Deep-sea sedimentary processes in the Argentine Basin revealed by high-resolution seismic records (3.5 kHz echograms)

Abstract

The regional distribution of nine 3.5 kHz seismic echo types reveals the areal extent of deep-sea sedimentary processes in the Argentine Basin. Correlation between four echo types (IB, IIA, IIB, IIIF) and the relative abundance of sand and silt layers in piston cores shows that the majority of coarse sediment bypasses the continental slope and rise. This coarse sediment is deposited on the proximal abyssal plain with progressively lower amounts reaching basinward across the distal plain. Scarps, irregular and blocky hyperbolic zones, and transparent layers along the Argentine continental margin indicate the widespread occurrence of mass-flow deposits. One large area of mass-flow deposits covers at least 5 × 10 4 km 2 of the continental rise and adjacent abyssal plain east of the Rio de la Plata. A field of large migrating mud waves, approximately 1.0 × 10 6 km 2 in extent, occurs on sediment drifts in the central basin. The mud waves range in amplitude up to 137 m and average 26 m; wavelengths are about 3–7 km. The migrating mud waves are current-controlled features which form in areas of relatively weak Antarctic Bottom Water (AABW) benthic circulation. A variety of hyperbolic echo types on the abyssal plain adjacent to the Argentine continental margin, south of the Rio Grande Rise, and in the Georgia Basin, are also interpreted as AABW current-produced erosional/depositional bedforms, although downslope sedimentary processes may also produce similar hyperbolic echoes. The distribution of bedforms inferred from 3.5 kHz echo character suggests that sediments is supplied to the basin principally by gravity-controlled mass flows. Sediment transported by AABW from higher latitudes is a secondary source. Sediments from both sources is winnowed by strong AABW flow along the Argentine continental rise. The fine-grained component is transported to the central basin where it is deposited as migrating mud waves in regions of relatively weaker AABW flow.