A fluvial‐aeolian system in response to aridification during the Late Mesozoic, Junggar Basin, Central Asia

• Published in: Basin research 2024-05, Vol.36 (3), p.n/a
• Main Authors: Guan, Xutong, Wu, Chaodong, Xu, Yan, Jolivet, Marc, Xiu, Jinlei, Lin, Cong
• Format: Article
• Language: English
• Subjects: Aerial photography; Age structure; Alluvial fans; Aridification; Braided rivers; Braiding; Cretaceous; Current meandering; Deposits; Earth Sciences; Environmental changes; Eolian deposits; Evolution; Fluvial deposits; fluvial‐aeolian interaction; Garnet; Geochronology; Geochronometry; Heavy minerals; Ilmenite; Jurassic; Jurassic/Cretaceous transition period; Lake shores; Lamination; Magnetite; Meandering; Mesozoic; Orogeny; Photogrammetry; River meanders; Rivers; Saltation; Sandstone; Scanning electron microscopy; Sciences of the Universe; Sediment; Sediment deposits; Sediments; Stratigraphy; Tectonics; Tianshan Mountains; Tourmaline; Unmanned aerial vehicles; unmanned aerial vehicle‐based photogrammetry; Zircon
• ISSN: 0950-091X; 1365-2117
• DOI: 10.1111/bre.12879

Aridification of Central Asia in the Late Mesozoic led to drastic environmental changes characterized by widespread aeolian deposits. We systematically investigated fluvial‐aeolian deposits in the Middle Jurassic Toutunhe Formation, Upper Jurassic Kalazha Formation, and Lower Cretaceous Tugulu Group in the Junggar Basin to the north of the Tianshan Orogenic Belt via unmanned aerial vehicle‐based photogrammetry, scanning electron microscope, grain‐size analysis, and detrital zircon geochronology. Paludal and deltaic environments transitioned to a fluvial‐aeolian environment from the late Middle Jurassic to the Late Jurassic. Fan delta and incisive braided river deposits accumulated in the earliest Cretaceous and evolved into a lacustrine environment with aeolian deposits in the lakeshore. Aeolian deposits are characterized by moderate‐ to well‐sorted and subangular to subround sandstones with large‐scale, high‐dip cross‐bedding, inversely graded lamination, dominant saltation grains, crescent‐shaped, and dish‐shaped impact structures. Aeolian deposits contain heavy minerals including more ilmenite, zircon, garnet, and, tourmaline and less magnetite and epidote than the fluvial deposits. The preserved aeolian sediments of the Kalazha Formation extend west–east for more than 100 km, suggesting a wide desert area during the latest Jurassic. The detrital zircon age patterns indicate that the provenance of the aeolian deposits was similar to that of coeval fluvial deposits. The cooccurrence of fluvial and aeolian deposits and the similar provenances but orthogonal flow directions indicate that the aeolian deposits were mainly sourced from the nearby fluvial material within the basin. The evolution of the fluvial‐aeolian system responded to a complete base‐level cycle controlled by the aridification and tectonics. Due to decreased sediment supply caused by aridification, the base level rose, leading to the change from braided rivers to meandering rivers, along with the deposition of aeolian sediments. Due to the tectonic reactivation in the Late Jurassic, the base level fell, causing the occurrence of alluvial fans and the expansion of the aeolian sediments. Previous studies revealed that the Tianshan in the Jurassic exhibited low relief. The fluvial‐aeolian system played an important role in maintaining the limited relief in southern Central Asia. The aeolian sediments were sourced from fluvial sediments with a short transport distance. Controlled by the arid cl