Characteristics of Sedimentary Facies and Lithofacies of Modern Weihe River in Xi'an

Key words: 
• modern deposit /
• Weihe River /
• lithofacies /
• facies /
• characterisitc of grain size /
• sand orebody

Abstract: Taking modern deposit of Weihe River at Caotan, Xi'an, as an example, particle size, sedimentary facies, sedimentary sequences and depositional model were studied based on outcrops and trench observation, and test results of selected samples. The results indicate that modern Weihe River in Xi'an is a meandering river which composed by three sedimentary cycle, and sediments in the river include sandy and argillaceous sediments, and only a little of gravely sediments. There are 6 kinds of lithofacies identified in Caotan deposit of modern Weihe River, and they are coarse sandstone with some fine gravel (parallel bedding) lithofacies, medium to fine (trough cross bedding) sandstone lithofacies, medium to fine sandstone (parallel bedding) lithofacies, medium sandstone (massive bedding) lithofacies, medium sandstone with some gravel(cross bedding) lithofacies and mudstone (massive bedding) lithofacies. Three kinds of sedimentary microfacies developed well, including channel lag deposit, point bar and flood-plain microfacies, and three sedimentary sequences were composed by these sedimentary microfacies. Lower sedimentary sequence with large thickness of sandstone was composed mainly by coarse and medium sandstone. Middle sedimentary sequence is a whole meandering river sedimentary body, and is composed by channel lag deposit, point bar and flood-plain deposit. Upper sedimentary sequence is dominantly composed by point bar and flood-plain deposit. Grain size analysis show that diameter of particles in channel lag deposit is 0.2~1.2 mm, and 0.1~1.0 mm in point bar, and they are favorable sand orebody which used for building sand.