Abstract
Abstract. The Valley of Lakes basin (Mongolia) contains a unique continental sedimentary archive, suitable for constraining the influence of tectonics and climate change on the aridification of Central Asia in the Cenozoic. We identify the sedimentary provenance, the (post)depositional environment and the palaeo-climate based on sedimentological, petrographical, mineralogical, and (isotope) geochemical signatures recorded in authigenic and detrital silicates as well as soil carbonates in a sedimentary succession spanning from ∼34 to 21 Ma. The depositional setting was characterized by an ephemeral braided river system draining prograding alluvial fans, with episodes of lake, playa or open-steppe sedimentation. Metamorphics from the northern adjacent Neoarchean to late Proterozoic hinterlands provided a continuous influx of silicate detritus to the basin, as indicated by K–Ar ages of detrital muscovite (∼798–728 Ma) and discrimination function analysis. The authigenic clay fraction is dominated by illite–smectite and “hairy” illite (K–Ar ages of ∼34–25 Ma), which formed during coupled petrogenesis and precipitation from hydrothermal fluids originating from major basalt flow events (∼32–29 and ∼29–25 Ma). Changes in hydroclimate are recorded in δ18O and δ13C profiles of soil carbonates and in silicate mineral weathering patterns, indicating that comparatively humid to semi-arid conditions prevailed in the late(st) Eocene, changing into arid conditions in the Oligocene and back to humid to semi-arid conditions in the early Miocene. Aridification steps are indicated at ∼34–33, ∼31, ∼28 and ∼23 Ma and coincide with some episodes of high-latitude ice-sheet expansion inferred from marine deep-sea sedimentary records. This suggests that long-term variations in the ocean–atmosphere circulation patterns due to pCO2 fall, reconfiguration of ocean gateways and ice-sheet expansion in Antarctica could have impacted the hydroclimate and weathering regime in the basin. We conclude that the aridification in Central Asia was triggered by reduced moisture influx by westerly winds driven by Cenozoic climate forcing and the exhumation of the Tian Shan and Altai Mountains and modulated by global climate events.
Highlights
The Cenozoic era (66 Ma to the present day) saw several dramatic changes in the marine and continental ecosystems, major tectonic events and global climate forcing (Cerling, 1993; Houben et al, 2013; Norris et al, 2013; Cermeño et al, 2015; Mutz et al, 2018; Komar and Zeebe, 2021)
The acceleration of Cenozoic climate cooling started after the early Eocene climatic optimum (EECO; ∼ 52–50 Ma), with temperatures ∼ 10–12 ◦C warmer than the modern deep ocean, followed by the appearance and expansion of the Antarctic ice sheets after the Eocene–Oligocene transition (EOT; ∼ 34 Ma) and culminating in the extensive Northern Hemisphere glaciation of the Pleistocene (∼ 2.6– 0.01 Ma; Zachos et al, 2001; Lear et al, 2008; Mudelsee et al, 2014; Abdullayev et al, 2021)
We greatly extend the existing mineralogical and geochemical dataset previously reported in Richoz et al (2017) for the Eocene–Miocene sediments from the Valley of Lakes (Mongolia): K–Ar ages and polytype analysis of detrital and authigenic illitic phases coupled with discrimination function analysis and sedimentological–petrographical–geochemical inspection are used to constrain provenance, palaeo-environmental conditions and post-depositional alteration history of this sedimentary succession
Summary
The Cenozoic era (66 Ma to the present day) saw several dramatic changes in the marine and continental ecosystems (e.g. the evolution of large plankton feeders such as baleen whales, a shift towards cold-water high-nutrient plankton assemblages at high latitude and the expansion of terrestrial mammals), major tectonic events (e.g. opening of Southern Hemisphere oceanic gateways, shift to the four-layer structure of the modern ocean, collision of the African– Arabian–Eurasian plates, and uplift of the Alpine and Himalayan mountain belt) and global climate forcing (e.g. change from greenhouse to icehouse conditions) (Cerling, 1993; Houben et al, 2013; Norris et al, 2013; Cermeño et al, 2015; Mutz et al, 2018; Komar and Zeebe, 2021). The acceleration of Cenozoic climate cooling started after the early Eocene climatic optimum (EECO; ∼ 52–50 Ma), with temperatures ∼ 10–12 ◦C warmer than the modern deep ocean, followed by the appearance and expansion of the Antarctic ice sheets after the Eocene–Oligocene transition (EOT; ∼ 34 Ma) and culminating in the extensive Northern Hemisphere glaciation of the Pleistocene (∼ 2.6– 0.01 Ma; Zachos et al, 2001; Lear et al, 2008; Mudelsee et al, 2014; Abdullayev et al, 2021) This long-term transition in Earth‘s climate is well documented in marine sedimentary archives, but its impact on the evolution of continental ecosystems remains poorly constrained, mainly because continuous, well-preserved terrestrial records are scarce and the responses to climate change in these settings are highly complex, depending on factors such as latitude, proximity to coast and mountain ranges, position relative to climatic winds, and vegetation (e.g. Caves Rugenstein and Chamberlain, 2018; Baldermann et al, 2020). A correlation of the global marine record with the terrestrial record of Mongolia has barely been developed (Harzhauser et al, 2016, 2017; Richoz et al, 2017), which limits our understanding of the relative influences of climate change and regional tectonics on the evolution of hydroclimate and weathering conditions in Central Asia in the Cenozoic
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
