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.
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.
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.
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.
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.