SEDIMENTOLOGY AND LIMNOLOGY OF SINGKARAK AND TOBA LAKES, SUMATRA, INDONESIA: DEPOSITIONAL AND PETROLEUM SYSTEM MODEL FOR TROPICAL FLUVTO-LACUSTRINE AND VOLCANIC RELATED RIFT BASINS IN SOUTHEAST ASIA

摘要

Lake Singkarak and Lake Toba are situated in Northeast - Southwest (NE-SW) trend of The Great Sumatera Fault. Lake Singkarak and Lake Toba could be ideal models for similar lacustrine sedimentary environments in Tertiary basins around Southeast Asia especially for hydrocarbon exploration. The goals of this study are to create a depositional-environment model (sedimentology), compile paleo-climate evolution information and develop a petroleum system analogue. Research methodologies include the comprehensive field observations of sedimentology-geometry using PVC-pipe sampler, gravity coring, grabber, and outcrop observation. Bathymetry-geometry field observations have utilized the echo-sounder and strata-box multi beam, while the laboratory analyses covered the carbon dating analyses for stratigraphy, geochemistry analyses for total organic content, and pollen analyses for paleo-climate reconstruction. Singkarak Lake is modern tropical rift basin classified as pull-apart basin related with Great Sumatra Fault. The Lake Toba is classified as subduction related basin in continental margin controlled by Great Sumatra Fault and associated volcanic activities. The sedimentary sections in the last 11,400 years at Lake Singkarak, and 28,000 years at Lake Toba have been recorded during the field observations. The depositional environment can be divided into nine facies comprising fluvial braided-meandering complex, lacustrine delta, fan delta, shoreline complex, inner shelf-middle shelf lacustrine, sub-lacustrine channel and levee complex, deep lacustrine, and sub-lacustrine fan. The development of these facieses has been strongly controlled by the present-day tectonic and volcanic activities.