Shoreline trajectory and stratal stacking patterns: Relation to sediment partitioning and types of deep-lacustrine deposits

Abstract

This study utilizes drilling data to investigate shoreline trajectory, associated stratal stacking patterns and their relationships to sediment partitioning within the Lower Triassic in the Mahu Sag, northwestern Junggar Basin. Accretionary transgression occurred with changing of shoreline trajectory, sediment partition and basin-margin morphology. Two main types of shoreline trajectory and their associated stratal stacking patterns were recognized: (1) slightly rising trajectory, which has low trajectory angle (0.065°–0.072°) and is associated with retrogradational to aggradational back-stepping stacking patterns with low slope relief, and (2) moderately rising trajectory, which has relatively higher trajectory angle (0.09°–0.27°) and is associated with aggradational to retrogradational stacking patterns with moderate slope relief. The rising shoreline trajectory is associated with a fan-delta system with facies belts that migrate landward and are fining-upward, which is characterized by thick plain and thin front architecture. In vertical, the ascending trajectory developed with upward decreasing of sediment grain-size, muddy matrix changed to sandy matrix and even changed to clast supported in conglomerates. In planar, shoreline trajectory angle variations exist associated with different delta-front processes and different prodelta/deep-lacustrine deposits. Shoreline trajectory angle variations generated by sediment partition represents the relations between aggradation and retrogradation which determines the basin-margin growth pattern and morphology. It also indicates the vertical succession of basin-margin deposits and the preservation potential of deposits generated in various depositional environments. The results of this study show that shoreline trajectory could be a good indicator for basin-margin process and reservoir interpretation.