Dean, William Edward; (1994) The relationship between sea-level changes, facies changes and ammonite distributions in the Aptian-Albian of the Anglo-Paris Basin. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

New data on the Aptian and Aibian sequences of the Anglo-Paris Basin has allowed a revision of their lithostratigraphy and ammonite biostratigraphy to a modern standardised format. The results are combined with a sequence stratigraphic analysis to correlate strata and determine the changes in relative sea-level. With this approach more detailed correlations are made possible than previously recognised. As the sea-levels changed, so did the palaeogeography and lithofacies distributions. Ammonites were highly susceptible to such environmental changes and their distributions fluctuated accordingly, both vertically and laterally. Statistical methods have been utilised to examine the changes in both ammonite diversity and abundance through time. Generic/species diversity is based on all available material. Six diversity zones are recognised, three of high and three of low diversity. The boundary of each diversity zone coincides with a sea-level rise. The abundance of families/genera is based solely on the author's collections. It was analyzed in relation to the biogeographic affinity of the taxa. This shows that there is a close link between diversity and abundance, both related to changes in sea-level. There were two main periods when endemic and heteromorph ammonites were abundant, the first corresponding to the Deshayesitid and lower part of the Cheloniceratinid diversity zones, the second peaked in the Hoplitid Diversity Zone. The ammonite distributions are used as a tool for determining the relative importance of the various transgressions across the basin. Of the 23 transgressive surfaces recognised, 11 are marked by important faunal turnovers. A combination of all the data is used to propose a revised sea-level curve for the Aptian-Aibian in the Anglo-Paris Basin.

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