Braided-meandering system evolution in the rock record: Implications for climate control on the Middle-Upper Jurassic in the southern Junggar Basin, north-west China

This paper presents the current body of knowledge regarding the evolution of a braided-meandering system in the southern Junggar Basin, north-west China, based on the preserved architecture evidences. The response to climate change was also discussed. Herein, 10 types of lithofacies are summarized, including information of their primary sedimentary structures, characteristic lithology, and geometry. This study focuses on recognizing the architectural elements within the channels (migrating channel: CHm, switching channel: CHs, transiting channel: CHt, and filling channel: CHf), the bar units (downstream accretion: DA, lateral accretion: LA, unit bar: UB, and compound bar: CB), and fine-grained clastic deposits (floodplain fines: FF and overbank fines: OF). Three representative sections of outcrops were selected, and detailed observation and analysis of these sections revealed 3 stages can be divided: the braided stage, in which the deposits show an evidence of CHm, DA elements which are the mainly architectural elements, multichannel with aggradational filling; The transformation between braided-meandering stage, during which the fluvial system consists of CHt and CHm elements with lateral accretion; and meandering stage which is characterized by dominance of CHm, LA elements, and the channels become isolated and meandering. Finally, this paper concludes with an interpretation of climate events as manifested by the fluvial archives of the colours of sedimentary rocks, special mineral, palaeontology, geochemistry spanning the Middle-Upper Jurassic (between 166.1 and 152.1 Ma).