May 2008 GEOLOGY media highlights

Boulder, CO, USA –Topics include high-resolution lunar images related to the Orientale impact; possible methane release event at the icehouse-greenhouse transition 635 million years ago; evidence of oil smoke in sediment from the K-P boundary dinosaur extinction; Greenland Ice Sheet’s sensitivity to global warming; what the San Andreas fault-area landscape reveals about earthquakes; a new record of greenhouse warming from central Utah; evidence of a possible glacial land system on Mars; and a sea-level climate change fingerprint.

Highlights are provided below. Representatives of the media may obtain complimentary copies of articles by contacting Ann Cairns at . Please discuss articles of interest with the authors before publishing stories on their work, and please make reference to GEOLOGY in articles published. Contact Ann Cairns for additional information or other assistance.

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Earth-based radar data reveal extended deposits of the Moon’s Orientale basin
Rebecca R. Ghent et al., Department of Geology, University of Toronto, Earth Sciences Centre, 22 Russell St., Toronto, Ontario M5S 3B1, Canada. Pages 343-346.

Analysis of new, high-resolution Earth-based radar images of the Moon by Ghent et al. reveal that the products of the Orientale impact can be found over much of the southern polar highlands. These products include a blocky, melt-rich deposit and a block-poor, fine-grained facies. These results show that production of an extensive ejecta facies depleted in rocks 10 centimeters and larger occurs for a wide range of crater sizes. This fine material can therefore contribute significantly to the physical characteristics of lunar surface materials. Furthermore, Ghent et al.’s study refines earlier views of the significance of melt in large-crater ejecta, and has implications for future exploration of the lunar south polar region, likely a key target for future landed and sample-return missions.

Carbon isotope evidence for widespread methane seeps in the ca. 635 Ma Doushantuo cap carbonate in south China
Jiasheng Wang et al., China University of Geosciences, Wuhan, Hubei 430074, China. Pages 347-350.

Earth’s most severe glaciation occurred about 635 million years ago, with the ice sheet potentially extending to tropic oceans. The end of this severe glaciation marked a major perturbation of the global carbon cycle and ocean chemistry, which was partially recorded in thin "cap carbonate" units that ubiquitously overlie glaciogenic rocks. Although the exact mechanism for cap carbonate deposition and its associated alkalinity and isotope anomaly remains debated, it has been proposed that methane release from gas hydrate destabilization may have played an important role. The finding of carbon isotope values as low as -48 parts per million (VPDB) in multiple sections of the Doushantuo cap carbonate in South China confirms the widespread distribution of methane seeps in the Doushantuo cap carbonate and supports a regional methane release event about 635 million years ago. Wang et al. propose that this methane release event may have played a critical role at the icehouse-to-greenhouse transition.