Geomorphic constraints on surface uplift, exhumation, and plateau growth in the Red River region, Yunnan Province, China

Abstract

Field observations, digital elevation model (DEM) data, and longitudinal profile analysis reveal a perched low- relief upland landscape in the Red River region, Yunnan Province, China, which correlates to an uplifted, regional low- relief landscape preserved over the eastern margin of the Tibetan Plateau. As with other major rivers of the plateau margin, the Red River has deeply incised the low-relief upland landscape, which we interpret to be the remnants of a pre- uplift or relict landscape. We examine longitudinal river profiles for 97 tributaries of the Red River. Most profiles consist of three segments separated by sharp knickpoints: an upper, low-gradient channel segment, a steeper middle channel segment, and a very steep lower channel segment. Upper channel segments correspond to the relict landscape and have not yet experienced river incision. Steeper middle and lower segments indicate onset of rapid, two-phase river incision, on the basis of which changes in external forcings, such as climate or uplift, can be inferred. In terms of two end-member scenarios, two-phase incision could be the result of pulsed plateau growth, in which relatively slow uplift during the first phase is followed by rapid uplift during the second phase, or it could reflect adjustments of the main channel to changing climate conditions against the backdrop of steady plateau growth. Reconstruction of the paleo-Red River indicates 1400 m river incision, 1400-1500 m surface uplift, and a maximum of 750 m vertical displacement across the northern Red River fault, elevating the northern Ailao Shan range above the surrounding relict landscape. On the basis of stratigraphic constraints, incision along the Red River likely began in Pliocene time