Distribution and origin of authigenic minerals in the Triassic Sherwood Sandstone Group, UK

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Authors:Burley, S. D.
Author Affiliations:Primary:
Univ. Hull, Dep. Geol., Hull, United Kingdom
Other:
Univ. London, Queen Mary Coll., Dep. Geol. Sci., United Kingdom
Volume Title:Patterns of mineral diagenesis on the NW European continental shelf and their relations to facies and hydrocarbon accumulation
Volume Authors:Morgan, D. J., editor; Rawson, P. F.
Source:Clay Minerals, 19(3), p.403-440; Joint meeting of the Clay Minerals Group of the Mineralogical Society and the Petroleum Exploration Society of Great Britain ; Patterns of mineral diagenesis on the NW European continental shelf and their relations to facies and hydrocarbon accumulation, Cambridge, United Kingdom, April 7-8, 1984, edited by D. J. Morgan and P. F. Rawson. Publisher: Mineralogical Society, London, United Kingdom. ISSN: 0009-8558
Publication Date:1984
Note:In English. 69 refs.; illus. incl. 6 tables, sketch map
Summary:The Triassic Sherwood Sandstone group comprises a complex of continental red beds deposited by a major fluvial system flowing dominantly down a northerly-inclined palaeoslope. Sedimentation took place in several distinct, tectonically active basins with varying maximum burial depths (<1-3 km). Despite proximal to distal variations in stream type, a distinct suite of early diagenetic events can be recognized throughout all the depositional basins, which is related to the depositional environment. These events are best preserved in basins with shallow burial histories, such as that on the margins of the Irish Sea basin in Cumbria, where the detrital grains underwent changes to reach equilibrium with the near-surface chemical environment. Unstable silicates were dissolved or replaced and released ions were precipitated as authigenic phases, typically mixed-layer illite-smectite, K-feldspar, non-ferroan carbonates and hematite. Lateral variations in early diagenetic assemblages reflect chemical and spatio-temporal changes of interbasin depositional and diagenetic environments. Deeply buried equivalents in the Irish Sea show a series of depth-related changes superimposed on the early diagenetic fabric. In the absence of early cements, compaction reduced porosity to low levels. Mixed-layer illite-smectites were converted to highly crystalline illites with low Fe and Mg contents. Early framework-preserving non-ferroan carbonates were extensively dissolved, generating widespread secondary porosity. Late pore-filling carbonate cements comprise ferroan dolomites and ankerites. Following late Mesozoic burial, inversion of the Triassic basins resulted in the re-exposure of basin margin sequences and shallow-burial basins. In the Wessex basin, the Triassic sandstones of the South Devon aquifer were extensively modified by the percolation of post-inversion acidic ground-waters, resulting in in situ breakdown of feldspar to produce abundant authigenic kandite, widespread dissolution of carbonate cements and removal of early-formed iron oxide cements. In contrast, the concealed, deeply buried eastern margin of the Wessex basin exhibits a diagenetic evolution resulting from deep burial and shows no development of authigenic kandite. [D.J.M.]
Subjects:Authigenic minerals; Burial metamorphism; Cement; Clastic rocks; Clay mineralogy; Compaction; Deposition; Depositional environment; Diagenesis; Early diagenesis; Electron probe data; Fabric; Ground water; Ions; Materials; Matrix; Mesozoic; Metamorphism; Outcrops; Overgrowths; Patterns; PH; Porosity; Precipitation; Red beds; Sandstone; Secondary porosity; Sedimentary petrology; Sedimentary rocks; Sherwood Sandstone; Solution; Textures; Triassic; X-ray data; England; Europe; Great Britain; United Kingdom; Wessex Basin; Western Europe; Areal studies; Devon Basin; Evolution
Abstract Numbers:85M/2025
Record ID:1985033740
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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