Late Quaternary sedimentation in the Lesser Antilles island arc
Investigation of patterns and processes of late Quaternary sedimentation in the Lesser Antilles island arc indicates that the major components of deep-water sediment are volcaniclastic silt and clay, redeposited shallow-water carbonate (mainly aragonite and high-Mg calcite), pelagic carbonate (mainly low-Mg calcite), and windblown dust from Africa. Although sediment derived from the adjacent South American continent is included in accreted trench deposits, marine deposition of this sediment within the arc is insignificant, except at the south end of the forearc. Distribution of sedimentary components within the Lesser Antilles arc is controlled primarily by arc volcanism. A Miocene shift in the locus of volcanism, which caused the arc to bifurcate, created two sedimentologic regimes. In the southern part of the arc, which is characterized by volcanically active islands with high relief, deep-water sediment is dominantly volcaniclastic. In contrast, in the northern part of the arc, where a broad arc platform separates high-relief, active volcanoes from low-relief, extinct volcanoes surrounded by wide carbonate shelves, deep-water sediment is composed mainly of redeposited shallow-water carbonate, pelagic carbonate, and eolian-transported Saharan dust. Superposed on the facies patterns determined by arc volcanism is a subtle, but distinct record of Quaternary climate change. Glacial-interglacial periods are recorded in deep-water sediment by variations in sedimentation rate, composition, and texture. Volcaniclastic sedimentation responded to lowstands of sea level by increased sedimentation rates and thicker and/or more frequent turbidites, reflecting intensified currents in interisland passages and increased erosion of exposed insular shelves. Deep-water carbonate sedimentation records decreased carbonate productivity on exposed shelves and in the open ocean during glacial lowstands, as well as variations in carbonate preservation associated with changes in ocean circulation. Deposition of Saharan dust increased during glacial periods because of intensified wind strengths.