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Complex Sediment Dispersal in the Campeche Deepwater Province, Offshore Southern Mexico – An Example of a Hybrid Tectonically Active Margin

Abstract

The Tertiary deepwater Campeche province exhibits features of a classic, tectonically active, passive margin tectonic setting. Active plate subductions in the west and the passage of the Chortis continental block to the south have resulted in long-lived Tertiary orogenesis and volcanism in the hinterland. Sediments are delivered to the deepwater Campeche basin in 2 fundamentally different ways; along an unstructured slope floored by oceanic crust in the west and a highly structured and salt-influenced slope, underlain by attenuated continental crust to the east. In the west, coarse-grained sediments are mainly confined to relatively straight submarine canyons and channel complexes that are sourced from the hinterland. These systems extend for over 250km, are up to 5km wide and 400 meters thick. Core and log data show extremely thick (>300 meters), amalgamated sequences that exhibit evidence for both turbidite and debrite sedimentary processes. Sediments delivered to the basin via the structured slope to the east are dominated by channel complexes and ponded minibasins. These channel systems have similar thicknesses to the channel systems to the west but rarely exceed 2km in width. They exhibit lateral to sub-horizontal stacking of individual channels, which differ to the channel complexes on the unstructured slope that are predominantly vertically stacked. Additionally, channel systems on the structured slope exhibit highly tortuous routing directions, within an overall trend to the north, in response to incipient bathymetric variability. Channel systems transition downdip into more unconfined deposition along the structured slope profile, in contrast to the long run-out distances of channels on the unstructured slope to the west. These long run-out distances are somewhat enigmatic for active margins with limited continental drainage basins, but perhaps reflect the interplay between active orogenic processes in the nearby hinterland and frequent seismically triggered slope failures. Because no evidence is seen of these channels systems entering the eastern salt basin downslope, but rather deflecting away from the structured slope, it is likely that the underlying crustal architecture exerts a primary control on sedimentation. Sediments are focussed along a relatively narrow trough toward the basin, thus achieving elevated runout distances on the seafloor.