Increase in marine productivity during the recovery phase of carbon isotope excursion from the Toarcian Oceanic Anoxic Event at the Northwest of the Panthalassa Ocean

Environmental perturbations across the Early Jurassic Toarcian Oceanic Anoxic Event (T-OAE) are represented by a − 3 to −8 ‰ negative shift in both carbonate and organic carbon isotopic excursion (CIE), reflecting a significant disturbance of the carbon cycle at that time. The positive CIE during the recovery phase of the T-OAE, following the negative CIE, is generally interpreted as carbon sequestration activated by marine primary productivity in response to increases in chemical weathering and nutrient supply. To investigate the marine primary productivity across the T-OAE, we analyzed marine chlorophyll-derived fossils (geoporphyrins), maleimides in the black mudstones from the continental shelf of the northwest Panthalassa Ocean, currently located in the Toyora area of Yamaguchi, Japan. During the transition from the main phase to the recovery phase of the T-OAE, we observed an increase in maleimide concentrations, which does not correlate well with oceanic redox conditions inferred from the ichnofabric index of the same sample and redox-sensitive trace metal data from the previous study. This relationship suggests that high concentrations of maleimide may reflect an increase in marine primary productivity, rather than an increase in preservation potential. These results suggest that changes in nutrient supply may have played an important role in regulating marine primary productivity during the recovery phase from the T-OAE. • Marine primary productivity reconstruction from NW Panthalassa during T-OAE. • Analysis of maleimides, photosynthetic pigment fossils, from matured shales. • Marine primary productivity increased from CIE's main phase, peaking in recovery. • Ocean circulation changes and terrestrial detritus may have boosted productivity.