Abstract:

The lacus sediments in Sebei Formation of Quaternary in Tainan Area, Qaidam Basin is developed along one of the growing lowuplifting dome in the center of the depression basin. The sediments are weakly cemented as siltstone and mudstone. Data from core that was cored under sealing highpressure nitrogen environment were adopted in this study. It is proved that 7 types of lithofacies and 5 types of lithofacies group could be classified in the Sebei Formation of Quaternary in Tainan Area. Accordingly, 3 types of microfacies (called energy units sometimes) could be acquired, which are sandbar, matstone and matmud. These 3 types of microfacies distributed orderly. Sandbars concentrated on the higher position of the dome and close to the low water surface of lacustrine. Matstones concentrated on the flank of the dome and under the low water surface of the lacustrine. Sandbars set among matstones often. Matmud concentrated in the trough bend and could extend to the entire area when the lake surface moved upward relatively. The physical property of sandbars is better than that of matstones, and the heterogeneity of matstones are better than that of sandbars. Matmud acted not only as the biogenesisgas generating rock but also as the infiltrating barrier wall of the natural gas.

Key words: Key words: Qaidam; Quaternary; fine sediment; lithofacies; microfacies; reservoir