ORDOVICIAN OXYGEN ISOTOPES AND PALEOTEMPERATURES

Valid marine delta(18)O proxies have been defined from three Ordovicia n units and with previously estimated sea water delta(18)O values we h ave calculated paleotemperatures for low latitude settings during a gr eenhouse climatic era. Valid marine proxies include: marine equant, bl aded and translucent fibrous calcite. These cements are interpreted to be valid marine proxies based on cathodoluminescence, minor element c ontent, abundance of microdolomite and stable isotopic (both altered m arine and non-marine calcite phases) values. Valid marine proxies from the Chickamauga (Alabama), Holston (Tennessee) and Kullsberg (Sweden) formations have an overall range of delta(18)O values in each unit th at is confined to within 1 parts per thousand unlike altered marine ce ments, which exhibit significantly wider ranges of delta(18)O values. We suggest a likely non-glacial Ordovician sea water value of -2 +/- 1 parts per thousand MMOW from which paleotemperatures can be calculate d. Calculated paleotemperatures are broadly consistent with Crowley an d Baum's (1995) Late Ordovician paleoclimatic model.