ABSTRACT

An extensive grid of oil industry seismic profiles is used to develop a sequence stratigraphic framework for the Main Pass area, northeastern Gulf of Mexico. Twenty Type 1 sequence boundaries (SB20-SB1) bounding 20 sequences (named in this study by the letters T-A) are defined within the Oligocene to Recent section (post 30 m.y.). Most sequences comprise highstand (HST) and lowstand (LST) systems tracts (Type 1 sequences). Lowstand can be subdivided into early lowstand and late lowstand in some sequences. Late lowstand are progradational and downlap onto early lowstand.

Isochron maps of sequences F to N between SB14 (10.5 m.y.) and SB 5 (3.8 m.y.) document depocenter migration and basin sedimentary history. Furthermore, mapping of individual systems tracts within several sequences is demonstrated to be an excellent technique for providing additional information about depositional history, which can aid hydrocarbon exploration.

In this study, sequences are inferred to be of eustatic origin, but their 3-D architectures respond to local depositional controls, particularly changing sediment sources. Four major depositional episodes are documented. 1) Below SB 14 (10.5 m.y.), deposition 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 m.y.). 3) After SB 9 depocenters migrated eastward and progradation continued to the south, primarily in the east. 4) Early LST deposition moved from a basinal to a slope setting after 3.8 m.y. (SB5), and reflection patterns changed from oblique with high amplitudes at clinoform toes to sigmoid, probably reflecting a transition from sandier to more muddy deposition.