Baltoscandian Ordovician and Silurian brachiopod carbon and oxygen stable isotope trends: implications for palaeoenvironmental and palaeotemperature changes

Authors

  • Bilal Gul University of Tartu
  • Leho Ainsaar
  • Tánu Meidla

DOI:

https://doi.org/10.7306/gq.1742

Keywords:

Stable carbon and oxygen isotopes, sea-level, brachiopods, palaeotemperature, Ordovician, Silurian

Abstract

Oxygen isotope palaeotemperature studies of Paleozoic limestones are based mainly on brachiopod shell material which is resistant to diagenesis and generally precipitated in oxygen isotopic equilibrium with ambient sea water. Here we present brachiopod C and O stable isotopic data from the Baltoscandian Ordovician-Silurian succession, and evaluate palaeotemperature and palaeoenvironmental variability during deposition of the Estonian Shelf facies. As the region has not been influenced significantly by tectonic events or deep burial diagenesis, the carbonate rocks and fossils are well-preserved in most of the locations studied. δ18O  values for the Ordovician and Silurian carbonates and brachiopods range between ~–7 and 0‰. High δ18O values, locally accompanied by higher δ13O values, correspond to cooling if the isotope signal reflects the original oxygen isotopic composition in sea water and vice versa. Several Ordovician-Silurian δ13Obrac excursions identified on the Estonian Shelf reflect global palaeoenvironmental history and events, being synchronous with previously documented excursions in the bulk carbonate stable isotopic curves. Combining the published and new d13Cbrac and δ13Obrac data allows us to address chemostratigraphic correlation of the interval from Lower Ordovician (Floian) up to the topmost Silurian (Přídolí). The δ18Obrac data corroborate warmer temperatures during Early Ordovician (Floian-Dapingian) and a cooling trend into the Mid-Ordovician documented by previous studies in different palaeobasins. The Hirnatian isotopic carbon excursion (HICE) episode reveals the minimum temperature in this interval and the post-HICE data suggest a rising temperature trend. Another temperature minimum is evident in the strata reflecting the Ireviken Event (Sheinwoodian). Our study shows that brachiopod d18O values from the Ordovician-Silurian carbonates may tentatively be interpreted as reflecting major temperature trends 

Downloads

Published

2024-04-20

Issue

Vol. 68 No. 2 (2024)

Section

Articles

License

Authors who publish with this journal agree to the following terms:
  1. Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under a Creative Commons Attribution License that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.
  2. Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
  3. Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as this can lead to productive exchanges and earlier and more frequent citation of the published work (See The Effect of Open Access).