GRAIN-SIZE DISTRIBUTION PATTERN OF THE DEPOSITIONAL SEQUENCE IN CENTRAL BADAIN JARAN DESERT AND ITS GENETIC INTERPRETATION

Grain size of the samples taken from the drilling hole WEDP02 in the central Badain Jaran Desert are analyzed with the high-resolution laser grain size instrument of Mastersize 2000. Normal or Weibull function is adopted to fit the measured grain-size data, and simultaneously to extract numerical grain-size components. Upon the comparison made with the field observation of sedimentary facies, grain size-frequency and proportion-frequency plots for all the components are used as evidence for genetic analysis. Results suggested that the sequence of the Hole WEDP02 is dominated by aeolian sand, mixed aeolian and lacustrine sediment, and mixed aeolian and alluvial sediments. In the aeolian deposits, such components as the pedogenic product, long-term suspended dust, short-term suspended dust, aeolian sand and coarse aeolian sand are changing around the modal size of 2,12,105,270μm,and the dust and desert sand ratio changing around 2:8. They all lie on the top right corner of the size-proportion plot; In the mixed lacustrine depositional system, however, the boundaries among the chemically suspended fine clay, suspended coarse clay and aeolian sand are located at 4,12,45,150-230μm respectively, and the lacustrine suspension components may reach 35% of the total proportion, thus they occur on the bottom of the size-proportion plot. In alluvial sediments, boundaries of are 2,12,80,150-200,300μm are visible. This case indicates that grain size components could be used as a efficient tool for genetic analysis.