A NEW CONCEPT OF SEDIMENTARY FORMATIONS AND THE PRINCIPLES FOR ANALYSIS

According to a study of the sedimentology of China and in comparison with the plate-tectonic settings of the sedimentary basins in the world, a new concept concerning sedimentary formations（sequences）has been developed. The sedimentary formation is defined as a rock association accumulating attridutable to certain continuous （time rank＞10~7years） tectonical seting. Its characteristics may be determined by its mateal sourceri, depositional environments and energy equilibrium. The relation of the development of sedimentary formations to plate tectonics is also discussed. Based on the three criteria（material source,depositional environment and energy equilibrium）mentioned above, the sedimentary formations may be divided into 8 main types. The main criteria for recognition of sedimentary formations and their tectonic settings include the consanguineous association of trace elements, sedimentation rate, shape of the formation, sedimentary rhythm and characteristics of compensation of sediments. The basic characteristics of persistent formations are as follows: association of CQ+SQ+MQ+OQ, Q=90％, low matrix content, regular ME distribution and low sedimentation rate. Less persistent formations show the following characteristics: CF+SF+MF+OF association, Q=90-65％,high matrix content, gradual ME distribution, banding, high sedimentation rate. Impersistent formations may be recognized using the following criteria:CR+SR+MR+OR association, Q=65-15％,high matrix content, irregular ME distribution, indefinite shape and variable sedimentation rate.