Quaternary deposits on the South Barbados accretionary prism

Abstract

A study of recent Quaternary deposits of the South Barbados prism has been carried out over a limited area close to the Venezuela margin. 3.5 kHz lines, submarine photographs and many piston and gravity cores have been collected throughout this area during the cruise of the Caracolante II. The detailed morphology of this area comprises a jumble of microbasins and mud diapiric highs: In the basins, the predominant deposits are sandy and muddy turbidites. On the tops of the highs, the diapiric mud is a mixture of Late Miocene, Pliocene and Quaternary sediments. These muds are clearly identified by their high content of smectite and sometimes by the presence of muddy gravels with a diagenetic calcareous cement. On the seafloor, the muds are often covered by an indurated crust on which deep-sea communities are frequently observed. The three major factors controlling sedimentation on the prism are tectonics, sea-level variations and sediment sources. Tectonics play the major role, being responsible for the mud diapiric processes, the fluid circulation throughout the deposits and the triggering of gravity flows on the steep slopes of the diapiric highs. As a consequence, significant inputs of diapir mud supply the deposits of the adjacent basins, and local calcareous crusts, linked to the upward fluid migration, occur on the seafloor at the tops of the diapirs. Sea-level variations and continental sediment sources partly control the character of the deposits in the ponded basins. During the Holocene, the sediment flux was low (1.7–3.7 g cm −2 ∗ 10 −3 yrs) and the deposits were composed of fine-grained particles comprising equally biogenic calcareous and continental material. The continental material is provided by the Orinoco and the Amazon rivers. During the last glacial period, the flux was much higher (8.5–19 g cm −2 ∗ 10 −3 yrs) as a consequence of a huge increase in coarse-grained terrigenous material introduced by the Orinoco river.