DIAGENETIC STUDY AND MICROFACIE ANALYSIS OF CALLOVIAN-BANTHONIAN (JURASSIC) SAMANA SUK FORMATION, EASTERN KALACHITTA RANGES (LESSER HIMALAYAS), PAKISTAN

Abstract

The Samana Suk Formation, exposed in the Trans-Indus Ranges of Pakistan, is composed of stratified Jurassic age carbonate rocks. To understand the deposition setting and microfacies of the Samana Suk Formation, fieldwork, petrographic study and microfacies analayis were conducted. The sequence in the study area, exhibits a variety of sediments, and structures, and is composed predominantly of limestone and dolomitic limestone with minor interbedded marl. Microfacies analysis reveal four microfacies i.e. bioclastic wackestone, packstone, and dolomitic grainstones, demonstrate the considerable lateral and vertical changes of the carbonate platform deposits. The microfacies associations signify carbonate deposition in a shallow marine environment with variable hydrodynamic energy conditions, and within the inner to middle shelf. The host Limestone has undergone diagenetic alterations which have formed Dolomites. The dolomitic grainstone facies indicate high-energy conditions in the subtidal zones while the bioclastic wackestone and packstone facies represent low to moderate energy conditions in the inner shelf zones. The lateral facies transitions and textural variations are the result of local alterations in sedimentation topography, water depth, salinity, and energy. Overall, the study resulted in the development of a conceptual depositional model which beastly explains inner to middle shelfal environment for Samana Suk Formation of the Jurassic successions in the Trans-Indus Ranges.