ORIGIN AND DEMARCATION OF THE DEPOSITIONAL ENVIRONMENT BASED ON CONCRETIONS PRESENT IN SAMANA SUK FORMATION, HAZARA BASIN, ABBOTTABAD, PAKISTAN

Abstract

The present study is focused on the origin and demarcation of the various types of concretion and non-skeletal grains, depositional environments and their significance. The area under study lies in the vicinity of the Abbottabad region of the Khyber Pakhtunkhwa province Pakistan. The study area being topographically close-to-theMBT has been under intense deformation. The_study_area is marked by South East moving thrust faults, and North-East Trending Anticlines. The Samana Suk Formation consists of well bedded limestone which is light brown to grey in color. The.Samana.Suk.Formation includes brachiopods, belemnite guards, micritic beds and Oolitic limestone. The Concretions and non-skeletal grains interpreted.are; 1) Ooids grains have been further divided into 6 types which are Micritic Ooids, Concentric Ooids, Radial Ooids, Superficial Ooids, Broken Ooids, Deformed Ooids. These Ooids are characterized by well-rounded to sub-rounded and differ from each other on the basis of number of cortices and the structures of the Ooids, the environment of deposition for the ooids range from a lower intertidal to lagoonal shallow marine environment. 2) Aggregates, grains have been characterized as grapestones based on the stage of transformation. Grapestones grains are sub rounded and moderately sorted. The features indicate a platform to marginal reef marine environment. 3) Peloids grains have been further divided into 2 types which are Fecal Pellets and Bioerosional Peloids. These are characterized by elongated rod like to angular shaped grains formed by burrowing of micro-organisms. The present features indicate upper to middle intertidal shallow marine environment. The depositional environments for the concretions and non-skeletal grains range from inter tidal zone to marginal reef zones. The significance of these concretions and non-skeletal grains are such that they’re presence of absence can indicate Sea level fluctuations, these grains can be used for correlations on a regional scale, Specific depositional settings can be interpreted on the basis of abundance and type of grains present, carbonate concretions and grains are of high economic importance and their geometries have a significant influence on the reservoir qualities of carbonate rocks.