Age, origin and climatic signal of English Mesozoic clays based on K/Ar signatures
The K/Ar characteristics of 53 clay assemblages (Triassic-Cretaceous), representing the detrital, volcanogenic and arid-facies clay mineral associations, are interpreted in relation to their mineralogy, chronostratic age and geological origins. The K-beating mineral components of the 1–2m, 0.2–1m and <0.2 m fractions of each clay assemblage together display one of two characteristic patterns of K2O and 40Ar values (the K/Ar signature of the assemblage) on a 40Ar/K2O correlation diagram. Interpretation of the K/Ar signatures indicates that (1) all of these clay assemblages are apparently unaffected by burial diagenetic illitization; (2) the Jurassic and Cretaceous detrital clay assemblages are derived from the reworking of weathered Caledonian metasediments (420-500 Ma) and weathered kaolin-bearing sediments of Upper Devonian/Carboniferous age; and (3) the role played by palaeoclimate in developing the pattern of clay minerals in the Mesozoic sediments of England is much less significant than previously believed.
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Document Type: Research Article
Publication date: 2001-12-01