Linking
Selenium Sources to Ecosystems
Food
web from particulates through prey to predators
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| Linking
Selenium Sources to Ecosystems |
Food
web from particulates through prey to predators |
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TETHYAN
A constructed global plot shows 1) the areal association of major basins hosting phosphate deposits and petroleum source rocks; and 2) the importance of a paleo-latitudinal setting in influencing the composition of the deposits. The Tethyan basins, which are emphasized, were characterized by a warm, moist climate that sustained abundant organic richness in broad, shallow continental shelves or in epi-continental seas during transgressive oceanic events throughout the Mesozoic Era and into the Cenozoic Era. The Tethyan oceanic realm can be thought of as an east-west corridor for oceanic circulation that was nearly parallel to the equator, separating North America, Europe, and Asia to the north from South America, Africa, India, Australia and Antarctica to the south. The Tethyan realm far out-weighs the producitivity of other defined realms encompassing much greater areas (i.e., Boreal or northern group of basins, the Pacific accreted terrains, and Gondwana or southern group of basins). This realm constitutes less than one-fifth of the world's land area and continental shelves, yet 68% of the world's petroleum reserves and greater than 70% of phosphate resources were deposited at low latitudes in the Tethyan realm.
Originally, source-rock age was hypothesized as controlling Se sources, with Cretaceous-Period sedimentary rocks such as the Pierre and Niobrara Formations identified as important sources of Se. However, formations selected for our case studies range in age from the Permian Phosphoria Formation to the Miocene Monterey Formation, with significant Tertiary-Period sources in the California Coast Ranges. A compilation by age of major phosphate resources and effective petroleum source rocks (nmormalized as a percentage of total world resources of of the world's original petroleum reserves, respectively), show that some geologic ages are more important than others in determining productivity, but no apparent predictable periodicity can be discerned from them. Some 50% of phosphate resources were deposited in the Eocene and Miocene. Ninety percent of the world's discovered oil resources come from six stratigraphic intervals, with the middle Cretaceous and upper Jurassic accounting for 54%. |
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