A Fossil Paleozoic Subduction-Dominated Trench-Arc-Basin System Revealed by Airborne Magnetic-Gravity Imaging in West Junggar, NW China

A Carboniferous trench-arc-basin system related to oceanic slab subduction has been thoroughly imaged by various geophysical probing approaches and proposed for the formation of West Junggar, Northwest China, located in the southwest of the Central Asian Orogenic Belt. However, debate on the origin of West Junggar still continues. Here, we present an integrated aeronautic magnetic–gravity observation to further identify the trench-arc-basin system and constrain the subduction mode. By deploying an integrated aerial magnetic–gravity survey consisting of 66,000 survey-line kilometers from August 3, 2015 to April 22, 2016, we determine the magnetic and gravitational anomaly across the study region by using geophysical potential-field processing. Our results reveal curial crust-scale variations in magnetic and gravitational structures beneath West Junggar and that a prominent Bouguer gravity high is located between the Darbut and Karamay–Urho faults, likely corresponding to a trapped oceanic slab. Notably, the Tacheng Basin is characterized by high-frequency magnetic signal and gravity highs, as well as the Carboniferous rifting–related sedimentary cover, which could be reasonably interpreted to be a back-arc basin. Integrated with these comprehensive geological and geophysical observations across West Junggar, the previous model of West Junggar trench-arc-basin system related to a fossil intra-oceanic subduction during the Late Paleozoic is further renewed.

Morphology and Nomenclature of Barsassia (Lycopsida) from the Middle Devonian of West Junggar, Xinjiang, China

Morphology and nomenclature are essential issues of botany, in which both extant and fossil plant taxa follow the same nomenclature code. Devonian (419.2–358.9 Ma) herbaceous lycopsid Barsassia, one of the earliest coal-forming plants in geological history, possesses a characteristic, easily recognized, step-like stem and has been thought to be an index fossil for dating and correlating the Middle Devonian strata, especially those in the paleoblocks of Siberia, Kazakhstan, Xinjiang, and North China. Here, we systematically study the Devonian lycopsid Barsassia in terms of its morphology and nomenclature, based on the new materials from the Middle Devonian Hujiersite Formation of West Junggar, Xinjiang, China, and the International Code of Nomenclature for algae, fungi, and plants (Shenzhen Code). Barsassia ornata is determined as the type species of the genus, and a neotype is designated for that name. Barsassia ornata consists of fan- or rectangular-shaped leaves with awl-shaped or finger-like distal tips. Its leaves are pseudo-whorls and imbricately arranged on the stem surface forming distinct step-like structure.