湘西黔东下、中寒武统沉积环境

Dynamic Stratigraphy of Lower and Middle Collbrian in Western Hunan and Eastern Guizhou

本文论述了对湘西黔东地区早、中寒武世的碳酸盐岩和陆源碎屑沉积的分析研究结果,着重探讨了控制该区陆表海沉积层序的各种动力因素。在研究区内,4种垂向层序均具有向上变浅的旋回性。早寒武世晚期的藻丘缓斜坡与中寒武世的鲕粒陡斜坡上的沉积动力学特征为:滨岸正常波浪潮汐流,滨岸及内陆棚的风暴营力,垂直于古岸线的大规模地滑和重力流,沿古岸线及斜坡的等深流。沉积小旋回的成因系构造断块的脉动,而盆地边缘的海退序列则由板块相对扩张、海平面变动及碳酸盐岩自身成长所控制。

By using graphic analysis to study carbonate and terrigenous clastic sediments of the western Hunan and eastern Guizhou provinces, the different dynamic factors uneiital carbonate sequences in this area are studied especially. With the analysis, the ooidalpisolitic grainstone, oncolitic packstone and intraclastic gram and tidal dominated environments are discussed.Furthermore, the characten and gravity flow sediments are analyzed, and the sedimentary mechanics of st is idscussed. Particularly, the authors studied the hummocky cross-stratifie in tempestite sequence. Which was to be the product of unidirectional back-flow of gradient current- formed by storm interpays with storm wave action, this bed-form is a transitional type betwwen syn ripples with straight crest and the upper flat bed- form of gradient currents.Pale rent sis of Cambrian contour currents in studied area indicates the paleocurrent flown from NE to S and along the edge of the basin. Four ki difterent veruend es are recognized, which includes the shallowing-upward cycles, and minor' transgoressive regressive pulses. Lateral distribution of facies may indicates paleogeograp ter diferent periods: a gentle slope consists of algal mound during the early Cambrian and a steep slope consists of ooidal shoal in the middle Cambrian.The sedimentary dynamics of the mentioned slope is suggested: (1) wavy and tidal action that affected the shore belt; (2) storm events that influenced the shore and shelf environments; ( 3) sliding and gravity flow that developed across to the shoreline; (4) contour current that flowed along the slope and parallelled to the shoreline. Comparision of minor cycles suggests that the dynamic factors controlling these cycles may be derived from the block faulting. The regressive sequence of basinal edge was controlled by the .interaction of plate spreading, sealevel changing and the developing of carbonate itself.