DIAGENETIC EVOLUTION OF A CRETACEOUS QUARTZ ARENITE, NARMADA RIFT BASIN, INDIA

The Nimar Sandstone forms the basal unit of a siliciclastic-carbonate sequence (Albian-Turonian) cropping out in the Narmada basin, situated below the Maastrichtian flood basalts (Deccan Traps) and above Precambrian basement. The sandstones are mostly moderately well-sorted, fine- to medium-grained quartzarenites of marginal marine origin. The diagenetic history of the Nimar Sandstone comprises several events. Mechanical compaction due to depth of burial in the range 1000-3500 m reduced the porosity to an average 25%. Quartz overgrowths resulted from partial silica cementation. Uplift of the sediments preceding the outpouring of the flood basalts (Maastrichtian) resulted in dissolution and leaching of feldspars by meteoric water, formation of infiltrated clay and iron oxide that line the interparticle pore spaces and subsequent deposition of calcite cement in a freshwater phreatic zone. Diagenetic effects of grain dissolution have contributed to the highly quartzose nature of the sandstones. During the Maastrichtian, thick basalts flows covered the sedimentary sequence giving rise to extensive silicification near the contact.