Baltoscandian Middle Ordovician brachiopod oxygen stable isotope trends: implications for palaeotemperature changes

Over the last two decades, there has been an intensive research effort focused on studying the climate fluctuations during the Ordovician period. In this study, we provide brachiopod and bulk carbonate rock stable isotopic data for oxygen (O) and carbon (C) from the Middle Ordovician succession from northern Estonia for evaluating the Middle Ordovician palaeotemperature and palaeoenvironmental history. We present .18O curves from eight northern Estonian outcrops. This new data, together with the published results, enable compiling the first complete stable oxygen isotopic curve for Middle Ordovician to early Silurian for the eastern Baltoscandian Palaeobasin. Combining the published and new .13Cbrac and .18Obrac data allows us to address chemostratigraphic correlation in the Middle Ordovician. The Baltoscandian .18O data generally confirm a cooling trend from Early to Middle Ordovician documented by previous studies in different palaeobasins.