Sediment distribution and Cenozoic sedimentation patterns on the Agulhas Plateau

摘要

Unconsolidated sediments on the Agulhas Plateau range in age from Maestrichian to Quaternary and consist of calcareous ooze. A composite sedimentary record from piston cores suggests three hiatuses in sedimentation which can be correlated with angular unconformities inferred from seismic profiles. These hiatuses encompass late Miocene–Pliocene, middle Oligocene, and late Paleocene–middle Eocene time and correlate with similar stratigraphic gaps widely distributed in Deep Sea Drilling Project boreholes. The deeper basins surrounding the plateau contain terrigenous and calcareous or siliceous hemipelagic sediments; sediment composition is controlled by depth and locality of deposition. Strong influence of bottom currents on sediment distribution during Cenozoic time is demonstrated by a well-developed erosional zone near 4,500-m depth around the plateau as well as by local erosion and sediment drifts on the plateau itself. The plateau can be divided into a northern and a southern province on the basis of differences in the nature of acoustic basement. Basement in the southern province is smooth with some faulting and contains weak internal reflectors unconformable with the basement surface; the reflectors may represent layered basalt flows or consolidated Mesozoic sediments deposited shortly after the formation of the plateau. Acoustic basement in the northern section is intensely faulted and shows no evidence of internal stratification.