Title: Re: paleonet Coal formation
Question:
In compiling
a study on petroleum source rocks, I have bumped into the problem of
why the large deposits of northern Hemisphere coal are Carboniferous
and why those in the former Gondwana (mostly southern Hemisphere) are
Permian. Is it simply a matter of climate, or are there other
parameters to be considered?
Dr John R.
Laurie
Eastern and Onshore Petroleum
GEOSCIENCE
AUSTRALIA
GPO Box 378
Canberra ACT
2601
Australia
Reply:
Hello,
The
pattern of major coal deposits is indeed intriguing. The
Carboniferous coal deposits are only now in the Northern Hemisphere.
They were formed in the tropics of Carboniferous times.
Peat
formation requires a climate with high precipitation rates (wet to
ever wet), suitable fast growing plants (not present before the
Devonian), and a setting in which the water level remains more or less
consistently a few centimeters above the soil surface (soil as in
histosol = peat). This equilibrium can be created by subsidence
of an area. Subsidence can come about through many processes,
for instance solution of underground layers of halite or by
geotectonics creating just the right speed of subsidence. For
wide-spread peat deposits the proper geotectonic setting is required
that exists over a large area.
Regards,
Hermann Pfefferkorn
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Hermann W. Pfefferkorn
Professor of Geology and Environmental Science
Department of Earth and Environmental Science
University of Pennsylvania
240 S. 33rd St.
Phone: 215-898-5156
Philadelphia, PA
19104-6316
Fax: 215-898-0964
U.S.A.
e-mail:hpfeffer@sas.upenn.edu
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