Junggar basin, northwest China: trapped Late Paleozoic ocean

The Junggar basin originated during the late Paleozoic as either a remnant lower to mid-Paleozoic ocean basin or a mid-Carboniferous back-arc (intra- or inter-arc) basin bounded by emergent volcanic arcs south of the Siberian Craton. The retreating Junggar Sea left behind a regressive sedimentary section comprising at least 3-4 km of marine volcaniclastics in the southern Junggar area. Sandstones deposited in the Junggar basin since the Devonian are exclusively volcaniclastic, demonstrating that Precambrian basement rocks have never been exposed in the basin, and supporting the hypothesis that the Junggar is underlain by oceanic crustal materials. The mid-Carboniferous Junggar Ocean may have been a remnant ocean basin of early to mid Paleozoic age, or alternatively may have been an extending intra- or inter-arc basin formed behind an emergent volcanic arc in the northern Turpan region. Subsequent strike-slip deformation and the general sparsity of geologic and geophysical data from the Junggar area make it difficult to distinguish between these models. Late Early Permian through Triassic sediments of the Junggar basin are exclusively non-marine, deposited in a flexurally subsiding foreland basin during initial uplift of the ancestral Tian Shan mountains. The sedimentary section deposited during the Late Permian-Early Triassic appears to be inconsistent with a proposed rifting episode during this period.