Sedimentary characteristics of deep-marine gravity flows influenced by island–arc volcanism: A case study of Carboniferous sedimentary successions in the Junggar Basin, NW China

The Carboniferous sedimentary successions of the north-western and southern margins of the Junggar Basin in northwest China show a gradual vertical transition from deep- to shallow-marine depositional environments. Stratigraphically, these successions are composed of sedimentary and igneous lithologies (volcaniclastic), which record the closure and subduction of the remnants of the western Junggar and northern Tianshan oceanic basins that formed branches of the Paleo-Asian Ocean. In the current study, 16 facies and 7 facies associations related to sediment gravity flows were identified. These lithofacies associations collectively reflect five depositional elements, which include mass transport deposits, gravity flow channel deposits, lobe complex deposits, submarine volcanic ridge deposits, and submarine volcanic turbidite fans. Submarine and subaerial arc volcanism are shown to have controlled the characteristics of gravity flow sedimentation recorded in these successions. Island–arc volcanic material in the Junggar Basin is divided into three sources: erosion of the arc by fluvial systems, island–arc eruption materials, and submarine volcanism. Volcaniclastic deposits were transported into the deep-marine basin by submarine sediment gravity flows. These flows included turbidity currents, supercritical flows, gravel-rich debris flows, sandy debris flows, and muddy debris flows. Submarine vents generated lava flows that were deposited onto the abyssal plain and triggered subaqueous pyroclastic density flows. This study and its analysis of the characteristics and likely genesis of these gravity flow sediments improve the understanding of the dynamic relationship between volcanic activity and gravity flow sedimentation in near-arc basins. These findings provide a useful case-example of sediment gravity flow systems in island–arcs, which can be compared with and used as a relevant analog for other deposits in similar settings globally.