Modern sedimentation in the wave-dominated delta beach bar sedimentary system of the Fenghe River in Jiaonan, Qingdao

Abstract

Detailed analysis of a typical wave-dominated delta beach bar sedimentary system of the Fenghe River, in Qingdao, China, concentrated on identifying the sedimentological characteristics of wave-dominated delta beach bar sedimentary system. The aim of the study was to establish a sedimentological facies model for similar deposits. Using well-established sedimentological criteria for recognizing the characteristic of wave-dominated delta beach bar. This modern sedimentary system mainly hosts front subfacies, as well as sedimentary microfacies like underwater snake-like channel, mouth bar, distal bar, and sheet sand. From the river entrance to the mouth bar, more than 80% of the area is occupied by sheet sand, which is distributed widely across a flat terrain. The sheet sand is dominated by wave-built sedimentary structures, plus a few current-formed sedimentary structures. The sheet sand can be divided into an underwater shoal parallel to the coastline and a stable crescent-shaped above-water bar. The underwater shoal is a long ellipse in the plan and an asymmetric shape that is gentle seawards and steep landwards in the vertical section. The sedimentary structures are dominated by wave-formed ripple marks and cross bedding, overlaid with swash bedding. The above-water bar is composed of two bars formed at different stages. The sedimentary structures are dominated by swash bedding, low-angle wedge bedding, and wind-formed sedimentary structure. Both underwater shoal and the above-water bar are resulted from the transformation and redistribution of the sediments on the delta front sheet sand by waves. The two parts reflect a sedimentary association of genetic significance in the sedimentary environment of wave-dominated delta front.