Paleogeography, Paleoclimate, and Source Rocks

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 up welling 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-C -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.