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. The Valley of Lakes basin (Mongolia) contains a unique continentalsedimentary archive, suitable for constraining the influence of tectonicsand climate change on the aridification of Central Asia in the Cenozoic. Weidentify the sedimentary provenance, the (post)depositional environment andthe palaeo-climate based on sedimentological, petrographical, mineralogical,and (isotope) geochemical signatures recorded in authigenic and detritalsilicates as well as soil carbonates in a sedimentary succession spanningfrom ∼34 to 21 Ma. The depositional setting was characterized byan ephemeral braided river system draining prograding alluvial fans, withepisodes of lake, playa or open-steppe sedimentation. Metamorphics from thenorthern adjacent Neoarchean to late Proterozoic hinterlands provided acontinuous influx of silicate detritus to the basin, as indicated by K–Arages of detrital muscovite (∼798–728 Ma) and discriminationfunction analysis. The authigenic clay fraction is dominated byillite–smectite and “hairy” illite (K–Ar ages of ∼34–25 Ma),which formed during coupled petrogenesis and precipitation from hydrothermalfluids originating from major basalt flow events (∼32–29and ∼29–25 Ma). Changes in hydroclimate are recorded inδ18O and δ13C profiles of soil carbonates and insilicate mineral weathering patterns, indicating that comparatively humid tosemi-arid conditions prevailed in the late(st) Eocene, changing into aridconditions in the Oligocene and back to humid to semi-arid conditions in theearly Miocene. Aridification steps are indicated at ∼34–33, ∼31, ∼28 and ∼23 Maand coincide with some episodes of high-latitude ice-sheet expansioninferred from marine deep-sea sedimentary records. This suggests that long-termvariations in the ocean–atmosphere circulation patterns due to pCO2fall, reconfiguration of ocean gateways and ice-sheet expansion inAntarctica could have impacted the hydroclimate and weathering regime in thebasin. We conclude that the aridification in Central Asia was triggered byreduced moisture influx by westerly winds driven by Cenozoic climate forcingand the exhumation of the Tian Shan and Altai Mountains and modulated byglobal climate events.

climate of the past

Palaeo-environmental evolution of Central Asia during the Cenozoic: new insights from the continental sedimentary archive of the Valley of Lakes (Mongolia)