Paleogene to Neogene aeolian dust provenance in the Chinese Loess Plateau region

Understanding atmospheric circulation in the geologic past under warm climates is crucial for projection of future climate scenarios. One of the few ways to unravel past atmospheric circulation is to study aeolian mineral dust deposits that link the geosphere to the atmosphere. Atmospheric mineral dust both affects and is affected by climate changes, but its role in the Earth system is poorly constrained. The aeolian dust deposits on the Chinese Loess Plateau (CLP) and adjacent regions provide an exceptionally vast amount of material to study Central-East Asian atmosphere and environments since the Eocene. Moreover, provenance research on these deposits is the key to reconstruct past atmospheric circulation and to understand the evolution of regional aridity and dustiness, which are closely linked with global climate.

In this study, we investigate the Paleogene to Neogene dust deposits in and near the CLP at latitude ~40°N. We present multiproxy provenance data from the Paleogene Ulantatal dust sequence in Inner Mongolia, China, approx. 400 km northwest of the central CLP, and from the Neogene Baode Red Clay in the northern CLP. As the first comprehensive study using detrital rutile trace element geochemistry combined with detrital zircon U-Pb ages in the CLP region, our data reveal both longer- and shorter-term pre-Quaternary provenance trends in the area. The Ulantatal dust sequence shows constant dust provenance during c. 34–29 Ma, including through the Eocene-Oligocene global climate transition. Strikingly, this provenance signal, which suggests dominant northerly to northwesterly dust transport, is very similar to that of the Neogene Baode Red Clay, reinforcing suggestions that a pre-Quaternary East Asian winter monsoon (EAWM) regime existed in the region for at least 30+ million years despite changes in paleogeography. However, the late Miocene (c. 8–7 Ma) extension of dust deposition to the eastern CLP was coupled with an increasing dominance of Northern Tibetan Plateau (NTP) provenance signal in Baode, implying an at least 1–2 Myr period of enhanced dust production in the NTP, a dominance of westerly winds over the EAWM, and/or contribution of silt-sized material by a proto-Yellow River. After, in the latest Miocene and in the Pliocene the EAWM again dominated the dust transport to the northern CLP. While the long-term temporal variability of dust provenance is small through Paleo-Neogene in the northern CLP latitudes, spatial variability of Paleogene dust in the CLP region is similar to that of the Neogene Red Clay and Quaternary loess in the area: the Ulantatal dust provenance differs from the Paleogene southwestern CLP dust provenance. This spatial variability confirms previous conclusions that local sources define most of the dust provenance signals in the silt fraction, complicating the interpretation of possible global climate forcing in the Central-East Asian dust cycle, and reinforcing the need for multiproxy provenance analysis of loess dust.