Assessing redox-related biotic changes during the Sinemurian–Pliensbachian transition in the Lusitanian Basin, Portugal
- 1Royal Netherlands Institute for Sea Research (NIOZ), Department of Marine Microbiology and Biogeochemistry, Netherlands
- 2Netherlands Earth System Science Centre (NESSC), Netherlands
- 3University of Coimbra, Department of Earth Sciences, Coimbra, Portugal
- 4Marine and Environmental Sciences Centre (MARE), Coimbra, Portugal
- 5Royal Netherlands Institute for Sea Research (NIOZ), Department of Ocean Systems, Netherlands
- 6Department of Biogeochemistry, Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Japan
- 7Utrecht University, Department of Earth Sciences, Utrecht, Netherlands
The geochemical record of the Early Jurassic Sinemurian–Pliensbachian transition (S–P transition; ~193 Ma) is marked by a prominent negative carbon-isotope excursion and a short-lived increase in pCO2. The paleoenvironmental responses to this carbon-cycle disturbance within the Eastern European Seaway are limited to a widespread, but minor increase in organic matter burial when compared to, e.g., the Toarcian oceanic anoxic event. In contrast, coeval deposits from the Água de Madeiros and Vale das Fontes formations, Lusitanian Basin (Portugal), located in the north-western fringes of the Tethys, comprise highly organic-rich black shales. Here, we reconstruct the paleoenvironmental and redox changes in the Lusitanian Basin across the S–P transition (oxynotum to raricostatum Zone), which are transitioning from euxinic to anoxic to oxygenated conditions. We combine major- and trace-element concentrations, biomarker analysis, and compound-specific carbon- and nitrogen isotope data including those of geoporphyrins. We assess the impact of redox changes and associated shifts in nitrogen cycling and bioavailability (e.g. denitrification) on the abundance and species composition of the marine microflora, the compound-specific carbon-isotope record and phytane-based pCO2 reconstructions. The exceptionally well preserved, thermally immature and highly organic-rich succession allows new insights into the characteristics and the local processes governing the development of low oxygen conditions outside the temporal realm of large-scale global warming and widespread ocean anoxia.
How to cite: Storm, M., Duarte, L. V., Kraal, P., Hennekam, R., Isaji, Y., Ogawa, N. O., Ohkouchi, N., Schouten, S., and van der Meer, M. T. J.: Assessing redox-related biotic changes during the Sinemurian–Pliensbachian transition in the Lusitanian Basin, Portugal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20350, https://doi.org/10.5194/egusphere-egu24-20350, 2024.