Geochemistry of Sediments from the Romanche Fracture Zone, Equatorial Atlantic

Abstract

A suite of sediment samples from the Romanche Fracture Zone in the equatorial Atlantic has been subjected to bulk and partition chemical and mineralogical analyses, together with radiometric dating in order to study the main controls on composition and origin. The inter-element relationships in the sediments revealed by geo-statistical analysis indicate that (1) Ca, Sr and P, (2) AI, Fe, Ti, V, Zn, Li, Be and K, (3) Mn, Co, Ni and Cu and (4) Mg, Cr and Ni are associated. Partition chemical data suggest that these element associations represent respectively biogenic, terrigenous, igneous and hydrogenic phases of the sediment. Surface and downcore sediment data indicate that the distribution of the biogenic component of the sediment is influenced by water depth. The distribution of the igneous component is largely controlled by a contribution from ultramafic sources and shows the influence of sub-sea erosion on the surface sediments. The distribution of the hydrogenic component is influenced by contribution from the water column. Sediment accumulation rate data indicate that these sediments have accumulated fairly rapidly. Bottom topography and turbidity current activity are probably the main factors controlling their accumulation. Metal accumulation rate data indicate that then is no significant hydrothermal contribution to the deposits as has been suggested by other workers.