Print this pageWorld Source Rock Potential through Geological Time
The world's source rocks include black shale & carbonates & these large accumulations of organic matter & petroleum have an irregular temporal beat. The higher concentrations of organic matter are tied to sporadic super-plumes, plate configurations, climate, east coast/west coast ocean circulation, monsoons, allochtonous vs. autothonous carbon, preservation mechanisms, & other phenomena. Most of the world's largest oil fields are restricted to areas along the southern margin of the Tethys where specific areas are sweet & others not so productive!
We argue that though 60% of the globe's (preserved) oil deposits are associated with superplume timing, the explanation for its (preserved) oil potential is also controlled by a combination of an enveloping continental rain shadow, lack of clastic input & organic production fostering concentrations of organic matter in the geological section from the Precambrian & through the Phanerozoic, particularly the Mesozoic, This is principally true of the lea shore of Pangea & the resulting Middle Eastern Giant Fields! Here accumulation of organic rich sediments appears tied to marine transgressions with shelf margin flooding as one of the major factors controlling accumulations of organic rich sediment. Evidence for this relationship is recorded in the Cretaceous section of the southern Mediterranean margin & the Eastern Arabian shelf. The Silurian section of northern Gondwanaland records a glacial ice cap melt, & a major transgression occurred during the Early Silurian, resulting in organic rich sediments represented by the Tanezzuft Shale of Libya, the Mudawwara Fm. of Jordan, & the Qusaiba Mbr. of Saudi Arabia & the Akkas Fm. of Iraq.
In the Precambrian the Shunga Event ~2.0 Ga also records accumulation of vast quantities of organic carbon preserved in organic-rich black shale source rocks. Details of this accumulation of petroleum are poorly defined but appear tied to plume magmatism &/or volcanism plus interlayered volcanic rocks that may have played a role in preservation. The Shunga Event occurred during the dispersal of continents rather than the closure of oceans associated with the Mesozoic Middle Eastern Oil reserves. This highlights a major requirement for accumulation & preservation of organic matter through time as the presence of a restricted basin, rich in nutrients, exposed to rapid sedimentation during times of transgression (relative sea-level rise).
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009