Paleocene-Eocene carbon isotope excursion recorded in the western Jianghan Basin, China

Paleocene-Eocene Thermal Maximum (PETM), occurring at Paleocene/Eocene boundary, was a rapid global warming event caused by the release of massive carbon into ocean-atmosphere system. The western Jianghan Basin in central China was documented as a sedimentary archive spanning the Paleocene/Eocene boundary, but the PETM event has never been well constrained. Here, we report the carbon isotope results of pedogenic carbonate and lacustrine carbonate from a newly exposed section in the western Jianghan Basin (close to Yidu city). The ~80-m-thick section consists of Gongjiachong and Yangxi Formations, which can be interpreted as being deposited in a marginal lacustrine environment, dominated by interlayered, medium to thick-bedded gray limestone, calcareous sandstone, and red siltstone with minor conglomerate. From bottom upward, the carbon isotope of total carbon (δ^13 C) shows a rapid decrease from -6.5‰ to -13‰, while the carbon isotope of organic matter (δ^13 C_org) decreases from -24.5‰ to -27.4‰, suggesting a carbon isotope excursion in a short period of time. The carbon isotope records, like the ocean record, clearly show a “Three-Phase Model”: it starts with a rapid carbon isotope negative excursion from about 15 to 20 meters, followed by a slow decline trend from 20 to 36 meters, and then a gradual recovery to the pre-PETM level from 36 to 46 meters. This pattern of carbon isotope change corresponds to a positive feedback process of carbon in the Earth's surface system. Our findings indicate a possible records of PETM events and provide a new perspective for studying early Cenozoic climate change in central China.