Reconstruction of Late Quaternary Environmental Changes in Large Endorheic Basins: Challenges and Problems

Abstract:

In paleoclimate and geodynamic studies large endorheic drainage basins generally provide long-term archives of hydro-climatological and tectonic changes including a transient topography. Sediment cascades from sources to sinks are playing a scale-depending role in the reconstruction of process dynamics by using sedimentary records.

We present a holistic study on the Hei He drainage basin at the northern margin of the Tibetan Plateau by combining multi-disciplinary and multi-site approaches. The drainage system is crossing margins of extreme climatic conditions from the glaciated and permafrost sources within the >5000m high Qilian Shan to the hyper-arid Ejina Basin as endorheic sink with a catchment size of ca. 180,000 km² and a endorheic basin area of approx. 28,000 km². Two 230 m long drill-cores at the depocenter of Ejina basin recover a sedimentation history of about 250,000 years and integrate at least two glacial-interglacial cycles of climate change and a considerable geodynamic within the second largest strike-slip system in the world.

Sedimentation rate/subsidence estimations with consideration of climate-induced hydrological changes affecting the wider study and sink area provided data on the mountain uplift/basin development and the effects of tectonically induced changes of the drainage system. Based on 15 paleohydrological records covering the last ca. 35,000 years corroborated by >75 ¹⁴C AMS data, we can demonstrate that water divides have been spatially variable with temporal opening of the endorheic system. Thus, small-scale changes in topography are able to explain extreme changes of sedimentation rates within long-term records in the depocenter.

The major fault systems in the drainage centers intensely modified the drainage system and catchment size resulting in extreme hydrological changes in the basin as recorded in the long-cores. A brief view into the Okavango system in Botswana indicates that the complexity of interrelated non-climatic processes of huge drainage basins crossing large fault systems and climate zones is not unique.