Late Devonian Phytoplankton Productivity Enhanced by Aeolian Iron?
Frasnian-Famennian organic-rich marine sediments have contributed oil to numerous petroleum systems. In North America, these include the Anadarko Woodford, Illinois New Albany, Michigan Antrim, Appalachian Ohio/Chattanooga, Williston Bakken, and Western Canadian Exshaw and Duvernay. Elsewhere, Frasnian source rocks are well known from the Ghadames, Canning, Timan Pechora, and Volga-Ural basins. The end Frasnian was one of the “big five” global mass extinction events, and was likely caused by extremely high phytoplankton productivity and resulting widespread anoxia. Drawdown of atmospheric CO2 and resultant global cooling and sea level drop together with the massive burial of organic carbon all contributed to the demise of benthic marine animals. Various mechanisms for supplying abundant nutrients include prevalent upwelling, increased riverine transport of nutrients due to extensive colonization of vascular land plants as well as coeval orogenesis. Recent reports specify that aeolian transport of iron (a necessary nutrient for phytoplankton growth) to the modern Southern and Pacific oceans greatly enhances gross primary productivity downwind of dry continental regions. In our paleogeographic and paleoclimatic modeling of the Late Devonian earth system, we show an extensive equatorial arid belt south and east of the Appalachian/Anadarko basins with strong offshore winds that may have supplied wind-blown iron nutrients for optimal phytoplankton growth. Late Devonian crude oil biomarkers attest to both strong upwelling and environments of intense photic zone euxinia.
AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas