--> Timing of Upland Erosion for Petroleum System and Geodynamic Implications: An Apatite (U-Th)/He Thermochronologic Approach

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Timing of Upland Erosion for Petroleum System and Geodynamic Implications: An Apatite (U-Th)/He Thermochronologic Approach

Abstract

The timing of sediment erosion from source regions has a direct implication in petroleum exploration in a number of ways including deciphering the formation timing of major reservoir rocks in the depositional sink areas, and understanding the thermal evolution of petroleum-producing basins. However, the timing of major erosional pulse/s is often associated with uncertainties due to the lacking of proper data in the source region. The Blue Nile River network on the Ethiopian Plateau, East African Rift System has incised a 1.6 km deep canyon, supplying ~96% of the Nile sediment load. The plateau has produced a minimum of 92,200 cubic km of sediments so far that are deposited in alluvial fans in Sudan, and the Nile Delta and Nile Deep Sea Fan in the Mediterranean Sea. We carried out low-temperature apatite (U-Th)/He thermochronology (AHe) dating on single apatite grains isolated from crystalline basement rock and overlying sedimentary rock samples from a vertical transect along the Blue Nile Canyon to constrain the timing of erosion in this source region. Our new thermochronologic cooling age data reveals the timing of tectonically-driven episodic pulses of erosion of the source area, the Ethiopian Plateau. The inverse thermal model simulations of individual samples, guided by reasonable thermal history of the plateau, indicate rapid cooling of the apatites in the helium partial retention zone after 10 Ma as the plateau experienced increased erosions at that time. This timing yields essential information on the likely development of extensive reservoir rocks younger than 10 Ma in the Nile sink area, which is a prolific hydrocarbon-producing region. This increased erosion is associated with the regional tectonics linked to the Afar mantle plume and rift-related activities. Our study of the timing of erosion is critical in understanding the Nile source-to-sink systems that operated during late Miocene. This will allow a better insight of the temporal probability of reservoir rock development and burial-related thermal evolution of the source rocks in the Nile petroleum systems, particularly in the Mediterranean Sea.