AAPG Annual Convention and Exhibition

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Earth System Controls on the Temporal Occurrence of Petroleum Source Rocks


Conventional models of source rock development have focused on the balance of productivity and preservation, and how various factors, such as upwelling and restriction, impact those processes. In the past two decades, the importance of sea level change has been recognized, with most marine source rocks associated with transgressive sequence tracts. The critical question of why source rocks predominate at particular moments in geological time has not been satisfactorily addressed. It is now well recognized that throughout at least the Phanerozoic, short-lived (<5-10 Ma) changes in the Earth's atmosphere-hydrosphere-lithosphere system have been driven by catastrophic events of global reach. Such events are typically associated with the emplacement of Large Igneous Provinces (LIPs) or cosmic impacts (e.g. Chicxulub). Herein, we focus on LIP formation and their influence on the biological and physical environmental conditions. Such Earth System changes inevitably affect productivity and preservation, thereby influencing source rock deposition. However, the dynamic nature of the Earth's tectonic plate framework results in each of these events being superimposed on a unique, global geography of depositional environments. The interplay of the timing and location of a LIP, extent of climatic disturbance, and the available depositional environments, dictate the sedimentological response to the event, including source rock formation. Understanding such dependencies can help explain why certain geological periods are more conducive to the formation of productive hydrocarbon source rocks than others, even when LIPs are present in each case. In this talk, we compare and contrast Earth System conditions for several major LIP episodes, and how source rock extents and character varied accordingly.