Progressive Confinement and Downslope Propagation of Submarine Slope Channels

Abstract

Deep-marine channels are the primary conduit through which sediment is transported to the basin floor to form submarine fans; the largest sedimentary deposits on the planet. Repeated phases of ‘cut-and-fill’ within these channels results in a basal erosion surface that is time-transgressive in the rock record, representative of a number of flow events of variable magnitudes. These diachronous sediment pathways are represented in the ancient record as composite surfaces that may be responsible for huge sediment accumulations in the deeper basin. Consequently, understanding the way in which these conduits evolve spatially and temporally is key to predicting timing of sediment supply to the basin floor, and the distribution of associated deposits.

The Lavani channel system, located offshore Tanzania, is a major Paleogene slope valley that developed under the influence of various controlling factors including the slope profile, which was influenced by syn-depositional tectonism, and bottom currents. Fundamentally different cross-sectional geometries are observable along the channel profile, often over relatively short distances. These range from individually resolvable migrational-aggradational channel complexes of variable fill, to aggradationally confined, bottom current influenced channel complex sets.

Biostratigraphically-constrained cored intervals through the channel axis, channel margin, and laterally adjacent extensive lobe deposits were studied and integrated with high-resolution 3D seismic mapping. The results suggest that the Lavani system evolved as a series of frontal lobes developed on the slope which were progressively incised into, allowing basinward propagation of the channel system; during this phase, extensive bottom-current influenced levee and drift systems accumulated on top of the earlier lobes. These new insights into channel evolution on topographically complex slopes affected by bottom currents may be useful in many areas of active exploration.

AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018