Petrographic Characterization and Diagenetic Impact on Bhuban Sandstones of Surma Group, Aizawl, Mizoram

Abstract

Abstract A comprehensive study based on petrographic analyses of Bhuban sandstones belonging to the Surma Group have been carried out in order to determine the various aspects such as depositional environment, tectono-provenance, textural and mineralogical properties, as well as to assess the depositional environment. The most dominant detrital framework constituents of Bhuban sandstone are Quartz (average 83.59%), which is followed by Feldspars (average 7.94%), and Lithic fragments (average 8.47%), matrix, cement, secondary and accessory minerals. The Bhuban sandstone samples are classified as sublith arenite to subarkosic varieties, tightly packed and are characterized by fine to medium-grained with poor to moderately sorted grains. The provenance discrimination diagrams depict the derivation of the detrital framework grains mostly from the upper and middle ranks of metamorphic rocks. The studied sediments were derived from recycled orogen as well as from quartzose recycled, which are marking a composite provenance in humid climate conditions. The study reveals that the area has undergone three distinct diagenetic stages. The Bhuban sandstones have been impacted by several diagenetic processes, which include compaction, cementation, mineral overgrowth, grain fracturing, albitization, recrystallization, replacement, and dissolution of minerals grains. These diagenetic processes that affected the studied samples underwent three different stages of diagenesis, which include early, late, and uplift-related stages. Cementation, minerals replacement, authigenic minerals, quartz and feldspars overgrowth, mechanical compaction, muscovitization, chloritization, concave-convex-suture contacts, recrystallization, albitization, etc. are present which indicates the early to late diagenetic stages of the examined Bhuban sandstones, whereas mechanical compaction, alteration & dissolution of framework grains, precipitation of authigenic minerals and cementation that leads to the decrease the porosity and permeability of the Bhuban sandstones.