Coarse-grained deep water, slope & basin-floor systems : influence of tectonic processes on internal and external architecture
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Internal and external architecture of a series of coarse-grained, deepwater deposits have been investigated and the role of intra- and extra-basinal tectonic forces on the sedimentary record has been highlighted within a source-to-sink context. Six hundred (600) meters of coarse-grained sediment gravity flow deposits of a submarine fan were measured in the Jurassic Los Molles Formation in the southern Neuquén Basin, Argentina. This fan is encased in a thick (km scale), fine-grained, hydrocarbon source-prone unit and is characterized by well-sorted, thick-bedded turbidite deposits in the axial and proximal parts of the fan, which transitions to more poorly-sorted and heterolithic facies on the fan margin and downdip fringe. Measured thinning rates of ~7m/km suggest a fan that is ~15km long, smaller than other systems with similar slope dimensions. Bed thicknesses are consistent across the fan but much larger numbers exist in the axial locations, suggesting stratigraphic truncation and fan confinement, probably the result of a structured basin floor inherited from syn-tectonic processes. At the regional or basin scale, a combination of 3D seismic data, well log and core data were used to describe a relatively undocumented deepwater sedimentary system in the offshore Veracruz Basin, Mexico. Sandstone-prone Miocene channelized fairways are present in the basin, downdip from an active plate boundary zone and active foldbelts. Deposits are poorly-sorted and exhibit similar spatially-controlled facies associations as the Los Molles Formation, however the depositional system is much more extensive, facilitated by regional tectonic forces and uplift in the hinterland resulting in extremely high sedimentation rates to the basin. A large channel complex, initiated by tectonic uplift on the margin and an eastward migration of the depocenter, which parallel’s the migration of the deformation front in the hinterland, provide additional influence of tectonic forces on the resultant deepwater sedimentary systems.