Journal of Earth Science & Climatic Change
Open Access

Abstract

The Devonian-Carboniferous Khusayyayn Formation of Wajid Group, Southwest Saudi Arabia is a uniform succession of medium to coarse-grained sandstone, deposited in a fluvial braided stream system and exposed in Wadi Al-Dawasir area and extend southward to the Najran city. The formation is the main groundwater aquifer in Wadi Al-Dawasir and Najran areas. it is also considered as a reservoir rock for hydrocarbon in Rub' Al-Khali Basin. This study aims to define the natural fractures network present within Khusayyayn Formation in multi-scale approach. In regional scale, lineaments (that may represent regional fractures) have been traced from Landsat satellite images with 15 m resolution and Spot-5 satellite images with a resolution of 2.5 m. Additionally, the digital elevation models (DEMs) with a resolution of 30 m were also used to enhance the lineaments trace maps. In outcrop scale, natural fracture attributes were measured and characterized in twenty locations. Five major regional trends were defined within Khusayyayn Formation in both lineaments and outcrop fractures scales. Those trends are NNW, NNE, NE, NW, and ENE. The northerly and Easterly trends are predominant and coincided with the major basement grain trends. However, the NW-trending fractures are corresponding with the trend of the Najd fault system. The NE-trend of lineaments and outcrop fractures might be related to the opening of Red Sea as they are following the weakness zones extend from the Red Sea to the continent. In outcrop scale natural fractures within Khusayyayn Formation are subvertical to vertical and Mode I open fracture type. Few of these fractures are filled with calcite and/or iron oxide material. The northwesterly-trending fractures cut across the northerly trending ones, whereas, the northerly trending fractures cut across the easterly trending fractures. This crosscutting relationship may indicate that the easterly trending fractures are the oldest fractures, and the northwesterly -trending fractures are younger than the northerly trending fractures. On the other hand, there is no clear relationship has been noticed between the northeasterly -trending fractures and the other trends. The fracture data obtained from outcrops and lineaments traces were combined to build a conceptual fracture model, which can help in defining the possible stress regime and the distribution of fracture pattern within Khusayyayn Formation.

Biography

Email: benaafi@kfupm.edu.sa