Sequence Stratigraphic and Quantitative Seismic Sedimentology Analysis of Lower Cretaceous in Chepaizi Area, Junggar Basin, China

Based on the analysis of seismic, drilling, paleontological data, and combined with the characteristic of sedimentary sequence, tectonic evolution and climate periodic change, the lower Cretaceous in Chepaizi area of Junggar... [ view full abstract ]

Based on the analysis of seismic, drilling, paleontological data, and combined with the characteristic of sedimentary sequence, tectonic evolution and climate periodic change, the lower Cretaceous in Chepaizi area of Junggar Basin could be divided into 4 3rd order sequences. A sequence stratigraphic model for depression basin without slope break was established according to the gentle slope tectonic setting in Chepaizi area. In this model, the third-order sequence consists of 2 system tracts, transgressive system tract (TST) and regressive system tract (RST). Coarse-grained fan delta front and fine-grained shore-shallow lacustrine was mainly developed in TST, and relatively coarse-grained beach-bar of shore-shallow lacustrine was developed in RST.
Seismic sedimentology is regarded as a very effective tool for mapping high-frequency sequence and depositional systems. In Cretaceous, Chepaizi area mainly deposited shore-shallow lacustrine beach-bar microfacies, which are characterized by thin single sand layer (usually 2~5 m), fast lateral pinchout and strong reservoir heterogeneity. In this study, by making use of the 90° phase shift technique, frequency spectrum decomposition and stratal slicing, the sliced cubes were processed to display the distribution of sedimentary microfacies and reflect the evolutionary history. The beach-bar sandbodies of the typical slices was interpreted subtly. They are NE-extended, usually 5~10km long and 2~3km wide. Meanwhile, two typical beach-bar sedimentary models were established, normal bedrock beach-bar and fan delta beach-bar.