The chemistry of six sediment cores (1-11m in length), recovered in the eastern equatorial Pacific, has been investigated in an attempt to determine spatial and temporal variations in the biogenic and terrigenous components, and to relate these to local and global changes in palaeoproductivity and palaeoclimate. Cores P5 and P12 were recovered in the Panama basin during the R.R.S. Shackleton cruise (May, 1976), whereas CD38 cores were recovered during the R.R.S. Charles Darwin cruise (Valparaiso-Balboa, May, 1989). The cores represent a range of sediment composition from a suite of oceanographic environments (eg. water depth). The eastern equatorial Pacific is an area of very high biological productivity, lying at the interaction of the equatorial divergence and the continental margin upwelling systems, making it an ideal setting in which to conduct such a study. Cores were sampled at 2cm (P5 and P12) and 10cm (CD38 cores) intervals and subjected to geochemical (Si, Al, Fe, Mg, Na, K, Mn, P, Ca, Ti, Zn, V, Ni, Cu, Y, Nd, Nb, Ce, Zr, Cr, Sc, Sr, Rb, Ba, I, Br, Mo, U, Pb, Th and La) analysis using XRF; wet chemical techniques (biogenic silica, organic carbon and Cl); preliminary mineralogical analysis using XRD, and stable isotope (δ18O and δ13C) analysis using mass spectrometry. The δ18O signals in the carbonate tests of <i>Neogloboquadrina dutertei</i> and <i>Globigerinoides ruber</i> from cores CD3822, CD3826 and CD3827 provided oxygen isotope chronostratigraphies which were refined by geochemical correlation with well dated nearby cores (AII54-25PC and P6). The sediments are of Pleistocene age and the base of the cores in this study range from 24ka in P5 to 472ka in CD3826. The sediments divide into two groups: an eastern, hemipelagic set (CD3826, CD3827 and AII54-25PC) which is carbonate poor but enriched in terrigenous material; and a western, pelagic set (CD3814, CD3822 and P5) which is carbonate rich but depleted in terrigenous material. Terrigenous input increases during low sea level stand glacial times (especially stage II), and with decreasing distance from land; consistent with increased input of source material from the shelf, and/or increased wind intensity. The Holocene is a time of rapidly decreasing terrigenous input. Hydrothermal deposits, which have unusually high Si<SUB>terrig</SUB>/Al, Fe/Al and K/Al ratios, are present at 13.93ka in core P5 and at the base of core CD3814. Volcanic ash layers 'D'(56ka), 'L'(234ka) and 'K'(328ka), identified by their low Ti/Al and Cr/Al ratios, are present in core CD3826, and were used in age model development. Very high Ti contents in core P5 (especially during stage II) result from increased continental aridity and wind intensity, which promotes increased input of basaltic material from the Galapagos archipelago. Ti in other cores is derived from central America and the Galapagos archipelago. Cores CD3826 and CD3827, in the eastern part of the Panama basin, contain greater contents of quartz, feldspar and chlorite compared to the other cores; whereas cores P5 and CD3822, recovered in the western part of the basin, have higher contents of opaline silica and barite. Montmorillonite is the most common clay mineral present in these sediments.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:660418 |
| Date | January 1992 |
| Creators | Patience, Andrew John |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/11238 |
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