Inverted stream channels in the western Qaidam Basin, northern Tibetan Plateau, and implications to martian inverted landforms

Abstract

A unique landform, inverted stream channel (ISC), has been broadly discovered on the surfaces of Earth and Mars. The ISCs have been continuously studied for over a century, and recent studies reveal that the ISCs can be formed through volcanic, fluvial, tectonic, and aeolian processes. In western Qaidam Basin (QB), 5 ISC concentrated fields that contain 16 ISC areas are identified, in which various ISC associated features, such as superposition relations and meanders, are extensively reported on the Martian surface as well. The dry, cold, air-thin, and radiational environment of QB makes the basin excellently analogous to the modern Martian climate. In this thesis, the remote sensing approach is applied for the analyses of ISC morphologies and identifications of ISC distributions. The field study is conducted in one of the ISC areas for sediment sample collections and analysis of ISC geometry and architecture. ISCs in western QB with sinuous appearances have the interior of the channel body is mainly composed of sand deposits that are capped by densely packed pebble-size gravels. The collected sand samples are used for the ISC age determination through the Optically Stimulated Luminesce (OSL) method. The geometric analyses of one of the individual ISCs, including the grain size distribution, channel slope, channel width, channel height, and topographic gradient, are used for the reconstruction of paleo-hydraulic conditions. The possible formation mechanism and successive evolution of ISCs are discussed based on our analyses, in which these processes reflect the paleoclimatic conditions of western QB. Such large-scale concentration of ISCs records the transition of paleoclimate from humid to arid. The further development of hyperarid climate let the wind erode the sandy bank and sculpt the ISCs on the ground. The OSL age of interior sediments from ISCs indicates this climatic transition possibly happened at Marine Isotope Stage (MIS) 6. The hydraulic condition reconstruction suggests the single ISC can sustain the water amount 10 times larger than the modern river in the nearby region. Therefore, our study results imply that the ISCs are incised during the episodic flood events, in which the dried channels are buried by sandy deposits with continuous aridification after MIS 6. The aeolian deflation continuously lowers the terrain and causes the excavation and inversion of ISCs. These formation and evolution processes of ISCs may provide reasonable interpretations for the similar geomorphologies of Martian inverted landforms that are widely reported, which also opens a window for the exploration of early Martian climate conditions.