Clay minerals in the sediments as useful paleoclimate proxy: Lake Sentarum case study, West Kalimantan, Indonesia

Lake Sentarum is a flood-plains lake that will dry and flood as climate cycle that is interesting to be studied climate change from the past to near the present. The objective of this study is to reveals paleoclimate conditions by analysing clay minerals that present in the lake sediments. The study investigated clay mineral in lake sediments from 70 cm long core, X-RD analysis was obtained to identify various of clay minerals. The clay minerals of Lake Sentarum comprises of illite, chlorite, and kaolinite. The relative change in abundance of clay minerals indicating climate conditions, besides numbers of chemistry and crystallinity of illite represents weathering mechanism. Our research reveals that climate history of Lake Sentarum from sediments core began cold and arid climate episode. This episode was characterized by low value of illite chemistry and illite crystallinity were 0.37-0.41 and 0.19°Δ2θ-0.2°Δ2θ, respectively, and slight decrease abundance of kaolinite. There was no significant changes until the middle of the sediments core. Significant changes of abundance of kaolinite and illite chemistry occurred in top of the core. The percentage of kaolinite and illite chemistry became the highest value that reflected strong chemical weathering occurred in the watershed with warm and high rainfall climate conditions.