STRUCTURAL CONFIGURATION OF THE SIRT BASIN Tarek Sabri Elakkari March, 2005 STRUCTURAL CONFIGURATION OF THE SIRT BASIN by Tarek Sabri Elakkari Thesis submitted to the International Institute for Geo-information Science and Earth Observation in partial fulfilment of the requirements for the degree of Master of Science in Geo-information Science and Earth Observation, Specialisation: Geological Resources Management and Environmental Geology (GRMEG) Thesis Assessment Board Prof. Dr. F.D. van der Meer (Chairman of the Board, ESA Department, ITC, The Netherlands) Prof. Dr. C.V. Reeves (External examiner, Delft, The Netherlands) Dr. S.D. Barritt (1st Supervisor, ESA Department, ITC, The Netherlands) Dr. M. van der Meijde (1st Supervisor, ESA Department, ITC, The Netherlands) Dr. P.M. van Dijk (2nd Supervisor, EREG Programme Director, ITC, The Netherlands) INTERNATIONAL INSTITUTE FOR GEO-INFORMATION SCIENCE AND EARTH OBSERVATION ENSCHEDE, THE NETHERLANDS I will not use data used in the thesis that are owned by ITC or third parties for publishing without written permission of the ITC thesis supervisor. I certify that although I may have conferred with others in preparing for this assignment, and drawn upon a range of sources cited in this work, the content of this thesis report is my original work. Signed ……………………. Disclaimer This document describes work undertaken as part of a programme of study at the International Institute for Geo-information Science and Earth Observation. All views and opinions expressed therein remain the sole responsibility of the author, and do not necessarily represent those of the institute. Abstract The Sirt basin is one of the youngest sedimentary basins in Libya and covers an area of approximately 600.000 km² in north central Libya. It is located on the northern margin of the African plate, with approximate coordinates (14°00`-20°00`E) and (28°00`-31°00`N). The northern margin of the African plate was affected by a series of tectonic activities due to interaction of the African and Eurasian plates that formed the structural features of the Sirt basin. The formation of the Sirt basin was associated with series of subsidence events which caused number of troughs along E-W trending basement faults during the Early Cretaceous and NW-SE trending basement faults during the Late Cretaceous. The troughs are separated by a series of platforms. These structures are obscured by a thick sedimentary cover. Geophysical data including ground survey gravity and aeromagnetic data is very important for studying the subsurface structures within the Sirt basin. It is revealed the NW-SE subsurface structures within the Sirt basin as well as NE-SW structures continuing towards the east of the Sirt basin. The gravity data reveals the difference in the structural trend within the Sirt basin compared to the surrounding area of Al Bottnan basin and Jaghbub uplift on the eastern edge of the Sirt Basin. The low gravity expression of the Murzuq and Ghadamis basins indicates the extent of the Sirt basin to the west. The low gravity anomaly expressions are normally associated with the trough structures, while the high gravity expressions are normally associated with the platform structures within the Sirt basin. The Agedabia trough is one the structural features within the Sirt basin, which is located in the eastern part of the Sirt basin with approximate coordinates (19°10`-20°50`E) and (26°30`-30°00`N). The gravity anomaly expression within the Agedabia trough is varied from high gravity anomaly expression in the northern part of the Agedabia trough to low gravity anomaly expression in the southern part of the Agedabia trough. The magnetic expression in the northern part of Agedabia trough is characterized by NW-SE trending structures which coincide with late Cretaceous structures of the Sirt basin, while the southern part is characterized by NE-SW trending features which coincide with a late Palaeozoic trend. The northern part of the Agedabia trough is separated from the southern part by a prominent NE-SW lineament that is expressed in both the gravity and magnetic data. It is interpreted as a basement fault, which separates a thicker southern crust from a thinner northern crust. The high gravity anomaly within the northern part of the Agedabia trough is interpreted as result of mantle upwelling which caused thinning the continental crust beneath the northern part of the Agedabia trough. Keywords: African plate, Eurasian plate, Sirt basin, gravity data, aeromagnetic data, crustal thickness. i Acknowledgements I would like to express all of my sincere respect to my mother, father, sisters and brothers in Libya for their encouragement and support during my study in Netherlands. I would like to thank Biruni Remote Sensing Center Tripoli, Libya for giving me this opportunity to study here in ITC. I am very grateful to my supervisors Dr. S.D. Barritt, Dr. P.M. van Dijk and Dr. M. van der Meijde for their encouragements and guidance during the research work. Without their help this work will not be possible. I would like to thank Abdulbaset Musbah Abadi for his permission to use the gravity data available in ITC. Special thanks to Dr. P.M. van Dijk for providing me the gravity data and the references related to study and also for his encouragement during the thesis period. Special thanks for Dr. S.D. Barritt who provided me by the magnetic data, for her help and guidance during data processing and for her explanation to the geophysical dataset. Special thanks for Dr. M. van der Meijde for his tectonic explanation and guidance during the thesis period. I extend special thanks to Mrs. Drs. N.C. (Nanette) Kingma for having organized the core module very well, which is the backbone of the study here at ITC and for her encouragement during the final exam. I would like to thank all of the EREG staffs for their guidance and explaining during the modules and field work in Spain. Special thanks are also dedicated to Christopher Andreas Hecker, Ernst Schetselaar and Frank van Ruitenbeek for their guidance in the specialization and elective modules related to my need. My thanks are also to my friends Ms. Beatriz Lao Ramos from Cuba, Mr. Zhengquan Lu form China and Muhibuddin Bin Usamah from Indonesia for their friendship and for sharing such good experiences here at ITC. I would not feel homesick with the companion of my fellow Libyans who gave me strength during the hard time. I must say thanks to Khaled Madi, Khaled Abujanah, Ali Atia, Sami and Yousef. ii Table of contents 1. Introduction ......................................................................................................................................1 1.1. Background.............................................................................................................................1 1.2. Location ..................................................................................................................................2 1.3. Problem definition ..................................................................................................................3 1.4. Objective of the research ........................................................................................................3 1.4.1. Main objective....................................................................................................................3 1.4.2. Specific objective ...............................................................................................................3 1.5. Research questions..................................................................................................................3 1.6. Datasets...................................................................................................................................4 1.6.1. Gravity dataset....................................................................................................................4 1.6.2. Aeromagnetic dataset .........................................................................................................4 1.6.3. Well data.............................................................................................................................4 1.6.4. Regional tectonic map ........................................................................................................5 1.7. Methodology...........................................................................................................................5 2. Literature review ..............................................................................................................................7 2.1. Sirt Basin ................................................................................................................................7 2.2. Geological setting ...................................................................................................................7 2.3. Stratigraphic units.................................................................................................................10 3. Gravity data....................................................................................................................................15 3.1. Introduction...........................................................................................................................15 3.2. Gravity dataset ......................................................................................................................15 3.3. Grid processing.....................................................................................................................16