Provenance of the pre-Quaternary aeolian dust deposits of East Asia

Sammanfattning: Atmospheric mineral dust is a key component in the climate system, but its effect on and response to climate changes are poorly understood, especially over long timescales. This thesis investigates the sources of late Paleogene and Neogene dust deposits that formed under warmer-than-present global climates in the northern Chinese Loess Plateau (CLP) region in mid-latitude East Asia. Provenance research on wind-blown (aeolian) dust is one of the few available methods to constrain past wind directions, dust sources and transport pathways, which is crucial for understanding regional paleoclimate and its changes during global climate transitions.Aeolian dust deposits from three sites are analysed here: the late Paleogene (35–27 Ma) Ulantatal dust sequence, the late Neogene (7–2.6 Ma) Baode Red Clay, and a c. 4 Ma sample from the Nihewan Red Clay. A joint single-grain analysis of detrital zircon (DZ) U-Pb geochronology and detrital rutile (DR) trace element analysis was applied to trace provenance. This thesis is the first use of DR geochemistry as a provenance indicator for CLP dust, and the thesis therefore summarizes the tectonic history of potential primary source regions and presents DR data from 14 potential secondary/sedimentary dust source regions, for comparison to dust deposits.The results highlight the importance of multimineral single-grain analysis, as some provenance signals were not evident from DZ data alone. Fundamentally, the results demonstrate the long-term stability of overall atmospheric circulation in Central-East Asia, with modern-type atmospheric components existing since the late Paleogene. Dust was mostly transported by Siberian High pressure system (SH) -induced northwesterly winds, and planetary mid-latitude circulation -driven westerly winds from primary source regions of the Central Asian Orogenic Belt and Northern Tibetan Plateau, respectively. The results also show provenance changes at the Eocene-Oligocene, Miocene-Pliocene, and Pliocene-Pleistocene boundaries, indicating a long-term link between the Central-East Asian dust cycle and global cooling events. This thesis further argues that overall, both the dust provenance, and possibly the formation of northern CLP region dust deposits since the latest Eocene in general, were controlled by the Northern Hemisphere glaciations via the SH and northwesterly winds. The results shed light on the long-term environmental history of Central-East Asia and demonstrate the link between the regional dust cycle and global cooling. The findings of this thesis provide important constraints to guide future modelling work on dust-climate interactions under warmer-than-present global climates in Central-East Asia, one of the most populated regions on Earth.