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Re: Extinctions



In a message dated 98-02-19 03:18:36 EST, you write:

> Subject:  Extinctions
>  
>  I'm searching for information on ocean transgression and regression and
>  it's possible effects upon extinctions.  I have no idea who or what kind
>  of information is out there upon the subject but here looks like the best
>  place to search. 


Try the WEB! Or at least any good geology, or sed/strat text.

Most of these will have some sort of graph of First Order and Second Order
global sea level curves for at least the entire Phanerozoic Eon (~570 My). As
for the K-T sea level, it was considerably _higher_ than that of today but was
actually in a regressive stage. It is this regression that some have
hypothesized is the actual cause of most of the extinctions observed at the K-
T "mass extinction" because many of the  shallow epieric or epicontinental sea
ways and shallow coastal regions  would have become subaerial resulting in
extinctions of taxa adapted to such environs. Similarly, increased continental
erosion could have led to anoxia in deeper waters also possibly causing some
extinctions. 

This is just a very brief and general description of what _may_ have happened
at the K-T. It is not intended as an argument for or against the impact or any
other hypothetical cause, I won't try to sway your opinion either way and I
encourage you to research all aspects of this facinating time and form your
own conclusions! 

A good source for the eustatic sea level curves can be found in "The Cambridge
Encyclopedia of Earth Sciences" which shoul be available at most libraries.
But use the WEB too!


Cheers!


Thomas R. Lipka
Paleontological/Geological Studies
2733 Kildaire Drive
Baltimore,  Md. 21234
http://members.aol.com/tompaleo/Maryland.Dinosaurs.html