Chalk Group Lithostratigraphy: Marlborough Downs/Berkshire Downs/Chilterns - Chalk Marl: Difference between revisions
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This is mostly synonymous with the Chalk Marl of the Southern Region Chalk Group, except that a less complete succession is usually developed due to erosion at the base of the overlying Totternhoe Stone (Wood, 1996). Several distinctive horizons are recognisable, including silty chalks near the base, dominated by the bivalve ''Aucellina'' ('Aucellina Beds', c. +20 m thick in the Chilterns) (Wood, 1996). Higher in the succession is the Crippsi Limestone, dominated by the ammonite ''Schloenbachia varians'' and the inoceramid bivalve ''Inoceramus crippsi'', overlain by the Dixoni Limestone (with common ''Inoceramus'' ''virgatus'') (Wood, 1996). | This is mostly synonymous with the Chalk Marl of the Southern Region Chalk Group, except that a less complete succession is usually developed due to erosion at the base of the overlying Totternhoe Stone (Wood, 1996). Several distinctive horizons are recognisable, including silty chalks near the base, dominated by the bivalve ''Aucellina'' ('Aucellina Beds', c. +20 m thick in the Chilterns) (Wood, 1996). Higher in the succession is the Crippsi Limestone, dominated by the ammonite ''Schloenbachia varians'' and the inoceramid bivalve ''Inoceramus crippsi'', overlain by the Dixoni Limestone (with common ''Inoceramus'' ''virgatus'') (Wood, 1996). | ||
Latest revision as of 14:53, 7 October 2013
This is mostly synonymous with the Chalk Marl of the Southern Region Chalk Group, except that a less complete succession is usually developed due to erosion at the base of the overlying Totternhoe Stone (Wood, 1996). Several distinctive horizons are recognisable, including silty chalks near the base, dominated by the bivalve Aucellina ('Aucellina Beds', c. +20 m thick in the Chilterns) (Wood, 1996). Higher in the succession is the Crippsi Limestone, dominated by the ammonite Schloenbachia varians and the inoceramid bivalve Inoceramus crippsi, overlain by the Dixoni Limestone (with common Inoceramus virgatus) (Wood, 1996).
Macrofossil Biozonation: M. mantelli Zone and M. dixoni Zone (pars), but where erosion is pronounced below the Totternhoe Stone, only M. mantelli Zone (pars).
Correlation: see Correlation with other parts of the UK
References
WOOD, C. J. 1996. Upper Cretaceous: the Chalk Group. In SUMBLER, M. G., British Regional Geology: London and the Thames Valley. Fourth Edition. (London: HMSO for the British Geological Survey).
See: Totternhoe Stone