Northern Appalachian Basin Research Articles

Changes in soils and terrestrial landscapes of the Appalachian Basin (Conemaugh, Monongahela, and Dunkard groups), U.S.A., at the onset of the late Paleozoic climate transition

ABSTRACT Changes in global climate from the Late Pennsylvanian to early Permian resulting from the destabilization of ice sheets in the Southern Hemisphere had important effects on terrestrial landscapes around the Paleozoic world. In the northern Appalachian Basin (U.S.A.), evidence for this transition and its effects on terrestrial systems is preserved in numerous paleosols in the Conemaugh, Monongahela, and Dunkard groups that formed in various alluvial environments. Several studies along a 50 km west–east and 40 km north–south transect through southeast Ohio and southwest West Virginia resulted in the recognition of 24 different pedotypes. An up-section shift in pedotypes from Argillisols to Vertisols and Calcisols as well as an overall upward increase in the diversity of pedotypes records a significant change in soil-forming processes and landscapes. The landscapes of the Late Pennsylvanian were largely characterized by well-developed, clay-rich Alfisols of woodland ecosystems on distal floodplains bordered by poorly developed Inceptisols of early successional or marshland ecosystems on proximal floodplains. By the early Permian, these landscapes began to experience strongly seasonal climates and increasingly prolonged dry periods, resulting in the production of pronounced shrink–swell features and well-developed carbonate horizons. These landscapes were characterized by Vertisols and Inceptisols of highly heterogeneous brakeland ecosystems, with rapid changes in sedimentation, hydrology, and vegetation over short distances. Climatic conditions were prone to fluctuations between wet and dry states during the transition, resulting in a highly heterogeneous landscape that changed significantly through time.

Body-size reductions in dacryoconarid tentaculitoids during Late Devonian warming

Body size is an essential factor in an organism’s survival, and when paired with paleoenvironmental proxies, size trends can provide insights into a lineage’s evolutionary responses to changing environmental conditions. This study explores the diversity and body-volume trends of dacryoconarid tentaculitoids, globally abundant marine zooplankton, in the Devonian of the Appalachian Basin (eastern United States), spanning the late Givetian through the middle Frasnian punctata carbon isotope excursion. Using statistical approaches to model trends, we find evidence of a gradual, within-lineage reduction in styliolinid adult body sizes starting at the Givetian-Frasnian boundary. This reduction is followed by a significant decrease in both adult and initial chamber volumes during the punctata excursion. At the Givetian-Frasnian boundary, annulated forms (nowakiids) become rare and smooth forms (styliolinids) begin to dominate the assemblage. Using pre-existing geological and geochemical data sets, we consider environmental factors, including sea level, anoxia, nutrient availability, and temperature, as potential drivers of body-size reductions. Bottom-water anoxia most likely did not influence body-size trends of this pelagic group, but frequent water-column overturning in the Frasnian or other exchange between deep and shallow water may have affected taxonomic composition, favoring styliolinids. Sea-surface temperature correlates inversely with body size, suggesting that warming beginning in the early Frasnian may have contributed to gradual, long-term size reductions. Rising temperatures through the middle Frasnian may have led to the disappearance of dacryoconarids in the northern Appalachian Basin after the excursion.

Comparative organic geochemistry of shale deposits of northern Appalachian Basin

The organic-rich black shales in the Appalachian basin are a vital producer of natural gas. In this study, we present new multiproxy geochemical data from the Ordovician and Devonian black shales in New York (NY) and Pennsylvania (PA). The samples include outcrop samples collected in NY (Utica Group and Marcellus Formation) and core samples from PA (Marcellus Formation, Skaneateles Formation, and Genesee Group). We combined organic geochemical data (% total organic carbon or %TOC, δ13Corg, C/N ratio, and lipid n-alkane distribution) with trace element (TE) data to identify the organic matter (OM) sources and depositional conditions. The TE analysis data shows that water conditions were variable during the deposition of these black shales, fluctuating between oxic and dysoxic conditions with occasional anoxia. There was probably a change from an open water condition (Co∗Mn = 0.2) during the deposition of the Flat Creek Formation to a more restricted exchange later during the deposition of the Indian Castle Formation (Co∗Mn = 2.9) in the Ordovician. Basin circulation likely remained restricted during the deposition of the Devonian black shales (Co∗Mn ranges from 0.4 to 1.3). Based on δ13Corg values (−32.9‰ and −29.6‰) that are more depleted than marine OM δ13Corg, C/N ratios (11.2 and 9.2) higher than marine OM, and the presence of longer chain n-alkanes in the range of C25 to C33, we suggest that bryophytes were possibly a significant organic source to the Ordovician Utica Group in NY. The kerogen type in Utica Group samples is type III, mostly terrestrial OM. The Devonian NY and PA samples show mostly bimodal distributions. In some samples, a secondary, though sometimes dominant, shorter chain peak in the range of C14 to C20 is present, in addition to the long chain peak. We suggest the bimodal n-alkane distribution signifies a mixed OM source consisting of terrestrial and marine contributions with differing degrees of thermal maturation compared to the samples with a unimodal distribution. Our results suggest that samples from the NY Marcellus Group are composed of type III kerogen, while samples from the PA Marcellus Formation, Skaneateles Formation, and Genesee Group contain both type II and type III kerogens.

Social Vulnerability and Groundwater Vulnerability to Contamination From Unconventional Hydrocarbon Extraction in the Appalachian Basin.

Unconventional oil and gas (UOG) development, made possible by horizontal drilling and high-volume hydraulic fracturing, has been fraught with controversy since the industry's rapid expansion in the early 2000's. Concerns about environmental contamination and public health risks persist in many rural communities that depend on groundwater resources for drinking and other daily needs. Spatial disparities in UOG risks can pose distributive environmental injustice if such risks are disproportionately borne by marginalized communities. In this paper, we analyzed groundwater vulnerability to contamination from UOG as a physically based measure of risk in conjunction with census tract level sociodemographic characteristics describing social vulnerability in the northern Appalachian Basin. We found significant associations between elevated groundwater vulnerability and lower population density, consistent with UOG development occurring in less densely populated rural areas. We also found associations between elevated groundwater vulnerability and lower income, higher proportions of elderly populations, and higher proportion of mobile homes, suggesting a disproportionate risk burden on these socially vulnerable groups. We did not find a statistically significant association between elevated groundwater vulnerability and populations of racial/ethnic minorities in our study region. Household surveys provided empirical support for a relationship between sociodemographic characteristics and capacity to assess and mitigate exposures to potentially contaminated water. Further research is needed to probe if the observed disparities translate to differences in chemical exposure and adverse health outcomes.

Natural and Anthropogenic Processes Affecting Domestic Groundwater Quality within the Northwestern Appalachian Basin.

Domestic wells serve as the primary drinking-water source for rural residents in the northern Appalachian Basin (NAB), despite a limited understanding of contaminant distributions in groundwater sources. We employ a newly collected dataset of 216 water samples from domestic wells in Ohio and West Virginia and an integrated contaminant-source attribution method to describe water quality in the western NAB and characterize key agents influencing contaminant distributions. Our results reveal arsenic and nitrate concentrations above federal maximum contaminant levels (MCLs) in 6.8 and 1.3% of samples and manganese concentrations above health advisory in 7.3% of samples. Recently recharged groundwaters beneath upland regions appear vulnerable to surface-related impacts, including nitrate pollution from agricultural activities and salinization from road salting and domestic sewage sources. Valley regions serve as terminal discharge points for long-residence-time groundwaters, where mixing with basin brines is possible. Arsenic impairments occurred in alkaline groundwaters with major-ion compositions altered by ion exchange and in low-oxygen metal-rich groundwaters. Mixing with as much as 4-10% of mine discharge-like waters was observed near coal mining operations. Our study provides new insights into key agents of groundwater impairment in an understudied region of the NAB and presents an integrated approach for contaminant-source attribution applicable to other regions of intensive resource extraction.

Multi-proxy provenance of the lower Pennsylvanian Pottsville sandstone of the northern Appalachian basin in Pennsylvania, U.S.A: Paleodrainage, sources, and detrital history

ABSTRACT The lower Pennsylvanian Pottsville Formation, in the Appalachian foreland basin, constitutes a late Paleozoic clastic wedge formed close to the Appalachian orogenic belt. In this study, we analyzed Pottsville sandstone from the western bituminous and eastern anthracite fields in Pennsylvania to evaluate the detrital history of the sediments. Petrographic modal analyses show that sandstone in the western bituminous field ranges from quartzarenite to sublitharenite, with mean composition of Qt84F1L15; sampled sandstone from the eastern anthracite field is dominated by sublitharenite to litharenite with mean composition of Qt70F2L29. Heavy-mineral assemblages from both fields are dominated by ultrastable minerals (zircon, rutile, and tourmaline), apatite, sphene, spinel, siderite, and abundant opaques. Almost all the studied sandstone samples are garnet-depleted except one from the eastern anthracite field. The chemical composition of chromium- and zinc-rich spinel in samples from both fields might suggest exhumation of an arc terrane and ophiolitic belt with ultramafic igneous rocks. Particularly, the ternary plot of Fe3+–Cr3+–Al3+ end members for the chrome spinels possibly suggest a derivation from an alpine-type peridotite complex. Laser 40Ar/39Ar analyses of detrital muscovite from eastern anthracite fields and western bituminous fields record separate ages, with the former characterized by prominent Middle to Late Ordovician Taconic and Middle Devonian Acadian ages with two discrete modes at 463 and 369 Ma, and the latter dominated by Late Ordovician Taconic, Middle Devonian Acadian, and Late Devonian Neoacadian ages with discrete modes at 445, 397, 360, and 351 Ma. The new data suggest that early Pennsylvanian sedimentation in the Appalachian foreland basin was controlled by southward, southwestward, and westward drainage systems that originated in the Appalachian orogenic belt to the east and northeast.

Sequence stratigraphic reconstruction of the late Middle Devonian Geneseo Formation of NY, USA: Developing a genetic model for “Upper Devonian” unconventional targets in the Northern Appalachian Basin

The late Middle Devonian Geneseo Formation and its lateral equivalents in the northern Appalachian Basin are significant secondary targets to the extensively explored Marcellus Sub-group. Surface to sub-surface characterization of the mudstone-dominated Geneseo Formation combines detailed observations of facies, facies associations, stratal architecture, stratal geometry, and stratal terminations, in combination with geochemical proxies to assess proximal to distal trends and enable prediction of hydrocarbon play element quality and distribution. Correlations within this mudstone-rich succession are conducted at the parasequence-scale, and incorporate detailed descriptions of four drill cores, >100 outcrops, and mapping of >500 wireline logs.The Geneseo Formation herein has been subdivided into two depositional sequences comprising three lithostratigraphic units (i.e., Lower Geneseo, Fir Tree, and Upper Geneseo members respectively). The Lower and Upper Geneseo members show systematic aggradational to progradational parasequence stacking patterns, as well as downlap‒onlap stratal terminations with underlying strata; these members represent highstand systems tracts. The Fir Tree Member occurs between the Lower and Upper Geneseo members, truncates the underlying Lower Geneseo, shows progradational‒aggradational‒retrogradational parasequence stacking patterns, and spans two systems tracts: lowstand and transgressive.Isopach maps were constructed within the high-resolution sequence-stratigraphic framework to better understand thickness trends at the landing-zone scale. Thickness variation across the basin suggests reactivation of basement structures and syndepositional faulting strongly influenced accommodation. Specifically, the N–S trending Clarendon-Linden Fault System appears to have been a western sediment barrier during Geneseo time and the primary depocenter of fine-grained clastics occurs in south-central NY in a structural low. As the Geneseo system advanced, the succession sequentially filled topographic lows from east to west (proximal to distal). Understanding the controls on reservoir quality and distribution of secondary and tertiary targets to the Marcellus can facilitate ranking and prioritization of landing-zones, as well as optimization of well placement for completion design.

Relay ramps and rhombochasms in the northern Appalachian Basin: Extensional and strike-slip tectonics in the Marcellus Formation and Utica Group

Relay ramps and rhombochasms in the northern Appalachian Basin: Extensional and strike-slip tectonics in the Marcellus Formation and Utica Group

Constraining fault architecture and fluid flow using crustal noble gases

Deformational features, such as faults, strongly affect the pathways, rates, and length-scales of fluid flow in sedimentary basins. The hydrologic properties of faults vary greatly, allowing them to exhibit hydrologic behaviors spanning the gamut from open and conductive pathways for fluid flow to closed barriers to fluid flow. As a result, determining the role of faults with respect to fluid flow and their impact on geologic fluid migration throughout the life cycle of sedimentary basins remains challenging. Previous studies interrogate fault behavior using structural characteristics of fault cores and damage zones or the geochemistry of fluid inclusions and mineral veins associated with these features. Here, we evaluate the utility of crustal noble gases as tracers of fluid flow in fault systems by examining the composition of a well-constrained fault system in the Northern Appalachian Basin. The Seneca Stone Thrust fault, located near Seneca Falls, NY, USA, displays ~5 m of offset in the Onondaga Limestone and Marcellus Shale. Significant loss of 4He and 21Ne* near the fault appears to occur prior to basin exhumation, likely resulting from compactive dewatering or hydrocarbon generation and migration. Subsequent cooling shifted fault function from acting as a conduit to acting as a barrier, allowing accumulation of crustal noble gases for extended geologic time (~140 Myr) apparently in a closed-system. We identify significantly lower [4He] and 4He/21Ne* in a discrete zone that includes the fault core and extends ~30 cm into the intensely fractured portion of the fault damage zone as compared to the rest of the fault damage zone (~5 m in width) and other nearby samples from the Marcellus Fm. in the quarry pavement. These results imply that the Seneca Stone Thrust fault has reverted to behaving like a localized conduit in recent geological time. We interpret the discrete zone of extreme 4He loss near the fault plane as evidence of recent focused fluid flow within the fault core at temperatures below 94 °C, possibly within the past ~45,000 years. Our data suggest that crustal noble gases can be used to evaluate the timing of crustal isolation and/or hydraulic communication in fault zones locally in the Marcellus Shale and potentially in other geological settings. Future work can further develop this approach to examine the long-term suitability of geological formations for permanent subsurface storage of CO2, other gases (e.g., H2), or nuclear waste, as well as to determine if various subsurface intervals represent zones of hydrocarbon accumulation and/or loss over geological time.

Critical metal recovery potential of Appalachian acid mine drainage treatment solids

Rare earth elements (REE) are critically important in clean energy technologies, but their mining and refining is energy intensive and generates significant quantities of environmentally harmful waste. The treatment of acid mine drainage (AMD), which is both a global environmental problem and a potential source of these elements, preconcentrates REE and critical metals such as manganese and cobalt into oxide/hydroxide waste products from which they can potentially be recovered. Analysis of 281 treatment solids from coal AMD remediation systems across the northern Appalachian Basin, eastern USA, indicate that the most promising solids (REE value >$400 USD/metric ton) are produced in systems that use limestone or sodium hydroxide to treat low pH (<5) AMD with elevated dissolved aluminum and manganese content. In particular, recovering REE from passive treatment systems could both subsidize treatment of AMD while reducing the environmental footprint of REE extraction.

Methane concentrations in streams reveal gas leak discharges in regions of oil, gas, and coal development

As natural gas has grown in importance as a global energy source, leakage of methane (CH4) from wells has sometimes been noted. Leakage of this greenhouse gas is important because it affects groundwater quality and, when emitted to the atmosphere, climate. We hypothesized that streams might be most contaminated by CH4 in the northern Appalachian Basin in regions with the longest history of hydrocarbon extraction activities. To test this, we searched for CH4-contaminated streams in the basin. Methane concentrations ([CH4]) for 529 stream sites are reported in New York, West Virginia and (mostly) Pennsylvania. Despite targeting contaminated areas, the median [CH4], 1.1 μg/L, was lower than a recently identified threshold indicating potential contamination, 4.0 μg/L. [CH4] values were higher in a few streams because they receive high-[CH4] groundwaters, often from upwelling seeps. By analogy to the more commonly observed type of groundwater seep known as abandoned mine drainage (AMD), we introduce the term, “gas leak discharge” (GLD) for these waters where they are not associated with coal mines. GLD and AMD, observed in all parts of the study area, are both CH4-rich. Surprisingly, the region of oldest and most productive oil/gas development did not show the highest median for stream [CH4]. Instead, the median was statistically highest where dense coal mining was accompanied by conventional and unconventional oil and gas development, emphasizing the importance of CH4 contamination from coal mines into streams.

Maximum Removal Efficiency of Barium, Strontium, Radium, and Sulfate with Optimum AMD-Marcellus Flowback Mixing Ratios for Beneficial Use in the Northern Appalachian Basin.

Mixing of acid mine drainage (AMD) and hydraulic fracturing flowback fluids (HFFF) could represent an efficient management practice to simultaneously manage two complex energy wastewater streams while reducing freshwater resource consumption. AMD discharges offer generally high sulfate concentrations, especially from the bituminous coal region of Pennsylvania; unconventional Marcellus shale gas wells generally yield HFFF enriched in alkaline earth metals such as Sr and Ba, known to cause scaling issues in oil and gas (O&G) production. Mixing the two waters can precipitate HFFF-Ba and -Sr with AMD-SO4, therefore removing them from solution. Four AMD discharges and HFFF from two unconventional Marcellus shale gas wells were characterized and mixed in batch reactors for 14 days. Ba could be completely removed from solution within 1 day of mixing in the form BaxSr1-xSO4 and no further significant precipitation occurred after 2 days. Total removal efficiencies of Ba + Sr + SO4 and the proportion of Ba and Sr in BaxSr1-xSO4 depended upon the Ba/Sr ratio in the initial HFFF. A geochemical model was calibrated from batch reactor data and used to identify optimum AMD-HFFF mixing ratios that maximize total removal efficiencies (Ba + Sr + SO4) for reuse in O&G development. Increasing Ba/Sr ratios can enhance total removal efficiency but decrease the efficiency of Ra removal. Thus, treatment objectives and intended beneficial reuse need to be identified prior to optimizing the treatment of HFFF with AMD.

Statistical learning based predictive models to assess stress changes-reservoir deformation due to CO2 sequestration into saline aquifers

Mechanical integrity of saline reservoirs is necessary to ensure the safe and effective storage of CO2. In this work, three poroelastic metrics, total stress changes (horizontal and vertical) and reservoir displacement, were considered to evaluate the mechanical performance of a sandstone aquifer with a single reservoir and overlying caprock and a carbonate aquifer comprising multiple reservoirs and intermediate caprock units in the Northern Appalachian basin. While the coupled multiphase flow - geomechanics simulations could be computationally expensive, the statistical learning based simplified predictive model is used as an alternative method to assess the poroelastic performance of saline aquifers during CO2 injection. A combination of experimental design and a response surface model (proxy model) is used to develop a simplified predictive model to evaluate the poroelastic response of carbonate and sandstone reservoir caprock systems using combinations of different predictors. In this work, Box Behnken experimental design combined with polynomial proxy models were used to evaluate mechanical performance metrics using five poroelastic predictors. The predictive models, developed in this work, provide a simpler and quicker tool to evaluate the mechanical performance of the deep aquifers with similar characteristics to the reference cases. The overall conclusion of the work is that each metric parameter has its own control parameters. In addition, carbonate reservoirs with multiple caprocks use different control parameters than the sandstone reservoir. In this work, we also developed a simple linear regression model to predict surface uplift using top vertical reservoir displacement data.

δ13C stratigraphy of a Turinian-Chatfieldian (Upper Ordovician) foreland succession, Ottawa Embayment (central Canada): resolving local and inter-regional isotope excursions in a tectonically active basin

Positive δ13Ccarb excursions are correlated through an upper Turinian to lower Chatfieldian carbonate-platform succession along the axis of the Ottawa Embayment and into outliers of the northern Ottawa-Bonnechere graben in central Canada. Successive Turinian excursions (E1 and E2) are lithostratigraphically constrained by erosional surfaces and hosted within the Watertown and overlying L'Orignal formations, respectively, the latter coeval with the Selby Formation in the adjacent northern Appalachian Basin. The excursions coincide with periods of regional transgression, but geographic patterns of 13C depletion versus enrichment coincide with structurally defined areas of stratigraphically condensed and preferentially thickened formation successions, respectively. Differential subsidence is interpreted to have created bathymetric variation resulting in intrabasinal restriction of seawater exchange between these areas, with preferential Corg recycling with stratigraphic condensation. By early Chatfieldian time, segmentation of the once regional carbonate platform (L'Orignal Formation) produced a regional mosaic of low-energy muddy carbonate banks (Rockland Formation) and a deeper water platform (lower Hull Formation) settings subject to fluctuating high to low energy current flow. Excursion E3 occurs in both successions, but 13C enrichment is associated only with the bank-top muddy facies. This may identify preferential photosynthetic drawdown of 12C across the bank tops due to limited seawater exchange across the bank-deeper platform boundaries. Excursions E1 to E3, and a younger excursion (E4) in the Hull Formation, are correlated with varying confidence with excursions across southern Laurentia, excursion E3 being the local expression of the Guttenberg δ13C excursion. Our study supports local modulation of regional, if not global, δ13C excursions arising from structurally controlled changes in oceanography and productivity.

A screening framework study to evaluate CO2storage performance in single and stacked caprock–reservoir systems of the Northern Appalachian Basin

AbstractIn the context of geologic carbon dioxide (CO2) sequestration, the storage effectiveness of a caprock–reservoir system is a function of the properties of both the caprock and reservoir – namely, the ability of the caprock to prevent upward leakage of CO2(caprock sealing capability), the mechanical response of the reservoir and caprock (by evaluatingin situstress changes), and the extent and degree to which CO2can be trapped over long periods of time. In this work, all three parameters were considered to evaluate the storage effectiveness of the Cambrian–Ordovician sequence of the Northern Appalachian Basin. We constructed a series of hydro‐mechanical models to investigate interactions between CO2flow and geomechanical processes and to evaluate the three aspects of storage performance. Models were built to evaluate two scenarios: (1) single reservoirs with a single overlying caprock, and (2) systems comprising multiple reservoirs and multiple intermediate caprock units in addition to the primary (uppermost) caprock unit. The overall conclusion of the work is that focusing only on one aspect of storage effectiveness might not necessarily warrant long‐term CO2storage. Results of the sensitivity analysis for the single caprock–reservoir system show that each storage effectiveness metric has its own control parameters. A comparison among three stacked caprock–reservoir systems in different parts of the study area shows that each location in the study area could be appropriate for one of the storage effectiveness metrics. Therefore, we conclude that the screening process to select the best site for CO2sequestration should be based on an evaluation of all three metrics. © 2019 Society of Chemical Industry and John Wiley &amp; Sons, Ltd.

Post‐orogenic thermal history and exhumation of the northern Appalachian Basin: Low‐temperature thermochronologic constraints

AbstractApatite fission‐track (AFT) thermochronology and (U‐Th)/He (AHe) dating, combined with paleothermometers and independent geologic constraints, are used to model the thermal history of Devonian Catskill delta wedge strata. The timing and rates of cooling determines the likely post‐orogenic exhumation history of the northern Appalachian Foreland Basin (NAB) in New York and Pennsylvania. AFT ages generally young from west to east, decreasing from ~185 to 120 Ma. AHe single‐grain ages range from ~188 to 116 Ma. Models show that this part of the Appalachian foreland basin experienced a non‐uniform, multi‐stage cooling history. Cooling rates vary over time, ~1–2 °C/Myr in the Early Jurassic to Early Cretaceous, ~0.15–0.25 °C/Myr from the Early Cretaceous to Late Cenozoic, and ~1–2 °C/Myr beginning in the Miocene. Our results from the Mesozoic are broadly consistent with earlier studies, but with the integration of multiple thermochronometers and multi‐kinetic annealing algorithms in newer inverse thermal modeling programs, we constrain a Late Cenozoic increase in cooling which had been previously enigmatic in eastern U.S. low‐temperature thermochronology datasets. Multi‐stage cooling and exhumation of the NAB is driven by post‐orogenic basin inversion and catchment drainage reorganization, in response to changes in base level due to rifting, plus isostatic and dynamic topographic processes modified by flexure over the long (~200 Myr) post‐orogenic period. This study compliments other regional exhumation data‐sets, while constraining the timing of post‐orogenic cooling and exhumation in the NAB and contributing important insights on the post‐orogenic development and inversion of foreland basins along passive margins.

Assessment of coal mine methane (CMM) and abandoned mine methane (AMM) resource potential of longwall mine panels: Example from Northern Appalachian Basin, USA

Coal mine methane (CMM) and abandoned mine methane (AMM) are by-products of underground mining of gassy coal beds. The quantity and the emission rate of CMM and AMM may vary depending on the type of mine, gas content of the mined coal bed, and gas sourced from strata and coal beds in overlying and underlying formations affected by mining. Therefore, if a mine has the potential of accumulating gas after being abandoned and sealed properly, that methane may be produced and used as an energy source to serve local communities in the area. Producing AMM also prevents methane, which is a potent greenhouse gas, from leaking to the atmosphere through seals, shaft plugs or surface cracks.A technical barrier to economical utilization of CMM and AMM is the uncertainty about how much methane may be available in the gas emission zone (GEZ) as a resource during mining, as well as after the panels are sealed and the mine is abandoned. Another difficulty is estimating how much of the potential methane resource can be produced from gob gas ventholes (GGV) converted to capture AMM.In this study, a comparative assessment is presented to address the issues stated above. The assessment was conducted on two adjacent panels of a longwall mine that operated in Pennsylvania until 2016 in the Northern Appalachian Basin. The study is based on two approaches that might be used depending on the availability of data. The first approach uses an extensive geological data set, geostatistics, and measured shaft gas emission and GGV production values that were collected while the panel (s) were active to assess the AMM resource. The second approach uses a minimal amount of geologic data, uncertainty of the data as probabilistic distributions, and the use of publicly available software to predict during-mining emissions. Results showed that both approaches provide relatively comparable estimates of AMM resources and AMM recovery potential using wellbores. The differences in assessed quantities are mostly due to the characteristics of the two methods. In that regard, this paper can be considered as guidance to choose the assessment approach based on data availability.

A global biogeochemical perturbation during the Middle Frasnian punctata Event: Evidence from muted carbon isotope signature in the Appalachian Basin, New York State (USA)

Abstract A modest positive stable carbon isotope excursion coincident with the Upper Devonian Middlesex Formation of western New York State and beneath the Palmatolepis transitans - Palmatolepis punctata zonal boundary is interpreted to define the beginning of the Middle Frasnian punctata Event. The broad positive excursion that defines this global isotopic event elsewhere, however, appears to have been muted in the northern Appalachian Basin by a tectonically induced regression and associated deposition of the organic-deficient Cashaqua Formation. δ13Corg increases upward through the lower two-thirds of the Cashaqua, peaking approximately 4.5 m below its contact with the overlying Rhinestreet Formation in the mid-punctata Zone. Above this stratigraphic level, δ13Corg diminishes 2.2‰ over a vertical distance of 41 cm that encompasses a newly recognized interval of microtektite-like spherules. Thus, that part of the studied section between the middle of the Middlesex Formation and the peak δ13Corg value in the upper Cashaqua Formation embraces the stratigraphic range of the punctata positive excursion dampened by the regional base level reduction and associated increased flux of 13C-depleted terrestrial weathering runoff, including dissolved inorganic carbon (DIC). δ13Corg values recover to pre-negative excursion levels through the top of the Cashaqua Formation into the lower Rhinestreet Formation. The sharp negative excursion terminating the punctata Event of western New York likely records the sudden introduction of 12C into the ocean - atmosphere system, perhaps related to destabilization of sea-floor methane hydrates. However, hydrate dissociation concurrent with rising global sea level and in the absence of a closely preceding thermal event sufficient to raise bottom-water temperature is problematic. The coincidence of the stratigraphic interval containing the microtektite-like spherules and the onset of the negative carbon isotope excursion suggests that impact-induced mechanical disruption of the ocean floor may have triggered the release of methane.

Heat flow and thermal conductivity measurements in the northeastern Pennsylvania Appalachian Basin depocenter

The northern Appalachian Basin depocenter of Pennsylvania represents one of the most economically important hydrocarbon-producing areas in the United States, yet the thermal conditions that promoted hydrocarbon formation within the basin are only marginally constrained. The prolific coal, oil, and natural gas fields of Pennsylvania are the direct result of thermal maturation of once deeply buried organic-rich sediment. Understanding how, why, and where thermal maturation occurred in the Appalachian Basin requires high-quality heat flow and thermal conductivity measurements, as well as paleotemperature estimates and basin modeling. To improve the understanding of heat flow, we present, to our knowledge, the first direct measurements of (1) thermal conductivity on Devonian core samples and (2) equilibrium temperature versus depth logs for the northern Appalachian Basin depocenter. Results from three well sites demonstrate that heat flow is conductive and nearly uniform, averaging 34 ± 2.5 mW/m2, with an average thermal gradient of 29 ± 4°C/km. The new heat-flow measurements are significantly lower (30%–50% less) than previously published estimates that used nonequilibrium bottomhole temperature values and empirically derived thermal conductivity estimates. Our analysis indicates that previous studies correctly estimated the regional thermal gradient using bottomhole temperatures but overestimated heat flow in this region by as much as 50% because of inaccurate extrapolation of thermal conductivity. The results highlight the importance of directly measuring thermal conductivity to accurately quantify heat flow in deep sedimentary basins. Ultimately, additional paleotemperature data are necessary to improve our understanding of Appalachian Basin thermal evolution.

Lithostratigraphy of the upper Turinian – lower Chatfieldian (Upper Ordovician) foreland succession, and a U–Pb ID–TIMS date for the Millbrig volcanic ash bed in the Ottawa Embayment

Three stages of carbonate-platform development are preserved in the upper Turinian – lower Chatfieldian succession of the Ottawa Group in the Ottawa Embayment and represent deposition along the Late Ordovician Taconic foreland interior of paleo-southern Laurentia. Compared with contemporary stratigraphy in the adjacent northern Appalachian (southern Ontario, New York state) and western Quebec basins, the intermediate Stage 2 succession, which brackets the Turinian–Chatfieldian boundary, preserves embayment-specific stratigraphic patterns. These include: (i) dramatic west-to-east thickening of the upper Turinian Watertown Formation that defines differential subsidence along the present axis of the embayment, (ii) post-Watertown base-level fall defined by appearance of shoreface siliciclastics, (iii) early Chatfieldian marine transgression represented by the proposed L’Orignal Formation that is coeval with but lithologically distinct from the Selby Formation in the northern Appalachian Basin, and (iv) platform segmentation that resulted in a depositional mosaic of shallow banks (Rockland Formation) and equivalent deeper water mico-seaways (lower Hull Formation). The latter event immediately follows accumulation of the Millbrig bentonite, here dated at 453.36 ± 0.38 Ma. Bracketing these local stratigraphic patterns are the bounding stages (1 and 3) represented by the upper Turinian Lowville Formation and middle Chatfieldian Hull Formation, respectively, that contain facies attributes in common with the adjacent basins and characterize inter-regional depositional systems of first warm, then cooler oceanographic conditions. Stage 2 identifies a structurally controlled transition between these end-member stages: a far-field response in the foreland interior, localized along the axis of a late Precambrian fault system, to contemporary change in subsidence rates and tectonomagmatic events along the Laurentian margin.