Cold-water coral habitats of Rockall and Porcupine Bank, NE Atlantic Ocean: sedimentary facies and benthic foraminiferal assemblages

Abstract

A facies model is presented for the various environmental settings presently encountered on and around carbonate mounds of Rockall and Porcupine Bank, which may be used for reconstruction of fossil coral habitats and carbonate mound development from long sediment cores. The model is based on detailed sedimentological and micropaleontological analyses of recent sediment, in combination with analysis of available multibeam bathymetric data and underwater camera footage. Our data show that a first distinction – of on-mound environments with variable coral cover, off-mound areas covered with recent mobile sediment, and relict glacial sediment – can be based on grain size distributions in combination with calcium carbonate content of the <63 μm fraction, even if the coral aragonite has disappeared due to downcore dissolution. Benthic foraminifera proved to be the key to distinguish different on-mound environments: hardgrounds, coral debris, isolated corals, and patchy and dense coral covers. The distribution of foraminifera is mainly related to substrate, which is governed by the presence or absence of corals and current speed. Lead−210 profiles predominantly reflect diffusive biological mixing down to 5−10 cm depth, and show that fine sediment is preferentially deposited on-mound.