Perpustakaan Digital ITB

Lake sediment is a potential source of natural archive recording environmental change. One of these records is a variation in magnetic mineralogy and magnetic abundance that reflect the environmental condition during the time of deposition. In this research, magnetic properties on sediments from two different environmental settings in Indonesia were studied using rock magnetic method and survey of SEM. In the first setting, magnetic measurements were conducted on core sediments from two maar lakes in East Java (Lakes Lading and Bedali) that represent very confined environments where sediments were derived mainly from rocks and soils around the crater. In the second setting, similar measurements were also conducted on core sediment from Lake Matano, a cryptodepression lake in tectonically active South Sulawesi where the area around the lake is dominated by highly magnetic lateritic soils. The results show that the predominant magnetic mineral in sediments from Lakes Lading, Bedali, as well as Matano is pseudosingle domain (PSD) magnetite (Fe3O4). In terms of size, magnetic grains in sediment of Lake Matano are relatively larger than that of Lakes Lading and Bedali. Nevertheless, the Lake Matano sediment also has more superparamagnetic (SP) grains compared to that of Lakes Lading and Bedali. On the other hand, compared to that of Lake Matano, the maar lake sediments of Lakes Lading and Bedali have higher magnetic susceptibility as well as high intensity of artificial magnetic remanence. In this study, the variation of magnetic susceptibility in all core sediments is controlled mainly by concentration of magnetic mineral. The magnetic susceptibility profile for the cores of Lake Bedali as well as Matano shows an increase in value with depth in upper section and rather stable in lower section suggesting that the accumulation of magnetic minerals is compactioncontrolled. The small peaks at 12 cm and 30 cm depth on susceptibility profile of Lake Lading suggest a possible record of climatic event during period of high erosion in the catchments area. Finally, the homogeneity of magnetic minerals in these three lakes sediment provides an excellent background for paleoclimatic signals as they will be recorded as anomalies of magnetic susceptibility.