--> Abstract: Architecture and Seismic Geomorphology of Shelf-edge Deltas Along an Active Tectonic Margin: Eastern Offshore Trinidad and Ven; #90063 (2007)

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Architecture and Seismic Geomorphology of Shelf-edge Deltas Along an Active Tectonic Margin: Eastern Offshore Trinidad and Venezuela

 

Maher, Julie A.1, Lesli J. Wood2 (1) The University of Texas at Austin, Austin, TX (2) University of Texas at Austin, Austin, TX

 

The South American continental margin, offshore eastern Trinidad and Venezuela, has a Tertiary and near-modern history of sedimentation at the shelf margin, whose architecture and morphology are influenced by margin tectonics. These influences include strike-slip faulting; compressional folding; extensional, counter-regional faulting; and upper-slope-graben development. In addition, frequent, large-magnitude earthquakes destabilize deltas building at the shelf edge. A ~20,000-sq-km 3D-seismic data volume includes the nearly 80-km-long shelf margin, which was deposited as the Orinoco delta prograded to the ancient shelf edge and developed significant shelf-edge deltas. We mapped the last ~500,000 years of strata using seismic tied to 14 well logs, documenting cycles of sandy, progradational shelf and coastal-delta-plain systems, interspersed with eustatically driven flooding events. Intervals were isopached and proportional attribute slices taken for seismic geomorphologic analysis, facies mapping, and documentation of depositional changes comprising these shelf-edge systems.

 

Observations show that throughout the shelf edge, the setting changes visibly from aggradational to progradational, capped by modern, transgressive flooding deposits. Also, we can distinguish two clinoform facies across the shelf edge: horizontal delta topsets cut by possibly distributary facies and delta-front clinoforms, varying in steepness. Southward, deltas prograde into upper-slope minibasins formed by normal faulting, with toe-of-slope turbidites ponding against downslope, counterregional, accommodation sinks. Alternatively, northward, shelf-edge deltas along the same margin prograde well onto the upper slope into accommodation sinks formed by extensional grabens and growth faults. In addition, their more-point-sourced nature and proximity to the continental-plate boundary leads to rapid destabilization, resulting in basinward deposition of large mass-transport deposits.

 

AAPG Search and Discover Article #90063©2007 AAPG Annual Convention, Long Beach, California