End-Cretaceous mass extinction papers

[Ben Creisler <bscreisler@yahoo.com>]

From: Ben Creisler
bscreisler@yahoo.com
 
A couple of recent papers about the K/Pg extinction:
 
Laia Alegreta, Ellen Thomas and Kyger C Lohmann (2011)
End-Cretaceous marine mass extinction not caused by productivity collapse.
Proceedings of the National Academy of Sciences (advance online publication)
doi: 10.1073/pnas.1110601109 
http://www.pnas.org/content/early/2011/12/28/1110601109.abstract
 
　
An asteroid impact at the end of the Cretaceous caused mass extinction, but 
extinction mechanisms are not well-understood. The collapse of sea surface to 
sea floor carbon isotope gradients has been interpreted as reflecting a global 
collapse of primary productivity (Strangelove Ocean) or export productivity 
(Living Ocean), which caused mass extinction higher in the marine food chain. 
Phytoplankton-dependent benthic foraminifera on the deep-sea floor, however, 
did not suffer significant extinction, suggesting that export productivity 
persisted at a level sufficient to support their populations. We compare 
benthic foraminiferal records with benthic and bulk stable carbon isotope 
records from the Pacific, Southeast Atlantic, and Southern Oceans. We conclude 
that end-Cretaceous decrease in export productivity was moderate, regional, and 
insufficient to explain marine mass extinction. A transient episode of surface 
ocean acidification may have been the main
 cause of extinction of calcifying plankton and ammonites, and recovery of 
productivity may have been as fast in the oceans as on land. 
=====
 
Jaime Urrutia-Fucugauchi and Ligia Perez-Cruz (2011)
 
Buried impact basins, the evolution of planetary surfaces and the Chicxulub 
multi-ring crater.
 
Geology Today 27: 220–225 
doi: 10.1111/j.1365-2451.2011.00814.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2451.2011.00814.x/abstract
 
Impact craters are distinctive landforms on Moon, Mars, Venus and other bodies 
of the Solar System. In contrast, the Earth has few craters, due to the dynamic 
nature of the planet, where craters and other geological structures are 
destroyed, modified or covered. Planetary missions have also shown that in 
other worlds where craters are numerous and well preserved, the crater record 
has been modified, through the identification of buried structures. Studies of 
the concealed crater record have major implications for the crater-size 
frequency distribution and crater-counting chronologies. On Earth, Chicxulub is 
an example of a large multi-ring buried basin. Its study provides clues for the 
investigation other planetary surfaces. In addition, geophysical surveys have 
unravelled its deep 3-D structure, providing data and constraints for new 
planetary missions.