Sedimentary facies of the Paleogene Shahejie Formation in the Bonan depression, Shengli Oil Field

The alluvial-lacustrine deposits from the Paleogene Shahejie Formation in the Bonan depression, Shengli Oil Field consist of the meandering delta facies, braided delta facies, fan delta facies, subaqueous fan facies and lacustrine facies, including 14 subfacies and 35 microfacies. Among them the braided delta facies is best developed and distinctive from the other types. The braided delta facies comprises the braided delta front subfacies and prodelta subfacies. The braided delta front subfacies consists chiefly of the subaqueous distributary channel bars composed of gravel-bearing sandstones and medium-to coarse-grained sandstones. In the deltas outlined above, there occur the cross-beddings, especially the horizontally aggraded cross-beddings produced by the lateral migration of the channel bars.