Late Pleistocene Deep Water Stratigraphy and Depositional Processes, Offshore Trinidad & Tobago, Using 3D Seismic Data

Brami, T.R., C.M. Tenney, ExxonMobil Exploration Company, Houston, TX, Carlos Pirmez, ExxonMobil Production Research Company, Houston, TX, K.L. Holman, ExxonMobil Exploration Company, Houston, TX, Curtis Archie, Petrotrin, Trinidad & Tobago, Sookdeo Heeralal Petrotrin, Trinidad & Tobago, and Rachel Hannah Michigan State University

Abstract

A 3,000 km² 3D seismic dataset on the continental slope (600-1500 m water depth) offshore Trinidad provide detailed images of the seafloor and shallow subsurface, which help interpret the stratigraphic architecture and depositional/erosional processes in this frontier deepwater basin. Three main elements comprise the deposits imaged: channel complexes, mass-transport complexes and mud volcanoes.

Channel complexes range from being nearly straight to highly meandering, and from single thread to distributary and braided/anastomosed patterns. Two main channel systems having clear seafloor expression, are interpreted to represent the most recent conduits for Orinoco River sediment to the deepwater braided plain at the toe of the Barbados accretionary prism. Seismic images illustrate the spatial and relative temporal variation in channel patterns and provide clues to what are the causes for channel pattern changes. Failure of the continental slope is clearly revealed by several thick (up to 300 ms) and widespread (>750 km²) mass-transport complexes (MTCs) in the study area. Seismic images illustrates variations in size, transport direction/distance and emplacement mechanisms for these MTCs.

Syndepositional thrusting and long linear basal scours as opposed to internally chaotic deposits are interpreted to indicate slump-dominated versus debris-flow dominated MTCs, respectively.

Sediment pathways are clearly affected by the presence of large volcanic cones up to 100 m relief and several km radius. Local slope failure on the flanks of the mud volcanoes also generate slump/debris-flow deposits that extend for several km downdip.

The main depositional elements observed are repetitively organized in sequence beginning with MTCs at the base, followed by channel complexes and capped by a pelagic abandonment interval. This vertical organization is similar to that observed in other intraslope basin and basin-floor fans and is interpreted to reflect eustatic control on the stratal architecture.