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Find Your Science at GSA
19 Oct. 2012
GSA Release No. 12-75
Kea Giles
Managing Editor,
GSA Communications

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Geosphere Explores the Sierra Nevada, Colorado River System, Laurentia, and the Deep Sea

Geosphere articles posted online 18 October 2012

Boulder, CO, USA – Geosphere, The Geological Society of America’s peer-reviewed online journal, has added papers to four special issues: Origin and Evolution of the Sierra Nevada and Walker Lane; CRevolution 2: Origin and Evolution of the Colorado River System II; Exploring the Deep Sea and Beyond; and Making the Southern Margin of Laurentia. Geosphere specializes in accommodating animations, sound, and movie files, along with high-resolution figures.

Abstracts for these and other Geosphere papers are available at Representatives of the media may obtain complimentary copies of Geosphere articles by contacting Kea Giles at the address above.

Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to Geosphere in articles published. Contact Kea Giles for additional information or assistance.

Non-media requests for articles may be directed to GSA Sales and Service, .

Basin and Range volcanism as a passive response to extensional tectonics
Keith Putirka and Bryant Platt, Department of Earth and Environmental Sciences, California State University, 2576 E. San Ramon Avenue, MS/ST24, Fresno, California 93740, USA. Posted online 18 October 2012; doi: 10.1130/GES00803.1.

Keith Putirka and Bryant Platt of Cal-State-Fresno present a new model to explain Tertiary to recent volcanic activity in the Basin and Range province of the United States. Volcanism and extensional faulting occur due to the development of the San Andreas fault system, which initiates the degradation or physical loss of lithospheric mantle. This process migrates north with time, and at any given latitude lasts for about 20 million years and at the end of this period, volcanism rapidly wanes and suddenly approaches mid-ocean ridge-like compositions.

Diachronous episodes of Cenozoic erosion in southwestern North America and their relationship to surface uplift, paleoclimate, paleodrainage, and paleoaltimetry
Steven M. Cather et al., New Mexico Bureau of Geology and Mineral Resources, New Mexico Institute of Mining and Technology, Socorro, New Mexico 87801, USA. Posted online 18 October 2012; doi: 10.1130/GES00801.1.

The uplift and erosion history of southwestern North America has been the topic of much debate. We present data that demonstrate that deep erosion did not occur synchronously throughout the region, but that erosion occurred in local regions at various times during the Cenozoic. These areas of uplift can be associated with local processes of contemporaneous tectonic uplift, and thus suggest that deep erosion was intimately related to episodes of surface uplift. Except for the oldest uplift episode (Laramide; Late Cretaceous-early Eocene) that was associated with local areas of crustal shortening, the remaining three episodes of uplift and erosion (late middle Eocene, late Oligocene-early Miocene, late Miocene–Recent) were related to processes in the mantle. Only the late Miocene to recent episode of erosion is well correlated to climate change. Results presented by Steven M. Cather and colleagues suggest that near-modern elevations in southwestern North America were generally not attained until the Neogene.

Planform geometry, stacking pattern, and extrabasinal origin of low strength and intermediate strength cohesive debris flow deposits in the Marnoso-Arenacea Formation, Italy
P.J. Talling et al., National Oceanography Centre, European Way, Southampton SO14 3ZH, UK. Posted online 18 October 2012; doi: 10.1130/GES00734.1.

P.J. Talling and colleagues discuss the only location where individual layers of rock, each deposited by a single underwater flow of sediment, have been mapped in detail across a mountain belt for 120 km. It therefore provides unique information on how submarine sediment density flows evolve. Some of these ancient underwater sediment flows were huge, as just one of the flows could transport more than the annual sediment flux from all of the world's present-day rivers. Although these ancient rocks were deposited in a flat basin plain, our work shows that the submarine flows were surprisingly complex, and not like our textbook models. This study shows how a single flow event could comprise several different types of flow (dilute and turbulent or dense and laminar), and that transformations occurred between flow types. In particular, Talling and colleagues show that mud-rich debris flows with very low yield strength could run out for remarkable distances into the deep ocean.

Ages of pre-rift basement and synrift rocks along the conjugate rift and transform margins of the Argentine Precordillera and Laurentia
William A. Thomas et al., Geological Survey of Alabama, 420 Hackberry Lane, P.O. Box 869999, Tuscaloosa, Alabama 35486-6999, USA. Posted online 18 October 2012; doi: 10.1130/GES00800.1.

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. These data, presented by William A. Thomas and colleagues, 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 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 at the rifted margin.