Quantifying the biogeographical patterns of Ordovician ostracods

MEIDLA, T.; TINN, O.; SALAS, MARIA JOSE; WILLIAMS, MARK; VANDENBROUCKE, T.; SIVETER, DAVID J.

Copenhagen, Dinamarca

Otro; Absolutely final meeting of IGCP503: Ordovician palaeogeography and palaeoclimate.; 2009

The biogeographical occurrence and patterns of distribution of shelf marine ostracod genera are analyzed quantitatively for two Ordovician time slices, thought to reflect global greenhouse and icehouse climate states respectively. These correspond to the earliest Late Ordovician and to the latest Ordovician. The earlier time slice is equivalent to the Nemagraptus gracilis interval, and is defined as the total range of the eponymous graptolite species. In reality the limits of stratigraphical resolution means that some ostracod-bearing strata from immediately below and immediately above this interval may have been incorporated into the dataset. The Hirnantian time slice includes data from some areas, in particular Anticosti Island, where the exact age of the terminal Ordovician strata has still to be resolved. The results from the N. gracilis interval reveal a subdivision into four broad biogeographical areas, namely Laurentia, Peri-Gondwana (with Ibero-Armorica, Saudi-Arabia and Bohemia at the center), Baltoscandia and Russian Siberia, while the position of the Precordillera, Kazakhstan, Holy Cross Mountains and Norway remains poorly resolved. The Hirnantian interval contains data from a limited number of localities, mainly in Baltoscandia and North America. A decrease of provincialism is suggested by an increase in ostracod faunal affinities between Baltoscandian and Peri-Gondwanan areas. However, a response to global cooling is not identified in the analyses of the distribution patterns. As the taxonomic status of many of the taxa - published over the last fifty years - is still in flux, the results of these analyses must be regarded as provisional.