Sequence Stratigraphy and Facies Variations within Neogene Turbidite Systems, Northern Deep Gulf of Mexico

Abstract

The Neogene strata of the northern deep Gulf of Mexico are characterized by turbidite systems of different stages of evolution and depositional setting. These Neogene sequences are the basinal, downdip equivalent strata to the petroleum-producing intervals in the continental shelf and slope to the north and northwest. The middle to late Miocene Upper Mexican Ridges sequence (12.5-5.5 Ma) and Cinco de Mayo sequence (5.5-4.5 Ma) are interpreted to consist primarily of unchannelized to partially channelized basinal turbidite systems. Many small cut-and-fill features are present in the sequences; small channel-levee systems may be present only in a few places. The overlying Mississippi Fan (4.5 Ma to present) consists of 17 seismic sequences that have a much larger areal distribution than the two underlying Miocene sequences. Each fan sequence is characterized primarily by sediments deposited in channel, levee, and overbank settings. The differences among these turbidite sequences are caused by both the overall progradation of the continental margin and differences in the magnitude of sea-level fluctuations and volumes of sediment deposited in the deep Gulf of Mexico during the Neogene. The Upper Mexican Ridges and Cinco de Mayo sequences are interpreted to be the first coarse-grained turbidite systems deposited in this areamore » of the deep Gulf of Mexico, with the overlying Mississippi Fan being part of a continuum in deep-water depositional systems. The oldest sequences in the Mississippi Fan were relatively small and approximately the same size as the Upper Mexican Ridges and Cinco de Mayo sequences. The magnitude of sea-level fluctuations, which controlled the timing of deep-water sedimentation, was not as large during the middle to late Miocene as during the Plio-Pleistocene.« less