ABSTRACT Organic-rich mudstones of the Appalachian Basin hold a sizable portion of the natural gas produced in the United States. Indeed, in 2015, Pennsylvania and West Virginia accounted for 21% of produced natural gas, driven in part by production from the Point Pleasant Limestone. The critical role that unconventional reservoirs will play in future global energy use necessitates the need for an enhanced understanding of those geological aspects that shape and influence their reservoir architecture. Foremost among these is a clearer understanding of the preservation and accumulation of organic carbon, as it is the source of hydrocarbons, and often provides the dominant host of interconnected porosity and hydrocarbon storage. To this end, pyrite morphology can offer insight into the redox conditions of the bottom and pore water environment at the time of sediment deposition and early diagenesis and can be especially useful in the analysis of deposits devoid of redox sensitive trace metals. Pyrite contained in cuttings and core chips retrieved from vertical and horizontal Point Pleasant Limestone wells were analyzed by scanning electron microscope. Results demonstrate a dearth of pyrite in the Point Pleasant (0.02–1.7% of the surface area analyzed). Pyrite morphology is dominated by euhedral grains and masses (~80% of pyrite encountered) co-occurring with infrequent framboids. Framboids are uniformly small (average = 4.7 μm) with just a few examples >10 μm. The presence of small amounts of euhedral pyrite grains and masses is consistent with accumulation under a dysoxic water column. Conversely, the size of the framboids suggests that they formed in a water column containing free hydrogen sulfide. A model invoking a lack of reactants necessary to sustain diagenetic pyrite growth in anoxic pore waters may explain this apparent paradox. In such a case, the framboid size distribution may reflect newly forming diagenetic framboids competing for a finite amount of reactants resulting in a population of small framboids and few large examples. Indeed, the low total iron/aluminum (Fe/Al) content of the Point Pleasant (average Fe/Al = 0.45) would indicate a low delivery of reactive iron to the seafloor during Point Pleasant deposition. The data suggests a model in which organic carbon preservation occurred by rapid burial and removal from oxygen-bearing water. In turn, more organic-rich and potentially higher quality reservoir facies of the Point Pleasant Limestone occur in areas of higher clastic delivery to basin.

Abstract The Point Pleasant-BrassfieldO) petroleum system, located in eastern Ohio and western parts of Pennsylvania and West Virginia, created a charge of 150 billion bbl of oil equivalent. The system covers 40,000 km 2 and encompasses numerous small oil and gas fields in eastern Ohio. Sedimentary rocks included in this system are Ordovician-Triassic in age and were deposited in the Appalachian basin. Several source rocks exist within the basin, including shales of the Ordvocian Point Pleasant Formation, the Devonian Ohio Shale and Olentangy Shale, and the Mississippian Sunbury Shale. Most of the oil in the Silurian Clinton reservoir rock (Brassfield Formation) originated from the Point Pleasant Formation. Oil generated from the Point Pleasant source rock has chemical characteristics similar to early Paleozoic oils. Based on paraffin indices, oil from this source rock is very mature to supermature and has lost most biological markers. Generation-migration-accumulation lasted from Point Pleasant deposition in Middle Ordovician time through maximum deposition in the Late Triassic-Early Jurassic, a duration of about 250 m.y. The mass of hydrocarbons generated by the source rock in the Point Pleasant Formation totaled 75 billion bbl of oil. Of this, some found its way to traps with Silurian reservoir rocks on the east flank of the Cincinnati-Findlay arch. Only 400 million bbl of in-place oil can be accounted for in known fields. The remaining oil and gas generated by the Point Pleasant source rock was probably lost in subeconomic accumulations along the migration pathway between the pod of active source rock and the geographic extent of the Point Pleasant-Brassfield petroleum system.

Abstract The top surface of the Trenton Limestone and equivalent carbonate units has be variously described as a subaerial exposure surface (paleokarst), a submarine erosion surface, and a submarine hardground. Detailed study of the contact between the carbonates and overlying shale in outcrop and core and regional stratigraphic analysis indicate that the surface represents a drowning unconformity on the Galena and Lexington carbonate platforms in Ohio and Indiana. This unconformity also appears within the Sebree Trough in Indiana between the platforms, but it is within the overlying shale section rather than at its base. The unconformity has not been recognized in the Point Pleasant Basin in central and southern Ohio. Paleokarst may locally exist on this surface in southern Ontario.

A new stratigraphic and structural synthesis is presented for Precambrian rocks of the Adirondack Mountains, New York, an amphibolite-granulite facies terrane in the 1.1-b.y.-old Grenville province exposed in a dome on the North American craton. The geology of the Adirondacks appears to be explicable in terms of a stratigraphic sequence that has been subjected to multiple folding, metamorphism, and intrusive activity. This stratigraphic sequence is correlated across the entire width of the Adirondacks and westward into Ontario. Recognition of the widespread nature of this stratigraphic sequence has resulted in a coherent structural framework for the Adirondacks, consisting of two stages of nappe formation followed by three stages of upright to overturned folding. Both widespread intrusive activity and subsequent mylonitization of intrusive rocks occurred mostly during the second phase of nappe formation. The stratigraphy of the Adirondacks is interpreted to consist of an older granitic basement, referred to as the Piseco Group, overlain unconformably by a metamorphosed clastic/carbonate sequence, referred to as the Oswegatchie Group in the northwest and the Lake George Group in the east. The oldest recognized formation in the Piseco Group is the Pharaoh Mountain Gneiss, consisting of charnockitic and granitic gneiss. This unit is overlain in many places by the Alexandria Bay Gneiss, consisting of pink leucogranitic gneiss. The Alexandria Bay Gneiss is equivalent to the Brant Lake Gneiss in the eastern Adirondacks. The basal formation of the metasedimentary rocks of the Oswegatchie Group is the Baldface Hill Gneiss. This thin and discontinuous unit consists of garnet-sillimanite gneiss and quartzite. The overlying Poplar Hill Gneiss consists of biotite-quartz-plagioclase gneiss that contains granitic portions. Rocks of the Baldface Hill and Poplar Hill may represent metamorphosed basal quartz sand and conglomerate, shale, shaly arkose, and possibly reworked Fe- and Al-rich regolith that was formed by weathering of the basement prior to deposition of the cover rocks. The Baldface Hill and Poplar Hill are equivalent to the Eagle Lake Gneiss of the Lake George Group. Overlying these thin basal clastic deposits of the Oswegatchie Group is the Gouverneur Marble that consists of five members, two of which contain three subdivisions within them. Member A at the base consists of thick, calcitic, dolomitic, and siliceous marbles. Member B is a thin, pyritic biotite schist. Member C consists of interbedded siliceous marbles, quartzites, and calc-silicate rocks. Member D consists of well-layered calcareous gneiss, and Member E, only locally present, is a quartz-feldspar granulite. To the east, the Gouverneur Marble correlates with carbonate rocks of the Cedar River, Blue Mountain Lake, and Paradox Lake Formations, and correlates via facies changes to metamorphosed calcareous clastics of the Cranberry Lake, Sacandaga, Tomany Mountain, and Springhill Pond Formations. The previously defined upper and lower marble may be stratigraphically equivalent in the Northwest Lowlands and possibly in the Adirondack Highlands. The Pleasant Lake Gneiss overlies the Gouverneur Marble and consists largely of migmatitic gneiss equivalent to the Treadway Mountain Formation of the Lake George Group. K-feldspar megacrystic granitic gneisses overlie the Pleasant Lake Gneiss. These rocks are equivalent to the Lake Durant Formation in the Lake George Group and probably represent intrusive sheets. Anorthosite, charnockite, hornblende granite, and gabbro successively intruded the metamorphosed sedimentary rocks and themselves were later metamorphosed and deformed. Mangerite-charnockite suites that mantle anorthosite contain xenoliths of anorthosite and are thought to be produced by partial melting of Pharaoh Mountain Gneiss by heat from the anorthosite. Megacrystic hornblende granitic gneisses intrude various formations of the Lowlands and Highlands but show gross structural concordance. Five phases of folding affected all stratigraphic units, but only the last four phases affected the intrusive rocks. The first phase of folding resulted in northwest-directed nappes and formation of regional foliation and lineation. A second phase of isoclinal folding folded the regional foliation and lineation. Intrusion of anorthosite, charnockite, hornblende granite, and gabbro accompanied second-phase folding, as well as local mylonitization of charnockite and local thrusting. The third-phase folds are upright to overturned and responsible for the “grain” of the Adirondacks. The axial traces of these folds form an arc convex to the north that swings continuously from N70°W to east-west to N45°E from south to northwest. Peak 1.1 to 1.02-b.y.-old granulite facies metamorphism outlasted third-phase folding in the Adirondack Highlands and second-phase folding in the Lowlands. Fourth-phase, northwest-trending folds are open and best developed in the northwestern Adirondacks, where they are associated with retrograde metamorphism and possibly with intrusion of diabase dikes at mid-amphibolite facies. Fifth-phase, north-northeast-trending folds are open and best developed in the Adirondack Highlands, where they are associated with retrograde metamorphism and with 930-m.y.-old pegmatite dikes. The fourth- and fifth-phase folds interfere with third-phase folds to produce dome and basin map patterns. Hook and heart and anchor map patterns result from interference of the later folds with first- or second-phase isoclinal folds.

Abstract The Michigan structural basin is symmetrically centered in the Southern Peninsula of Michigan and extends outward into surrounding states and the Province of Ontario. Outcrops of Precambrian rocks bound the basin to the north; on the east the Algonquin axis in Ontario is the basin border, and to the south and west, the limiting features are the Findlay and Kankakee arches of northern Ohio and Indiana and the Wisconsin arch in central Wisconsin. Paleozoic rocks crop out, or underlie the glacial drift, in circular bands with the youngest rocks occurring near the center of the Southern Peninsula where the floor of the Paleozoic rocks in the basin reaches its maximum depth of about 14,000 feet. Oil production in the Michigan basin had its beginning at Petrolia in Ontario in 1858, but production in volume began with the discovery of the Muskegon field on the west side of the basin and the Mount Pleasant field near the center of the basin in 1928. Approximately 270 oil fields and more than 100 gas fields have been discovered in the basin. The Michigan basin contains about 108,000 cubic miles of sedimentary rocks of which about 80 per cent is Cambrian, Ordovician, and Silurian in age, and most of the remainder Devonian in age. Lithologically, carbonate rocks constitute 47 per cent of the sedimentary rocks of the basin, 12 per cent being evaporites, and the remaining 41 per cent sandstones and shales. More than 95 per cent of the oil has come from carbonate rocks of Middle Devonian age, and most of the gas is from sandstones of Mississippian age. The oil yield to date amounts to 3,700 barrels per cubic mile of sedimentary rock. The producing formations, from oldest to youngest, are the Black River and Trenton limestones of Middle Ordovician age, the upper part of the dolomite of the Niagara Series of Middle Silurian age, and dolomite in the lower part of the Salina formation of Late Silurian age, various limestones and dolomites of Middle and Late Devonian age including the Detroit River group, the Dundee and Rogers City limestones, and Norfolk formation of Canada, the Traverse group, and sandstones of Mississippian age. Accumulation of oil is largely anticlinal, with northwest-southeast trends predominating in the central basin area. Most of the folding took place during late Paleozoic time. The greater part of the oil has been produced from porous zones below unconformities. This is due mainly to the development of secondary porosity at the top of the limestones, but some accumulations beneath unconformities are in porous zones due to secondary dolomitization.

Abstract This three-day field trip will examine the nature of contemporary tectonic processes in the western Basin and Range province by focusing on the historical faulting and paleoseismology of the central Nevada seismic belt (CNSB) (Fig. 1 ). The trip begins in Reno and includes travel through Fallon, Nevada to major faulting sites in the 1954 Rainbow Mountain, Fairview Peak, and Dixie Valley rupture area ~125 km east of Reno (Fig. 2 ). The principal topics addressed by this trip will include: Map showing surface ruptures (bold lines) and focal mechanisms reported for major historical earthquakes of the central Nevada-eastern California seismic belt. Other Quaternary faults of the Basin and Range are shown as thinner lines. Compressional quadrants of focal mechanism are black. Focal mechanisms are from Doser (1986) and the National Earthquake Information Center. Area of Figure 2 is shown by the gray box. Within the central Nevada seismic belt, right-normal-oblique surface ruptures of 1954 Rainbow Mountain-Fairview Peak sequence mark a transition between dominantly right-lateral events to the south within the northwest-trending Walker Lane belt ( Stewart, 1988 ), and the dominantly dip-slip Dixie Valley and Pleasant Valley earthquakes to the north, where the Basin and Range is characterized by a consistent north-to northeast-trending structural grain. The structural pattern, distribution, and characteristics of surface faulting and secondary effects associated with large-magnitude historical earthquakes as they bear on the nature of modern tectonic processes in the CNSB. The paleoseismicity of the historical fault zones within

ABSTRACT The Middle Devonian Marcellus shale play has emerged as a major world-class hydrocarbon accumulation. It has rapidly evolved into a major shale gas target in North America and represents one of the largest and most prolific shale plays in the world with a prospective area of approximately 114,000 km 2 (44,000 mi 2 ). Two major core areas have emerged, each with a unique combination of controlling geologic factors. Production from the Marcellus play reached 16 billion cubic feet of gas equivalent per day (BCFepd) in 2015, and it has been recognized as the largest producing gas field in the United States since 2012. The organic-rich black shales comprising the Marcellus shale were deposited in a foreland basin that roughly parallels the present-day Allegheny structural front. The Marcellus shale accumulated within an environment favorable to the production, deposition, and preservation of organic-rich sediments. The key geologic and technical factors that regionally define the Marcellus play core areas include organic richness, thermal maturity, degree of overpressure, pay thickness, porosity, permeability, gas in place, degree of natural fracturing, mineralogy, depth, structural style, lateral target selection, completion design, and important rock mechanics issues such as the ability to be fractured, rock brittleness versus ductility, and the ability to generate complex fractures. Structural setting and deformation styles are critical to address natural fracture trends, potential geologic hazards such as faulting and fracturing in structurally complex areas, and fracture stimulation containment issues. Since the Marcellus shale unconventional shale gas reservoir discovery in 2004 until May 2015, more than 8600 horizontal Marcellus shale wells had been drilled in Pennsylvania, West Virginia, and limited portions of eastern Ohio. Many decades of future drilling potential remain due to the enormous extent of the Marcellus shale play. Horizontal Marcellus wells report initial production rates ranging from less than 1 MMCFe/day to over 47.6 MMCFe/day. Despite the large number of wells drilled and completed to date and production of 16 BCFepd in 2015, the play is still in its infancy due to its vast geographic extent and production potential. The Marcellus shale represents a continuous-type gas accumulation and when fully developed will comprise a large continuous field or series of fields. Over its productive trend, the Marcellus shale play has significant additional reserve potential in the overlying organic shales in the Devonian Age Rhinestreet, Geneseo, and Burket units as well as deeper potential in the Ordovician Age Utica/Point Pleasant units. Estimates of recoverable reserves from the world’s largest gas fields combine their reserve estimates for all key productive units in the field/play trend. Likewise, estimates of in-place gas resources for the Marcellus play range from 2322 tcf for the Marcellus (Hamilton Group) to over 3698 tcf for the combined Devonian Age Marcellus-Geneseo-Rhinestreet system. This represents the largest technically accessible in-place gas resources in the world.