Seismic-Stratigraphic Geochemical Model of Occurrence of Oils in Gulf of Mexico Flexure Trend: ABSTRACT

Abstract

Several models have recently been proposed for the generation and migration of the oil and gas in the Gulf of Mexico flexure trend. However, geologic and geochemical data suggest that much of the flexure trend oil was generated in Cretaceous-upper Tertiary sediments and migrated vertically through the faulting associated with continued salt tectonism. Generalized cross sections along the continental margin commonly show a thick, continuous salt layer. Regional seismic stratigraphic analysis shows that the salt is discontinuous in many places along the middle and lower slope owing to thinning and perforation caused by basinward creep, withdrawal, diapirism, and tonguing. The discontinuous salt distribution allows direct stratigraphic contact in places between the late Tertiary sediments and the underlying Paleogene and Cretaceous intervals. Seismic data indicate the salt movement has captured large volumes of slope and basinal sediments through ridging and tonguing. The onset of significant sediment loading on the shelf during the mid-Miocene to Pleistocene implies that shelf instability and sediment capture did not commence until the late Miocene. This scenario is consistent with geochemical data indicating that flexure trend oils are probably from carbonate-rich sources deposited in relatively shallow water. In contrast, Neogene sediments in the Gulf are clastic inmore » nature, and were deposited in environments unfavorable for the accumulation of oil-prone organic matter. Mature migrated bitumens from carbonate sections recovered at DSDP Sites 535 and 540 are very similar geochemically to flexure trend oils.« less