磷块岩的胶结作用

磷块岩胶结物有泥质、硅质、磷质和碳酸盐质4种,共形成19种胶结结构,其中尤以磷泥晶环边结构、等厚纤状环边结构、似重力式结构、磷质纤状环边叠加云质亮晶充填结构特征突出,具有指示沉积成岩环境的意义。4种类型的胶结物在剖面和平面上的演变与水体深度和沉积成岩环境有关,而胶结作用的地球化学特征,既是磷块岩的环境指示,又反映微生物的影响状况。

CEMENTATION PROCESSES OF PHOSPHORITES

Having studied the industrial phosphorite deposits in different parts of China,we find that there are four kinds of cements in the phosphorites,i.e..argillaceous,siliceous,phosphate and carbonate cements.They form 19 types of cementation texture:four argillaceous,eight phosphate,four dolomite and three siliceous. Among them,the micrite-phosphate rim texture,the equal-thickness fibrous phosphate texture, the gravity-b3ng texture and the texture of pore-filling dolomite within fibrous phosphate rims are very distinct and can be used as indicators of sedimentary and diagenetic environments.The four kinds of cements have regular spatial occurrence. From bottom to top of a profile or from the center to the margins of a basin,cements are usually changed from siliceous through argillaceous and phosphate to carbonate.The cementatiolt processes of phosphorites had been affected by micro-organisms.The δ¹⁸O and δ¹³C values in the cements are usually negative,and pH values range from weakalkaline to alkaline.The Eh values were negative during precipitation of the argillaceous,siliceous and micrite phosphate cements,but positive during the precipitation of fibrous phosphate and dolomite cements.The behaviors of trace elements in phosphorites show that the water medium was more dense and saline but less influenced by terrigenous materials during the cement precipitation than during the phosphate grain sedimentation.The change of cement components and cement textures in phosphorites are closely related to the sedimentary and diagenetic environments. So we can use the differences of the cement components and textures as atool to reconstruct their environments.