Abstract:
The study area, Harnoi section is located in Abbottabad city in the Hazara region of Khyber Pakhtunkhwa province in Pakistan. It is 110 kilometers north of the capital Islamabad. The present study is focused on the Microfacies, depositional environments and diagenetic analysis of the sequence of Samana Suk Formation of Jurassic age. The Samana Suk Formation consists of well bedded limestone which is light brown to grey in color. The Samana Suk Formation is composed brachiopods, belemnite guards, micritic beds and Oolitic limestone. The features present indicate a shallow marine deposit. There were four Microfacies recognized as; 1) Bioclastic Oolitic Packstone microfacies is characterized by sub rounded to angular and moderately sorted grains, with substantial amount of oolites and bioclasts which indicate a subtidal or lower intertidal shallow marine environment. 2) Bioclastic Packstone microfacies is characterized mostly by Allochems which include brachiopods, belemnite guards and cephalopods along with the presence of oolites. The grains and sub rounded and moderately sorted. The features indicate a ramp margin shallow marine environment. 3) Dolomitized Oolitic Mudstone-Wackestone microfacies is characterized by dolomite matrix along with idiomorphic dolomite crystals. Calcite veining is also present. Allochems are present in minute amount and substantial amounts oolites are present. The present features indicate subtidal or lower intertidal shallow marine environment. 4) Bioclastic Oolitic Wackestone microfacies is characterized by mainly oolites and bioclasts. The difference between Bioclastic Oolitic Packstone microfacies and Bioclastic Oolitic Wacke-Packstone microfacies is on the basis of grain packing. The grains are angular and moderately sorted. The present features indicate a intertidal shallow marine environment. The processes of compaction, Neomorphism, dolomitization and microfractures are a clear manifestation of diagenetic processes that occurred in the formation.
