Variation of kerogen assemblages and δ13CKerogen in Lower Toarcian successions of the southern Tethyan margin
- Published
- Accepted
- Subject Areas
- Aquatic and Marine Chemistry, Atmospheric Chemistry, Environmental Impacts
- Keywords
- Organic geochemistry, Palynofacies, δ13CKerogen, T-OAE, Lusitanian Basin (Portugal), Betic Cordillera (Spain), Middle Atlas (Morocco)
- Copyright
- © 2019 Rodrigues et al.
- Licence
- This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, reproduction and adaptation in any medium and for any purpose provided that it is properly attributed. For attribution, the original author(s), title, publication source (PeerJ Preprints) and either DOI or URL of the article must be cited.
- Cite this article
- 2019. Variation of kerogen assemblages and δ13CKerogen in Lower Toarcian successions of the southern Tethyan margin. PeerJ Preprints 7:e27945v2 https://doi.org/10.7287/peerj.preprints.27945v2
Abstract
The early Toarcian Oceanic Anoxic Event (T-OAE) is associated with an “excess” of C12 in the atmospheric and ocean carbon reservoirs and widespread occurrence of organic-rich facies around the globe. The T-OAE is recorded as a pronounced negative carbon isotopic excursion (CIE) in carbonates, fossil wood, and kerogens at the base of the Serpentinum (=Falciferum=Levisoni) Chronozone, positioned within a broad δ13C positive trend initiated at the base of the Lower Toarcian. Contrasts in deposition and preservation of OM between the northern and southern Tethyan margins are observed during the T-OAE. Several sections of the northern Tethyan margin are enriched in OM, whereas in the southern Tethyan margin, organic-rich facies are spatially and temporally restricted and have lower TOC. This dichotomy reflects differentiated depositional and environmental conditions between the two margins, controlled by the interplay of local, regional, and global constraints (distinct palaeogeographical location, OM type and source, palaeoceanography, climate, tectonics, etc.). This study investigates the variation of kerogen assemblages and δ13CKerogen in the Upper Pliensbachian–Lower Toarcian interval along the southern Tethyan margin, i.e. Lusitanian Basin (Portugal), Betic Cordillera (Spain), and Middle Atlas (Morocco). The objective is to contribute to the understanding of the paleoenvironmental variables and dynamics that influenced deposition and preservation of OM during the Late Pliensbachian–Early Toarcian in the Tethyan region. Preliminary analysis revealed that Upper Pliensbachian–Lower Toarcian kerogen assemblages from the Betic Cordillera, Lusitanian, and Middle Atlas basins are dominated by terrestrial particles (phytoclasts and sporomorphs) and have relatively more positive δ13C values when compared with correlative North-European sections. In the Lusitanian Basin and Betic Cordillera, the T-OAE negative CIE is observed in the δ13CKerogen record and is accompanied by an increase in terrestrial palynomorphs, non-opaque phytoclasts (NOP), and cuticle fragments. These increases are in line with the posited intensification of continental weathering, acceleration of the hydrological cycle, and increased export of terrestrial OM into marine environments during the T-OAE.
Author Comment
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