The sandstones of the Proterozoic Rajgarh Formation are texturally immature and compositionally sub-mature quartz arenite to arkose in composition. The reservoir quality of sandstones is strongly influenced by depositional facies and various types of diagenetic modifications. A significant reduction in primary porosity in the studied sandstone is mainly due to high mechanical compaction followed by chemical compaction rather than the cementation process. Arkose from the river-dominated estuary facies show infiltrated clay coating, feldspar dissolution, iron-oxide cementation, leaching of detrital by iron-oxide cement, kaolinization of feldspar, the fracturing of detrital, partial albitization and folding of mica. The pore-lining clay has helped in retaining primary porosity, and leaching and dissolution processes were the main process generating secondary porosity in this facies. Tidal flat sub-arkose petrofacies display compaction of micas and unstable rock fragments into the pseudomatrix, expansion of muscovite by kaolinite, and pore-filling silty matrix that occupied intergranular spaces. Quartz-arenite petrofacies from shallow marine deposit show grain replacive kaolinite, pyrite precipitation, glauconite authigenesis, muscovite bending, albitization of plagioclase, feldspar overgrowths, dissolution, and grain fracturing. Pyrite plays a significant role in the reduction of both primary and secondary porosity by precipitating in intergranular spaces and in dissolution voids of feldspar. Moreover, fractures in detrital act as a second cycle porosity generation process in the shallow marine petrofacies. The linking between the diagenetic processes and depositional facies provides a geologic model for hydrocarbon exploration through reservoir quality prediction. Therefore, the petrographic observations indicate quartz-arenite (shallow marine facies) and sub-arkosic sandstones (tidal flat facies) are the least suitable latent reservoir because of their lowest primary and secondary porosity and unconnected pore spaces. Arkosic (river-dominated estuary facies) compositions are considered to be appropriate frameworks for potential reservoir rocks. This study reveals that the depositional environment largely controls the diagenetic pathways and hence, influences the reservoir quality.

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The fining upward sequence of Proterozoic Rajgarh Formation mainly consists of feldspathic sandstone, quartzarenite, bands of shale and have a restricted lateral extent with variable palaeoflow pattern. Eight major lithofacies identified from this succession collectively indicate fluvial to marginal marine depositional set up. The Rajgarh quartzose to feldspatho-quartzose siliciclastics are fine- to coarse grained, poorly- to moderately sorted derived from a stable continental block provenance that deposited in a fault bounded graben. The deposition of the Rajgarh siliciclastics can be best explained by short transportation, high relief and fast sedimentation in rapidly subsiding fault-bounded basin and indicate radial slope and source located in the Dausa uplift in the east and banded gneissic complex (BGC) in the south and southeast.