中国东部震旦纪和寒武纪磷块岩的结构成因类型及其沉积相和环境

磷块岩矿床的形成总是同特定的沉积相和沉积环境相联系的。从古地理分布看,它们多半产在该成矿时期的海侵前缘带、陆表海和深水盆地的过度部位或水下高地的周围地带。磷矿层多出现于海侵序列的底部或下部,但是含磷岩系本身则既可以是退积式的,也可以是进积式的。

TEXTURE-GENETIC TYPES, FACIES CHARACTERISTICS AND FORMATION ENVIRONMENT OF PHOSPHORITES OF SINIAN AND CAMBRIAN IN EASTERN CHINA

There are different principals and types of classification of phosphorites for different investigation purposes. The principal of the author’s classification is based upon the genetic textural characteristics of the phosphorites, because these characteristics suggest directly the origin and depositional environment of phosphorite.The phosphorites in Eastern Chinese, mostly Late Sinian and Early Cambrian, may be divided into seven texture-genetic types. They are granular (allothchemical), mic-ritic (orthochemical), biogenic, sandy, nodular, recrystallised and metasomatic, among which, the granular phosphorite may be subdivided into pelletic, oolitic, pisolitic, in-traclast.ic and bioclastic.There are different types of phosphorites formed in different subenvironments. Phosphorites of different, texture-genetic types recorded different subenvironments of formation.The sandy and intraclastic phosphorites are the important texture-genetic types in Northern China. They were deposited mostly within the beach zone of rocky coast. In the Yangzi Platform, the predominant texture-genetic types are the intraclastic, pelletic and micritic phosphorites. Sometimes, the oolitic and bioclastic phosphorites are of secondary importance. They occure in carbonate sequences of a kind of rather gentle inclined "silting" beach, which was one of inner shelf fades. The siliceous phosphorite occur predominantly in the far-coastal zone of the inner shelf. Types of the Upper Sinian phosphorites of Southwestern China are the intraclastic, columnar stromatolite and oolitic phosphorites. Their environments of deposition include coastal, near-shore shallow marine, shallow marine and carbonate platform. The micritic, grain-micritic and nodular phosphorites occur predominantly in basin.Variation of different texture-genetic types of phosphorites reflect the evolution of mineralizational environment in time and space. Therefore, it is possible that depositional environment of phosphorites could be reconstructed by studying the texture-genetic types, as well as their textural association and evolution. Eventually, it may also be as a bases for the construction of the depositional models of marine phosphorites.