Climatic control on primary productivity changes during development of the Late Eocene Kiliran Jao lake, Central Sumatra Basin, Indonesia

A 102 m long core section of the late Eocene Kiliran Jao oil shale has been studied by means of palynofacies and inorganic geochemistry to examine the role of climate change on the development of the Kiliran Jao paleo-lake. Climate changes during deposition of the studied oil shale are interpreted from the abundance variation of fungal remains. Higher abundance of fungal remains in the middle part of the oil shale profile indicates relatively warmer climate during deposition. The warmer climate is thought to have led to changes in lake productivity. Carbon isotopic compositions of organic matter (δ¹³C) range from − 27.0 to − 30.5‰. These are generally more depleted in the middle part of the profile indicating lower primary productivity of the lake during deposition. Botryococcus braunii varies from 3 to 16% and is generally more abundant in the middle part of the profile. This is consistent with the less trophic preference of this algal blooming. The warmer climate is thought to have induced stratification, limiting the introduction of recycled nutrients to the epilimnion, thereby reducing the lake productivity.