Post mid-Cretaceous seismic stratigraphy and depositional history, deep Gulf of Mexico
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A detailed seismic stratigraphic analysis of post mid-Cretaceous sedimentary rocks has resulted in the definition of eighteen post mid-Cretaceous seismic sequences in the deep Gulf of Mexico basin, based mainly on a pronounced depositional cyclicity. Each seismic sequence is interpreted to consist of distal lowstand systems tracts overlain by a regional condensed section, which is interpreted to be the basinal equivalent of transgressive and highstand systems tracts present on the adjacent shelf margins. True sequence boundaries, therefore, represent correlative conformities directly overlying the condensed sections. A chronostratigraphic framework established in this study allows for the first time a detailed comparison of deep basin stratigraphy with that on the peripheral Gulf regions. This comparison reveals genetic relationships between deep water sediments and Cenozoic shelf margin depocenters. Major depositional and tectonic events on the surrounding shelf margins control the development of deep basin sequences and determine the temporal and spatial distribution of deep water sediments. Late Cretaceous to middle Eocene sequences reflect the influences of the Laramide orogeny and mountain building in the southern Cordilleran. Tremendous amounts of sediments were derived mainly from the west and were deposited in the western deep basin. A backstripping study reveals an anomalous tectonic subsidence event (2.5km) in the western deep basin as compared to normal thermal subsidence of oceanic crust. It suggests that the Laramide orogeny possibly modified the western deep basin into a foreland basin. Late Cenozoic sequences reflect a major reorganization of source areas and the development of the Mississippi River drainage system. Sediments were delivered through the Mississippi River drainage system and progressivly filled the northern part of the deep basin. Isochron, seismic facies, and depositional systems maps for the eighteen sequences reveal the detailed infill and depositional history of the deep basin. Each sequence contains several submarine fan or fan lobes along the deep basin margins, while the remaining area is dominated by basinal mud-rich turbidites and sediment starvation. The persistent outbuilding of Cenozoic deltaic shelf margins brought a progressive change in depositional systems in the deep basin, from distal to more proximal part of fan systems.