The Kachchh Basin is a pericratonic rift basin situated at the western margin of the Indian plate. The Habo Dome embodies an important exposure of Bathonian to Kimmergian sediments among the Kachchh Mainland exposures. Based on vertical facies transitions, facies associations were documented: mixed shallow marine (Facies association 1), shoreface and lagoon deposits (Facies association II) and subtidal innershelf below fair weather wave base (Facies association III). The documented facies associations reflect that Habo Dome sediments deposited in a variety of environments from shallow marine to fluvio-deltaic and were strongly influenced by fluctuation of relative sea level. The dominance of floating grains and point contacts in the sandstone indicate that detrital grains do not show much pressure effects as a result of either shallow burial or early cementation. The sandstones were cemented by iron oxide, carbonate and silica in order of abundance. Three types of cements, blocky, rim and fibrous cement occur in the studied limestone representing phreatic, fresh water phreatic and deep burial diagenetic stages. Neomorphism and micritization are common. Both primary and secondary porosity exists in these sediments. Different graphs of porosity versus depth suggest a depth of burial in the range of 615 -769 m.

The Upper Bhander Sandstone is dominantly composed of quartzarenites. The basal and top portions are sandstones, with the middle section comprising thinly bedded shales with interlayer silt and sandstone units. The sandstone units are composed of several varieties of quartz, feldspar, micas, rock fragments and heavy minerals. The Upper Bhander Sandstone was deposited in a transgressive phase and later modified by tidal processes and wave- and storm-dominated processes in a tide-influenced Barrier Beach Complex of the shallow marine environment. This study reveals that, during mechanical compaction, a rearrangement of grains took place and point and long contacts were formed. The early silica cementation and shallow burial resulted in high primary porosity. This phase was followed by chemical compaction and the replacement of silica cement by iron cement (Fe-cement) under the deep burial phase of these sandstones. Dissolution of Fe-cement and feldspars resulted in secondary porosity development. Quartz overgrowths are better developed on coarse- to medium-sized grains than on fine-sized grains. These observations suggest a progressive compaction, which initiated at the sediment–water interface and continued till deep burial diagenesis in a rapidly subsiding basin. The existing optical porosity of the Upper Bhander Sandstone is 4% and the minus cement porosity is 18%.

No abstract

No abstract

No abstract