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Tertiary sediments are thickly deposited in most part of the northeast India attaining a maximum thickness of ±7 km sedimentary succession. Surma basin located in the eastern proximity of India is also characterized by a thick sedimentary column which can be considered as the northeastern extension of Greater Bengal basin. This basin was initiated due to the mutual collision between Indian and Burmese Plate. Due to this collision, the bed rocks have undergone folding which are oriented N-S trending hill ranges. The basin was also cut by a number of parallel to sub-parallel transverse faults and thrusts. The litho association is consisting of sandstone, siltstone, shale and their various proportions. The present study focused on the provenance of the sediments, tectonic settings of the basin and various paleoclimatic conditions prevailing during the time of deposition by using petrography, granulometric and heavy mineral analysis of representative rock samples which were collected from various parts of Aizawl district of Mizoram belonging to the Upper Bhuban Formation. Based on the various proxies it was confirmed that the sediments were primarily derived from surrounding orogens and deposited in a shallow marine basin under the influence of fluvial-deltaic conditions which were basically sourced from felsic provenance. The sediments were moderately weathered under semi-humid to humid climatic condition before they deposited into Surma basin. Sandstones samples are litharenite and wacke type which were deposited in an active continental margin to recycled orogen settings.

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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.

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