Thomas W.A.,Geological Survey of Alabama |
Tucker R.D.,U.S. Geological Survey |
Astini R.A.,National University of Cordoba |
Denison R.E.,15141 Kingstree Drive
Geosphere | Year: 2012
New geochronologic data from basement rocks support the interpretation that the Argentine Precordillera (Cuyania) terrane was rifted from the Ouachita embayment of the Iapetan margin of Laurentia. New data from the Ozark dome show a range of ages in two groups at 1466 ± 3 to 1462 ± 1 Ma and 1323 ± 2 to 1317 ± 2 Ma, consistent with existing data for the Eastern Granite-Rhyolite province and Southern Granite-Rhyolite province, respectively. Similarly, a newly determined age of 1364 ± 2 Ma for the Tishomingo Granite in the Arbuckle Mountains confirms previously published analyses for this part of the Southern Granite-Rhyolite province. Along with previously reported ages from basement olistoliths in Ordovician slope deposits in the Ouachita embayment, the data for basement ages support the interpretation that rocks of the Southern Granite-Rhyolite province form the margin of Laurentian crust around the corner of the Ouachita embayment, which is bounded by the Ouachita rift and Alabama-Oklahoma transform fault. In contrast, both west and east of the corner of the Ouachita embayment, Grenville-Llano basement (approximately 1325-1000 Ma) forms the rifted margin of Laurentia. New U/Pb zircon data from basement rocks in the southern part of the Argentine Precordillera indicate crystallization ages of 1205 ± 1 Ma and 1204 ± 2 Ma, consistent with previously reported ages (approximately 1250-1000 Ma) of basement rocks from other parts of the Precordillera. These data document multiple events within the same time span as multiple events in the Grenville orogeny in eastern Laurentia, and are consistent with Grenville-age rocks along the conjugate margins of the Precordillera and Laurentia. Ages from one newly analyzed collection, however, are older than those from other basement rocks in the Precordillera. These ages, from granodioritic-granitic basement clasts in a conglomerate olistolith in Ordovician slope deposits, are 1370 ± 2 Ma and 1367 ± 5 Ma. These older ages from the Precordillera are consistent with indications that the Iapetan margin in the Ouachita embayment of Laurentia truncated the Grenville front and left older rocks of the Southern Granite-Rhyolite province (1390-1320 Ma) at the rifted margin. Chronostratigraphic correlations of synrift and post-rift sedimentary deposits on the Precordillera and on the Texas promontory of Laurentia document initial rifting in the Early Cambrian. Previously published data from synrift plutonic and volcanic rocks in the Wichita and Arbuckle Mountains along the transform-parallel intracratonic Southern Oklahoma fault system inboard from the Ouachita embayment document crystallization ages of 539-530 Ma. New data from synrift volcanic rocks in the Arbuckle Mountains in the eastern part of the Southern Oklahoma fault system yield ages of 539 ± 5 Ma and 536 ± 5 Ma, confirming the age of synriftvolcanism. © 2012 Geological Society of America.
Pashin J.C.,Oklahoma State University |
McIntyre-Redden M.R.,Geological Survey of Alabama |
Mann S.D.,Geological Survey of Alabama |
Kopaska-Merkel D.C.,Geological Survey of Alabama |
And 2 more authors.
International Journal of Coal Geology | Year: 2014
Water and gas chemistry in coalbed methane reservoirs of the Black Warrior Basin reflects a complex interplay among burial processes, basin hydrodynamics, thermogenesis, and late-stage microbial methanogenesis. These factors are all important considerations for developing production and water management strategies. Produced water ranges from nearly potable sodium-bicarbonate water to hypersaline sodium-chloride brine. The hydrodynamic framework of the basin is dominated by structurally controlled fresh-water plumes that formed by meteoric recharge along the southeastern margin of the basin. The produced water contains significant quantities of hydrocarbons and nitrogen compounds, and the produced gas appears to be of mixed thermogenic-biogenic origin.Late-stage microbial methanogenesis began following unroofing of the basin, and stable isotopes in the produced gas and in mineral cements indicate that late-stage methanogenesis occurred along a CO2-reduction metabolic pathway. Hydrocarbons, as well as small amounts of nitrate in the formation water, probably helped nourish the microbial consortia, which were apparently active in fresh to hypersaline water. The produced water contains NH4 + and NH3, which correlate strongly with brine concentration and are interpreted to be derived from silicate minerals. Denitrification reactions may have generated some N2, which is the only major impurity in the coalbed gas. Carbon dioxide is a minor component of the produced gas, but significant quantities are dissolved in the formation water. Degradation of organic compounds, augmented by deionization of NH4 +, may have been the principal sources of hydrogen facilitating late-stage CO2 reduction. © 2013 Elsevier B.V.
Powell C.A.,University of Memphis |
Thomas W.A.,Geological Survey of Alabama
Geology | Year: 2016
The Eastern Tennessee seismic zone extends more than 300 km from as far north as southeastern Kentucky southward into Alabama, southeastern United States. We propose that a large-scale shear zone, which originated as a continental transform fault during the Grenville orogeny and assembly of supercontinent Rodinia, constitutes the framework for earthquake activity in the Eastern Tennessee seismic zone. This new seismotectonic model is based on a diverse set of geophysical and geological observations, including paleomagnetic and isotopic constraints on the growth of southeastern Laurentia during the Grenville orogeny. © 2015 The Authors.
Mueller P.A.,University of Florida |
Heatherington A.L.,University of Florida |
Foster D.A.,University of Florida |
Thomas W.A.,Geological Survey of Alabama |
Wooden J.L.,Stanford University
Gondwana Research | Year: 2014
In southeastern Laurentia the Suwannee suture separates the undeformed part of the Gondwanan Suwannee terrane (SWT) from crust of Laurentia and previously accreted Gondwanan terranes that were deformed during the Alleghanian orogeny. Undeformed early Paleozoic sedimentary rocks of the SWT are considered of Gondwanan-African derivation on the basis of various considerations, including a lack of Mesoproterozoic (Grenville) detrital zircons. The cratonic heritage of Suwannee lithosphere is complicated, however, because Sm-Nd depleted mantle model ages from both Neoproterozoic and Alleghanian (Carboniferous-Permian) granites north and south of the suture zone are Mesoproterozoic. Mesoproterozoic lithosphere has not been reported in conjugate West Africa, but is present in Amazonia, suggesting that the SWT: 1) may be a composite terrane, containing both African upper crust and Amazonian lower crust/lithosphere, 2) was separated from Gondwana during Atlantic Ocean rifting along a Mesoproterozoic-Neoproterozoic suture, and/or 3) contains Laurentian Grenville-age lower crust and lithosphere that must also underlie other accreted proximal Gondwanan terranes (e.g., Uchee terrane). In addition, the ~300Ma, syn- to post-tectonic granitoids emplaced across the Suwannee suture zone are the product of crustal anatexis, not supra-subduction magmatism, on the basis of Mesoproterozoic Sm-Nd Tdm and zircon xenocrysts. The lack of documented ~300Ma, supra-subduction magmatism in both Laurentian and Gondwanan components in southern Laurentia (e.g., southernmost Appalachian and Ouachita orogens) strongly suggests that accretion of the SWT and related Gondwanan terranes occurred during dextral transpressional convergence between Laurentia and a combined African-Amazonian craton, a characteristic shared with conjugate crust in southwestern Europe. In this interpretation, intervening oceanic lithosphere and contemporary volcanic arcs (if any) were largely removed by disaggregation and dispersion along the transpressional boundary possibly combined with highly oblique overthrusting and/or partly subducted at the leading edge(s) of other blocks of Gondwanan lithosphere that were accreted to southern Laurentia in the late Paleozoic (e.g., Wiggins, Sabine, Coahuila, Maya, etc.). Mesozoic opening of the Gulf of Mexico has subsequently and variably altered the original configuration of these terranes. © 2013 International Association for Gondwana Research.
Elrick M.,University of New Mexico |
Rieboldt S.,Geological Survey of Alabama |
Saltzman M.,Ohio State University |
McKay R.M.,Geological Survey Bureau
Geology | Year: 2011
The globally recognized Late Cambrian Steptoean positive C-isotope excursion (SPICE) is characterized by a 3‰-5‰ positive δ13C shift spanning <4 m.y. Existing hypotheses suggest that the SPICE represents a widespread ocean anoxic event leading to enhanced burial/preservation of organic matter (Corg) and pyrite. We analyzed δ18O values of apatitic inarticulate brachiopods from three Upper Cambrian successions across Laurentia to evaluate paleotemperatures during the SPICE. δ18O values range from ~12.5‰ to 16.5‰. Estimated seawater temperatures associated with the SPICE are unreasonably warm, suggesting that the brachiopod δ18O values were altered during early diagenesis. Despite this, all three localities show similar trends with respect to the SPICE δ13C curve, suggesting that the brachiopod apatite preserves a record of relative δ18O and temperature changes. The trends include relatively high δ18O values at the onset of the SPICE, decreasing and lowest values during the main event, and an increase in values at the end of the event. The higher δ18O values during the global extinction at the onset of the SPICE suggests seawater cooling and supports earlier hypotheses of upwelling of cool waters onto the shallow shelf. Decreasing and low δ18O values coincident with the rising limb of the SPICE support the hypothesis that seawater warming and associated reduced thermohaline circulation rates contributed to decreased dissolved O2 concentrations, which enhanced the preservation/burial of Corg causing the positive δ13C shift. © 2011 Geological Society of America.
Hills D.J.,Geological Survey of Alabama
GeoResJ | Year: 2015
Adopting standards for data and metadata collection is necessary for success of data rescue and preservation initiatives. Physical sample data and metadata rescue and preservation can be particularly challenging in that much of the available information may not be readily digitized or machine-readable. Making the legacy data rescue and preservation process as simple as possible through the development of template workflows can enable wider adoption of standards by personnel. Template workflows also simplify training of additional personnel to assist in the registration process. © 2015 The Authors.
Thomas W.A.,Geological Survey of Alabama
Geoscience Canada | Year: 2014
Transform faults along the Iapetan rifted continental margin of Laurentia offset the continental rift and/or bound domains of oppositely dipping low-angle detachments. Rift-parallel and transform-parallel intracratonic fault systems extend into continental crust inboard from the rifted margin. Ages of synrift igneous rocks, ranging from 765 to 530 Ma, document non-systematic diachroneity of rifting along the Iapetan margin. Synrift sedimentary accumulations show abrupt variations in thickness across transform faults, and some concentrations of synrift igneous rocks are distributed along transform faults and transform-parallel intracratonic fault systems. The greatest thicknesses of Cambrian–Ordovician passive-margin shelf-carbonate deposits are along transform margins and in continental-margin basins along transform faults, as well as along transform-parallel intracratonic fault systems, indicating anomalously great post-rift thermal subsidence along transform faults. Along the Ordovi-cian–Permian Appalachian-Ouachita orogenic belt, a diachronous array of synorogenic clastic wedges fills foreland basins, recording tectonic-load-driven flexural subsidence of the litho-sphere. The greatest thicknesses of synorogenic clastic wedges of all ages are consistently in foreland basins along transform margins and inboard from intersections of transform faults with the rifted margin, indicating systematically weaker lithosphere along transform faults. The distinctive and pervasive properties and behaviour of the lithosphere along transform faults in successive tectonic settings suggest fundamental controls on tectonic inheritance at transform faults. Recent models for continental rifting incorporate ductile extension of the mantle lithosphere beneath brittle extension of the crust; the domain of ductile extension of the mantle lithosphere may reach significantly inboard from the rifted margin of the brittle crust, accounting for rift-parallel extensional faults in the crust inboard from the rifted margin. A transform offset of a rift in brittle crust requires a similar offset in ductile extension of the mantle lithosphere, leading to differential ductile flow on opposite sides of the transform and imparting a transform-parallel distributed-shear fabric. Transform-parallel distributed shear in the mantle lithosphere provides a mechanism for brittle transform-parallel fault systems in the continental crust. Studies of seismic anisotropy show fast directions parallel with transform faults, indicating systematic orientation of crystals through transform-parallel distributed shear in the mantle litho-sphere © 2014 GAC/AGC®
Bearden B.L.,Geological Survey of Alabama
Water Policy | Year: 2012
The Mekong is the archetypal dissevered river basin, separated, divided into parts and broken up by ambiguous and undefined terms in the 1995 Agreement on the Cooperation for the Sustainable Development of the Mekong River Basin. The treaty's text generalizes and redefines the concept of a river basin in which tributaries are marginalized and headwaters are excluded, yet on paper the 1995 Mekong Agreement creates the legal fiction of a holistic water resources management paradigm primarily by focusing on the 'imported' (Affeltranger, 2005, p. 54) concept of sustainable development. In effect, transboundary tributaries in the Mekong legal regime are managed by each state unilaterally through application of the limiting language embodied in Article 5(A) which emphasizes hydrosovereignty. The modern trend and badge of responsibility are to provide a legal framework for the entire watercourse, defined as including its tributaries, and to promote basin-wide governance. Analysis of selected legal regimes and case law demonstrates that ironically, despite their volumetric contributions to flow, tributaries remain at the margin of many legal regimes of international and interstate watercourses including the Mekong. The Lower Mekong River Basin states should consider use of joint development agreements (JDAs), subcompacts or subsidiary agreements for negotiating and dealing with intrabasin water use and interbasin water diversions on tributaries. © IWA Publishing 2012.
Pashin J.C.,Geological Survey of Alabama
International Journal of Coal Geology | Year: 2010
Gas saturation is highly variable in Carboniferous coalbed methane reservoirs of the Black Warrior Basin (USA), and diverse geologic data derived from more than three decades of exploration and development provides insight into the origin of this variability and the consequences for production performance. Coalbed methane is produced from numerous thin (~0.3 to <4. m) coal seams that are distributed through 700 to 1200. m of stratigraphic section. Gas content tends to increase with depth, and gas saturation typically ranges from <10 to >95%. Importantly, this range of variation is commonly developed among closely spaced seams within the same well. Exploration has to date been successful where coal seams are in the thermogenic gas window. Geochemical evidence indicates that thermogenic gases have been altered by subsurface water movement and may have been augmented with late-stage biogenic gases, particularly in areas affected by fresh-water recharge.Adsorption isotherms of coal samples in the Black Warrior Basin typically have Langmuir volume between 15 and 30cm 3/g and Langmuir pressure between 2 and 6MPa. Both Langmuir pressure and Langmuir volume correlate significantly with coal rank. In deep, normally pressured coal beds where reservoir pressure is substantially above Langmuir pressure, even a small degree of undersaturation can necessitate prolonged dewatering before a large reservoir volume can reach the critical desorption pressure. Permeability, moreover, decreases exponentially with depth, which can make dewatering coal seams deeper than 800m difficult. Where reservoir pressure is relatively low, however, isotherm geometry indicates that significantly undersaturated reservoirs can be near the critical desorption pressure. Consequently, areas of underpressure favor high gas production along with minimal water production. © 2009 Elsevier B.V.
Ponta G.,Geological Survey of Alabama |
George L.D.,Inc. PELA
Environmental Earth Sciences | Year: 2016
Between 1975 and 2006, drilling rigs and utility trucks were assembled at the site. The geology and hydrogeology at the site was defined based on subsurface data, soil descriptions and geophysical logs from 38 wells and 3 coreholes. The results of the water samples collected from shallow and deep wells indicate that many wells have concentrations of halogenated hydrocarbons above regulatory standards and that contaminant migration has occurred vertically, laterally, and along strike. Impacted groundwater covers most of the property and has migrated to 68.5 m below land surface. Two pilot studies (one bench-scale and one on-site) have been completed to evaluate the application of technologies in addressing contamination of shallow and deep groundwater at the site underlain by the Conasauga Formation. © 2016, Springer-Verlag Berlin Heidelberg.