Geomorphology of the Alluvial Sediments and Bedrock in an Intermontane Basin: Application of Variogram Modeling to Electrical Resistivity Soundings |
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| Authors: | Adnan Ahmad Khan Asam Farid Gulraiz Akhter Khyzer Munir James Small Zulfiqar Ahmad |
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| Institution: | 1.Geophysical and Data Management Technology Centre,LMK Resources Pakistan (Private), Limited,Islamabad,Pakistan;2.Fugro Middle East,Abu Dhabi,United Arab Emirates;3.Department of Earth Sciences,Quaid-i-Azam University,Islamabad,Pakistan;4.Oil and Gas Research Centre,King Abdul Aziz City for Science and Technology,Riyadh,Saudi Arabia;5.Department of Arts and Sciences,The Petroleum Institute,Abu Dhabi,United Arab Emirates |
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| Abstract: | The study describes a methodology used to integrate legacy resistivity data with limited geological data in order to build three-dimensional models of the near subsurface. Variogram analysis and inversion techniques more typically found in the petroleum industry are applied to a set of 1D resistivity data taken from electrical surveys conducted in the 1980s. Through careful integration with limited geological data collected from boreholes and outcrops, the resultant model can be visualized in three dimensions to depict alluvium layers as lithological and structural units within the bedrock. By tuning the variogram parameters to account for directionality, it is possible to visualize the individual lithofacies and geomorphological features in the subsurface. In this study, an electrical resistivity data set collected as part of a groundwater study in an area of the Peshawar basin in Pakistan has been re-examined. Additional lithological logs from boreholes throughout the area have been combined with local outcrop information to calibrate the data. Tectonic activity during the Himalayan orogeny has caused uplift in the area and generated significant faulting in the bedrock resulting in the formation of depressions which are identified by low resistivity values representing clays. Paleo-streams have reworked these clays which have been eroded and replaced by gravel–sand facies along paleo-channels. It is concluded that the sediments have been deposited as prograding fan-shaped bodies and lacustrine deposits with interlayered gravel–sand and clay–silt facies. The Naranji area aquifer system has thus been formed as a result of local tectonic activity with fluvial erosion and deposition and is characterized by coarse sediments with high electrical resistivities. |
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