Cd isotope evidence for elevated productivity in the Middle Triassic Ordos Basin

The Middle Triassic witnessed the ecosystem recovery from the End-Permian Mass Extinction.The Ordos Basin is the globally earliest recovered lacustrine ecosystem and preserves a suit of hydrocarbon source rocks.However, dominant mechanisms for the abnormal accumulation of organic matter and ecosystem recovery remain highly debated.We present Cd isotope and redox sensitive trace element data of the Middle Triassic black shales from two wells in the Ordos Basin.The southern well is characterised by extremely high TOC contents (7.6-32.6 wt.%), enhanced Mo-U enrichments, and higher 114 Cd auth values (0.37 0.26 ), while the northern well has moderate TOC contents (3.4-10.2wt.%), slight Mo-U enrichments, and lower 114 Cd auth values (0.06 0.29 ).The results suggest that an increase in primary productivity likely driven by active volcanism should play a first order role in the accumulation of organic matter, which was further promoted by local anoxia.The elevated primary productivity and massive burial of organic matter likely contributed to the ecosystem recovery in the Ordos Basin.