Abstract:
I present results from chemical analyses of bulk sediment recovered from the anoxic Cariaco Basin, Venezuela (ODP Leg 165, Site 1002). The sedimentary record spans approximately 578,000 years, with an average age resolution of approximately 2.5 kyr. Samples were analyzed by inductively coupled plasma emission spectroscopy (ICP-ES) for Al, Ti, K, Mn, Fe, Mo, and V. Elemental ratios were used as the main strategy for interpreting the data. The goal is to determine whether variations in terrigenous input and redox conditions correspond to glacial-interglacial climate change. Visually; all ratios vary closely with delta (super 18) O, which is confirmed with cross-spectral analyses. Al/Ti and K/Al, both significantly higher during interglacials and lower during glacials, are used to interpret potential wind-blown fractionations and sources of hemipelagic deposition. As shown through chemical and mineralogical comparison with potential sources, terrigenous deposition in Cariaco Basin during glacials is dominated by local Venezuelan fluvial sediment (due to lower sea level which serves to decrease transport into the basin from external sources) and by eolian material from the northern Sahara (due to increased glacial wind strength). Ratios of redox sensitive metals (Mn, Fe, Mo, and V) to Al show a strong relationship between sea level and bottom water oxygenation in Cariaco Basin. Sedimentary enrichments of Mo and V occur during interglacials, indicating bottom water anoxia at the time of deposition. During glacial periods, sedimentary enrichments of Mn and Fe represent oxic bottom water conditions at the time of deposition.