Following are highlights from the June issue of Geology and a summary of the science article from the June issue of GSA Today. These articles are embargoed until June 1. We ask that you discuss articles of interest with the authors before publishing stories on their work, and that reference be made to Geology in stories published. Please contact Anika Burkard for additional information and assistance.

Geology

Dinosaur abundance was not declining in a "3 m gap" at the top of Hell Creek Formation, Montana and North Dakota
Peter M. Sheehan et al., p. 523

The mode of dinosaur extinction has long been contentious. One camp argues that dinosaurs went extinct suddenly (as would have occurred if an asteroid killed them), while the other argues that the dinosaurs went extinct gradually (as would have occurred if a non-catastrophic event were responsible for their demise). A key piece of evidence is the so-called "3 meter gap," a supposedly fossil-free 3 meter interval just below the Cretaceous-Tertiary boundary preserved in eastern Montana and western North Dakota. This study addresses the abundance of dinosaur fossils below and even within that 3 meter gap. The authors suggest that the gap does not really exist and that it is simply an illusion due to the rarity of dinosaur fossils. The uppermost 3 meters before the boundary is no more or less devoid of fossils than any other 3 meter interval. For this reason, the authors conclude that there is no evidence that dinosaurs went extinct gradually before the boundary. Rather, the extinction was catastrophic and the data are fully concordant with an asteroid impact as the cause of the dinosaur extinction.

Overlapping volcanoes: The origin of Hilo Ridge, Hawaii
Robin T. Holcomb et al., p. 547

University of Washington scientists have found evidence that the volcanic Island of Hawaii grew differently than was previously thought. A prominent submarine ridg
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Contact: Ann Cairns
acairns@geosociety.org
303-447-2020 x 156
Geological Society of America
31-May-2000