Jurassic-Lower Cretaceous Sequence Stratigraphy And Allogenic Controls In Proximal Terrestrial Environments (Southern Junggar Basin, Nw China)

The terrestrial sequence stratigraphy in proximal terrestrial environments is different from its counterpart in distal terrestrial and marine environments. The Southern Junggar Basin in NW China has preserved well-exposed proximal terrestrial outcrops and its Jurassic-Cretaceous sequence boundary remains contentious. The goal of this paper is to (a) establish a model of allogenic-controlling mechanisms of a proximal terrestrial sequence, (b) investigate the Jurassic-Cretaceous sequence boundary, (c) the Jurassic climate, and (d) tectonic movements in Central Asia. The sequence stratigraphic framework was established assisted by the determination of the accommodation space/sediment supply (A/S) ratio, including two second-order sequences (SS) and six third-order sequences (SQ) in the Jurassic, as well as a second-order sequence in the Cretaceous. SS1 was mainly controlled by a warm and humid climate and lake level fluctuations in a weak extensional tectonic setting; SS2 was mainly controlled by an arid climate and compressional tectonic movements; SS3 was mainly controlled by a semi-humid climate and lake transgression in a stable tectonic setting. Additionally, the Jurassic-Cretaceous sequence boundary was distinguished within the Kalazha Formation based on its sedimentary characteristics, sedimentary evolution, and different allogenic controls. It is concluded that the proximal terrestrial sequences exhibit rapid sedimentary facies change, thick coarse-grained sediments, and multiple provenances. Climate, tectonic movements, and lake level fluctuation dominate in different stages of basin evolution. Moreover, the sediment supply is more emphasized, and the accommodation space/sediment supply ratio, which corresponds to different channel geometry types, plays a critical role in identifying system tracts and sequence stratigraphic surfaces.