Creek Shale Research Articles

Micro-facies characterization of the Cane Creek Shale, Paradox Basin, Utah: implications of diagenetic controls on reservoir quality

The fine-grained Pennsylvanian Cane Creek Shale of the Paradox Formation, Paradox Basin, Utah exhibits relatively thin cyclic interbeds of contrasting lithologies including fine sandstone to siltstone, organic-rich carbonate and dolomitic mudstone, and evaporites. As such, it provides a unique opportunity to evaluate micro-facies and the fluid storage capacity potential of mixed fine-grained systems. Micro-facies descriptions were performed using core and petrographic analyses, including scanning electron microscopy with energy dispersive spectroscopy. The study leverages core-based porosity and permeability data, as well as previous core description. These data are used together to explore mineralogical depositional and diagenetic controls on porosity and permeability. Twelve micro-facies were described based on sedimentological textures, grain size, lithology, and mineralogy categorized into three groups: 1) sandstone to siltstone, 2) mudstone, and 3) evaporitic micro-facies. Sandstone to siltstone micro-facies exhibit variable porosity and permeability. Porosity connectivity is dependent on the degree of authigenic cementation and compaction that negatively impacts porosity. Mudstone micro-facies show less variability in porosity and permeability; and are characterized by carbonate content, organic-matter, and clay nanopores. The development of early carbonate grains maintains porosity in mudstone and dolomitic siltstone micro-facies. Evaporitic micro-facies represented by evaporitic sabkha-like conditions are characterized by pore-reducing anhydrite and halite cement. A diagenetic paragenetic sequence was developed to assess the timing and impact of mineralogy on reservoir quality. Early (eogenetic), Middle (mesogenetic), and Late (telogenetic) stages correspond with diagenetic stages and known tectonic basin events. Syndepositional dolomite and diagenetic illite/smectite authigenic cements are the main controls on reservoir quality and have opposing effects related to porosity and permeability by preserving early pore space or reducing porosity and permeability.

An ichnotaxonomic assessment of the Cretaceous Dakota Group, Front Range, Colorado, USA, and its comparison to other Western interior seaway deposits

The Aptian-Cenomanian Dakota Group along the Colorado Front Range is known for its dinosaur tracks; however, it also contains extensive invertebrate marine and continental trace fossils. The Dakota Group in Colorado is subdivided into the Lytle, Plainview, Glencairn (Cañon City), Skull Creek Shale (Denver, Fort Collins), and Muddy formations. Thirty-two invertebrate ichnogenera and 34 ichnospecies were identified: Archaeonassa, Arenicolites, Asterosoma, Asthenopodichnium, Aulichnites, Chondrites, Cochlichnus, Conichnus, Cruziana, Cylindrichnus, Diplocraterion, Gyrolithes, Lockeia, Macaronichnus, Margaritichnus, Naktodemasis, Ophiomorpha, Palaeophycus, Planolites, Protovirgularia, Rhizocorallium, Rosselia, Rusophycus, Schaubcylindrichnus, Scolicia, Skolithos, Taenidium, Teichichnus, Teredolites, Thalassinoides, Treptichnus, and Zoophycos. Six tetrapod ichnogenera and three ichnospecies were identified: Caririchnium, Dromaeosauripus, Hatcherichnus, Ostendichnus, Magnoavipes, and Tetrapodosaurus. Three tetrapod ichnogenera Chelonipus, Ignotornis, and Mehliella have been reported at other sites in the Dakota Group, but none were found at our study sites. Rhizohaloes are reported in the Muddy Formation. Three vertebrate ichnogenera and two ichnospecies were previously described elsewhere by other workers. The Dakota Group trace fossils comprise eight ichnocoenoses–Caririchnium, Diplocraterion, Lockeia, Naktodemasis, Rhizohalo, Scolicia, Skolithos-Teichichnus, and Zoophycos–representing dwelling, deposit- and filter-feeding, and locomotion behaviors of plants, invertebrates, and tetrapods. Twelve previously unreported ichnogenera were identified: Archaeonassa, Asthenopodichnium, Conichnus, Cylindrichnus, Gyrolithes, Macaronichnus, Naktodemasis, Protovirgularia, Rusophycus, Taenidium, Treptichnus, and Zoophycos. This study is the first systematic ichnotaxonomic assessment of the invertebrate trace fossils of the Dakota Group along the Colorado Front Range, which has the highest reported ichnodiversity when compared to other Western Interior Seaway deposits.

Potential drilling hazards for wells targeting the Cane Creek shale, Pennsylvanian Paradox Formation, Paradox fold and fault belt, southeastern Utah and southwestern Colorado

The Cane Creek shale of the Pennsylvanian Paradox Formation represents a major target for oil and gas in the Paradox fold and fault belt of the northern Paradox Basin of southeastern Utah and southwestern Colorado. Early exploration and development attempts resulted in blowouts due to unexpected gas-bearing intervals and casing collapses caused by salt flowage in the Paradox Formation. These problems represent some of the types of drilling hazards that could be expected when planning Cane Creek wells. Horizontal drilling first used in the early 1990s changed the Cane Creek shale play from one of mostly drilling failures to a more successful commercial play. Depending on the location, exploratory Cane Creek wells may penetrate a section that ranges in age from Cretaceous through Pennsylvanian. Drilling in the region often encounters a wide variety of lithologies (carbonates, shale, mudstone, sandstone, and evaporites) and associated potential hazards that may include: (1) swelling clays, (2) high porosity-permeability or fractured zones resulting in lost circulation or excessive mudcake buildup, (3) “kicks” due to the influx of reservoir fluid (oil, water, or gas) into the wellbore, (4) uranium-rich zones, (5) washouts, (6) hole deviation, sticking, and other well-integrity problems, (7) chert, and (8) overpressured intervals. In addition, natural carbon dioxide, which flows from the partially human-made Crystal Geyser near some Cane Creek wellsites, represents an unusual drilling hazard if encountered in the northernmost part of the fold and fault belt. Using the lessons learned from the recently completed research well, State 16-2 (renamed the State 16-2LN-CC, API No. 43-019-50089, after the horizontal leg was drilled), and other wells in the region, drilling engineers and operators can better plan for potential hazards when exploring for hydrocarbons in the Cane Creek shale or deeper targets (Mississippian Leadville Limestone and Devonian Elbert Formation) in the fairly remote, relatively sparsely explored Paradox fold and fault belt. The goal is to de-risk wells, lower expenses, and mitigate problems before they occur. The expected results are safer and more successful drilling of wells to the Cane Creek shale and deeper reservoirs ultimately leading to additional commercial hydrocarbon discoveries in the region.

Geochronology of late Albian–Cenomanian strata in the U.S. Western Interior

Abstract Since the publication of 40Ar/39Ar dates from Cretaceous bentonites in the Western Interior Basin by J.D. Obradovich in 1993 and in Japan by J.D. Obradovich and colleagues in 2002, improvements in the 40Ar/39Ar method have included a shift to astronomically calibrated ages for standard minerals and development of a new generation of multi-collector mass spectrometers. Thus, the 40Ar/39Ar chronometer can yield results that are synchronous with U-Pb zircon dates and astrochronologic age models for Cretaceous strata. Ages determined by Obradovich have ± 2σ analytical uncertainties of ± 400 ka (excluding J value or systematic contributions) that have been used to discriminate stratigraphic events at ca. 1 Ma resolution. From among several dozen sanidine samples, 32 of which were dated by Obradovich in 1993, we present new multi-collector 40Ar/39Ar ages that reduce the average analytical uncertainties by nearly an order of magnitude. These new ages (where the uncertainties also include the contribution of the neutron fluence J value) include: Topmost Bentonite, Mowry Shale, Kaycee, Wyoming, USA, 97.52 ± 0.09 Ma Clay Spur Bentonite, Mowry Shale, Casper, Wyoming, 98.17 ± 0.11 Ma Arrow Creek Bentonite, Colorado Shale, Montana, USA, 99.12 ± 0.14 Ma Upper Newcastle Sandstone, Black Hills, Wyoming, 99.49 ± 0.07 Ma Middle Newcastle Sandstone, Black Hills, Wyoming, 99.58 ± 0.12 Ma Shell Creek Shale, Bighorn Basin, Crow Reservation, Wyoming, 99.62 ± 0.07 Ma Shell Creek Shale, Bighorn Basin, Greybull, Wyoming, 99.67 ± 0.13 Ma Shell Creek Shale, Bighorn Basin, Lander, Montana, 100.07 ± 0.07 Ma Muddy Sandstone, Wind River Basin, Wyoming, 101.23 ± 0.09 Ma Thermopolis Shale, Bighorn Basin, Wyoming, 101.36 ± 0.11 Ma Vaughn Member, Blackleaf Formation, Sweetgrass Arch, Montana, 102.68 ± 0.07 Ma Taft Hill Member, Blackleaf Formation, Sweetgrass Arch, Montana, 103.08 ± 0.11 Ma Base of the Skull Creek Shale, Black Hills, Wyoming, 104.87 ± 0.10 Ma Thermopolis Shale, Bighorn Basin, Wyoming, 106.37 ± 0.11 Ma A new U-Pb zircon age of 104.69 ± 0.07 Ma from the Skull Creek Shale at Dinosaur Ridge, Colorado, USA, is close to the new 40Ar/39Ar age of the Skull Creek Shale in the Black Hills, Wyoming, but 5 m.y. is missing in the unconformity between the Skull Creek Shale of the Black Hills and the overlying Newcastle Sandstone. Considering the average total uncertainties that include decay constant and standard age or tracer composition for the 40Ar/39Ar (± 0.19 Ma) and the U-Pb (± 0.13 Ma) ages does not alter this finding. Moreover, the lower Thermopolis Shale in the Bighorn Basin is 1.5 Ma older than the Skull Creek Shale in the Black Hills. The 100.07 ± 0.07 Ma Shell Creek Bentonite in Montana is close to the Albian–Cenomanian boundary age of 100.2 ± 0.2 Ma of Obradovich and colleagues from Hokkaido, Japan, and 100.5 ± 0.5 Ma adopted in the 2012 geological time scale of J.G. Ogg and L.A. Hinnov. Our findings indicate that correlations based on similarity of lithology, without independent radioisotopic ages or detailed biostratigraphic constraints, can be problematic or invalid. There is much more time missing in unconformities than has been previously recognized in these important, petroleum-bearing reservoir strata.

Horseshoe crab trace fossils and associated ichnofauna of the Pony Creek Shale Lagerstätte, Upper Pennsylvanian, Kansas, USA

The uppermost Pennsylvanian Pony Creek Shale Lagerstätte (Pony Creek Shale Member, Wood Siding Formation, Wabaunsee Group) near Maple Hill, Wabaunsee County, Kansas, contains exceptionally preserved horseshoe crab (Xiphosura) fossils. Associated with these fossils is an ichnofauna that includes trace fossils assumed to be produced by xiphosurids, as well as coprolites and a few burrows. Of the trace fossils recovered from the Pony Creek Shale Member, 26 specimens represent the ichnogenera Arborichnus, Crescentichnus, Kouphichnium, and Selenichnites, all of which are commonly associated with xiphosurids. The other trace fossils consist of the ichnogenus Rhizocorallium, several unidentified burrows, and coprolites, some preserving animal remains. The xiphosuran locomotion traces from the Pony Creek Shale Member are primarily crawling trails. These trace fossils are distinguished by back and forth scratch imprints, as opposed to the typical xiphosurid tracks that show independent foot marks in the substrate. Other trace fossils include resting traces and feeding traces. Previous paleoenvironmental interpretations and the trace and body fossil record indicate a marginal-marine depositional system for the Pony Creek Shale.

What do Ce anomalies in marine carbonates really mean? A perspective from leaching experiments

Yttrium and rare earth elements (REY) in aqueous environments have been intensively studied because they record important geochemical information. For example, the cerium anomaly, measured in marine sedimentary rocks, has been widely applied as a paleoredox indicator. Marine carbonates are the main substrate used to reconstruct REY signal in paleo-oceans with the underlying assumption that REY incorporated into carbonate minerals preserve the authigenic seawater signal. However, extracting authigenic REY signals from carbonate rocks are challenging. It requires dissolving carbonate phases using acid leaching procedures without contamination from other non‑carbonate phases such as Mn/Fe oxides (hydroxides), clay minerals, siliciclastic and organic phases. Multiple dissolution protocols, especially partial leaching, were proposed to eliminate potential contaminations. Yet, the efficiency of these procedures in reducing contamination remains ambiguous. Additionally, no systematic study on how each non‑carbonate phase can modify the authigenic REY signal from carbonates. First, we systematically investigated the efficiency of using ammonium acetate buffer pre-treatment to remove exchangeable ions prior to dissolution. We tested a range of concentration, pH, and reaction time of the buffer and we found that ammonium acetate of 1 M with a pH slightly <7, and 30 mins for reaction time works best for efficiency. Second, we tested a range of acid species and molarity to dissolve common non‑carbonate contamination phases including USGS standards NOD-A-1 (manganese nodule) and SBC-1 (Brush Creek shale), as well as montmorillonite, kaolinite, illite from the Clay Minerals Society. We used three batches of acetic and nitric acids with different molarity and found that both the acid species and molarity are key parameters to avoid leaching of non‑carbonate phases. We observed a negative Ce anomaly during leaching of Mn nodule using acetic acid versus a positive anomaly using nitric acid suggesting that nitric acid may introduce false positive Ce anomalies into samples. We also demonstrated that it is essential to filter the leachate to prevent the later dissolution of floating particles. For instance, Mn oxides, which carry positive Ce anomalies, can overprint the carbonate REY signal because the nitric acid (i.e. 2% v/v) used during later ICP-MS analysis could dissolve tetravalent Ce. Third, we conducted a series of leaching experiments on mixed samples consisting of 80% pure modern limestone and 20% mixed pure contaminants to identify the best protocol to avoid contamination. We demonstrate that using acetic acid with a molarity lower than 0.5 M is sufficient to avoid contaminations from Mn oxides, clay minerals, and siliciclastic phases. Finally, we present a new sequential leaching protocol for calcite (>75% CaCO3) using two steps of ammonium acetate pre-leaching followed by three steps of 0.3 M acetic acid leaching.

Unconventional petroleum potential in the Mowry Shale, Southern Powder River Basin, Wyoming

The Lower Cretaceous Mowry Shale is a major source rock in the northern Rocky Mountain region (Schrayer and Zarrella, 1968; Nixon, 1973; Byers and Larson, 1979; Burtner and Warner, 1984; Momper and Williams, 1984; Davis et al., 1989; Modica and Lapierre, 2012). The source rock contains primarily Type II organic matter with an admixture of Type III kerogen towards the west. Thermally mature Mowry Shales are closely associated with petroleum accumulations in both Lower and Upper Cretaceous reservoirs. The Mowry Shale has produced modest amounts of oil from older vertical wells in the Powder River basin (Figure 1). With technology improvements (horizontal drilling and multistage hydraulic fracture stimulation) over the past decade, the Mowry is now a prospective target for hydrocarbon production (Finley, 2017). Horizontal drilling is currently targeting the Mowry in the deeper parts of the Powder River Basin. The Mowry Shale overlies the Shell Creek Shale or Muddy/Newcastle sandstones and is overlain by the Frontier Formation or Belle Fourche Shale (Figure 2). The Mowry petroleum system consists of the Mowry source rock and the following Cretaceous reservoirs: Lakota, Fall River, Muddy, Newcastle, Mowry, Frontier, and Turner.

Frasnian scolecodonts from the Grassy Creek Shale, eastern Iowa, United States

Four scolecodont species are described from the lower 1ft of the Grassy Creek Shale at the type section of the Sweetland Creek Shale. This stratigraphic interval yields abundant and well-preserved Maxillae I and II scolecodont elements of Paulinites and Kielanoprion, and some partial apparatuses of Kielanoprion. The scolecodont assemblage recovered from the Grassy Creek Shale is similar to other Devonian assemblages from shales, and is distinct from other Devonian assemblages found in carbonates. Comparison of the species from this reportwith previous publications suggest that the scolecodonts from the Grassy Creek Shale have different stratigraphic ranges and may be useful biostratigraphic tools.

Climatic and paleogeographic significance of eolian sediment in the Middle Permian Dog Creek Shale (Midcontinent U.S.)

Middle Permian fine-grained redbeds of Midcontinent North America are analogous to many Permian units globally. They archive an interesting time in Earth history, but the lack of fossils and the fine grain size have confounded attempts to refine the age and depositional setting, respectively. Here we focus on the Dog Creek Shale and correlatives of Oklahoma and Kansas (paleo-tropical western Pangaea), which are representative of many analogous Permian units across the region and globe, to assess the age, depositional environment, and provenance of siliciclastic material.These mudstone-dominant units have long been interpreted to record marine deltaic or tidal flat deposition based primarily on the presence of evaporites and an inferred relationship with sandstone units southward. However, the uniform grain size, and occurrence of common paleosols, together with the lack of typical deltaic attributes such as hyper/hypo-pycnites, proximal deltaic channels, and large-scale upwardly coarsening trends, in addition to the problematic correlation, complicate this interpretation. Sheet-like tabular siliciclastic units thin northward from the Anadarko foredeep (Oklahoma) onto the Anadarko shelf (Kansas), and undergo lateral facies changes into marginal marine evaporites of the San Andres Formation in the Palo Duro Basin (Texas Panhandle). The fine and uniform grain size, massive bedding, and sheet-like geometry indicate that the siliciclastic units are eolian in origin, but at times were transported by wind and deposited and reworked in mudflats. Abundant Vertisols within the Dog Creek Shale indicate periods of wetting and drying in a low-relief setting. Major detrital zircon age populations reflect a dominantly east to southeasterly Appalachian–Ouachita source, with minor input from derivative sediment from the Ancestral Rocky Mountains to the west and northwest. These data indicate prevailing easterlies, and some westerly and southwesterly winds in western equatorial Pangaea, possibly representing north to south shifting of the Inter-Tropical Convergence Zone (ITCZ), likely associated with monsoonal circulation. The predominance of eolian-transported material and its capture in a series of mudflats and soils indicates that midcontinent North America (western equatorial Pangaea) formed a major sink for large volumes of atmospheric dust in middle Permian time, quite unlike the modern and recent tropics.

Bayhead delta interpretation of an Upper Pennsylvanian sheetlike sandbody and the broader understanding of transgressive deposits in cyclothems

The Rakes Creek Shale is noteworthy as a non-incised sheetlike sandstone body in the Shawnee Group of the Midcontinent, USA, succession of Upper Pennsylvanian cyclothems. Relative to contemporaneous settings in North America, there are comparatively few major sandy lithosomes on the low-accommodation northern high shelf of the Midcontinent, and those that have been described in detail are incised valley fills. In our study area, the Rakes Creek Shale is characterized by a consistent internal succession of eight dominant lithofacies ranging from largely nonrhythmic heterolithic strata at the base, to large-scale cross-stratified and massive sandstones, to carbonaceous and heterolithic sandstones at the top. Eight other lithofacies of minor volumetric importance also appear in the Rakes Creek Shale in our study area. At the base of the succession is a widespread well-drained paleosol that shows no evidence for incision across a transect of 30km. Sandstones in the upper part of the Rakes Creek Shale contain abundant root casts and carbonaceous root traces, indicating colonization by land plants after accommodation space had been filled. The Rakes Creek Shale is comparatively unique in the enclosing regional Pennsylvanian succession because it provides evidence for: (1) the filling of accommodation space in the early stages of a marine transgression by comparatively coarse clastic sediments (with minimal influence by tides and waves), and (2) higher rates of sediment supply and/or slower rates of relative sea level rise compared to most other transgressive intervals in cyclothems of the Midcontinent.The regional lithofacies succession of the Rakes Creek Shale, as well as changes in that succession that appear at the eastern edge of our study area, lead us to interpret it as a series of landward-stepping, bayhead delta parasequences deposited rapidly in an embayment with minimal wave and tide energy. The Rakes Creek Shale represents a rare, and perhaps previously undocumented, variation in the expression of transgressive deposits. Ancient bayhead deltas described from the literature are typically associated with the deposits of comparatively narrow incised valleys. We also interpret the ~10m thickness of the Rakes Creek Shale in the Weeping Water Valley of southeastern Nebraska as the minimum rise in relative sea level during its associated transgression. We interpret the discrepancy between this value and others calculated for Midcontinent Pennsylvanian cyclothems as direct evidence for glacioeustatic sea-level rises of varying magnitudes during the Late Paleozoic Gondwanan ice ages.

A Labyrinthodont Amphibian from the Margin of the Pennsylvanian Epicontinental Sea in Kansas

A partial labyrinthodont amphibian skull was collected from the Pony Creek Shale Member of the Wood Siding Formation (Virgilian Stage, Upper Pennsylvanian) in Wabaunsee County, Kansas. The partial skull provides supporting evidence that labyrinthodonts frequented marginal marine environments. The fossil is from an animal that probably was about 1.5 meters long in life and was ecologically similar to an alligator.

Unusual Albian (Early Cretaceous) Brachyura (Homoloidea: Componocancroidea New Superfamily) from Montana and Wyoming, U.S.A.

Brachyuran specimens collected from the Albian (Early Cretaceous) age Shell Creek Shale in Montana and Wyoming provide the basis for description of two new species, Zygastrocarcinus waagei and Componocancer roberti. The former represents only the fourth species of a genus that is endemic to the Cretaceous of mid-continental North America. The latter species is assigned to a new superfamily, Componocancroidea; new family, Componocancridae; and new genus, Componocancer, within Heterotremata. Componocancer exhibits a combination of primitive and derived features that is unique among Brachyura.

Upper Ordovician microphytoplankton of the Bill's Creek Shale and Stonington Formation, Upper Peninsula of Michigan, U.S.A.: Biostratigraphy and paleogeographic significance

An abundant, diverse, and well-preserved organic-walled microphytoplankton assemblage is described from the Upper Ordovician Bill's Creek Shale and the lower Stonington Formation (Bay de Noc Member) in the Upper Peninsula of Michigan, U.S.A. Based on graptolite and conodont evidence, the Bill's Creek Shale and Stonington Formation are Richmondian (=Ashgill) in age. The assemblage is dominated by acritarchs, which comprise 29 species (including the enigmatic palynomorph Gloeocapsomorpha prisca) assigned to 20 genera. The prasinophyte phycomata are represented by undifferentiated species of Leiosphaeridia and Tasmanites. In addition, chitinozoans are abundant, and scolecodonts and graptolite fragments are common. Paleontologic-palynologic and sedimentologic evidence indicates that the Bill's Creek Shale was deposited in a low-energy, shallow, nearshore marine environment. The overlying Bay de Noc Member of the Stonington Formation also accumulated in a low-energy, normal marine environment, but in a more offshore, somewhat deeper water setting. Both formations experienced minor transgressive and regressive episodes as indicated by fluctuations in the composition of the palynoflora. The combined Bill's Creek/Stonington acritarch assemblage closely resembles those described from the Richmondian-aged Maquoketa Shale (Missouri and Kansas), Sylvan Shale (Oklahoma), and Vauréal Formation (Anticosti Island, Québec, Canada). The overall composition of the acritarch assemblage from these four formations reflects a distinctive, recognizably Laurentian character. Nonetheless, many of the Bill's Creek/Stonington acritarchs have been reported from Upper Ordovician localities elsewhere, providing additional evidence for Late Ordovician cosmopolitanism of the marine microphytoplankton community. Additionally, the restricted stratigraphic range of many of the taxa further enhances their biostratigraphic application, both regionally and globally, and reaffirms the Richmondian (=Ashgill) age of the Bill's Creek Shale and Stonington Formation.

Historical analysis and reinterpretation of the lower part of the Canyon Group (Missourian, Upper Pennsylvanian), Wise County, Texas: A fine can of worms

Late Pennsylvanian (Early Missourian) age limestone strata exposed in several isolated outcrops in the Trinity River Valley in southwest Wise County, Texas were last described by Bose (1917), and Scott and Armstrong (1932). These strata can be correlated with the Upper Pennsylvanian Palo Pinto and Posideon formations of Laury (1962) in the lower part of the Canyon Group in the Brazos River Valley. The two reports were stratigraphically inconsistent concerning the seven limestone units of the Palo Pinto Formation as named by Scott and Armstrong (1932), and both included many poorly located type sections. The Bose (1917) report included no map and many key geographic references were to 1914 ranch names. Wise County records have helped to pinpoint these locations and allowed the reconciliation of the Bose (1917) Palo Pinto limestone localities to those of Scott and Armstrong (1932). Examination of exposures of these strata, and their associated fusulinid and conodont faunas has demonstrated that the following correlations to the Canyon Group in the type area in the Brazos River Valley in Palo Pinto County can be made (in descending order): (i) a conodont-rich black mudstone (indicating maximum transgression and a deep basin environment) at the base of the Wolf Mountain Shale and just above the Wiles Limestone correlates to a similar interval just above the Willow Point Limestone, well exposed in the area around the southwest shore of Lake Bridgeport; (ii) the Willow Point Limestone (= Bridgeport Limestone of Bose) correlates to the Wiles Limestone (top of the Posideon Formation); (iii) strata in the Martin Lake area just south of Bridgeport correlate to equivalent age conodont-rich black mudstones present in the middle part of the Posideon Formation; (iv) the Martin Lake Limestone is a fusulinid/algal grainstone containing a distinctive nankinellid fusulinacean at all outcrops and indicates very shallow marine deposition. It correlates with the top part (= Wynn Limestone) of the Palo Pinto Formation; (v) the Hudson Bridge Limestone correlates with the lower part of the Palo Pinto Formation. A black shale interval a few centimeters thick found in a core taken in an abandoned quarry in the Palo Pinto Formation in southwestern Wise County is correlated to a crinoid - conodont-rich 10-25cm unit that marks the base of the Palo Pinto Formation on top of the Keechi Creek Shale in much of Palo Pinto County. The new correlation of the Willow Point Limestone, the uppermost member that Scott and Armstrong (1932) reported as being in the Palo Pinto Formation, and its placement into the overlying Posideon Formation, leaves six limestone members in the Palo Pinto Formation identified in Wise County. Its top and bottom members, the Martin Lake Limestone and the Hudson Bridge Limestone, respectively, now are firmly correlated to the top and bottom, respectively, of the Palo Pinto Formation in the type area. A 1937 revision of the geologic map of Wise County raised the lower boundary of the Palo Pinto Formation, placing its lowest two members into the older Mineral Wells Formation of the Strawn Group (Armstrong 1937).

English

Most previous coal mine drainage leaching studies have not investigated the effect of surface area, effects of elevated Pco2, which are typical of mine spoil, and solubility constraints on water chemistry. The leaching column and humidity cell tests were designed to evaluate the importance of these parameters. Surface area was examined on three rock types before and after leaching: the Brush Creek shale; a well-indurated calcareous sandstone; and a coal refuse. The surface area, as measured by BET, for the shale was an order of magnitude greater than the other rock types. Surface area after leaching decreased slightly for the shale, and by half for the refuse. The sandstone area remained the same. Plots of sulfate concentration through time closely resemble those expected for diffusioncontrolled kinetics. Plots of alkalinity through time are characteristic of a material that dissolves quickly at first and then approaches or reaches saturation. Saturation with respect to calcite was confirmed by equilibrium calculations. The water in the leaching columns was undersaturated with respect to gypsum, indicating that sulfate was a conservative parameter and could be used to measure pyrite oxidation rates. The target 10% CO2 was achieved in the column tests, but not achieved in the humidity cell tests. At the end of 12 to 14 weeks, between 1.5 and 2% of the calcite and between 4 and 6% of the sulfur in the rock had been removed by weathering. Predictions, based on power function equations, indicate that the Brush Creek shale sample would remain alkaline even if weathered for years. Comparisons between leaching chemistry and field data for the Brush Creek shale and the coal refuse sample showed similar water chemistry.

MAPESITES, A NEW UPPER PENNSYLVANIAN (LOWER VIRGILIAN) AMMONOID FROM KANSAS

In recent years, the authors, along with colleagues, have documented the lower Virgilian ammonoid faunas of the Midcontinent and north-central Texas (Boardman et al., 1989, 1994a, 1994b; Work and Boardman, 1995, 1996). Generic diversity for this interval is the highest in any Upper Pennsylvanian succession: at least 18 genera (representing 15 families) have been recovered from the Colony Creek Shale in north-central Texas alone (Boardman et al., 1989). An additional, previously unrecognized ammonoid from the correlative Little Pawnee Shale in southeastern Kansas is described herein as Mapesites chautauquaensis new genus and species. It is a highly original taxon with no obvious close relatives. Representatives of Mapesites chautauquaensis n. gen. and sp. were recovered from the Little Pawnee Shale Member of the Cass Limestone from a roadcut exposure along US Highway 166, 1.4 km west of Peru, Chautauqua County, Kansas (NE NE sec. 20, T34S, R12E, Peru 7.5′ quadrangle). The Little Pawnee sequence at Peru consists of 2.6 m of dark gray fossiliferous shale with a 0.6-m black phosphatic zone 0.2 to 0.8 m above the base. Ammonoids occur as limonitic internal casts in the lower part of the shale sequence, 0 to 0.2 m above the base, and as calcitic casts in the middle part, 1.1 to 1.9 m above the base. The Little Pawnee Shale immediately overlies a thin, 0.1-m-thick dark skeletal packstone-wackestone unit, the Haskell Limestone Member, which contains the provisional Missourian-Virgilian Stage boundary (see Heckel et al., 1999, p. 50, 51 for additional details). The assemblage from the Little Pawnee Shale at this locality, in addition …

The Frasnian/Famennian boundary in central and eastern United States

The Frasnian/Famennian (F/F) Boundary in the northern Appalachian Basin is found in the Hanover Shale and equivalent strata where it is locally associated with a black shale interval equivalent to the Upper Kellwasser interval in Europe. The boundary is immediately below the Dunkirk–Huron black shale that represents the IIe T–R cycle transgression. In the southern Appalachian Basin, the southern edge of the Cincinnati Arch, and the southeastern Illinois Basin the F/F boundary is at or near the base of the Gassaway Member of the Chattanooga Shale or the Morgan Trail Member of the New Albany Shale, or was eroded during the IIe T–R cycle beginning in the Middle triangularis Zone. In the western Illinois Basin (Grassy Creek Shale), Michigan Basin (Lachine Member of Antrim Shale), and southern continental margin (Woodford Shale) the F/F boundary is within black shale strata, indicative of an earlier development of the IIe T–R transgression inboard of the Appalachian Basin or the juxtaposition of the IIe T–R transgression over the Upper Kellwasser black shale interval without significant or recognizable lithologic change.

Indian Castle Shale: late synorogenic siliciclastic succession in an evolving Middle to Late Ordovician foreland basin, eastern New York State

The thick, organic-rich, Indian Castle Shale, is a major component of the greater Utica Shale basinal facies succession associated with the Taconian Orogeny. Detailed correlations of numerous Indian Castle sections, presented herein, are based on physical matching of numerous altered ash layers (K-bentonites) coupled with use of submarine discontinuities and other distinctive beds. Several important trends are observed: first, the Dolgeville Formation extends eastward into the eastern Mohawk Valley region (Hoffmans Fault area) lithologically separating an older Utica division (Flat Creek Shale) from Indian Castle Shale proper. Second, Indian Castle Shale strata are observed to overlap the regional top-Dolgeville and post-Trenton disconformity towards the northwest. Third, the lower part, and possibly the upper part, of the Indian Castle succession is differentially thickened in the west-central Mohawk Valley region due to differential subsidence and syntectonic fault activity. Fourth, the lower part of the Indian Castle Shale succession in the central-to-eastern part of the Mohawk Valley region continues to thin slightly with little evidence for major eastward transition of Utica facies into turbiditic Schenectady deposits. Fifth, K-bentonitic beds, many displaying distinctive sedimentological features, are clustered in intervals of apparent Indian Castle stratigraphic condensation. Ashes also display an overall upward decrease in abundance within the Indian Castle Shale succession. These patterns indicate that Indian Castle deposition, influenced by lithospheric flexural processes, localized fault activity and eustatic fluctuations, occurred when the foreland basin was maximally developed. Indian Castle deposition was probably linked to a collisional tectophase of Taconian overthrusting.

Horseshoe Crabs (Arthropoda: Xiphosurida) from the Pennsylvanian of Kansas and Elsewhere

Pennsylvanian strata of Kansas have yielded two species of xiphosurids (horseshoe crabs). The exceptionally preserved fossils are from inferred coastal (estuarine or tidal flat) paleoenvironments. One species, the euproopid Euproops danae (Meek and Worthen), occurs in the Lawrence Formation (Upper Pennsylvanian: Virgilian) in Douglas County, Kansas. Siderite concretions in the Lawrence Formation preserve organisms similar to those from Braidwood-type assemblages of the Mazon Creek biota of Illinois. This occurrence of E. danae in the Virgilian Stage (North American usage) is one of the few stratigraphically above the Desmoinesian Stage of North America or the Westphalian D Series of Europe. Another xiphosurid, the limuline Paleolimulus signatus (Beecher), occurs in the Pony Creek Shale Member of the Wood Siding Formation (Upper Pennsylvanian: Virgilian) in Wabaunsee County, Kansas. This occurrence extends the known stratigraphic range of P. signatus downward from the Permian into the Pennsylvanian. Another specimen that is here referred to P. signatus, and which was collected from the Mazon Creek biota of Illinois, shows that the species ranges downward to the Desmoinesian Stage (of North American usage).

Study of the Oxidation of Oil Shale and Kerogen by Fourier Transform Infrared Emission Spectroscopy

Infrared emission spectroscopy has been used to monitor the chemical modifications taking place during the oxidation of bitumen-free Kerosene Creek shale, the bitumen-carbonate-free shale, and the bitumen-carbonate-silicate-free shale (kerogen). The samples were heated, in air, at temperatures in the range 50-700 °C at intervals of 50 °C. Oxidation of the samples at increasing temperatures showed a steady decrease in the signals due to aliphatic hydrocarbons (3000 cm -1 to 2700, 1460, and 1375 cm -1 ) as well as in the carbonyl/carboxyl signals (∼1710 cm -1 ) and the carbonyl signal at 1740 cm -1 , along with an increase in the anhydride signals at 1775 cm -1 and at ∼1850 cm -1 . Constant temperature (300 °C) oxidation produced a steady increase in the anhydride peaks at ∼1775 cm -1 and at ∼1850 cm -1 while the 1710 and 1740 cm -1 peaks slowly decreased. Of the mineral bands, those characteristic of carbonates totally disappeared at 700 °C while the other bands remained. The rate of decomposition of organic functionalities is generally fastest for the bitumen-carbonate-free sample. Analysis of the kinetic data clearly showed that the presence of carbonates and silicates lowered the activation energy for the oxidation of aliphatic C-H groups.