Niektóre wyniki badań diagenezy i katagenezy osadów kambru syneklizy perybałtyckiej

Abstract

SOME RESULTS OF STUDIES ON DIAGENESIS AND KATAGENESIS OF CAMBRIAN DEPOSITS OF PERIBALTIC SYNECLIZE Summary Cambrian deposits of Peribaltic syneclize (north-eastern Poland) are represented by a series of siltstone-sandstone rocks with claystone and, occassionally, limestone intercalations. The petrographic studies have shown some differences in mineral composition, sorting and roundness of detrital material, making possible to distinguish four stages of sedimentation (Table I). From the point of view of lithostratigraphy it is most important to establish criteria for delineation of the Eocambrian/Cambrian baundary. This problem is intensely studied in several countries. The petrographic studies hitherto carried out on deposits of Peribaltic syneclize have shown that the first stage of sedimentation, related to Early Cambrian marine transgression, took place under the conditions of intense accumulation of detrital material. It resulted in origin of rocks of the arkose character, differing from the Eocambrian rocks in the lack of chlorites in matrix and lower degree of secondary alteration. Such features are traceable under the microscope. The studies have shown that the Cambrian sandstone rocks, despite of fairly uniform composition of detrital, material, are markedly differentiated in mineral composition of cementating materials originating at various stages of diagenetic and postdiagenetic alterations. It was found that the succession of origin of components of matrix was as follows: clay minerals, iron oxides, locally bituminous-coal matter - regenerational quartz - calcite, dolomite, clay minerals, gIauconite, locally siderite and pyrite - barite, anhydrite and some carbonates. Multiple changes proceeding in interstices of sandstones are important for defining collector properties of these rocks, primarily dependent on postsedimentational changes and almost not on conditions prevailing in the sedimentary environment.