HR: 1340h
AN: PP43B-1284    [Abstracts]
TI: δ¹⁵N changes during Paleogene climatic events in organic-rich, marine clays from coastal Tanzania
AU: * O'Halloran, A
EM: ohalloao@tcd.ie
AF: Department of Geology, Trinity College Dublin, Dublin, 2, Ireland
AU: Nicholas, C J
AF: Department of Geology, Trinity College Dublin, Dublin, 2, Ireland
AU: Goodhue, R
AF: Department of Geology, Trinity College Dublin, Dublin, 2, Ireland
AB: A mid- to outer-shelf, passive margin sequence, consisting of organic-rich marine clays, has been cored by the Tanzanian Drilling Project (TDP) on southern coastal Tanzania. Drilling recovered an expanded Paleogene section — from latest Cretaceous to early Oligocene. Intervals cored include at least two periods of global climatic change: the Paleocene-Eocene Thermal Maximum (PETM), and the Eocene-Oligocene boundary. The organic- rich nature of these clays makes them ideal for nitrogen isotope analysis across these global climate change boundaries. Shifts in the δ¹⁵N of sediments represent changes in the primary productivity regime of the local ocean at that time. An increased or high δ¹⁵N signal in sediment corresponds to regions of greater nitrate depletion in the surface waters (i.e. higher productivity). A low δ¹⁵N signal represents a lack of nitrate uptake in the surface waters, possibly due to phytoplankton migration, phytoplankton collapse or lack of nutrient supply. A sharp and significant decrease in δ¹⁵N is seen at the onset of the PETM. This negative shift in δ¹⁵N coincides with an extinction of benthic foraminifera at this site and may indicate a broader ecosystem collapse. Productivity collapse is a likely result of switching off the nutrient supply to the planktonic biomass. This may indicate stratification of the water column — much like that seen during El Niño events, but over a longer timescale. Preliminary investigations of mineralogy across the Eocene-Oligocene boundary have indicated that through the transition, increased amounts of detrital material (e.g. SiO₂) entered the coastal system. The increasing abundances of detrital quartz are coeval with increases in Ti/Al ratios, also indicating increased terrigenous input. A likely cause is the lowering of global sea-levels during initiation of glaciation on Antarctica. Analyses of the Fe/Al and Ba/Al ratios of the sediments indicate brief periods of increased productivity after the boundary, during the earliest Oligocene. A shift to higher sedimentary δ¹⁵N values would corroborate these preliminary results and further clarify the productivity conditions in the Paleogene.
DE: 4901 Abrupt/rapid climate change (1605)
DE: 4912 Biogeochemical cycles, processes, and modeling (0412, 0414, 0793, 1615, 4805)
DE: 4948 Paleocene/Eocene thermal maximum
DE: 4964 Upwelling (4279)
DE: 4999 General or miscellaneous
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2007 Fall Meeting