[B-PT04] Biotic History

[BPT04-P03] N₂-fixation as a response to Large Igneous Province activity during the end-Triassic mass extinction

*Calum Peter Fox¹, Yuta Isaji¹, Nanako O. Ogawa¹, Jessica H. Whiteside², Aisha Al Suwaidi³, Naohiko Ohkouchi¹ (1.Japanese Agency for Marine-Earth Science and Technology, , 2.Department of Earth and Environmental Sciences, San Diego State University, United States of America, 3.Department of Earth Science, Khalifa University of Science and Technology, Abu Dhabi, United Arab Emirates )

Keywords:Mass Extinction, Triassic, Compound-specific isotopes, Biomarker

The end-Triassic mass extinction (ETE), that occurred 201 Ma, saw fundamental ecological and environmental shifts resulting from the laterally extensive Large Igneous Province (LIP) termed the Central Atlantic Magmatic Province (CAMP). This event serves as an ancient analogue to potential future climate-forced ecological and environmental changes given similar rates of CO₂ increases observed between the CAMP and anthropogenic activity. A critically overlooked aspect of the ETE is resolving changes in the aquatic nitrogen cycle. Currently, no compound-specific nitrogen isotopes exist for the ETE, despite their importance in accurately recording nitrogen cycle shifts in the geological record. We investigated the nitrogen and carbon isotopic composition of deoxophylloerythroetioporphyrin (DPEP; d¹⁵N_DPEP, d¹³C_DPEP) that derives from chlorophyll-a at a pivotal ETE locality; St. Audrie’s Bay, UK. During a correlative carbon isotope excursion, elevated d¹⁵N_DPEP values further support the emergence of microbial mats driving this excursion. In the extinction horizon, ¹⁵N_DPEP, d¹³C_DPEP, and the d¹⁵N differences between DPEP and total nitrogen (TN) reveals the expansion of cyanobacteria and increases in N₂-fixation, estimated to account for 50-75% of production. Although further d¹⁵N_DPEP investigations are needed, d¹⁵N_TN records from diverse depositional settings suggest N₂-fixation was wide-spread during the ETE and likely a common response to LIP activity.