April 2010 Geosphere highlights

Boulder, CO, USA – The April issue of GEOSPHERE, The Geological Society of America's Web science journal, is now online. Included are analyses of oxygen in snail shells to determine climate change in Tibet and analyses of seismic and gravity data to determine the geologic history of the Pahrump and Mesquite Valleys, USA.

Climate-driven environmental change in the Zhada basin, southwestern Tibetan Plateau
Joel Saylor et al., Dept. of Geosciences, University of Arizona, Tucson, Arizona 85721, USA

The Zhada basin, at an elevation of 4500 m and with an area almost equal to that of Connecticut, USA, is the largest sedimentary basin to have existed in southwestern Tibet in the last 20 million years. The sediments in the basin were laid down, first by a large river superseded by a lake and finally by coarse alluvial fans over the course of 9 million years. Analysis of the oxygen in snail shells shows that the lake had distinct, repeated drying episodes. The frequency of the drying episodes is consistent with the frequency of global climate changes resulting from variation in the style of Earth's orbit around the sun. We conclude the global climate changes effected the local environment of this high elevation basin over at least the last 6 million years. Further, this study suggests that the Zhada basin contains a sensitive, high elevation record of global climate change over at least the past 6 million years.

This study uses two types of geophysical data to elucidate the geological history of two valleys that straddle the border of California and Nevada. In this region, two distinct explanations have been proposed for the origin of these valleys. Using seismic data from the oil industry and gravity data from many years of data collection, we conclude that the opening history of these basins occurred in two distinct phases, with an early phase of extension followed by tectonic shearing that continues to this day.

Highlights are provided below. Review abstracts for this issue at http://geosphere.gsapubs.org/.

Representatives of the media may obtain complementary copies of GEOSPHERE articles by contacting Christa Stratton 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 Christa Stratton for additional information or assistance.

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