HR: 1340h
AN: PP13B-1273    [Abstracts]
TI: Ar-Ar Ages of Detrital Hornblendes from Glacial Sediments of the North Sea Trough Mouth Fan
AU: * Hemming, S R
EM: sidney@ldeo.columbia.edu
AF: Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory of Columbia University, 61 Rt 9W, Palisades, NY 10964, United States
AU: Haflidason, H
EM: Haflidi.Haflidason@geo.uib.no
AF: Department of Earth Science, University of Bergen Allegt. 41, Bergen, N-5007, Norway
AU: Sejrup, H P
EM: Hans.Sejrup@geo.uib.no
AF: Department of Earth Science, University of Bergen Allegt. 41, Bergen, N-5007, Norway
AB: Determining the relative timing of major iceberg calving from different ice sheet margins around the North Atlantic remains an important goal that will lead to a better understanding of causes and consequences of rapid climate variability during the last glacial period. Characterization of the composition of potential contributors is a necessary step towards this goal. The North Sea trough mouth fan is one of the largest glaciogenic debris flow complexes in the North Atlantic/Arctic region, with an approximate area of 142,000 square km (King et al., 1998, Marine Geology v. 152, pp. 217-246; Nygard et al., 2007, Geology, pp. 395-398). The large ice stream trough crosses the shelf along the southern margin of Norway. The crystalline rocks along the southern margin of Norway are Grenville (approximately 1 Ga old orogen). We undertook a study of the Ar-Ar age populations of individual detrital hornblende grains from a sediment sample of the glacigenic debris lobe created during the last phases of the last glacial maximum from the North Sea trough mouth fan. The goal is to test the hypothesis that the ice stream that fed this fan is the source of abundant Grenville age grains found on Bjorn drift site ODP984, at times when North American Grenville sources are not found in the North Atlantic ice rafted detritus belt (Hemming et al., 2005, AGU Spring meeting, PP23A-04). Hornblende grains from North Sea TMF core NH071-B01\SC1 (1) (63.24N, 3.36E, 1049m) have a dominant age population of Grenville (921 Ma, 19 of 48 grains) with subordinate populations of 1108 Ma (n=3) and 1779 Ma (n=4). Accordingly they lend support to the hypothesis that this ice stream could be the source of IRD on the Bjorn drift. These results could additionally shed light on the pathways of fine grain sediment transport to the Bjorn drift which would contribute a better understanding of sediment processes in the region. For example, the provenance implied for the IRD by the Ar-Ar hornblende ages is consistent with that implied by the Nd isotope data from fine grained sediments reported for glacial intervals by DePaolo et al. (2006, EPSL, v. 298, pp. 394- 410). It is well known that much of the debris carried by icebergs is fine grained, and thus this provenance match suggests that it is likely that much of the fine grained material may also be carried to this site by icebergs.
DE: 0730 Ice streams
DE: 0732 Icebergs
DE: 1051 Sedimentary geochemistry
DE: 1115 Radioisotope geochronology
DE: 3022 Marine sediments: processes and transport
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting