Inverted relief landforms in the Kumtagh Desert of northwestern China: a mechanism to estimate wind erosion rates

Although commonly found in deserts, our knowledge about inverted relief landforms is very limited. The so‐called ‘Gravel Body’ in the northern Kumtagh Desert is an example of an inverted relief landform created by the exhumation of a former fluvial gravel channel. The common occurrence of these landforms indicates that fluvial processes played an important role in shaping the Kumtagh Desert in the past 151 ka. A physical model is presented to reconstruct the palaeohydrology of these fluvial channels in terms of several measurable parameters including terrain slope, boulder size, and channel width. Combining the calculated palaeoflood depth, the maximal depth of channel bed eroded by wind, and the current height of inverted channels with the age of the aeolian sediments covered by gravels, the local wind erosion rate is estimated to be 0.21–0.28 mm/year. It is shown that wind erosion occurring in the Kumtagh Desert is no more severe than in adjacent regions. Since the modern Martian environment is very similar to that of hyperarid deserts on Earth, and Mars was once subjected to fluvial processes, this study will be helpful for understanding the origin of analogous Martian surface landforms and their causative processes. Copyright © 2015 John Wiley & Sons, Ltd.

Palaeoenvironmental implications of geochemistry and radiolarians from Upper Devonian chert/shale sequences of the Truong Son fold belt, Laos

A new locality of Frasnian radiolarian chert and siliceous shale is reported in the Vilabouly area, within the Truong Son fold belt of central Laos, in the eastern part of the Indochina Terrane. Samples from this locality, together with previously described radiolarian–bearing siliceous shale from Ban Phonxai, 100 km further north, have been geochemically analysed. Most of the Ce anomalies from Vilabouly and Ban Phonxai exhibit negative normalized values suggesting deposition in an open–marine basin and in a transition zone between open–marine and continental margin environments, respectively. NASC and chondrite‐normalized REE and La/Ce plots and trace element contents support this interpretation. Normalized La/Yb values indicate removal of LREEs relative to HREEs from the water column, suggesting deposition far from terrigenous sources for the Vilabouly samples. The Eu/Eu* values are not pronounced which, with the high values of Al2O3/(Al2O3 + Fe2O3), indicate minimal hydrothermal influence. Both sections are characterized by a distinctive Frasnian radiolarian and tentaculitid assemblage. The new radiolarian fauna from Vilabouly includes 23 species including Ceratoikiscum sp. cf. C. bujugum, Archocyrtium sp., Astroentactinia cf. stellata, Helioentactinia aster, H. perjucunda, Spongentactinella corynacantha, S. veles, Spongentactinia concinna, S. exquisita, Stigmosphaerostylus profundisulcus, Trilonche davidi, T. echinata, T. elegans, T. hindea, T. palimbola, T. vetusta, Palaeoscenidium cladophorum and others. The tentaculitids, Homoctenus ultimus and Costulatostyliolina vesca, have been previously described from South China and from Ban Phonxai. The similarity of the radiolarian fauna to those from South China, northern Thailand and Western Australia suggests free interchange of species. Based on geochemistry, stratigraphic sequences and structural geology, the radiolarian chert/siliceous shales are interpreted as highstand deposits in pull‐apart basins. This was possibly caused by transtension along the NW–SE–trending strike–slip fault of the Thakhek–Danang Shear Zone during the Late Devonian. Copyright © 2015 John Wiley & Sons, Ltd.

Provenance of the Middle Permian Zhesi Formation in central Inner Mongolia, northern China: constraints from petrography, geochemistry and detrital zircon U–Pb geochronology

The exceptionally thick Middle Permian Zhesi Formation is considered key to understanding the late Palaeozoic tectonic setting of the North China–Mongolia segment of the Central Asian Orogenic Belt, yet its sedimentary environment and provenance remain ambiguous. An integrated approach incorporating detailed field observation and measurement, framework petrography, whole‐rock geochemistry and detrital zircon U–Pb geochronology is applied here to investigate this problem. The framework petrography and whole‐rock geochemical characteristics jointly suggest that the Zhesi Formation was derived primarily from felsic upper continental crust, with the source rocks undergoing intermediate weathering and short‐distance transportation. Furthermore, the source rocks were composed of granites/granitoids that occurred in a transitional recycled orogen. LA–ICP‐MS U–Pb detrital zircon data from sandstone samples show two main age groups of 480–410 and 290–265 Ma. Accordingly, we deduce that the dominant provenance of the Zhesi Formation was northerly early to mid‐Palaeozoic orogenic belt, late Palaeozoic granites/granitoids and volcanics, with a possible contribution from the Hunshandake Block. The subsiding depositional environment of this succession is in response to the Middle Permian extensional tectonic setting of the orogenic belt. Copyright © 2015 John Wiley & Sons, Ltd.