Implications of Plio-Quaternary Climate change on deposition and erosion of the Qaidam Basin, NE Tibet-Qinghai Plateau, China

Recent studies from central Asia hypothesize that a change to a cooler, drier climate between 2-3 Ma caused increased erosion rates due to glaciation within the mountains, forced rock-uplift due to the isostatic response to increased erosion, caused an influx of coarse-grained strata into depositional systems, and correlate with the initiation of deposition in the Chinese Loess Plateau. Direct stratigraphic evidence for such a climate shift at 2-3 Ma, however, is complicated or obscured by concurrent tectonic processes within these active orogens.  Thus differentiating between climatic and tectonic control on sediment deposition can be difficult or impossible.  To understand the affect of climate shift on sedimentation, my colleagues and I are studying the Plio-Pleistocene lacustrine sediments within the Qaidam basin, an internally drained basin near the northeast corner of the Tibet-Qinghai plateau.  Lacustrine sediments preserve a pristine record of deposition over > 5 million years.  We combine magnetostratigraphy, oxygen isotope analysis, detailed mapping of sedimentary facies, and interpretation of sedimentary structures to infer a pronounced change in climate at 2-3 Ma (work in progress).  This climate change caused the onset of rapid lake-level fluctuation and the initiation of regional wind-erosion of exhumed lake sediments.  Wind erosion within early Pleistocene lacustrine sediments has produced remarkable sedimentary structures called paleoyardangs (see figure below), which provide direct evidence for a shift to aeolian erosion near the Pliocene-Pleistocene boundary.  Moreover, this work demonstrates a probable source for sediment within the Loess Plateau, and may provide evidence for feedbacks between erosion and deformation in central Asia (Kapp et al., 2011 in GSA today; Heermance et al., 2013, GSA Bulletin).

A) Google Earth image of active yardang field in the northern Qaidam Basin.  Outlined areas labeled X, Y, and Z are the locations of paleoyardangs observed within the lacustrine strata.  Strike and dip of bedding is shown in degrees.  B,C) Photograph and geologic interpretation of paleoyardang X, view to north.  D)  Schematic model of paleoyardang formation.