PETROGRAPHY OF UPPER NARI FORMATION, GANDRI JABAL, PAKISTAN

The petrographic study has been well carried out in order to understand the mineralogical and geochemical characteristics of the Nari Formation at “Gandri Jabal” section near Nooriabad, Jamshoro. The formations were found to be mainly composed of sandstone, limestone, shale and variegated clays in the studied section. Sandstones are compact to semi-compact, ferruginous, fine to coarse grained and range from pinkish, reddish, brownish to camel in color. It was unusual that one bed of camel colored limestone with maga fossils was observed in the upper part of the formation. Petrographic study of the Gandri Jabal Section, Upper part of Nari Formation on the texture of most of the samples is medium to coarse grained as well as the shape of the grains is angular to sub-angular. Dominant cementing material is calcite along iron oxide. It was further justified by geochemical analysis of major elements through automated Scanning Electron Microscopy Energy Dispersive Spectrometer (SEM-EDS), that the highest peak was silicon (Si), the second dominant peak was of calcium (Ca), and a third dominant peak was fermium(Fe). This mean that the major mineral constituent was quartz and within the sandstone the cementing material is calcite and iron oxide, and highly calcium (Ca) bed found means that major mineral constituent was Calcite within mega fossils limestone. These finding demonstrate that majority of the lithologic units of this formation are daltatic or beach and one bed is in Marine environment as considered by earlier workers. The samples having higher proportion of quartz grains belonging to quartz arenite category. Hence it is concluded based on the shape of detrial quartz grains, that the source of these sediments neither came from northern Himalayan nor from Indian shield, but very likely came from the western highlands and on the basis of the present rock fragments, we conjecture that source is igneous, sedimentary or metamorphic