Multi-proxy analysis of the sedimentary and climatic response to the Palaeocene-Eocene Thermal Maximum in the Hengyang Basin, Hunan Province, China

Abstract

The Paleocene-Eocene Thermal Maximum (PETM) was a time of relatively abrupt climate change with intensive atmospheric greenhouse warming of 5 - 8˚C and is regarded as quasi-analogous for the modern anthropogenically-induced global warming. It therefore attracted considerable attention from geologists over the last decades. The PETM occurred 56 million years ago and is characterized by a sharp negative δ13C isotope excursion which has been observed in terrestrial and marine sediment records the world over. The PETM global warming led to a significant alteration in regional climate and to an enhanced hydrologic cycle which triggered an increase in weathering and sediment discharge from catchments to basins.
The sedimentary, biotic, and climatic responses to the PETM have been studied intensely on the American and European continents. However, detailed analyses of the impact to the PETM on the Asian continent remain rare. Here, a detailed analysis of the sedimentary and climatic response to the PETM in the Hengyang Basin, Hunan Province, China, is presented. High-resolution isotope measurements of pedogenic carbonate nodules reveal the characteristic isotope excursion of the PETM and strongly improve the previous low-resolution isotope series. Pedogenic features and clay types of PETM floodplain deposits indicate oxic conditions and a climate with pronounced seasonality in which intensive dry periods alternated with wet seasons. Grain size analysis of the paleosols support the hypothesis of coarsening deposits as a response to the PETM even though the coarsening is not strongly pronounced. Sediment bypassing and a depleted regolith in coarse material is suggested as the main reasons for the only minor pronounced coarsening in the PETM units. A generalized PETM model, which was simulated in PaCMod, a spatially lumped numerical model developed at the University of Delft, Netherlands, predicts an increase in net precipitation and erosion in the catchment area during the PETM. As a result, the simulated water discharge increases and lead to increased bedload and suspend load transport within the river system. These modelled results are correlative with the geological findings in the Hengyang basin. The Chinese terrestrial PETM record studied here corroborates the global continental impact of the greenhouse warming event through a shift towards pronounced aridity alternating with intensified wet seasons resulting in an oxic floodplain environment with a minor coarsening in grain size.