Apoderoceras

Abstract: Following votes by the Pliensbachian Working Group, the Jurassic Subcommission and the International Commission on Stratigraphy, IUGS rati.ed the proposed Global Boundary Stratotype Section and Point (GSSP) for the base of the Pliensbachian Stage (Lower Jurassic) at the base of bed 73b in the Wine Haven section, Robin Hood's Bay, Yorkshire Coast, UK. This level contains the characteristic ammonite association Bifericeras donovani Dommergues and Meister and Apoderoceras sp. Complementary data include: a) Strontium-isotope stratigraphy, based on analysis of belemnites which yield a calcite 87Sr/86Sr ratio for the boundary level of 0.707425 and data supporting interpretation of continuous sedimentation; b) Belemnite oxygen-isotope data indicate a signi.cant temperature drop (~5 oC) across the boundary at this locality; c) A Transgressive Systems Tract (TST) initiated in the Aplanatum Subzone (uppermost Sinemurian) continues into the Lowermost Pliensbachian (Taylori Subzone); it forms part of a transgressive facies cycle sensu Graciansky et al. (1998); d) The Upper Sinemurian to lowermost Pliensbachian at Wine Haven section has a predominantly normal magnetic polarity, but two discrete reversed polarity magnetozones are present. The .rst spans much of the latest Sinemurian Aplanatum Subzone. It terminates <0.5m below the Sinemurian-Pliensbachian boundary and may prove a valuable chronostratigraphic marker. The second extends from the latest Oxynotum Subzone probably through to the lower part of the Raricostatum Subzone.

Abstract: Introduction 82Leslie Bairstow 82Biography 82Bairstow's unpublished work 84Geological maps 84Geological structure of Robin Hood's Bay 93Stratigraphical succession 93Bed numbers 95Detailed succession in Robin Hood's Bay 96Lithostratigraphy 111Staithes Sandstone Formation 111Redcar Mudstone Formation 111Exposures in Robin Hood's Bay now 114Correlation with previous descriptions 114Bairstow's ammonite collection 115Systematic description of the ammonites and nautiloids 118Family Juraphyllitidae 118Family Lytoceratidae 118Family Psiloceratidae 119Family Schlotheimidae 119Family Arietitidae 119Subfamily Arietitinae 119Subfamily Agassiceratinae 123Subfamily Asteroceratinae 123Family Echioceratidae 125Family Oxynoticeratidae 129Family Cymbitidae 132Family Eoderoceratidae 132Family Coeloceratidae 136Family Phricodoceratidae 137Family Polymorphitidae 137Family Liparoceratidae 141Family Nautilidae 144Biostratigraphy 144Acknowledgements 150References 150Rocks of Lower Liassic (Sinemurian and Lower Pliensbachian) age exposed in Robin Hood's Bay, near Whitby, north Yorkshire, are described from the mapping, stratigraphical descriptions and ammonite collections made by Mr Leslie Bairstow in the years 1927–1970, and preserved in the Palaeontology Department, The Natural History Museum, London. His large-scale map of the geology of the foreshore is published on five sheets at a scale of approximately 1:5000. The stratigraphical sequence from bed 418 at the base up to bed 600.5 at the top of the Lower Pliensbachian is 163.74 m thick, and consists of the Redcar Mudstone Formation, for which four members are formally defined – the Calcareous Shale (at the base), Siliceous Shale, Pyritous Shale and Ironstone Shale Members – overlain by the lower part of the Staithes Sandstone Formation. The lowest beds exposed by the lowest spring tides are Sauzeanum Subzone, Semicostatum Zone, in age; ammonites occur in all subzones, and the only uncertain boundary is that between the Masseanum and Valdani Subzones (Ibex Zone), where there are few characteristic ammonites. Bairstow's ammonite collection consists of more than 2360 specimens, all from recorded horizons, and is notably rich in Promicroceras, Asteroceras, Eparietites and Oxynoticeras from the Obtusum and Oxynotum Zones, Echioceratids, Eoderoceras and Apoderoceras from the Oxynotum, Raricostatum and Jamesoni Zones, and Liparoceratids from the Davoei Zone, making it a primary source for Sinemurian and Lower Pliensbachian ammonite biostratigraphy. The recently proposed selection of Wine Haven at the south-eastern end of the bay as the Global Stratotype Section and Point (GSSP) for the base of the Pliensbachian Stage (ie. the world standard definition), is supported by the sequence of ammonites across the Sinemurian/Pliensbachian boundary. All previously figured ammonites from Robin Hood's Bay are listed in a systematic section that includes the evidence on which the ammonite identifications in the paper are based, and 56 of the best preserved ammonites are figured. Eparietites bairstowi sp. nov. is proposed for an early species of Eparietites and a Sowerby Collection ammonite from the Aplanatum Subzone, Raricostatum Zone, in the bay, is designated neotype of Eoderoceras armatum (J. Sowerby).

Abstract: A temporary section exposed at Westfield, Radstock (Somerset) is described in detail. Here, the Lower Lias ‘Armatum Bed’ is divisible into five layers, each containing a discrete ammonite assemblage. A highly condensed basal conglomerate with a fauna representing much of the Echioceras raricostatum Zone is overlain by a thin limestone of Paltechioceras aplanatum Subzone age -possibly a faunal horizon. These are here grouped as the ‘Gleviceras Limestone'. Above, three beds grouped as the ‘Apoderoceras Limestone’ show a succession of Apoderoceras sub-triangulare, A. ferox and A. sparsinodum . Hence, three ammonite horizons can be recognized, at least locally, within the Phricodoceras taylori Subzone, Uptonia jamesoni Zone. The systematics of Apoderoceras are discussed. The stratigraphical position of Fastigiceras clausum within the raricostatum Zone is determined, and its phylogenetic affinities considered. The frequent occurrence of Epideroceras with an acme in the aplanatum Subzone is noted and the stratigraphical position of Vicininodiceras , close to the Sinemurian-Pliensbachian boundary, confirmed. The occurrence of Tetraspidoceras in Britain is reported, and its stratigraphical and systematic positions considered, with the description of a new species, T. westfieldense .

Abstract: The lowermost Portuguese Pliensbachian is characterized by the association of Apoderoceras dunrobinense Spath, Tragophylloceras numismale (Quenstedt) and Vicininodiceras aff. mouterdei Donovan. This ammonite fauna indicates the lower part of the Jamesoni Chronozone (lower to middle Taylori Subchronozone). Thanks to the numerous specimens collected, the ontogeny and variability of A. dunrobinense Spath, could also be investigated. The paleogeographical distribution of these ammonites underlines the close connections between the Lusitanian Basin and the Euroboreal seas during the Early Pliensbachian.