Carbon isotopic and paleoenvironmental changes recorded in the Upper Ordovician Daduhe Formation, Upper Yangtze, China

The Late Ordovician was a time interval witnessing significant changes in Earth’s history during which the first mass extinction event of the Phanerozoic occurred in the end-Ordovician. While extensive research has focused on this event, fewer studies have examined the bio-environmental changes in the pre-extinction interval. Here, we investigate the Upper Ordovician Daduhe Formation, composed mainly of mixed carbonates and black shales in the Upper Yangtze region, which is a succession deposited before the end-Ordovician mass extinction. Both δ¹³C_carb and δ¹³C_org datasets were analyzed in the Upper Ordovician Daduhe Formation from Wanhe, northeastern Yunnan Province. Of these, paired δ¹³C_carb (−2.62 ‰ to 2.27 ‰ VPDB, avg. 0.12 ‰) and δ¹³C_org (−30.75 ‰ to − 26.17 ‰ VPDB, avg. − 29.62 ‰) records from Wanhe (northeastern Yunnan) reveal a positive carbon isotope excursion in the lower member of the Daduhe Formation. This positive carbon isotope excursion in the Daduhe Formation is comparable to that, namely the PAROVEJA event, in the equivalent strata in North America and Europe, as a result of enhanced organic burial. We hypothesize that enhanced continental weathering due to climate warming and enhanced terrestrial nutrient fluxes into the ocean, promote organic production/burial. This drives positive δ¹³C_carb excursion while simultaneously leading to de-oxygenation of the water column and the destruction of the carbonate factory.