Provenance and Climatic Implications of the Middle-Pleistocene Loess Deposit, Southern China

The middle-Pleistocene Xiashu loess deposit in the lower reaches of the Yangtze River (LRYR), southern China, may yield evidence with significant climatic and environmental significance. However, its provenance remains controversial. In this study, grain size analysis, and quartz grain surface microtextural and morphological observations, enabled comparison of the provenance of loess in the LRYR with those on the Loess Plateau in northern China. The results show that the grain size characteristics of the Xiashu loess do not follow the coarse-fine NW-SE trend in northern China, and the surface microtextures of the quartz grains in the Xiashu loess are distinctly different from those on the Loess Plateau in northern China, indicating that the loess deposits in the two regions have different provenances. The Gobi Desert in inland northwestern China are not considered as the primary provenance of the Xiashu loess. Instead, the adjacent floodplains in the LRYR, the alluvial plains of the Huai River and the Yellow River to the north during glacial periods are suggested as the dominant source materials for the Xiashu loess. Under the background of middle-Pleistocene climate transition (MPT), regional aridity and a strengthened east Asian winter monsoon (driven by global cooling and the rapid uplift of the Tibetan Plateau) were considered as the primary drivers for the development of the Xiashu loess. The sustained eolian loess accumulation represent a regional response of the northern subtropical area of southern China to the MPT global cooling event at around 0.9 Ma.

Did an earthquake located off Jersey trigger a mudflow preserving the only loess outcrop known under the seas?

A 5 m long core sample, retrieved from between Jersey and the Cotentin (France) has been studied using different techniques. Between the lower part and the top, the core is a yellowish loess, a black mud and a grey shelly formation. The basal formation, which displays a typical loess granulometry, is the only loess found anywhere in situ on the subtidal seabed worldwide. Elsewhere, this fragile sediment has always been washed out by the successive Quaternary transgressions. The overlying mud formation, which displays characteristics of a landslide, sealed the loess deposit. Because this core has been sampled on the rim of a submarine valley located in front of a major onshore geological disruption, clearly associated with an active seismic zone, it is possible that an earthquake triggered a slope failure causing a gravity collapse of materials that protected the loess deposit from subsequent erosion, although we cannot completely rule out the effects of a large flood.Supplementary material: Tables showing the results of the pollen analysis and distribution of mollusc shells and other fossils in borehole O-VC15, and a figure showing the distribution of mollusc species in core O-VC15 and a possible reconstruction of the palaeoenvironment during sediment deposition are available at https://doi.org/10.6084/m9.figshare.c.4991753

Desert loess: a selection of relevant topics

In discussions on loess, two types are often demarcated: glacial loess and desert loess. The origin of the idea of desert loess appears to lie with V.A. Obruchev who observed wind-carried silt on the Potanin expedition to Central Asia in 1895. It might be considered that desert loess would be defined as loess associated with deserts but it came to be thought of as loess produced in deserts. This led to some controversy as no mechanism for producing silt particles in deserts was readily available. Bruce Butler in Australia in particular cast doubt on the existence of desert-made loess. Butler indicated loess-like deposits in Australia which he called Parna; these are very like loess but the silt sized particles are actually clay mineral agglomerates of silt size- formed in dry lake regions. At the heart of the desert loess discussion is the problem of producing loess material in deserts. It has been suggested that there are no realistic mechanisms for forming large amounts of loess dust but there is a possibility that sand grain impact may produce particle shattering and lead to the formation of quartz silt. This would appear to be a reasonable mechanism for the African deposits of desert loess, but possibly inadequate for the huge deposits in China and Central Asia. The desert loess in China and Central Asia is loess associated with a desert. The material is formed in cold, high country and carried by rivers to the vicinity of deserts. It progresses then from deserts to loess deposit. Adobe ground may be defined as desert loess. Adobe occurs on the fringe of deserts, notably in the Sahelian region of Africa, and in SW USA. The use of adobe in construction represents the major utilization of desert loess in a social context. More understanding of adobe is required, in particular with respect to the adobe reaction, the low order chemical reaction which provides modest cementitious properties, and can be likened to the pozzolanic reactions in hydrating cement systems. The location of loess and loess-like ground on the peripheries of deserts is aided by the observation of the nesting sites of bee-eater birds. These birds have a determined preference for loess ground to dig their nesting tunnels; the presence of nest tunnels suggests the occurrence of desert loess, in desert fringe regions. We seek amalgamation and contrast: ten main topics are considered: words and terms, particles, parna, geotechnical, adobe, people, birds, Africa, Central Asia, Mars. The aim is some large generalizations which will benefit all aspects of desert loess investigation.

PETROFYZIKÁLNÍ CHARAKTERISTIKA SPRAŠE A FOSILNÍ PŮDY V HLINÍKU U LITOVLE

Loess-paleosol sequences are an important source of terrestrial paleoclimatic proxy-data. Quaternary loess and loess loam cover the most of surface of the Upper Moravian Basin. Samples from loess-paleosol sequence in vicinity of Litovel town were studied using magnetic susceptibility, spectrophotometry and laser granulometry. Obtained petrophysical data were compared with detailed lithological description of section and geochemical characteristics determined by ED-XRF method. The results contribute to interpretation of paleoclimate in the Upper Moravian Basin during the last glacial.Section with total thickness of about 5 m is formed by loess in its upper part. This layer covers several soil horizons. It is most probably youngest loess deposit formed during the last glacial maximum. Petrophysical and geochemical data and comparison with nearby sites indicate relatively humid cold tundra conditions with bush-steppe vegetation during deposition of loess. Lithological features, position below youngest loess deposit and petrophysical and geochemical data allow interpretation of soil horizons as PK I. Low values of magnetic susceptibility indicate formation of soil in arctic interstadial conditions with higher humidity compared to interstadial average. Values of magnetic susceptibility of PK I are equal or even lower than in overlaying loess which doesn´t correspond with usual behaviour of magnetic susceptibility in loess-paleosol sequences in the Czech Republic. It could be explained by formation of soil horizons in cold interstadial climate (low production of oxi/hydroxide of Fe) supplemented by increased humidity and hence, intensive illimerization process (clay migration and Fe-minerals depletion).