Climatically forced moisture supply, sediment flux and pedogenesis in Miocene mudflat deposits of south‐east Kazakhstan, Central Asia. (19th September 2017)

• Record Type: Journal Article
• Authors: Voigt, Silke; Weber, Yuki; Frisch, Konstantin; Bartenstein, Alexander; Hellwig, Alexandra; Petschick, Rainer; Bahr, André; Pross, Jörg; Koutsodendris, Andreas; Voigt, Thomas; Verestek, Verena; Appel, Erwin
• Is Part Of: Depositional record. Volume 3:Number 2(2017)
• Page Start: 209
• Page End: 232
• Publication Date: 2017-09-19
• Subjects: Central Asia -- climate -- Miocene -- pedogenesis -- sediment flux -- terrestrial sedimentation; Sediments (Geology) -- Periodicals; Sedimentology -- Periodicals; Sedimentation and deposition -- Periodicals; 552.5
• DOI: 10.1002/dep2.34
• Languages: English
• ISSNs: 2055-4877

Abstract

Abstract: The continental settings of Central Asia witnessed increased desertification during the Cenozoic as a result of mountain uplift and the Paratethys retreat. The interaction of these tectonic‐scale processes with orbitally forced climate change and their influence on Asia's atmospheric moisture distribution are poorly constrained. A Miocene succession of continental mudflat deposits, exposed in the Aktau Mountains (Ili Basin, south‐east Kazakhstan), has great potential as a terrestrial palaeoclimate archive. About 90 m of the 1700 m thick succession comprise alluvial mudflat deposits and appear as cyclic alternation of coarse sheet floods, mudflat fines and semi‐arid hydromorphic soils. In this study, bulk‐sediment mineralogy and geochemistry, magnetic susceptibility, sediment colour and palynology are used to reconstruct environmental conditions by determining changes and forcing mechanisms in the intensity of sediment discharge, weathering and pedogenesis. The results presented here indicate four major periods of arid soil formation and one palustrine interval characterized by higher evaporation rates under highly alkaline/saline conditions. A positive correlation between weathering indices and the Mg/Al ratio suggest that these horizons correspond to maximum rates of evapotranspiration and aridity. The formation of mudflat fines is, instead, interpreted as representing higher detrital sediment production by more intense alluvial fan activity during times of higher precipitation. Time series analysis of weathering indices, colour and magnetic susceptibility data yields cycle‐to‐frequency ratios with the potential to represent Milankovitch cyclicity with short and long eccentricity as dominant periodicities. Periods of pronounced aridity, paced by long eccentricity forcing, reflect changes in moisture availability. On longer tectonic timescales, the persistent appearance of gypsum indicates a shift towards more arid conditions. This trend in climate is considered to result from the closure of the eastern gateway of the Mediterranean to the Indian Ocean that restricted circulation and enhanced salinity within the Eastern Paratethys. Abstract : The effects of Cenozoic orbitally forced climatic change on Central Asia's atmospheric moisture distribution are not well constrained so far. Here, we study a Miocene succession of continental mudflat deposits in SE Kazakhstan to reconstruct environmental conditions affecting the intensity of sediment discharge, weathering and pedogenesis by an integrated approach of bulk‐sediment mineralogy and geochemistry, magnetic susceptibility, sediment colour and palynology. We identified periods of pronounced aridity to be paced by long eccentricity reflecting changes in moisture availability. On tectonic time scales, a climatic shift towards more aridity was probably caused by restriction within the Eastern Paratethys.