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    Discussion of 'isotopic variation in fossils and matrix of the Cretaceous Red Chalk at Speeton and South Ferriby, Yorkshire, England'

    Mitchell, S. and Underwood, Charlie J. (1998) Discussion of 'isotopic variation in fossils and matrix of the Cretaceous Red Chalk at Speeton and South Ferriby, Yorkshire, England'. Proceedings of the Yorkshire Geological Society 52 (1), pp. 107-112. ISSN 0044-0604.

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    We welcome the study of G. D. Price on the isotopic composition of fossils and matrix from the Red Chalk, but would like to make a few additional points that we feel relate to this work. Price quoted the works of Ditchfield & Marshall (1989) and Jeans et al. (1991) as references on the study of stable isotopic compositions of matrix (or bulk sediment samples) and micro-fossils from the Lower Chalk. The Ditchfield & Marshall study suggested that cyclic oscillations in oxygen isotopic compositions were related to lithology, with chalk beds deposited under warmer surface water conditions than the intervening marl beds (i.e., they represented carbonate productivity cycles). This interpretation has been subsequently accepted by many authors (e.g., Jeans et al. 1991, amongst others). Mitchell et al. (1997), however, demonstrated that the cyclical oscillation in oxygen isotope values in these rhythmic chalk–marl successions in the Lower Chalk was the result of differential cementation of the limestone beds (where cement was concentrated in large pores such as planktic foraminifera and calcispheres) and that there appeared to be very little primary difference between the isotopic composition of the chalks and the marls. Price (1998, p. 109) suggested that the variation in the oxygen isotopic composition of the belemnite Neohibilites [sic] might be due to surface water temperature variations related to Milankovitch forcing, particularly as “well developed rhythmicity that may be due to Milankovitch climatic forcing” (Mitchell, 1995) is present in the Red Chalk.


    Item Type: Article
    School: Birkbeck Faculties and Schools > Faculty of Science > School of Natural Sciences
    Depositing User: Sarah Hall
    Date Deposited: 21 May 2019 16:08
    Last Modified: 02 Aug 2023 17:51


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