Oligocene moisture variations as evidenced by an aeolian dust sequence in Inner Mongolia, China

Abstract

The aridification of Central Asia since the Eocene has widespread evidence, but climate-controlled environmental reorganizations during the Oligocene remain ambiguous. We employed environmental magnetic, mineralogical and geochemical methods on a latest Eocene to late Oligocene terrestrial sequence in Inner Mongolia, China, to examine how global climatic trends and regional factors influenced the evolution of moisture and weathering in the region. Highlighting the climatic influence, our weathering and rainfall proxy data document the drawdown of atmospheric CO2 and global cooling during the early Oligocene semi-arid phase, which culminated in the Early Oligocene Aridification Event at 31 Ma. Moreover, for the first time in the terrestrial eastern Central Asian setting, we provide geochemical and geophysical evidence for a second major Oligocene aridification event nearly synchronous to the mid-Oligocene Glacial Maximum at around 28 Ma. These aridification events were interrupted by periods of increased rainfall and weathering and can be associated with the terminations of glacial events seen in marine oxygen isotope records.

Equatorial Pacific dust fertilization and source weathering influences on Eocene to Miocene global CO2 decline

“…Our ODED CIA data have the expected characteristics of eolian deposition from the Asian interior, similar to coeval Inner Mongolian dust deposits (Supplementary Fig. 5) 49 . These characteristics include (a) a nearly parallel distribution along the CN-Al (CaO*+Na 2 O-Al 2 O 3 ) trend, which suggests weak K-metasomatism (K 2 O) and negligible diagenetic influences 43,44 , and (b) the same value range as Mongolian deposits across the EOT, which suggests an absence of obvious sorting influence.…”

Rodent faunas, their paleogeographic pattern, and responses to climate changes from the early Eocene to the early Oligocene in Asia

“…Ulantatal in Nei Mongol is another important site. Recently, Wasiljeff et al (2020) derived a chronostratigraphic framework for the Ulantatal sequence, using paleomagnetic reversal stratigraphy and biostratigraphic correlation, and the time spanned by the strata was 35 to 27 Ma (from the latest Eocene to late Oligocene). The rodents in the lower part of the Kekeamu section in Ulantatal were representative of the latest Eocene (Wasiljeff and Zhang, 2022).…”

“…Based on earlier research in the area, the Ulantatal sequence was considered to be constrained to the Oligocene (Wang, 1997b;Gomes Rodrigues et al, 2014). Recently, Wasiljeff et al (2020) redefined the stratigraphy and suggested that the Ulantatal Formation spans from the latest Eocene to the late Oligocene. Here, the Hsandagolian rodent assemblage in the Ulantatal area has been revised based on the latest work.…”

Modern‐Type Eolian Regime and Global Cooling‐Modulated Dust Provenance in the Late Paleogene of Central‐East Asia

“…The Ulantatal dust sequence covers the Eocene‐Oligocene Transition (EOT; c. 34 Ma), which marks the dramatic global shift from warmhouse to coolhouse state as permanent ice sheets appeared on Antarctica (e.g., Coxall et al., 2005; Westerhold et al., 2020) and may have stabilized in eastern Greenland (Tripati & Darby, 2018). While there are sites (Xining, Lanzhou, and Weihe Basins) in Central‐East Asia that record the EOT as an episode of significant drying (Abels et al., 2011; Ao et al., 2020; Dupont‐Nivet et al., 2007; Y. Wang et al., 2023), the climate in Ulantatal remained remarkably stable through the transition (Wasiljeff et al., 2022). Rather, major aridification events in Ulantatal are recorded in precipitation proxies after the EOT, at c. 31 and 28 Ma, roughly corresponding to the Early Oligocene Aridification Event (EOAE) and the Mid‐Oligocene Reorganization of fauna in Central Asia (Harzhauser et al., 2016), respectively (Wasiljeff et al., 2022).…”