Multi-proxy Characterization of the Feni and Gardar Drifts

Sediments from two North Atlantic drift deposits - the Feni Drift (DSDP Leg 94, Site 610) and the Gardar Drift (DSDP Leg 94, Site 611) provide a monitor for water flowing over the Iceland-Faero Ridge and through the Rockall Trough and Maury Channel. The Feni Drift was sampled at holes 610 and 610A (53^o13.297'N, 18^o53.213'W, 2417 m), east of Rockall Bank and west of the Rockall Trough. The Gardar Drift was sampled at hole 611C (52^o50.15'N, 30^o19.10'W, 3230 m), near the Charlie-Gibbs Fracture Zone. The sediments were light-colored nannofossil oozes and chalks. Paleomagnetic sample cubes were taken for rock- and paleo-magnetic studies and standard scoop samples for geochemical and textural analyses. The non-terrigenous fraction of the sample was removed prior to geochemical and partical-size analysis. Bulk magnetic susceptibility was determined using a KLY-2 Kappa Bridge. In general, the bulk magnetic susceptibility for samples from hole 611C is higher than for hole 610. Hole 610 has a downcore decrease in susceptibility at 2.5 Ma, which reflects a decline in the terrigenous mineral component. A peak in the susceptibility and in the % terrigenous mineral component occurs ~1.0 Ma. Hole 611C has two sharp upcore increases in bulk susceptibility, one at 3.5 Ma and another at 4.5 Ma. Two pronounced peaks occur at about 1.5 Ma and 2.6 Ma in both the bulk susceptibility and % terrigenous component; a second, lower peak occurs ~4 Ma in both data sets. The terrigenous grain size and sorting are similar at each site (φ50 = 6.35 for hole 610 and 6.41 for hole 611C; IGSD, a measure of sorting, = 1.17 for hole 610 and 1.27 for hole 611C). However, between 4 Ma and 5 Ma, the particle distribution pattern is flatter and the grain size is coarser for hole 610, implying a higher energy flow. In this same time frame, the φ50 and distribution patterns for hole 611C are more variable. The δ 13C and δ ¹⁸O values of benthic foraminifera were determined at UC Santa Cruz. The δ ¹⁸O becomes more enriched upcore for both sites, starting around 4 Ma, consistent with the development of Northern Hemisphere glaciation. However, at 6 Ma, there is an interesting divergence - older values remain constant at site 610, whereas δ ¹⁸O values at site 611, the deeper site, decline 1.2 \permil in about 1.5 Ma. Younger samples from both sites become gradually more depleted in δ 13C. Hole 611C has a very sharp negative peak at 4Ma. Geochemical analysis of the terrigenous component shows that fraction to be dominantly continental at Feni Drift. However, at Gardar Drift, sediments younger than 3 Ma are largely oceanic.