Danced january 2002 Author: Assoc. Professor Dr. Felix Tongkul Geology Program, School of Science and Technology, Universiti Malaysia Sabah, Locked Bag 2073, MY 88999 Kota Kinabalu, Malaysia Phone: + 60 88 320000-5756 Fax +60 88 435324 E-mail: [email protected] ' I I I F. Tongkul Geology Program School of Science and Technology I Universiti Malaysia Sabah 1\ I January, 2002 II Summary In an attempt to understandthe evolution of Maliau Basin a structural geology study within and outside the basin based on secondary information, satellite and radar imageries,aerial photographs, primary field and laboratorydata was carriedout. The study has documentedthe natural architectureof Maliau Basin, unravelled the tectonic evolution of the basin and detenninedongoing geologicalprocesses. These are importanttowards the managementof Maliau Basin. Maliau Basin is made up interbedded layers of sandstoneand mudstone, approximately 7500 metres thick, which were deposited, in an ancient deltaic-coastal environment, between 9-15 million years ago. The layers at the base of the basin consist mainly of mudstones reaching up to 2000 metres thick. Near the rim of the basin, thick sandstone interbedded with thin mudstone and coal seams occur. Towards the centre of the basin a series of sandstone-dominated and mudstone-dominated strata of various thicknesses occur. The youngest sediment is located near the Camel Trophy Field Station, whereas the oldest can be found near Lake Linumunsut. The basin sits on older sedimentary rocks, also comprising of thick layers of sandstoneand mudstone, with slight unconformity. The evolution of Maliau Basin was structurally controlled. Faults trending NW -SE and NE-SW together with the structural trends and topography of the underlying sedimentary I rocks played important roles in the development of the basin. The underlying sedimentary rocks, which began its deposition about 20 million years ago on a large elongate basin trending NE-SW was subjected to NW -SE compression between 14-15 million years ago. The tectonic compression resulted in the gentle folding of the underlying sedimentary rocks forming the initial concentric shape of Maliau Basin. The newly formed concentric-shaped basin was subsequently filled by Neogene sediments until about 9 million years ago when the basin was uplifted above sea level due to continued compression in eastern Sabah. The compression resulted in the gentle folding of the sedimentary layers and at the same time accentuated the concentric shape of the basin, through the reactivation of old fault system. About 5 million years ago Maliau Basin, and the surrounding areas was probably uplifted to its present height with a slight tilt to the Southeast. Following the uplift, Maliau Basin and surrounding areas were subjected to intense weathering and erosion that continued up to this day. The presenceof different lithological units, orientation of layers and fracture planes affects the ongoing geological processesthat shapethe unique landscapeof Maliau Basin. It is importantthat thesediverse lithologies and geologicalstructures be takeninto accountwhen developingany part of the basinto ovoid geologicalhazards. It is equally important to control any activities that can drastically alter the existing geological processeswithin the basin. Future studies may look into the possibleoccurrence of an ancientlake inside Maliau Basin and a systematic characterisationand evaluation of the waterfalls apart from detailedsedimentological characteristics of the sedimentarylayers. -11 - I II Table of Contents Summary ...ii Table of Contents ...iii List of Figures/Table/Photographs ...iv Acknowledgements. ..v INTRODUCTION Background... I Objectives/Scope. Methodology. ..I II. REGIONAL GEOLOGICAL SETTING.. 5 Tectono-stratigraphicUnits... 5 Major Structures...8 ill. GENERAL GEOLOGY OF MALIAU BASIN AREA 8 Stratigraphy. ..8 Lithological Units. ..11 Environment of Deposition ...19 IV STRUCTURAL GEOLOGY. ..19 Geometry ...19 I Lineament ...19 Bedding /Strata ...19 Fractures/Joints... 26 Faults ...26 Deformation/Stress. ..26 v. BASIN ARCHITECTURE AND EVOLUTION 26 I Architecture (Structural Plan of the Basin) ...26 Evolution (How the Basin Formed) ...31 VI. ONGOING GEOLOGICAL PROCESSES Drainage System Evolution... 37 ' I Waterfall Development ...38 i Landslide Occurrences. ..38 Soil Development... 38 VI. MANAGEMENT IMPLICATION .45 YD, FUTURE STUDIES... 45 Sedimentological and Paleontology. ..45 Occurrence of an Ancient Lake ...45 Intrinsic Geological ResourcesDevelopment... 45 References 45 Enclosures -111- I List of Figures/Table/Photographs Figures 1. Locationmap of the Maliau Basin. ..2 2. Routeand samplelocation map... 4 3. Regionalgeological map of centraland SoutheastSabah ...6 4. Regionalstructural cross-sections in centraland SoutheastSabah ...7 5. Simplified stratigraphyof the Maliau Basinarea... 10 6. Geologicalmap of the Maliau Basin ...13 7. Depositionalenvironment for the Maliau Basinarea... 20 8. Satelliteand radar imagesof the Maliau Basin ...21 9. Morpho-structuralmap of the Maliau Basin... 22 10. Rosediagram showing negative lineament pattern within the Maliau Basin 23 11. Geologicalcentre of the Maliau Basin... 25 12. Rosediagram showing fracture pattern within the Maliau Basin... 29 13. Schematictectonic evolution of the Maliau Basin ...32 14. Schematictectonic modelto showdevelopment of the Maliau Basin ...35 15. Evolution of Maliau Basindrainage system ...39 16. Schematicmodel to showriver undercuttingone valley... 40 17. Schematicmodel to show developmentof gorges,benches and waterfalls. 40 18. Schematicmodel to show detachmentof sandstonebeds ...41 19. Schematicmodel to showhow different rock typescontrol soil types. ..41 Table 1. Results of biostratigraphical studies on mudstone samples ...9 I Photographs 1. Temporarycamp site ...3 2. Crossingthe Maliau River... 3 3. Compositionof sandstone...12 4. MudstoneUnit ...14 5. MudstoneUnit ...14 6. Mudstonewith Thin SandstoneUnit ...15 7. Rare coal layer ...15 8. Sandstoneand MudstoneUnit... 16 9. Sandstoneand MudstoneUnit with ripple mark... 16 10. Gastropodfossil... 17 11. Vertical trace fossil... 17 1\ 12. SandstoneUnit ...18 13. SandstoneUnit showingcross-bedding. ..18 14. Gently dipping layers ...24 15. Nearly horizontallayers ...24 16. Two setsof fractures...27 17. Fracturesperpendicular to river flow... 28 18. Fracturesparallel to river flow... 28 II 19. Normal fault ...30 20. Shearedzone ...30 21. River downcuttingutilizing existing fractures... 42 22. Lateral erosionon weakermudstone layers... 42 23. Hard sandstonelayers produces structural benches and waterfalls 43 24. Rockfall due to headwarderosion... 44 25. Landslideon a steepside of a river valley... 44 -IV- Acknowledgement The project could never have happened without the kind invitation of Dr. Waidi Sinun and Dr. Tony Greer. Similarly the project could never have been realised without the generous financial and technical support from Yayasan Sabah and DANCED, Denmark and logistical and technical support from Universiti Malaysia Sabah. During the early part of the research, aerial photographs were extensively used. This would not have been possible without the full co-operation of the Aerial Photograph Section of the Land and Survey Department, Sabah. The research would have been incomplete without the biostratigraphical analysis of mudstone samples by Shell-Miri, led by Pedro P. Barbeito with contribution from Ajeng Imang Baya, Lau Ping Kiong, Musa Musbah and Voon Hian Fah. Throughout the research, Chang Fui Khiong, my research assistant, gave full support and drafted the geological map. My colleague, Dr. Marcus Jopony gave useful suggestions along the way. The field work was made easier with logistic support by staffs and students of Universiti Malaysia Sabah (Mohamad Yusuf, Sanin, Cyprian, John and Peter), field staffs of Yasasan Sabah (Jadda Suhaimi, Norhaidah Maral, Andy, Hasan, Shapie and Chak) and friends (Epip, Phillip, Vitalis, Abel and Melvin). The Geological Team. From left—Melvin, Epip, Sanin, Chang, Chak, Hasan, Shapie, Author and Andy. - v - I. INTRODUCTION Background The Maliau Basin is one of a series of saucer-shaped basins found in Central and Southeast Sabah (Fig. 1). These basins are depositional sites of ancient sedimentary rocks. The peculiar shape of the basin has puzzled many people--scientists and non- scientists. Earlier regional geological studies indicate that the development of these saucer-shaped basins are controlled by deep-seated geological structures (e.g. Lee & Coong, 1989; Tongkul, 1993). Recent local geological studies within the Maliau Basin by Tjia et al., (1990) and nearby Malibau Basin by Allagu (1997) also support the above interpretation. However, the exact mechanism as to how the geological structures controlled the shape of these saucer-shapedbasins is not clear. This is basically due to the lack of geological and structural information on these basins, including the Maliau Basin. In other to obtain a deeper understanding on how the Maliau Basin developed a more detailed and systematic study on its structural geology was carried out. 0 b j ectives/Scope The aim of the study was to produce a geological and structural map of the Maliau Basin; to determine the architecture (structural plan of the basin) and tectonic evolution of the basin; and to understand the ongoing geological processesoperating within the basin. I Methodology Aerial photographs together with satellite and radar imageries were used to determine the regional structure