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Liquid water and ice are the dominant agents of erosion and sediment transport in most actively growing mountain belts. An exception is in the western Qaidam basin along the northeastern margin of the Tibetan plateau where wind and wind-blown sand have sculpted enormous yardang fields (linear, streamlined bedrock ridges and parallel troughs) in actively folding sedimentary strata. This project aims to quantify the history of wind erosion in the Qaidam basin and its implications for tectonics, paleoclimate, and the source of the Loess plateau. Collaborators funded by this project include Assistant Professor Richard Heermance at California State University, Northridge (stratigraphy and magnetostratigraphy), graduate student Alexander Rohrmann (cosmogenic isotopes), and undergraduate student Andrew McCallister (U-Pb zircon provenance studies). Observations and analytical data obtained during this project suggest that since the late Pliocene, wind episodically removed strata from the western Qaidam basin at high rates (>0.12-1.1 mm/yr) and may have enhanced tectonic folding, and that the Qaidam basin was a major source of dust to the Chinese Loess plateau.

Investigations of Plio-Pleistocene Qaidam basin fill show that lacustrine sedimentation was punctuated by periodic episodes of sub-aerial exposure and wind erosion. The latter is evidenced by the presence of salt paleosols/crusts, deflation lag deposits, wind-storm deposits, paleopans filled with lacustrine and/or eolian deposits, and even paleoyardangs separating meter-scale laucstrine parasequences. Magnetostratigraphic samples have been sampled and are in the process of being analyzed to precisely date the episodes of wind erosion, which we hypothesize occurred during glacial/stadial periods when central Asia was drier and the main axis of the polar jet stream was located ~10° closer to the equator (over the Qaidam Basin), as predicted by global climate models.

 Industry seismic-reflection profiles show that sediment accumulation was continuous across the entire Qaidam basin until ~2.8 Ma, when the appearances of growth strata indicate accelerated growth of folds within the western Qaidam basin. The absence of angular unconformities imaged in ~2.8 Ma and older Neogene strata indicate that the erosion of Qaidam basin folds has occurred since 2.8 Ma. We used geological cross sections to estimate how much strata has been removed from above Qaidam folds since 2.8 Ma (providing estimates of time-averaged erosion rates). Sedimentary deposits younger than 2.8 Ma in the western Qaidam basin are overwhelmingly evaporative lacustrine/playa, indicative of closed-basin conditions. Hence, removal of sediment from the western Qaidam basin must have occurred by wind. Our analysis yielded a basin-wide average erosion/removal rate of 0.29 mm/yr over the past 2.8 Ma. This rate overlaps with Quaternary erosion rates (locally, >0.3 mm/yr) that we quantified in the basin using cosmogenic nuclides. There are localized erosion hotspots above anticline crests where up to three kilometers of strata have been removed, corresponding to a time-averaged erosion rate of 1.1 mm/yr.

Our estimates of wind-erosion rates in the sandblasted portion of the Qaidam basin are comparable to rates of fluvial and glacial erosion in tectonically-active mountain ranges. At least locally above crests of actively growing anticlines, the erosion rates are comparable to those in the Himalaya and other orogens where it has been proposed that erosion has had a positive feedback relationship with rock deformation and rock uplift. We propose that the onset of severe wind erosion in the Qaidam basin may have enhanced fold growth. A supporting observation is the unlikely coincidental, coeval (at 2.8-2.5 Ma) acceleration of loess accumulation on the Loess Plateau, suggesting enhanced wind erosion in its source region(s) at this time, and initiation of rapid fold growth in the western Qaidam basin as indicated by growth strata. An analysis of Qaidam fold geometries and their relationship to the prevailing wind directions reconstructed from modern yardang orientations raises the additional possibility that wind erosion may have influenced fold geometry and kinematics. The regional shortening direction along the northeastern margin of the Tibetan plateau is NE-SW. Hence, we would expect the axial traces of Qaidam folds to trend NW-SE. However, in many places, axial traces trend more E-W than expected and many folds are crescent shaped in map view, with axial trace trends that vary from NW-SE to more E-W orientations. Many Qaidam anticlines are fault-propagation folds with steeper dipping forelimbs and shallower dipping backlimbs. For most Qaidam anticlines, the forelimbs are located on the northern sides of the axial traces, indicating that the anticlines are propagating northward to northeastward, roughly in the up-wind direction. We raise the possibility that northerly to northwesterly winds caused more erosion on the northern forelimbs, where winds were forced to move up and over the anticlines, relative to the backlimbs. This enhancement of erosion along the northern forelimbs might have facilitated northward fault propagation, which in turn would create a topographically more abrupt forelimb that would further enhance and localize wind erosion.

Despite being located down-wind of the wind-eroded Qaidam basin, it is widely argued that the bulk of the Loess plateau deposits in China was sourced from the Gobi and adjacent sand deserts. However, reconstructed wind patterns, the estimated volume of Qaidam basin material removed by wind, numerical models of dust transport, and U-Pb eolian zircon provenance studies (all conducted as part of this project) all support the hypothesis that the Qaidam basin was a major source of dust to the Loess plateau.

Collectively, our results transform current paradigms about the efficacy of wind as an erosion agent compared to liquid water and ice in some arid basin settings and its potential interaction with tectonics, and the history of paleoatmospheric circulation and dust production in Asia. This project was pivotal in allowing the principal investigator to pursue research avenues outside of his primary field of expertise in hard-rock structural geology and which span the fields of stratigraphy, geomorphology, tectonics, and paleoclimate. Without hesitation, it is stated that this project has been the most intellectually stimulating and scientifically exciting part of the principal investigator's career to date and that multiple new research directions for multiple people have been successfully established as a consequence of funding it.