Early Diagenetic Chert Nodules in Bhander Limestone, Maihar, Satna District, Madhya Pradesh, India

Abstract

Differential compaction of oolites in the limestones around and lack of compression of the same within most of the chert nodules in the upper part of the Bhander Limestone point to emplacement of silica at early stages of dewatering-compaction. As precipitated, silica was possibly a plastic material and its time of hardening varied within and between the nodules. The degree of deformation of the oolites varied according to the stage of hardening of the silica within the nodules at the time of compaction. Replacement of carbonate sediments took place due to addition of carbon dioxide derived from decomposition of organic matter, preferentially concentrated in the burrows formed by deposit feeders. Silica, on the other hand, was immobilized initially in the burrows by adsorption on organic matter. In all probability, silica was derived by post-mortem dissolution of siliceous organisms trapped in the sediment. Contemporaneous with silicification, dissolved carbonates released from areas enriched in organic matter were reprecipitated in zones lacking organic matter as calcito veinlets, that were subsequently deformed during compaction. Circumstantial evidences are, therefore, consistent with the hypothesis postulated by Siever for the origin of early diagenetic chert nodules in limestones.