Microfacies analysis and sequence stratigraphic modeling of the Samana Suk Formation, Chichali Nala, Trans Indus Ranges, Punjab, Pakistan

The depositional environment and sequence stratigraphy of the Samana Suk Formation (of CollovianBathonian age) based on field and petrographic data is presented. The formation is mainly composed of limestone with subordinate sandstone and marl. The limestone is medium to thick bedded and nodular at places with inter beds of sandstone and thin conglomerate intervals. The sandstone is reddish brown in color, quartzose and bioturbated. Four carbonate microfacies and one calcareous sandstone lithofacies have been identified, these microfacies include; 1) Laminated Lime Mudstone, 2) Bioclastic Lime Mud-Wackestone, 3) Bioclastic Wacke-Packstone and 4) Bioclastic Grainstone; a) Bioclastic Peloidal Grainstone Sub-microfacies, b) Bioclastic Ooidal Grainstone Sub-microfacies. On the basis of these four microfacies and a lithofacies, the Samana Suk Formation is interpreted to represent deposition on the inner ramp having microfacies of near shore to beach, lagoonal, barrier shoal and deeper sub-tidal ramp. Vertical successions of microfacies indicate fluctuating sea level changes marked by two transgressive/regressive cycles. Two second order and four third order sequences have been recognized within the Samana Suk Formation. Their regional correlation based on sea level curve helped to understand facies dynamics. Hard grounds are present within the Formation at seven different intervals vertically representing condensed section located in lower, middle and upper part of Formation.