Jurassic clay-mineral assemblages and their post depositional alteration: upper Great Estuarine Group, Scotland

Andrews, JE (1987) Jurassic clay-mineral assemblages and their post depositional alteration: upper Great Estuarine Group, Scotland. Geological Magazine (124). pp. 261-271. ISSN 1469-5081

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Abstract

Clay minerals from Middle Jurassic lagoonal mudrocks, siltstones and silty fine-grained sandstones of the upper Great Estuarine Group (Bathonian) are divided into four assemblages. Assemblage 1, the most common assemblage, is rich in mixed-layer illite–smectite with attendant illite and kaolinite. Assemblage 2 is dominated by smectitic clay. These assemblages are indicative of primary Jurassic deposition. Illite and kaolinite were probably derived from the weathering of older rocks and soils in the basin hinterland and were deposited in the lagoons as river-borne detritus. The majority of smectite and mixed-layer illite–smectite is interpreted as the argillization product of Jurassic volcanic dust, also deposited in the lagoons by rivers. Near major Tertiary igneous intrusions these depositional clay mineral assemblages have been altered. Assemblage 3 contains smectite-poor mixed-layer illite–smectite, whilst Assemblage 4 contains no smectitic clay at all. Destruction of smectite interlayers occurred at relatively shallow burial depths (< 2500 m) due to enhanced geothermal gradients and local convective hot-water circulation cells associated with the major Tertiary igneous intrusions.

Item Type: Article
Faculty \ School: Faculty of Science > School of Environmental Sciences
University of East Anglia > Faculty of Science > Research Groups > Environmental Earth Sciences
University of East Anglia > Faculty of Science > Research Groups > Geosciences and Natural Hazards
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Depositing User: Rachel Snow
Date Deposited: 03 Mar 2011 14:01
Last Modified: 25 Jul 2018 08:22
URI: https://ueaeprints.uea.ac.uk/id/eprint/25624
DOI: 10.1017/S0016756800016289

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