Bureau of Economic Geology, The University of Texas at Austin (www.beg.utexas.edu).
AAPG Annual Convention, Houston, Texas, April 9–12, 2006
Seismic Geomorphology of Mass Transport Deposits
Mass transport complexes form a significant component of the stratigraphic record in ancient and modern deep water basins worldwide. One such basin, the deep marine margin of eastern offshore Trinidad, West Indies, 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 possible migration and sequestration of hydrocarbons. Major structural elements found in the deep water slope regions include: large transpressional faults (i.e., Darien Ridge, Central Range, Los Bajos)along which significant extrusive mud features occur; fault-cored anticlinal structures overlain by extrusive seafloor mud volcano trains; shallow-rooted sediment bypass grabens near the shelf break; and normal and counter-regional faults. A 10,708 sq. km. of merged 3D seismic surveys enable subseafloor interpretation of several erosional surfaces that form the boundaries of enormous mass transport complexes (MTC). The data shows numerous episodes of MTC developments which are characterized by chaotic, mounded seismic facies and fan-like geometry. Their extent (up to 2017 sq. km) and thickness (up to 250 m) is strongly influenced by surrounding structural features. Mass transport flows show run-out distances from the source area of 60-140 km. Depositional architecture identified with these units includes: (1) large magnitude lateral erosional edges; (2) linear basal scours; and (3) side-wall failures. Mud volcanoes act as buttresses to cross-slope mass sediment movements preserving sediment within their downslope "Shadow";. The subsequent Erosional-Shadow-Remnants (ESR's) are comprised of leveed channel complex sediments from older sequences, and are considered for the first time in this research as potential stratigraphic traps in deep water deposits.