Geochemical characteristics and provenance of late Quaternary sediments from the Madeira Abyssal Plain, N Atlantic

Abstract

Late Quaternary sediments of the Madeira Abyssal Plain (MAP) consist of alternations of metre-thick distal turbidites and thin (centimetre to decimetre) pelagic clays, marls and oozes. The geochemical characteristics of 29 turbidites are described using major- and trace-element data from more than 350 samples. These were obtained from two representative piston cores located in the NE and W central parts of the MAP. Three separate groups of turbidites are defined by the geochemical data: (a) organic-rich, (b) ‘volcanic’ and (c) calcareous turbidites. ‘Organic’ turbidites contain 0.3–2% organic carbon. Their sediment originated from the lower continental slope of NW Africa N of 20°N, although one turbidite may have been derived from S of this latitude. ‘Volcanic’ turbidites contain a large proportion of volcaniclastic material and are distinguished by their high TiO₂ contents (about 1.5% on a carbonate-free basis). Much of their sediment originated from the oceanic islands of the Canaries and Madeira to the E. Calcareous turbidites are composed predominantly of pelagic carbonate and are defined by high CaCO₃ values (more than 75%). Their sediment was derived from the Great Meteor-Cruiser Seamount Chain, W of the MAP.