Diagenetic Environment of Oligocene Barail Sandstones, North-West of Kohima, Nagaland, India

Petrographies, Scanning Electron Microscopy (SEM) along with XRD analysis were used to thoroughly examine the physical and diagenetic characteristics of the Oligocene Barail siliciclastics exposed in the NW of Kohima town of Nagaland, India. The hard and compact sandstones of the study area are represented by very fine to medium sand fractions and belong to sublithic arenite/quartz arenite categories. Compaction effects, authigenesis and albitization, silica overgrowth, neo-morphic quartz, modified grain to grain contacts, bending of flaky minerals, and corroded grain boundaries are the diagenetic features observed in the Barail sandstones. Locomorphic and redoxomorphic diagenetic stages are common, while features showing phyllomorphic stage of diagenesis are less common. A progressive diagenetic regime has also been envisaged on the basis of various diagenetic signatures and stages. Preserved diagenetic features and stages suggest a depth range of 3 to 5km and temperature above 150oC. Chemistry of seawater, pH, increasing pressure and temperature were responsible for diagenetic modifications in the Oligocene Barail sandstones. Keywords: Petrography, Diagenesis, Oligocene, Barail sandstone, Nagaland