中国南方震旦纪地层问题

关于南方震旦系的下界,主要有两种意见:(1)以澄江组或莲沱群的底板为下界;(2)往下移到包括昆阳群、板溪群及其相当岩系。主张后一意见主要根据葛利普“寒武系之下的不变质或只轻变质的沉积岩系属震旦系”的概念,及“滹沱页岩群”和“东峪灰岩”等实例,认为昆阳群和板溪群等变质并不很深,而在岩性上有其相似之点,故可以归入震旦系。经过多年来的研讨,大多数趋向于将昆阳群及其相当岩系归属于前震旦系。但问题并不就此解决。

THE BOUNDARY, CLASSIFICATION, AND PALAEOGEOGRAPHY OF THE SINIAN SYSTEM IN SOUTH CHINA

The lower boundary of the Sinian is determined at the base of the first mantle deposits, the Chenkiang sandstone and its equivalents, which are defined by a profound unconformity (Tsinning disturbance) upon the Yangtze platform. The upper or Sinian-Cambrian boundary is drawn at the base of the supra Hyolithes-bearing phosphate formation, where is noted a disconformity. A twofold division for the system into series, Upper and Lower, is determined by the evidence of a weaker but distinct unconformity (Chenkiang disturbance). Subdivisions for both series into formations are denoted by local denominations. On the Yangtze platform, the Sinian represents a completed cycle of sedimentation. Lower Sinian series is mainly composed of red piedmont mollase and lake-alluvial detritus occasionally intermixed with volcanic debris. The tillite in the basal part of the Upper series, occurred by accompanying the Chenkiang disturbance may be considered as a "basal conglomerate", and as a key for the stratigraphic identification. The marine beds lying concordantly upon the tillite are characterized by various types of constituent, though chemical deposits and ore layers predominent from place to place. In a later period, marine silico-carbonate rocks characterized by stromatolites locally are extensively distributed. Chenkiang disturbance did not end the development of geo-synclines in South China. There existed a synclinal sea trough between Proto-Kiangnania and Cathaysia, and an embayment belt along the foreside of Proto-Kiangnania to accumulate more than two thousand meters of flysch and lagoonal deposits. The tendency of lithofacies changes is shown on a palaeogeographic-lithofacies map. The highest value of clastic ratio is found along the foreside of Proto-Kiangnania, and is generally decreasing toward NW upon the Yangtze platform.