Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.642614
Title: Quaternary sediments of a tropical estuary and bay : Phangnga Bay, South Thailand
Author: Carr, Deborah Jacqueline
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1992
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Abstract:
Phangnga Bay is a 2000km2 shallow marine tropical embayment on the peninsula coast of South Thailand. The surrounding catchment area consists of Sn-bearing granites. Permian and Mesozoic sediments and Sn-rich pegmatites intruded in NE-SW trending fault systems. Grain size analysis of surface sediments reveals that mean grain size and sediment sorting show an overall increase southwards towards the more open marine environment. This is thought to reflect the transition from fine grained recent sediments presently settling out in the low energy sheltered conditions in the north to coarse relict sands in the south deposited during Pleistocene low sea-level stands and not covered by recent sedimentation. Geochemical analysis of the sediments reveals that the majority of elements studied (namely, Fe, Mn, AlP2O5, K, Rb, Nb, Y, Th, Pb, V, Cr, Zr, Nl, La, Ce Nb and Organic Carbon) are closely associated with clays through adsorption and cation exchange processes. These elements show concentration distributions which mirror that of the clay content. Sn, Zr and Tl when ratioed to Al, show highest values in the south of the area which is thought to reflect the concentration of these elements in heavy minerals which themselves are concentrated in the relict sands of the south. Both Sn and Rb show distributions strongly controlled by the distribution of cassiterite and lepidolite respectively in the catchment area. Both Mg and Sr show distributions partly controlled by clays and partly by carbonates. CaCO3 shows a general increase southwards reflecting improved conditions for carbonate-secreting organisms and a decrease in the diluting effect of terrigenous material. The carbonate mineralogy varies in relation to the biogenic content of the sediments. Kaolinite is the dominant clay mineral due to the intense chemical weathering of granites in the catchment area, however, clay mineral proportions change from north to south as a result of the variations in settling velocities of different clay minerals. The sediments of 8 depositional environments which have been distinguished on the basis of geomorphology and water depth are compared. Different techniques for distinguishing populations from the data are discussed particularly in relation to the 8 depositional environments mentioned above. From radiocarbon dates of core material sediment accumulation rates in the north of the Bay have been calculated and vary between 0.3 and 1.5mm/year. Progradation rates of the main mangrove development in the north of the Bay have been estimated at approximately 1.5m/year. From the study of cored material and the distribution of surface sediments it is concluded that Holocene sedimentation in Phangnga Bay represents a regressive, fining-upward sequence. Comparisons are made between this model of sedimentation in Phangnga Bay and possible analogues in the geological record.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.642614  DOI: Not available
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