121 Geol. Bull. Punjab Univ. 43, 2008. FRACTURE ANALYSIS OF EOCENE SAKESAR LIMESTONE AT MARDWAL ANTICLINE, SOAN-SAKESAR VALLEY, WESTERN PART OF CENTRAL SALT RANGE, DISTRICT KHUSHAB, PAKISTAN. BY A. H. BAITU Pakistan Petroleum Limited, Karachi RIAZ A. SHEIKH, NAZIR AHMAD Institute of Geology, University of the Punjab, Quaid-i-Azam Campus, Lahore-54590 Pakistan AHSAN JAVED DEO Petroleum Exploration (Pvt.) Limited, Islamabad ATIQ UR REHMAN Baker Hughes, Pakistan AND ABDUL WAHAB Nespak, Lahore ABSTRACT:-By using circle inventory method, fracture density at different part of Mardwal Anticline was calculated. It is preceded by estimation of fracture porosity as well as permeability of Sakesar Limestone exposed at Mardwal anticline which is present at flattened part of Ramp-Flat-Ramp geometry of Salt Range Thrust (SRT). Anticline is formed under flexure slip folding mechanism which creates offset between fractures across the beds and slikensides on bedding plane as well. That offset disconnects the continuity of fractures across the bedding plane and results in elimination of permeability for inter-bedded migration of fluid. Crest of the anticline as well as local shear zones at places, where axial trace of the anticline turns, are characterized by more fractures. INTRODUCTION Mardwal Anticline is present on left side of the main road while going from Naushahra to Jaba near Mardwal village (Long. 72°09'55'': Lat.32°36'25'') Fig.1. It lies on topo-sheet no. 43D/2 of Survey of Pakistan and has extension from Long. 72°08'35'' to 72°10'05'' and from Lat. 32°35'56'': to 32°36''30''. It is mainly E-W trending anticline with asymmetric geometry (Plate 1). It has steeper northern limb while gentler southern limb. The anticline also shows the effect of flexure slip folding mechanism which is evident from slickensides on bedding planes and presence of offset between fractures across the bedding plane (Plate 4). There is bending in the axis from WNW to ENE because of shear zones one of these was observed at vicinity of Mardwal Anticline (Plate 4&5). Development of fractures, at Mardwal fractures Anticline, is very pronounced and sparking for analysis (Plate 2&3). Sakesar Limestone of Early Eocene is exposed through out the anticline. Here, main purpose of fracture analysis is to calculate density of fractures at different part of fold; and it is to estimate porosity and permeability of Sakesar Limestone. TECTONIC SETUP The mighty Himalayan mountain chain is a geological expression of collision of Indian Plate with Eurasian Plate (Tahirkheli, 1979). The ongoing northwards movement of Indian Plate caused crustal shortening that gave rise to fold and thrust belts (Lillie, et. al 1987). Since the collision in Eocene, deformation progressively shifted from the collision zone in north to the frontal fold and thrust belt in the south (Powel, 1979) (Table 1). About 2 M.Y. ago, major deformation front shifted to the present day frontal fold and thrust belt named as Salt Range – Potwar (Yeats et al., 1987) . It is an active fold and thrust belt that emerged in response to the underthrusting of
FRACTURE ANALYSIS OF EOCENE SAKESAR LIMESTONE AT MARDWAL ANTICLINE, SOAN-SAKESAR VALLEY, WESTERN PART OF CENTRAL SALT RANGE, DISTRICT KHUSHAB, PAKISTAN
Jun 23, 2023
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
