Origin of sediments and provenance study for natural hazards potential detection in Togean Islands, Tomini Bay, Indonesia Yunia Witasari, Helfinalis
BRIN
Abstract
Clay minerals cover almost all of the Earth^s surfaceas the main constituents of sediment and fine-grained rocks- therefore, some geological purposes use clay minerals as a proxy. The information based on clay mineral on a short core sample in Togean Islands, Tomini Bay, Indonesia, aimed to reveal natural and/or anthropogenical hazard signature on several decades and to provide the sedimentary environment referencein the research area. The research was deployed in September, 2015- single core samples were taken using a simple core made of two inches diameter PVC pipe. X-Ray Diffraction was used to determine clay minerals^ chemical properties, and C14 isotope was used to determine the chronological period of sedimentary layers. Based on clay mineral proxies, Togean Islands and its surrounding areas have experienced several disasters over five decades. Based on the main mineral and rock composition as well as the main chemical element content obtained from the sediments, it can be interpreted that the origin of the sediments in Tomini waters is derived from volcanic rock formations, lava deposits, and bioclastic deposits in the form of parent limestone and coral reefs. Based on the content of carbonate and bioclastic materials, it can also be estimated that up to a thickness of 50 cm, these sediments are still part of sedimentation in a continental shelf environment influenced by active volcanic activity. The presence of opaque and mica minerals are most likely derived from malachite rocks (gneiss and schist). The presence of rare minerals indicates that the origin of the sediments is mainly from the southern area of the Tomini Basin which is dominated by ofiolite rocks. The concentration of Barium in the bottom surface sediments of the Tomini Basin is thought to be related to the simultaneous decomposition of organic material and the absorption of Barium during the deposition of sediment particles. Volcanic rock fragments are thought to originate from Una-una Island which is a solitary volcanic island formation, then limestone fragments and coral fragments are thought to originate from the Batudaka karst island formation. Volcanic rocks in the form of tuff and andesite breccia are thought to come from the Togean Island lava dome. While the content of quartz minerals, and metamorphic rock fragments are thought to come from the ophiolite formation on Walea Island.
Keywords: sediment, minerals, natural hazards, environment, Togean, Tomini Bay
