Seismic Record
of Drift Deposits, Offshore Western Madagascar: Implications
for Regional Tectonics and Sedimentation
Burke, Benjamin C.1, Jeffrey
U. Kraus1 (1) ExxonMobil Exploration
Company, Houston, TX
Offshore western Madagascar, a 5500 km2
sedimentary sequence with clear internal structure visible on seismic data has
been interpreted as a sedimentary drift deposit. These deposits sit at the base
of the continental slope in an average of 3000 m of water in the Mozambique Channel. Seismic interpretation
of the deposits indicates five major seismic–stratigraphic
units and provides strong evidence that this unit not a slump feature. Mapping
of depositional packages in the deposits reveals several unconformities, as
well as inferred changes in sedimentation rate and paleocurrent
direction. Unconformities within the sequence may record changes in ocean
circulation and submarine erosion associated with an increase in regional tectonism.
The drift deposits are ponded against a prominent oceanic transform fault that
appears to have been reactivated during the Late Cretaceous. This relationship
suggests a South-North deep ocean current system existed at that time, well
before the establishment of the modern Antarctic Bottom Water system. The drift
deposits, which are up to 2 km thick, were shed in to the basin from western Madagascar during Late Cretaceous-Paleogene uplift. Understanding the complex interplay
between tectonics, sedimentation, and paleocurrent
patterns is fundamental to developing a model for reservoir deposition in the
deepwater offshore basins.