Abstract: Sequence Stratigraphy of Pliocene-Pleistocene Sediments in North Central Green Canyon and Western Ewing Bank, Northern Gulf of Mexico

Zurilma Acosta, Paul Weimer

The Pliocene-Pleistocene sediments of north central Green Canyon and western Ewing Bank are deformed by complex salt features and normal and high-angle reverse faults. A sequence-stratigraphic interpretation of the area was done using 2140 km of 2-D multifold migrated seismic data, biostratigraphic data from 31 wells, and well logs. The study area covers 2447 km² and was informally subdivided into five mini-basins within which sediments were deposited in bathyal and abyssal environments.

Nine depositional sequences were recognized (4.2, 3.8, 3.4, 3.0, 1.4, 1.1, 0.8, 0.7, and 0.5 Ma). Most of sediments were deposited in lowstand systems tracts consisting of basin-floor fan, slope-fan complex, and prograding complex. Transgressive system tracts and highstand system tracts are thin where present. A major condensed interval (3.0 to 1.4 Ma) is relatively thin (80-100 ft) and is widespread across the entire study area.

In general, the sequences are dominantly shale as indicated by well penetrations. Sandy intervals are present within the sequences 4.2-3.8 Ma and 1.4-1.1 Ma. A prominent basin-floor fan is present in the 1.4-1.1 Ma sequence as indicated by the subparallel, high-amplitude reflections and the blocky well log patterns (140 ft). The slope-fan complex has wide variability in its seismic expression and sand percentage both within and between sequences; it consists of hummocky, chaotic, and subparallel reflections interpreted to reflect a number of depositional processes (channel fill, overbank, slides).

The complex salt and faulting generated structures that control the geometry of the depositional units and the entrapment of petroleum. Discoveries in the area include Green Canyon Blocks 22 and 65 (Bullwinkle) and are associated with amplitude anomalies on the flank of salt features.

AAPG Search and Discovery Article #90983©1994 GCAGS and Gulf Coast SEPM 44th Annual Meeting, Austin, Texas, October 6-7, 1994