DETERMINING THE GEOMETRY AND FORMER EXTENT OF THE NORTH MOUNTAIN

THRUST FROM FLUID INCLUSION AND MICROSTRUCTURAL ANALYSES

Megan Castles

A Thesis

Submitted to the Graduate College of Bowling Green

State University in partial fulfillment of

the requirements for the degree of

MASTER OF SCIENCE

May 2010

Committee:

Charles Onasch, Advisor

James Evans

John Farver

ii

ABSTRACT

Charles Onasch, Advisor

Fluid inclusion microthermometry, microstructural analysis, and vitrinite reflectance

measurements were used to determine pressure and temperature conditions in several Paleozoic

rock units in the Valley and Ridge province in order to determine the former extent and geometry

of the North Mountain thrust sheet. Overburden thicknesses determined for the Devonian

Hampshire/Catskill Formation, Mississippian Pocono Sandstone, and Pennsylvanian Pottsville

Sandstone were found to be 5.5-6.0, 4.5-10.5, and 4.8-8.0 km, respectively. Differences in

salinity and CH4 content between the Hampshire/Catskill Formation and the Pocono Sandstone

and Pottsville Formation indicate that the Hampshire/Catskill Formation was affected by fluids

from a different source than the younger units. These fluids were also cooler than those in

overlying units, which explains why the older Hampshire/Catskill Formation yielded lower overburden thicknesses. All units experienced considerably greater overburdens than can be explained stratigraphically, which supports the model of Evans (1989) that the North Mountain thrust once extended over these rocks so that the large overburdens are of tectonic origin. iii

This paper is dedicated to my family and loved ones. Especially my parents Kevin and Mary

Castles who have always had faith in my abilities and pride in my accomplishments, I could not

have completed this project without their love and support. I would also like to dedicate this paper to my grandfather William Sheehan who sadly passed away while I was in graduate school,

I love and miss you Grampy and wish you could be here with me to celebrate my

accomplishment. iv

ACKNOWLEDGMENTS

I would first like to thank my advisor Charles Onasch, without whose patience, dedication and guidance I would never have completed this project. I would also like to thank John Farver and Jim Evans for taking time in their busy schedules to be on my committee. I would like to thank the Geology Department at BGSU and the Geological Society of America for funding my research. Special thanks to James Hower for analyzing and measuring my vitrinite samples. A final thank you to my fiancé Mark Humphrey and friends Laura Webb, Erin Sullivan,Will

Emery, Colleen O’Shea, Jessica Lawrence, Kelsey Garner, Gary Michelfelder and Aaryn

Goldbaum for their love, friendship, support and most importantly comic relief though this long process. v

TABLE OF CONTENTS

Page

CHAPTER I. INTRODUCTION ...... 1

CHAPTER II. BACKGROUND ...... 2

CHAPTER III. METHODS ...... 21

CHAPTER IV. RESULTS ...... 27

CHAPTER V. DISCUSSION ...... 41

CHAPTER VI. SUMMARY ...... 52

CHAPTER VII. CONCLUSIONS ...... 53

REFERENCES ...... 54

APPENDIX A. SAMPLE LOCATIONS AND TYPE OF ANALYSIS PERFORMED ..... 56

APPENDIX B. HISTOGRAMS OF FLUID INCLUSION DATA...... 58

APPENDIX C. PRESSURE/TEMPERATURE DIAGRAMS ...... 75 vi

LIST OF FIGURES

Figure Page

1 Geologic map of the study area showing sample locations and type of analysis

performed on samples at each location...... 4

2 Partial stratigraphic column for study area showing detachment zones (large

horizontal arrows) and hydrostratigraphic units...... 7

3 Geometry of the NMT interpreted from Evans (1989)...... 11

4 Geometry of the NMT interpreted from Kulander and Dean (1986) ...... 13

5 Geometry of NMT interpreted from Mitra (1986)...... 13

6 Photomicrograph of quartz vein from Pocono Sandstone taken with CL microscope 24

7 Examples of primary fluid inclusions found in the Pocono Sandstone ...... 26

8 VX plot of CH4-rich inclusions showing that inclusions are >90% methane ...... 29

9 Relationship between two-phase aqueous inclusions (with bubble) and single-

phase methane inclusions (grey, no bubble) at room temperature as observed in a

sample from the Pocono Sandstone (Sample TH 5)...... 31

10 Example of Pressure/temperature diagram showing trapping pressures determined

from the ThA-isochore intersection method for Pocono Sandstone, in central

portion of study area...... 32

11 Example of Pressure/Temperature diagram showing range of trapping pressures and

temperatures as determined from the Geothermal Gradient methodfor the

Hampshire/Catskill Formation, cental part of study area...... 33

12 Example of pressure/temperature diagram showing trapping pressures as determined

from ThH isochore method for the Pocono Sandstone, in eastern portion vii

of study area ...... 34

13 Common quartz microstructures found in the Pocono Sandstone (TH 48) ...... 36

14 Abundance of deformation mechanisms as a function of location relative to the

NMT trace (east), Broadtop synclinorium/Sideling Hill (central) and the

Alleghany front (west)...... 37

15 Abundance of each deformation mechanism as a function of rock unit within the

Broadtop synclinorium/Sideling Hill region ...... 38

16 Correlation between %R (mean) and LOM (Level of Metamorphism) for Pocono

Sandstone samples collected in eastern portion of study area ...... 40

17 Relationship between LOM, burial time in millions of years and maxium

temperature in °C for vitrinite samples collected from the Pocono Sandstone the

eastern portion of the study area...... 40

viii

LIST OF TABLES

Table Page

1 Summary of abbreviations used for fluid inclusions measurements ...... 15

2 Summary of modal homogenization temperatures determined from fluid

inclusion microthermometry ...... 28

3 Summary of TmA and corresponding wt. % NaCl equivalent, as well as Te

values of primary fluid inclusions measured from each rock unit in its given

locality...... 30

4 Summary of trapping pressure/temperature determinations by region, rock

type, and method ...... 35

5 Summary of overburden thicknesses for each rock unit and region determined

from fluid inclusion data using each of the three methods (see text for

descriptions) assuming a hydrostatic pressure gradient ...... 43

6 Maximum burial temperatures and overburden thicknesses from vitrinite

reflectance measurements from the Pocono Sandstone ...... 48

7 Summary of the overburden determinations in km derived from each method

used in this study for each rock unit in central and eastern portions of the

study area ...... 49

1

CHAPTER I. INTRODUCTION

The central and southern Appalachians are dominated by a series of imbricated thrust sheets consisting of Paleozoic sedimentary rocks that have been displaced northwestward over a gently sloping basement of Precambrian crystalline rocks (Evans, 1989). Of the major sheets, the North Mountain thrust (NMT), is the most significant in terms of extent and displacement

(Evans, 1989). Despite its importance, its geometry, history, and relationship to other thrusts in the region have been the subject of considerable debate (Evans, 1989). Thrust sheets can advance either by bodily displacing hanging wall rocks over footwall rocks or by transferring hanging wall displacement in the rear of the sheet to homogeneous shortening in the front of the sheet (Davis and Reynolds, 1984). In the case of the NMT, both models have been proposed for the displacement history. Evans (1989) proposed that a significant amount of displacement took place up the upper ramp, which placed a portion of the sheet on top of Paleozoic rocks of the

Valley and Ridge Province to the west. He cited anomalously high thermal maturities and fluid inclusion trapping temperatures in the Paleozoic rocks as evidence that they were buried by the

NMT. Kulander and Dean (1988), however, proposed that the surface expression of the NMT at the North Mountain ramp is a minor splay and that most of the displacement on the thrust was transferred into shortening of the middle and upper Paleozoic cover rocks of the Valley and

Ridge to the west.

The purpose of this study is to test various models that have been proposed for the former extent and geometry of the NMT using overburden thicknesses derived from paleobarometry and paleothermometry determined from fluid inclusions, microstructure suites, and vitrinite reflectance measurements. 2

CHAPTER 2. BACKGROUND

Regional geologic setting

There are three major thrust systems in the Central Appalachian foreland: (1) the North

Mountain thrust (NMT), which has a upper plate comprised of imbricated Cambrian-Ordovician

carbonates; (2) the Blue Ridge thrust, which is composed mostly of crystalline rocks; and (3) the lower carbonate duplex, which is made up of Cambrian-Ordovician carbonates (Evans, 1989).

The NMT extends from south-central Pennsylvania to west-central Virginia (Fig. 1). It emplaces

Cambrian-Ordovician carbonates over strata ranging from the Upper Ordovician Martinsburg

Formation to the Mississippian Pocono Sandstone. The NMT is characterized by imbricated

Cambrian-Ordovician carbonates that are deformed into large fault-bend folds and fault- propagation folds. The leading edge of the NMT was deformed into a fold with fault-bend fold geometry and was juxtaposed against middle Paleozoic rocks (Evans, 1989). In Pennsylvania, the upper plate of the NMT consists of a fault propagation fold at the surface, while the fault itself continues in the subsurface beneath the Great Valley. In Virginia, displacement on the

NMT is progressively transferred to the Pulaski thrust (Kulander and Dean, 1986) located southwest of the study area, which is outlined in Figure 1.

Stratigraphy

The sedimentary rock units analyzed in this study were deposited in the Appalachian foreland basin. Foreland basins are areas of subsidence that develop in front of fold and thrust belts as an isostatic response to the crustal thickening/loading from thrust sheets (Miall, 1999).

Sedimentary rock units found in the study area were deposited in a variety of depositional environments throughout the Paleozoic in response to a series of tectonic events. The oldest units, 3

Cambrian and Ordovician carbonates, were deposited along the passive margin of the Iapetus

Sea, which formed as a result of continental rifting during the late Precambrian (Prothero and

Dott, 2002). The Taconic orogeny at the end of the Ordovician and subsequent erosion of

uplifted areas resulted in deposition of an Early Silurian clastic wedge, which in the study region

are mostly quartz sandstones and conglomerates. Further subsidence of the Taconic foreland

basin resulted in higher sedimentation rates of marine sediments. Carbonate and marine shales

were deposited during the Middle Ordovician to early Devonian. The late Devonian gave rise to

the Acadian orogeny. Rapid erosion of this orogenic belt resulted in the Catskill clastic wedge.

The Catskill clastic wedge formed a massive colluvial coastal plain, which was composed mostly

of red sandstones and conglomerates and was estimated to have been 300 to 500 km wide at its

largest extent (Prothero and Dott, 2002). The Catskill clastic wedge ranges up to approximately

1500 m thick (White et al., 1885). During the late Paleozoic, the Alleghanian orogeny began.

Clastic sediments shed westward from the central Appalachian Mountains were deposited in a deep offshore trough (Cotter and Driese, 1998). The deposits range in age from late

Mississippian to Permian. Much of the Permian age rocks have since been eroded away, but the maximum thickness of the whole sequence from Precambrian to Permian in east-central

Pennsylvanian is estimated to have been as much as 12,000 m (Colton 1970).

The Paleozoic stratigraphy in the central Appalachians can be reevaluated as either lithotectonic units (based on competency), or hydrostratigraphic units (based on paleo- hydrologic properties) (Fig. 2). Within this region, there are three competent lithotectonic units separated by regional detachments localized within incompetent units (Evans and Battles, 1999).

4

Figure 1. Geologic map of the study area showing sample locations and type of analysis

performed on samples at each location. BTS- Broadtop synclinorium, SH – Sideling Hill, SCM-

Sleepy Creek Mountain. Inset map shows location of structural features of central Appalachians showing location of NMT relative to the provinces and the Massanutten synclinorium (MS).

WV – west Virginia, VA – Virginia, MD – Maryland, PA – Pennsylvania. Inset map adapted

from Evans (1989). 5

The lowermost competent unit is made up of Precambrian crystalline basement rock and Lower

Cambrian sedimentary rocks, the middle competent unit is made up of middle Cambrian to

Ordovician carbonates, and the uppermost unit is comprised of the Lower Silurian

Massanutten/Tuscarora Sandstone through Lower Devonian sedimentary rocks. Separating the lower and middle competent units is the Waynesboro detachment, which acts as a regional decollement zone (Evans and Battles, 1999). The middle and upper competent units are separated by a weak shale unit, the Martinsburg detachment, which is also a regional detachment zone (Fig. 2). In addition, there are two other small-scale detachment zones located in the

Tonoloway and Marcellus formations.

Evans and Battles (1999) defined three hydrostratigraphic units in the study area based on their paleo-hydrologic properties and nature of the fluids found in them as determined from fluid inclusions (Fig. 2). The first of these units is a regional aquitard and is comprised of the

Ordovician Trenton Formation through the Devonian Helderberg Group, (Unit 3 in Figure 2).

The fluids in this unit are connate high salinity brines saturated with CH4. The second unit is the

Devonian Oriskany Formation through the Lower Chemung Formation (Unit 2 in Figure 2),

which acted as a regional aquifer for warm, migrating CH4-saturated, NaCl-CaCl2 brines

according to Evans and Battles (1999). The third regional aquifer is the Upper Devonian

Chemung Formation through the Pocono Sandstone (Unit 1 in Figure 2) and is characterized by

mixed meteoric and connate waters.

Two fluid migration events in these paleoaquifers were described by Evans and Battles

(1999). The first event is believed to have occurred late synfolding to post-folding during the

Alleghanian orogeny. The second migration event occurred post-folding. The source of these

fluids is under some debate, but is believed to be from the hinterland where fluids were driven 6

tectonically through the fold-and-thrust belt by large-scale out-of-sequence thrusting (Evans and

Battles, 1999).

Upper Paleozoic units

This study focused on the three youngest units in the region: The Hampshire/Catskill

Formation (Hampshire in Maryland and West Virginia, Catskill in Pennsylvania), Pocono

Sandstone, and Pottsville Sandstone. The Pocono Sandstone was the primary unit of focus for this study because it is the youngest unit in the Valley and Ridge Province that is widely exposed.

It also has fewer uncertainties about stratigraphic overburden than older units. The underlying

Hampshire/Catskill Formation is more widely exposed than the Pocono Sandstone and offers a larger area from which to sample, but has greater uncertainty about the former overburden. The overlying Pennsylvanian Pottsville Sandstone is exposed only in a small area within the core of the Broadtop synclinorium (Fig. 1), but was included because it is one of the youngest rock units exposed in the Valley and Ridge.

The Hampshire/Catskill Formation is massively bedded, red to green, medium to very fine-grained, well sorted, feldspathic arenite and shale. The Pocono Sandstone is a massively

bedded, white to tan, fine to coarse-grained, well sorted, quartz arenite and wacke. The

Pottsville Sandstone is a massively bedded, gray to white, medium-grained, moderately to well

sorted, quartz arenite and wacke and minor conglomerate and shale.

7

Figure 2. Partial stratigraphic column for study area showing detachment zones (large horizontal arrows) and hydrostratigraphic units. Adapted from Evans and Battles (1999). 8

Depth of burial of the Pocono Sandstone

Although the Mississippian Pocono Sandstone is the youngest rock unit exposed in most

of the study area, it was overlain by younger rocks prior to erosion to the present-day surface.

To estimate the depth of maximum burial experienced by the Pocono Sandstone, the thickness of

younger rocks preserved some 80 km west on the eastern edge of the Alleghany Plateau, were

totaled (Overbeck, 1954). The thickness of the Greenbriar Formation, (91m), Mauch Chunk

Formation, (213 m), Pottsville Sandstone, (76 m), Allegheny Formation, (99 m), Conemaugh

Formation, (290 m), Monongahela Formation, (82 m), and Quaternary sediments, (21 m), total

872 m (Fig. 2). Assuming a geothermal gradient of 25°C/km for the study region at the time of deformation, and a surface temperature of 20°C, this overburden would produce a maximum burial temperature of ~40°C. This calculation is significantly lower than the 160-220°C paleo-

temperatures determined by Evans and Battles (1999), using conodont alteration indices. This

suggests that the Pocono Sandstone must have been buried at a greater depth than can be

accounted for by the simple reconstruction of the present-day stratigraphic section.

The stratigraphic thickness of the Broadtop synclinorium (Fig. 1) was measured by White et al. (1885). From youngest to oldest, the units measured and their thicknesses are as follows:

Monongahela, Conemaugh, and Alleghany formations (62.7 m), the Pottsville Sandstone (85.3 m), the Mauch Chunk and Greenbriar formations (335.2 m), the Pocono Sandstone (650.1 m), and the Hampshire/Catskill Formation (816 m), totaling 487.7 m above the Pocono Sandstone.

Assuming a geothermal gradient of 25°C/km, with a surface temperature of 20°C, the maximum burial temperature was ~30°C. Once again, this suggests that in this region, the maximum burial 9 temperature provided by the simple reconstruction of the stratigraphic overburden is too low to explain the paleo-temperatures found (Evans and Battles, 1999) using conodont alteration indices.

Permian clastic wedge

A relatively uniform stratigraphic thickness was calculated for the early Pennsylvanian age Pottsville, Mauch Chunk/Greenbriar units and thicker middle Pennsylvanian age units between the Broadtop synclinorium and the Alleghany plateau. This uniform thickness of the older Pennsylvanian age units suggests that the middle and upper Pennsylvanian age units most likely followed the same trend in thickness in the east as can be found further west in the Plateau.

If these units were part of a clastic wedge deposited from the Alleghanian orogeny, then the units would be thicker in the eastern Broadtop synclinorium. Therefore, the Pennsylvanian age deposits found in the central Appalachians do not appear to be associated with the Pennsylvanian clastic wedge deposits found in the Southern Appalachians. In the central Appalachians, the

Alleghanian clastic wedge has been determined to have been Permian in age; however, few if any Permian age rocks are still present in this region. A thickness for the Permian clastic wedge could be postulated by drawing a comparison with the Acadian clastic wedge. If one can assume the scale of the two orogenic events and the sedimentation rate was similar then the Permian clastic wedge might have had to have been at least ~1500 meters thick based on the thickness of the Hampshire/Catskill Formation and Pocono Sandstone found in the Broadtop synclinorium

(White et al., 1885).

Geometry and deformation history of the North Mountain thrust

The NMT has been interpreted to be the dominant thrust in a series of imbricated thrusts that make up the central Appalachians (Evans, 1989). There has been considerable debate over 10

its geometry, raising questions about its deformational history and the deformation of the province as a whole.

Evans (1989) discussed four possible models to explain the more than 60 km of cover rock displacement that occurred during thrusting. The first of these models is that displacement

of the cover rocks moved forelandward along the Martinsburg detachment into the Valley and

Ridge province during the Alleghanian orogeny and that the displacement was taken up by

shortening in the cover rocks. The second model proposes that the NMT was emplaced during

the Taconic orogeny before the cover rocks were deposited. The third model is that the cover

rock displacement occurred as a result of backthrusting of cover rocks over the NMT. The last

theory states that the displacement of the cover rocks was transferred up the North Mountain

ramp to a higher stratigraphic level leading to overthrusting and duplication of the cover rocks in

the Valley and Ridge province. Of the four models presented, the two that Evans (1989) believes

are most plausible are backthrusting of the cover rocks and displacement over the North

Mountain sheet across the upper North Mountain ramp over a similar section of carbonate rocks

in the western Valley and Ridge Province (Fig. 3). For the first model to be plausible a

shortening of approximately 90 km in the Paleozoic cover rocks would be necessary to account

for that magnitude of displacement; however, total shortening of the cover rocks as a result of

folding and faulting is only about 30 km (Evans, 1989). The issue with the second model is that

the cover rocks display the same cleavage and deformation history as the underlying rocks

suggesting that all of the rocks underwent the same deformational history; therefore, the NMT

could not have been emplaced before the cover rocks were deposited. Third, the backthrusting

model requires around 60 km of movement which is not unheard of in thrust faults so it could be

a viable explanation. The fourth model, favored by Evans (1989), calls for overthrusting and 11

emplacement of the NMT on top of the Paleozoic cover rocks (Fig. 3), which is based on

anomalous thermal maturities determined from conodont alteration indices (CAI), which indicate

that the section was thickened. The CAI is based on the changes in color that occur in conodont

fossils as a result to changes in temperature over time, and covers a large range of temperatures

from 50 ºC to 600 ºC (Garcia-Lopez et al., 2001). Based on CAI, the thermal maturity of lower

Paleozoic rocks just west of the NMT trace indicates they were buried under 5-7.5 km of

overburden of which only 2 km can be accounted for by the existing stratigraphic section. Evans

(1989) explains this by adding the NMT sheet having been emplaced on top of these rocks (Fig.

3). Furthermore, Evans and Battles (1999) found fluid inclusion evidence, 160-220°C, for

anomalous pressures in Devonian rocks in the Valley and Ridge that indicated an overburden

consistent with the presence of the NMT sheet.

Figure 3. Geometry of the NMT interpreted from Evans (1989). Key: NMT - North Mountain

Thrust, Cc – Cambrian carbonates, Oc – Ordovician carbonates, Om – Ordovician Martinsburg

Formation, S-Dv – Silurian to Devonian rocks. 12

Kulander and Dean (1986) proposed a different model for the NMT in which it did not play a major role in the deformation of the Paleozoic Rocks in the Valley and Ridge Province.

They propose that the NMT is only a minor splay within the Massanutten-Blue Ridge sheet (Fig.

4) and that the Massanutten-Blue Ridge sheet and westward transport of the Martinsburg sheet

was a result of layer-parallel shortening. According to them, movement on the Martinsburg

detachment resulted in tight folding and faulting of all of the overlying Paleozoic strata and an

overall shortening of 30-40% west of the North Mountain thrust ramp.

A third model for the evolution of the NMT comes from Mitra (1986), who also

interpreted the NMT as a minor splay off of the Massanutten-Blue Ridge sheet (Fig. 5). He

states that the deformation in the Upper Ordovician-Devonian rocks is a result of slip along

thrusts within the Cambrian-Ordovician succession. This deformation, which was transferred

along the thrusts into the Upper Ordovician-Devonian, died out in a series of imbrications

towards the foreland. In this model, the NMT acts as a slip surface, which led to the formation

of the Broadtop duplex. Shortening of the upper Paleozoic rock units resulted from slip along

thrusts of the Wills Mountain and Paterson Creek anticlines, located west of the study area on the

eastern boundary of the Alleghany structural front, being transferred into the frontal zone of the

structures as well as the Appalachian Plateau itself. A difference in scale amongst the diagrams

reflects scales of original cross section constructed for each model by each author.

13

Figure 4. Geometry of the NMT interpreted from Kulander and Dean (1986). NMT - North

Mountain thrust, Cc - Cambrian carbonates, Oc - Ordovician carbonates, Dv - Devonian rocks.

Figure 5. Geometry of NMT interpreted from Mitra (1986). NMT - North Mountain thrust, Cc -

Cambrian carbonates, Oc - Ordovician carbonates, UOr – Upper Ordovician rocks, Dv -

Devonian rocks, UDv – Upper Devonian rocks.

14

Fluid inclusion microthermometry

Fluid inclusions, which are samples of fluid trapped during crystal growth or fracture

healing, display a variety of compositions and phases. Single-phase inclusions occur when there

is only one phase present, either a liquid or a vapor phase. Two-phase inclusions can be either liquid-rich, with a small vapor bubble occupying <50% volume, or vapor-rich with the vapor bubble occupying > 50% volume of the inclusion. Although less common than single- and two- phase inclusions, inclusions may also contain more than two phases, including solids (Sheperd et al., 1985).

Primary inclusions form as a result of fluids trapped in imperfections on the crystal face during mineral growth. Secondary inclusions are trapped along microfractures as they heal.

There can be several generations of secondary inclusions as new fractures form and heal under different stresses (Goldstein and Reynolds, 1994).

As fluid inclusions cool from the trapping temperature (Tt), they undergo phase changes

as a result of differential shrinkage between the fluid and the host mineral. The most common of

these phase changes is the separation of a liquid and vapor phase. Other phases include multiple

immiscible fluids and the crystallization of daughter crystals (Roedder and Bodnar, 1980).

Heating the sample until the vapor phase disappears will yield the temperature of

homogenization (Th). Fluid composition (salinity) can be determined from the freezing behavior.

Upon warming of a frozen aqueous inclusion, the temperature at which the first liquid appears

(eutectic temperature or Te) can be used to determine which salt is present. The temperature at which the last ice crystal melts (Tm) is used to calculate the salinity, which is typically reported

as equivalent wt. % NaCl, regardless of the actual salt composition (Roedder and Bodnar, 1980). 15

Fluid inclusions can be used to determine pressure and temperature conditions during

deformation assuming that they trapped a homogeneous fluid and have not changed volume

since trapping (Roedder, 1984). The trapping temperature of an aqueous inclusion (Tt) can be

estimated from ThA, ThA will always underestimate Tt, but depending on the salinity and density

of the fluid, the two values may be close (Goldstein and Reynolds, 1994). If the trapping

pressure (Pt) is known independently, Tt can be determined from ThA and the isochore

corresponding to the fluid density. Conversely, if the trapping temperature is known

independently, the trapping pressure can be determined from the isochore. If two coexisting immiscible fluids, such as a brine solution and a carbonic solution, are present in separate, but coeval, inclusions both Tt and Pt can be determined from the intersecting isochore method

(Bodnar and Roedder, 1980). Once Pt is known, the depth can be estimated by assuming either a

lithostatic or hydrostatic paleo-geothermobaric gradient. Table 1 displays different abbreviations

used and their meaning.

Table 1. Summary of abbreviations used for fluid inclusions measurements.

Abbreviation Definition

Tt Trapping temperature

Tp Trapping pressure

ThA Homogenization temperature of aqueous inclusions

ThH Homogenization temperature of CH4-rich inclusions

TmA Temperature of last ice melt for aqueous inclusions

TmCO2 Temperature of CO2 ice melt for CH4-rich inclusions

TeA Eutectic temperature (temperature of first ice melt) for aqueous inclusions

16

In the study area, inclusions were found to be two-phase aqueous or single phase CH4-

rich at room temperature. Upon cooling, the latter develop into two-phase (CH4 liquid + vapor)

or three-phase (CH4 liquid + vapor + CO2 ice) inclusions. The temperature at which pure CH4

homogenizes back to a single phase is -84.4 ºC, which is known as the critical temperature

(Sheperd et al., 1985). Deviations from this temperature occur as a result of phases other than

CH4 being present. CH4-rich inclusions that homogenize at temperatures lower than the critical temperature, in the range of -90ºC to -110°C, are interpreted to be a mixture of CH4 and CO2.

Upon warming, the CO2 ice melts (sublimates) at temperatures between -118° and -90°C,

followed by the homogenization of the CH4 liquid and vapor at temperatures between -117 and

-74°C. CH4-rich inclusions that homogenize at temperature higher than the critical temperature,

- 84.4 to -79ºC are combinations of CH4, CO2, and higher molecular weight hydrocarbons

(Evans and Battles 1999).

Microstructural analysis

Microstructural suites (assemblage of interrelated microstructures), can be used to infer

differential stress, temperature, and pressure conditions at the time of peak deformation

(Groshong, 1988; Knipe, 1989). Microstructures are characteristic of the dominant type of

deformation mechanism that created them, which are in turn controlled by the physical and

chemical conditions during deformation, such as changes in temperature and confining pressure

or changes in fluid chemistry (Davis and Reynolds, 1984). Knipe (1989) describes three main

categories of deformation mechanisms: diffusive mass transfer, crystal-plasticity, and

microfracturing.

Diffusive mass transfer – Diffusive mass transfer (DMT), also sometimes synonymous

with the term pressure solution, occurs as a result of strain associated with redistribution of 17 material by diffusive processes and results in macroscopically ductile behavior. Diffusion occurs as a result of differences in chemical potential induced by stress variations in the rock aggregate, differences in fluid pressure, and variation in internal strain energy of grains. It is the dominant deformation mechanism in fine-grained materials deformed at a variety of temperatures because the diffusion path length is short and differential stress is generally low. Longer path length and greater differential stresses typically lead to crystal-plastic deformation (Knipe, 1989).

Microstructures indicative of DMT in the rocks examined include sutured grain boundaries and stylolites, both of which are a result of removal and redistribution of material within the rock. Sutured grain boundaries are also known as grain-to-grain stylolites. A stylolite as defined by Groshong (1988) is a thin seam or contact surface that is interlocking due to mutual penetration by each side of the contact and is typically lined by accumulations of insoluble residue, such as clay minerals, opaque minerals, or organic material.

Crystal-plasticity – Crystal-plasticity is a constant-volume ductile process that occurs primarily as a result of the formation and movement of dislocations in the crystal lattice. The movement of dislocations is divided into three categories based on an inverse relationship between temperature and strain rate. These are dislocation glide, dislocation climb, and dislocation creep (glide + climb). During dislocation glide, the dislocations move along slip planes in the lattice structure. Glide occurs at high strain rates and lower temperatures (<250 ºC), because it takes very little energy for dislocations to move. However, in order for them to overcome obstacles in their path they must climb to a different glide plane via dislocation climb.

Climb requires moderate strain rates and higher temperatures (> 450 ºC). Dislocation creep is a combination of glide and climb and requires the most energy in the form of high temperatures

(~800-1200 ºC) and lower strain rates (Blenkinsop, 2000). Hirth and Tullis (1992) conducted a 18 series of rock deformation experiments on quartz aggregates and defined three deformation regimes based on different microstructures that formed at different temperatures and strain rates.

Regime I (low temperature and high strain rate) is characterized by patchy extinction. Regime II

(moderate temperature and strain rate) is characterized by sweeping undulatory extinction, deformation lamellae and subgrains. Regime III, (high temperature and low strain rate) is characterized by a mosaic of strain-free grains resulting from grain boundary migration and subgrain rotation recrystallization.

Microstructures indicative of crystal plasticity in the rocks examined include undulatory extinction, deformation lamellae, deformation bands, and recrystallized grains. Undulatory extinction occurs when the crystal lattice is bent during deformation and results in the extinction sweeping smoothly across a grain as the microscope stage is rotated. If the lattice is broken and new boundaries are formed, then the grain will exhibit patchy extinction (Groshong 1988).

Patchy extinction has sharper boundaries between extinction domains, which look like different grains although it is only one grain.

Deformation lamellae, which are the product of intracrystalline slip (Groshong, 1988) are thin bands of recovered material that occur in parallel sets. They are identifiable in thin section under crossed polarized light because they have a slightly different extinction angle and/or birefringence than the host grain.

Deformation bands form as a result of kinking of the crystal lattice by slippage on a weak direction within the lattice (Groshong, 1988) and occur as subparallel, tabular bands with a different extinction position than the host grain. Where deformation lamellae and bands occur in the same grain, they are typically at high angles to each other. 19

Recrystallized grains are a response to the accumulation of strain energy that accompanies dislocation glide and climb (Groshong, 1988). In order to lower that energy and make the grain more stable, grain boundaries begin to migrate, which is called grain boundary migration recrystallization, and/or subgrains form and progressively rotate, which is called subgrain rotation recrystallization (Blenkinsop, 2000). Recrystallization can be recognized by a polygonal network of strain-free grains that are smaller than the original grain.

Brittle deformation – Grain-scale brittle deformation can be divided into two types: that in which fracturing (Mode I) dominates, and that in which frictional sliding (Modes II and III) dominates (Knipe 1988). Both are a result of tensile and/or shear failure. The microstructures associated with this mechanism include fluid inclusion planes and microveins.

Fluid inclusion planes (FIPs) form as a result of fluids being trapped during healing of a

Mode I microfracture. They appear in thin section as very thin lines consisting of bubble arrays often occurring in parallel sets. Upon racking the focus up and down, the bubble arrays can be seen to lie along planes. FIPs can often be mistaken for deformation lamellae; however, FIPs can cross grain boundaries where as deformation lamellae do not. Also FIPs do not have any birefringence differences associated with them.

Microveins are also Mode I fractures, but differ from FIPs in that they have dilated upwards of 100-μm, and are filled with cement in optical continuity with the wall rock grain. In plane-polarized light, they can be seen as relatively inclusion-free stripes cutting several grains.

In crossed-polarized light, they are indistinguishable from the host grains due to the optical continuity of the quartz cement.

20

Determining temperature and pressure from microstructures

As described above, microstructures are indicative of the deformation mechanisms and conditions under which they formed. DMT is associated with ductile behavior and occurs under relatively low differential stresses and over a wide range of temperatures, although it is most commonly described (e.g., stylolites) in rocks deformed at temperatures < 300°C (Groshong,

1988). Crystal plasticity is also associated with ductile behavior and occurs under relatively low differential stresses and higher temperatures (>~300°C). Grain-scale brittle deformation is associated with high differential stresses and low temperatures (<~300°C).

Because of the range of temperatures at which DMT can occur, the presence or absence of crystal-plastic and brittle microstructures is most useful in estimating temperature (i.e., brittle- ductile transition zone). According to Ashby (1972), the temperature regime for the brittle- ductile transition zone is between 150ºC and 300ºC, so depth estimates would be between 6 to 12 km, assuming 25°C/km geothermal gradient. This temperature regime and depth estimation may fluctuate due to the presence of fluids, which would promote crystal-plastic deformation at lower temperatures than if dry. Because the presences of fluids are indicated by the presence of ubiquitous fluid inclusions, the lower depth value of (6 km) is probably most appropriate for the brittle-ductile transition. Pressure can then be estimated from assuming either a hydrostatic pressure gradient (6 km = ~59 MPa) or lithostatic gradient (6 km = ~159 MPa). From temperature and pressure conditions determined from fluid inclusion data, the depth of burial at the time the microstructures estimated. Given the uncertainties in the numerous factors that control the operation of different deformation mechanisms, the microstructural suites can be used only as a general check on the fluid inclusion and vitrinite reflectance data: specific temperatures and pressures cannot reliably be determined from them. 21

Vitrinite reflectance

Vitrinite reflectance is a measure of coal rank (organic metamorphism), which is

determined by measuring the maximum reflectance in polarized reflected light or the random reflectance (also known as mean or average reflectance) in non-polarized reflected light.

Random reflectance is thought to be a function of maximum depth of burial, independent of

pressure (Levine and Davis, 1989). It was observed by White (1925, 1935) that coal rank in the

Appalachians increases towards areas with greater deformation. It was therefore concluded that

coal metamorphism is a result of regional temperature gradients. Therefore, measurements of

coal metamorphism can be used to infer regional paleo-geothermal gradients (Hower and Davis,

1981).

22

CHAPTER III. METHODS

Sample collection

A total of 58 samples were collected in Pennsylvania, Maryland, and West Virginia from the Devonian Hampshire/Catskill Formation, Mississippian Pocono Sandstone, and

Pennsylvanian Pottsville Sandstone from just west of the NMT trace to the eastern edge of the

Alleghany Plateau (Fig. 1). Samples were collected from the Plateau to test how far west the

NMT extended. The distribution of samples defines three general areas that will be referred to in subsequent sections: eastern – just west of the NMT trace along Hill and Sleepy Creek

Mountains; central – Broadtop synclinorium, including Sideling Hill; and western – Alleghany

Plateau.

The primary locations for sample collection were road cuts and outcrops, particularly at the tops of Hill and Sleepy Creek Mountains, and Sideling Hill (see Figure 1). In general, samples were collected along traverses normal to the strike of the NMT, from the trace of the

NMT westward to the Allegheny Plateau. Within outcrops, sampling was focused primarily on veins and mineralized fault surfaces. Samples for microstructural analysis were collected along with vein/fault samples.

Sample preparation and analysis

Of the samples collected, 30 were chosen based on presence and size of vein material, and prepared for microstructural analysis, and 22 of these were also prepared for fluid inclusion analysis based on the size and quality of the vein material. For the fluid inclusion analysis, doubly-polished thick plates of approximately 50 – 150 µm thick were prepared in the Geology

Department at BGSU. For the microstructural analysis, polished thin sections of standard thickness were also prepared at BGSU. 23

Thin sections were examined for microstructures and point-counted to determine their relative abundance. For each thin section, microstructures were counted in 250 quartz grains along a rectilinear grid. In the circumstance where a grid intersection landed on a non-quartz grain, the nearest quartz grain below the intersection was used. For each quartz grain, a tally of all the deformation microstructures present was taken. After 250 grains were analyzed, each deformation microstructure was then tallied and the percentage of the total grains counted was calculated. The different microstructures were used to infer which deformation mechanism(s) was/were dominant in the rock: DMT, crystal-plastic, or brittle deformation. From the relative abundances, the general P/T conditions were then inferred from the suites of microstructure present (e.g., Knipe, 1990).

Thin sections containing vein material were examined in cathodoluminescence (CL). CL is useful for detecting growth zoning and different generations of mineralization in a sample, especially in quartz which has characteristically low amounts of trace elements making it difficult to detect growth zoning under normal microscopy (Marshall, 1989). Zoning can indicate changing physical and/or chemical conditions during crystal growth. In such cases, fluid inclusion measurements must be made with respect to specific zones. In Figure 6 below are photomicrographs taken of a quartz vein from sample TH 11 of the Pocono Sandstone. Image A was taken under normal microscope conditions while photo B was taken with the cathode beam on. If the vein sample had growth zoning it would be visible as banding in Image B. Vein samples from all three units were examined with CL microscopy and none were found to have growth zoning.

24

Figure 6. Photomicrograph of quartz vein from Pocono Sandstone taken with CL microscope.

(A) Image under normal microscopy. (B) Image with cathode beam on, indicates no zoning

present in quartz vein.

The best way to estimate the amount of overburden was to use microthermometric data from fluid inclusion analysis (e.g., Roedder & Bodnar, 1980; Roedder, 1984; Goldstein &

Reynolds, 1994). The doubly-polished plates were prepared from vein samples for fluid inclusion microthermometry according to the methods of Goldstein and Reynolds (1994) being careful to not heat the sample above 100°C during sample preparation in order to avoid inclusion stretching and decrepitation of lower temperature inclusions.

Inclusions were first classified as primary or secondary on the basis of several criteria.

Primary inclusions were observed to be larger, independent of fluid inclusion planes, and in some cases, more irregular and isolated. Secondary inclusions were found to be in planar arrays and smaller in size than primary inclusions. Primary inclusions, which were the only ones used in this study, were found to be of two varieties, aqueous and CH4-rich inclusions (Fig. 7). For

aqueous inclusions, the homogenization (ThA), last ice melting (TmA), and eutectic (TeA) 25

temperatures were measured. For CH4-rich inclusions, the homogenization (ThH) and CO2 ice

melting (TmCO2) temperatures were measured. All measurements were obtained using the

USGS-type heating and cooling stage built by FLUID Inc. located at BGSU. Examples of

primary inclusions observed are displayed in Figure 7 below.

Level of precision in fluid inclusion analysis

Fluid inclusion temperatures were measured within a few degrees of uncertainty. For

ThA the temperatures should be considered to be within 1.0 to 2.0°C of the homogenization

temperature due to timing errors between when the bubble disappears and when the thermometer

was stopped. Likewise, measurements collected from freezing behavior such as ThH, TmCO2, TeA

and TmA are within 0.5 to 1.0°C of their respective temperatures. Histograms for each fluid inclusion measurement were constructed (Appendix B) for each measurement taken per sample.

These histograms were based on set bin sizes for each type of measurement.

Organic-rich samples of the Pocono Sandstone were collected from Sleepy Creek

Mountain and Sideling Hill (Fig. 1) and prepared for vitrinite reflectance determination in order

to determine coal rank. The measurements were performed by Dr. James Hower at the

University of Kentucky Institute for Mining and Minerals Research.

26

Figure 7. Examples of primary fluid inclusions found in the Pocono Sandstone. (A, B). Two- phase aqueous inclusions at room temperature. (C) CH4-rich inclusions at room temperature.

The inset is an enlargement of the boxed fluid inclusion. (D) The same fluid inclusion array at -

120ºC shows the presence of a CH4 vapor bubble.

27

CHAPTER IV. RESULTS

Vein orientations

Veins in the study area were found to have two different orientations: NW and NE-

striking. The NE-striking veins are bed-parallel and have the regional NE strike of bedding.

Dips vary with bedding. The NW-striking veins are subvertical cross fold veins. The majority of fluid inclusions and microstructures analyzed came from the NW-striking set. Only four samples, TH 20 (Pocono Sandstone), TH 32 (Hampshire/Catskill Formation), TH 37 (Pottsville

Sandstone) and TH 43 (Pocono Sandstone) came from the NE, bed-parallel vein set.

Fluid inclusion measurements

All Hampshire/Catskill vein samples examined have only two-phase aqueous inclusions.

Both of the Pocono and the Pottsville vein samples contain two-phase aqueous as well as single-

phase CH4-rich inclusions. Data were collected for each sample (Appendix B), and then

compiled into a single dataset for each rock unit in both the eastern and central areas. From

these data, Modal homogenization temperatures were determined for use in subsequent trapping temperature and pressure determinations (Table 2). These modal values were determined by plotting histograms of ThA and ThH measurements. These histograms can be observed in

Appendix B.

Modal ThH values (Table 2 and Appendix B) show that CH4-rich inclusions in samples

from the Pocono Sandstone in the eastern portion of the study area are almost pure methane.

TmCO2 values range from -140 to -65°C. The amount of CO2 ranges from 10% to 0% (pure methane) as determined from plotting modal TmCO2 values with the partnering modal ThH value

on a VX plot (Fig. 8). 28

The salinity of aqueous inclusions in wt. % NaCl equivalent was determined for each sample from the modal TmA values derived from histogram plots (appendix B); these values are summarized in Table 3. Fluid measured from the Hampshire/Catskill yielded a wt. % NaCl equivalent of 7.2 to 11.8%. Aqueous fluids in the Pocono Sandstone from the eastern area were found to have a wt. % NaCl equivalent of 7.2 to 9.4%, whereas those from the central locality were between 4.5 and 7.2%. The Pottsville Sandstone was found to have aqueous fluids with a wt. % NaCl equivalent of 1.5 to 7.2 %. Eutectic temperatures (TeA) (Table 3 and Appendix B) measured from fluid inclusions were used to determine the salt species in each rock unit for its given locality (Sheperd, 1985). The Hampshire/Catskill Formation in the Broadtop Synclorium had a higher TmA and TeA measurement then the other two units (Table 3), it was found be an

NaCl brine. The Pocono Sandstone and Pottsville Sandstone found within the Broadtop

Syclinorium had slightly lower TmA and TeA measurements and were found to be NaCl-CaCl2 brine. This difference in salinities and salt species indicates at least two different fluid populations between the Hampshire/Catskill Formation and the overlying Pocono Sandstone and

Pottsville Sandstone.

Table 2. Summary of modal homogenization temperatures determined from fluid inclusion microthermometry. Pottsville Sandstone in central part of study are had a histogram with bi- modal distribution (Appendix B). n = number of measurements used for each histogram from which these modal homogenization temperatures were determined.

Region Central East Rock Unit n ThA n ThH n ThA n ThH Pottsville 99 180 109 -84 - - - - 99 180 109 -74 - - - -

Pocono 117 180 52 -74 134 185 295 -84

Hampshire/Catskill 96 125 ------29

Figure 8. VX plot of CH4-rich inclusions showing that inclusions are >90% methane. Key: V

(with bar over it) = molar volume, X = composition, TmCO2 = (TmCO2) melting temperature of

CO2 ice, ThH= homogenization temperature of aqueous inclusions. Adapted from Evans and

Battles, 1999. 30

Table 3. Summary of TmA and corresponding wt. % NaCl equivalent, as well as Te values of primary fluid inclusions measured from each rock unit in its given locality.

Region

Central East

wt. % wt. % Sample NaCl Sample NaCl Rock Unit # TeA TmA equiv. # TeA TmA equiv. Pottsville 37 -19 -5 7.2 - - - - 38 -20 -3 4.5 - - - - Pocono - - - - 2 -23 -7 9.0 - - - - 5 -27 -5 7.2 - - - - 6 - -7 9.4 - - - - 20 - -6 8.5 26 - -5 7.2 - - - - 27 - -3 4.5 - - - - 46 - -3 4.5 - - - - 48 -20 -5 7.2 - - - - Hampshire/ 29 - -5 7.2 - - - - Catskill 31c -23 -10 11.8 - - - - 32 -19 -5 7.2 - - - - 53 - -3 4.5 - - - - 54 - -5 7.2 - - - -

Determination of pressure from fluid inclusions

Pressure was determined by using modal temperatures determined from ThA and ThH

values. Three methods were used depending on what fluid inclusion data were available: the

ThA-isochore method, the geothermal gradient method and the ThH -isochore method.

The first of these methods, the ThA-isochore method (Fig. 10), can be used when coeval

two-phase aqueous and single-phase CH4 inclusions are present. Because these inclusions

represent the trapping of immiscible aqueous and CH4-rich fluids, the ThA does not have to be

corrected for pressure and represents the true Tt (van den Kerkoff, 1990). This temperature is 31

intersected with the CH4 isochore, determined from Flincor program (Brown and Hagermann,

1994) to yield the trapping pressure, Pt. Isochores were determined using the modal TmA and

calculated wt. % NaCl equivalent in conjunction with the modal ThA for a given sample with the

Flincor program. The two populations of fluid inclusions were determined to be coeval based on

the observation that they were relatively the same size and shape, and were located in close

proximity with one another as illustrated in Figure 9. The ThA-ishochore method is the most precise of the three fluid inclusion methods because the ThA measurements are considered to be

the true trapping temperature; therefore, the pressures they yield from the P/T diagrams are

considered to be the true trapping pressures.

Figure 9. Relationship between two-phase aqueous inclusions (with bubble) and single-phase

methane inclusions (grey, no bubble) at room temperature as observed in a sample from the

Pocono Sandstone (Sample TH 5). 32

Figure 10. Example of Pressure/temperature diagram showing trapping pressures determined

from the ThA-isochore intersection method for Pocono Sandstone, in central portion of study area.

Pressures and temperatures derived from this diagram represent actual trapping pressure and

temperatures and not a range as is the case with previous pressure temperature plots.

The second method, the geothermal gradient method, was performed when only two-

phase aqueous inclusions were present. This method involves intersecting the isochore calculated via the Flincor program (Brown and Hagermann, 1994) for the given ThA value with

both the hydrostatic and lithostatic pressure gradients. A paleo-geothermal gradient of 25ºC/km

was used, as estimated by Evans and Battles (1999). They chose this gradient based on the

observation that prior to thrusting; these sediments were deposited in a foreland basin. Foreland

basins typically have a cooler geothermal gradient then other sedimentary basins because

subsidence is so rapid that they do not have time to equilibrate thermally. This value is also the

average of geothermal gradients observed in the modern Appalachians. In this study 26 MPa/km

and 10 MPa/km were used for the lithostatic and hydrostatic pressure gradients, respectively. 33

Figure 11. Example of Pressure/Temperature diagram showing range of trapping pressures and

temperatures as determined from the Geothermal Gradient methodfor the Hampshire/Catskill

Formation, cental part of study area. Intersection of isochore for modal ThA with lithostatic and

hydrostatic pressure gradients yields upper and lower limits, respectively, of trapping pressures

and temperatures. Shaded bars on the pressure and temperature axes are ranges of trapping

pressures and temperatures, respectively.

The third method, the ThH -isochore method (Fig. 12), was used when only single-phase

CH4 inclusions were present. In this instance only upper and lower limits for trapping

temperatures can be determined by intersecting the ThH values with the hydrostatic and lithostatic

geothermal gradients determined as above. 34

Figure 12. Example of pressure/temperature diagram showing trapping pressures as determined from ThH -isochore method for the Pocono Sandstone, in eastern portion of study area. Shaded bars on the pressure and temperature axes are ranges of trapping pressures and temperatures, respectively

In each of these methods, modal temperatures determined from composite histograms

(Appendix B) were used for each rock unit in each location (Table 2). Appendix C shows the temperature/pressure plots with the isochore constructions for each of the units in the central and eastern sampling areas. The results are summarized below in Table 4.

Microstructures

Microstructures present that are indicative of crystal-plastic deformation include deformation lamellae and deformation bands (Fig. 13A) as well as recrystallized grains (Fig

13B). Other crystal-plastic deformation microstructures observed were undulatory extinction and patchy extinction (Fig. 13C and 13D). Brittle deformation microstructures observed include microveins and fluid inclusion planes (Fig. 13E). Microstructures associated with DMT observed in this study include sutured grain boundaries and transgranular stylolites. Sutured grain 35 boundaries showed a zig-zag contact between two grains or a concavo-convex grain boundary

(Fig. 13F).

After each sample was point-counted, they were grouped together according to geologic unit and location. Abundances of deformation mechanisms were plotted versus distance from the NMT trace west to the Alleghany Structural front. As can be observed in Figure 14 there is a decrease from east to west in the abundance of all three deformation mechanisms. Most notable of the three mechanisms is the observation that there is almost no brittle deformation found in the west.

Table 4. Summary of trapping pressure/temperature determinations by region, rock type, and method. Temperature and pressure are calculated separately using purely hydrostatic (hydro) and lithostatic (litho) fluid pressure gradients, based on and assumed geothermal gradient of

25°C/km.

Region Central East T (°C) P (MPa) T (°C) P (MPa) Rock Unit hydro litho hydro litho hydro litho hydro litho Pottsville Geothermal Gradient 230 600+ 80 410 - - - - ThH- ishochore - - - - ThA-isochore 185 225 48 53 - - - - Pocono Geothermal Gradient 230 600+ 80 420 240 600+ 80 420 ThH-isochore ------45 60 ThA-isochore 185 225 95 105 - - - - Hampshire/Catskill Geothermal Gradient 155 260 55 255 - - - -

36

Figure 13. Common quartz microstructures found in the Pocono Sandstone (TH 48). (A)

Deformation band (db) and deformation lamellae (dl). (B) Recrystallized grains (arrow). (C)

Undulatory extinction (arrow). (D) Patchy extinction (arrow). (E) Fluid inclusion planes

(arrows). (F) Sutured boundary between two grains.

37

The importance of each mechanism was also found to vary by rock unit within each of

the three sampling areas. Within the central area, a noticeable decrease in brittle deformation

from youngest to oldest units can be observed in Figure 14. There are, however, no observable

trends in DMT or crystal-plastic deformation.

Figure 14. Abundance of deformation mechanisms as a function of location relative to the NMT

trace (east), Broadtop synclinorium/Sideling Hill (central) and Alleghany front (west). Y-axis represents a cumulative percentage of microstructures point-counted for each deformation mechanism. DMT- Diffusive mass transfer, CP- Crystal-plastic and BD- Brittle deformation. 38

Figure 15. Abundance of each deformation mechanism as a function of rock unit within the

Broadtop synclinorium/Sideling Hill region . Y-axis represents a cumulative percentage of microstructures point-counted for each deformation mechanism. DMT- Diffusive mass transfer,

CP- Crystal plastic and BD- Brittle deformation.

39

Vitrinite reflectance

Rmax and Rmean values were determined from three samples of organic matter in the

Pocono Sandstone collected in the eastern portion of the study area (Fig. 1). For TH 9, the Rmax

was 1.76% with a standard deviation of 0.11%, the Rmean of 1.47% with a standard deviation of

0.21% and was ranked as low volatile bituminous coal. Sample TH 21 was found to have Rmax

of 2.49% with standard deviation of 0.15% and Rmean of 2.39%with standard deviation of 0.16%

and was ranked as semi-anthracite. TH 22 had an Rmax of 2.03% with a standard deviation of

0.21% and an Rmean of 1.86% with standard deviation of 0.19% and was ranked as semi- anthracite just slightly above volatile bituminous coal. By applying the Rmean of each of these

samples to the corresponding level of (coal) metamorphism (LOM) a maximum burial

temperature can be inferred. Sample TH 9 had a LOM of 11.9, sample TH 21 had a LOM of

15.20 and TH 22 had a LOM of 13.75 (Fig. 16).

These LOM values were correlated using a specialized temperature LOM gradient, which

is dependent on effective heating time, or the maximum time of burial for a given rock unit ( Fig.

17). A value of 90 million years was used based of conclusions made by Hower and Davis

(1981) that the coals found within the Valley and Ridge region reached their deepest level of

burial by the end of the Permian. A similar observation was made by Reed et al. (2005) based on

exhumation estimates determined for the Pennsylvanian Pottsville Sandstone. This effective

heating time yielded the following set of temperatures: for TH 9~145°C, for TH 21~192° and for

TH 22~170°C.

40

Figure 16. Correlation between %R (mean) and LOM (Level of Metamorphism) for Pocono

Sandstone samples collected in eastern portion of study area. Adapted from Hower and Davis,

1981.

Figure 17. Relationship between LOM, burial time in millions of years and maxium temperature in °C for vitrinite samples collected from the Pocono Sandstone the eastern portion of the study area. Adapted from Hower and Davis, 1981. 41

CHAPTER V. DISCUSSION

Age of veins, microstructures, and fluid inclusions relative to deformation.

In order to interpret the fluid inclusion and microstructure data in the context of the

deformation, the age of the veins and their inclusions, as well as the microstructures, need to be

determined relative to one another and to the deformation. Two orientations of vein sets were

observed in the study region: a NE-striking, bed-parallel set and a NW-striking cross-fold set.

According to Evans and Battles (1999), the bed-parallel veins formed during to the Alleghanian orogeny, prior to any significant folding while the cross-fold veins formed later in the

Alleghanian, when folds had begun to form. Because the two veins were not found together in the field, the relative age relations of Evans and Battles (1999) will be assumed. Veins samples were examined using cathode luminescence to determine if veins contained zoning which would indicate that they contained different generations of fluids and thus different generations of mineralization. No zoning was observed which indicates that the chemistry of the fluids present and/or the physical conditions did not change during mineralization of the vein.

Because crystal-plastic and DMT microstructures do not occur in the vein cement and the

cement is relatively clean with the exception of fluid inclusion planes, crystal-plastic and DMT

microstructures are considered to be older then the veins; thus, the microstructures formed in the

early stages of the Alleghanian orogeny. An early, pre-folding age of microstructures such as

deformation lamellae is also suggested by the observation that they tend to form when stress

levels are at their highest, which would be during layer-parallel shortening prior to folding

(Dietrich and Carter, 1969).

Primary fluid inclusions found in the vein minerals must be the same age as the veins

themselves. Fluid inclusion planes were found to be generally parallel and confined within the 42

veins. They are interpreted to form as the vein, which is a Mode I fracture, opens in a series of

steps, each one resulting in fractures followed by healing and trapping of secondary inclusions.

Therefore, they are younger than the primary inclusions, but still within the general age of the

vein itself. If they were younger, then they would cut across the vein boundaries.

Determination of overburden from fluid inclusions

The isochore intersection method yields true trapping pressures. The other two methods require choosing a fluid pressure gradient: hydrostatic, lithostatic, or something intermediate

(known as geostatic). Evans and Battles (1999) used lithostatic and hydrostatic gradients to

determine the upper and lower bounds of the trapping pressures respectively. However in this

study, temperatures and pressures derived from the geothermal gradient and ThH-isochore

methods using the lithostatic pressure gradient were found to be unreasonably high for the burial

and stress conditions experienced by these rock units in this region. Also, based on the

observation that trapping pressure/temperature conditions determined from the ThA- isochore intersection method plot closer to the hydrostatic gradient than the lithostatic gradient (Appendix

C), the hydrostatic gradient pressures were favored over the lithostatic gradient. Table 5 summarizes the overburdens derived from applying the hydrostatic pressure gradient for each rock unit and the locality it was collected in.

For the Pocono and Pottsville Sandstones, the depth of burial estimates taken from the

coeval sets of inclusions (ThA-isochore method) is considered to be more precise, owing to the

fact that the ThA temperatures and the pressures in these inclusions determined for these samples

are considered to be the true trapping temperatures and true trapping pressures. 43

Table 5. Summary of overburden thicknesses for each rock unit and region determined from fluid inclusion data using each of the three methods (see text for descriptions) assuming a hydrostatic pressure gradient.

Region Central East Rock Unit Pressure Overburden Pressure Overburden Method MPa km MPa km Pottsville Geothermal gradient 80 8.0 - -

ThH isochore - - - - ThA isochore 48-53 4.8-5.3 - -

Pocono

Geothermal gradient 80 8.0 80 8.0 ThH isochore - - 45 4.5 ThA isochore 95-105 9.5-10.5 - -

Hampshire/Catskill Geothermal gradient 55 5.5 - -

An unusual trend in the data in Table 5 is that the oldest unit, the Hampshire/Catskill

Formation, appears to have had less overburden than the overlying units. There are several possible explanations to this trend. It should be noted that the Hampshire/Catskill depth was determined from fluid inclusion populations that contained only aqueous inclusions. The trapping temperatures and pressure determined from them are less precise than those from samples with coeval aqueous and CH4-rich inclusions. The trapping pressures determined from samples with coeval inclusions in the Pocono Sandstone and the Pottsville Sandstone are considered to be more precise.

A second explanation for higher overburdens in the Pocono Sandstone and the Pottsville

Sandstone comes from Evans and Battles (1999). They found three hydrostratigraphic units

(Fig. 2) each with a unique fluid composition related to two fluid migration events, one of which 44

occurred during folding, the second of which occurred afterward. The uppermost

hydrostratigraphic unit, representing the Hampshire/Catskill Formation was described by Evans

and Battles (1999) as a regional aquifer system containing a low salinity, CH4-saturated, NaCl-

CaCl2 brine, with temperatures between 160 and 220°C. This brine represents the first fluid

migration event and is believed to be the product of mixing of meteoric water and original

basinal brines within the rock unit itself. The second fluid migration event occurred during the

late Alleghanian emplacement of the Blue Ridge thrust sheet on top of the NMT sheet, which

created localized topographic fluid flow. This event would have forced out existing fluids via

compression and is believed to have brought in warm fluids from the hinterland region which

would have migrated along the Martinsburg detachment zone into the Ordovician carbonates and

up into the overlying Devonian and Mississippian clastic rocks. The presence of at least two

different fluids between the older Hampshire/Catskill Formation and the overlying Pocono and

Pottsville Sandstones is suggested by the higher wt. % NaCl equivalent calculated from TmA

values measured during fluid inclusion microthermometry. Also Te values yielded different salt species in the Hampshire/Catskill Formation in the central locality was found to be exclusively

NaCl brine while the Pocono Sandstone was found to contain NaCl brine and NaCl-CaCl2 brine.

The Pottsville Sandstone samples collected were also found to be NaCl brine. It is therefore likely that a hotter brine solution was present in the Pocono and Pottsville Sandstones, which was trapped at higher temperatures than fluids trapped in the Hampshire/Catskill Formation. With the ThA-isochore method, these higher temperatures would yield a higher pressure (greater overburden). The observation that in this study only aqueous inclusions were found to be in the

Hampshire/Catskill Formation while the Pocono Sandstone and Pottsville Sandstone both 45

contained coeval aqueous and CH4-rich inclusions is also evidence that there were two different

fluids partitioned between these three rock units.

A third explanation is that the higher fluid temperatures found in the Pocono Sandstone

and the Pottsville Sandstone could be unrelated to the fluids trapped before and during the

Alleghanian orogeny and could be from a later trapping event. Although based on the

observation made earlier of the relationship between fluid inclusion planes and vein boundaries

in conjunction with assumptions made about the relative age of the veins this is an unlikely

explanation.

Uncertainties in fluid inclusion analysis

There are several uncertainties in the precision of the fluid inclusion analysis. First the

temperatures measured have a 1.0 – 2.0°C for heating temperatures measured and a 0.5-1.0°C

uncertainty for freezing temperatures. Second, the bins chosen for the histograms in some cases

created a large distribution range with several outliers and in some cases even multi-modal

distribution. These patterns could be attributed to several things. First there could be more then

one fluid population present which would create more then one modal distribution, but this could

also be attributable to an inappropriate bin size for a given sample. As previously mentioned bin

sizes were chosen for each measurement based on the range of temperatures amongst all samples

for that one measurement. For example for ThA measurements a bin size of 5°C was chosen with a range between 70 and 300°C for all three units in all locations. The reason for this was so that all ThA histograms had the same range and bin sizes for ease of comparison. However, it is

probable that creating unique ranges and bin sizes for each unit or even each sample would have

presented a different distribution that would have been more accurate for that given sample. This

is one of the reasons why all ThA measurements for each rock unit in each location were 46

compiled into a single histogram (Appendix B, Figures B5 – B11). So multi-modal distribution

should not be considered as multiple fluid generations. A second explanation for variation in

histograms is that some peaks may represent fluid inclusions that experience stretching or

decrepitation which would change the temperatures under which they go through phase changes,

such as homogenization or freezing.

Overburden determined from microstructures

All three deformation mechanisms presented in Figure 14 show a steady decline in

abundance from east to west in the study region. This decrease is evidence of the decrease in

stress magnitude in the Appalachian fold and thrust belt from east of the NMT to the Alleghany

Plateau. In the west, the decreasing trend can most clearly be observed in brittle deformation

microstructures, which are almost non-existent in the samples from the west. Indicating that the

NMT did not extend this far west. The abundance of crystal-plastic microstructures varies less, which can be explained by a portion of the microstructures being inherited from the source rocks.

If one assumes that the samples from the Alleghany Plateau were little deformed by the

Alleghanian orogeny or the NMT then the abundance of crystal-plastic microstructures in those samples represents an inherited component. This amount should then be subtracted from the abundances in the central and eastern areas to see the abundance of microstructures resulting from deformation in situ (i.e., Alleghanian orogeny). The scale of the columns would be shorter, but the abundance in comparison to one another would be relatively the same. The relatively small variation in DMT microstructures can be explained by the presence of grain-grain suturing and stylolites that formed during compaction. Because there would be no difference in appearance, there was no way to separate DMT microstructures formed during compaction from 47 those formed during deformation; therefore, an assessment of their regional variation in abundance cannot be made.

In the Broadtop synclinorium, there was a noticable decrease in brittle deformation with depth, which is to be expected. Brittle processes would occur at shallow depths giving rise to ductile processes such as crystal-plastic and DMT with increasing depth. Ashby (1972) placed the the temperature regime for the transition between brittle to ductile processes between 150ºC and 300ºC, with depth estimates between 6 to 12 km. Because there is not a noticable pattern in crystal-plastic and DMT microstructures, this could indicate that these units underwent deformation around the brittle-ductile transition zone owing to the observation that there is a varied abundance of brittle and ductile processes in all three units.

For the Broadtop synclinorium, relative abundances and relationships observed between crystal-plastic, DMT and brittle deformation process microstructures in all three units suggests that these units formed in an environment that was affected by both brittle and ductile processes.

Since the Pocono Sandstone and the Pottsville Sandstone are clearly dominated more by brittle deformation, it is likely that they would have been deformed at a depth of 5 to 6 km, with the

Hampshire/Catskill Formation being closer to 6 km.

Vitrinite reflectance

There is some debate over whether or not effective heating time plays a role in advancing cole rank. Hood and others (1975) determined that the length of time a coal is within 15°C of its maximum temperature to be the duration of of its metamorphism. In other words even though a coal may no longer be at its maximum burial depth it is still considered to be at its maximum temperature within 15°C. Thus using effective heating time as a variable is not precise because the coal may maintain maximum temperature for an extended period of time after it has begun to 48

go through exhumation (Hower and Davis, 1981). For the purposes of this study the effective

heating time of 90 million years as determined by Hower and Davis (1981) and Reed et al.

(2005) was used. However, as a conformation to this study, a LOM plot with an effective age of

40 Ma was tested and maximum temperatures were found to only fluctuate by 2-5 degrees.

Applying the temperatures determined from vitrinite reflectance data (Figure 17) to a geothermal gradient of 25°C/km for a foreland basin and assuming a surface temperature of 20°C yields the depths of burial for each vitrinite sample provided in the Table 6. Therefore, according to the vitrinite reflectance measurements, the Pocono Sandstone in the eastern portion of the study area

reached a maximum temperature of approximately 192°C and was buried between 5.0 to 6.8 km.

Which is comprable to the burial estimates derived from microstructural suite analysis of 5-6 km

and within the range of fluid inclusion determinations of 4.5 to 8 km for the Pocono Sandstone in

the eastern part of the study region (Table 7).

Table 6. Maximum burial temperatures and overburden thicknesses from vitrinite reflectance

measurements from the Pocono Sandstone. Burial depth is determined using 25°C/km

geothermal gradient.

Estimated Sample # Max Burial Temp (°C) Overburden (km) TH 9 145 5.0 TH 21 192 6.8 TH 22 170 6.0

Comparison of overburden determinations

Overburden measurements determined from all three analysis methods,

microthermometry, microstructural suite analysis and vitrinite reflectance were as follows from

youngest to oldest. The Pottsville Sandstone in central locality was found to be between 4.8 to 8 49

km. The Pocono Sandstone in the central locality was found to be between 5 to 10.5 km and in

the eastern locality the Pocono Sandstone was between 4.5 to 8 km. The Hampshire/Catskill

Formation in the central locality had a calculated overburden of between 5.5 to 6 km. In order to

better compare these overburden measurements Table 7 was constructed so the measurements

can be viewed side by side.

Table 7. Summary of the overburden determinations in km derived from each method used in

this study for each rock unit in central and eastern portions of the study area. The methods used

are: ThA-iso- Th-isochore method of fluid inclusion microthermometry, Geotherm- geothermal gradient method of fluid inclusion microthermometry, ThH-iso- ThH-isochore method of fluid

inclusion microthermometry, MS-microstructual analysis, VR-vitrinite reflectance.

Region

Central East

Geo- Geo- ThH ThA- ther ThH- Rock Unit ThA-iso therm -iso MS VR iso m iso MS VR Pottsville 4.8-5.3 8 - 5-6 Pocono 9.5-10.5 8 - 5-6 8 4.5 5-6 5- Hampshire/Catski 5.5 6

Geometry and former extent of the North Mountain thrust

As previously reviewed in this paper, there are several opposing models for the geometry

and former extent of the NMT. Evans (1989) sited thermal maturity of lower Paleozoic rocks

based on CAI just west of the NMT trace indicating a burial depth 5 to 7.5 km of as a result of

overburden of which only 2 km was accounted for by the normal stratigraphic section in Evans’s

(1989) findings. This, he proposed, can be explained by adding the NMT sheet on top (Fig. 3).

Furthermore, Evans and Battles (1999) found fluid inclusion evidence for anomalous pressures 50

in Devonian rocks in the Valley and Ridge that indicated an overburden consistent with the

presence of the NMT.

In this study stratigraphic thickness of the cover rocks younger then the Pocono

Sandstone were calculated to be 487 m (White et al., 1885) in the Broadtop synclinorium and

872 m (Overbeck, 1954) in the Alleghany Plateau. Overburden thicknesses determined from

fluid inclusion microthermometry, microstructural suite analysis and vitrinite reflectance

measurements in the Broadtop synclinorium was found to be between 4.8 to 8.0 km, 4.0 to 10.5 km and 5.5 to 6.0 km for the Pottsville Sandstone, Pocono Sandstone and Hampshire/Catskill

Formation respectively. Uncertainties in fluid inclusion analysis, as highlighted above could have affected the overburden determinations calculated from fluid inclusion microthermometry in this study by several km. However, even with a difference of a few kilometers from uncertainties the overburden determinations still exceed the 487 m measured as the thickness of the current stratigraphic section above the Pocono Sandstone in the Broadtop synclinorium. It can also be noted that ThA temperatures, which are an estimation of trapping temperature, measured from all three units would have yielded greater depths. Furthermore the overburden determinations inferred from microstructural suite analysis and vitrinite reflectance confirm that the overburden estimates are over 487 m. This shows that it was buried to a depth greater than the 487 m that the current thickness of the overlying stratigraphic section accommodates for.

Therefore, the model proposed by Evans (1989), which suggests that the missing overburden was provided by overthrusting of the NMT and duplication of the cover rocks in the Valley and

Ridge province is supported by results of this study.

Another possible explanation for the missing overburden is a Permian clastic wedge, which has since eroded away. Although there is no direct evidence for the former existence of a 51 thick section of Permian rocks, it might be inferred based on the existence of clastic wedges for the Taconic and Acadian orogenies in the Appalachians. Even if this wedge did exist, it would have had to have been much greater than the thickness of the older wedges (~1500 m), to account for the overburden estimates determined in this study.

52

CHAPTER VI. SUMMARY

Fluid inclusion microthermometry, microstructural analysis, and vitrinite reflectance measurements were performed on the Devonian Hampshire/Catskill Formation, Mississippian

Pocono Sandstone, and the Pennsylvanian Pottsville Formation in order to determine the former geometry and extent of the North Mountain thrust sheet in the central Appalachians. Pressure and temperature conditions determined in these analysis methods were used to determine depth of burial of all three units. Depths of burial estimates were then used to evaluate different models for the geometry and extent of the NMT. The maximum burial depth for the

Hampshire/Catskill Formation from fluid inclusion microthermomerty is estimated to be approximately 5.5 km. For the Pocono Sandstones fluid inclusions yield depth estimates of approximately 5 to 10.5 km. The Pottsville Sandstone had depth estimates of 4.8 to 8 km based on fluid inclusions. Microstructural suites found in the three units indicate depths during deformation of 5 to 6 km. Lastly, a depth of 5-6.8 km was determined from the Pocono

Sandstone using vitrinite reflectance.

53

CHAPTER VII. CONCLUSIONS

All three of the rock units were buried to at least a depth of 5 km based of burial estimates for the older Hampshire/Catskill Formation. The present stratigraphic section above the Pocono Sandstone in the Broadtop synclinorium only accounts for 487 m of overburden.

Therefore, the more plausible explanation for the geometry and former extent of the NMT follows Evans’ (1989) model, which states that the displacement of the cover rocks was transferred up the North Mountain ramp to a higher stratigraphic level leading to overthrusting and duplication of the cover rocks in the Valley and Ridge province.

54

REFERENCES

Ashby, M.F. 1972. A first report on deformation mechanism maps. Acta Metallica 20, 887-897.

Blenkinsop, T.G. 2000. Deformation Microstructures and Mechanisms in Minerals and Rocks. Springer, 164.

Brown, P.E., Hagermann, S.G. 1994. MacFlinCor: a computer program for fluid inclusion data reduction and manipulation.

Colton, G. W. 1970. The Appalachian Basin Its Depositional Sequences and Their Geologic Relationships. In: Studies of Appalachian Geology: Central and Southern (ed. by Fisher, G.W., Pettijohn, F.J., Reed J.C. Jr., Weaver, K. N.) 5-47. Wiley, New York

Cotter, E., Driese, S., G. 1998. Incised-Valley Fills and Other Evidence of Sea-Level Fluctuations Affecting Deposition of the Catskill Formation (Upper Devonian), Appalachian Foreland Basin, Pennsylvania. Journal of Sedimentary Research. 68. 347- 361. Davis, G. H., Reynolds, S. J. 1984. Structural geology of rocks and regions: New York, John Wiley & Sons, 776. Dean, S.L., Kulander, B.R., Lessing, P., Evans, M.A., 1990. The structural geometry and evolution of foreland thrust systems, northern Virginia: Alternative interpretation and reply. Geological Society of America Bulletin. 102. 1442–1445. Dietrich, J.H., Carter, N.L. 1969. Stress-history of folding. American Journal of Science. 267. 129-154. Evans, M.A. 1989. The structural geometry and evolution of foreland thrust systems, northern Virginia. Geological Society of America Bulletin. 101. 339–354. Evans, M.A., Battles, D.A. 1999. Fluid inclusion and stable isotope analyses of veins from the central Appalachian Valley and Ridge province: Implications for regional synorogenic hydrologic structure and fluid migration. Geological Society of America Bulletin. 111. 1841– 1860. Garcia-Lopez, S., Bastida, F., Aller, J., Sanz-Lopes, J. 2001. Geothermal palaeogradients and metamorphic zonation from the conodont colour alteration index (CAI). Terra Nova. 13. 79- 83. Goldstein, R.H., Reynolds, T.J. 1994. Systematics of fluid inclusions in diagenetic minerals. Society of Sedimentary Geologists. Hower, J.C. and Davis, A. 1981. Application of vitrinite reflectance anisotropy in the evaluation of coal metamorphism. Geological Society of America Bulletin. Part I. 92. 350-366. Hood, A., Gutjar, C.C.M., and Heacock, R.L. 1975. Organic metamorphism and the generation of petroleum. American Association of Petroleum Geologists Bulletin. 59. 986-996. Knipe, R.J. 1989. Deformation mechanisms – recognition from natural tectonites. Journal of Structural Geology. 11. 127-146. 55

Kulander, B.R., Deans, S.L. 1986. Structure and tectonics of central and southern Appalachians Valley and Ridge and Plateau provinces, West Virginia and Virginia. American Association of Petroleum Geologists Bulletin. 70. 1674-1684. Levine, J.R., Davis, A. 1989. The relationship of coal fabrics to Alleghanian tectonic deformation in the central Appalachian fold-and-thrust belt, Pennsylvania. Geological Society of America Bulletin. 101. 1333-1347. Marshall, D., 1988. Cathodoluminescence of Geological Materials. Boston, Unwin Hyman, 146. Miall, A.D. 1999. Principles of Sedimentary Basin Analysis: Berlin, Springer-Verlag, 615. Mitra, S. 1986. Duplex Structures and Imbricate Thrust Systems: Geometry, Structural Position, and Hydrocarbon Potential. The American Association of Petroleum Geologists Bulletin. 70. 1087-1112. Overbeck, R.M. 1954. Ground water resources. Department of Geology, Mines and Water Resources State of Maryland Bulletin. 13. 117-254. Prothero. D.R., and Dott, R.H., Jr. 2002. Evolution of the Earth: New York, McGraw-Hill Higher Education, 569. Reed, J.S, Spolita, J.A., Erikson, K.A., Bodnar, R.J. 2005. Burial and exhumation history of Pennsylvanian strata, central Appalachian Basin: an integrated study. Basin Research. 17. 259-268. Roedder, E. 1984. Fluid inclusions. Mineralogical Society of America Review In Mineralogy. 12. 646. Roedder, E.; Bodnar, R. J. 1980. Geologic pressure determinations from fluid inclusion studies. Annual Review of Earth and Planetary Sciences. 8. 263-301. Sheperd, T.J., Rankin, A.H., Alderton, D.H.M. 1985. A Practical Guide to Fluid Inclusion Studies: Glasgow, Blackie, 52-54. van den Kerkhof, A. M. 1990. Isochoric phase diagrams in the systems CO2 -CH4 and N2 application to fluid inclusions. Geochimica et Cosmochimica Acta. 54. 621-629. White, D. 1925. Progressive Regional Carbonization of Coals. American Institute of Mining and Metallurgical and Petroleum Engineers Transactions. 71. 253-281 White, D. 1935. Metamorphism of Organic Sediments and Derived Oils. American Association of Petroleum Geologists Bulletin. 19. 589-617. White, I.C., Lesley, J.P., D’Invilliers, E.V., Ewing, A.L. 1885. The Geology of Huntington County Volume 59. Board Of Commissioners for the Second Geological Survey. Harrisburg. 529.

56

APPENDIX A: SAMPLE LOCATIONS AND TYPE OF ANALYSIS PERFORMED

Table A1. Summarizes GPS coordinates of each sample collected, the rock unit it belongs to, and which type of measurement was performed on each given samples. FI-Fluid Inclusion, MS-

Microstructure, VR- Vitrinite Reflectance.

Sample Easting Northing Unit FI MS VR 1 749683.2 4389899 Pocono 1 1 0 2 749683.2 4389899 Pocono 1 1 0 3 749683.2 4389899 Pocono 0 0 0 4 749683.2 4389899 Pocono 0 0 0 5 749683.2 4389899 Pocono 1 1 0 6 746099.433 4376891.338 Pocono 1 1 0 7 746099.433 4376891.338 Pocono 0 0 0 8 746099.433 4376891.338 Pocono 0 0 0 9 745863.538 4376955.094 Organic 0 0 1 10 745863.538 4377233.1 Pocono 0 0 0 11 745863.538 4377233.1 Pocono 1 1 0 12 745863.538 4377233.1 Pocono 0 0 0 13 745863.538 4377233.1 Pocono 0 0 0 14 745675.46 4376559.811 Pocono 0 0 0 15 745675.46 4376559.811 Pocono 1 1 0 16 745021.969 4376588.501 Pocono 0 0 0 17 745021.969 4376588.501 Pocono 0 1 0 18 745021.969 4376588.501 Pocono 0 0 0 19 745021.969 4376588.501 Pocono 0 1 0 20 745021.969 4376588.501 Pocono 1 1 0 21 745021.969 4376588.501 Organic 0 0 1 22 731496.7 4396727.1 Organic 0 0 1 23 731646.5 4396891.2 Pocono 0 0 0 24 731646.5 4396891.2 Pocono 0 0 0 25 731646.5 4396891.2 Pocono 0 0 0 26 731646.5 4396891.2 Pocono 1 1 0 27 731646.5 4396891.2 Pocono 1 1 0 28 731646.5 4396891.2 Pocono 0 0 0 29 733622 4431143.6 Hampshire 1 1 0 30 733622 4431143.6 Hampshire 0 0 0 31 729030.2 4432619.5 Hampshire 1 1 0 32 729030.2 4432619.5 Hampshire 1 1 0 33 739112.624 4433152.453 Pocono 0 0 0 34 739112.624 4433152.453 Pocono 0 0 0 35 742782 4445193 Pottsville 1 1 0 36 742782 4445193 Pottsville 1 1 0 37 742783 4445194 Pottsville 1 1 0 38 742183 4445194 Pottsville 1 1 0 39 742183 4445194 Pottsville 0 0 0 57

40 742183 4445194 Pottsville 0 0 0 41 742183 4445194 Pottsville 0 0 0 42 720186 4372555 Hampshire 0 1 0 43 721763 4374628 Pocono 1 1 0 44 721764 4374632 Pocono 0 0 0 45 721764 4374632 Pocono 1 1 0 46 744926 4432088 Pocono 1 1 0 47 744929 4432091 Pocono 0 1 0 48 744270 4432933 Pocono 1 1 0 49 744270 4432933 Pocono 0 0 0 50 744270 4432933 Pocono 0 0 0 51 748351 4446552 Pocono 0 0 0 52 748431 4446724 Pocono 0 0 0 53 748431 4446724 Pocono 1 1 0 54 730027 4398294 Hampshire 1 1 0 55 730027 4398294 Hampshire 0 0 0 56 674202 4394478 Pocono 0 0 0 57 674202 4394478 Pocono 0 1 0 58 674202 4394478 Hampshire 0 1 0

58

APPENDIX B: HISTOGRAMS OF FLUID INCLUSION DATA

Figure B1. ThA histograms for Pottsville Sandstone in central locality (See Figure 1).

59

Figure B2. ThA histograms for Pocono Sandstone in central locality (See Figure 1).

60

Figure B3. ThA histograms for Pocono Sandstone in central locality(See Figure 1).

61

Figure B4. ThA histograms for Hampshire/Catskill Formation in central locality(See Figure 1).

Figure B5. Composite ThA histogram for Pocono Sandstone from in eastern part of study area (see Figure 1). n = 134

62

Figure B6. Compotite ThA histogram for the Catskill/Hamphire Formation found in the central region of the study area (See Figure 1). n = 96

Figure B7. Compostie ThA histogram for the Pocono Sandstone found in central region of study area (See Figure 1). n = 117

Figure B8. Composite ThA histogram for the Pottsville Sandstone found in the central region of study Area (See Figure 1). n = 99

63

Figure B9. Composite ThH histogram for Pocono Sandstone in eastern region of study area(See Figure 1). n = 295

Figure B10. Composite ThH histogram for the Pocono Sandstone found in the central region of study area(See Figure 1). n = 52

64

Figure B11. Composite ThH histogram for the Pottsville Sandstone found in the central region of the study area (See Figure 1). n = 109

Figure B12. Histograms of TmCO2 and ThH for sample TH 1a, Pocono Sandstone in eastern part of study area (See Figure 1). n = 23. 65

Figure B13. Histogram of TmCO2 and ThH for sample TH 1b, Pocono Sandstone in eastern part of study area (See Figure 1). n = 21

Figure B14. Histogram of TmCO2 and ThH for sample TH 5, Pocono Sandstone in the eastern part of the study area (See Figure 1). n = 27

66

Figure B15. Histograms of TmCO2 and ThH for sample TH 11, Pocono Sandstone in the eastern part of the study area (See Figure 1). n = 41

Figure B16. Histograms of TmCO2 and ThH for sample TH 15, Pocono Sandstone in the eastern part of the study area (See Figure 1). n = 23 67

Figure B17. Histograms of TmCO2 and ThH for sample TH 20, Pocono Sandstone in the eastern part of the study area (See Figure 1). n = 22

Figure B18. Histograms of TmCO2 and ThH for sample TH 36, Pottsville Sandstone in the central

part of the study area (See Figure 1). n = 25 68

Figure B19. Histograms of TmCO2 and ThH for sample TH 37, Pottsville Sandstone in the central

part of the study area (See Figure 1). n = 27

Figure B20. Histograms of Te for the Pottsville Sandstone, in central part of study area (See

Figure 1). 69

Figure B21. Histograms of Te for Pocono Sandtone, in eastern part of study area (See Figure 1).

Figure B22. Histogram for Te for the Pocono Sandstone, in central part of study area (See

Figure 1). 70

Figure B23. Histograms for Te for the Hampshire/Catskill Formation, in central part of the study area (See Figure 1). 71

Figure B24. Histograms of Tm for the Pottsville Sandstone, in central portion of study area (See

Figure 1).

72

Figure B25. Histograms of Tm for the Pocono Sandstone, in the eastern part of the study area

(See Figure 1). 73

Figure B26. Histrograms of Tm for the Pocono Sandtone, in the central part of the study area

(See Figure 1). 74

Figure B27. Histograms of Tm for the Hampshire/Catskill Formation, in central part of the study area (See Figure 1).

75

APPENDIX C: PRESSURE/TEMPERATURE DIAGRAMS

Figure C1. Pressure/Temperature diagram Figure C2. Pressure /Temperature diagram showing range showing range of trapping pressures and of trapping pressures determined from the Geothermal temperatures determined from the Geothermal Gradient method for the Pocono Sandstone in the eastern

Gradient method for the Hampshire/Catskill portion of study area (See Figure 1). Intersection of

Formation, cental part of study area (See Figure isochore for modal ThA with lithostatic and hydrostatic

1). Intersection of isochore for modal ThA with pressure gradients yields upper and lower limits, lithostatic and hydrostatic pressure gradients respectively, of trapping pressures and temperatures. yields upper and lower limits, respectively, of Shaded bar on the pressure axis and temperature axes are trapping pressures and temperatures. Shaded ranges of trapping pressures and temperatures, respectively. bars on the pressure and temperature axes are ranges of trapping pressures and temperatures, respectively.

76

Figure C3. Pressure /Temperature diagram showing range Figure C4. Pressure /Temperature diagram showing range of trapping pressures and temperatures determined from the of trapping pressures and temperatures determined from the

Geothermal Gradient method for the Pocono Sandstone, Geothermal Gradient method for the Pottsville Sandstone, central part of study area (See Figure 1). Intersection of in the central part of the study area (See Figure 1). isochore for modal ThA with lithostatic and hydrostatic Intersection of isochore for modal ThA with lithostatic and pressure gradients yields upper and lower limits, hydrostatic pressure gradients yields upper and lower respectively, of trapping pressures and temperatures. limits, respectively, of trapping pressures and temperatures.

Shaded bars on the pressure and temperature axes are Shaded bars on the pressure and temperature axes are ranges of trapping pressures and temperatures, respectively. ranges of trapping pressures and temperatures, respectively.

77

Figure C5. Pressure/temperature diagram showing trapping Figure C6. Pressure/temperature diagram showing trapping pressures determined from ThH-isochore method for the pressures determined from the ThA-isochore intersection

Pocono Sandstone, in eastern portion of study area (See method for Pocono Sandstone, in central portion of study

Figure 1). area (See Figure 1). Pressures and temperatures derived

from this diagram represent actual trapping pressure and

temperatures and not a range as is the case with previous

pressure temperature plots.

78

Figure C7. Pressure/temperature diagram showing trapping pressures determined from the ThA-isochore intersection method for Pottsville Sandstone, in central portion of the study region (See Figure 1). Pressures and temperatures derived from this diagram represent actual trapping pressure and temperatures and not a range as is the case with previous pressure temperature plots.