Sedimentary Succession and Model of Gravel Beach-Bars in The Southeastern Qinghai Lake

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The modern is the key to the past. Based on the field investigation of the Qinghai Lake, the authors have carried out the elaborate dissection of profiles parallelly and vertically with the shoreline and the surface analysis of the forming beach-bars. The sedimentary successions of gravel beach-bars are summarized and the model of gravel beach-bars are established. The gravel beach-bars have a fixed sedimentary succession, the “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. In the actual gravel beach-bars, three intervals are often presented in a variety of combinations, such as “ABCABC”, “BCBCBC”, “ABABAB” and other combinations. The hydrodynamic conditions of gravel beach-bars can be divided into three zone, wave asymmetric zone, breaker zone and surfing zone. The three zones respectively correspond with the A interval, B interval, and C interval. These findings provide an important basis for the reconstruction of paleoenvironment and the identification and distribution prediction of beach-bars in the ancient continental lake basins.