Oriskany Sandstone Research Articles

Quantifying the effects of gaseous pore pressure and net confining stress on low-permeability cores using the “RaSSCAL” steady-state permeameter

Subsurface engineering systems undergo large changes in pore pressure, which can have drastic effects on their ability to transport and store fluids. For rock samples retrieved from conventional reservoirs, standard core analysis procedures provide suitable estimates of petrophysical properties, such as porosity and permeability. However, performing similar investigations on low-permeability systems like shales and tight gas sands remains a challenge. Steady-state gas permeametry is considered the gold standard for analyzing low-permeability cores, but researchers often forego it in favor of faster but less reliable methods. Attempting a conventional permeability test on a tight plug sample typically results in miniscule flow rates that only expensive, specialized equipment can measure directly. Furthermore, these time-consuming tests are best run multiple times under varying ranges of pore pressure and confining stress. Doing so allows one to anticipate suitably the changes in permeability that will occur because of the expected changes in reservoir conditions.This study describes the methodology of the Randolph Steady-State Core Analysis Laboratory (RaSSCAL), a new experimental design and data analysis algorithm that accounts for changes in permeability over the range of pore pressures and confining stresses that occur during processes like unconventional hydrocarbon recovery and geologic carbon sequestration. Routine steady-state core analysis requires relatively small pressure drops across the sample so a uniform apparent permeability can be assumed. The approach outlined here enables an effective interpretation of core-flood data in the presence of arbitrarily large pressure gradients. The experiment maintains a near-constant pressure difference of arbitrary magnitude across a core-plug sample and indirectly measures the flow rate induced by that gradient using a differential pressure transmitter. Tests were performed on a Marcellus Shale sample from Bedford, Pennsylvania and an Oriskany Sandstone sample from Berkeley Springs, West Virginia over a wide array of pore pressures and net confining stresses using helium and methane gas. Having a quantifiable understanding of how the permeability of the system may change during the various stages of subsurface activity should significantly enhance the ability to optimize design outcomes. This will ultimately lead to improved oil and gas recovery and better predictions of injectivity and storage capacity during carbon-storage operations.

Revisiting the Appalachian Basin for CO2 Storage Resources Using the SRMS Classification Framework

One major challenge for the CCS is to understand if CO2 geological storage could be implemented at the scale of the climate change issue. In 2017, the Storage Resource Management System (SRMS) was developed by the Society of Petroleum Engineers (SPE) with the support of the Oil and Gas Climate Initiative (OGCI) CO2 storage workgroup. SRMS is based on the concepts of the Petroleum Resource Management System (PRMS), also developed by the SPE, which provides a classification framework for oil & gas resources and reserves. The SRMS provides guidelines on how to classify CO2 storage resources within various storage categories. It is done based on the assessment level of confidence and maturity of the assessment. It also provides guidelines on how assess mature storage resources capacity, increasing its chance of commerciality and ultimately allow for operational deployment of CO2 geological storage. The Appalachian Basin is a mature basin that contains oil, gas and coal resources and extends over an area of 50,000 km2. Despite it is well known for the reserves, it has been studied as a potential CO2 storage system. It is identified as one of the larges storage systems in North America. The basin was extensively exploited causing a large number of wells especially on Marcellus asset. For the volumetric estimation of CO2 sequestration, several formations were studied, especially Oriskany sandstone and Medina and Tuscarora Sandstone. Some of the analyses are probabilistic using stochastic variables in a Montecarlo method to determine the uncertainty in the storage volume. The result of the review is that the Appalachian basin storage resources remain prospective resources, in the Play subcategory. An important point to be considered is to evaluate and quantify the storage capacity of the shales of this basin. Indeed, it is known that organic rich shales desorb methane while adsorbing CO2. Experiments performed in Marcellus shale show that those shales can adsorb 4 times more CO2 than Methane. Consequently, if all of the methane absorbed for the shale could be displaced by CO2 the additional capacity of the shale could be of approximately 50 Gt. Engineering studies need to be performed in order to verify this numbers. Two issues that can affect the storage capacity are: CO2 migration through connexion of shallow formation and the number of wells performed in the basin that can condition the injection strategy or the seal between formations. The complexity of the basin is important with a fractured system. Several studies affirm that there are evidences of migrations from Marcellus formation to shallow aquifers. These evidences are recorded in the NE of Pennsylvania and the mechanics of migration are inferred faults. Gravity data suggest that some of these structures can possibly extended to the basement. Some shale like Marcellus was used as a cap-rock and these well that are crossing the cap-rock can be potential conduits for the CO2 injected. Also they will determine the placement of the injection well for CO2. Recommendations are finally provided in order to ensure compatibility with SRMS.

CO2-SCREEN tool: Application to the oriskany sandstone to estimate prospective CO2 storage resource

The ability to accurately predict the CO2 storage resource in saline formations is important to make high-level, energy-related government policy and business decisions. CO2-SCREEN (Storage prospeCtive Resource Estimation Excel aNalysis) is a tool developed by the United States Department of Energy − National Energy Technology Laboratory (US-DOE-NETL) to screen saline formations for prospective CO2 storage resources. CO2-SCREEN uses DOE methods and equations to serve as a consistent mechanism for calculating prospective CO2 storage resources. CO2-SCREEN is comprised of two files: an Excel file used for inputs and outputs and a GoldSim Player file used to run Monte Carlo simulations. CO2-SCREEN requires input of physical geologic parameters (i.e. thickness, porosity) as well as efficiency factor ranges (i.e. net-to-gross thickness) to calculate a mass storage estimate. An application of CO2-SCREEN is demonstrated here using well log data from the Oriskany Sandstone portion in Pennsylvania. The Oriskany Sandstone is divided into 20 km x 20 km grid cells in which 151 cells contain well log data. CO2-SCREEN calculates prospective CO2 storage resource for each grid cell based on the well log data and uses lithology and depositional environment information for efficiency factor ranges. The Oriskany Sandstone CO2 storage resource estimate for Pennsylvania, calculated by CO2-SCREEN, ranges from 0.07 to 1.28 gigatons (Gt) with a P50 value of 0.32 Gt. This resource assessment analysis is done to demonstrate the use of CO2-SCREEN and results are comparable to previous studies which encourages the application of CO2-SCREEN to other saline formations and warrants exploring the expansion of this tool to assess the CO2 storage resource in other formations such as shale and depleted oil and gas reservoirs.

Neoformed magnetic minerals as an indicator of moderate burial: The key example of middle Paleozoic sedimentary rocks, West Virginia

In order to help unravel the thermal history of middle Paleozoic sedimentary rocks in West Virginia, a rock magnetic study was conducted with a focus on the Marcellus Shale. Vitrinite reflectance, fluid inclusions microthermometry and conodont alteration index data yield contradictory burial temperature within the range 150–250°C (302–482°F). The characterization of magnetite and pyrrhotite may be used as an index to track burial temperature around 200°C (392°F). Low-temperature and room-temperature magnetic measurements were performed in order to determine the magnetic assemblage. Three magnetic assemblages were identified that were stratigraphically distributed. The goethite and nanosized magnetite (A1) assemblage is mainly found in the Clinton Group–Oriskany Sandstone stratigraphic interval (Silurian–Lower Devonian). Nanosized fraction of magnetite and probably pyrrhotite (A3) assemblage essentially constitutes the Marcellus Shale–Chemung Formation sequence (Devonian). Microsized pyrrhotite is the typical mineral for A2 that is only identified near the Alleghenian structural front. Overall, the rare occurrence of micron pyrrhotite in our samples suggests that the study area has not experienced burial temperatures higher than 200°C (392°F).

Fracture Height Containment in the Stimulation of Oriskany Formation

The Oriskany sandstone formation has been a prolific producer of natural gas in the Appalachian basin since 1930s. Lot of production wells have been converted to gas storage wells for the ease of operation. Natural gas storage industry is a vital part of North American energy driven economy because of the fluctuation in seasonal demand and in maintaining the reliability of supply needed to meet the demands of the consumer. However, the storage wells suffer from an annual deliverability loss of 5% owing to the various damage mechanisms. A lot of work pertaining to the issue of identification of damage mechanisms and subsequent development of stimulation technology in order to mitigate the damage and restore the wells deliverability have been done in a joint effort between The Gas Research Institute, Department of Energy, American Gas Association and the various other operator companies involved in the storage industry. Operators mostly rely on traditional methods such as blowing, washing, reperforating, acidizing, infill drilling to restore wells deliverability. These traditional methods do provide short term benefits, but the longevity is not sustained and the overall situation remains same. Hydraulic fracturing is not preferred in terms of legitimate concerns over excessive vertical height growth, long fracture fluid cleanup times, lack of expertise and cost. This research study was carried out to understand the various damage mechanisms affecting the Oriskany wells, with a focus on gas storage wells. We then developed a dataset of reservoir properties, rock properties and fracture treatment data for Oriskany based on a complete literature review and calculations from a sonic log. Parametrical studies were carried out to investigate the effect of type of fracture fluids, injection rate, types of proppant, treatment volume, reservoir pressure and treatment schedule on fracture geometries in the Oriskany formation. Based on the results, we developed new stimulation methods that lead to increased well deliverability, fracture height containment, and higher average fracture conductivity. This new understanding and knowledge help in practicing engineers design better treatments in stimulating Oriskany wells.

Thickness trends and sequence stratigraphy of the Middle Devonian Marcellus Formation, Appalachian Basin: Implications for Acadian foreland basin evolution

Analysis of more than 900 wireline logs indicates that the Middle Devonian Marcellus Formation encompasses two third-order transgressive-regressive (T-R) sequences, MSS1 and MSS2, in ascending order. Compositional elements of the Marcellus Formation crucial to the successful development of this emerging shale gas play, including quartz, clay, carbonate, pyrite, and organic carbon, vary predictably within the proposed sequence-stratigraphic framework. Thickness trends of Marcellus T-R sequences and lithostratigraphic units reflect the interplay of Acadian thrust-load-induced subsidence, short-term base-level fluctuations, and recurrent basement structures. Rapid thickening of both T-R sequences, especially MSS2, toward the northeastern region of the basin preserves a record of greater accommodation space and proximity to clastic sources early in the Acadian orogeny. However, local variations in T-R sequence thickness in the western, more distal, area of the basin may reflect the reactivation of inherited Eocambrian basement structures, including the Rome trough and northwest-striking cross-structural discontinuities, induced by Acadian plate convergence. Episodes of block displacement locally warped the basin into northeast-southwest–trending regions of starved sedimentation and/or erosion adjacent to depocenters in which regressive systems tract deposits were ponded. Block movement appears to have initiated in late Early Devonian time, resulting first in thinning and local erosion of the Oriskany sandstone in northwest Pennsylvania. This study, in addition to providing the basis for a predictive sequence-stratigraphic model that can be used to further Marcellus exploration, tells of a foreland basin more tectonically complex than accounted for by simple flexural models.

Sequestration of CO2 in Mixtures of Caustic Byproduct and Saline Waste Water

Ex-situ carbonation of mixtures of caustic byproduct materials and produced oil-field brine provides a niche opportunity to sequester anthropogenic CO2, while concomitantly reducing the basicity of the reactive slurry. A series of tests were conducted to investigate a novel reaction concept designed to achieve neutralization of mixtures of acidic oil field produced brine and caustic industrial byproducts while sequestering substantial quantities of anthropogenic carbon dioxide (CO2) in a mixed-flow reactor. Experiments were conducted to determine the CO2-bearing capacity of reactive mixtures of brine from the Oriskany Sandstone Formation with three caustic industrial byproducts: flue gas desulfurization (FGD) spray dryer ash, Class C fly ash subbituminous coal combustion byproduct, and bauxite residue slurry from the alumina production process. Reactions were conducted in a closed, well-mixed (1,500 rpm) reactor with gas composed of 29.46% vol./vol. CO2 balanced by nitrogen gas (N2) fed at a rate of 300 mL/min. Reactions were carried out at ambient conditions. Results show linear relationships between caustic byproduct addition and CO2-bearing capacity, with relatively small impact of brine addition as compared to deionized water addition. FGD spray dryer ash/brine mixtures exhibited higher CO2 reactivity than those using Class C fly ash (0.759 moles CO2, at 23.6% solids by weight and 0.036 moles CO2 at 23.3% solids by weight, respectively). Bauxite residue exhibited moderate capacities in mixtures with higher percent solids (0.335 moles CO2 in 40% solids bauxite residue slurry). Carbonation capacity of caustic byproduct/acidic brine mixtures was shown to increase linearly with respect to percent caustic byproduct addition, but enhanced mineral carbonate precipitation resulting from synergistic reaction of brine cations with increased dissolved carbonate species was not observed in the short term.

Unraveling the stratigraphy of the Oriskany Sandstone: A necessity in assessing its site-specific carbon sequestration potential

The widespread distribution, favorable reservoir characteristics, and depth make the Lower Devonian Oriskany Sandstone a viable sequestration target in the Appalachian Basin. The Oriskany Sandstone is thickest in the structurally complex Ridge and Valley Province, thins toward the northern and western basin margins, and is even absent in other parts of the basin (i.e., the no-sand area of northwestern Pennsylvania). We evaluated four regions using petrographic data, core analyses, and geophysical log analyses. Throughout the entire study area, average porosities range from 1.35 to 14%. The most notable porosity types are primary intergranular, secondary dissolution, and fracture porosity. Intergranular primary porosity dominates at stratigraphic pinch-out zones near the Oriskany no-sand area and at the western limit of the Oriskany Sandstone. Secondary porosity occurs from dissolution of carbonate constituents primarily in the combination-traps natural gas play extending through western Pennsylvania, western West Virginia, and eastern Ohio. Fracture porosity dominates in the central Appalachian Plateau Province and Valley and Ridge Province. Based on average porosity, the most likely regions for successful sequestration in the Oriskany interval are (1) updip from Oriskany Sandstone pinch-outs in eastern Ohio, and (2) western Pennsylvania, western West Virginia, and eastern Ohio where production occurs from a combination of stratigraphic and structural traps. Permeability data, where available, were used to further evaluate the potential of these regions. Permeability ranges from 0.2 to 42.7 md. Stratigraphic pinch-outs at the northern and western limits of the basin have the highest permeabilities. We recommend detailed site assessments when evaluating the sequestration potential of a given injection site based on the variability observed in the Oriskany structure, lithology, and reservoir characteristics.

Characterization of the Helderberg Group as a geologic seal for CO2 sequestration

The Midwest Regional Carbon Sequestration Partnership recognizes that both the Devonian Oriskany Sandstone and the Silurian Salina Group offer potential for subsurface carbon dioxide storage in northern West Virginia. The Silurian–Devonian Helderberg Group lies stratigraphically between these two units, and consequently, its potential as a geologic seal must be evaluated. Predominantly a carbonate interval with minor interbedded siliciclastics and chert, the Helderberg Group was deposited in an ancient epeiric sea. Although most previous investigations of this unit have concentrated on outcrops in eastern West Virginia, new information is available from an injection well drilled along the Ohio River at First Energy's R. E. Burger electric power plant near Shadyside, Ohio. Geophysical, seismic, and core data from this well have been combined with existing outcrop information to evaluate the Helderberg Group's potential as a seal. The data collected suggest that only secondary porosity remains, and permeability, if it exists, most likely occurs along faults or within fractures.

Basinwide stratigraphic synthesis and sequence stratigraphy, upper Pragian, Emsian and Eifelian stages (Lower to Middle Devonian), Appalachian Basin

Abstract A new synthesis of the Lower to Middle Devonian (upper Pragian, Emsian and Eifelian) succession across the Appalachian Basin has been developed by high resolution event and sequence stratigraphic analysis. The correlation of numerous marker beds and a hierarchy of cycles in the interval of the Oriskany Sandstone to lower Hamilton Group provide a refined picture of the depositional patterns, faunal changes, formation to member-level (and finer) relationships, and sea-level trends. The succession begins above the Wallbridge Unconformity, or its correlative conformity, which lies beneath the Oriskany Sandstone, not above it as previously thought. The new sequence-stratigraphic framework of Oriskany to lower Hamilton strata comprises nine ‘third order’ stratigraphic sequences (cycles), though an interval of some 25 million years. At a coarse scale, the eustatic Pragian to Eifelian sea-level curve for Euramerica of Johnson et al. (1985) shows broad variance with the Appalachian curve, reflecting the regional influence of the Acadian orogeny. However at the finer sequence-scale, the Euramerican sea-level trends are recognizable in the Appalachian Basin succession.

Subsurface Structure of the North Summit Gas Field, Chestnut Ridge Anticline of the Appalachian Basin: ABSTRACT

The Chestnut Ridge anticline is the westernmost of the High Plateau folds in southwestern Pennsylvania and north-central West Virginia that are detached primarily in the Marcellus Shale, and the Martinsburg, Salina, and Rome Formations. The primary, basal detachment at the Summit field occurs in the Salina salt. Production from fracture porosity in the Devonian Oriskany Sandstone commenced in 1936. During the late 1980s and early 1990s, 14 wells were drilled preparatory to conversion of the reservoir to gas storage. Schlumberger`s Formation MicroScanner (FMS) logs were run in each of these wells to provide information on the structural configuration and fracture patterns of the reservoir. These data indicate that two inward-facing, tight folds at the Oriskany level form the upper flanks and core of the anticline at the northern end of the field, whereas the main part of the field to the south is a comparatively simple, broad closure at the Oriskany level. The structure is a broad, slightly asymmetric open fold in the Mississippian Greenbrier Formation at the surface. Fracture patterns mapped using FMS logs indicate a complex fracture system which varies slightly along the trend of the fold and among the units analyzed, including the Helderberg Formation, Huntersville Chert,more » Oriskany Sandstone, and Onondaga Formation. An orthogonal joint system strikes toward the northwest and northeast slightly askew to the trend of the fold`s crestal trace. A similar, but more complex fracture pattern is found in an oriented core of these units.« less

UIC Permitting Process for Class IID and Class III Wells: Protection of Drinking Water in New York State: ABSTRACT

The U.S. Environmental Protection Agency (EPA) Region II, Underground Injection Control (UIC) Program regulates injection wells in the State of New York to protect drinking water; UIC regulations can be found under Title 40 of the Code of Federal Regulations Parts 124, 144, 146 and 147. Operators of solution mining injection wells (UIC Class IIIG) and produced fluid disposal wells (UIC Class IID) are required to obtain an UIC permit for authorization to inject. The permitting process requires submittal of drinking water, geologic and proposed operational data in order to assure that pressure build-up within the injection zone will not compromise confining layers and allow vertical migration of fluid into Underground Sources of Drinking Water (USDW). Additional data is required within an Area of Review (AOR), defined as an area determined by the intersection of the adjusted potentiometric surface produced by injection and a depth 50 feet below the base of the lowermost USDW, or a radius of 1/4 mile around the injection well, whichever is greater. Locations of all wells in the AOR must be identified, and completion reports and plugging reports must be submitted. Requirements are set for maximum injection pressure and flow rates, monitoring of brine propertiesmore » of the injection well and monitoring of water supply wells in the AOR for possible contamination. Any noncompliance with permit requirements constitutes a violation of the Safe Drinking Water Act and is grounds for enforcement action, including possible revocation of permit. Presently four Class IID wells are authorized under permit in New York State. The Queenston sandstone, Medina sandstone, Salina B, Akron dolomite and Oriskany sandstone have been used for brine disposal; the lower Ordovician-Cambrian section is currently being considered as an injection zone. Over one hundred Class IIIG wells are authorized under permit in New York State and all have been utilized for solution mining of the Syracuse salt.« less

Selective silicification of fossils by syntaxial overgrowths on quartz sand, Oriskany Sandstone (Lower Devonian), New York

Some fossil fragments in the Oriskany Sandstone (Lower Devonian) of New York were partially replaced by syntaxial quartz overgrowths. These replacive overgrowths are significant in that they provide insights into the mechanism and controls of quartz replacement of calcite. The susceptibility of the different calcite types of quartz replacement was governed by their microstructural complexity. Fossil fragments with finely crystalline microstructures, such as brachiopods, ostracods, and bryozoans, were partially replaced by quartz, whereas echinoderm ossicles, which consist of single large calcite crystals, were not replaced. Calcite cement was also immune to replacement. Brachiopod, bryozoan, and ostracod bioclasts (with minor exceptions) underwent partial replacement by quartz (with its concomitant shell calcite dissolution) only where the shell fragments were in contact with detrital quartz grains. Proximity to authigenic crystal nucleation sites (i.e., quartz sand grains) was thus the prime control over whether host mineral dissolution occurred, which is a situation unique to the force of crystallization-driven replacement mechanism.

History and Geology of the Giant Elk-Poca Field, West Virginia, USA

The 165,000 acre Elk-Poca field was discovered in 1933 when a wildcat well tested the Oriskany Sandstone (Lower Devonian) on the Milliken Anticline in Elk District, Kanawha County. Rapid expansion occurred northward, along the anticline, and westward into Poca District on the Sissonville high. Begun as a structural play, it soon became an exploration program for thick, well-developed clean sandstones. Elk-Poca is a combination stratigraphic and structural trap. In Jackson County, salt water is present downdip, and updip production is limited by a loss of highly permeable beds. The reservoir was developed in clean, highly permeable sandstones in the upper part of the Oriskany. The average pay section is 30 ft thick, and characterized by high permeabilities, and consistent, but low porosities. High initial flow rates for both natural wells and wells stimulated by shooting correlate with areas of thick sandstone. Nearly 1200 wells were drilled in the field, and more than 1100 produced gas. Since 1933, nearly 1 tcf of gas have been produced, with the best wells in areas of thick sandstone. Production decline was rapid, due to the high permeability and moderate porosity. This giant field is in the only area in West Virginia where a certainmore » set of geologic factors coincide. The north-south structural strike is paralleled by an east-west decrease in sandstone thickness, and a westeast increase in thickness of the organic-rich Devonian shales. Gas migrated from the shales into the permeable Oriskany before compaction and cementation by carbonate eliminated all porosity and permeability. The presence of gas in open pores may have retarded further cementation.« less

Atlas of Appalachian Basin Oil and Gas Plays: The Oriskany Sandstone Play--a Preliminary Example

The assessment of the nation's undiscovered petroleum resources by the US Geological Survey uses the identification of geologically defined plays and the estimation of the size distribution and number of undiscovered fields in each play from historical production data. The Appalachian basin contains six major oil and gas plays, but in contrast to more recently drilled basins, the plays of the mature Appalachian basin lack a complete geologic and production database. Data such as reservoir porosity, permeability, thickness, saturation, drilling depth, and historical production are either unknown, scattered in the literature, deeply buried in company and government files, or exist in incomplete regional government and private commercial data files. In an effort to increase the database and to improve the assessment of the basin, an informal atlas was initiated to test the feasibility of acquiring additional data and the utility of these data in improving the assessment. Critical to the assessment procedure and noticeably incomplete in the basin are the historical cumulative production data necessary for analyzing the distribution of the number of fields and field sizes for the individual plays. Of the Appalachian basin plays, the Oriskany Sandstone play was initially selected and encouraging amount of previously unidentified productionmore » data is available. Achieving the maximum amount of the quality of data for each play in the atlas will require the cooperation of those working in the Appalachian basin.« less

Oil and Gas Developments in New York in 1989

About 150 wells were completed in New York during 1989, about 25% fewer than in 1988. Five exploratory wells were completed in 1989. These consisted of a dry Oriskany sandstone wildcat in Allegany County, 2 Medina sandstone gas-field extensions in Cattaraugus County, a dry Clinton wildcat in Delaware County, and a dry outpost to Stagecoach field in Tioga County. Oil production in 1989 was 494,770 bbl. Gas production was about 25.5 bcf. The average price paid for New York crude oil during 1989 was $18.12/bbl, and the estimated average wellhead price paid for gas was $2.00/mcf. In 1989, 12 crew-weeks of reflection seismic work were accomplished in New York. Drilling is expected to remain at this level in 1990. Almost all drilling will be for gas.

Fabric-retentive, Non-luminescent Brachiopods as Indicators of Original 13C and 18O Composition: A Test

ABSTRACT Fabric-retentive, non-luminescent Helderbergian brachiopods from open marine deposits, analogous to brachiopods used in other studies to determine paleo-oceanic stable isotopic composition, exhibit depleted 13C values immediately below the erosional contact and more enriched values of 13C at greater stratigraphic distances below this surface. In addition, 13C values of these brachiopods display a marked shift across the erosional surface, and values above it are essentially the same as those 30 m or more beneath the surface. Complementing these trends, whole rock analyses, metastable, high- agnesian calcite constituents (echinoderms), as well as early equant calcite cement, also exhibit an increased depletion trend in 13C values as the Helderberg-Oriskany contact is approached from below. Fabric-retentive luminescent, as well as obviously recrystallized brachiopods, display stable isotopic values similar to those of fabric-retentive, non-luminescent brachiopods. Thus, best-preserved fabric-retentive, non-luminescent brachiopods exhibit values similar to obviously recrystallized brachiopods, diagenetically altered metastable constituents (echinoderms), stable early meteoric cements, and whole rock samples. Helderberg strata of New York State were affected by early meteoric diagenesis during a Siegenian exposure event prior to deposition of the overlying marine Oriskany Sandstone. Meteoric diagenesis during this exposure gave rise to a characteristic carbon isotopic depletion trend approaching the Helderberg/Oriskany contact. All of the skeletal constituents underwent isotopic exchange during early diagenetic exposure to meteoric waters. Consequently, the practice of using fabric-retentive, non-luminescent brachiopods as indicators of their original chemistry and, by extension, paleo-oceanic chemistry is questioned.

Large quaternary landslides in the central appalachian valley and ridge province near Petersburg, West Virginia

Geological mapping and photointerpretation of side-looking airborne radar images and color-infrared aerial photographs reveal two large Quaternary landslides in the Valley and Ridge province of the central Appalachians near Petersburg, W. Va. The Elkhorn Mountain rock avalanche occurs on the thrust-faulted northwestern flank of the Elkhorn Mountain anticlinorium. A minimum of 7 × 10 6 m 3 of quartzite colluvium was transported more than 3 km from a 91 m high escarpment of Silurian Tuscarora Quartzite. The extensively vegetated deposit may owe, in part, its transport and weathering to periglacial conditions during the Pleistocene. In contrast, the Gap Mountain rock block slide is a single allochthonous block that is 1.2 km long, 0.6 km wide, and at least 60 m thick. The 43 × 10 6 m 3 block is composed of limestone of the Helderberg Group and the Oriskany Sanstone of Early Devonian age. Planar detachment probably occurred along a dissolution bedding plane near the Shriver Chert and the Oriskany Sandstone contact. Failure probably was initiated by downcutting of the South Branch Potomac River during the Pleistocene. Landslides of this magnitude suggest accelerated erosion during periglacial climates in the Pleistocene. The recognition of these large slope failures may provide evidence of paleoclimatic conditions and, thereby, increase our understanding of the geomorphologic development of the Valley and Ridge province.

New occurrences of color patterns in Devonian articulate brachiopods

Significant new occurrences of Devonian articulate brachiopods retaining color patterns includingStringocephalus burtiniDefrance from the Givetian of southern England with both concentric and radial bands, an undetermined stringocephalid brachiopod with concentric bands from the Givetian of the western Brooks Range, Alaska,Beachiacf.B. thunii(Clarke) from the mid-Early Devonian Oriskany Sandstone of Schoharie, New York, with a prominent pair of radial color bands, andAthyris vittataHall from the early Givetian Ferron Point Formation of Michigan with numerous radial color bands are illustrated. The presence of preserved color patterns is documented for the first time in members of the family Stringocephalidae King and in the family Athyrididae McCoy.

New occurrences of color patterns in Devonian articulate brachiopods

Significant new occurrences of Devonian articulate brachiopods retaining color patterns includingStringocephalus burtiniDefrance from the Givetian of southern England with both concentric and radial bands, an undetermined stringocephalid brachiopod with concentric bands from the Givetian of the western Brooks Range, Alaska,Beachiacf.B. thunii(Clarke) from the mid-Early Devonian Oriskany Sandstone of Schoharie, New York, with a prominent pair of radial color bands, andAthyris vittataHall from the early Givetian Ferron Point Formation of Michigan with numerous radial color bands are illustrated. The presence of preserved color patterns is documented for the first time in members of the family Stringocephalidae King and in the family Athyrididae McCoy.