Sedimentology Facies Model From Modern Tropical Rift Basin of Lake Singkarak, Research Study for Central Sumatera and Ombilin Basins, Sumatera, Indonesia

Abstract

Lake Singkarak is the biggest modern pull apart basin in Indonesia and closes modern analogue model for Central Sumatera and Ombilin Basins. This lake is situated at Solok District, West Sumatera Province. Lake Singkarak was originally developed by active transtensional tectonic regime at one of many compartment of Great Sumatera Fault. This study is aimed to give alternative sedimentology analogue model for fluvio lacustrine environment in tropical area by made similarity comparation between modern to ancient sediment. Results of comprehensive field sedimentology work showing series of Quaternary Holocene (12,700 – 2,700 years) sediments which are distinguished by particular association of individual facies (10 defined facies) related to fluvio - lacustrine system. Alluvial fan facies was characterized by coarsening sequence pattern of intercalation gravity flow and traction sediments. Braided river facies was characterized by high energy traction sediment at steep slope river with volcanic clastic sediment supply with soil layer at top part. Meandering river facies was characterized by low sinuosity meandering belt with high traction current sediment and fining upward sequence. Fan delta facies was divided become three part, upper, medial and lower which dominantly characterized combination of gravity flow and traction current. Shoreline lacustrine facies was characterized by low energy of wave current creating wash over sediment. Lacustrine delta facies was divide become four sub-facies consisting of delta plain, distributaries channel, and mouth bar. Shallow lacustrine facies was characterized by falling out suspension creating interlaminate of clay, algae, silt and medium grain sand and poorly massive clay. Shelf slope – deep lacustrine facies is distributed from first bathymetry slope (25–35 meter) to the basin floor or deepest part of lacustrine (267 meter). Results of strata box measurement which is integrated with bathymetry survey, gravity coring and sediment grabbing on systematic mechanism showing that this depositional was divided becomes four sub-facies consisting of sub-lacustrine channel and levee complex, sub-lacustrine fan, shelf turbidity and pelagic facies. Shelf – deep lacustrine facies was characterized by high density turbidity and falling out of suspension sediment.

AAPG Datapages/Search and Discovery Article #90217 © 2015 International Conference & Exhibition, Melbourne, Australia, September 13-16, 2015