Deep- water traction currents of internal - wave and internal - tide origin are well developed on modern seafloor. They can not only produce sedimentary structures of cm- size but also build large - scale sediment waves ofkm- size. Moreover, most of these sediment waves migrate upslope. In ancient stratigraphic record, small - scalesedimentation units of internal - wave and internal - tide origin have been recognized but large - scale sedimentwaves of internal - wave origin have not. Based on detailed studies, different kinds of internal - wave and internal-tide deposits have been recognized in the clastic rocks of the middle- upper Ordovician in the Central TarimBasin. Four basic sedimentary microfacies and five identical successions of internal - wave and internal - tide de-posits have been recognized and summarized. These microfacies are (1)bi - directional cross- laminated very fine-grained sandstone microfacies, (2)unidirectional cross - bedded and bi - directional cross - laminated medium - tofine-grained sandstone microfacies, (3)alternating sandstone and mudstone microfacies, and (4)oolitic limestoneand sandy oolitic limestone microfacies. The vertical successions include (1)symmetrical gradedsuccession consistingentirely of cross-laminated sandstone, (2)normal graded succession consisting of cross- laminated sandstone, (3)normal graded succession consisting of medium scale cross - bedding and bi - directional cross - laminations, (4)symmetrical graded- couplet succession, (5)mudstone- oolitic limestone- mudstone succession. More importantly,based on detailed studies of seismic profiles, the authors discovered large - scare sediment waves of upslope migra-tion developed in the continental slope facies of the middle - upper Ordovician. The characteristics of these sedi-ment waves are similar to those of the sediment waves well developed on modern seafloor. According to the theoryof internal wave, the origin of these sediment waves can be explained satisfactorily.%现代海底普遍发育由内波、内潮汐引起的深水牵引流，内波、内潮汐不仅可形成各种厘米级的深水牵引流沉积构造，还可建造千米级的大型沉积物波。这种大型沉积物波既可沿斜坡向下迁移，也可沿斜坡向上迁移。在古代地层记录中已发现各种厘米级的内波、内潮汐沉积单元，但尚未发现内波成因的大型沉积物波。塔中地区中上奥陶统碎屑岩段内发育内波及内潮汐形成的各种牵引流沉积构造单元。通过详细的岩心观察，识别出4种内波、内潮汐沉积微相类型及5种基本垂向沉积层序。此外，通过地震剖面分析，在研究区中上奥陶统陆坡相中识别出顺坡向上迁移的大型沉积物波，该沉积物波的特征与现代海底发育的沉积物波的特征类似，运用内波理论可对其成因进行合理的解释。
展开▼
