Petrologic feature of phosphatic peloid and nonpeloids of Lower Cambrian, Soltanieh Formation, Vali-Abad, Middle Elburz

ABSTRACT

The Lower Cambrian phosphate horizon with different thicknesses and with the combination of the different microfacies at the lower part of the Sultanieh Formation at the upper shale member has outcrop. On the basis of petrographic studies and electronic microscope SEM  with EDX data, phosphate cement is in two manner from formation environment point of view and the kind of  mineralization, 1) has algal origin and it has been formed in shallow part of costal areas in quiet water conditions. Later, this cement scattered as the result of environment agitation and it is transported and settled in the form of interaclast accompanied by other coastal sediments to the sea depths. 2)Globular cement which has Rod-like bacterial origin and it has been formed in see depths in  madstone and inside of diagenetic micro cavities. Bacterial activity might be involve decomposition of organic matter then released Co₂, P₂O₅ and H₂S  which resulted form of precipitation of apatite crystals as isopachous cement and globular structures in under the special conditions of Ph and Eh of the microenvironment. The sulphide combined with iron and forms the pyrite minerals in the same environment. Meanwhile contemporary with the pyrite and apatite mineral formation, the carbonate  and silica grain has been glauconitized, too