Study On Internal-wave And Internal-tide Of Xujiajuan Formation In Xiangshang Group Of Ningxia

Internal-wave and internal-tide deposit is a new kind of deep water sedimentation type discovered and researched in recent years. Combine with the relevent material and examples this article makes an comparative analysis through the analysis of Middle Ordovician Xujiajuan formation in Xiangshang group of Ningxia about its regional geological background, paleocurrent, Sedimentary Structure, Lithologic Features, and Deposition Mechanism, etc. The result shows that Xujiajuan formation has the feature of cross-bedded and two way cross-bedding structure and a special kind of “rhythm sand and mud interbedding”. Comprehensive analysis: the two way cross-bedding be regarded as the most reliable standard of identifying the internal-wave and internal-tide;the research area has internal-wave and internal-tide deposits; Xujiajuan formation in Xiangshang group may be the complex formation of gravity flow,deep-water traction current(internal-waves and internal-tide), and the situ deposits,meanwhile,the proposal is that classify the “rhythm sand and mud interbedding” as a kind of sedimentary sequence type of internal-wave and internal-tide.