September Geology and GSA Today media ...(e vetted using tools such as scanning el...)

Date:8/28/2007

e vetted using tools such as scanning electron microscopy before radiocarbon dates are accepted uncritically.

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Sediment mixing and stratigraphic disorder revealed by the age-structure of Tellina shells in Great Barrier Reef sediment
Matthew A. Kosnik, 6330 Sanaa Place, Dulles, VA 20189, USA; et al. Pages 811-814.

Coral reefs, one of the world's most charismatic ecosystems, are currently threatened by a variety of human impacts, and biologists have been studying them for only a few decades. Thus, the sedimentary record is the best option for adding historical perspective to questions in reef conservation biology. Kosnik et al. used dating techniques to examine the accumulation of dead shells in shallow-water Great Barrier Reef sediments. The top 20 centimeters of sediment was dominated by living clams, while the meter of sediment below that was thoroughly mixed on a sub-century scale. Kosnik et al. also found that small shells were more likely to be destroyed quickly leading to a size-biased death assemblage and that large shells are more likely to be buried quickly creating a size-biased age structure within lagoonal sediments. This study provides an important context for paleoecological studies in shallow-water reef systems, and emphasizes the importance of sediment mixing in these environments.

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Physical and chemical evidence of the 1850 Ma Sudbury impact event in the Baraga Group, Michigan
Peir K. Pufahl, Acadia University, Earth and Environmental Science, Wolfville, Nova Scotia B4P 2R6, Canada; et al. Pages 827-830.

A catastrophic extraterrestrial impact 1850 million years ago produced the Sudbury crater, the second largest known impact site on Earth. Pufahl et al.s discovery of debris in northern Michigan, USA, produced from this impact has provided new information regarding the nature of this event. A prominent iridium anomaly in impact-generated tsunami deposits containing shocked quartz, sph
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Contact: Ann Cairns acairns@geosociety.org 303-357-1056 Geological Society of America Source:Eurekalert

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