Clay record of climate change since the mid‐Pleistocene in Jiujiang, south China

Abstract

To obtain a better understanding of climate change in south China in the Quaternary, a clay mineralogical study was undertaken on the red earth profile at Jiujiang, using X-ray diffraction (XRD) and particle-size distribution analysis methods. The XRD results showed that the clay minerals of the Jiujiang red earth were mainly mixed-layer illite-smectite (I/S), illite, kaolinite and vermiculite, with trace amounts of mixed-layer kaolinite-smectite (K/S). Changes in clay mineral composition displayed a trend of three-stage evolution. The higher mixed-layer I/S clays and kaolinite contents in the lower portion suggest extremely warm and humid climates over the period c. 700 to c. 350 ka ago. A gradual decrease in I/S clays and kaolinite reveals a gradual climate change from warm/humid to cool/dry during the period c. 350 to c. 130 ka ago. The higher illite and vermiculite contents indicate a relatively cool and dry climate during the period since c. 130 ka ago. The particle-size distribution pattern of the upper section was similar to that of the Xiashu loess, while that of the middle to lower section was similar to those of fluvially reworked red earth. A rapid increase in the abundance of large grain-size components at 2.6 m depth indicates an intensification of the winter monsoon and a cool and dry climate during the period, in good agreement with results from the clay mineral composition and homogeneous structure. The red earth sequences in south China could probably be used to test the response of tropical to subtropical regions to global climate changes.

Fe-oxide mineralogy of the Jiujiang red earth sediments and implications for Quaternary climate change, southern China

“…The main clay minerals in the Jiujiang red earth section are illite, kaolinite, and vermiculite, with trace amounts of mixed-layer kaolinite–smectite and mixed-layer illite–vermiculite, as determined from oriented clay samples in previous XRD studies 8 , 34 – 36 . Bulk-sample XRD data show that the clay assemblages of the lower and middle units are dominated by illite and kaolinite, whereas the upper unit contains illite, vermiculite, and kaolinite.…”

“…The OSL method is usually more reliable for materials <100 ka and the ESR method more reliable for materials >100 ka. An age of 685(±65) ka for the base of the Jiujiang section indicates that the red earth accumulated after the middle Pleistocene 8 , and ages of 40.8(±4.9) and 51.9(±5.8) ka for the top of this section demonstrates that the upper unit was deposited during the late Pleistocene 9 . Average sedimentation rates are 12.6 cm/kyr for the upper unit (based on ages at 0.8 and 2.2 m) and 2.57 cm/kyr for the middle and lower units (based on ages at 6.3 and 13.8 m).…”

“…In response to climatic warming and increased humidity, the red earth sediments in southern China were subject to relatively intense pedogenic alteration 8 , resulting in soil-mineral transformations, especially among iron oxides. The Jiujiang red earth sediments were accretionary in nature, reflecting some degree of syndepositional pedogenesis under tropical to subtropical conditions 8 . Therefore, we take it that post-depositional diagenesis played a very weak role in the red earth.…”

Climate control on the palaeo-lake evolution in the southern Datong Basin, North China: Evidence from 800-ka core records

“…In addition, the high content of illite and chlorite indicates the weak chemical weathering attributed to coldedry conditions (M edard, 2000;Manalt et al, 2001;Perederij, 2001;Hong et al, 2010). Therefore, the ratio of kaolinite and smectite to illite and chlorite might reflect the occurrence of climate change, such as the alternation of coldedry and warmehumid conditions (Hong et al, 2010(Hong et al, , 2013. According to the depth distribution of the clay mineral contents and the ratio of V (S þ Ka)/V (I þ Ch), five stages of climate changes in the past 800 ka in the Datong Basin are exhibited (Fig.…”

Micromorphology, mineralogy, and geo-chemistry of sediments at the Tham Lod rock shelter archaeological site in Mae Hong Son, Thailand: suggestions of a late Pleistocene climate

“…Kaolinite is a climatic indicator and the product of a high weathering intensity environment (Dixon, 1989;Alam et al, 2008;Hong et al, 2013). The results reveal that the kaolinite contents of the lower zone (from 338 to 450 cm depths in particular) are more prominent than those of the upper zone.…”