GSA Paper Demonstrates Single Impact at Cretaceous-Tertiary Boundary

Paul bristolia at yahoo.com
Mon Apr 2 08:28:10 EDT 2007

Dear friends,

There is a new paper on the impact and extinction
at the Cretaceous-Tertiary Boundary. It is:

MacLeod1, K. G., Whitney, D. L., , Huber, B. T.,
and Koeberl, K., 2007, Impact and extinction in
remarkably complete Cretaceous-Tertiary boundary
sections from Demerara Rise, tropical western
North Atlantic. Geological Society of America.
vol. 119, no. 1, pp. 101-115.

http://www.gsajournals.org/perlserv/?request=get-abstract&doi=10.1130%2FB25955.1

They found a single, about 2-cm thick, layer of
spherules, which is interpreted to a primary air-
fall deposit. They found no other spherule layers
in the multiple cores of the K-T boundary section,
which were recovered.

They concluded:

"Sedimentological, geochemical, and paleontological
changes across the boundary closely match patterns
expected for a mass extinction caused by a single
impact."

Best Regards,

Paul
Baton Rouge, LA

Crater question???

Paul H bristolia at yahoo.com
Tue Nov 9 23:05:43 EST 2004

Tom AKA James Knudson wrote;


>Hello List, It seems that every meteorite made

>crater was first thought to be volcanic,

>including the craters on the moon. We all know

>what Barringer had to go through to prove meteor

>crater was in fact a meteor made crater. If you

>compare the crater pictured in this link with the

>craters on page 152 in your rocks from space

>book, they look quite a bit a like. I am wondering

>if anyone ever searched for evidence of this crater

>being meteoric as apposed to volcanic? It would

>make a fine dinosaur killer!



>http://goafrica.about.com/library/gallery/afar/tanzania/blgallery-afar-tanzania1.htm


Geologists have studied the Ngorongoro Crater. It is a

caldera, a crater of volcanic origin. It is only 2.4
million years old.

Some publications about it are:

Gromme, C. S., Reilly, T. A., Mussett, A. E., and Hay,

R. L., 1971, Palaeomagnetism and potassium-argon ages
of volcanic rocks of Ngorongoro Caldera, Tanzania.
Geophysical Journal of the Royal Astronomical Society.

vol. 22, no. 1, pp. 101-115.

Searle, R. C., 1972, A Gravity Survey of Ngorongoro
Caldera, Tanzania. Bulletin Volcanologique. vol. 35,
no. 2, pp. 350-357.

Walter, R. C., Manega, P. C., Farmer, G. L., and Hart,

W. K., 1990, Geochemical and temporal constraints on
magma genesis of the Ngorongoro volcanic highland,
Tanzania. Seventh international conference on
Geochronology, cosmochronology and isotope geology;
abstracts volume. Abstracts - Geological Society of
Australia. voll. 27, pp. 108.

What I would like to know, is what ever came of the
huge, crater-like feature found by seismic surveys
buried beneath the continental shelf of Columbia.
Before the Chixulub Crater was recognized, a number
of people thought that it might be the site of a
Cretaceous-Tertiary boundary impact.

Best Regards,

Paul
Baton Rouge, LA