SEDIMENTATION AND TECTONIC EVOLUTION OF CENOZOIC SEQUENCES FROM BENGAL AND ASSAM FORELAND BASINS, EASTERN HIMALAYAS Except where reference is made to the work of others, the work described in this thesis is my own or was done in collaboration with my advisory committee. This thesis does not include proprietary or classified information. _____________________________________ Mohammad Wahidur Rahman Certificate of Approval: ______________________ ______________________ Charles E. Savrda Ashraf Uddin, Chair Professor Associate Professor Geology and Geography Geology and Geography ______________________ ______________________ Willis E. Hames George T. Flowers Professor Interim Dean Geology and Geography Graduate School SEDIMENTATION AND TECTONIC EVOLUTION OF CENOZOIC SEQUENCES FROM BENGAL AND ASSAM FORELAND BASINS, EASTERN HIMALAYAS Mohammad Wahidur Rahman A Thesis Submitted to the Graduate Faculty of Auburn University in Partial Fulfillment of the Requirement for the Degree of Master of Science Auburn, Alabama August 9, 2008 SEDIMENTATION AND TECTONIC EVOLUTION OF CENOZOIC SEQUENCES FROM BENGAL AND ASSAM FORELAND BASINS, EASTERN HIMALAYAS Mohammad Wahidur Rahman Permission is granted to Auburn University to make copies of this thesis at its discretion, upon the request of individuals or institutions and at their expense. The author reserves all publication rights. __________________________ Mohammad Wahidur Rahman __________________________August 9, 2008 Date of Graduation iii VITA Mohammad Wahidur Rahman, son of Mr. Bazlur Rahman and Mrs. Begum Shamsunnahar Chowdhury, was born in 1978 in Comilla, Bangladesh. He passed his Higher Secondary Certificate Examination in 1995 from Comilla Victoria Govt. College with distinctions. He received his Bachelor of Science and Master of Science degrees in Geology in 2003 and 2006, respectively, from the University of Dhaka, Bangladesh. He entered the graduate school at Auburn University to pursue his second Masters degree from the Department of Geology and Geography in Fall 2006. iv THESIS ABSTRACT SEDIMENTATION AND TECTONIC EVOLUTION OF CENOZOIC SEQUENCES FROM BENGAL AND ASSAM FORELAND BASINS, EASTERN HIMALAYAS Mohammad Wahidur Rahman Master of Science, August 9, 2008 (Master of Science, University of Dhaka, Bangladesh, 2006) (Bachelor of Science, University of Dhaka, Bangladesh, 2003) 180 Typed pages Directed by Ashraf Uddin The Himalayan Mountains developed due to the collision of the Indian and Eurasian plates. There are two large foreland basins south of the eastern Himalayas: Assam Basin, located near the eastern syntaxis of the Himalayas, and the Bengal Basin further to the south. The Indo-Burman Ranges lie to the southeast of Assam and east of the Bengal Basin. The Indian craton is located to the west of the Bengal Basin. Mineralogical, geochemical, and geochronological studies provide critical information for the evolution of the Tertiary sequences of these basins. Sandstone modal analyses document that Eocene Disang (Qt56F5L40), Oligocene Barail (Qt59F7L34), Miocene Surma (Qt68F3L29), and Mio-Pliocene Tipam (Qt53F9L38) from Assam Basin, and Oligocene Barail (Qt83F3L14), Miocene Surma (Qt59F18L23), Mio- Pliocene Tipam (Qt57F14L29), and Pliocene Dupi Tila (Qt54F21L25) from the Bengal Basin v plot in the “recycled orogenic” provenance field of Dickinson, indicating an orogenic source from the Himalayas and/or Indo-Burman Ranges. Studies of detrital heavy- minerals, including garnets, also suggest orogenic source terranes with input from low- to medium-grade metamorphic rocks. Chrome spinels from the Bengal Basin were probably derived either from Himalayan arc material or Indo-Burmese Alpine-type ophiolites, while those of Assam were mostly derived from the Indo-Burman Ranges. Oligocene muscovite grains from Assam give a cooling age range from 35 to 204 Ma, indicating that they likely sourced from the Gangdese batholith of Tibet and the Mogok Metamorphic Belt of Indo-Burman Ranges (Myanmar). Cooling ages of Miocene muscovites from Assam range from 28 Ma to 81 Ma, with noticeable modes at 28-50 Ma and 65-80 Ma. This suggests that source rocks for Assam Miocene units, most likely the Gangdese batholith of Tibet and the Mogok belt of Myanmar, are older than that from the Bengal Basin. Whole-rock chemistry data reveal that sediments from the Assam Basin and the post-Oligocene sediments from the Bengal Basin were derived from granitic source rocks. Oligocene samples from Bengal Basin, however, show high silica contents suggesting intense chemical weathering during deposition closer to the equator. Depocenters in the foreland basins of the eastern Himalayas progressed generally south and west through time (in Assam during the Paleogene and in the Bengal Basin during the Neogene). The right-lateral Kaladan fault may have brought these two depositional systems closer in the Miocene. vi ACKNOWLEDGMENTS I am pleased to thank the almighty God who has been with me all the way and given me the scope to study about the mystery of the Earth. I would like to express my thanks and gratitude to my dear teacher Dr. Ashraf Uddin for bringing me to Auburn University and giving me the chance to get a Master’s degree in Geology. Dr. Uddin helped me not only as the principal advisor but also as a real guardian to get the best outcome of this research. I would like to express my sincere thanks to Dr. Charles Savrda, who helped with significant editing in this thesis. It would have been difficult to get this research work done without Dr. Savrda. I also would like to thank Dr. Willis Hames for help with geochronology part of this thesis. This research was funded by the U.S National Science Foundation (NSF-EAR- 0310306), Geological Society of America, and the Department of Geology and Geography of Auburn University. I also acknowledge Mr. Chris Fleisher of University of Georgia for help during microprobe analysis. I thank Dr. Humayun Akhter and few friends, specially Himel, Bahar, and Babu for help in field. All faculty members and fellow graduate students here at Auburn gave me moral support. I show gratitude to my beloved Mother, my loving sisters and brothers for their endless love, encouragement, and inspiration. I dedicate this thesis to my Mother. vii Style manual or journal used Geological Society of America Bulletin Computer software used Adobe Acrobat 6 Professional Adobe Illustrator 8.0 Adobe Photoshop 5.5 ArcGIS 9.1 Golden Software Grapher 3.0 Golden Software Surfer 8.0 Microsoft Excel 2003 Microsoft Word 2003 viii TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................... ix LIST OF FIGURES ..... ………………………………………………………………….xii LIST OF TABLES .......... ………………………………………………………………xvii CHAPTER 1: INTRODUCTION…………………………………………………………1 1.1 Introduction .....................................................................…………………………1 1.2 location of the study area .....................…………………………………………...8 1.3 Previous Works……………………. ..........……………………………………..13 CHAPTER 2: TECTONIC SETTING AND REGIONAL GEOLOGY ...........................15 2.1 Introduction ..................................................……………………………………15 2.2 Indian Craton ...........................…………………………………………………16 2.3 Indo-Burman Ranges .......................……………………………………………17 2.4 Bengal Basin ....................................……………………………………………17 2.5 Assam Basin.....................................……………………………………………22 CHAPTER 3: STRATIGRAPHY AND SEDIMENTATION ..…………………………26 3.1 Introduction .................…………………………………………………………..26 3.2 Bengal Basin ..............…………………………………………………………..31 3.3 Assam Basin................…………………………………………………………..36 CHAPTER 4: SANDSTONE PETROGRAPHY ............................……………………..37 4.1 Introduction ..............................…………………………………………………37 4.2 Methods......................................………………………………………………..38 ix 4.3 Petrography ......................................................…………………………………41 4.4 Sandstone mode and petrofacies evolution ..........................................................51 CHAPTER 5: HEAVY MINERAL ANALYSIS ..........................………………………64 5.1 Introduction ............................................……………………………………….64 5.2 Methods...............................……………………………………………………65 5.3 Results .............................................................…………………………………67 5.4 Provenance history .......................................……………………………………78 CHAPTER 6: MICROPROBE ANALYSIS…… .............................................................80 6.1 Introduction .........................................………………………………………….80 6.2 Mineral chemistry ..............................…………………………………………..81 6.3 Methods.................................................................……………………………...82 6.4 Results ............................................................…………………………………..87 6.4.1 Garnet .........................................................................................................87 6.4.2 Chrome spinel ............................................................................................94 6.4.3 Tourmaline .................................................................................................98 6.5 DISCUSSION ...................................................................................................101 6.5.1 Garnet .......................................................................................................101 6.5.2 Chrome Spinel .........................................................................................102