Braided-river Delta of the Lower Jurassic Sangonghe Formation in the Nileke Region, Xinjiang

Key words: 
• braide-river deita /
• Sangonghe Formation /
• Yining Basin /
• Xinjiang

Abstract: Braided-river deita that braided river systems prograde into an iniand iake is very abundant in the Lower Jurassic Sangonghe Formation in the Yining Basin, Xinjiang. Their characters are distinct and significantiy different from the other types of deitas. The braided-river deitas are deposited by river tractive current sediments, controiied by torrentiai fiood in generai, and are seasonai sediments. There three sedimentary subfacies from bottom to top：probraided-river deita subfacies, braided- river deita front subfacies and braided-river deita piain subfacies, in the braided-river deitas. Nine microfacies are recognised. The deposits of braided-river deitas are mainiy composed of pebbied sandstone and medium-coarse sandstone. The bars of the braided channei and subagueous distributary channei are the main bodies of deitas, and they take the form of ienticuiar bodies. A singie ienticuiar channei sand body has a thickness of 0. 5m ~ 3m. Many, finger-upward ienticuiar channei sand bodies piie verticaiiy up each other. Cross-stratifications are abundant in the braided-river deitas, but iaterai accretion cross-beddings resuiting from iaterai accretion of channei sand bodies are the most principai sedimentary structures and one of the most distinct character of braided-river deitas.