October Geology and GSA Today media ...(tion that ended the age of dinosaurs 65....)

Date:9/25/2007

tion that ended the age of dinosaurs 65.5 million years ago. Iglesias et al. report the discovery of diverse and well-preserved fossil plants from Paleocene rocks in the Patagonian deserts of Argentina. The flora show a much warmer and wetter climate than today and more than 40 species of plantsmany more than the better-known North American floras of the same age that tended to have 1015 species. The discovery raises new questions about whether extinction effects were much less severe in southern South America, whether recovery was faster, or if pre-extinction floras were more diverse.

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Evidence for a sedimentary origin of clay minerals in the Mawrth Vallis region, Mars
Joseph R. Michalski, Jet Propulsion Laboratory, Mail Stop 183-501, Pasadena, California 91109, USA; and Eldar Z. Noe Dobrea, Malin Space Science Systems, P.O. Box 910148, San Diego, California 92121, USA. Pages 951-954.

Clay minerals detected spectroscopically in the Mawrth Vallis region of Mars correspond to a complex, layered, thick (>600 m) stratigraphic section of ancient bedrock. Because the light-toned, clay-bearing rocks are lithologically diverse over a broad area (>80,000 km2), have significant internal layering and complexity, and contain buried impact craters within the section (demonstrating that they were deposited over a geologically significant duration of time), Michalski and Dobrea interpret the host rocks as sedimentary or possibly pyroclastic. Crater counts date the clay-bearing rocks to early-middle Noachian time (estimated as 3.84.1 Ga). Geomorphic observations suggest that the rocks were lithified early, and deeply eroded during the late Noachianearly Hesperian. The combination of a probable ancient sedimentary context of the clays and a moderate pH formation environment implied by the occurrence of smectites clearly places these rocks among the most important targets for future astrobiological exploration.

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GSA TODAY
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Contact: Ann Cairns acairns@geosociety.org 303-357-1056 Geological Society of America Source:Eurekalert

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