FINE FRACTION MINERALOGY AS AN INDICATOR OF DETRITAL PROVENANCE IN THE SOUTHEASTERN ATLANTIC OCEAN

Mineralogy of the fine fraction in deep sea sediments can provide information about sediment provenance and transport pathways. For example, particles >150 um were likely transported as ice-rafted debris, while grains <63um were possibly transported by either dust or ocean currents. In addition, identification of specific minerals may provide useful insight into the provenance of those particular grains. A chemical extraction was performed to isolate the terrigenous fraction of three different particle sizes: <63 um, < 150um, and >150 um from sediments representing the last glacial maximum and Holocene from the southeastern Atlantic Ocean collected during Ocean Drilling Program Leg 177 at Sites 1089 (40S), 1093 (49S), and 1094 (53S) spanning the Polar Front Zone. Thin sections were prepared for the <63 um size fraction and discrete grains in the other size fractions are currently being identified.

Previous work from Sites 1089 and 1094 based on Al/Ti ratios of bulk sediment suggest provenance has varied on glacial/interglacial time scales at Site 1089, while Sites 1093 and 1094 exhibit long intervals of relative consistent provenance across glacial/interglacial intervals. Radiogenic isotopes (Sr and Nd) of the detrital component indicated that Sites 1089 and 1094 have different provenance. In particular, Site 1089 has provenance more similar to South Africa while Site 1094 has provenance more like South America (Latimer et al., 2006). Radiogenic isotopes from the last glacial maximum and the Holocene at both sites suggest the sites have slightly different provenance on these temporal time scales as well. This previous work also highlighted the importance of ocean currents (surface and deep), in addition to winds in transporting fine grained sediments long distances from their source. It is hoped that the mineralogy of the <150 um sediment grains will also shed light on detrital provenance and sediment transport.