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Tectonic control of the crustal organic carbon reservoir during the PrecambrianCarbon isotopic trends indicate that the crustal reservoir of reduced, organic carbon increased during the Proterozoic, particularly during periods of widespread continental rifting and orogeny. No long-term trends are apparent in the concentration of organic carbon in shales, cherts and carbonates. The age distribution of 261 sample site localities sampled for well-preserved sedimentary rocks revealed a 500-700-Ma periodicity which coincided with tectonic cycles. It is assumed that the numbers of sites are a proxy for mass of sediments. A substantial increase in the number of sites in the late Archean correlates with the first appearance between 2.9 and 2.5 Ga of extensive continental platforms and their associated sedimentation. It is proposed that the size of the Proterozoic crustal organic carbon reservoir has been modulated by tectonic control of the volume of sediments deposited in environments favorable for the burial and preservation of organic matter. Stepwise increases in this reservoir would have caused the oxidation state of the Proterozoic environment to increase in a stepwise fashion.
Document ID
20040089758
Acquisition Source
Ames Research Center
Document Type
Reprint (Version printed in journal)
Authors
Des Marais, D. J.
(NASA Ames Research Center Moffett Field CA United States)
Date Acquired
August 21, 2013
Publication Date
January 1, 1994
Publication Information
Publication: Chemical geology
Volume: 114
ISSN: 0009-2541
Subject Category
Geosciences (General)
Distribution Limits
Public
Copyright
Other
Keywords
NASA Center ARC
NASA Discipline Exobiology
NASA Discipline Number 52-30
NASA Program Exobiology

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