Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
Association of Petroleum Geologists Annual Meeting, Dallas, April 18-21,
Debris Flow Distribution and Controls on Slope to Basin Deposition, Offshore Trinidad
Lorena Moscardelli, Lesli Wood, and Paul Mann
The deep marine margin of eastern offshore Trinidad, situated along the obliquely converging boundary of the Caribbean and South American plates and proximal to the mouth of the Orinoco River, is characterized by catastrophic shelf margin processes, intrusive and extrusive mobile shales, active tectonics and prolific migration and sequestration of hydrocarbons. Major structural elements that characterize the deep water slope regions include, (1) Large transpression fault zones (ie., Darien Ridge, Central Range, Los Bajos) along which mobile shale walls are extruded, (2) fault-cored anticlinal structures overlain by extrusive seafloor mud volcanos, (3) shallow-rooted sediment bypass grabens near the shelf break, and (4) normal and counter-regional faults. A mega-merged, 10,000 sq. km., 3D seismic survey reveals several erosional surfaces that form the boundaries of enormous mass transport complexes (MTC). The data shows numerous episodes of MTC development. MTCs are characterized by chaotic, mounded seismic facies and map in a fan-like geometry. Their extent and thickness is strongly influenced by seafloor topography. These deposits are up to 250 m thick and are 250 km sq, with run-out distances from the source area of 60-100 km. Depositional architecture identified with these units includes: (1) huge lateral erosional edges (2) linear basal scours and (3) side-wall failures. Mud volcanos buffer deposition and sediment shadows are produced on their downdip side. Conditions responsible for initiating these MTCs are not yet clearly defined, but the MTCs are believed to be produced by sediment accumulation and oversteepening of the slope, tectonic movement and possibly hydrate destabilization and dissolution.