Sedimentological, Mineralogical and Geochemical Studies of Holocene Coastal Sediments, South-Western Scotland

Kadem, Liftaa Selman (1990) Sedimentological, Mineralogical and Geochemical Studies of Holocene Coastal Sediments, South-Western Scotland. PhD thesis, University of Glasgow.

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Abstract

Holocene raised coastal sediments of the Dalbeattie, Kirkcudbright and New Abbey areas in Galloway, and the area of the former Lochar Gulf in Dumfriesshire, together with present-day intertidal surface sediments from the first three of these areas, were studied. In Part I, the nature of the research project and previous related work is considered. A summary of the geological setting of the field areas is also given. The first half of Part II is concerned with the methods used in data-recording and sample collection in the field and with stratigraphical correlation of the Holocene raised coastal sediments within the Dalbeattie, Kirkcudbright and New Abbey areas on the basis of exposed vertical sections and auger-drilled boreholes. Correlation of the sedimentary sequences recorded in these sections and boreholes suggests that several sedimentary facies can be distinguished in the three areas studied in this way. Four sedimentary facies are also recognised within the present-day intertidal deposits of the same areas. Following a discussion of the concept of sedimentary facies, previous recognition of such facies in SW Scotland and the criteria on which sedimentary facies were distinguished in the course of the research project, descriptions of the present-day and Holocene facies are given. The four sedimentary facies recognised within the present-day intertidal deposits are: tidal-flat; tidal-creek; salt marsh; sand-barrier. The seven sedimentary facies recognised within the Holocene sediments are: A, complex of fine-grained sediments; B, inter-laminated fine sand and silt; C, coarse sand with pebbles; D, fine sand, rich in microfaunal remains; E, clays, rich in plant debris; F, coastal gravel and sand; G, peat. In Part III, data on the shapes, sphericity, roundness and lithological compositions of Pleistocene glaciofluvial and Holocene storm-beach gravel deposits in the Dalbeattie area are presented and compared. Pleistocene clasts are mainly discs, Holocene clasts mainly blades; sphericity ranges between 0.5 and 0.9 in both cases, but the degree of roundness is greater in the Holocene clasts than in the Pleistocene. Greywacke is the commonest rock type in both. The Pleistocene gravels probably were derived mainly from the NW and west, the Holocene gravels partly from the Criffell-Dalbeattie granodioritic pluton and partly from Pleistocene glaciofluvial deposits. The results of orientation studies of (mainly) Holocene gravel clasts in the Dalbeattie and New Abbey areas are also given. They suggest deposition by SE-NW water flow. Detailed grain-size analysis indicates that most of the Holocene sediments in the Dalbeattie area and in the upper part of the successions in the Kirkcudbright and New Abbey areas (sediments of facies A) are of silt grade and bimodal or polymodal in grain-size distribution, whereas sand-grade and unimodal grain-size distribution predominate in the Holocene sediments (of facies D) in the area of the former Lochar Gulf and in the lower part of the succession in the Kirkcudbright and New Abbey areas. The present-day intertidal sediments of the Dalbeattie, Kirkcudbright and New Abbey areas are mainly of fine-sand grade and unimodal in grain-size distribution. In descending order of abundance, illite (mainly with the composition of biotite and muscovite), chlorite (mainly Fe-chlorite), kaolinite and vermiculite are the main clay minerals present in both the present-day intertidal and Holocene raised coastal sediments in the areas studied. Both detrital and authigenic illite, chlorite and kaolinite are present; detrital material greatly predominates over authigenic material in the cases of chlorite and kaolinite. Vermiculite is more abundant in the uppermost facies, A, than in the various underlying facies. Mixed-layer clays and montmorillonite are present in minor amounts in the Holocene sediments. Geochemical analysis of bulk samples and samples of the clay fraction of both the Holocene and present-day sediments indicates that the SiO2 content, which is inversely related to the content of Al2O3, total iron, TiO2, MgO and K2O, is higher in the Holocene sediments of the Lochar Gulf area than in the sediments of the same age in the three other areas studied. The CaO content in Holocene sedimentary facies D, which is approximately equal to that in the present-day sediments and higher than in the other Holocene sediments, may have been derived from fossil shell and other organic carbonate fragments in facies D. The trace elements Y, Sr, Rb, Th, Pb, Zn, Ni, Co, Ce, Cr, Ba and La are associated with the clay minerals present in the sediments. Environments of deposition and possible provenances of the Holocene sediments are discussed in Part IV.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Geology, Sedimentary geology, Geochemistry
Date of Award: 1990
Depositing User: Enlighten Team
Unique ID: glathesis:1990-77999
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 28 Feb 2020 12:09
Last Modified: 28 Feb 2020 12:09
URI: http://theses.gla.ac.uk/id/eprint/77999

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