The early Toarcian extinction event and associated Pliensbachian-Toarcian palaeoenvironmental perturbations in Bulgaria
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Abstract
The Early Toarcian was characterised by the eruption of the Karoo-Ferrar large igneous province (LIP), rapid global warming, significant perturbations in the global carbon cycle, the development of widespread anoxia known as the Early Toarcian Oceanic Anoxic Event (T-OAE) and a biotic crisis in the marine realm known as the Early Toarcian Mass Extinction (ETME). Despite the purported global nature of these environmental and biotic changes, the majority of records come from Western European sections, and remain particularly focused on settings in which the T-OAE was clearly expressed. Fewer studies focus on sections where the manifestation of ocean deoxygenation appears to have been considerably weaker, or even absent. We herein focus on Lower Jurassic successions of the Moesian Basin in the Balkan Mountains of the Balkan Mountains (Bulgaria) that were deposited on an open-ocean facing carbonate shelf. The Bulgarian δ13C and δ18O profiles show similar trends through the Lower Jurassic to coeval European sections, suggesting that seawater in the Moesian Basin was recording global palaeoclimatic and palaeoceanographic conditions during this time. Analysis of the carbon isotope record reveals a broad positive carbon isotope excursion (CIE) of 3‰ in δ13Cbel through the Early Toarcian, interrupted by a negative CIE of 3.5‰ recorded in organic carbon (Tenuicostatum–Falciferum zones). Progressive warming of seawater and increased influx of freshwater into the Moesian Basin through the Early Toarcian is recorded in δ18Obel isotopes. Such changes are attributed to the eruption of the Karoo-Ferrar LIP, reflected in the Moesian Basin by an enrichment in Mercury (Hg) recorded as a shift in sedimentary Hg/TOC values synchronous with the negative CIE. A biotic crisis is recorded amongst bivalves and considered to be part of the ETME, which is here recorded in Bulgaria for the first time. Although a significant loss amongst bivalves during the ETME often coincides with the spread of anoxia, this link is not clearly seen in Bulgaria as geochemical and sedimentological records do not support the prevalence of anoxic conditions. As such, oxygen deficiency cannot be considered a key driving mechanism for the ETME in this part of the ocean and other factors such as rapid warming may have been more important in this central Tethyan region.
Cite this as
2019. The early Toarcian extinction event and associated Pliensbachian-Toarcian palaeoenvironmental perturbations in Bulgaria. PeerJ Preprints 7:e27948v1 https://doi.org/10.7287/peerj.preprints.27948v1Author comment
This abstract was accepted for the 3rd International Workshop on the Toarcian Oceanic Anoxic Event
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Competing Interests
The authors declare that they have no competing interests.
Author Contributions
Autumn Pugh conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Crispin TS Little conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Ivan P Savov conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Lubomir Metodiev conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Paul B Wignall conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Robert J Newton conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, authored or reviewed drafts of the paper, approved the final draft.
James Riding conceived and designed the experiments, performed the experiments, analyzed the data, contributed reagents/materials/analysis tools, prepared figures and/or tables, authored or reviewed drafts of the paper, approved the final draft.
Data Deposition
The following information was supplied regarding data availability:
No data are submitted with this Abstract preprint.
Funding
This work was supported by a Natural Environment Research Council DTP studentship. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
