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The distribution of the ammonite Gravesia (Salfeld, 1913) in the Kimmeridge Clay Formation (Late Jurassic) in Britain

By R.W. Gallois and S.M. Etches

Abstract

Species of the ammonite Gravesia (Salfeld, 1913) have a widespread distribution in Europe over a relatively narrow stratigraphical\ud range in the late Kimmeridgian and early Tithonian stages. The genus is a warm-water form that reaches its maximum\ud stratigraphical range in the Submediterranean faunal province in central France and south Germany where six species have been\ud recognised. Four of these, G. gigas (Zieten, 1830), G. gravesiana (d’Orbigny, 1850), G. irius (d’Orbigny, 1850) and G. lafauriana\ud Hantzpergue, 1987 have been recorded in the Kimmeridge Clay Formation. A few examples have been found in cored boreholes,\ud but most have come from the cliff and foreshore outcrops at Brandy Bay and Kimmeridge Bay in Dorset. The distribution of\ud Gravesia in Britain is mostly restricted to the more calcareous parts of the succession where they represent migrations of a warmer\ud water fauna into a region in which the ammonite assemblages were dominated by Subboreal forms of Aulacostephanus and\ud Pectinatites. The palaeogeography of the late Jurassic in central and North West Europe comprised relatively small land areas\ud separated by seaways that became progressively more restricted with time. In late Kimmeridgian and early Tithonian/Volgian\ud times, migrations of warmer- and cooler-water ammonites through these seaways gave rise to mixed assemblages that enable\ud correlations to be made between the local zonal schemes in the Submediterranean and Subboreal faunal provinces. Gravesia is\ud one of the few ammonites that has a stratigraphical range that crosses the Kimmeridgian-Tithonian and Kimmeridgian-Volgian\ud boundaries, and which has a large geographical distribution which includes much of North West and Central Europe and as far\ud east as the Subarctic Urals. The known distribution of the genus in Britain is summarised herein, along with the first detailed\ud account of its occurrence in the Kimmeridge Clay Formation in the Dorset type section

Publisher: Ussher Society
Year: 2010
OAI identifier: oai:nora.nerc.ac.uk:15874

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