Pleistocene loess in the humid subtropical forest zone of East Asia

Abstract

Loess deposits in Asia have been used as indicators of palaeoclimate, because they are usually found bordering deserts. This paper reports extensive and thick deposits of loess in tropical southwest China, between latitudes 18 and 23°30′N, which is 1300 km south of known, and extensively researched loess deposits in north China. The present climate of the reported loess areas is hot and humid, with mean annual rainfall of 1000–2000 mm, and vegetation of subtropical evergreen broadleaf forest. This compares with less than 400 mm rainfall and vegetation of semi‐desert steppe, in areas of current loess accumulation on desert margins in north China. The source area of the loess, which is dated by optical luminescence to the late Pleistocene, from 90–222 ka, is thought to be the exposed East Asian Shelf, which was up to 140 m below present sea level during Quaternary arid phases. Recent research on the nature of the shelf environment, and the relatively large particle size of the loess, suggests a local origin. The reported loess is not interbedded with palaeosols, and small amounts of soil cover the loess, compared with well developed soils in loess in semiarid regions in north China. This is explained by elimination of the supply source by sea level rise following each arid phase, as continued dust supply appears necessary for soil to form. This preliminary report of loess in southwest China conflicts with palynological evidence, and suggests that recent reconstructions of Pleistocene aridity in east Asia may be conservative.

Cyclic magnetite dissolution in Pleistocene sediments of the abyssal northwest Pacific Ocean: Evidence for glacial oxygen depletion and carbon trapping

“…The dominant terrigenous component is eolian dust, uplifted by strong wind gusts from the large arid regions in China and Mongolia, the Taklimakan desert in northwest China, and the deserts of Inner Mongolia [e.g., Serno et al, 2014] and carried seaward by upper level westerly winds (jetstream) and lower level northwesterly winds (Eastern Asian winter monsoon) [Nilson and Lehmkuhl, 2001]. East Asian shelves falling dry during glacial sea level lowstands have been considered as additional, more proximal dust sources of the northwest Pacific [Nichol and Nichol, 2013]. Loess accumulation in China and dust deposition in the Pacific show equivalent changes in composition and flux [Hovan et al, 1989[Hovan et al, , 1991Balsam et al, 2005;Maher et al, 2010].…”

Quest for the Australasian impact crater: Failings of the candidate location at the Bolaven Plateau, Southern Laos

“…As a coarse sand and fine clay mixture formed by eolian transport of strongly weathered sediments from the exposed Sunda shelf during low sea level of glacial epochs, the Indochina loess-like sediments are quite different from Chinese loess ( Šibrava, 2000). Further weathering removed almost completely alkali and alkaline earth metals (Nichol & Nichol, 2013, 2015. The pre-impact loess was probably deposited during severe glacials MIS 24 and MIS 22, and weathered during the long interglacial MIS 21 and the fast onset of interglacial conditions during the MIS 20/MIS 19 transition (Head & Gibbard, 2015).…”

Late Pleistocene Climate Variation On The Khorat Plateau, Northeastern Thailand Inferred From The Remnants Of Sand Dunes

“…Due to the greatly reduced size of the South China Sea (Huang et al, 1997), and loss of warm water input from the Indian Ocean, the summer monsoon would have been much drier (Wang & Sun, 1994;Wang et al, 1999). It would have approached the TKR across dry land, including the exposed shelf from southern Borneo across Indo-China to Nanning, a distance of over 4000 km over land, and would thus have been much drier than today (Nichol & Nichol, 2013). We suggest that the formation of the dune caused by the lower base level leave a vast amount of sand, which was transported by the fluvial system, on the high and low terraces.…”

“…Apart from loess that has been analyzed from several locations in northeastern Thailand (e.g. Phien-wej et al, 1992;Nichol & Nichol, 2013), sand ridge deposited on paddy field (Pramojanee et al, 1985) non-organic aeolian sand deposits (Loffler et al, 1984) and sand splay (Hokjaroen, 1989;Parry, 1990) were reported. However, none of the detail geological and geomorphological analyzes in the aeolian sand dune in Thungkula Ronghai (TKR) has been carried out.…”