Geochemistry and mineralogy of the Oligo-Miocene sediments of the Valley of Lakes, Mongolia

Abstract

The Valley of Lakes is approximately a 500-km elongate depression in Central Mongolia, where Eocene to Miocene continental sediments are long known for their outstanding fossil richness. The palaeontological record of this region is an exceptional witness for the evolution of mammalian communities during the Cenozoic global cooling and regional aridification. In order to precisely elucidate the climatic evolution of the region, we studied the mostly siliciclastic sediments with several levels of paleosols for their sedimentology, mineralogy, major and trace element composition and δ13C and δ18O composition. The obtained results show that temperate hydrothermal fluids induced a strong illitization of the fluvial and lacustrine sediments. This finding contradicts the current conceptual view that the fine fraction of the sediments is of aeolian origin. Moreover, the diagenetic growth of illite resulted in a strong overprinting of the sediments and, subsequently, largely disturbed the pristine mineralogical and geochemical composition of the sediments that could have carried any palaeo-climatic information. An exception is the δ13C (and δ18O) isotope values of authigenic carbonate found in calcrete horizons that still record the ambient climatic conditions prevailing during paleosol formation. Our novel δ13C and δ18O record suggests an early Oligocene aridification in Central Asia at ∼31 Ma, whereas the Oligocene glacial maximum shows no increase in aridification. A second, regional-scale aridification occurs at ~25 Ma and corresponds to a late Oligocene marked mammalian turnover in the Valley of Lakes sediments.

Climatically forced moisture supply, sediment flux and pedogenesis in Miocene mudflat deposits of south‐east Kazakhstan, Central Asia

“…C; Hellwig et al ., ). Illite formation by post‐depositional alteration, as observed for Oligocene sediments in south‐western Mongolia (Richoz et al ., ), is not considered a relevant process here. Illite percentages of mudflat sediments in the Bastau Formation are about 10% higher than those of the underlying Alakul Formation which underwent higher burial temperatures, but show a similar proximal‐distal relationship in the abundance of unweathered quartz and feldspar to illite typical for detrital transport (Fig.…”

“…A variety of proxy records suggests a temporally differentiated pattern for the onset of desertification in Central Asia, ranging from the Eocene/Oligocene transition in north-east Tibet and south-western Mongolia (Dupont-Nivet et al, 2007; to the mid-to-late Miocene north of Tibet (Dettman et al, 2003;Kent-Corson et al, 2009;, and the mid-Pliocene on the Chinese Loess Plateau (Wang, 2006). Mammal diversity changes in Oligocene-Miocene successions in Mongolia provide evidence for intermittent episodes of increased precipitation (Harzhauser et al, 2016) and the aeolian origin of the Valley of Lakes successions was questioned by results of clay mineralogy (Richoz et al, 2017). The relative intensities of the westerlies and monsoonal wind systems played an important role in transporting moisture into Asia's continental interior (Caves et al, 2015).…”

Removal of Barium, Cobalt, Strontium, and Zinc from Solution by Natural and Synthetic Allophane Adsorbents

“…Therefore, the application of synthetic allophanes as sorbents in wastewater treatment plants is probably not yet sustainable. However, the applicability of using alternating layers of natural and synthetic allophanes and other low-cost sorbents (e.g., montmorillonite, geopolymers, and calcium-silicate-hydrates) in filter systems for water clean-up may be considered for a better cost-effectiveness [56][57][58]. From the application site, it is important to ensure a good performance, a proper workability, and a high robustness against modifications in surface charge and electrochemical properties, which could reduce the effectiveness of an adsorbent.…”

Fracture dolomite as an archive of continental palaeo-environmental conditions

“…The reconstruction of palaeo-environmental conditions recorded in continental and marine carbonate archives is the key to the understanding of the Earth's climatic evolution over time, and for the prediction of the potential responses of terrestrial ecosystems to modern climate change 53,54 . At present, the reconstruction of continental depositional environments of the past and evidence for particularly rapid climate change in modern times are largely derived from the study of speleothems, lake deposits, travertine, fracture carbonates and soil carbonates, i.e., calcrete 25,26,36,55,56 . Our study demonstrates the potential of authigenic carbonates infilling young fractures in the low temperature and high-altitude alpine environment of Erzberg to be used as a sensitive palaeo-environmental archive.…”