Fluid History of the Sideling Hill Syncline, Hancock County, Maryland

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FLUID HISTORY OF THE SIDELING HILL SYNCLINE, HANCOCK COUNTY, MARYLAND

William J. Lacek

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

August 2015

Committee:

John Farver, Advisor,

Charles Onasch,

Margaret Yacobucci ii

ABSTRACT

John Farver, Advisor

Fluid inclusion microthermometry was employed to determine the fluid history of the

Sideling Hill syncline in Maryland with respect to its deformation history. The syncline is unique in the region in that it preserves the youngest rocks (Mississippian) in the Valley and Ridge

Province and is the easternmost exposure of Mississippian rocks in this portion of the Central

Appalachians.

Two types of fluid inclusions were prominent in vein quartz: CH4-rich and two-phase aqueous with the former comprising about 60% of the inclusions observed. The presence of the two fluids in inclusions that appear to be coeval indicates that the migrating fluid was a CH4- saturated aqueous brine that was trapped immiscibly as separate CH4-rich and two-phase aqueous inclusions. Cross cutting relations show that at least two generations of veins formed during deformation. Similarities in chemistry of the inclusions in the different vein generations suggests that a single fluid was present during deformation.

Older veins were found to have formed at depths of at least 5 km while younger veins formed at minimum depths of 9 km. Overburden for older veins is attributed to emplacement of the North Mountain Thrust (NMT) sheet (~6 km thick). The thickness of the Alleghanian clastic wedge is calculated to be ~2.5 km in the Appalachian Plateau which accounts for most of the remaining overburden in younger veins. Due to the sediment load imposed by the NMT it is likely that the clastic wedge was thicker at Sideling Hill, with this increased thickness accounting for the remaining 0.5 km. iii

ACKNOWLEDGEMENTS

I would not have been able to complete my thesis were it not for the support of my family, advisor, committee members and friends. First I want to acknowledge my advisor Dr. John

Farver for his support and patience as well as keeping me on track throughout my research as well as comic relief when needed. I would also like to thank Dr. Charles Onasch who provided great insight into the subject of my research and assistance when problems occurred. Dr.

Margaret Yacobucci who provided assistance with the historical aspect of my research and critiques of my research. I would like to thank Dr. David Matchen and Dr. Joe Allen as well as

Lisa Karnes, Vickie Hart, and Dr. Rodney Klein for their encouragement to pursue a graduate degree in geology. I would like to express my gratitude to my family who provided endless encouragement and support as well as the friends that I made during the time that I was at BGSU who provided entertainment during the difficult times and a were always willing to chat for a few minutes. Lastly I want to thank my loving wife Monica who always encouraged me to keep moving forward and provided endless support. iv

TABLE OF CONTENTS

Page

INTRODUCTION…...... 1

CHAPTER I BACKGROUND...... 3

Stratigraphy...... 3

Lithostratigraphy and Hydrostratigraphy...... 4

Patterson Creek Anticline Fluid History...... 5

Pre-Folding Conditions and Fluid History...... 6

Syn-Folding Fluid History...... 6

Post-Folding Fluid History...... 8

Structural Features...... 8

Thrust Sheets...... 9

Depositional Environments and Tectonic History...... 10

Alleghanian Clastic Wedge...... 10

Conodont Alteration...... 11

Fluid Inclusions...... 11

CHAPTER II METHODS...... 14

Samples...... 14

Fluid Inclusions...... 14

CH4-Rich Inclusions...... 14

Two-Phase Aqueous Inclusions...... 15

CO2 Rich inclusions...... 15

Single-Phase Aqueous Inclusions...... 16

Fluid Inclusions Microthermometry...... 16

Uncertainty in Analysis of Fluid Inclusions...... 17

Pressure and Temperature at Trapping...... 18

Th Isochore Intersection Method...... 18

ThH Isochore Method...... 19

Geothermal Gradient Method...... 19

CHAPTER III RESULTS...... 21

Vein Relations...... 21

Older Veins...... 21

Younger Veins...... 21

Fluid Inclusions...... 22

CH4-Rich Inclusions...... 23

Two-Phase Aqueous Inclusions...... 23

CO2 Rich Inclusions...... 24

Single-Phase Inclusions...... 25

CHAPTER IV DISCUSSION...... 26

Fluid Migrations...... 26

Conditions of Entrapment and Determination of Overburden...... 26

Comparison to Castles (2010) and Evans and Battles (2012)...... 27

CHAPTER V CONCLUSIONS...... 29

REFERENCES...... 31

APPENDIX A MICORTHERMOMETRIC DATA...... 60

APPENDIX B HISTOGRAMS...... 70 vi

LIST OF FIGURES

Figure Page

1 Geology of Maryland with accompanying cross-section...... 31

2 Geology of Washington County, Maryland...... 32

3 Stratigraphic section of central Appalachians...... 33

4 Examples of fluid inclusion types...... 34

5 Example of pressure determined using ThH isochore method...... 35

6 Example of pressure determined using geothermal gradient method...... 36

7 Example of pressure determined using Th isochore intersection method...... 37

8 Locations of sample collection...... 38

9 Relative age of veins in sample WP-05-1...... 39

10 Relative age of veins within sample WP-05-2...... 40

11 Relative age of veins in sample TH-26...... 41

12 Histogram of ThH homogenization temperatures...... 42

13 Example of volume vs composition graph...... 43

14 TmIce vs ThA for all two-phase aqueous inclusions...... 44

15 TmIce vs ThA for two-phase aqueous inclusions divided by age...... 45

16 Trapping conditions for older veins as determined using the geothermal gradient

method...... 46

17 Trapping conditions for older veins as determined using the ThH isochore method…. 47

18 Trapping conditions for younger veins as determined using the geothermal gradient

method...... 48

19 Trapping conditions for younger veins as determined using the ThH isochore method 49 vii

20 Composite plot of all coeval inclusions...... 50 viii

LIST OF TABLES

Table Page

1 Microthermometric analysis abbreviations and definitions...... 14

2 Summary of Sideling Hill fluid events...... 25 1

INTRODUCTION

The central Appalachian mountain range formed during the Alleghanian orogeny (Dott Jr. and Prothero, 1994) causing the migration of fluids to the west (Evans and Battles, 1999). As these fluids migrated, they formed veins in which small amounts of fluids were trapped as inclusions. These inclusions record the conditions under which they were formed and can be correlated to the movement of thrust sheets (Evans and Battles, 1999) and the stage of deformation in which they formed (Evans et al., 2012). Fluid inclusions can also help in the reconstruction of paleo-aquifers and paleo-aquitards (Evans and Battles, 1999) as well as assist in mapping out the extent of eroded thrust sheets (Castles, 2010). The youngest formation deformed in the Valley and Ridge province during the Alleghanian orogeny is the Pocono

Sandstone, which is the focus of this study. Sideling Hill is the eastern most exposure of the

Pocono Sandstone and fluid inclusions in quartz veins show anomalously high trapping temperatures and pressures (Castles, 2010). The goal of this study is to determine the cause of the anomalously high trapping conditions at Sideling Hill.

Evans and Battles (1999) determined that emplacement of the Blue Ridge Thrust (BRT) resulted in a migration of fluids from the hinterland to the northwest across the central

Appalachian Valley and Ridge province and into the Appalachian Plateau. Fluid flow was confined to two paleo-aquifers separated by paleo-aquitards. A total of seven fluids and two migration events were deduced from this study (Evans and Battles, 1999). Conodont Alteration

Indices (CAI) mapped throughout the Appalachian Valley and Ridge (Harris et al., 1978) indicate greater overburden than the current stratigraphic sections. Evans (1989) suggested that the increased overburden was due to the emplacement of cover rock caused by the NMT. Through the use of fluid inclusion microthermometry, microstructural suite analysis, and vitrinite 2 reflectance, Castles (2010) proposed that the NMT had extended into the area including southern

Pennsylvania, western Maryland, and northeastern West Virginia, resulting in an overburden greater than can be accounted for by the stratigraphic section in adjacent areas.

Fluid inclusion microthermometry also shows an inversion of homogenization temperatures for aqueous inclusions (ThA) between the oldest studied rocks, the

Hampshire/Catskill Formation, and the overlying Pocono Sandstone and Pottsville Formation

(Castles, 2010). The modal homogenization temperature of aqueous inclusions (ThA) in the

Hampshire/Catskill Formation was 125°C while the overlying Pocono and Pottsville Formations showed a modal ThA of 180°C. Three hypotheses were proposed to explain the high ThA associated with the Pocono: 1) anomalous overburden caused by overthrusting of the NMT during the Alleghanian orogeny, burying the area; 2) anomalous overburden caused by the

Alleghanian clastic wedge being unusually thick in the area; and 3) a fluid migration through the

Pocono and Pottsville Formations of “warm” fluids resulting in elevated ThA and thus an apparently greater overburden.

Sideling Hill in western Maryland (Figs. 1 and 2) is the eastern most exposure of

Mississippian strata within this portion of the Valley and Ridge Province. Because of the quality of exposure, abundance of veins, and intensity of deformation, Sideling Hill provides the best opportunity to rigorously test these hypotheses. Accordingly, this study employed fluid inclusion microthermometry of the veins and healed microfractures to determine temperatures, pressures, and composition of fluids that were present during Alleghanian deformation. These data provide constraints on the depth of burial and hence, can be used to test the hypotheses for the origin of the high fluid temperatures reported by Castles (2010) and Evans and Battles (1999). 3

CHAPTER I BACKGROUND

1.1. Stratigraphy

The stratigraphy of the central Appalachian Valley and Ridge Province consists of

Cambrian through Mississippian units (Fig. 3). The formation that is the focus of this study is the Pocono Sandstone which is the youngest of these. In the Appalachian Plateau, the Pocono

Sandstone comprises the basal member of the Mississippian (Price, 1929) and overlies the

Devonian Hampshire/Catskill Formation. In West Virginia, the Pocono consists of coarse reddish-brown, often cross-bedded, conglomeratic sandstones, with brownish-bluish-gray and occasionally red shales together with some impure and lenticular coals. In Maryland and

Pennsylvania, the Pocono Sandstone consists of coarse, occasionally pebbly, greenish-gray, massive sandstones interstratified with thin gray shales and thin (1 to 6 in) seams of coal (White,

1885). The Pocono Sandstone forms a rough and rugged topography due to its resistant nature, capping many ridges and flats (Price, 1929). The Pocono Sandstone often forms synclinal ridges such as Sideling Hill. In Maryland, the Pocono Sandstone is divided into the Rockwell and

Purslane Formations. The Rockwell Formation consists of interbedded, tan and gray-green clay- rich sandstones with gray-green silty shales and gray sandy- siltstones containing several intervals of red-brown claystone near its top. Within the Rockwell Formation are thin, shaly coals interbedded with the shales and siltstones. The Purslane Formation is typified by gray- green, tan, and white cross-bedded sandstone and quartz pebble conglomerates with gray siltstones, shales, and coaly shales. Approximately 137 m of the Rockwell Formation and 107 m of the Purslane Formation are exposed along the I-68 road cut at Sideling Hill near mile marker

74 (Brezinski, 1994). 4

1.2. Lithostratigraphy and Hydrostratigraphy

The stratigraphy of the central Appalachians has been divided mechanically into competent and incompetent units (Fig. 3) (Evans, 1989). Other researchers (Willis, 1893; Currie et al., 1962; Jacobeen et al., 1974; Jacobeen, 1975) have proposed that the competent units acted as mechanical struts that controlled the deformation (fold frequency and wavelength) within the incompetent units, which acted as weaker boundary layers.

Evans and Battles (1999) divided the Upper Paleozoic formations into three hydrostratigraphic systems based upon fluid chemistry and temperature. These units consist of an aquitard at the base with two aquifers above it separated by another aquitard (Fig. 3). Fluids in the lower aquifer migrated to the northwest likely due to lithostatic loading caused by the BRT.

In the upper aquifer, in-situ fluids mixed with an influx of meteoric water likely caused by out of sequence emplacement of the BRT. Castles (2010) found that fluid inclusions within vein quartz in Mississippian strata yielded higher fluid inclusion homogenization temperatures than the strata directly below. This was attributed to the fluids passing through the Mississippian strata being hotter than the fluids passing through the lower strata.

Evans and Battles (1999) found that the Valley and Ridge province of the Appalachians yielded seven different fluid inclusion populations corresponding to different fluids. These populations include light hydrocarbon (HHC) fluids and CH4±CO2±HHC fluids in the Oriskany

Sandstone through lower Chemung, low-ThA high salinity aqueous fluid found in the Black River

Group through Helderberg Group, low-ThH CH4+CO2 fluid, high-ThH CH4±CO2 fluid, high-ThA low salinity aqueous fluid found in the Oriskany Sandstone through Lower Chemung Formation, and low-ThA low salinity aqueous fluid in the Upper Chemung Formation through the Pocono 5

Sandstone. Castles (2010) found high ThA low salinity inclusions in the Pocono Sandstone and

Pottsville Formation where Evans and Battles (1999) found low ThA low salinity inclusions in the

Upper Chemung Formation through the Pocono Sandstone further to the east.

1.3 Patterson Creek Anticline Fluid History

A fluid history of the Appalachian Valley and Ridge has been determined with respect to the structural/tectonic history and the overall fluid history (Evans and Battles, 1999). Evans et al.

(2012) documented the changing fluid conditions of the Patterson Creek anticline in the central

Appalachians. Due to the proximity of the Sideling Hill syncline to the Patterson Creek anticline it is likely that they underwent similar histories during the same phases of the Alleghanian orogeny. The difference between the two structures is that the Sidling Hill syncline exposes younger rocks than the Patterson Creek anticline. Castles (2010) found few NE striking veins at

Sideling Hill, suggesting that the Pocono sandstone may have lacked the pore fluid pressure to initiate NE striking fractures (Evans et al., 2012). Evans et al. (2012) also noted that at the

Patterson Creek anticline units above the Devonian shales lack NE-NW veins. Many of the aqueous inclusions reported by Castles (2010) and this study homogenize at similar temperatures to those that Evans et al. (2012) classified as syn-folding, indicating that most of the fluids trapped at Sideling Hill occurred during or after folding related to the Alleghanian orogeny.

During the final stages of deformation, EW fractures were formed by out-of-sequence thrusting of the BRT during the latter part of the Alleghanian orogeny (Evans, 2010). These fractures were rarely mineralized in the Patterson Creek anticline (Evans et al., 2012) and show a similar trend at Sideling Hill (Castles, 2010). The two vein orientations may represent different stages of syn- folding deformation and a change in the regional stress field. If this is the case, veins (and 6 microthermometric data) could represent pre-, syn-, or post-emplacement of the NMT and formation of the Adams Run-Cacapon Mountain anticline.

1.3.1 Pre-Folding Conditions and Fluid History

Fracture sets oriented ENE-NNW are present largely in the Devonian shales with fewer sets in the Brailler Formation and none in the Chemung or younger formations (Evans and

Battles, 1999). The only mineralized fracture sets are those in the Devonian shales with calcite and dolomite. Calcite and dolomite were likely sourced from pre-folding, layer parallel shortening pressure solution. The absence of mineralization in the strata above the Devonian shales suggests that these units lacked the pore fluid pressure necessary to initiate fracturing and the fluid conditions required for mineralization. The earliest trapped fluids were light hydrocarbons that degraded with continued heating and maturation. Later trapped fluids in calcite are high salinity aqueous fluids and CH4 ± HHC condensate-like fluids and nearly pure

CH4. Fluid temperatures and composition of ENE-NNW, and bed parallel veins suggest that a stratified fluid sequence existed prior to Alleghanian folding (Evans et al., 2012).

1.3.2 Syn-Folding Fluid History

Development of the Cambrian-Ordovician duplex and passive folding was driven by an increase in pore fluid pressure imposed by an increased thrust and sediment load from emplacement of the NMT (Evans and Battles, 1999). This was accompanied by a change in the regional stress system to NW-SE shortening. CH4-saturated, high-salinity inclusions yielded homogenization temperatures of -80 oC to -130 oC indicating overburdens of 4.0-6.3 km during this stage of deformation (Evans et al., 2012). Early veins are oriented NE-NW and consist of

7 calcite. Fluid inclusion salinities suggest that fluids in the McKenzie Formation through the

Devonian shales were stratified. Salinities of aqueous inclusions from veins in the McKenzie

Formation are approximately 26 wt.% NaCl equivalent and decrease stratigraphically upward to

22 to 24 wt.% NaCl equivalent in the Devonian Helderberg Group and near 15 wt.% NaCl equivalent in the Oriskany and Middle Devonian shales. Late NE-NW quartz veins trapped fluids yielding significantly higher temperatures (140 to 224 oC) and lower salinities. Significant additional syn-deformational overburden, up to 7.7 km, was determined by coeval aqueous and

CH4±CO2 inclusions in the Devonian shales. It has been suggested (Evans, 2010; Evans and

Hobbs, 2003; Evans and Battles, 1999) that these fluids are “exotic” and migrated from the hinterland as modified formation fluids and/or metamorphic fluids. Fluids are interpreted to have been mobilized by emplacement of the NMT and development of the Adams Run-Cacapon

Mountain anticlinorium, which imposed a thrust and erosion-sourced sediment load on the Upper

Paleozoic strata (Evans and Battles, 1999). Migration of these fluids was focused in the clastic section of the Devonian shales through the lower portion of the Devonian Chemung Formation and would have mixed with pre-existing fluids. The preferred migration of these “warm” fluids through the clastic sequence and not underlying carbonate rocks resulted in a fluid temperature and density inversion. The most likely explanation as to why the migrating fluids did not uniformly infiltrate the Oriskany Sandstone or carbonate rocks is that fractures that formed in these sections were quickly cemented (healed) by locally derived calcite, which restricted fluid infiltration, causing the Oriskany Sandstone to act as an aquitard instead of a fluid conduit.

Unexpectedly high temperature fluids are absent in the carbonate section, with the exception of late stage quartz veins, given that the amount of overburden was near 8 km. The most likely explanation for the lack of high temperature fluids is that the carbonate section did not have

8 adequate time to reach thermal equilibrium due to syn-tectonic sedimentation (Evans et al.,

2012).

1.3.3 Post-Folding Fluid History

Post-folding EW fracturing marks the final stage of deformation and is related to late

Alleghanian out-of-sequence thrusting in the BRT. These fractures are rarely mineralized, indicating that pore fluid conditions changed and were no longer conducive to mineral precipitation (Evans et al., 2012). Evans and Elmore (2006) hypothesized that these fractures coupled with erosional breaching may have played a key role for late infiltration of meteoric waters into the structures.

1.4. Structural Features

The structures in the Valley and Ridge province of the central Appalachians were formed during the Alleghanian orogeny (Gwinn, 1962; Perry, 1978). During the mid-Carboniferous, the collision of Gondwanaland and North America resulted in the Alleghanian orogeny following the

Acadian orogeny of the Mid to Late Devonian (Dott Jr. and Prothero, 1994). This resulted in the formation of multiple westward-verging thrust sheets and the formation of the Appalachian orogen (Dott Jr. and Prothero, 1994; Stanley, 2005). Accompanying the orogeny was a migration of fluids to the northwest and the creation of the Nittany anticlinorium and the Broadtop synclinorium in Northern Virginia (Evans, 1989).

The region comprising northwestern Virginia, western Maryland, and northeastern West

Virginia can be divided into four distinct structural subareas, the Nittany anticlinorium, the

Broadtop synclinorium, the Adams Run-Cacapon Mountain anticlinorium, and the Meadow

Branch synclinorium (Evans and Battles, 1999). The Nittany anticlinorium and the Broadtop synclinorium are the larger of the two structures, extending further south than the other two. A complete duplication of the lithotectonic Cambrian-Ordovician unit characterizes the Nittany anticlinorium while the Broad Top synclinorium is characterized by a partial duplication of the same unit in a blind duplex (Evans, 1989).

1.5. Thrust Sheets

Three major thrust systems have been identified in the central Appalachian foreland in northern Virginia (Evans, 1989). These are the North Mountain thrust (NMT), the Lower carbonate duplex (LCd), and the Blue Ridge thrust (BRT). The NMT is comprised of Mid-

Ordovician through Pennsylvanian strata. The LCd consists of multiple horsts of Cambrian and

Ordovician carbonates that were emplaced beneath the NMT. The BRT is composed of an imbricated composite thrust sheet consisting primarily of Precambrian crystalline rocks.

The NMT is characterized by imbricated Cambrian-Ordovician carbonates that have been deformed into high amplitude Mode-II fault-bend and fault-propagating folds. Displacement along the NMT ranges from 54 km in northern Virginia (Evans, 1989) to as much as 80 km in central Virginia (Harris et al., 1982). The NMT extends from south-central Pennsylvania to west- central Virginia and is bounded by the Valley and Ridge province to the west and Cambrian-

Ordovician carbonates to the east. Multiple imbricate thrusts cut the NMT sheet with associated

Mode-II fault-bend folds or fault-propagating folds that have steeply dipping or overturned and sheared northwest limbs.

1.6. Depositional Environments and Tectonic History

The Rockwell Formation was likely deposited in an alluvial plain environment near sea- level with a major shift of the shoreline as recorded by the Riddlesburge Shale. An alluvial plane is also recorded in the Purslane Sandstone as evidenced by the abundant thick quartz-pebble conglomerates and sandstones which lack marine fossils. Coal beds and coaly shales were likely formed in swamps adjacent to the fluvial channels (Brezinski, 1994).

1.7. Alleghanian Clastic Wedge

The Devonian through Permian stratigraphy of the central Appalachians in the area of

West Virginia, Virginia, and Maryland consists of two clastic wedges. The first clastic wedge

(cw1) is represented by Devonian through early Pennsylvanian strata and the second clastic wedge (cw2) is represented by units ranging from the middle Pennsylvanian to Permian, including the Pocono Sandstone. Cw1 is a late Paleozoic molasse sequence consisting of a four- unit clastic wedge that was derived from the northern and central Appalachians. These units represent a progradational sequence bounded by marine transgressions. Cw2 is recognized by two progradational sequences derived from the southern Appalachian orogenic area. This wedge is represented by a deltaic sequence (West Virginia deltaic complex) as well as lacustrine environments (Pittsburgh coal and Monogahela strata). Delta lobes in the deltaic sequence suggest delta switching by a single river (Donaldson and Shumaker, 1981). In the study area, cw1 consists of the Devonian Chemung Group through the lower Pennsylvanian New River

Formation and cw2 is represented by the middle Pennsylvanian Kanawha Formation and the

Pennsylvanian/Permian Charleston Formation. Combined, these formations and groups would provide an overburden for the Pocono Sandstone of ~2.5 km.

1.8 Conodont Alteration

Previous studies (Epstein et al., 1977, Harris et al., 1978) examined the amount of overburden in the Appalachians using Conodont Color Alteration and the Conodont Alteration

Index (CAI). As conodonts are exposed to increasing temperatures, their color changes in a predictable and quantifiable way. This method is effective over temperatures ranging from 50 to

600°C. Even though problems with this method exist (e.g., heating may occur at variable temperatures), it is useful in areas where the temperature distribution is largely a result of burial as long as the thickness of the stratigraphic section and the boundaries of the chronostratigraphic units are known (Garcia-Lopez et al., 2001). Harris et al. (1978) mapped the CAI of the

Appalachian basin and found that the CAI was between 4 and 5 in eastern West Virginia. This, combined with work done by Epstein et al. (1977) in Ordovician carbonates, gives an overburden ranging from 5.5 km to 9.2 km, leaving ~3 km to ~6.7 km unaccounted for if overburden was from the overlying stratigraphy alone.

1.9. Fluid Inclusions

Roedder (1984) defines three categories of fluid inclusions: primary, secondary, and pseudosecondary. Primary inclusions (Fig. 4a) are classified as having formed during crystal growth either by fluids filling defects on a crystal surface or nucleating (wetting) onto the crystal surface with the crystal forming around the nucleated fluid. Secondary fluid inclusions (Fig. 4b) are formed by processes that act on the crystal after growth, such as fracturing and subsequent healing, commonly resulting in an array of inclusions along a plane. Fluid inclusion planes

(FIPs) within detrital grains can be intergranular or transgranular. Intergranular FIPs are planes that do not cross grain boundaries, indicating formation prior to the deposition and cementation

12 of the rock they are found in today. Transgranular FIPs are planes that cross grain boundaries and extend through multiple grains. This type of FIP is formed after grains were consolidated into the current formation. Pseudosecondary inclusions (Fig. 4c) are trapped along fractures that form coevally with crystal growth. Although primary inclusions typically occur as singular isolated inclusions with relatively large diameters, the only unequivocal evidence for a primary origin is the association with growth bands. Both secondary and pseudosecondary inclusions occur in planar arrays, with the difference being that secondary inclusion planar arrays may cut across a single grain or multiple grains and pseudosecondary planar arrays terminate within individual crystals or grains.

In this study, inclusions were further divided based on the phases contained within them.

Single-phase inclusions appear homogeneous when observed at room temperature. This is due to the contents being a super critical fluid that when cooled may separate into liquid and vapor phases with the possibility for a solid daughter crystal to form. Multiphase inclusions may contain two or three phases in any combination of solid, liquid, or vapor (i.e., vapor and liquid; solid, liquid and vapor; two vapors and one liquid; etc.) when observed at room temperature

(Roedder, 1984, and references therein).

Parry (1998) describes multiple methods for calculating and estimating fluid pressures using fluid inclusions: 1) estimating fluid density from its homogenization temperature and pressure, then calculating the pressure and temperature of the isochore using an appropriate equation of state. The isochore is then projected to its intersection with the lithostatic and hydrostatic pressure gradients (Figs. 5 and 6); 2) using the intersection of the fluid inclusion isochore and temperature determined from mineral equilibria, metamorphic conditions, or isotope fractionation; 3) isochore intersection method utilizing inclusions containing CH4 and/or CO2, in 13 addition to water/brine. Because the isochores for the different phases have different slopes on a

P-T plot, when two or more of these phases are present the corresponding isochores can be calculated and extended to the pressure and temperature of intersection (Fig. 7); 4) the presence of substantial CO2 together with the CO2-H2O-NaCl phase relationships permits an estimate of the minimum pressure and minimum temperature of fluid entrapment. 14

CHAPTER II. METHODS

2.1 Samples

Fourteen samples were prepared at Bowling Green State University from billets cut from slabs of hand samples until optical clarity was achieved for the given sample. This was to ensure that the sample was strong enough to be used, yet contained enough inclusions to obtain a sufficient number of data points. Sections were then polished down to 1 μm using a diamond slurry to remove as many imperfections in the surface as possible. All preparation was done keeping the samples below 50 oC to avoid decrepitation of any low temperature inclusions that might be present. Samples WP-18 and WP-13 were collected at the crest of Sideling Hill along

Interstate 68, the remaining samples were collected from the crest of Sideling Hill along Rte. 40

(Fig. 8). Samples collected at the I-68 road cut were collected from the stratigraphic center of the

Pocono Sandstone. The samples collected along Rte. 40 were collected from the upper portion of the Pocono Sandstone. All samples were collected from the center of the syncline.

2.2 Fluid Inclusions

Four types of fluid inclusions were found in the samples examined: CH4-rich, two-phase aqueous, CO2-rich, and single phase aqueous. The behavior of each is described below. A list of abbreviations and their meanings for employing fluid inclusions for microthermometric analysis are provided in Table 1.

2.2.1 CH4-rich Inclusions

These inclusions are monophase at room temperature and will separate into a liquid and vapor when cooled to temperatures lower than -82.4 °C. Further cooling to -160°C may result in 15 the formation of a crystal of solid CO2, if present. The temperature at which the last of this crystal melts (TmCO2) depends on the concentration of CO2 relative to CH4 within the inclusions.

Continued warming causes the vapor bubble to homogenize (ThH).

Table 1. Definitions of abbreviations used for microthermometric analysis.

Abbreviations Definition

Tt Trapping temperature

Tp Trapping pressure

ThA Homogenization of vapor phase in aqueous inclusions

ThH Homogenization of CH4 phase in CH4-rich inclusions.

TmIce Last ice melting temperature for aqueous inclusions

TmCO2 Last CO2 ice melting temperature for CH4-rich inclusions.

Te Eutectic temperature for aqueous inclusions.

ThTotal Complete homogenization of all phases in the inclusion.

2.2.2 Two-Phase Aqueous Inclusions

Two-phase aqueous inclusions are two-phase colorless inclusions at room temperature

(Fig. 4a). Upon heating these inclusions will homogenize (ThA) into a supercritical fluid. When cooled an ice crystal will form which can provide the species of salt, or mixture of salts, based on the first melting temperature (Te) of the ice crystal. The concentration, in wt.% NaCl equivalent, will control the temperature at which the last of the ice crystal melts (TmIce).

2.2.3 CO2 Rich Inclusions

CO2 inclusions appear similar to two-phase aqueous inclusions in that a vapor phase and a

16 liquid phase exist at room temperatures. The vapor phase in CO2 inclusions tends to be larger and slightly darker. When cooled, a solid phase of water will form followed by a solid phase of

CO2. When warmed the first (Te) and last (TmIce) ice melting temperatures are recorded similarly to two-phase aqueous inclusions. The last melting temperature of the CO2 crystal can be used to determine the amount of CO2 in the inclusion. Upon heating, the CO2 vapor will homogenize

(ThCO2) first followed by homogenization of all fluids/phases (ThTotal) within the inclusion. This data can then be used to estimate minimum trapping pressures and temperatures.

2.2.4 Single-Phase Aqueous Inclusions

Single-phase aqueous inclusions are colorless, monophase inclusions at room temperature similar to single-phase CH4-rich inclusions. When cooled these inclusion act the same as two- phase aqueous inclusions forming an ice crystal with the first (Te) and last (TmIce) melting temperatures indicating concentration and species of salt, respectively. A vapor bubble may also form when these inclusions are cooled which can be heated until the fluid re-homogenizes into a supercritical fluid, but it is unlikely that it will reform when cooled back to room temperature.

2.3 Fluid Inclusion Microthermometry

Fluid inclusions have become one of the best and most widely applied geothermometers in the field of geology (see Roedder, 1984, and references therein). To use fluid inclusions for microthermometry, the conditions at the time of their formations need to be replicated. In this study, the isochore intersection method as outlined by Parry (1998) as well as the geothermal gradient method and ThH isochore method (Evans, 2010) were used to determine the pressure and temperature conditions at the time of trapping of fluid inclusions in order to constrain the 17 overburden on the Pocono Sandstone in the study location.

This study documents the fluid conditions (T-P-X) of inclusions within the Pocono

Sandstone at Sideling Hill, Maryland. Primary inclusions as well as secondary inclusions were examined in samples of vein quartz. Primary inclusions formed as the vein minerals were growing from fluids passing through the area. FIPs were examined for secondary fluid inclusions in both the veins and host rock. FIPs of interest within veins are ones that parallel the strike of the vein itself. These FIPs formed as the vein reopened creating fractures that were later healed.

The quartz grains in the host rock were also examined for secondary fluid inclusions.

Transgranular fluid inclusion planes were of particular interest when examining the host rock because they could only have formed after the deposition and cementation of the host rock grains. Transgranular fluid inclusion planes had similar orientations to those of the veins due to having been formed in the same stress regime. Documenting the fluids within veins allows for the determination of the fluid that passed through the area following deformation associated with the Alleghanian orogeny. By examining the fluids in FIPs within vein material the evolution of the fluids as vein material was forming could be documented, provided that the relative ages of the FIPs can be determined and if more than one set is present. Transgranular FIPs in the grains of wall rock likely formed from the same stresses that formed the veins and had the same fluids pass through them as those from which the vein material formed. Data collected from secondary inclusions were used to gather a larger sample set and to obtain a more accurate representation of the fluids that have passed through the Pocono Sandstone at Sideling Hill.

2.4 Uncertainties in Analysis of Fluid Inclusions

Uncertainties in fluid inclusion analysis can result from multiple different sources.

Temperatures recorded on the heating and freezing stage have a margin of error of 1.0-2.0°C for heating and for 0.5-1.0°C for freezing, as determined by repeated measurements on inclusions.

These errors result from the delay between when the phase change occurred and when the temperature display was stopped (or locked in). Due to reaction times or observational errors, phase changes being obscured by sample clarity or the shape/orientation of the inclusion, phase changes may have occurred at slightly different temperatures than when the display was frozen.

2.5 Pressure and Temperature at Trapping

In order to determine the pressure and temperature during fluid migration, the trapping conditions of fluid inclusions must be determined. This is done by calculating an isochore and plotting it on a pressure/temperature plot along with the lithostatic and hydrostatic pressure gradients, and in some cases a second isochore calculated from inclusions.

2.5.1 Th Isochore Intersection Method

This method involves calculating the isochores for coeval or genetically related two-phase aqueous and CH4-rich inclusions. Inclusions are considered coeval if they occur in the same crystal growth zone. Inclusions that are found in different primary or pseudosecondary assemblages in the same mineral stage in a vein are considered genetically related. Isochores from two-phase aqueous and CH4-rich inclusions are plotted on the same P-T plot and the point at which the isochores intersect provides a unique value for the trapping pressures and temperatures (Fig. 7). Because the fluid is saturated in CH4 and does not require a pressure correction (Evans and Battles, 1999) the mean measured ThA for two-phase aqueous inclusions can be used to represent the real trapping temperatures. The mode was used for ThH inclusions 19 because that temperature was the most common temperature found and the most representative of trapping conditions.

2.5.2 ThH Isochore Method

This method uses CH4-rich inclusions that are not found to be coeval or genetically related to two-phase aqueous inclusions. Isochores calculated using this method are plotted against the lithostatic and hydrostatic gradients. Trapping conditions are constrained to be between where the isochore crosses the lithostatic and hydrostatic pressure gradients (Fig. 5).

This method results in a range of possible trapping conditions. Due to possible fluctuations in pore-fluid pressure during deformation, pressure determinations using the hydrostatic gradients should be considered a minimum as the inclusions may have been trapped at conditions above the hydrostatic pressure. Similarly pressures determined using the lithostatic gradient should be considered a maximum (Evans, 2010).

2.5.3 Geothermal Gradient Method

This method was used to constrain trapping conditions using aqueous inclusions that were not genetically related or coeval with CH4-rich inclusions. A key assumption of the geothermal gradient is that the aqueous inclusion liquid is saturated in CH4 and that the mean inclusion trapping temperature reflects a fluid in thermal equilibrium with its burial depth and geothermal gradient during the time of trapping (Evans, 2010). Background geothermal gradients for the

Valley and Ridge Province range from 20-30 °C/km (Evans and Battles, 1999; Evans, 2010;

Chandonais, 2012). Isochores that are calculated from these inclusions are plotted against the lithostatic and hydrostatic gradients. Like the ThH method, the geothermal method results in a 20 range of possible trapping conditions. Conditions are determined in a similar fashion as in the

ThH isochore method (Fig. 6).

CHAPTER III. RESULTS

3.1 Vein Relations

Several samples contained multiple veins, some of which cut across each other, allowing for relative ages to be determined. Five samples (TH-25-1, TH-25-2, TH-26, WP-05-1, and WP-

05-2) were found to contain multiple vein sets. Of these five samples only WP05-1, WP-05-2, and TH-26 (Figs. 9 - 11) contained cross cutting veins with usable inclusions. Based on orientation within samples and cross cutting relationships two generations of veins were identified.

3.1.1 Older Veins

The abundance of CH4-rich and two-phase aqueous inclusions was found to be nearly the

o same within older veins. ThH for CH4-rich inclusions was found to have a mode of -80 C and

o o o o ranged from -75 C to -115 C. TmCO2 for CH4-rich inclusions ranged from -85 C to -115 C

o o with a mode of -90 C (Fig. 12). The mode for ThA for two-phase aqueous inclusions was 150 C

o o o o with a range of 140 C to 250 C. TmIce was found to have a range from -1 C to -9 C with the

o o o o mode at -4 C. The mode for Te is -30 C with temperatures ranging from -25 C to -50 C.

3.1.2 Younger veins

Unlike the inclusions in the older veins, CH4-rich inclusions were found to be much more abundant than two-phase aqueous inclusions within the younger veins. Similarly to the older

o o o veins, ThH ranged from -75 C to -115 C with a mode of -80 C. The TmCO2 values show a bi- modal distribution with one mode at -85 oC and the other mode at -100 oC with a range of -85 oC 22 to -115 oC (Fig. 12). Due to having fewer two-phase aqueous inclusions being in younger veins, distributions are not as clear as they are for CH4-rich inclusions. This results in a range of modes or the appearance that a distribution has multiple modes. ThA was found to have two modes with

o o o o the first being between 190 C to 210 C and the second between 220 C to 230 C. Overall ThA

o o o o ranged from 160 C to 290 C. The mode for TmIce ranged from -4 C to -6 C with the entire

o o o o distribution ranging from -3 C to -9 C. The distribution for Te is -25 C to -55 C with a mode between -35 oC and -40 oC.

3.2 Fluid Inclusions

Four different types of inclusion were found. The two most common inclusion types were

CH4-rich inclusions and two-phase aqueous inclusions. Inclusions containing CO2 clathrate and single-phase aqueous inclusions were also identified, but in a single sample each. Appendix A presents the microthermometric data collected during the course of this study. Appendix B contains histograms for each group of veins showing the distribution of the microthermometric data.

Primary inclusions (Fig. 4a) were between 10 and 20 μm in length and ranged from near spherical to irregular in shape. The average liquid: vapor (L: V) ratio was between 2:1 and 3:1 with some inclusions having a ratio as high as 5:1. Primary inclusions occurred as either singular inclusions or small groupings of inclusions with a random distribution. Cathodoluminecsence observations revealed that the veins were homogenous and that no zoning was present.

Secondary and pseudosecondary (Figs. 4b and 4c) inclusions were smaller, typically no larger than 5 μm in size with a sub-spherical shape. The L: V ratios for secondary and pseudosecondary inclusions were near 1:1 and never greater than 3:1. One sample (WP-13) was found to have 23 secondary and pseudosecondary CH4-rich inclusions that were larger and had a more irregular shape, similar to those found for primary inclusions.

3.2.1 CH4-rich Inclusions

CH4-rich inclusions were found in every vein sample from Sideling Hill. These inclusions consisted of CH4±CO2 with CO2 concentrations ranging from 0% to 17% of the composition. Homogenization temperatures for these inclusions ranged from -116 °C to -75 °C with a large portion in the -90 °C to -80 °C range (Fig. 12). Both older and younger veins have the same range of homogenization temperatures (-75 °C to -115 °C) and a modal homogenization temperature between -80 °C and -85 °C. Even though both have the same range and mode for homogenization temperatures, older veins contained fewer inclusions below -90 °C. The CO2 ice melting temperatures ranged from -118 °C to -85 °C. In several inclusions in sample WP-13, homogenization occurred before the CO2 crystal had melted. This was observed in secondary inclusions only. Homogenization temperatures for these inclusions were lower than other CH4- rich inclusions studied. Composition (% CH4) and molar volume for these inclusions were determined by plotting TmCO2 and ThH values on a VX plot (Fig. 13). Though molar volume was found to vary, ranging from ~45 cm3/mole to ~100 cm3/mole, the composition for many samples was greater than 90% CH4. The only inclusions to have less than 90% CH4 were secondary inclusions found in sample WP-13, which had a composition as low as 85% CH4. Isochores and bulk density were calculated using the LonerW program (Bakker, 2009; 2012) from the FLUIDS package (Bakker, 2003).

3.2.2 Two-Phase Aqueous Inclusions

Two-phase aqueous inclusions were the most common inclusion type after CH4-rich inclusions. Last ice melting temperatures ranged from -0.4 °C to -9.3 °C indicating a salinity of between 0.7 and 13.1 wt. % NaCl equivalent; a few inclusions were found to have a salinity greater than 10% (Fig. 14). Eutectic temperatures were between -56 °C and -31 °C (Appendix A) indicating that the salt species in the inclusions was likely a mixture of NaCl and CaCl2. For inclusions in which both TmIce and ThA could be determined, salinity and isochores were calculated using HokieFlincs (MacInnis et al., 2012). For inclusions in which only ThA could be obtained isochores were calculated using FLINCOR (Brown, 1989).

3.2.3 CO2-Rich Inclusions

CO2-rich inclusions were found in only one sample (SS-70-2). These inclusions consisted of CO2±H2O. The melting temperatures of CO2 crystals were found to be between -58 °C and -

62 °C indicating entrapment of nearly pure CO2. Few data could be collected for Te, TmIce, or

Tmclath because of the high concentration of CO2. What data were collected from these inclusions indicated that the aqueous phase of the inclusions consisted of a mix of NaCl and CaCl2 in concentrations of 1.2 to 4.4 wt.% NaCl equivalent (Appendix A). Clathrate melting was found to occur between 8 and 10 °C. Because of the difficulty in collecting Te, Tmice, and Tmclath, these calculations represent only a small portion of the inclusions studied and may not represent the population accurately. Total homogenization temperatures for the CO2 inclusions ranged from

312 °C to 355 °C without breaching. Primary two-phase aqueous inclusions within the same vein also showed very high 309 °C to 337 °C homogenization temperatures. Secondary inclusions within the vein are similar to those of other veins with homogenization temperatures ranging from 193 °C to 289 °C, with most near or below 250 °C. Few secondary inclusions 25 could be accurately identified and as such, the data may not be representative of the entire population.

3.2.4 Single-Phase Aqueous Inclusions

Single-phase aqueous inclusions were found only in sample TH-24. One inclusion separated into liquid and vapor phases when cooled to near -60 °C. The fluid re-homogenized at a temperature of approximately 110 °C. Salinity for these inclusions was found to range from 8.1 to 11.8 wt.% NaCl equivalent. Few inclusions were studied from this sample because of the lack of a phase separation, making calculations of pressure at time of entrapment, and therefore burial depth, impossible. 26

CHAPTER IV. DISCUSSION

4.1 Fluid Migration

Cross cutting relationships within samples (WP-05-1, WP-05-2, and TH-26) indicate that different generations of veins formed during deformation. Homogenization and last ice melting temperatures (Fig. 15) show veins were formed from a single fluid during progressive deformation at Sideling Hill. Salinities for older inclusions average 6.9 wt.% NaCl equivalent.

The average salinity for younger inclusions was found to be 6.5 wt.% NaCl equivalent (Fig. 15).

Eutectic temperatures for older inclusion vary more, with a high of -30 °C and a low of -53 °C, while eutectic temperatures for younger inclusions varied from -30 °C to -39 °C. The compositions for both vein sets were below 10 %CO2 with the only difference being that older inclusions had a larger range (0 to 10 % CO2) than did younger inclusions (0 to 5 % CO2).

To the east, of Sideling Hill Evans and Battles (1999) identified a fluid that had migrated into the Pocono Sandstone resulting in the mixing of in-situ fluids and meteoric water. This fluid is most similar to the fluid found at Sideling Hill with continued mixing possibly explaining the increase in both melting and eutectic temperatures.

4.2 Conditions of Entrapment and Determination of Overburden

Two-phase aqueous inclusions within older veins were found to have been trapped at pressures of 54 MPa (5.7 km) (Fig. 16) with CH4-rich inclusions being trapped at a minimum of

97 MPa (9.9 km) (Fig. 17). Inclusions in younger veins were found to be trapped at pressures of

91 MPa (9.3 km) (Fig. 18) for two-phase aqueous inclusions and 132 MPa (13.5 km) (Fig. 19) for CH4-rich inclusions. Coeval inclusions indicate that older veins were trapped at depths from 27

5.6 to 8.5 km and younger veins were trapped at depths of 12.8 to 13.7 km (Table 2). Many of the coeval isochores intersected within or near the hydrostatic gradients as well as near the 30 oC/km geothermal gradient (Fig. 20). Because of this hydrostatic conditions were assumed when calculating burial depth and the hydrostatic pressure gradient of 9.8 MPa and geothermal gradient of 30 oC/km were used to determine trapping pressure and temperature (Table 2).

Table 2. Summary of Sideling Hill Fluid Events. Conditions were determined assuming a hydrostatic pressure gradient of 9.8 MPa and geothermal gradient of 30 oC/km.

Method

ThH Geothermal Intersection

Fluid Te(°C) Salinity Pt Tt (°C) Pt Tt (°C) Pt Tt (°C) (wt % NaCl) (MPa) (MPa) (MPa) 1 - 28.3 to 3.39 to 12.85 97 + 220 + 58 to 203 to 54 to 195 to -53.3 103 228 83 230 2 -29 to 5.11 to 13.18 65 to 155 to 89 to 305 to 333 to 440 to -56.2 133 425 161 350 356 450

4.3 Comparison to Castles (2010) and Evans and Battles (1999)

Previous hypotheses to explain the anomalously high temperatures and pressures at

Sideling Hill include: 1) Sideling Hill being overridden by the NMT, resulting in greater overburden than previously proposed; 2) warm or hot fluids migrated through the Sideling Hill area without reaching thermal equilibrium at a shallower depth, which resulted in elevated

28 trapping temperatures for fluid inclusions, and; 3) an increased amount of overburden was caused by a thicker clastic wedge than previously theorized (Evans and Battles, 1999).

Trapping conditions of all fluid inclusions measured in this study indicate a minimum overburden of ~6 km. Castles (2010) concluded that the NMT had overridden the central

Appalachians and resulted in a greater depth of burial than previously proposed. While this could account for the overburden in older veins it does not alone account for the overburden of younger veins (Table 2). As stated above, stratigraphic reconstructions indicate the Permian clastic wedge, from thicknesses determined elsewhere, accounted for only ~2.5 km of overburden leaving a minimum of 2.5 km of unaccounted overburden for older veins and 7.5 km of unaccounted overburden for younger veins. Evans and Battles (1999) show a migration of fluids toward Sideling Hill. While it is possible that the fluid may have migrated stratigraphically upward, the fluids would have cooled before reaching Sideling Hill.

A possible explanation for the temperature inversion between the Pocono Sandstone and the underlying Hampshire/Catskill Formation is that the fluid was restricted to the Pocono

Sandstone at Sideling Hill.

CHAPTER V. CONCLUSIONS

Sideling Hill is a large syncline consisting of the Mississippian-aged Pocono Sandstone deformed during the Alleghanian orogeny. A previous study by Castles (2010) found that fluid inclusion trapping temperatures and vitrinite reflectance temperature measurements at Sideling

Hill were warmer than what was expected when compared to the expected burial depth. Castles

(2010) questioned the amount of overburden that had been placed on the Pocono Sandstone at

Sideling Hill and proposed that warmer temperatures may have been due to: 1) increased overburden from the NMT; 2) migration of “warm” fluids through the Pocono Sandstone; or 3) increased overburden caused by a greater amount of overlying strata from a thicker clastic wedge.

The fluid inclusion trapping conditions and homogenization temperatures determined in this study indicate that a single fluid was present at Sideling Hill as it underwent progressive stages of deformation. Microthermometric data indicate that the Pocono Sandstone was at a minimum depth of ~6 km during the early stages of deformation and a minimum depth of ~9 km during the late or end stages of deformation, leaving at least 2.5 km and 6.5 km of overburden that cannot be accounted for through reconstructions of the overlying strata that are present in the

Appalachian Plateau. The fluid was determined to be a mixture of in-situ and meteoric waters as identified by Evans and Battles (1999) that migrated into the Pocono Sandstone.

While emplacement of the NMT sheet would have resulted in an overburden of ~6 km, which is similar to the overburden of the Pocono Sandstone at Sideling Hill during the early stages of deformation, it alone does not account for the ~9 km of overburden recorded by younger veins. Similarly to Patterson Creek, the NMT would have imposed both a thrust and sediment load (Evans and Battles, 1999) on Sideling Hill. Assuming ~6 km for the thickness of 30 the NMT sheet (Evans, 1989) combined with the 2.5 km of sediment overlying the Pocono

Sandstone from clastic wedges in the Appalachian Plateau (Donaldson and Shumaker, 1981) results in a total of ~8.5 km of overburden leaving only 0.5 km unaccounted for. The remaining

0.5 km could be the result of additional sediment caused by the increased sediment load imposed by the NMT. 31

REFERENCES

Bakker, R.J., 2003. Package FLUIDS 1. Computer programs for analysis of fluid inclusion data and for modeling bulk fluid properties: Chemical Geology, v. 194, p. 3-23

Bakker, R.J., 2009. Package FLUIDS Part 3: correlations between equations of state, thermodynamics and fluid inclusions: Geofluids v. 9, p. 63-74

Bakker, R.J., (2012). Thermodynamic Properties and Applications of Modified van-der-Waals Equations of State, Thermodynamics - Fundamentals and Its Application in Science, Dr. Ricardo Morales-Rodriguez (Ed.), ISBN: 978-953-51-0779-8, InTech, DOI: 10.5772/50315 Brown, P.E., 1989. FLINCOR: A microcomputer program for the reduction and investigation of fluid-inclusion data: American Mineralogist, v. 74, p. 1390-1393

Boyer, S.E., Elliot, D., 1982. Thrust systems: American Journal of Science, v. 281, p. 1196- 1230

Brezinski, D.K., 1989. Geology of the Sideling Hill Road Cut: Maryland Geological Survey. p. 5

Castles, M., 2010. Determining the Geometry and Former Extent of the North Mountain Thrust from Fluid Inclusion and Microstructural Analyses: Masters Thesis, Bowling Green State University. p. 78

Chandonais, D.R., 2012. Deformation and Fluid History of late Proterozoic and early Cambrian Rocks of the Central Appalachian Blue Ridge: Masters Thesis, Bowling Green State University. p. 126

Currie, J.B., Patnode, H.W., Trump, R.P., 1962. Development of folds in sedimentary strata: Geological Society of America Bulletin, v. 73, p. 655-674

Davis, G.H., Reynolds, S.J., 1984. Structural geology of rocks and regions: New York, John Wiley & Sons, p.776

Donaldson, A.C., Shumaker, R.C., 1981. Late Paleozoic Molasse of Central Appalachians: Geological Association of Canada Special Paper 23, p. 99-124

Dott. Jr, R.H., Prothero, D.R., 1994. Evolution of the Earth 5th edition: McGraw Hill. p. 569

Elliot, D., Fisher, G.E., Snelson, S., 1982. A restorable cross section through the central Appalachians: Geological Society of America Abstracts with Programs, v. 14, No. 7, p. 482

Epstein, A.G., Epstein, J.B., Harris, L.D., 1977. Conodont Color alteration-An index to Organic 32

Metamorphism: U.S. Geological Survey Professional Paper 995, p. 27

Evans, M.A., 1989. The structural geometry and evolution of foreland thrust systems, northern Virginia: Geological Society of America Bulletin, v. 101. p. 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, v. 111. p. 1841-1860

Evans, M.A., 2010, Temporal and spatial changes in deformation conditions during the formation of the central Appalachian fold-and-thrust belt: Evidence from joints, vein mineral paragenisis, and fluid inclusions: Geological Society of America Memoir 206, p.477-552

Evans, M.A., Bedout, G.E., Brown, C.H., 2012. Changing fluid conditions during folding: An example from the central Appalachians: Tectonophysics, 576-577. p. 99-115

Garcia-Lopez, S., Bastida, F., Aller, J., Sanz-Lopez, J., 2001. Geothermal paleogradients and metamorphic zonation from the conodont alteration index (CAI): Terra Nova, v. 13. p. 79- 83

Harris, A.G., Harris, L.D. Epstein, J.B., 1978. Oil and Gas data from Paleozoic rocks in the Appalachian Basin: Maps for assessing hydrocarbon potential and thermal maturity (conodont alteration isograds and overburden isopachs): U.S. Geological Survey Map I- 917-E

Harris, L.D., de Witt, W., Jr., Bayer, K.C., 1982. Interpretive seismic profile along interstate I-64 from Valley and Ridge to Coastal Plain in central Virginia: U.S. Geological Survey Chart OC-123

Jacobeen, F., Jr., Kanes, W.H., 1974. Structure of Broadtop synclinorium and its implications for Appalachian structural style: American Association of Petroleum Geologists Bulletin, v. 58. p. 362-365

Jacobeen, F., Jr., Kanes, W.H., 1975. Structure of Broadtop synclinorium, Wills mountain anticlinorium, and Allegheny frontal zone: American Association of Petroleum Geologists Bulletin, v. 59. p. 1136-1150

MacInnis, M.S., Sanches, P.L., Bodnar, R.J., 2012. HokieFlincs_H2O-NaCl: A Microsoft Excel spreadsheet for interpreting microthermometric data from fluid inclusions based on the PVTX properties of H2O-NaCl: Computer & Geosciences, v. 49. p. 334-337

Parry, W.T., 1998. Fault-fluid compositions from fluid-inclusion observations and solubilities of fracture-sealing minerals: Tectonophysics, v. 290. p. 1-26 33

Perry, W.J., Jr., de Witt, W., Jr., 1977. A field guide to thin-skinned tectonics in the central Appalachians: American Association of Petroleum Geologists Annual Convention, Washington, D.C., Field Trip 4, p. 54

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Figure 1. Geology of Maryland modified from the Maryland Geological Survey. Bold line marks the approximate transect of the cross section.

Figure 2. Geology of Washington County Maryland. Modified from the Maryland Geological Survey.

Figure 3. Stratigraphic column of the central Appalachian Valley and Ridge Province. Stippling-Sandstone; Dashes-Mudstone/Shale; Blocks-Limestone; Slanted blocks- Dolostone. Modified from Evans (1989), Evans and Battles (1999), and Evans et al., (2012).

Figure 4. Types of fluid inclusions found within the Pocono Formation. a) Two-phase primary inclusion. Note the irregular shape and size compared to inclusions in b and c. b) secondary inclusions within a fluid inclusion plane (FIP). Note that the inclusions are much smaller than a primary inclusion and more rounded, c) pseudosecondary inclusions in a planar array. Notice that the inclusions are similar to secondary inclusions but that the plane ends within the crystal and not at a crystal boundary.

Figure 5. Example of Pressure/Temperature diagram for the ThH isochore method. This method results in a range of possible trapping condition between where the isochore crosses the hydrostatic and lithostatic gradients. Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

Figure 6. Example of a Pressure/Temperature diagram using the geothermal gradient method to determine trapping conditions. As with the ThH isochore method, limits for trapping pressure and temperature are determined where the isochore crosses the different pressure gradients. Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

Figure 7. Example of pressure/Temperature diagram for a coeval set of inclusions and the trapping conditions determined from this method. The trapping conditions in this sample represent actual trapping pressures and temperatures, not a range or maximum. . Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

Figure 8. Collection locations for samples. All samples were collected along the crest of Sideling Hill. Photo courtesy of Google Earth.

Figure 9. Map of sample WP-05-1. Older veins are oriented bottom left to top right with younger veins oriented left to right cutting across the older veins .

Figure 10. Map of sample WP-05-2 highlighting cross cutting relations. The oldest vein is the vein oriented top left to the bottom right and is cut twice by younger veins oriented top right to bottom left.

Figure 11. Cross cutting relations of sample TH-26.The older vein is oriented top left-bottom right with a younger vein cutting across oriented left-right.

30 Frequency 20

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 Temperature (C)

30 Frequency 20

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 Temperature (C)

Figure 12. Histograms of CH4 homogenization temperatures for older (top) and younger (bottom) veins.

Figure 13. Volume vs composition plot for older (top) and younger (bottom) veins. Data points show that fluids are mostly greater than 90% CH4.

o ThA ( C) 100 150 200 250 300 350 0 WP-18 -1 WP-13

-2 WP-05-1 WP-05-2 -3 TH-28 -4 TH-26 C) o ( -5 TH-25-1 mIce

T TH-25-2 -6 SS-70-2 -7 MP-2 (Secondary) -8 WP-3B (Secondary) SS-70-2 (Secondary) -9

-10

Figure 14. Composite TmIce vs ThA plot of all samples. See Appendix A for data. 48

o ThA ( C) 100 150 200 250 300 350 0

-1

-2

-3 Older -4 Younger C) o ( -5 Average of Younger

mIce Average of Older T -6

-7

-8

-9

-10

Figure 15. TmIce vs ThA plot with the samples divided based relative on age.

500

400

L 20 300 L 25 L 30 H 20 200 Pressure Pressure (MPa) H 25 H 30 100 ThA

0 0 100 200 300 400 500 Temperature (oC)

o Figure 16. ThA isochore for older veins. Trapping temperatures range from 203 to 228 C with pressures ranging from 54 to 98 MPa. Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

500

400

L 20 300 L 25 L 30

200 H 20 Pressure Pressure (MPa) H 25 H 30 100 ThH

0 0 100 200 300 400 500 Temperature (C)

Figure 17. ThH isochore for older veins. This isochore indicates minimum trapping conditions of 225 oC and 97 MPa. Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

500

400

ThH 300 L 20 L 25

200 L 30 Pressure Pressure (MPa) H 20 H 25 100 H 30

0 0 100 200 300 400 500 Temperature (oC)

o Figure 18. ThA isochore for younger veins. Trapping conditions range from 305 to 355 C with pressures of 89 to 159 MPa. Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

500

400

L 20 300 L 25 L 30

200 H 20

Pressure Pressure (MPa) H 25

100 H 30 ThH

0 0 100 200 300 400 500 Temperature (C)

Figure 19. ThH isochore for younger veins. Range for trapping conditions determined to be 155 to 425 oC at pressures of 64 to 129 MPa. Key: L=Lithostatic, H=Hydrostatic and the value following is the assumed geothermal gradient (e.g., L 20 = lithostatic pressure gradient geothermal gradient of 20 oC/km)

500

L 20 L 25 L 30 400 H 20 H 25 H 30 WP-05-1 Vein Set 1 Coeval 1

300 WP-05-1 Vein Set 1 Coeval 1 WP-05-1 Vein set 1 Coeval 2 WP-05-1 Vein set 1 Coeval 2 TH-25-1 Coeval 1

Pressure Pressure (MPa) TH-25-1 Coeval 1 200 TH25-1 Coeval 2 TH25-1 Coeval 2 WP-05-2 Vein set 1 Coeval 1 WP-05-2 Vein set 1 Coeval 1 100 WP-05-2 Vein set 1 Coeval 2 WP-05-2 Vein set 1 Coeval 2 WP-13 Coeval WP-13 Coeval

0 0 100 200 300 400 500 Tempeature (oC)

Figure 20. Composite plots of all coeval isochores. Dotted lines represent lithostatic gradients and dashed lines represent hydrostatic pressure gradients using geothermal gradients of 20, 25, and 30 oC/km. 60

APPENDIX A. MICROTHERMOMETRIC DATA WP-18 AQUEOUS METHANE Te Tm Th Tm-CO2 Th-CH4 -31.1 -4.3 142.3 -2.4 146.6 140.9 -2.8 154.8 156 -2 174.8 -1.9 160.8 140.1 145.7 159.6 -5.2 140.8 133.8 -6.8 156.2 112.3 -2.5 150.7 -3.2 142.9 -4.4 141.5 -3.4 156.9 -3.2 165.9 141.8 -3.4 149 -2.4 141.7 -3.1 142.8 -4.4 143.7 -2.4 134.8

WP-13 AQUEOUS METHANE Te Tm Th Tm-CO2 Th-CH4 -51 -7.3 210.5 -97.1 -41.2 -7.8 223.2 -96.4 -56.2 -9.1 204.5 -82.3 -41 -8.5 214.8 -95.7 -46.4 -9.3 217.5 -102.4 -90 -42.3 -5.7 218.1 -103.8 -92.5 -4.5 220.3 -98.1 -95.1 -29 -3.1 247.8 -93.4 288.3 -95.8 -83.4 -5.9 279.6 -102.1 -84.9 -36.2 -6.4 191.1 -114.9 -97.2 -6.6 -90.8 -6.6 214.3 -115.2 -107.7 -6.6 154.4 -116.8 -98.8 -37.8 -5.8 193.3 -105 -94.4 61

-37.8 -7.5 -97.1 -82.6 -6.2 183.9 -81.3 -35.2 -8.6 224.5 -81 -6.6 159.4 -104.2 -86.5 -5.9 -106.1 -86.5 -100.9 -76.8 -92.7 -82.6 -82.5 -87.7 -87.8 -84.7 -84.7 -84.7 -81.1 -83.2 -83.2 -83.2 -87.9 -86.4 -85.3 -96.7 -85.1 -96.7 -85.1 -88.9 -86.1 -83.4 -87.7 -87.5 -89.8 -84.1 -86.3 -89.8 -80.9 -94.7 -87.9 -116.1 -83.7 -104.9 -83.7 -95.9 -86.7 -101.9 -87.8 -85.4 -84.3 -102.3 -83.3 -116 -102.6 -116 -90.7 -103.1 -103.1 -83.7 -85.2 -84.8 -84.8 -86.6 -85 -87.6 -86.1 -103 -88 -85.2 -81.9 -103.2 -93.5 -90.3 62

-81.7 -81.8 -82.5

WP-13(Secondary) AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -87.2 -95 -85.6 -101.7 -85.6 -94.7 -96.4 -96.4 -84 -90.8 -86.9 -108.1 -82.9 -106.9 -85.1 -102.1 -85.7 -103.1 -90.1 -90.1 -89.9 -101.9 -89.9 -95.2 -88.2 -81.2 -96.2 -98 -85.5 -99.3 -91.3 -100.3 -85.4 -108.9 -84.8 -86.5 -85 -87.5 -86.1 -92.8

WP-05-1 AQUEOUS METHANE Te Tm Th Tm-CO2 Th-CH4 -4.8 231.3 -101.2 -88.7 -39.6 -4.2 226.6 -81.8 -2.9 223.6 -91.8 -85.2 260.4 -97.2 -92.8 -5.4 226.5 -105.1 -90.8 233.2 -95.2 -90.7 251.6 -95.2 -89.8 264.7 -95.2 -88.8 -5.8 212.2 -95.2 -88.1 233.5 -95 -3.5 237.7 -113.4 -102.1 222.5 -87.2 -84.4 -4.9 152.9 -108.2 -86.1 -41.7 -4.2 183.3 -88.2 -41.7 -4.2 186.2 -108.9 -82.1 -53.9 -5.3 160.7 -97 -87.2 63

-53.9 -3.4 160.7 -95.7 -81 -53.9 -3.4 160.7 -84.8 -80.7 -4.9 181.2 -97.4 -80.3 -39 -3.9 188.2 -81.7 -80.2 -45.3 -2.6 246.7 -80.5 -3.9 193.5 -96.9 -80.6 -37.8 -5.5 197.8 -99 -81 -5.5 197.8 -95.1 -80.9 -0.4 174.2 -89.6 -82.8 -0.4 120.8 -82.8 -9.2 180.1 -95.1 -80.7 244.2 -105.2 -81 -6.3 236.5 -98.1 -80.2 -5.4 243.9 -81.9 141.4 -90.8 -82.9 230.2 -96.2 -83.1 -4.3 155.7 -98.3 -82.2 -5.4 193 -98.3 -83.1 -8.1 219 -96.4 -84.8 228.8 -90.6 -84.9 -97.6 -84.8 -90.1 -84.8 -98.1 -84.2 -98.1 -83.1 -97.4 -85 -104.4 -91.1 -100.8 -95.7 -94.2 -101.8 -103.3 -91.8 -97.9 -104.5 -99.1 -87.9 -95.3 -82.1 -100.5 -84.7 -104.7 -82.9 -88.8 -88.8 -88.3 -83 -95.1 -89.6 -105.5 -85.8 -105.6 -83.5 -92.9 -84.6 -80.1 -86.3 -82.7 -79.4 -94.8 -95.2 -89.9 -80.8 64

-82.8 -93.6 -83.9 -87.4 -104.8 -109.4 -85.7 -90.4 -80.4 -97.8 -89.7 -86.2 -85.3 -96.1 -100.7 -86.6 -94.4 -97.8 -94.6 -83.2 -85.8 -83.8 -97.4 -86.6 -94.4 -97.8

WP-05-1 AQUEOUS METHANE Te Tm Th Tm-CO2 Th-CH4 -3.8 180.1 -81.7 -4.2 184.2 -79.7 -4.6 179 -81.5 -2.3 165 -80.6 -45.2 -4.5 181.2 -80.6 -28.3 -5.1 189.7 -106.4 -83.7 -4.4 161.8 -95.2 -86.3 -30.7 -4.2 224.4 -93.6 -83 -3.2 197.1 -84 -4.5 186.6 -80.6 -5.4 157.1 -80 -6 197.7 -5.2 152 -53.3 -7.1 196.7 -81.4 -5.4 193.5 -97.1 -84.3 -4 202.2 -85.1 197.8 -81 -82.2 -81.7 -92 -90.2 -101 -79.4 -102.6 -84.7 -81.2 65

-82.4 -83.8 -83.2 -85.7 -82.4 -96.4 -84.7 -96.4 -84.3 -97.8 -82.3 -82.3 -90.4 -81.5 -85.5 -87.9 -84.6 -86.5 -81.2 -90 -80.7 -81.4 -81.2 -83 -81.1

TH-28 AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -34.7 -4.6 162 -80.1 -4.4 145.9 -78.9 -29.8 -4.9 154.2 -84.4 -4.2 169.3 -84.4 -3.9 166.1 -86.6 -85.8 -4.2 204.4 -87.5 -90.1 -4.4 163.7 -91.2 -4.4 194 -75 -32.7 -3.7 210.6 -76.1 -3.5 209.7 -75 -86.1 -86.1 -89.4 -86 -86.3 -84.4 -86.4 -85.8 -96 -83.7 -90.4 -80.1 -87.5 -93.1 -90.4 -78.7

-84.6 -78.8 -103.4 -82.4

TH-26 AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -42.1 -2.1 167.7 -82.4 -2.1 284.2 -106.8 -91 -2.1 199.4 -80.3 -4.6 221.6 -87.8 -45.2 -3.5 181.1 -84.4 -3.9 -81.7 -2.5 169.7 -97.8 -5.4 168 -85.8 -30.7 -4.9 183.1 -77.9 -39.3 -3.6 187.3 -93.6 -4.5 191 -82.3 -5.8 203.4 -80.7 -5.9 171.8 -80.4 -88.8 -104.3 -85.5 -82.3 -84.2 -86.4 -81 -84.4 -82.8

TH-25-1 AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -35 -4.6 183.6 -86.9 -3.1 153.2 -84.8 -3.8 114.2 -92 -87.8 -4 192.7 -94.7 -89.8 -39.1 -8.7 -82.3 -5.1 217.4 -83.7 -4.4 180.8 -83.8 -4.3 187.6 -83.7 -3.6 172.4 -83.7 -3.9 185.6 -95.8 -87.2 -36.7 -4.3 180.6 -87.3 -4.3 174.9 -95.3 -4.3 -92.5 -42.3 -4.1 207.2 -92 -4.1 -85.1 -4.4 151.5 -79.4 67

-4.4 161.2 -80.4 -4.4 172.9 -87.3 -31.8 -3.8 158.4 -101.9 -83.7 -3.2 182.4 -80.6 131 -81.3 -4 172 -78.8 -81.2 -80.2 -79 -98.2 -80.2 -82.8 -82.8 -79.3

TH-25-2 AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -4.7 188.8 -116.8 235 -116.8 -4.6 169.2 -117.2 -107.9 -5 169.2 -101.1 -4.2 188.2 -99.1 -4.8 247.3 -91.2 -99.2 -101.1 -113.5 -110.9 -89.3 -100.8 -94.1 -99.3 -95.1 -102.6 -103 -89.8 -95.2 -88.1 -99.7 -96.5

TH-24 AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -7.2 -8.1 110 -5.2 -7.3 68

SS-70-1 AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -112.9 -84.1 -112.9 -84.1 -112.1 -82.2 -112.1 -82.2 -111.6 -84.6 -85 -85 -85 -114 -88.9 -106.6 -86.6 -106.6 -86.6 -106.6 -86.6 -106.6 -86.6 -99.6 -85.3 -90.2 -82.5 -81.2 -92.6 -85.1 -101.9 -90.2 -115.4 -90.7 -110.9 -93.5 -107.6 -85.5 -107.6 -85.5 -118.4 -96.6 -118.4 -96.6 -104.5 -84.2 -104.5 -84.2 -104.5 -84.2 -109.7 -87.4 -109.7 -87.4 -109.7 -87.4 -103.1 -84.9 -80.4

SS-70-2 Aqueous Carbon Dioxide Te Tm Th TmCO2 Te TmH2O TmClath ThCO2 Th total -1.8 307.2 -56.9 -32.6 -2.7 22.6 -0.9 309.4 10.5 -2.5 337.9 -59.3 307.5 -60 12.9 -2 312 -59.4 7.2 -2 309.7 -57.1 10.2 -0.7 289.9 -59.5 15.7 324.9 0.7 69

0 197 -61 11.9 0 251.8 -59.3 14.5 343 0 216.4 -59.4 11.9 339.9 0 193.2 -58.8 342.3 -58.5 11.4 -60.3 355.9 -60.1 -1.8 18.2 312.7 -62.2 8.7 17.3 323.2

MP-2(Secondary) AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -8.7 153 -84.2 -8.3 165.3 -83.1 -79.6 -81.8 -80.8 -80.4 -83.7 -83.8 -103.2 -81.2

WP-3B(Secondary) AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 130.4 -88.9 -7.9 152.5 -88.9 -9 147.4 -81 -90.5 -89 -91.6 -90.8 -85.2 -94.1 -87.5 -87.2

WP-3V AQUEOUS METHANE

Te Tm Th Tm-CO2 Th-CH4 -68.8 -79 -80.1 -78.4 -77.2 -93.4 -77.3 -81.2 -79.8 70

APPENDIX B. HISTOGRAMS

ThA for Older Veins 30

15 Frequency 10

0 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 Temperature (C)

ThA for Younger veins 30

15 Frequency 10

0 100 110 120 130 140 150 160 170 180 190 200 210 220 230 240 250 260 270 280 290 300 310 320 330 340 350 Temperature (C) 71

TmIce for Older Veins 40

20 Frequency

0 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 Temperature (C)

TmIce for Younger veins 40

20 Frequency

0 0 -1 -2 -3 -4 -5 -6 -7 -8 -9 -10 Temperature (C) 72

Te for Older Veins 10

5 Frequency

0 -20 -25 -30 -35 -40 -45 -50 -55 -60 Temperature (C)

Te for Younger veins 10

0 -20 -25 -30 -35 -40 -45 -50 -55 -60

ThH for older Veins 60

30 Frequency 20

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 Temperature (C)

ThH for Younger veins 60

Frequency 20

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 Temperature (C)

TmCO2 for Older veins 20

10 Frequency

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 Tmeperature (C)

TmCO2 for Yougner veins 20

10 Frequency

0 -65 -70 -75 -80 -85 -90 -95 -100 -105 -110 -115 -120 -125 Temperature (C)