May 2008 GEOLOGY media highlights

Earthquakes that have occurred along the San Andreas fault during the past 120,000 years have uplifted rocks adjacent to the fault, and this uplift allows Hilley and Arrowsmith to study how this motion may be revealed by topography. In particular, in the Carrizo Plain of Southern California, rocks of the Pacific plate are deformed as plate tectonic processes move these rocks into and through a zone of active uplift, which is produced by changes in the San Andreas fault's geometry that are linked to the North American plate. Mapping of geologic units allowed the team to reconstruct the deformation that has occurred over time, while new, high-resolution Airborne Laser Swath Mapping (ALSM) data allowed them to study how the topography and erosional processes respond to this deformation. Thus, by combining traditional geologic mapping with new tools that allow the study of landscapes in unprecedented detail, Hilley and Arrowsmith explicitly linked the response of different elements of the landscape to ongoing deformation. The measures of topographic change that they found most well-correlated with deformation may allow us to infer patterns and rates of fault-related deformation in other areas where geologic relationships alone may provide insufficient information to allow us to infer these quantities.

Mechanisms of PETM global change constrained by a new record from central Utah
Gabriel J. Bowen and Brenda Beitler Bowen, EAS Department, Purdue University, 550 Stadium Mall Dr., West Lafayette, Indiana 47907, USA. Pages 379-382.

Rapid and extreme greenhouse warming of global climate that occurred 55 million years ago at the Paleocene-Eocene boundary is widely viewed as a test case for understanding the response of Earth systems to global climate change. The number and geographic distribution of sites where this event has been studied on the continents, however, is extremely limited. Bowen and Bowen report a new record of the event from central Utah, the first North American record that is comparable in quality to the best-documented records from Wyoming's Bighorn Basin. By comparing geochemical records from the two sites, they address a number of proposed hypotheses for earth systems response to climate change at the Paleocene-Eocene boundary, finding support for aridification of the Utah site, diversion of precipitation from lower- to upper-middle latitudes, and climate-induced shifts in vegetation composition during the event.

Sub-million-year age resolution of Precambrian igneous events by thermal extraction–thermal ionization mass spectrometer Pb dating of zircon: Application to crystallization of the Sudbury impact melt sheet
Donald W. Davis, University of Toronto, Earth Sciences Centre, 22 Russell St., Toronto, ON M5S 3B1, Canada; . Pages 383-386.