Late Cenozoic Sequence Stratigraphy, Main Pass Area, Northeastern Gulf of Mexico

By

HE, LEIPIN

ChevronTexaco, New Orleans, LA

BUFFLER, RICHARD T., and FULTHORPE, CRAIG S.

University of Texas Institute for Geophysics, Austin, TX

An extensive oil industry seismic grid has been used to develop a sequence stratigraphic framework for the Main Pass area, northeastern Gulf of Mexico. Twenty unconformities (SB20-SB1) bounding 19 sequences (T-A) have been defined for the Oligocene to Recent section (post 30 Ma). Most sequences comprise highstand (HST) and lowstand (LST) systems tracts (Type 1 sequences). LSTs can be subdivided into early and late LSTs in some sequences. Late LSTs are progradational and downlap onto early LSTs.

Isopach maps of sequences F to N between SB 14 (approx. 10.5 Ma) and SB 5 (approx. 3.8 Ma) illustrate how mapping the 3-D geometries of sequences reveals depocenter migration and basin sedimentary history. Furthermore, mapping of individual systems tracts within sequences is shown to be an excellent technique for providing additional details about geologic evolution, which can further aid exploration for hydrocarbons.

Four major depositional episodes are documented in the region. 1) Below SB 14 (10.5 Ma), sediments filled the southwestern deeper part of the basin seaward of the Lower Cretaceous shelf margin. 2) Uniform southward progradation and migration of depocenters occurred between SB 14 and SB 9 (10.5-5.5 Ma). 3) After SB 9 depocenters migrated eastward and southward progradation continued, primarily in the east. 4) Early LST deposition moved from a basinal to a slope setting after 3.8 Ma (SB5), and reflection patterns changed from oblique with high amplitudes at clinoform toes to sigmoid, probably reflecting a transition from sandier to more muddier deposition.