Abstract
Latest Ordovician–early Silurian palaeoenvironmental changes and palaeotemperature trends indicated by stable carbon and oxygen isotopes from northern Estonia
Highlights
Stable isotope changes are nowadays widely employed in the study of Palaeozoic sedimentary sequences and several of the carbon isotopic excursions are acknowledged as stratigraphic markers
The high-resolution stable carbon isotopic data reported from the bulk carbonates of the end-Ordovician–basal Silurian interval in the Lelle D-102 drill core characterize the pre-Hirnantian stable carbon isotopic excursion (HICE), HICE and post-HICE chemostratigraphy and palaeoenvironmental history in the Estonian Shelf of the Baltoscandian Palaeobasin
The stratigraphic extent of the HICE in the studied sections confirms the suggestion that the base of the Silurian System is located considerably higher than the base of the Varbola Formation and that of the Juuru Regional Stage in Baltoscandia
Summary
Stable isotope changes are nowadays widely employed in the study of Palaeozoic sedimentary sequences and several of the carbon isotopic excursions are acknowledged as stratigraphic markers. Stable oxygen isotopes provide a valuable means for tracking information about water temperature, precipitation and chemical composition. These isotopes could be taken as a function of original sea water palaeotemperature but the most common complicating factor here is a possibility of a depleted δ18O signal because of diagenetic overprinting of the primary carbonate composition. High sea level was characteristic of the Sandbian and Katian It was likely the highest level in the Palaeozoic, reaching 150–200 m higher than the presentday sea level (Haq & Schutter 2008). These unique conditions were associated with the rapid diversification of biota during the early Middle Ordovician
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