truncated by the Knox unconformity, so 

that Middle Ordovician rocks rest directly on Upper Cambrian rocks (Calvert, 1963; Coogan and Maki, 1988a). The 

Knox unconformity is probably absent in the eastern part of 

the Rome trough in section C-C' but probably reappears 

east of the Rome trough, above the South-central Pennsylvania arch, where it is marked by the minor truncation of 

uppermost Lower Ordovician and lowermost Middle Ordovician strata (pi. 1). Additional unconformities that may 

have caused a thinning of the sequence on the South-central 

Pennsylvania arch are an unnamed Middle Cambrian 

unconformity and two unnamed Middle Ordovician unconformities (pi. 1).

STRATIGRAPHIC FRAMEWORK

Basal Sandstone Unit and Tomstown Dolomite 

(Lower Cambrian)

Although not penetrated by drill holes, strata equivalent to the basal sandstone unit and the Shady Dolomite, as 

recognized by Ryder (1992) in section E-E' (fig. 1), 

probably are present in section C-C' (pi. 1). We speculate 

that these strata are present in the Rome trough and the 

adjoining South-central Pennsylvania arch and attain a 

thickness of 500 to 600 ft. The proposed sequence rests 

unconformably on Middle Proterozoic basement rocks of 

Grenvillian age and probably consists of two parts: (1) a 

thin, basal, sandstone-dominated unit and (2) an overlying 

carbonate-dominated unit. The top of the carbonate unit is 

possibly an unconformity.

Following Ryder (1992), the name basal sandstone 

unit is applied to the postulated thin sandstone unit beneath 

the ARS and SD drill holes (pi. 1). This unit is correlated 

here with the uppermost part of the Lower Cambrian 

Chilhowee Group that crops out in (1) the North Mountain 

fault block of northern Virginia and the adjoining West 

Virginia panhandle (fig. 1) (Edmundson and Nunan, 1973; 

Gathright and Nystrom, 1974; Rader and Biggs, 1975; 

Dean and others, 1989, 1991) and (2) the Carbaugh-Marsh 

Creek fault block of south-central Pennsylvania and adjoining Maryland (fig. 1) (Cloos, 1951; Root, 1968; Fauth, 

1978). The Early Cambrian age assigned to the undrilled 

basal sandstone unit (pi. 1) is based on trilobites collected 

from the upper part of the Chilhowee Group in Washington 

County, Md. (fig. 1) (Bassler, 1919).

The undrilled carbonate unit that probably overlies 

the basal sandstone unit beneath the ARS and SD drill holes 

correlates with (1) the Tomstown Formation (Limestone) in 

Franklin County, Pa. (Stose, 1906; Root, 1968; Fauth, 

1978), (2) the Tomstown Formation (Dolomite) in Washington County, Md. (Cloos, 1951; Reinhardt and Wall, 

1975; Edwards, 1978; Fauth, 1981), and (3) the Tomstown 

Dolomite in the easternmost part of the panhandle of West 

Virginia (Patchen and others, 1984; Dean and others, 1989, 

1991) and in the subsurface of Hardy County, W. Va. 

(Ryder, 1991). The name Tomstown Dolomite is applied 

here to the carbonate unit to be consistent with nomenclature used by Ryder (1991). The Early Cambrian age 

assigned to the undrilled Tomstown Dolomite is based on 

the occurrence of Salterella conulata in Washington 

County, Md. (Reinhardt and Wall, 1975), and of Salterella 

sp. and trilobite fragments in Franklin County, Pa. (Stose, 

1909).

The undrilled basal sandstone-Tomstown Dolomite 

interval was probably deposited as a transgressive unit 

before the rifting event that formed the Rome trough. 

Normal faults that bound the Rome trough and involve the 

postulated basal sandstone-Tomstown Dolomite interval are 

considered here to be latest Early Cambrian to early Middle 

Cambrian in age. Because of their probable transgressive 

nature, the proposed basal sandstone unit and Tomstown 

Dolomite may be as young as early Middle Cambrian in the 

Rome trough, but a late Early Cambrian age is more 

probable.

Waynesboro Formation (Lower and Middle 

Cambrian)

A 230-ft-thick, incomplete sequence of sandy dolomite and anhydritic red shale, penetrated at the base of the 

allochthonous Broadtop block (Shumaker and others, 1985) 

in the ARS drill hole, constitutes the oldest drilled sedimentary rocks shown in section C-C' (pi. 1). The top of the 

sandy dolomite and red shale sequence possibly is an 

unconformity. This sequence correlates with a lithologically 

similar unit that has been identified as the Waynesboro 

Formation in the thrust belt of south-central Pennsylvania 

and eastern West Virginia between the Allegheny structural 

front and the North Mountain thrust fault (fig. 1). Specific 

localities of the Waynesboro Formation that are relevant to 

this study are (1) local outcrops in Blair County, Pa., 

identified by Butts (1945), (2) drilled strata in the deep 

subsurface of Hardy County, W. Va., identified by Ryder 

(1991), and (3) undrilled strata along which major structural 

detachment has probably occurred in the subsurface of 

Hampshire County, W. Va. (Dean and others, 1985). On 

the basis of these correlations, the name Waynesboro 

Formation is assigned here to the sandy dolomite and red 

shale sequence in section C-C' (pi. 1). Following the 

drilled thickness of the Waynesboro Formation reported in 

Hardy County, W. Va., by Ryder (1991), the thickness of 

the Waynesboro Formation in section C-C' , east of the 

Allegheny structural front, is estimated to be about 500 ft.

K10 Evolution of Sedimentary Basins Appalachian Basin
The Waynesboro Formation crops out east of section 

C-C in (1) the Carbaugh-Marsh Creek fault block of 

Franklin County, Pa. (Stose, 1906; Root, 1968; Fauth, 

1978; Berg and others, 1980), and adjoining Washington 

County, Md. (Cloos, 1951; Edwards, 1978; Fauth, 1981), 

and (2) the North Mountain fault block of the panhandle of 

West Virginia (Patchen and others, 1984; Dean and others, 

1989, 1991) and adjoining northern Virginia (Rader and 

Biggs, 1975, 1976; Rader, 1982) (figs. 1, 2).

The Waynesboro Formation in Blair County, Pa., 

was assigned an Early Cambrian age by Butts (1945) on the 

basis of a small collection of fossils that included the 

trilobite Olenellus sp. and the possible mollusk Hyolithes 

sp. Stose (1909) assigned a Middle Cambrian age to the 

Waynesboro Formation in Franklin County, Pa., on the 

basis of the presence of phosphatic brachiopods but admitted that these fossils do not permit a conclusive age 

designation. More recently, in Franklin County, Pa., Root 

(1968) assigned the Waynesboro Formation to the Lower 

Cambrian. Following Stose (1909), Bassler (1919) assigned 

a Middle Cambrian age to the Waynesboro Formation in 

Washington County, Md. We believe that the Early and 

Middle Cambrian age assigned to the Waynesboro Formation by Berg and others (1983) is reasonable in view of the 

scant fossil data and thus suggest that this age be adopted 

for the Waynesboro Formation east of the Allegheny front 

in section C-C (fig. 2, pi. 1).

Although the Waynesboro Formation is most likely 

present in the Rome trough segment of section C-C' , it is 

not shown on plate 1 because its thickness, lithology, and 

lateral extent are unknown. The Ohio-West Virginia hinge 

zone is probably the western limit of the Waynesboro 

Formation in section C-C'. The Waynesboro Formation in 

the Rome trough segment of section C-C' correlates, at 

least in part, with the 1,000-ft-thick unnamed sandstone and 

shale member of the Rome Formation in the Rome trough 

segment of section E-E' (fig. 1). Ryder (1992) assigned a 

Middle Cambrian age to the unnamed sandstone and shale 

member of the Rome Formation on the basis of its probable 

correlation with trilobite-bearing drilled strata of Middle 

Cambrian age near the bottom of the middle one-third of the 

Rome Formation in Mingo County, W. Va. (Donaldson and 

others, 1975, 1988). However, the possibility remains that 

the lower one-third of the Rome Formation here, beneath 

the fossiliferous strata, is Early Cambrian in age (Patchen 

and others, 1984). We consider the Waynesboro Formation 

in the Rome trough segment of section C-C' to be Early and 

Middle Cambrian in age.

The sandstone unit that rests on Middle Proterozoic 

basement rocks west of the Ohio-West Virginia hinge zone 

is the Mount Simon Sandstone (Cohee, 1948). The Mount 

Simon Sandstone is a transgressive, basal sandstone that 

probably ranges in age from the latest Middle Cambrian 

near the Ohio-West Virginia hinge zone to early Late 

Cambrian at the western end of section C-C' (fig. 2, pi. 1).

East of the Ohio-West Virginia hinge zone, the Mount 

Simon Sandstone may merge with the uppermost part of the 

Waynesboro Formation.

Pleasant Hill Limestone, Warrior Formation, and 

Elbrook Formation (Middle and Upper 

Cambrian)

A 1,680-ft-thick limestone and dolomite sequence 

overlies the Waynesboro Formation in the ARS drill hole 

(pi. 1). In ascending order, the sequence consists of (1) a 

480-ft-thick limestone unit, (2) an 850-ft-thick oolitic, 

sandy dolomite unit, and (3) a 350-ft-thick sandy dolomitic 

limestone containing local chert and oolite beds. A partial 

section of the limestone and dolomite sequence, consisting 

of the upper 210 ft of the middle dolomite unit and an 

overlying 220-ft-thick upper dolomitic limestone unit, was 

penetrated at the bottom of the SD drill hole (pi. 1).

The lower limestone unit in the ARS drill hole 

correlates with (1) the Pleasant Hill Limestone as defined by 

Butts (1945) in outcrop in Blair County, Pa., (2) the 

Pleasant Hill Formation as defined by Wilson (1952) and 

Wagner (1966) in outcrop in Blair County, Pa., and by 

Wagner (1966) in the subsurface of Lycoming County, Pa., 

and (3) the lower part of the Elbrook Formation as defined 

by Ryder (1991) in the subsurface of Hardy County, W. Va. 

We assign the name Pleasant Hill Limestone to the lower 

limestone unit in the ARS drill hole (pi. 1) because the unit 

is near the type locality of the Pleasant Hill Limestone in 

Blair County, Pa., and consists predominantly of limestone.

The combined middle dolomite and upper dolomitic 

limestone units in the ARS and SD drill holes correlate with

(1) the Warrior Limestone as defined by Butts (1918, 1945) 

in outcrop in Bedford, Blair, and Huntington Counties, Pa.,

(2) the Warrior Formation as defined by Wilson (1952), 

Wagner (1966), and Knowles (1966) in outcrop in Bedford, 

Blair, and Huntington Counties, Pa., and by Wagner (1966) 

in the subsurface of Lycoming County, Pa., and (3) the 

upper three-fourths of the Elbrook Formation as defined by 

Ryder (1991) in the subsurface of Hardy County, W. Va. 

We assign the name Warrior Formation to the combined 

middle dolomite and upper dolomitic limestone units in the 

ARS drill hole because of their proximity to the type 

locality of the Warrior Limestone in Huntington County. 

The name Warrior Formation as used by Wilson (1952), 

Wagner (1966), Knowles (1966), and Berg and others 

(1983) is favored over the name Warrior Limestone as used 

by Butts (1918, 1945) because it better represents the 

dolomite and limestone lithology of the unit. The dolomite 

and limestone parts of the Warrior Formation in the ARS 

drill hole are assigned here to the unnamed dolomite and 

unnamed limestone members, respectively, of the Warrior 

Formation (pi. 1). In the SD drill hole, the combined 

undrilled equivalent of the Pleasant Hill Limestone, the

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K11
partly drilled middle dolomite unit, and the upper limestone 

unit are assigned here to the Elbrook Formation (pi. 1). We 

favor the name Elbrook Formation in the SD drill hole, 

rather than the name Warrior Formation used by Wagner 

(1966), because of the proximity of the drill hole to Hardy 

County, W. Va., where correlative strata are assigned by 

Ryder (1991) to the Elbrook Formation.

The combined Pleasant Hill Limestone and overlying 

Warrior Formation in Pennsylvania correlate with the 

Elbrook Formation (Limestone) in the Carbaugh-Marsh 

Creek fault block in Franklin County, Pa. (Stose, 1909; 

Root, 1968; Berg and others, 1983), and in adjoining 

Washington County, Md. (Bassler, 1919; Cloos, 1951; 

Fauth, 1981) (fig. 2). They also correlate with the Elbrook 

Formation in the North Mountain fault block of the West 

Virginia panhandle (Donaldson and Page, 1963; Dean and 

others, 1989, 1991; Patchen and others, 1984) and in 

adjoining northern Virginia (Rader and Biggs, 1975, 1976; 

Rader, 1982).

The 1,700-ft drilled thickness of the Pleasant Hill 

Limestone plus the Warrior Formation in section C-C", the 

1,500-ft estimated thickness of the Elbrook Formation in 

section C-C', and the 1,600-ft drilled thickness of the 

Elbrook Formation in Hardy County, W. Va., along section 

D-D' are each about one-half the thickness of the Elbrook 

Dolomite as defined by Perry (1964) and Ryder (1992) in 

the subsurface of Pendleton County, W. Va. These three 

sequences are probably equivalent to the upper one-half of 

the Elbrook Dolomite in Pendleton County, W. Va. (section 

E-E' of Ryder, 1992). Apparently, strata equivalent to the 

lower one-half of the Elbrook Dolomite in the subsurface of 

Pendleton County, W. Va., are missing in sections C-C' 

and D-D' as a result of erosion and (or) nondeposition. This 

suggested hiatus is shown on section C-C' as an unconformity between the Waynesboro Formation and the overlying Pleasant Hill Limestone or Elbrook Formation (pi. 1, 

fig. 2). The unconformity may be absent in Franklin 

County, Pa., where Stose (1909) and Root (1968) estimated 

that the Elbrook Formation is about 3,000 ft thick (fig. 2).

The Pleasant Hill Limestone is assigned a Middle 

Cambrian age by Butts (1945) and Wilson (1952) on the 

basis of a collection of trilobites, hyolithids, and brachiopods from Blair County, Pa. East of the North Mountain 

fault in northernmost Virginia, Butts (1940) assigned a 

Middle Cambrian age to the lowermost part of the Elbrook 

Formation on the basis of the trilobite Glossopleura sp. This 

lower(?) Middle Cambrian part of the Elbrook Formation in 

the North Mountain fault block is probably older than the 

Pleasant Hill Limestone rather than equivalent to the Pleasant Hill Limestone, as Wilson (1952) and Berg and others 

(1983) suggested. In this study, the Pleasant Hill Limestone 

is assigned to the middle and upper parts of the Middle 

Cambrian (pi. 1, fig. 2).

Trilobites have been collected from approximately 

the upper two-thirds of the Warrior Formation in Bedford,

Blair, Centre, and Huntington Counties, Pa. (Butts, 1945; 

Tasch, 1951; Wilson, 1952). All these trilobites are indicative of an early Late Cambrian (Dresbachian) age for the 

Warrior Formation. However, a late Middle Cambrian age 

is permissible for the lower part of the Warrior Formation, 

where fossils have not been collected (Wilson, 1952). 

Therefore, following Wilson (1952) and Berg and others 

(1983), we assign a Middle and Late Cambrian age to the 

Warrior Formation and to the correlative part of the Elbrook 

Formation (pi. 1, fig. 2).

Most certainly, strata equivalent to the Pleasant Hill 

Limestone and Warrior Formation combined and to the 

Elbrook Formation are present in the Rome trough segment 

of section C-C'. Although the Pleasant Hill, Warrior, and 

Elbrook are not shown in the Rome trough part of plate 1, 

they most likely correlate with the combined upper one-half 

of the Conasauga Group and the lowermost part of the 

Gatesburg Formation in the Rome trough segment of 

section E-E' (Ryder, 1992) (fig. 1). The Pleasant Hill 

Limestone that is present in the ARS drill hole (and that 

presumably is present in the Rome trough segment of 

section C-C') is approximately equivalent to the unnamed 

limestone member of the Maryville Limestone of the 

Conasauga Group in the Rome trough segment of section 

E-E' (Ryder, 1992). This suggested correlative of the 

Pleasant Hill Limestone is slightly younger than the Rogersville Shale of the Conasauga Group that Resser (1938) 

suggested as being correlative with the Pleasant Hill Limestone. Very likely, the pre-Maryville Limestone part of the 

Conasauga Group (Pumpkin Valley Shale, Rutledge Limestone, Rogersville Shale) in the Rome trough segment of 

section E-E' is also present in the Rome trough segment of 

section C-C'. However, as previously implied, the preMaryville Limestone part of the Conasauga Group is absent 

east of the Rome trough in section C-C' owing to erosion 

and (or) nondeposition (fig. 2).

The Warrior Formation in the ARS drill hole, the 

strata equivalent to the Warrior Formation in the Elbrook 

Formation in the SD drill hole, and the Warrior Formation 

presumed to be present in the Rome trough segment of 

section C-C' are approximately equivalent to the combined 

unnamed dolomite member of the Maryville Limestone and 

the lowermost part of the lower sandy member of the 

Gatesburg Formation in the Rome trough segment of 

section E-E' (Ryder, 1992). The unnamed limestone member of the Warrior Formation in the ARS drill hole and 

equivalent strata in the SD drill hole probably correlate with 

the uppermost part of the unnamed dolomite member of the 

Maryville Limestone and the lowermost part of the lower 

sandy member of the Gatesburg Formation in the Rome 

trough segment of section E-E' (Ryder, 1992). Our proposed correlation of the Warrior is in general agreement 

with that of Wilson (1952), who correlated the Upper 

Cambrian part of the Warrior Formation with the Nolichucky Shale and the Maynardville Limestone of the ConaK12 Evolution of Sedimentary Basins Appalachian Basin
sauga Group, the former of which Ryder (1992) considered 

to be a partial equivalent of the lower sandy member of the 

Gatesburg Formation. In addition, Wilson (1952) implied 

that the Middle Cambrian part of the Warrior Formation 

correlates with part of the Maryville Limestone. Resser 

(1938) correlated the entire Warrior Formation with the 

Upper Cambrian Nolichucky Shale of the Conasauga 

Group, a correlation that spans a chronostratigraphic interval that is smaller and slightly higher than the one proposed 

here.

The Pleasant Hill Limestone is not represented by 

equivalent strata west of the Ohio-West Virginia hinge 

zone, but the Warrior Formation is represented by a 

time-transgressive dolomite unit that Janssens (1973) identified as the Rome Formation (pi. 1). This unit thins 

westward from a thickness of about 590 ft in the Management Control No. 3 Murray (MM) drill hole (No. 3, fig. 1, 

pi. 1, table 1) to a thickness of about 390 ft in the WS drill 

hole at the western end of section C-C' (pi. 1). The Rome 

Formation of Janssens (1973) was assigned a Late Cambrian age, but, because of its transgressive nature, the 

lowermost part of the Rome, in the vicinity of the HM drill 

hole, may be latest Middle Cambrian in age (pi. 1, fig. 2).

Gatesburg Formation (Upper Cambrian)

A 1,650- to 1,790-ft-thick sequence of predominantly 

sandy dolomite conformably overlies the Warrior Formation and the equivalent Elbrook Formation in the ARS and 

SD drill holes (pi. 1). This sequence correlates with the 

Gatesburg Formation as defined by Butts (1918, 1945), 

Butts and Moore (1936), Wilson (1952), and Knowles 

(1966) in outcrop in central and south-central Pennsylvania 

and by Ryder (1991) in the subsurface of Hardy County, W. 

Va. Wagner (1966, 1976) assigned the name Gatesburg 

Formation to the sandy dolomite sequence in the SD drill 

hole, a practice that we accept for both the SD and the ARS 

drill holes in section C-C'. In ascending order, the Gatesburg Formation in the ARS and SD drill holes consists of 

(1) an approximately 790-ft-thick oolitic, sandy dolomite 

unit named the lower sandy member by Wilson (1952), (2) 

a 100-ft-thick limestone unit named the Ore Hill Limestone 

Member by Butts (1945), (3) a 550- to 700-ft-thick oolitic, 

sandy dolomite unit named the upper sandy member by 

Wilson (1952), and (4) an approximately 180-ft-thick, 

highly cherty, oolitic dolomite unit named the Mines 

Dolomite Member by Butts (1945) and Wilson (1952) (pi. 

1) (Wagner, 1966). The members of the Gatesburg Formation used here are the same as those used in the outcrop of 

central and south-central Pennsylvania, except that the 

Stacy Dolomite Member the basal unit of the Gatesburg 

recognized by Butts (1918, 1945), Wilson (1952), and 

Knowles (1966) in outcrop is not identified. By using the 

Mines Dolomite as the upper member of the Gatesburg

Formation, we follow the nomenclature suggested by Wilson (1952) and Berg and others (1983).

The sandstone and dolomite sequence in the bottom 

650 ft of the AS drill hole, in the Rome trough segment of 

section C-C', is correlated here with the upper part of the 

Gatesburg Formation (pi. 1, fig. 2). Following the terminology used by Ryder (1991) for the Gatesburg Formation 

in the Occidental No. 1 Burley drill hole (fig. 1), we name 

the incomplete 140-ft-thick dolomite unit at the base of the 

drilled sequence in the AS drill hole the middle dolomite 

member (pi. 1). The 430-ft-thick, sandstone-dominated 

middle part of the sandstone and dolomite sequence in the 

AS drill hole correlates with the upper sandy member in the 

ARS and SD drill holes and with the Olin Sandstone of 

Wagner (1976) in the Occidental No. 1 Burley drill hole 

(fig. 1). Wagner (1976) and Berg and others (1983) 

correlated the Olin Sandstone, an abnormally thick 

sandstone-dominated unit confined to the Rome trough in 

Pennsylvania and adjoining States, with the lower sandy 

member of the Gatesburg Formation. We disagree with the 

correlation by Wagner (1976) and Berg and others (1983) 

and, instead, correlate the Olin Sandstone with the upper 

sandy member of the Gatesburg Formation. Therefore, we 

assign the 430-ft-thick sandstone sequence in the AS drill 

hole to the upper sandy member of the Gatesburg Formation 

and abandon the name Olin Sandstone in this study (pi. 1). 

The 80-ft-thick cherry, oolitic dolomite unit that overlies the 

upper sandy member in the AS drill hole is assigned to the 

Mines Dolomite Member (pi. 1).

On the basis of trilobites from the Ore Hill Limestone 

Member in Bedford and Blair Counties, Pa., Butts (1945), 

Wilson (1951, 1952), and Taylor and Loch (1989) assigned 

a Late Cambrian (Franconian) age to the lower one-half of 

the Gatesburg Formation (fig. 2). Furthermore, Butts 

(1945) and Wilson (1952) assigned a Late Cambrian (Trempealeauan) age to the upper one-half of the Gatesburg 

Formation (fig. 2) by using local gastropods from the Mines 

Dolomite Member.

Approximately 25 mi east of the ARS drill hole, on 

the eastern side of the Carbaugh-Marsh Creek fault in 

Franklin County, Pa., the Gatesburg Formation correlates 

with an approximately 3,150-ft-thick limestone and subordinate dolomite sequence identified as the Conococheague 

Group (Root, 1968; Berg and others, 1983) (fig. 2). The 

name Conococheague Group of Root (1968) replaced the 

name Conococheague Formation (Limestone) of Stose 

(1909) and Wilson (1952). The lower 280 ft of the Conococheague Group in Franklin County, Pa., contains up to 

five thin beds of quartz sandstone (Root, 1968) that Wilson 

(1952) included with his Big Spring Station Member. Root 

(1968) subdivided the Conococheague Group in Franklin 

County, Pa., into (1) the Zullinger Formation (2,500 ft), 

which is approximately equivalent to the combined lower 

sandy member, the Ore Hill Limestone Member, and most 

of the upper sandy member, and (2) the Shadygrove

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K13
Formation (650 ft), which is approximately equivalent to 

the combined uppermost upper sandy member and the 

Mines Dolomite Member (fig. 2). The Conococheague in 

adjoining Washington County, Md., was assigned formation status by Bassler (1919), Cloos (1951), Wilson (1952), 

and Edwards (1978). The basal 200- to 300-ft-thick sandstone and dolomite unit at the base of the Conococheague 

Formation (Limestone) in Maryland was assigned to the Big 

Spring Station Member by Wilson (1952). The Conococheague Formation, including the Big Spring Station Member, is also identified in the North Mountain fault block of 

the West Virginia panhandle (Donaldson and Page, 1963; 

Dean and others, 1987) and adjoining northern Virginia 

(Young and Rader, 1973; Rader and Biggs, 1975, 1976).

Trilobites collected from the Conococheague Group 

(Limestone, Formation) in south-central Pennsylvania and 

adjoining Maryland and northern Virginia indicate that the 

Conococheague spans most of the Upper Cambrian (upper 

Dresbachian, Franconian, Trempealeauan ) (Stose, 1909; 

Wilson, 1951, 1952; Sando, 1958) and therefore correlates 

with the majority of the Gatesburg Formation in section 

C-C' (fig. 2). Dresbachian-age trilobites in the lower part 

of the Big Spring Station Member suggest that the lowermost part of the Conococheague correlates with the uppermost part of the unnamed limestone member of the Warrior 

Formation (fig. 2).

Strata equivalent to the Gatesburg Formation west of 

the Ohio-West Virginia hinge zone, in section C-C', 

consist of the upper part of the Rome Formation of Janssens 

(1973), the Conasauga Formation of Janssens (1973), the 

Krysik sandstone of driller's usage, the B zone of Calvert 

(1964), the lower part of the Knox Dolomite of Janssens 

(1973), and the Rose Run Sandstone Member (pi. 1). These 

units have a combined thickness of about 400 to 600 ft. The 

Krysik sandstone of driller's usage and the B zone of 

Calvert (1964) constitute the Steam Corners Member of 

Coogan and Maki (1988b). The upper Rome-ConasaugaKrysik-B zone interval correlates with the lower sandy 

member of the Gatesburg Formation, whereas the Rose Run 

Sandstone Member correlates with the upper sandy member 

of the Gatesburg Formation (pi. 1, fig. 2). The lower part of 

the Knox Dolomite of Janssens (1973) correlates approximately with the Ore Hill Limestone Member and the 

equivalent middle dolomite member and with the lower part 

of the upper sandy member of the Gatesburg Formation (pi. 

1, fig. 2). These correlatives of the Gatesburg Formation in 

eastern Ohio the Rome Formation (upper part), the Conasauga Formation, the Krysik sandstone, the B zone, the 

lower part of the Knox Dolomite, and the Rose Run 

Sandstone Member are here assigned a Late Cambrian age

(pl. 1, fig- 1).

The possibility exists that part or all of the upper 

sandy member, the Rose Run Sandstone Member, and the 

Mines Dolomite Member may be of Early Ordovician age. 

For example, McGuire and Howell (1963) assigned an

Early Ordovician age to the Rose Run Sandstone in eastern 

Kentucky, consistent with the Early Ordovician age tentatively assigned by Repetski (1985), on the basis of conodonts, to sandstone beds equivalent to the Rose Run 

Sandstone in the basal part of the Chepultepec Dolomite in 

the Thorn Hill section of eastern Tennessee (fig. 1). Also, 

on the basis of conodonts, Orndorff (1988) assigned an 

Early Ordovician age to the upper 141 ft of the Conococheague Formation as recognized in northern Virginia by 

Young and Rader (1974) and Rader and Biggs (1975, 

1976).

Beekmantown Group (Lower and Lower Middle 

Ordovician)

Near the depositional axis of the Rome trough in 

section C-C', where the AS drill hole is located, a 3,800- 

ft-thick dolomite sequence conformably overlies the upper 

sandy member of the Gatesburg Formation (pl. 1). This 

dolomite sequence thins gradually east of the Rome trough, 

between the Allegheny structural front and the North 

Mountain fault, to about 3,000 ft in the KMS drill hole and 

to between 2,250 and 2,500 ft in the ARS (includes 

adjoining outcrop section) and SD drill holes (pl. 1). These 

thicknesses of the dolomite sequence in and around the 

KMS, ARS, and SD drill holes are comparable to the 

2,400- to 2,650-ft measured outcrop thickness of the 

correlative Beekmantown Group in nearby Blair County, 

Pa. (Butts, 1945). West of the Rome trough, the dolomite 

sequence thins abruptly to about 550 ft in the HM drill hole 

astride the Ohio-West Virginia hinge zone down to about 60 

ft in the WS drill hole at the western end of section C-C'

(pl. 1).

Anhydrite and limestone are commonly found in the 

upper 1,410 ft of the dolomite sequence in the AS drill hole. 

The anhydrite is concentrated in the lower 480 and upper 

320 ft of the 1,410-ft-thick sequence, whereas the limestone 

is concentrated in the upper 590 ft of the 1,410-ft-thick 

sequence (pl. 1). Native sulfur is associated with the lower 

zone of anhydritic dolomite. The anhydrite- and limestonebearing zones in the AS drill hole are mainly confined to the 

Rome trough segment of section C-C', except where the 

upper zone extends eastward beyond the margin of the 

trough to the KMS drill hole along the Allegheny structural 

front (pl. 1). Moreover, a 320-ft-thick zone of anhydritic 

dolomite containing native sulfur occurs in the lower 

one-half of the dolomite sequence in the KMS drill hole. 

This anhydritic dolomite apparently is confined to the area 

near the Allegheny structural front. In the SD drill hole, a 

50-ft-thick limestone unit is present at the base of the 

dolomite sequence, and a 175-ft-thick calcareous dolomite 

is present near the top of the sequence.

Calvert (1963) identified the Knox unconformity at 

the base of the 60-ft-thick dolomite sequence in the WS drill

K14 Evolution of Sedimentary Basins Appalachian Basin
hole at the western end of section C-C' (pi. 1). This 

well-known regional unconformity extends eastward into 

the Rome trough but probably disappears west of the AS 

drill hole. The unconformity probably reappears at the 

eastern end of section C-C' above the South-central Pennsylvania arch. More details regarding the stratigraphic 

position and extent of the Knox unconformity in section 

C-C' will be discussed in the following section.

Wagner (1966) assigned the dolomite sequence in the 

KMM and SD drill holes to formations of the Beekmantown 

Group but did not refer to the name Beekmantown Group. 

Likewise, Knowles (1966) assigned the dolomite sequence 

in the KMM drill hole and in the outcrop section adjoining 

the ARS drill hole to formations of the Beekmantown 

Group without using the name Beekmantown Group. In 

ascending order, the formations recognized by Wagner 

(1966) and Knowles (1966) are the Larke Dolomite (Formation) and the equivalent Stonehenge Limestone (Formation), the Nittany Dolomite (Formation), and the Beliefonte 

Dolomite (Formation). All of these formations crop out in 

Bedford, Blair, and Centre Counties, Pa. (Butts, 1918, 

1945; Butts and Moore, 1936; Swartz and others, 1955; 

Spelman, 1966; Donaldson, 1969). Moreover, the 3,800- 

ft-thick dolomite sequence in the AS drill hole correlates 

with an estimated 3,100-ft-thick (drilled thickness is 2,600 

ft) anhydritic and calcareous dolomite sequence in the 

Phillips No. A-l Finch drill hole (fig. 1) that Wagner 

(1966) assigned to formations in the Beekmantown Group. 

Ryder (1991) assigned the name Beekmantown Group to 

the anhydritic and calcareous dolomite sequence in the 

Phillips No. A-l Finch without identifying specific formations. Another correlative unit of the dolomite sequence in 

the AS drill hole, the 2,150-ft-thick anhydritic and calcareous dolomite sequence in the Occidental No. 1 Burley drill 

hole (fig. 1), also was assigned to the Beekmantown Group 

by Ryder (1991). Following Wagner (1966) and Ryder 

(1991), we assign the name Beekmantown Group to the 

3,800-ft-thick dolomite sequence in the AS drill hole and to 

correlative dolomite sequences in the KMS, KMM, ARS, 

and SD drill holes (pi. 1). The Beekmantown Group in 

section C-C' is undivided, except for (1) the outcrop 

section near the ARS drill hole, where the Larke, Nittany, 

and Bellefonte Dolomites (Formations) have been identified 

by Knowles (1966), and (2) the drilled sequence in the SD 

drill hole, where Wagner (1966) assigned the basal limestone unit to the Stonehenge Limestone (Formation).

West of the Ohio-West Virginia hinge zone, the 

Beekmantown Group is replaced laterally by two formations. The lower formation, the lateral equivalent of the 

lower one-third of the Beekmantown Group in the AS drill 

hole, is assigned to the upper part of the Knox Dolomite of 

Janssens (1973). The upper formation, the lateral equivalent 

of the anhydritic and calcareous dolomite part of the 

Beekmantown Group in the AS drill hole, is assigned here 

to the Wells Creek Formation as used in Ohio by Janssens

(1973 ), Stith (1979, 1986), Wickstrom and others (1985), 

and Wickstrom and Gray (1988). The Wells Creek Formation consists largely of grayish-green shale and dolomite. 

The conspicuous westward-tapering wedge formed by the 

Beekmantown Group in the Rome trough segment of 

section C-C' and the Knox-Wells Creek interval west of the 

Ohio-West Virginia hinge zone resulted from a combination 

of depositional thinning and truncation beneath the Middle 

Ordovician Knox unconformity (pi. 1).

The Beekmantown Group is also recognized in the 

Carbaugh-Marsh Creek fault block in Franklin County, Pa., 

where it has a measured thickness of approximately 4,000 

ft. Following the names assigned by Sando (1957, 1958) to 

the Beekmantown Group in Franklin County and adjoining 

Washington County, Md., Root (1968) subdivided the 

Beekmantown Group in Franklin County into four formations (in ascending order): (1) the Stoufferstown Formation, 

a 260-ft-thick, coarse-grained, clastic limestone unit, (2) 

the Stonehenge Formation, a 775-ft-thick limestone unit, 

(3) the Rockdale Run Formation, an approximately 2,500- 

ft-thick limestone and subordinate dolomite unit, and (4) the 

Pinesburg Station Formation, an approximately 450-ft-mick 

dolomite and subordinate limestone unit. In this study, we 

follow Sando (1958) and Berg and others (1983) and treat 

the Stoufferstown as a member of the Stonehenge Formation (fig. 2). Similar nomenclature is applied to the approximately 4,000-ft-thick Beekmantown Group in the North 

Mountain fault block in the panhandle of West Virginia 

(Donaldson and Page, 1963; Dean and others, 1987) and to 

the 2,600- to 3,700-ft-thick Beekmantown Group in the 

North Mountain fault block in northern Virginia (Edmundson and Nunan, 1973; Young and Rader, 1974; Rader and 

Biggs, 1975, 1976).

An Early Ordovician age was assigned to the Beekmantown Group or to formations of the Beekmantown 

Group by Butts (1945), Knowles (1966), Spelman (1966), 

Lees (1967), and Donaldson (1969) where it crops out in 

Bedford, Blair, and Centre Counties, Pa. In addition, Sando 

(1957, 1958) assigned an Early Ordovician age to the 

Beekmantown Group in Franklin County, Pa., and adjoining Washington County, Md. This age designation was 

based on (1) the stratigraphic position of the Beekmantown 

between the Gatesburg Formation and the Conococheague 

Group of Late Cambrian [Orndorff (1988) recently assigned 

a Late Cambrian-earliest Early Ordovician age to the 

Conococheague] age and limestones of Middle Ordovician 

age and (2) local to common occurrences of probable 

age-diagnostic gastropods, conodonts, and trilobites. Macrofossils collected by Knowles (1966) and Spelman (1966) 

from the Beekmantown Group in the outcrop section near 

the ARS drill hole consist of (1) gastropods and chiton(?) 

plates from the Larke Dolomite (F6 on pi. 1), (2) gastropods 

and orthocone cephalopods from the middle part of the 

Nittany Dolomite (F5 on pi. 1), and (3) a coiled cephalopod 

from the lower part of the Bellefonte Dolomite (F4 on pi. 1).

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K15
These fossils suggest an Early Ordovician age for at least 

the lower two-thirds of the Beekmantown Group near the 

ARS drill hole (pi. 1, fig. 2). Trilobites collected from the 

Stonehenge Formation in central Pennsylvania by Taylor 

(1986) do not support the Late Cambrian age assigned to the 

lowermost Stonehenge Limestone (Formation) and the 

Larke Dolomite (Formation) by Berg and others (1983).

Wagner (1966), on the basis of intertonguing strata of 

the uppermost Beekmantown Group and the lowermost St. 

Paul Group of early Middle Ordovician age (Neuman, 

1951), tentatively assigned an early Middle Ordovician 

(Chazyan) age to the upper 200 ft of the Beekmantown 

Group in central and south-central Pennsylvania and adjoining Maryland and West Virginia. For the remainder of the 

Beekmantown Group in this area, Wagner (1966) agreed 

with the Early Ordovician age assigned by previous investigators. Conodont studies by Harris and Repetski (1982, 

1983) confirmed the early Middle Ordovician age proposed 

by Wagner (1966) for the upper part of the Beekmantown 

Group. Their studies indicated that, from about Harrisonburg, Va. (fig. 1), northward into central Pennsylvania, the 

upper 350 to 900 ft of the Beekmantown Group contained 

strata ranging from earliest to early Middle Ordovician 

(Whiterockian) age. In Blair County, Pa., approximately 

the upper 700 ft of the Bellefonte Dolomite was assigned an 

early Middle Ordovician age by Harris and Repetski (1982, 

1983). Berg and others (1983) have accepted the Early and 

Middle (Whiterockian and Chazyan) Ordovician age proposed by Harris and Repetski (1982, 1983) for the Beekmantown Group in Pennsylvania. However, the Whiterockian and Chazyan parts of the Middle Ordovician used by 

Berg and others (1983) (as defined in COSUNA charts) (see 

Patchen and others, 1984) occupy chronostratigraphic positions different from the Whiterockian and Chazyan defined 

by Barnes and others (1981) and Ross and others (1982) and 

adopted in this paper.

Conodonts were recovered (table 2) from three intervals in the Beekmantown Group in the AS drill hole: (1) 

17,000 to 17,200 ft (f4 on pi. 1), (2) 17,700 to 18,500 ft (f5 

on pi. 1), and (3) at about 19,900 to 20,000 ft (f6 on pi. 1). 

Drill-hole cuttings from the f4 interval yielded conodonts of 

Middle Ordovician age that are no older than the Phragmodus tangshanensis zone (Phragmodus pre-flexuosus zone of 

Sweet and Bergstrom, 1986) or the lower part of the 

Chazyan Stage as used in this paper. Cuttings from the f5 

interval exclusive of the top 100 ft in the AS drill hole 

yielded Middle Ordovician conodonts indicative of a twozone interval the P. tangshanensis zone and the succeeding Cahabagnathus friendsvillensis zone of Sweet and 

Bergstrom (1986) (lower to middle part of the Chazyan used 

in this paper). Conodonts from the f6 interval are of 

Middle(?) Ordovician age and are no younger than the P. 

tangshanensis and C. friendsvillensis zones. These conodonts suggest that the upper 700 ft of the Middle Ordovician 

part of the Bellefonte Dolomite in Blair County, Pa., is

represented by at least the upper 1,500 ft of the Beekmantown Group in the AS drill hole. If the conodonts in the f6 

interval are of Middle Ordovician age, at least 3,000 ft of 

the Beekmantown Group may be equivalent to the upper 

700 ft of the Bellefonte Dolomite in Blair County. However, a 3,000-ft thickness for the Middle Ordovician part of 

the Beekmantown Group seems excessive, particularly 

because the remaining 800-ft-thick Lower Ordovician part 

would be about one-half the thickness of the Lower Ordovician sequence near the ARS drill hole. Possibly, the 

Middle(?) Ordovician conodonts in the f6 interval resulted 

from downhole contamination. We tentatively place the 

Lower Ordovician-Middle Ordovician boundary at about 

19,000 ft in the AS drill hole, which indicates that about 

1,800 ft of the Beekmantown Group here is Early Ordovician in age and about 2,000 ft of the Beekmantown is of 

Middle Ordovician (Whiterockian) age (pi. 1).

In the KMS, KMM, ARS, and SD drill holes, east of 

the AS drill hole, the Lower Ordovician-Middle Ordovician 

boundary is placed in the upper one-half to one-third of the 

Beekmantown Group. In the ARS and SD drill holes, we 

suggest that the boundary coincides with the Knox unconformity (pi. 1). In eastern Ohio, the Lower Ordovician part 

of the Beekmantown Group is represented by the upper part 

of the Knox Dolomite of Janssens (1973), whereas the 

Middle Ordovician (Chazyan) part of the Beekmantown 

Group is represented by the Wells Creek Formation (pi. 1). 

From about 5 mi west of the Belden and Blake and 

Company No. 1-381 Westfall drill hole (BBW) (No. 2, fig. 

1, pi. 1, table 1) to the western end of section C-C' , the 

Lower Ordovician part of the Knox Dolomite has been 

completely truncated by the Middle Ordovician Knox 

unconformity.

Knox Unconformity

Between the Ohio-West Virginia hinge zone and the 

western end of section C-C', the Knox unconformity 

underlies the Wells Creek Formation and truncates, in 

succession, (1) the upper part of the Knox Dolomite of 

Janssens (1973) (equivalent to the Lower Ordovician part of 

the Beekmantown Group), (2) the Rose Run Sandstone 

(equivalent to the upper sandy member of the Gatesburg 

Formation), and (3) the top of the lower part of the Knox 

Dolomite of Janssens (1973) (equivalent to the middle 

dolomite member of the Gatesburg Formation). In eastern 

Ohio, the Knox unconformity is generally easy to recognize 

on geophysical and lithologic logs because of the abrupt 

lithologic change between the Wells Creek Formation 

(consisting of grayish-green shale, argillaceous, very finely 

crystalline dolomite, and, commonly, a thin basal sandstone) and the underlying Knox Dolomite (consisting of fine 

to medium crystalline dolomite). The Knox unconformity is 

more difficult to recognize in those drill holes where the

K16 Evolution of Sedimentary Basins Appalachian Basin
Wells Creek Formation contains a basal sandstone unit that 

overlies the Rose Run Sandstone or sandy dolomite of the 

Knox Dolomite.

The Knox unconformity continues east of the OhioWest Virginia hinge zone into the Rome trough segment of 

section C-C' , where it is situated in the upper 500 to 600 ft 

of the Beekmantown Group and decreases in magnitude 

toward the axis of the trough. In the westernmost part of the 

Rome trough, the Knox unconformity probably separates 

Lower Ordovician strata from overlying lower Middle 

Ordovician strata, whereas, in the central part of the Rome 

trough, the Knox unconformity is located entirely within 

lower Middle Ordovician strata (pi. 1). Successively 

younger strata appear beneath the Knox unconformity, 

eastward of the Ohio-West Virginia hinge zone, until the 

unconformity probably disappears near the AS drill hole 

(pi. 1). Because the Knox unconformity is probably present 

in the subsurface of Hardy County, W. Va. (Ryder, 1991), 

we suggest that it reappears in the KMS, KMM, and SD 

drill holes in section C-C'. In the outcrop section near the 

ARS drill hole, the Knox unconformity may coincide with 

the top of the thick, cherty zone described by Knowles 

(1966) in the lower part of the Bellefonte Dolomite. Middle 

Ordovician strata probably are present beneath the proposed 

Knox unconformity in the KMS and KMM drill holes; 

however, in the SD drill hole and the outcrop section near 

the ARS drill hole, Middle Ordovician strata may have been 

eroded by the unconformity, so that Lower Ordovician 

strata are unconformably overlain by lower Middle Ordovician strata (pi. 1).

The Knox unconformity was not recognized by Root 

(1968) and Berg and others (1983) in Franklin County, Pa. 

(fig. 2), or by Sando (1957) in Washington County, Md., 

and Donaldson and Page (1963) in the West Virginia 

panhandle. The Knox unconformity has been identified in 

northern Virginia, at the top of the Beekmantown Group 

between the North Mountain fault and the Blue Ridge, by 

Young and Rader (1974), Rader and Biggs (1975, 1976), 

and Mussman and Read (1986). However, as Ryder (1991) 

suggested in section D-D' (fig. 1), this unconformity 

appears to be too high stratigraphically to be the Knox 

unconformity, which, in northern Virginia, should most 

likely appear within the middle part of the Beekmantown 

Group, not at the top of the Beekmantown. If the Knox 

unconformity is present in Franklin County, Pa., it probably 

resides near the top of the Rockdale Run Formation (fig. 2).

Conodont studies by Harris and Repetski (1982, 

1983) show that, throughout most of southwestern and 

central Virginia, the Knox unconformity is defined in 

outcrop by limestone of early Middle Ordovician (Chazyan) 

age resting disconformably on the Beekmantown Group, 

which is of latest Early Ordovician age. Northward, from 

about Harrisonburg, Va. (fig. 1), to central Pennsylvania, 

the time span of the Knox unconformity is greatly diminished, as shown in outcrop by progressively younger

Beekmantown strata (Whiterockian) appearing above and 

below the unconformity. The abnormally thick conodontbearing (table 2) lower Middle Ordovician part of the 

Beekmantown Group in the AS drill hole suggests that 

continuous deposition occurred across the Lower 

Ordovician-Middle Ordovician boundary in south-central 

Pennsylvania.

The Knox unconformity at the eastern end of section 

C-C' probably represents a time span between 5 and 10 

million years (pi. 1, fig. 2). Across section C-C', the hiatus 

represented by the Knox unconformity is greatest near the 

Wooster arch. There, the lower part of the Knox Dolomite 

of Late Cambrian age overlain by the Wells Creek Formation of early Middle Ordovician (middle Chazyan) age 

implies that a time span of as much as 40 m.y. is 

represented by the Knox unconformity (fig. 2).

Loysburg Formation and Black River Group 

(Middle Ordovician)

The anhydritic and calcareous dolomite unit at the top 

of the Beekmantown Group in the AS drill hole and the 

laterally contiguous grayish-green shale and dolomite of the 

Wells Creek Formation in Ohio are overlain by a sequence 

of slightly to moderately dolomitic, locally fossiliferous, 

micritic limestone. Three to four metabentonite beds are 

located near the top of the micritic limestone in Ohio (pi. 1). 

The micritic limestone sequence is also present east of the 

AS drill hole between the Allegheny structural front and the 

eastern end of section C-C'. In the KMS and KMM drill 

holes, the micritic limestone sequence overlies the anhydritic and calcareous dolomite part of the Beekmantown 

Group, whereas, in the SD drill hole and the outcrop section 

near the ARS drill hole, the micritic limestone rests on 

nonanhydritic and noncalcareous dolomite of the Bellefonte 

Dolomite and equivalent strata. The contact between the 

micritic limestone sequence and the underlying Beekmantown Group appears to be conformable across section C-C', 

except at the SD drill hole, where the contact is probably 

unconformable. From its maximum thickness of about 

1,150 ft in the Rome trough, the micritic limestone 

sequence thins eastward to about 100 ft at the eastern end of 

section C-C' and westward to a thickness of about 580 ft at 

the western end of section C-C' (pi. 1). Thinning of this 

sequence between the Rome trough and the eastern end of 

section C-C' occurs in three ways: (1) by depositional 

thinning, (2) by the eastward stratigraphic rise of its basal 

contact with the underlying Beekmantown Group, and (3) 

by progressively eastward truncation beneath a widespread, 

postmicritic limestone unconformity and a local intramicritic limestone unconformity that is restricted to the area 

around the SD drill hole (pi. 1). Westward thinning of the 

micritic limestone sequence resulted from a combination of 

depositional thinning and the westward stratigraphic rise of

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K17
its basal contact with the underlying Beekmantown Group 

and the Wells Creek Formation (pi. 1). From near the 

Ohio-West Virginia hinge zone to the western end of 

section C-C', the upper part of the micritic limestone 

sequence increases in thickness by about 100 ft because of 

a slight stratigraphic rise of the contact between its top and 

the overlying highly argillaceous micritic limestone (pi. 1).

The micritic limestone sequence is subdivided here 

into (1) a lower part that is dolomitic in the Rome trough 

and on the adjoining South-central Pennsylvania arch and 

argillaceous west of the Ohio-West Virginia hinge zone and 

(2) an upper part that contains few, if any, dolomite beds 

and local thin gray shale beds. In addition, the lower part 

of the micritic limestone sequence contains micrite that, in 

general, is finer grained and has lighter shades of gray and 

brown than the micrite in the upper part of the sequence. 

From the MM drill hole westward to the western end of 

section C-C' , the shale beds in the lower part of the micritic 

limestone sequence are greenish gray to grayish green and 

thus are similar in color to the shale beds in the underlying 

Wells Creek Formation. In contrast, from the HM drill hole 

to an estimated 10 mi east of the Ohio-West Virginia hinge 

zone, the shale beds in the lower part of the micritic 

limestone are gray to dark gray.

Following Kay (1944a), Knowles (1966) and Chafetz 

(1969) assigned the name Loysburg Formation to the 

approximately 215-ft-thick lower part of the micritic limestone sequence in the outcrop section near the ARS drill 

hole (pi. 1). The Loysburg Formation here contains two 

members, the "tiger-striped" member of Kay (1944a) (Milroy Member of Rones, 1969) and the overlying Clover 

Member. In this area, the "tiger-striped" member (Milroy 

Member) is about 135 ft thick and consists of medium- to 

thick-bedded, predominantly laminated limestone and dolomitic limestone, whereas the Clover Member is about 80 ft 

thick and consists of thick-bedded, laminated micritic 

limestone. Furthermore, the Loysburg Formation and its 

constituent members were identified in the KMM and SD 

drill holes by Wagner (1966); however, the strata that he 

assigned to the Loysburg Formation are situated in the 

Beekmantown Group of this paper. We concur with 

Knowles (1966), Wagner (1966), and Chafetz (1969) that 

the Loysburg Formation is an appropriate name for the 

lower part of the micritic limestone sequence between the 

Allegheny structural front and the eastern end of section 

C-C (pi. 1). Following Berg and others (1983), we use the 

Milroy Member of Rones (1969) instead of the "tigerstriped" member of Kay (1944a).

The Loysburg Formation is absent in the SD drill hole 

owing to erosion and nondeposition associated with an 

intra-Loysburg Formation unconformity (pi. 1). West of the 

Allegheny structural front, the Loysburg Formation thickens to a maximum of about 590 ft in the AS drill hole by 

westward stratigraphic downstepping of the dolomitic limestone facies of the Milroy Member at the expense of the

underlying Beekmantown Group. In the Rome trough 

segment of section C-C', the Loysburg Formation thins 

westward between the AS and HM drill holes (pi. 1). This 

thinning results from the westward stratigraphic rise of the 

base of the Loysburg Formation and the less pronounced 

westward stratigraphic downstepping of the top of the 

Loysburg Formation. Westward from about 10 to 15 mi east 

of the Ohio-West Virginia hinge zone, the Clover Member 

is replaced by the downstepping upper part of the micritic 

limestone sequence, and the Milroy Member changes facies 

from dolomitic limestone to argillaceous limestone. This 

argillaceous limestone is about 220 ft thick in the HM drill 

hole and is referred to here as the Loysburg Formation 

undivided (pi. 1, fig. 2). Berg and others (1983) also 

identified an undivided Loysburg Formation in southwestern Pennsylvania.

The Loysburg Formation as used in the AS, KMS, 

and KMM drill holes and in the outcrop section near the 

ARS drill hole correlates with a 450-ft-thick argillaceous 

limestone sequence in the Phillips No. A-l Finch drill hole 

(fig. 1) and a 275-ft-thick argillaceous limestone sequence 

in the Occidental No. 1 Burley drill hole (fig. 1) that 

Wagner (1966) and Ryder (1991) assigned to the St. Paul 

Group. The equivalent of the Loysburg Formation in 

Franklin County, Pa., crops out near the Carbaugh-Marsh 

Creek fault as an approximately 1,000-ft-thick, predominantly light gray to brownish light gray, micritic limestone 

sequence that Neuman (1951), Root (1968), and Berg and 

others (1983) assigned to the St. Paul Group (fig. 2). 

Neuman (1951) originally defined the St. Paul Group and 

its constituent Row Park and New Market Limestones in 

outcrops east of the North Mountain fault in Washington 

County, Md., and adjoining West Virginia and Virginia. 

The St. Paul Group in Washington County is between 400 

and 600 ft thick (Neuman, 1951).

In Ohio, the lower part of the micritic limestone 

sequence (Loysburg Formation in Pennsylvania) has been 

identified most commonly as (1) the Chazy Group or 

Limestone (Calvert, 1963, 1964; Dolly and Busch, 1972), 

(2) the Black River Group (lower part) (Stith, 1979, 1986), 

and (3) the Black River Limestone (lower part) (DeBrosse 

and Vohwinkel, 1974; Wickstrom and others, 1985; Wickstrom and Gray, 1988). All three names are acceptable, but 

we have retained the name Black River Limestone because 

it seems to be most favored by the Ohio Division of 

Geological Survey.

The upper part of the micritic limestone sequence that 

crops out near the ARS drill hole was assigned by Knowles 

(1966) to the Hatter and Benner Formations (Limestones) of 

Kay (1944a, b). In neighboring Blair and Huntington 

Counties, Rones (1969) recognized the Hatter Formation of 

Kay (1944a) but changed the Benner Formation of Kay 

(1944a, b) to the Snyder Formation (Snyder Member of 

Kay, 1944a, b) and the overlying Linden Hall Formation 

(Stover and Oak Hall Members of Kay, 1944a, b). Berg and

K18 Evolution of Sedimentary Basins Appalachian Basin
others (1983) adopted the terminology suggested by Rones 

(1969). Likewise, we accept the terminology of Rones 

(1969) for the Hatter, Snyder, and Linden Hall, but we use 

the name Limestone instead of Formation and consider 

them to be subdivisions of the Black River Group (pi. 1, 

fig. 2).

Wagner (1966) identified the Hatter, Snyder, and 

Benner (Linden Hall of Rones, 1969) Formations in the 

KMM and SD drill holes; however, the strata to which he 

applied these names are either stratigraphically below or 

only partly coincident with the upper part of the micritic 

limestone sequence of this paper. Following Wagner 

(1966), we assign the name Black River Group to the upper 

part of the micritic limestone sequence in the KMM and SD 

drill holes (pi. 1). In the SD drill hole, the Black River 

Group is approximately 100 ft thick and bounded by 

unconformities, whereas, in the KMM drill hole, the Black 

River Group is approximately 130 ft thick, and an unconformity is present only at its top. The name Black River 

Group is also assigned here to the upper part of the micritic 

limestone sequence in the KMS and AS drill holes, where 

the sequence is 180 and 550 ft thick, respectively. Most of 

the eastward thinning of the Black River Group between the 

AS and SD drill holes is caused by the widespread postBlack River Group unconformity that has beveled successively older parts of the micritic limestone sequence toward 

the east (pi. 1). The 520-ft-thick Black River Group in the 

HM drill hole near the Ohio-West Virginia hinge zone is 

thicker than expected because of the westward stratigraphic 

rise of the top of the sequence and the slight stratigraphic 

downstepping of the base of the sequence (pi. 1). The top of 

the Black River Group in the HM drill hole is marked by a 

metabentonite that we identify as the a marker of Stith 

(1979) (pi. l.fig. 2).

The Black River Group as defined in the AS drill hole 

also is present in the Phillips No. A-l Finch and Occidental 

No. 1 Burley drill holes (fig. 1), where it attains a thickness 

of 575 and 660 ft, respectively. The thickness of the Black 

River Group is greater in the Occidental No. 1 Burley drill 

hole than it is in the Phillips No. A-l Finch drill hole 

because of the approximately 150-ft stratigraphic rise of the 

top of the Black River Group between the Phillips No. A-l 

Finch and Occidental No. 1 Burley drill holes (Ryder, 

1991).

In Franklin County, Pa. between the North Mountain and Carbaugh-Marsh Creek faults the Black River 

Group and its constituent Hatter, Snyder, and Linden Hall 

Limestones are represented by strata in the lower part of the 

approximately 750-ft-thick Chambersburg Formation 

(Limestone) (Stose, 1906, 1909; Root, 1968; Berg and 

others, 1983) (fig. 2). The Chambersburg Formation (Shippensburg and Mercersburg Formations of Craig, 1949) thins 

to between 100 and 300 ft in western Franklin County 

(Clark, 1970; Okuma, 1970). Approximately the lower 

one-half of the Chambersburg Formation (Shippensburg

Formation of Craig, 1949) in western Franklin County 

correlates with the Hatter-Snyder-Linden Hall interval in 

the outcrop section near the ARS drill hole (fig. 2). The 

widespread unconformity shown at the top of the Black 

River Group in the KMS, KMM, and SD drill holes and in 

the outcrop section near the ARS drill hole probably is a 

westward continuation of the intra-Chambersburg Formation unconformity (post-Shippensburg-pre-Mercersburg 

unconformity) recognized by Craig (1949) in Franklin 

County, Pa. (pi. 1, fig. 2).

The Chambersburg Formation (Limestone) continues 

southward into Washington County, Md., between the 

North Mountain and Carbaugh-Marsh Creek faults, where it 

is between 250 and 300 ft thick (Bassler, 1919; Craig, 1949; 

Edwards, 1978). As it does in adjoining Franklin County, 

the lower part of the Chambersburg Formation (Limestone) 

in Washington County, Md., correlates with the HatterSnyder-Linden Hall interval in section C-C. In northern 

Virginia, a 300- to 500-ft-thick sequence consisting of the 

Lincolnshire Limestone and the overlying unnamed tongues 

of the Liberty Hall and Lantz Mills Formations (Read, 

1980; Rader, 1982) is approximately equivalent to the 

Hatter-Snyder-Linden Hall interval in section C-C' . In the 

adjoining West Virginia panhandle, the names Black River 

Group (Limestone) (Cardwell and others, 1968; Patchen 

and others, 1984) or Chambersburg Limestone (Dean and 

others, 1987) are used in place of the unnamed tongues of 

the Liberty Hall and Lantz Mills Formations.

Following DeBrosse and Vohwinkel (1974), Wickstrom and others (1985), and Wickstrom and Gray (1988), 

we assign the upper part of the micritic limestone sequence 

in Ohio to the Black River Limestone (pi. 1, fig. 2). As 

previously mentioned, the Black River Limestone in Ohio 

also includes strata that are equivalent to the Loysburg 

Formation in Pennsylvania (pi. 1, fig. 2). The a marker of 

Stith (1979) marks the top of the Black River Limestone 

across the entire Ohio part of section C-C' (pi. 1, fig. 2). 

Another widespread metabentonite in the uppermost part of 

the Black River in Ohio and adjoining States underlies the 

a marker in section C-C'. This metabentonite is correlated 

here with the p marker of Stith (1979) (pi. 1, fig. 2). The a 

and 3 markers of Stith (1979) correlate with the Mud Cave 

and Pencil Cave bentonites, respectively, in Kentucky 

(Cressman and Noger, 1976; Cressman and Peterson, 

1986). In south-central Pennsylvania, bentonite R and 

bentonite No. 0 (Thompson, 1963) correlate with the a and 

3 markers of Stith (1979), respectively.

A Middle Ordovician (middle and late Chazyan and 

early Blackriveran) age is assigned here to the Loysburg 

Formation (fig. 2). This age is based on (1) the Chazyan age 

assigned to the Loysburg Formation in central and southcentral Pennsylvania by Butts and Moore (1936) (included 

in their Carlim Limestone), Kay (1944a), and Chafetz 

(1969) on the basis of mollusk, brachiopod, primitive coral, 

ostracod, and trilobite faunas, (2) the Chazyan age assigned

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K19
to the Row Park Limestone of the St. Paul Group (equivalent to the lower part of the Loysburg Formation) in 

Washington County, Md., by Neuman (1951) on the basis 

of brachiopods, and (3) the Chazyan age assigned to the 

Loysburg Formation (unnamed argillaceous limestone of 

the St. Paul Group of Ryder, 1992) in the Hope Natural Gas 

No. 9634 Power Oil Company drill hole in Wood County, 

W. Va. (fig. 1), by Prouty and others (1959) on the basis of 

brachiopod and primitive coral faunas. The upper part of the 

Loysburg Formation in the Rome trough and Allegheny 

front segments of section C-C' may be of early Blackriveran age (fig. 2). This additional age is based on (1) the 

eastward stratigraphic rise of the Loysburg Formation at the 

expense of the overlying Black River Group, (2) the 

Pamelian age (earliest Blackriveran age of this paper) that 

Neuman (1951) assigned to the New Market Limestone 

(equivalent to the upper part of the St. Paul Group) in 

Washington County, Md., on the basis of primitive coral 

faunas), and (3) the Marmor and Ashby Stages (lower 

Chazyan through middle Blackriveran Stages of Bergstrom, 

1971) assigned to the Loysburg-equivalent St. Paul Group 

in Franklin County, Pa., by Cooper (1956) on the basis of 

brachiopods. Conodonts identified by A.G. Harris and J.E. 

Repetski (table 2) in the Loysburg Formation in the AS drill 

hole (f3 and upper part of f4 on pi. 1) are consistent with a 

middle Chazyan through early Blackriveran age.

We assign a Middle Ordovician (Blackriveran 

through Rocklandian) age to the Black River Group in 

section C-C' (fig. 2). This age is based on brachiopod, 

conodont, mollusk, primitive coral, stromatoporoid, and 

ostracod faunas reported by (1) Kay (1944a, b) and Swartz 

and others (1955) from outcrops of the Hatter and Benner 

Limestones (Snyder and Linden Hall Limestones of this 

paper) in central and south-central Pennsylvania, (2) Prouty 

and others (1959) from cores of the Hatter and Benner 

Limestones (Snyder and Linden Hall Limestones of this 

paper) of the Black River Group in the Hope Natural Gas 

No. 9634 Power Oil Company drill hole, (3) Craig (1949) 

from outcrops of the Shippensburg Formation (correlates 

with Black River Group of this paper) in Franklin County, 

Pa., and (4) Sweet and Bergstrom (1976) from strata 

between the a (Mud Cave bentonite) and [3 (Pencil Cave 

bentonite) markers in southern Ohio and adjoining Kentucky. Because the Black River Limestone, as used in Ohio 

by DeBrosse and Vohwinkle (1974), Wickstrom and others 

(1985), and Wickstrom and Gray (1988), includes strata 

equivalent to the Loysburg Formation, its age ranges from 

middle Chazyan through Rocklandian (fig. 2).

Trenton Group (Middle and Upper Ordovician)

The Black River Group (Limestone) is overlain in the 

AS drill hole by a 1,125-ft-thick sequence consisting of 

bioclastic limestone, argillaceous micritic limestone, and

dark-gray and black shale (pi. 1). This sequence thins away 

from the AS drill hole to about 600 ft in the SD drill hole at 

the eastern end of section C-C' and to about 400 ft in the 

WS drill hole at the western end of section C-C'. Westward 

thinning of the limestone and gray and black shale sequence 

between the AS and WS drill holes occurs in three ways: (1) 

by depositional thinning, (2) by the westward stratigraphic 

rise of its basal contact with the underlying Black River 

Group, and (3) by the slight westward stratigraphic downstepping of the top of the sequence (pi. 1). Eastward 

thinning of the limestone and gray and black shale sequence 

from the AS drill hole resulted from a combination of 

depositional thinning and eastward stratigraphic downstepping of the top of the sequence.

The limestone and gray and black shale sequence is 

subdivided into a lower part dominated by bioclastic limestone and argillaceous micritic limestone and an upper part 

dominated by dark-gray and black shale (pi. 1). These two 

units are easily distinguishable from each other across the 

entire length of section C-C' , except that the lithologic 

change between them occurs across a 10- to 50-ft-thick 

transition zone and thus makes the contact somewhat 

arbitrary. In the SD drill hole, the dark-gray and black shale 

unit has been replaced through facies change by a predominantly argillaceous micritic limestone unit intercalated with 

gray and dark-gray shale (pi. 1). There, the lower and upper 

units are differentiated by the significantly higher percentage of shale in the upper unit. Metabentonite beds are 

common in the lower unit of the limestone and gray-toblack shale sequence across section C-C' (pi. 1).

Following Kay (1944b), Thompson (1963) and 

Knowles (1966) subdivided the approximately 380-ft-thick 

lower part of the limestone and gray and black shale 

sequence, which crops out near the ARS drill hole, into the 

Nealmont, Salona, and Coburn Limestones (Formations) 

(pi. 1). Moreover, Thompson (1963) applied the name 

Antes Shale of Kay (1944b) to the approximately 350-ftthick upper part of the limestone and gray and black shale 

sequence that crops out near the ARS drill hole (pi. 1). Kay 

(1944b) and Thompson (1963) considered the Nealmont, 

Salona, and Coburn Limestones (Formations) and the overlying Antes Shale to be formations in the Trenton Group. 

Berg and others (1983) recognized the same formations in 

central and south-central Pennsylvania without referring to 

the Trenton Group of Kay (1944a, b). Wagner (1966), also 

following Kay (1944b), assigned (in ascending order) the 

names Nealmont, Salona, and Coburn Limestones (Formations) and Antes Shale to the limestone and gray-to-black 

shale sequence in the KMM drill hole (pi. 1).

We accept the terminology applied by Kay (1944a, 

b), Thompson (1963), Knowles (1966), Wagner (1966), 

and Berg and others (1983) to the limestone and gray and 

black shale sequence in the KMM drill hole and in the 

outcrop sections near the ARS drill hole. We also accept the 

widespread unconformity that Kay (1944a, b) recognized at

K20 Evolution of Sedimentary Basins Appalachian Basin
the base of the Trenton Group. However, the Trenton 

Group of Kay (1944a, b) used in this study differs slightly 

from Kay's original definition. This difference results 

because we follow Rones (1969), who moved the base of 

the Trenton Group of Kay (1944a, b) and the associated 

widespread unconformity about 30 to 60 ft upsection from 

the base of the Oak Hall Member of the Nealmont Limestone of Kay (1944a, b) to the base of the overlying Centre 

Hall Member of the Nealmont Limestone of Kay (1944a, 

b). In addition, our log "picks" for the tops of the formations of the Trenton Group of Kay (1944a, b) in the KMM 

drill hole differ slightly from those of Wagner (1966). For 

example, the Nealmont Formation (Limestone) identified 

by Wagner (1966) in the KMM drill hole occupies the 

interval that we assign to the Black River Group in this 

study (pi. 1).

The Trenton Group of Kay (1944a, b) and its four 

constituent formations the Nealmont, Salona, and Coburn 

Limestones and the Antes Shale are also applied in this 

study to the limestone and gray and black shale sequence in 

the AS and KMS drill holes (pi. 1). Metabentonite beds No. 

0 and R which Thompson (1963) recognized at the base 

and top of the Salona Limestone, respectively, in outcrop 

near the ARS drill hole are identified here in the KMS and 

KMM drill holes. Bentonite beds No. 0 and R at these 

localities correlate with the [3 and a markers of Stith (1979), 

respectively, in the AS drill hole (pi. 1).

The name Trenton Group of Perry (1972) is applied to 

the limestone sequence in the SD drill hole, where the 

Trenton is subdivided into the Nealmont Limestone and the 

overlying Dolly Ridge Formation (pi. 1). This nomenclature is based on units applied to the Trenton Group by Perry 

(1972) and Ryder (1992) in the outcrop and subsurface at 

the eastern end of section E-E' (fig. 1) and by Ryder (1991) 

in the subsurface of Hardy County, W. Va. The Nealmont 

Limestone in the SD drill hole correlates with the combined 

Nealmont, Salona, and Coburn Limestones in the AS, 

KMS, and KMM drill holes and the outcrop section near the 

ARS drill hole, whereas the Dolly Ridge Formation in the 

SD drill hole correlates with the Antes Shale in the AS, 

KMS, and KMM drill holes and the outcrop section near the 

ARS drill hole (pi. 1). The S2 and S3 metabentonites 

defined by Perry (1964) in the middle part of the Nealmont 

Limestone in the subsurface at the eastern end of section 

E-E' (fig. 1) are also recognized in the middle part of the 

Nealmont Limestone in the SD drill hole. We suggest that 

the S2 metabentonite of Perry (1964) correlates with bentonite R of Thompson (1963) and the a marker of Stith 

(1979). The (3 marker of Stith (1979) in the AS drill hole 

and bentonite No. 0 of Thompson (1963) in the KMS and 

KMM drill holes and in the outcrop section near the ARS 

drill hole correlate with an unnamed metabentonite in the 

SD drill hole (pi. 1).

The Nealmont and Salona Limestones in the AS, 

KMS, and KMM drill holes and in the outcrop section near

the ARS drill hole and the Nealmont Limestone (lower part) 

in the SD drill hole correlate approximately with the upper 

one-half of the Chambersburg Formation (Limestone) (Mercersburg and Oranda Formations of Craig, 1949) in Franklin County, Pa., and adjoining Washington County, Md., 

between the North Mountain and Carbaugh-Marsh Creek 

faults (Stose, 1906, 1909; Bassler, 1919; Cloos, 1951; 

Root, 1968; Edwards, 1978; Berg and others, 1983) (fig. 

2). The Coburn Limestone and Antes Shale or the Nealmont 

Limestone (upper part) and Dolly Ridge Formation in the 

above-cited drill holes and outcrop section correlate approximately with the lower one-half of the Martinsburg Formation (Shale) in Franklin County, Pa., and adjoining Washington County, Md., between the North Mountain and 

Carbaugh-Marsh Creek faults (Stose, 1906, 1909; Bassler, 

1919; Cloos, 1951; Root, 1968; Clark, 1970; Edwards, 

1978; Berg and others, 1983) (fig. 2). The Salona Formation (Limestone) as mapped by Pierce (1966) and Okuma 

(1970) in western Franklin County, Pa., overlies the Chambersburg Formation and underlies the Martinsburg Formation (Reedsville Formation of Pierce, 1966 and Okuma, 

1970). In this area, the upper one-half of the Chambersburg 

Formation as used by Pierce (1966) and Okuma (1970) 

correlates with the Nealmont Limestone in the Pennsylvania 

part of section C-C'. Also, approximately the lower onehalf of the Martinsburg Formation in western Franklin 

County (Reedsville Formation of Pierce, 1966 and Okuma, 

1970) correlates with the combined Coburn Limestone and 

Antes Shale in section C-C'.

In the panhandle of West Virginia and adjoining 

northern Virginia, between the North Mountain fault and 

the Blue Ridge, the Trenton Group in section C-C' correlates with the lower one-half to two-thirds of the Martinsburg Formation and the thin underlying Oranda Formation 

(Edmundson and Nunan, 1973; Young and Rader, 1974; 

Rader and Biggs, 1975, 1976; Rader, 1982; Patchen and 

others, 1984).

The name Trenton Group is applied in this study to 

the limestone and gray and black shale sequence between 

the AS and HM drill holes (pi. 1). In this segment of section 

C-C', which consists of the western part of the Rome 

trough and the adjoining Ohio-West Virginia hinge zone, 

the Nealmont and Salona Limestones change facies westward and are replaced by the expanded upper part of the 

Black River Group. Consequently, the Coburn Limestone 

and the overlying Antes Shale are all that remain of the 

Trenton Group in the HM drill hole (pi. 1). The Trenton 

Group as defined in the Rome trough segment of section 

C-C' is also recognized in section D-D' (fig. 1). The 

Trenton Group in section D-D' is 630 and 320 ft thick in the 

Phillips No. A-l Finch and Occidental No. 1 Burley drill 

holes, respectively, and consists of an unnamed limestone 

and the overlying Antes Shale (Ryder, 1991).

In the Ohio part of section C-C' , we assign the lower 

unit of the limestone and gray and black shale sequence to

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K21
the Trenton Limestone as defined by Calvert (1963, 1964), 

DeBrosse and Vohwinkel (1974), Wickstrom and others 

(1985), and Wickstrom and Gray (1988) (pi. 1, fig. 2). In 

addition, we assign the upper unit of the limestone and gray 

and black shale sequence in Ohio to the Utica Shale, 

following Fettke (1960) and Calvert (1963, 1964). The 

Utica Shale as used here in the WS drill hole consists of the 

combined Utica Shale, Cynthiana Formation, and lower 

100 ft of the Eden Shale (all of Calvert, 1963, 1964) in the 

Pan American No. 1 Windbigler (fig. 1) and WS drill holes. 

We prefer the name Utica Shale for the upper part of the 

limestone and gray and black shale sequence in the Ohio 

part of section C-C' rather than the name Point Pleasant 

Formation used by Wickstrom and Gray (1988) in northwestern and north-central Ohio, because the upper part of 

the sequence contains beds of black shale (pi. 1) (Wallace 

and Roen, 1989). This characteristic of the upper part of the 

sequence makes it more akin to the Utica Shale of northwestern Pennsylvania and adjoining New York (Fettke, 

1960; Wagner, 1966) than to the Point Pleasant Formation 

of southern Ohio and adjoining Kentucky (Weiss and 

others, 1965).

The Trenton Group of Kay (1944a, b) is primarily 

Middle Ordovician (Rocklandian through Shermanian) on 

the basis of brachiopod, trilobite, conodont, and graptolite 

faunas reported by (1) Kay (1944b), Thompson (1963) (F3 

on pi. 1), Bergstrom (1971) and Sweet and Bergstrom 

(1976) from outcrops of the Trenton Group of Kay (1944a, 

b) in central and south-central Pennsylvania, (2) Prouty and 

others (1959) from cores of the Trenton Group in the Hope 

Natural Gas No. 9634 Power Oil Company drill hole, and 

(3) Sweet and Bergstrom (1976) from strata between the a 

(Mud Cave bentonite) and [3 (Pencil Cave bentonite) markers of Stith (1979) that crop out in southern Ohio and 

adjoining Kentucky. The conodonts (table 2) in the Nealmont, Salona, and Coburn Limestones in the AS drill hole 

(fl and f2 on pi. 1) are consistent with a Rocklandian 

through Shermanian age for the Trenton Group.

Conodont biostratigraphy of the Salona and Coburn 

Limestones in central Pennsylvania by Valek (1982) indicates that the zonal index fossil Amorphognathus tvaerensis 

ranges to the top of the Coburn Limestone; thus, the Coburn 

is no younger than middle Shermanian (Sweet and Bergstrom, 1986). No conodonts have been found in the Antes 

Shale, but, given the middle Shermanian age of the uppermost Coburn Limestone and the gradational nature of the 

Coburn-Antes contact, the Antes Shale very likely occupies 

the upper part of the Shermanian (Sweet, 1984) (fig. 2). 

Following Sweet (1984; oral commun., 1990) we assign a 

late Shermanian age to most of the Antes Shale in section 

C-C'. In the Rome trough segment of section C-C' where 

the Antes is thicker and occupies a higher stratigraphic 

position than it does in adjoining areas we assign a late 

Shermanian to early Edenian age to the Antes Shale. 

Moreover, we assign a late Shermanian age to the Dolly

Ridge Formation (equivalent to the Antes Shale in Pennsylvania) along the eastern West Virginia part of section C-C' 

and to the equivalent Utica Shale in the Ohio part of section 

C-C' (pi. 1).

The late Shermanian to earliest Edenian age assigned 

to the Antes Shale in this study refutes the early Edenian age 

assigned to the Antes Shale by Sweet and Bergstrom (1976) 

in central Pennsylvania and by Ryder (1991, 1992) in 

northern West Virginia. However, the Middle and Late 

Ordovician age assigned by Ryder (1991, 1992) to the 

Trenton Group of Kay (1944a, b) is still valid because of 

the probable Edenian age of the upper part of the Antes 

Shale in localities such as the AS drill hole.

The late Shermanian age assigned here to the Dolly 

Ridge Formation at the eastern end of section C-C' also 

refutes the Edenian age assigned to the Dolly Ridge 

Formation by Ryder (1991, 1992) in eastern West Virginia 

and adjoining Virginia. A late Shermanian age for the Dolly 

Ridge Formation accepted here is consistent with the 

Middle Ordovician age first proposed by Perry (1972) and 

supported by Diecchio (1985). Acceptance of a late Shermanian age for the Dolly Ridge Formation in this study 

requires a Middle Ordovician age rather than a Middle 

and Late Ordovician age (Ryder, 1991, 1992) for the 

Trenton Group of Perry (1972).

Unpublished correlations by the senior author (Ryder) 

along section A-A' (pi. 1) show that the Utica Shale rises 

stratigraphically to the north and northeast and thus is 

probably in part of early Edenian age in northeastern Ohio 

and northwestern Pennsylvania. These correlations suggest 

that, on a regional scale, the Utica Shale is Middle and Late 

Ordovician in age, although, in section C-C' of this study, 

the Utica Shale is probably confined to the Middle Ordovician. The Edenian age of the Utica Shale in southeastern 

Ohio (Ryder, 1991, 1992) is considered here to be invalid, 

and the age should be reassigned to the Shermanian.

Trenton Group strata of Rocklandian age in section 

C-C' are located in the Nealmont and Salona Limestones 

(below the a marker of Stith (1979), the bentonite R of 

Thompson (1963), and the S2 metabentonite of Perry, 

(1964)) (pi. 1, fig. 2). These Trenton Group strata of 

Rocklandian age are replaced through facies change by 

Rocklandian-age strata of the Black River Group within 

about 20 mi east of the HM drill hole (pi. 1). In contrast, 

Trenton Group strata of Kirkfieldian and Shermanian age 

are distributed throughout section C-C' (fig. 2). A Kirkfieldian through Shermanian age is assigned to the following parts of the Trenton Group and Trenton Limestone: (1) 

all of the Trenton Group of Kay (1944a, b) except the 

Nealmont and Salona Limestones and the uppermost part of 

the Antes Shale in the Rome trough, (2) all of the Trenton 

Group of Perry (1972) except the lower part of the Nealmont Limestone, and (3) all of the Trenton Limestone (pi. 

1). An Edenian age is assigned to the upper part of the

K22 Evolution of Sedimentary Basins Appalachian Basin
Antes Shale of the Trenton Group in the Rome trough (fig. 

2). The Utica Shale in Ohio is assigned a Shermanian age 

(fig. 2).

Reedsville Shale and Bald Eagle Formation 

(Upper Ordovician)

The Trenton Group and the combined Trenton Limestone and Utica Shale in section C-C' are overlain by a silty 

and calcareous gray shale sequence (pi. 1). This sequence 

gradually thins westward from a thickness of about 1,850 ft 

in the KMS drill hole near the Allegheny structural front to 

about 790 ft in the WS drill hole at the western end of 

section C-C'. Eastward from the KMS drill hole, the silty 

and calcareous gray shale sequence thins to about 950 ft in 

the outcrop section near the ARS drill hole and 1,160 ft in 

the SD drill hole (pi. 1). In the AS, KMS, and KMM drill 

holes and the outcrop section near the ARS drill hole, the 

silty and calcareous gray shale sequence grades upward 

through a 40- to 380-ft-thick sandy gray shale transition 

zone into a 220- to 530-ft-thick sandstone containing thin 

beds of red, gray, and green shale (pi. 1). The sandstone 

and underlying transition zone pinch out into the upper part 

of the silty and calcareous gray shale sequence about 20 to 

40 mi west of the AS drill hole (pi. 1). The silty and 

calcareous gray shale sequence in the SD drill hole is 

directly overlain by a 500-ft-thick sandstone unit without an 

intervening sandy shale transition zone (pi. 1).

Eastward from the Ohio-West Virginia hinge zone to 

the end of section C-C', the silty and calcareous gray shale 

sequence combines with the overlying sandstone unit to 

record a net upward coarsening of grain size. In ascending 

order, this upward coarsening sequence consists of (1) a 

180- to 550-ft-thick gray shale and local black shale beds, 

(2) a 720- to 900-ft-thick silty gray shale, (3) the previously 

described 40- to 380-ft-thick sandy gray shale transition 

zone, and (4) the previously described 220- to 530-ft-thick 

sandstone unit (pi. 1).

From the Ohio-West Virginia hinge zone to the 

western end of section C-C' , the silty and calcareous gray 

shale sequence becomes increasingly calcareous, and its 

upward-coarsening character is less distinct. For example, 

the lower gray shale unit identified east of the Ohio-West 

Virginia hinge zone also is identified west of the Ohio-West 

Virginia hinge zone, where it commonly contains thin 

micritic limestone beds in the BBW and WS drill holes. In 

addition, the silty gray shale unit identified east of the 

Ohio-West Virginia hinge zone is subdivided in the HM 

drill hole into (1) a lower calcareous, silty gray shale unit 

that continues at approximately the same thickness and 

lithologic character to the western end of section C-C' and 

(2) an upper silty gray shale unit that becomes more 

calcareous and, in general, less silty toward the western end 

of section C-C' (pi. 1). Near the BBW drill hole, the upper

silty gray shale splits into two calcareous gray shale units: 

(1) a lower calcareous shale tongue that continues to the 

western end of section C-C' and (2) an upper calcareous 

shale tongue that overlies and then merges laterally with a 

silty, calcareous gray shale unit about 10 mi west of the 

BBW drill hole (pi. 1).

Following Butts and Moore (1936), Butts (1945), 

Perry (1972), de Witt (1974), Berg and others (1983), and 

Ryder (1991), the silty gray shale sequence in the Pennsylvania and West Virginia parts of section C-C' is assigned to 

the Reedsville Shale (pi. 1). The name Bald Eagle Formation as used by Knowles (1966), Pierce (1966), Thompson 

(1970), Horowitz (1971), de Witt (1974), and Berg and 

others (1983) is assigned to the predominantly greenishgray sandstone overlying the Reedsville Shale in the Pennsylvania part of section C-C' , whereas the name Oswego 

Sandstone as used by Perry (1972), Patchen and others 

(1984), and Ryder (1991) is assigned to the predominantly 

greenish-gray sandstone overlying the Reedsville in the 

West Virginia part of section C-C' (pi. 1). Moreover, 

following Fettke (1960) and Calvert (1963, 1964), the name 

Reedsville Shale is applied to the silty and calcareous gray 

shale sequence in eastern Ohio. The Reedsville Formation 

of Calvert (1964) consists of both the Utica and the 

Reedsville Shales of this paper. Wickstrom and Gray (1988) 

applied the name Cincinnati Group (undifferentiated) to 

strata in northwestern and north-central Ohio that are 

referred to here as the Reedsville Shale.

The Reedsville Shale in section C-C' is also recognized in the Phillips No. A-l Finch and Occidental No. 1 

Burley drill holes, where it is 1,420 and 1,170 ft thick, 

respectively (Ryder, 1991). The Bald Eagle Formation in 

the Pennsylvania part of section C-C' correlates with a 

100-ft-thick, predominantly greenish-gray sandstone unit in 

the Phillips No. A-l Finch drill hole that Ryder (1991) 

identified as the Oswego Sandstone.

The Reedsville Shale in section C-C' correlates 

approximately with the upper one-half of the Martinsburg 

Formation (Shale) in Franklin County, Pa., and adjoining 

Washington County, Md., between the North Mountain and 

Carbaugh-Marsh Creek faults (Stose, 1906, 1909; Bassler, 

1919; Cloos, 1951; Root, 1968; Clark, 1970; Edwards, 

1978; Berg and others, 1983) (fig. 2). The Reedsville Shale 

in section C-C' also correlates approximately with the 

upper one-half of the Martinsburg Formation in the West 

Virginia panhandle and northern Virginia between the 

North Mountain fault and the Blue Ridge (Edmundson and 

Nunan, 1973; Young and Rader, 1974; Rader and Biggs, 

1975, 1976; Rader, 1982; Patchen and others, 1984; Dean 

and others, 1987). Paleozoic strata younger than the Martinsburg Formation are missing in Franklin County, Pa., 

and adjoining Washington County, Md., between the North 

Mountain and Carbaugh-Marsh Creek faults (Root, 1968; 

Edwards, 1978) and in the West Virginia panhandle 

between the North Mountain fault and the Blue Ridge

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K23
(Cardwell and others, 1968). In northern Virginia, between 

the North Mountain fault and the Blue Ridge, outcrops of 

post-Martinsburg strata indicate that the Oswego Sandstone 

was removed by pre-Early Silurian erosion (Rader, 1982). 

The Reedsville Shale and the Bald Eagle Formation 

(the Oswego Sandstone in West Virginia) are assigned a 

Late Ordovician age. The Reedsville Shale is approximately 

early Edenian through Maysvillian in age, and the Bald 

Eagle Formation (Oswego Sandstone) is approximately 

latest Maysvillian through earliest Richmondian in age (fig. 

2). These ages are based on brachiopod, mollusk, and 

conodont faunas reported by (1) Knowles (1966) and 

Wallace de Witt, Jr. (unpub. data, 1969) (Fl and F2 on pi. 

1), from outcrops of the Reedsville Shale in Bedford 

County, Pa., (2) Butts (1945) from outcrops of the Reedsville Shale in Blair County, Pa., (3) Butts and Moore (1936) 

from outcrops of the Reedsville Shale in Centre County, 

Pa., and (4) Sweet and Bergstrom (1976) and Sweet (1979) 

from Reedsville-equivalent outcrops in southern Ohio and 

adjoining Kentucky.

Juniata Formation and Queenston Shale (Upper 

Ordovician)

The Reedsville Shale-Bald Eagle Formation (Oswego 

Sandstone) interval in section C-C' is overlain by a silty 

and sandy red shale and red sandstone sequence (pi. 1). 

This sequence gradually thins westward from a thickness of 

1,500 ft in the outcrop section adjoining the KMM drill hole 

(Wallace de Witt, Jr., unpub. data, 1969) to 360 ft near the 

crest of the Wooster arch at the western end of section 

C-C. East of the KMM drill hole, the red shale and red 

sandstone sequence thins to a thickness of about 1,020 ft in 

the SD drill hole and a thickness of 1,000 ft in the outcrop 

section near the ARS drill hole. Red sandstone and local 

shale beds dominate the sequence in the SD drill hole (pi. 

1). Northward in the outcrop section adjoining the ARS drill 

hole, the sequence consists of lower and upper red sandstone units and a middle sandy red shale unit (Knowles, 

1966). The upper red sandstone unit pinches out about 13 

mi west of the outcrop section near the ARS drill hole, but 

the lower red sandstone continues westward to the outcrop 

section adjoining the KMM drill hole and to the KMS drill 

hole before pinching out between the KMS and AS drill 

holes (pi. 1).

The name Juniata Formation has been applied to the 

exposed red shale and red sandstone sequence throughout 

central and south-central Pennsylvania (Butts and Moore, 

1936; Butts, 1945; Knowles, 1966; Pierce, 1966; Okuma, 

1970; Thompson, 1970; Horowitz, 1971; de Witt, 1974; 

Berg and others, 1983) and in adjoining Maryland and West 

Virginia (Cardwell and others, 1968; Cleaves and others, 

1968; Patchen and others, 1984; Dean and others, 1985). 

Thompson (1970) and Horowitz (1971) showed that the

boundary between the Juniata Formation and the underlying 

Bald Eagle Formation in central Pennsylvania is commonly 

controlled by diagenetic alteration rather than lithofacies. In 

the subsurface of eastern Ohio and adjoining western 

Pennsylvania, where the sequence is dominated by silty and 

sandy red shale, the name Queenston Shale has been 

applied by Fettke (1960), Calvert (1964), Wagner (1969), 

DeBrosse and Vohwinkel (1974), Piotrowski (1981), and 

Berg and others (1983). Following these studies, we assign 

the name Juniata Formation to the red sandstone and red 

shale sequence in the Pennsylvania and West Virginia parts 

of section C-C' and the name Queenston Shale to the 

equivalent red shale sequence in the Ohio part of section 

C-C' (pi. 1). The Juniata Formation in section C-C' is also 

recognized in the Phillips No. A-l Finch and Occidental 

No. 1 Burley drill holes in section D-D' (fig. 1), where the 

formation is about 1,020 ft thick (Ryder, 1991).

No Paleozoic strata younger than the Martinsburg 

Formation are preserved in Franklin County, Pa., and 

adjoining Washington County, Md., between the North 

Mountain and Carbaugh-Marsh Creek faults (Root, 1968; 

Edwards, 1978) and in the West Virginia panhandle 

between the North Mountain fault and the Blue Ridge 

(Cardwell and others, 1968). In northern Virginia, between 

the North Mountain fault and the Blue Ridge, outcrops of 

post-Martinsburg strata indicate that the Juniata Formation 

was removed by pre-Lower Silurian erosion (Rader, 1982).

The Juniata Formation and the Queenston Shale are 

assigned a Late Ordovician (Richmondian and Gamachian?) 

age (fig. 2). This age is based on (1) the stratigraphic 

position of Juniata and Queenston strata between the underlying Reedsville Shale of probable early Edenian through 

Maysvillian age and overlying Lower Silurian strata and (2) 

conodonts from strata equivalent to the Juniata Formation 

and Queenston Shale that crop out in southern Ohio and 

adjoining Kentucky (Sweet and Bergstrom, 1976; Sweet, 

1979).

Tuscarora Sandstone and "Clinton" Sandstone 

and Shale (Lower Silurian)

From about the HM drill hole to the eastern end of 

section C-C' , the Juniata Formation is overlain by a 170- to 

420-ft-thick quartzose sandstone known as the Lower Silurian Tuscarora Sandstone or Tuscarora Quartzite (Darton 

and Taff, 1896; Butts and Moore, 1936; Butts, 1945; 

Cardwell and others, 1968; de Witt, 1974; Patchen and 

others, 1984; Dean and others, 1985) (pi. 1). In this study, 

we use the name Tuscarora Sandstone, whereas the Pennsylvania Geological Survey prefers the name Tuscarora 

Formation (Knowles, 1966; Pierce, 1966; Okuma, 1970; 

Berg and others, 1983). A 70- to 140-ft-thick transition 

zone consisting of quartzose sandstone and thin red shale

K24 Evolution of Sedimentary Basins Appalachian Basin
beds is included with the Tuscarora Sandstone in section 

C-C' (pi. 1). In northwestern Pennsylvania and adjoining 

western New York, the Tuscarora Sandstone interval is 

occupied by a sandstone and gray shale sequence known as 

the Medina Group (Fisher, 1954; Wagner, 1969; 

Piotrowski, 1981; Berg and others, 1983). In eastern Ohio, 

the Tuscarora Sandstone interval is occupied by a sandstone 

and gray shale sequence known informally as the "Clinton" 

sands of the drilling industry (Pepper and others, 1953) and 

the "Clinton" sandstone and shale (Janssens, 1977). The 

name "Clinton" sandstone and shale of Janssens (1977) is 

used in this paper. Pepper and others (1953) recognized that 

the "Clinton" sands are equivalent to the Albion Sandstone 

in western New York (now part of the Medina Group of 

Fisher (1954) and Piotrowski (1981) in northwestern Pennsylvania and western New York) rather than the stratigraphically younger Middle Silurian Clinton Formation in western New York (now the Middle Silurian Clinton Group of 

Fisher (1954) and Piotrowski (1981) in western New York 

and northwestern Pennsylvania). The "Clinton" sandstone 

and shale in the MM, BBW, and WS drill holes and the 

Tuscarora Sandstone in the HM drill hole are overlain by a 

continuous 15- to 60-ft-thick predominantly dolomite unit 

known in northwestern Pennsylvania as the Reynales Dolomite of the Clinton Group (Piotrowski, 1981; Berg and 

others, 1983) and in eastern Ohio as the Packer shell of 

driller's terminology (Pepper and others, 1953; DeBrosse 

and Vohwinkel, 1974). The Packer shell of driller's terminology and the Reynales Dolomite of Piotrowski (1981) and 

Berg and others (1983), on the basis of conodonts 

(Kleffner, 1985), are of late Early Silurian age.

SUMMARY AND CONCLUSIONS

A 275-mi-long restored section from Medina County, 

Ohio, through southwestern and south-central Pennsylvania 

to Hampshire County, W. Va., shows a Cambrian and 

Ordovician sequence that is thickest in an east-facing 

asymmetric graben and overlying sag basin that constitute 

the Rome trough, thinnest on the relatively stable craton 

that adjoins the western margin of the Rome trough, and 

moderately thick on the South-central Pennsylvania arch 

that adjoins the eastern margin of the Rome trough. The 

fault-controlled hinge between the relatively stable craton 

and the western margin of the Rome trough, identified here 

as the Ohio-West Virginia hinge zone, separates slightly 

extended Proterozoic basement rocks to the west from 

moderately to highly extended Proterozoic rocks to the east. 

The down-to-the-west normal fault that marks the eastern 

margin of the graben phase of the Rome trough had 

approximately 6,000 to 7,000 ft of pre-Middle Ordovician 

structural relief on Proterozoic basement between the trough 

and the adjoining South-central Pennsylvania arch. The 

Cambrian and Ordovician sedimentary cover in the study

area thickens across the Ohio-West Virginia hinge zone 

from about 3,000 ft near the crest of the Wooster arch in 

northeastern Ohio to an estimated 19,800 ft near the 

depositional axis of the Rome trough in southwestern 

Pennsylvania. East of the Rome trough, the sedimentary 

cover thins across the South-central Pennsylvania arch from 

about 12,700 ft near the Allegheny structural front in 

south-central Pennsylvania to about 10,150 ft in northeastern West Virginia about 20 mi west of the North Mountain 

thrust fault.

In general, the Cambrian and Ordovician sequence 

described here consists of four major lithofacies that are 

predominantly shallow marine to peritidal in origin. In 

ascending order, the lithofacies are identified by the following descriptive names: (1) sandstone, shale, limestone, and 

dolomite unit, (2) dolomite and sandstone unit, (3) limestone and black shale unit, and (4) shale and sandstone unit. 

Each of these units and associated subunits thicken from 

west to east across restored section C-C' to a maximum 

near the depositional axis of the Rome trough. The lower 

unit (sandstone, shale, limestone, and dolomite unit) 

abruptly reverses its eastward-thickening trend at the western edge of the positive fault block (South-central Pennsylvania arch) and from there thins gradually eastward and 

southeastward to the end of the restored section. The upper 

three units also begin to thin eastward from near the 

depositional axis of the Rome trough, but they have an 

overall convex-downward, lens-shaped geometry because 

of gradual eastward thinning in comparison with abrupt 

eastward thinning of the lower unit.

The sandstone, shale, limestone, and dolomite unit is 

largely confined to the asymmetric graben that marks the 

rifting phase of the Rome trough. Abrupt thickness changes 

in the unit across the border faults of the graben indicate that 

sedimentation was fault controlled. On the South-central 

Pennsylvania arch adjoining the eastern margin of the Rome 

trough, this unit consists, in ascending order, of an 

undrilled basal sandstone unit, the undrilled Tomstown 

Dolomite, the Waynesboro Formation, and the Pleasant Hill 

Limestone and the equivalent lower one-third of the 

Elbrook Formation in northeastern West Virginia. The 

undrilled basal sandstone unit, the undrilled Tomstown 

Dolomite, and the undrilled lower part of the Waynesboro 

Formation are probably of Early Cambrian age, whereas 

the upper part of the Waynesboro Formation, the Pleasant 

Hill Formation, and the strata equivalent to the Pleasant Hill 

Limestone in the Elbrook Formation are probably of Middle 

Cambrian age. The Tomstown Dolomite is probably overlain unconformably by the Waynesboro Formation, which 

in turn is probably overlain unconformably by the Pleasant 

Hill Limestone. The uppermost part of the sandstone, shale, 

limestone, and dolomite unit extends west of the Ohio-West 

Virginia hinge zone as a basal Cambrian sandstone known 

as the Mount Simon Sandstone. Although commonly 

assigned a Late Cambrian age in central and east-central

Cambrian and Ordovician Rocks, Ohio, Pennsylvania, and West Virginia K25
Ohio, the Mount Simon Sandstone, because of its transgressive nature, may very likely be of latest Middle Cambrian 

age in the vicinity of the Ohio-West Virginia hinge zone.

The sandstone, shale, limestone, and dolomite unit in 

the graben part of the Rome trough has not been drilled; 

however, proprietary seismic data suggest that it is present 

and has a thickness of about 7,500 ft. A basal sandstone and 

the Tomstown Dolomite probably occur at the base of the 

unit in the Rome trough and have a thickness that is 

probably similar to that suggested on the adjoining Southcentral Pennsylvania arch. The red shale- and sandstonedominated Waynesboro Formation should also be present in 

the undrilled part of the Rome trough, but it probably has a 

much greater thickness than the partly drilled Waynesboro 

Formation on the adjoining South-central Pennsylvania 

arch. The Pleasant Hill Limestone probably also has thickened significantly in the undrilled part of the Rome trough. 

The thickened Pleasant Hill Limestone interval here may 

contain abundant gray shale beds in addition to limestone 

beds and therefore may be akin to the Conasauga Group 

identified in the Rome trough in central West Virginia 

(Ryder, 1992).

The lens-shaped dolomite and sandstone unit forms 

the core of the Cambrian and Ordovician sequence. Near 

the crest of the Wooster arch, this unit occupies about 

one-quarter of the total sequence. In contrast, between the 

depositional axis of the Rome trough and the eastern end of 

the restored section, the dolomite and sandstone unit occupies between one-third and one-half of the total Cambrian 

and Ordovician sequence. The Knox unconformity of 

regional extent is located in the upper part of the dolomite 

and sandstone sequence except near the depocenter of the 

Rome trough, where the unconformity is probably absent.

Three subunits constitute the dolomite and sandstone 

unit. The lower subunit consists of (1) the Middle(?) and 

Upper Cambrian Rome Formation of Janssens (1973) 

between the Ohio-West Virginia hinge zone and the 

Wooster arch, (2) the Middle and Upper Cambrian Warrior 

Formation in the Rome trough and on the adjoining Southcentral Pennsylvania arch, and (3) the strata equivalent to 

the Warrior Formation in the upper two-thirds of the 

Elbrook Formation at the eastern end of the restored 

section. The middle subunit of the dolomite and sandstone 

unit in the Rome trough and on the adjoining South-central 

Pennsylvania arch consists of the Upper Cambrian Gatesburg Formation and its four members: the lower sandy 

member, the middle dolomite member and the equivalent 

Ore Hill Limestone Member, the upper sandy member, and 

the Mines Dolomite Member. West of the Ohio-West 

Virginia hinge zone, the stratigraphic position of the Gatesburg Formation is occupied by (1) the Rome (upper part) 

and Conasauga Formations of Janssens (1973), the Krysik 

sandstone of driller's usage, and the B zone of Calvert 

(1964) (lower sandy member equivalents), (2) the lower 

part of the Knox Dolomite of Janssens (1973) (middle

dolomite member-Ore Hill Limestone Member equivalent), 

and (3) the Rose Run Sandstone Member of the Knox 

Dolomite of Janssens (1973) (upper sandy member equivalent). The upper subunit of the dolomite and sandstone unit 

consists of (1) the Lower Ordovician and Middle Ordovician (Whiterockian) Beekmantown Group in the Rome 

trough and the adjoining South-central Pennsylvania arch 

and (2) the Lower Ordovician upper part of the Knox 

Dolomite of Janssens (1973) and the overlying Middle 

Ordovician (Chazyan) Wells Creek Formation between the 

Ohio-West Virginia hinge zone and the Wooster arch.

Between the Ohio-West Virginia hinge zone and the 

Wooster arch, the Knox unconformity is located at the base 

of the Wells Creek Formation (Chazyan) and truncates 

successively older parts of the Upper Cambrian and Lower 

Ordovician Knox Dolomite of Janssens (1973) and the 

associated Upper Cambrian Rose Run Sandstone. The Knox 

unconformity extends into the adjoining Rome trough, but 

the unconformity there is located approximately in the 

upper 600 ft of the Beekmantown Group, and its magnitude 

has diminished significantly. For example, on the western 

margin of the Rome trough, the Chazyan part of the 

Beekmantown Group rests unconformably on the Lower 

Ordovician (Ibexian) part of the Beekmantown Group. Yet 

farther eastward, the Chazyan part of the Beekmantown 

Group rests unconformably on older Whiterockian-age 

Beekmantown strata. Near the depositional axis of the 

Rome trough, the Knox unconformity seems to disappear, 

and Beekmantown Group deposition was more or less 

continuous across the Lower Ordovician-Middle Ordovician boundary. Conodonts recovered from the AS drill hole 

suggest that the Lower Ordovician-Middle Ordovician 

boundary near the depositional axis of the Rome trough is 

located approximately 2,000 ft below the top of the Beekmantown Group. The Knox unconformity probably reappears on the adjoining western flank of the South-central 

Pennsylvania arch, where Chazyan-age Beekmantown 

strata rest unconformably on older Whiterockian-age Beekmantown strata. From there, the Knox unconformity progressively increases in magnitude toward the eastern end of 

the restored section, where the Middle Ordovician (Chazyan) part of the Beekmantown Group probably overlies the 

Lower Ordovician part of the Beekmantown Group.

The lens-shaped limestone and black shale unit 

which thickens eastward from about 980 ft at the crest of 

the Wooster arch to about 2,020 ft at the depositional axis 

of the Rome trough and then thins eastward to about 700 ft 

at the eastern end of the section is the thinnest of the four 

major lithofacies. In the Rome trough and the adjoining 

Ohio-West Virginia hinge zone and South-central Pennsylvania arch, the limestone and black shale unit consists, in 

ascending order, of the Loysburg Formation, the Black 

River Group, and the Trenton Group. West of the OhioWest Virginia hinge zone, the Loysburg Formation and the 

Black River Group combine to form the Black River

K26 Evolution of Sedimentary Basins Appalachian Basin
Limestone, and the Trenton Group is replaced by the 

Trenton Limestone and the overlying Utica Shale.

The Middle Ordovician Loysburg Formation in the 

Rome trough and on the adjoining South-central Pennsylvania arch consists of the Milroy Member (late Chazyan and 

earliest Blackriveran ages) and the overlying Clover Limestone Member (early Blackriveran age). The Loysburg 

Formation at the Ohio-West Virginia hinge zone is undivided and is significantly thinner than it is in the Rome 

trough. West of the Ohio-West Virginia hinge zone, the 

Loysburg Formation interval contains greenish-gray shale 

along with the limestone and is identified as the lower part 

of the Black River Limestone. At the eastern end of the 

restored section, the Loysburg Formation is absent because 

of erosion and nondeposition caused by an intra-Loysburg 

unconformity.

The Middle Ordovician Black River Group is undivided from the Ohio-West Virginia hinge zone to the 

eastern end of the restored section, except in outcrop east of 

the Allegheny structural front, where it consists, in ascending order, of the Hatter, Snyder, and Linden Hall Limestones. There and at the eastern end of the restored section, 

the 100- to 150-ft-thick Black River Group is thinner than it 

is elsewhere on the section, partly because of eastward 

depositional thinning and partly because of the truncation 

of progressively older Black River strata beneath a widespread pre-Trenton Group unconformity. The Black River 

Group beneath the unconformity is probably entirely of 

Blackriveran age and attains a maximum thickness of about 

520 ft near the depositional axis of the Rome trough. 

Between the depositional axis of the Rome trough and the 

Ohio-West Virginia hinge zone, the Black River Group 

strata climb about 120 ft upsection, at the expense of the 

overlying Trenton Group, to include the a and P (metabentonite) markers of Stith (1979) and strata of Rocklandian 

age. The Black River Limestone west of the Ohio-West 

Virginia hinge zone, which correlates with the Loysburg 

Formation and the Black River Group combined, has a late 

Chazyan through Rocklandian age.

The Middle and Upper Ordovician Trenton Group of 

Kay (1944a, b) near the depositional axis of the Rome 

trough consists, in ascending order, of the Nealmont Limestone (Rocklandian age), the Salona Limestone (Rocklandian age), the Coburn Limestone (Kirkfieldian and Shermanian ages), and the Antes Shale (late Shermanian and 

earliest Edenian ages). The a and p markers of Stith (1979) 

are located at the top and base of the Salona Limestone, 

respectively. At the eastern end of the restored section, the 

combined Nealmont-Salona-Coburn limestone interval is 

represented by the Nealmont Limestone, whereas the Antes 

Shale interval is represented by the Dolly Ridge Formation. 

Here, the combined Nealmont Limestone and the Dolly 

Ridge Formation constitute the Trenton Group of Perry 

(1972). The S2 metabentonite of Perry (1964), identified at 

the eastern end of the restored section in the middle part of

the Nealmont Limestone, correlates with the a marker of 

Stith (1979) and the R bentonite of Thompson (1963). The 

Nealmont and Salona Limestones (Rocklandian age) near 

the depositional axis of the Rome trough grade westward 

into the upper part of the Black River Group near the 

Ohio-West Virginia hinge zone and the equivalent upper 

part of the Black River Limestone in eastern Ohio. The 

Coburn Limestone (Kirkfieldian and Shermanian ages) and 

the overlying Antes Shale (Shermanian and early Edenian 

ages) extend as far west as the Ohio-West Virginia hinge 

zone, beyond which their respective stratigraphic intervals 

are identified as the Trenton Limestone and the Utica Shale. 

The shale and sandstone unit is lens shaped and 

thickens eastward from about 1,160 ft (m) near the crest of 

the Wooster arch to about 3,650 ft near the Allegheny 

structural front and then thins to about 2,700 ft at the eastern 

end of the section. The shale and sandstone unit at the 

eastern end of the restored section consists, in ascending 

order, of the Reedsville Shale, the Oswego Sandstone, and 

the Juniata Formation. The gray shale of the Reedsville 

Shale (Upper Ordovician; lower Edenian through Maysvillian Stages) extends across the entire section, whereas the 

argillaceous sandstone of the Oswego Sandstone and the 

equivalent Bald Eagle Formation in the Pennsylvania part of 

the section (Upper Ordovician; upper Maysvillian and lower 

Richmondian Stages) pinches out westward near the center 

of the Rome trough. The Juniata Formation (Upper Ordovician; Richmondian and Gamachian? Stages) and its correlative in Ohio, the Queenston Shale, extend across the 

entire section and consist of silty red shale and red sandstone beds.

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K32 Evolution of Sedimentary Basins Appalachian Basin