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Using Grain-Size to Interpret Cretaceous-Paleogene Extinction Event



Bralower, T., L. Eccles, J. Kutz, T. Yancey, J. Schueth, M. Arthur, 
and D. Bice, 2010, Grain size of Cretaceous-Paleogene boundary 
sediments from Chicxulub to the open ocean: Implications for 
interpretation of the mass extinction event. Geology, v. 38, 
no. 3, p. 199-202; DOI: 10.1130/G30513.1 
 
http://geology.geoscienceworld.org/cgi/content/abstract/38/3/199 
 
Grain size of Cretaceous-Paleogene boundary sediments from 
Chicxulub to the open ocean: Implications for interpretation 
of the mass extinction event March 2010 Geology and GSA 
Today Highlights. 
 
http://www.physorg.com/wire-news/29077449/march-2010-geology-and-gsa-today-highl
ights.html 
 
âThe causes of the mass extinction of 75% of marine and 50% 
of terrestrial species (including the dinosaurs) at the 
Cretaceous-Tertiary boundary, 65 million years ago, has been 
the subject of raging debate. The majority of scientists support 
the theory that the impact of an asteroid on the Yucatan 
Peninsula (Mexico) was the trigger of the extinctions. The most 
potent evidence for this theory is a layer of rock containing 
telltale signs of impact, including melt droplets and shocked 
mineral grains that can be traced from the Yucatan around the 
world. Basing their research on fossils in rocks around the 
Gulf of Mexico, a group of scientists have recently proposed 
that the Yucatan impact preceded the mass extinction by 300 
thousand years, and that the extinction was caused by a 
massive volcanic event in India. The current study by Bralower 
et al., however, leads to a different conclusion through the 
analysis of sediment particle size in Cretaceous-Tertiary 
boundary samples to determine the origin of fossil shells. The 
data demonstrate that fossils in Cretaceous-Tertiary boundary 
rocks around the Gulf of Mexico region are eroded from 
underlying layers by a tsunami at the impact event. Thus 
they rule out the correlation of the mass extinction event with 
Indian volcanism and conclusively support the connection with 
the Yucatan impact.â 
 
Yours, 
 
Paul H.