Magnetostratigraphic and paleoclimatic studies on the Red Earth Formation from the Chengdu Plain in Sichuan Province, China

Abstract

Two red earth sections from the Chengdu Plain in Sichuan Province are dated using geomagnetic methods. The Brunhes/Matuyama (B/M) reversal boundary is recognized within the upper parts of the two sections, and the Jaramillo normal subzone occurs in the middle-lower parts of the vermiculated red soil (VRS), which indicate that the parent material for the VRS deposited in the middle Quaternary. Sedimentologic and geochemical studies suggest that the Chengdu Clay and part of the parent material for the VRS are of aeolian origin. Pollen analysis indicates that the Chengdu Plain was mainly covered by needle-leaved forest with a cool to cool temperate humid climate when the parent material for the VRS deposited. The relatively cool to cool temperate climatic condition in the Chengdu Plain in the middle Quaternary, which may be caused by the uplift of the Tibetan Plateau, was a response to the geo-environmental changes of global significance.

Quaternary activity of the range front thrust system in the Longmen Shan piedmont, China, revealed by seismic imaging and growth strata

“…Analysis of the growth strata above the Pengzhou thrust fault shows that fold growth occurred in the early to late Pleistocene, broadly simultaneous with the deposition of the lower Pleistocene conglomerate. Li et al [], Zhao et al [], and Kong et al [] individually used electron spin resonance, magnetostratigraphy, and cosmogenic dating methods to constrain the age of the conglomerate. Their analyses yielded ages of 3.6–3.1 and 2.5–1.8 Myr for the bottom and top of the conglomerate.…”

“…The increase in uplift rates was synchronous with the increase in sedimentation rates during the Quaternary along the RFTS and its splay faults (Pengzhou, Dayi, and Qiongxi). On the basis of the cumulative uplift and the maximum thickness of sediments in the upper Cretaceous Guankou Formation ( K ), the Dayi conglomerate ( N 2 ), a lower Pleistocene conglomerate ( Q 1 ), the Ya'an conglomerate ( Q 2 ), and the Q 3 layer, with ages defined by Li et al []; Zhao et al [], and Kong et al []. QXF, Qiongxi thrust fault.…”

“…[2006], Zhao et al [2007], and Kong et al [2011] individually used electron spin resonance, magnetostratigraphy, and cosmogenic dating methods to constrain the age of the conglomerate. Their analyses yielded ages of 3.6-3.1 and 2.5-1.8 Myr for the bottom and top of the conglomerate.…”

Mineral magnetism to probe into the nature of palaeomagnetic signals of subtropical red soil sequences in southern China

“…12f): one with normal polarity, N1 (0.6–6.55 m) and the other with reverse polarity, R1 (6.55 m to the bottom). Previous magnetostratigraphic studies of the red soil sequences in the middle–lower reaches of the Yangtze River have suggested that the sequences were deposited from the late Early to Middle Pleistocene (Jiang et al 1997; Qiao et al 2003; Zhao et al 2007; Liu et al 2008). The Xuancheng red soil sequence located in the lower reaches of the Yangtze River belongs to this geochronological framework.…”

“…A series of magnetostratigraphic studies reveals that some sequences can record reliable geomagnetic polarities whereas others fail. For example, the red soil sequences in the middle–lower reaches of the Yangtze River have recorded magnetic polarity stratigraphies (Jiang et al 1997; Qiao et al 2003; Zhao et al 2007; Liu et al 2008), whereas the sequences near the Tropic of Cancer failed to record reliable palaeomagnetic field reversals (Deng et al 2007; Yang et al 2008) as the primary natural remanent magnetization (NRM) has been seriously overprinted by secondary chemical remanent magnetization (CRM) (Deng et al 2007). Liu et al (2008) suggested that the complicated palaeomagnetic behaviour of the red soil sequences may result from climatic differences, which control the intensity of chemical weathering.…”