Walled sedimentary basins of China


A. R. Carroll, Department of Geoscience, University of Wisconsin, 1215 West Dayton Street, Madison, WI 53706. E-mail: carroll@geology.wisc.edu


Central Asia contains numerous closed geomorphic basins that are surrounded by active mountain ranges, but exhibit little internal deformation. These areas commonly coincide with sedimentary basins that record a much older history of continuous internal drainage, evidenced by lacustrine and associated alluvial deposits that date as back far as the Late Permian. We propose the new descriptive term ‘walled basin’, in recognition of the unique physiography of basins that impound sediments within peripheral orogenic walls that are maintained over relatively long geologic time scales. Walled basins are surrounded by dominantly contractional orogenic uplifts, but are themselves relatively undeformed. They typically record multiple episodes of alluvial and lacustrine sedimentation, that are often correlated with evidence for recurrent deformation of basin-bounding uplifts. The distribution of walled basins in Asia appears to correspond to crustal heterogeneities inherited from the complex accretionary history of the continent, but actual mechanisms for maintaining stable basin interiors over periods as long as ∼250 my remain uncertain. Modern walled basins in Asia are restricted to arid or semiarid regions, due to the capacity of large rivers to defeat drainage barriers in more humid areas. Walled basins lie at lower elevations than Asia as whole, and they appear to impede rather than promote plateau growth.