A comprehensive study of marine sediments collected during the <i>R.R.S. Charles Darwin</i> Leg 38 cruise from the Peruvian continental margin, has been carried out using a wide range of geochemical analysis technqiues. The prime objective of the study has been to determine the strength and down-core variation of many oceanographic processes during the glacial/interglacial stages of the Late Quaternary by means of geochemical palaeo-environmental indicators. Coastal upwelling is a physical movement of cold, nutrient-rich water to replace surface water which has been blown off-shore by Ekman transport, as a result of along-shore winds. This results in high marine productivity levels within the Peruvian coastal upwelling zone, and is recorded by enrichments of organic carbon and other biogenic-remains in the sediments accumulating below. Particular metals, which have a capacity to be scavenged from sea-water as organic matter falls through it, are also enriched in the sedimentary record. Organic matter and fish-remains supply a continuous source of phosphorus to the surface sediment. Upon bacterial decomposition of this biogenic debris, phosphate can become enriched in the pore-waters until precipitation of carbonate fluorapatite occurs to form the diagenetic mineral known as phosphorite. Within the Peru margin cores, the presence of disseminated phosphorite pellets and zones of nodular hardgrounds has been determined using pore-water modelling and geochemical partitioning equations. Many trace elements can be incorported into the phosphorite mineral structure. Quantitative analysis of the uranium, strontium and yttrium concentrations within phosphorite zones has allowed for the partitioning of these elements into the organic, carbonate and terrigenous phases respectively. Y-series radiochemical age dating of a phosphorite nodule yielded a 'maximum' age of about 114,000 years for the phosphatic material. This age corresponds to an initial pellet growth on the continental margin during an interglacial period and supports the hypothesis of nodule diagenesis during the last glacial period as a result of heavy mineral concentration by bottom-water currents during a eustatic drop in sea-level.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657110 |
| Date | January 1993 |
| Creators | McNeill, Gavin William |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/15360 |
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