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Abstract
Chapter from: SG
40:  Paleogeography , Paleoclimate, and Source Rocks
Edited By
Alain-Yves HucAuthor:
Judith Totman Parrish Geochemistry, Generation, Migration
Published 1995 as
part of Studies in Geology 40
Copyright © 1995 The American Association of Petroleum
Geologists. All Rights Reserved. |
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Chapter 1
*
Paleogeography
of Corg-Rich Rocks
and the Preservation Versus Production Controversy Judith Totman Parrish
University of Arizona
Tucson, Arizona, U.S.A.
*
ABSTRACT
New analyses of previously examined data
sets had the following results: (1) Nearly half of organic-carbon- (Corg-)
rich units were deposited in geographic settings that do not have modern
analogs. (2) If upwelling associated with western boundary currents is
included, predicted upwelling zones can explain up to 93% of oil-prone,
Corg-rich deposits through the Phanerozoic. The remaining deposits
occur in only three settings--rift basins; low-latitude, enclosed, epicontinental
seaways; and mid-latitude shelves. (3) Thirty-four phosphate deposits can
be identified in the literature that are part of the Si-P-C association,
which is widely regarded to be indicative of high productivity. Another
100 deposits had one of the pairs of adjacent facies, phosphate-glauconite
or phosphate-Corg-rich rock, which occur together in upwelling
zones. Together, these account for 82% of the 164 phosphate deposits identified
in the literature.
These results support conclusions that
high biologic productivity has strongly influenced sedimentation of organic
carbon. Although mechanisms for the genesis of anoxia have been widely
discussed, mechanisms for the genesis of high biologic productivity have
not; it is suggested that consideration be given to mechanisms, in addition
to localized upwelling, that might promote high productivity in the oceans
and the resulting high organic accumulation in sediments. |
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