Tectonic and Climatic Impacts on Environmental Evolution in East Asia During the Palaeogene

Abstract

It has previously been established that tectonic activity influences the evolution of fluviolacustrine sedimentary sequences by affecting the provenance supply, while climate change modifies the sedimentary record through weathering and denudation (Najman, 2006). During the Early Cenozoic, many rifted basins developed in eastern China, while an array of compressional basins formed in western China, mostly due to the India-Eurasia collision and continued convergence (Yin & Harrison, 2000) and/or subduction of the western Pacific Plate (Northrup et al., 1995). Most of these basins are filled with non-marine sediments (Ye et al., 1993) and the documented signals suggest that the environmental evolution has been driven mainly by tectonic activity and/or climate change (Ye et al., 1993).The Qinling-Qilian-Kunlun orogenic system (QQKOS) extends for ∼3,000 km from east to west and formed in response to late Mid-Proterozoic to Cenozoic tectonism (Meng & Zhang, 2000;Peltzer et al., 1985). The QQKOS represents an important tectonic zone in Asia linking the India-Eurasia collision with extensive deformation in eastern China (Meng & Zhang, 2000;Peltzer et al., 1985; Figure 1). Field observations show that the faults of the QQKOS are still active today and may have undergone several tens of kilometers of post-Eocene left-lateral displacement (Peltzer et al., 1985). However, the impact of the India-Eurasia collision on eastern China during the Palaeogene, which represents the critical period of the India-Eurasia collision, has not been determined. On the other hand, a broad belt of aridity stretched across China from west to east during the Palaeogene (X. Sun and Wang, 2005), overlapping spatially with the QQKOS, with only the southern-most and northeastern China being

Strongest chemical weathering in response to the coldest period in Guyuan, Ningxia, China, during 14-11 Ma

“…Therefore, an increase in the CIA value indicates the enhancement in chemical weathering, and the amelioration of climate [ 46 ]. Similarly, the ratio of Na 2 O/Al 2 O 3 can be used as an indicator of chemical weathering [ 46 , 47 ], as the mother rock undergoes chemical weathering, in which the unstable Na + is leached and the stable cation Al 3+ is basically unchanged and relatively enriched. Therefore, the smaller Na 2 O/Al 2 O 3 ratio, the stronger the chemical weathering, and vice versa.…”

“…On the other hand, global cooling leads to enhancement of westerlies circulation, which transports more Atlantic water vapor to Central Asia. Therefore, we believe that during 14–11 Ma, global cooling led to enhancement of the westerlies circulation, which brought more water vapor into the study area and resulted in the increase of chemical weathering intensity as during 50.5–37.6 Ma in eastern China [ 47 ]. This recognation is supported by the improvement of vegetation and climate conditions in the Xunhua Basin during 12.5–8.0 Ma, which was attributed to the decrease in evaporation rates caused by continuous global cooling [ 62 ].…”