Mass transport processes and deposits in offshore Trinidad and Venezuela, and their role in continental margin development
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Mass transport complexes (MTC) form a significant component of the stratigraphic record in ancient and modern deep water basins. One such basin, 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 possible migration and sequestration of hydrocarbons. Major structural elements found in the deep water slope regions include: large transpressional fault zones along which mobile shales extrude to form seafloor ridges; fault-cored anticlinal structures overlain by extrusive seafloor mud volcanos; shallow-rooted sediment bypass grabens near the shelf break; and normal and counterregional faults. A data volume consisting of 10,708 km2 of several merged 3D seismic data volumes enable subseafloor interpretation of several mass transport event deposits and the erosional surfaces that form their boundaries. The data shows numerous mass transport complexes which are characterized by chaotic, mounded seismic facies and fanlike geometries. Their extent (up to 2017 sq. km) and thickness (up to 250 m) is strongly influenced by seafloor topography. Depositional and erosional architectures identified with these units includes: large magnitude lateral erosional edges, thrust faulting, linear basal scours, side-wall failures, flow geometries, possible displaced blocks and chaotic matrix material. Active tectonism in the region, high sedimentation rates associated with the Orinoco Delta System, and abundant unstable gas hydrates suggest the presence of higher frequency mechanisms at work for MTCs generation than sea-level fluctuations alone. Three types of mass transport complexes are identified in offshore Trinidad; shelfattached systems that were fed by shelf edge deltas whose sediment input is controlled by sea level fluctuations, slope- attached systems which occur when upper slope sediments catastrophically fail due to gas hydrate disruptions, earthquakes and/or storm activity, and locally detached systems formed when local instabilities in the sea floor trigger small collapses. Such classification of the relationship between slope mass failures and the sourcing regions enables an understanding of the nature of initiation, length of development history, petrography and petrophysics of MTC’s. In addition, a collection of morphometric parameters of MTCs from different continental margins are analyzed in order to better understand their causal mechanisms, and to establish whether systematic morphometric parameters characterize these deposits across different tectonic settings. Observations suggest that there is a clear relationship between morphometric parameters of MTC and their causal mechanisms.
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