Study of Sedimentary Succession and Its Origin of Gravel Beach Bar: A Case from the Modern Beach Bar in the Southeastern Qinghai Lake

Based on the field investigation into Qinghai Lake, the author summarized the sedimentary characteristics and successions of gravel beach bar and analyzed the origin of sedimentary successions by means of trenching technology. The lithology of the gravel beach bar in the southeastern part of the Qinghai Lake is mainly medium conglomerates, fine conglomerates and coarse sandstones. The sedimentary structures are mainly low-angle swash bedding, parallel bedding, massive bedding and normally graded bedding. Gravel beach bar display an “ABC” sequence. “A” interval, the bottom of the sedimentary succession, is composed of coarse sands and gravels, which are sub-rounded, poorly-sorted, massive, and gravels oriented floating in the coarse sands; “B” interval, the middle of the sedimentary succession, is composed of gravels, which are sub-round, well-sorted, and massive bedding; “C” interval, the top of the sedimentary succession, is composed of coarse sands, which are well-sorted and normally graded bedding. The hydrodynamic conditions formed by gravel beach bar can be divided into three zones, i.e. asymmetric wave zone(A interval), breaking wave zone (B interval )and surfing wave zone (C interval).