Evolution of Early Cretaceous Multi-provenance deposition system in the northwestern margin of Kuqa Depression: Evidence from stratigraphic lithology proportions, mineral composition, and bedding dip direction

Provenance analysis is the foundation of basin analysis, and also an important means to restore the tectonic background of the sedimentary source area, estimate transport paths and distances of sediment, reconstruct paleocurrent systems, and reproduce the evolution history of sedimentary basins.The Bozi-Dabei area is located in the northwestern margin of Kuqa Depression in the Tarim Basin, where Bashijiqike Formation and Baxigai Formation of the Lower Cretaceous are held by multiple uplifts, which leads to the possibility of multiple provenances. Thus, detailed study of the provenance characteristics is needed to ascertain the the supply range and duration time of the indefinite provenances.

We identify the sediment provenance combining proportion of stratum lithology, rock and mineral compositions, and heavy mineral combination characteristic. And the paleocurrent direction is interpreted by the bedding dip direction obtained from imaging logging.

In the study area, there is an overall decreasing trend of the ratio between sandstone and stratum thickness from north to south, indicating that the South Tianshan on the north is the main provenance for this area, while the anomalous high-value zone in the southwest suggesting the possibility of regional provenance. According to the petrologic and mineralogical data of sandstone composition, detritus component, and heavy minerals, there is a certain regular variation from the northwest and northeast of the study area to the central location, such as the increasing proportion of quartz, metamorphic debris, and stable heavy minerals like garnet. Meanwhile, consistent heavy minerals combination with those in South Tianshan indicates that sediments originated from this provenance and were supplied to the study area along two paleocurrent systems.Consistent with the proportion of stratum lithology, the rock and mineral composition in the southwest, high magmatic grains and zircon for example, differs significantly from most parts of the study area. Combination characteristic of heavy mineral shows difference compared to those from South Tianshan provenance but matching those from Wensu Uplift, suggesting a local sediment supply from Wensu Uplift on the southwest. Paleocurrent data indicate three paleocurrent directions: NNW-SSE direction in northeast; NNE-SSW direction in northwest; SW-NE direction in southwest - all consistent with three paleocurrent systems indicated by rock and mineral compositions.

The results show that sediments originating from both South Tianshan and Wensu Uplift have been deposited into DFS during sedimentary period.The proportion of stratum lithology, rock and mineral composition, as well as bedding occurrence indicate that during Baxigai Formation deposition period, Wensu Uplift had a larger influence range which gradually diminished during Bashijiqike Formation deposition period - possibly implying a further tectonic uplift of Tianshan due to Himalayan movement.