ABSTRACT

A sequence-stratigraphic analysis of the Plio-Pleistocene sedimentary rocks of the north-central Green Canyon and western Ewing Bank areas was conducted using 1,330 mi of two-dimensional multifold migrated seismic profiles, biostratigraphic data from 31 wells, and logs. The study area covers 945 mi2 and was informally subdivided into five minibasins within which sediments were deposited in abyssal to middle neritic environments. Nine depositional sequences were recognized and correlated (4.2, 3.8, 3.4, 3.0, 1.4, 1.1, 0.8, 0.7, and 0.5 Ma). Most of the sediments were deposited in lowstand systems tracts consisting of basin-floor fan, slope-fan, and prograding wedge facies. Transgressive systems tracts and highstand systems tracts are thin in sequences older than 0.7 Ma and thicker in sequences 0.7 and 0.5 Ma. A major condensed interval (3.0 to 1.4 Ma) is relatively thin (70 to 1,600 ft) and is widespread across the entire study area.

In general, sequences range from 70 to 3,400 ft thick, and they consist dominantly of shale. Sandstone content ranges from 7 to 36% and is present mainly within the sequences 3.8 to 3.0 Ma, 1.4 to 1.1 Ma, and 1.1 to 0.8 Ma. Prominent basin-floor fans are present in the 1.4 to 1.1 and 1.1 to 0.8 Ma sequences and are indicated by subparallel, high-amplitude reflections and blocky well log patterns. Slope-fan complexes have wide variability in seismic expression and sandstone percentage both within and between sequences. They consist of hummocky, chaotic, and subparallel reflections interpreted to reflect a number of depositional processes recorded in channel-levee, overbank, slump-slide, and hemipelagic facies.

Complex salt structures and related faults control the geometry of the depositional units and the entrapment of petroleum. Discoveries in the area, which include Green Canyon blocks 65 (Bullwinkle), 110, and 19, are associated with amplitude anomalies on the flanks of salt features.