Diagenesis of Sandstones in a Part of the Tichna Structure of Tripura Fold Belt, India
Aim: The aim of the present research work is to study the petrography and diagenesis of the sandstones in a part of the Surma Group of the Tichna field located in the western part of the Tripura Fold Belt.
Methodology: The standard petrographic microscope and Scanning Electron Microscope (SEM) were used for studying the rock thin sections and in identifying the various diagenetic imprints in the sandstones.
Result: The study reveals that the samples are fine to medium grained, sub-angular to sub-rounded, mostly moderately sorted to well sorted and belong to sublithic-arenite, lithic arenite to feldspathic-arenite varieties. Quartz is the dominant mineral in all the samples followed by rock fragments and feldspar. Authigenic clay minerals observed are Illite, Chlorite, Kaolinite and mixed clay types. Important diagenetic changes include compaction, cementation and dissolution of detrital grains.
Discussion: Compaction of the framework grains lead to the development of different type of grain contacts, bending of flexible mica flakes and fracturing of detrital grains. Quartz cementation is observed by the development of euhedral secondary overgrowths of quartz. Authigenic clay minerals either form coating over the detrital grains or occupies the intergranular pores. At restricted depth intervals, calcite cement completely fills the pore spaces. The study shows several detrital grains including quartz, feldspar and lithic grains undergoing dissolution and subsequent replacement either partially or fully.
Conclusion: The analysed sandstones are mostly composed of quartz, rock fragments and feldspar. Compaction effects indicated by bending of mica flakes, grain fracturing, pressure solution and quartz overgrowth; clay authigenesis, cement precipitation, partial dissolution and replacement are the diagenetic signatures observed from thin section and Scanning Electron Microscope analyses.
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