Provenance of Late Quaternary ice-proximal sediments in the North Atlantic: Nd, Sr and Pb isotopic evidence

Abstract

In order to assess the isotopic characteristics of siliciclastic sediments delivered by the Laurentide, Greenland, Iceland and Fennoscandian ice sheets to the North Atlantic, the Nd, Sr, and Pb isotopic compositions were determined for twenty-six samples of Late Quaternary, fine-grained (<63 μm), ice-proximal glacimarine sediments throughout the northern North Atlantic. Along the eastern margin of the Laurentide Ice Sheet, ϵ Nd values of the glacimarine sediments vary from −23 to −29 in Baffin Bay and the West Basin of Hudson Strait to a high of −12.9 to −14.7 further south in the Gulf of St. Lawrence. The Sr and Pb isotopic compositions of these sediments are also variable ( 87Sr/ 86Sr=0.716–0.736; 206Pb/ 204Pb=16.81–18.75), with samples from Baffin Bay, Hudson Strait, and Cartwright Saddle having less radiogenic Pb than those from the Gulf of St. Lawrence. On the opposite side of the Atlantic fine-grained sediments from the Bear Island trough mouth fan and from the mid-Norwegian continental shelf have Nd, Sr and Pb isotopic compositions that are indistinguishable from sediments deposited in the Gulf of St. Lawrence. Glacimarine sediments deposited adjacent to northern and western Iceland have high ϵ Nd (5.7–6.2) and low 87Sr/ 86Sr (0.7042–0.7050), consistent with their derivation from Icelandic volcanic rocks, while sediments deposited nearby on the East Greenland shelf and slope trend towards lower ϵ Nd (−6.5–4.2) and higher 87Sr/ 86Sr (0.704–0.713). Overall, the isotopic variations observed for the ice-proximal glacimarine sediments mirror the variations that occur in immediately adjacent continental crust and hence represent the products of glacial erosion of the continental margins. A comparison of the isotopic compositions of the ice-proximal glacimarine and ice-rafted detritus (IRD) in the North Atlantic confirm that Hudson Strait is the probable source of low ϵ Nd (<−15) detritus in Heinrich events H1, H2, H4, and H5. Higher ϵ Nd (>−15) IRD comprising H3 and H6, and that was deposited before and after lower ϵ Nd IRD in other Heinrich events, could have been delivered to the North Atlantic from the Fennoscandian Ice Sheet, as previous workers concluded, but our data reveal that southeastern margin of the Laurentide Ice Sheet is a viable alternative source for the higher ϵ Nd IRD.