Quaternary sedimentation and origin of the Orinoco sediment–wave field on the Demerara continental rise (NE margin of South America)

Abstract

New core data from a sediment–wave field on the Demerara Outer Ridge show that the waves are mainly built from turbidity currents that flow northwards down the Demerara margin. The contour currents circulating parallel and obliquely to the margin are apparently not as important to wave formation as previously proposed. Detailed analysis of the sedimentary facies of cores taken on the crest and flank of a sediment wave indicates that fine-grained turbiditic deposits are dominant. Hemipelagic/pelagic deposits are interbedded with the turbidites. Sediment redistribution by contour currents was only evidenced by the presence of peculiar clay mineral assemblages and microfaunal associations, as well as some sedimentary structures such as truncations and cross-bedding. The turbiditic processes were active during the Last Glacial. In contrast, the Holocene is characterised by pelagic sedimentation. A combination of seismic and core data suggests that the sediment waves result from predominantly turbiditic depositional processes interacting with minor contour currents and synsedimentary deformation processes.