Seismic Stratigraphy and Seismic Geomorphology of a Slope Depositional Environment - Case Study from Offshore Angola, West Africa

Henry W. Posamentier
Chevron Energy Technology Center, Chevron Corporation, Houston, TX

The stratigraphy of the slope environment offshore Angola, West Africa, is characterized by multiple unconformities. These unconformities, comprise stratigraphic discontinuities and are defined by reflection truncations indicative of erosion. Moreover, each of these unconformities is marked by turbidite leveed channels of varying size and stratigraphic complexity. At one end, simple single-strand channels are observed, with channel widths of ~150 m or less. At the other end, complex channel belts range in width from ~2 km to upwards of 8 km. The relief of these larger slope channels can be up to 700 m. These larger slope channels commonly contain smaller leveed channels from 100 to 150 m wide. Typically, these smaller channels can be tracked for relatively short distances as a result of complex erosion and crosscutting relationships within the confines of the slope channels. The best preserved channels within these larger slope channels commonly are observed at or near the top of the fill section. Levees associated with channels, both large and small are not well developed, with maximum thickness up to ~30 m. Such deposits can be observed external to the smaller slope channels as well as within the larger slope channels.

Mass transport deposits are not well developed in this section. Thin MTD’s, less than ~20 m thick are observed. These deposits are characterized by slope parallel linear grooves at their base and contain clasts that are up to 150 m in diameter, though most are less than 100 m wide. Somewhat thicker MTD’s are observed within the larger slope channels, though here too these deposits do not comprise a significant part of the section.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas