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1 2006

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Integrated stratigraphical study of the candidate Oxfordian Global Stratotype Section and Point (GSSP) at Redcliff Point, Weymouth, Dorset, UK

Page K., Melendez G., Hart M., Price G., Wright J., Bown P., Bello J.

Volumina Jurassica

2006

Vol. 4, no. 1

200-201

Redcliff Point near Weymouth, Dorset (SW England) exposes one of Europe’s most complete Callovian-Oxfordian boundary sequences and has been the subject of a rigorous multidisciplinary assessment. The boundary sequence lies entirely within the clay facies of the Oxford Clay Formation, the relatively high carbonate content of which facilitates the excellent preservation of both macro- and microfaunas (and floras) as well as geochemical information. Ammonites, in particular, are conspicuous, and partly retain an aragonitic shell. By convention, the stage boundary is drawn at the first occurrence of the genus Cardioceras, which has been interpreted as corresponding to the transition between “Quenstedtoceras” paucicostatum (Lang) and Cardioceras ex gr. scarburgense (Young and Bird), specifically at the first occurrence of C. woodhamense Arkell sensu Callomon (non Marchand). This transition is well seen at Redcliff and provides the primary means through which the boundary can be correlated. Associated Perisphinctina (including Peltoceras, Alligaticeras, Properisphinctes and Euaspidoceras) provide additional biostratigraphical information. Other macrofossil groups show less discernible changes, although the end of the Callovian in England marks the local, virtual disappearance of Boreal cylindroteuthid belemnites with the persistence of Tethyan hibolithids into the Early Oxfordian. Isotopic studies of recovered belemnites record important information on carbon and strontium isotopes and provide new, high resolution data for the refinement of the global curves. The isotope data are also consistent with continuous sedimentation across the boundary. Foraminiferal assemblages are dominated by poorly preserved epistominids. Planktonic Foraminifera are recorded, mainly as pyrite steinkerns. This makes identification difficult although a flood close to the boundary appears to be Globuligerina oxfordiana. Other planktonic taxa are present, including one species that may be new. Nannofloras are well preserved, common to abundant and dominated by Watznaueria britannica with conspicuous Zeugrhabdotus erectus, podorhabdids and Stephanolithion bigotii. The presence of Stephanolithion bigotii maximum throughout, places the samples within the NJ14 biozone. Ostrocoda and holothurian spicules are also recorded. These results are synthesised to provide a multidisciplinary, integrated review of the suitability of Redcliff Point for the definition of an Oxfordian GSSP. Correlations with the French candidate site in Savournon, Haute-Provence are discussed and proposals made for formally establishing a GSSP for the base of the Oxfordian Stage in Europe.