Quantitative analysis of hydrodynamic conditions and sand body distribution dimensions of the braided river delta in Sangonghe Formation and Xishanyao Formation on the south margin of Junggar Basin

Abstract：Deltas, controlled by different dynamical conditions, are characterized by different plane shapes, distribution frequencies and dimensions of sand bodies. In order to quantitatively characterize the major dynamical conditions of lacustrine deltas, the authors divided the lacustrine deltas into four types on the basis of relative strength of hydrodynamic force, i.e., wave dominated, fluvialin fluenced-wave dominated, wave influenced-fluvial dominated and fluvial-dominated delta respectively. According to the quantitative analysis of measured outcrop columnar section, Sangonghe Formation was assigned to fluvial influenced-wave dominated braided river delta front, while Xishanyao Formation was considered to be of wave influenced-fluvial dominated braided river delta front. Three types of sand bodies were mainly developed in these two kinds of delta front, which are underwater distributary channel, river mouth bar and sheet sand. However, fluvial influenced-wave dominated braided river delta front was dominated by sheet sand, where the distribution frequency was up to 57%; wave influenced-fluvial dominated braided river delta front was dominated by underwater distributary channel and river mouth bar, where the distribution frequency was 42% and 33% respectively. The width/thickness ratio of the underwater distributary channel and river mouth bar in fluvial influenced-wave dominated braided river delta front was obviously larger than that in wave influenced-fluvial dominated braided river delta front. Because river mouth bar sand body is a residual genetic unit, the quantitative relation of its width/thickness ratio remains unclear.