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An Outcrop Study of Fracturing, Stylolitisation and Mechanical Stratigraphy in the Carbonate Carapace of a Salt Dome (Lower Cretaceous Units of Jebel Madar, Oman): A Template for Subsurface Analysis

Stehle, Manuela C.*1; Cosgrove, John W.1; John, Cedric M.1
(1) Earth Science and Engineering, Imperial College London, London, United Kingdom.

Carbonate units in the Lower Cretaceous of Jebel Madar, Oman form part of the exposed carapace above a salt dome. They contain a fracture network that reflects burial and exhumation in addition to the impact of regional tectonics and the local salt intrusion. A study of the 3D geometry and control on the fracture system in these rocks could be used as a template when attempting to reconstruct the fracture systems in the carapace above sub-surface intrusions. The carbonate units are made up of several beds and each bed has its own fracture network, the geometry of which reflects the stress history and intrinsic properties of each layer. These intrinsic properties include the lithology, specifically grain size, cleanness of carbonates (amount of clay), porosity, and bed thickness. Furthermore, the diagenetic fluid flow history, which is reflected in the cements present in the matrix of the host rock and infilling part of the fractures, is also impacting the complex geometry of the fracture network within each unit. Consequently, the intrinsic properties and diagenetic history of several individual rock units have been investigated in order to determine the influence of the above parameters on fracturing. The aim is to use the results to predict flow properties of sub-surface analogues. It is possible to distinguish between the fractures generated during burial from those linked to the emplacement of the salt body. The early burial fractures, which are normal to bedding, are intimately related to the formation of bedding parallel stylolites, and together these structures can have a significant impact on the movement of fluids through the rocks. The synchronous formation of the extension fractures normal to bedding and bedding parallel stylolites is shown by their mutual cross-cutting relationship. In addition, it is found that the specific lithology of individual beds and their thicknesses control both fracturing and the formation of stylolites. Two important components of the fracture network in these rocks are the bedding and the stylolites. Consequently, in addition to studying the relationship between the evolving stress regime, lithology and fracturing of the sequence, an attempt has been made to understand what controls the location, amplitude and lateral extent of the stylolites. This project is part of the Qatar Carbonates and Carbon Storage Research Centre, which is jointly funded by Qatar Petroleum, Shell, and the Qatar Science & Technology Park.


AAPG Search and Discovery Article #90141©2012, GEO-2012, 10th Middle East Geosciences Conference and Exhibition, 4-7 March 2012, Manama, Bahrain