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|Title:||The radiochemical evolution of the Devonian Orcadian Basin, NE Scotland and comparison with coeval clastic systems from Wales, Norway and the Clair Field.|
|Authors:||Davies, Sarah J.|
|Presented at:||University of Leicester|
|Abstract:||This thesis examines the radiochemistry of the Devonian sediments of the Orcadian Basin, NE Scotland, the Hornelen Basin, SW Norway, together with the SW Wales. A detailed study of the radiochemistry linked to standard sedimentological and geochemical techniques has permitted the utility of portable gamma-ray spectrometry to be assessed. There are no systematic stratigraphic changes in the relative abundances of K, U, Th or in the ratios Th/K and Th/U for either lacustrine or non-lacustrine sediments of the Devonian Orcadian Basin. Spatial radioelement variations related to lithology and source chemistry are more important for characterising the basin infill. Palaeoenvironmental reconstructions, combining sedimentology and radiochemistry, are presented for stages in the evolution of the northern Orcadian Basin. Differing K abundances from the Sandwick lacustrine sequence indicate separation of two depositional areas by a buried basement ridge. The different provenance of the southern and northern marginal fans in the Hornelen Basin, Norway, is reflected by Th and K. Provenance links between the basement and the marginal breccias of the Turriff Basin could be characterised radiochemically and were distinct from the main Lower Old Red Sandstone sediments derived from the Strichen granite. Gamma-ray characteristics linking basement and sediments elsewhere in the Orcadian Basin were less conclusive, implying that the local basement was a minor contributor to the sediment budget. Uranium enrichment is associated with (i) sediments in close proximity to Caledonian granitic basement and (ii) lacustrine intervals. U enrichment is a product of both syndepositional fixation in algal sediments and limited later mobilisation, predominantly restricted to the vicinity of the basement with the greatest concentration along synsedimentary faults. U (5 ppm) and Th (8 ppm) abundances define the zone of mineralisation associated with algal sediments. Lacustrine intervals were correlated using U only for widespread lacustrine conditions; as lacustrine intervals become marginal, U concentrations decrease and correlations are speculative. Lacustrine laminites are geochemically distinguished from sandflat sediments having higher Zr, Y, Cr, Nb, V and SiO2 contents.|
|Rights:||Copyright © the author. All rights reserved.|
|Appears in Collections:||Theses, Dept. of Geology|
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