Paleoecology and Paleoclimate of Tanjung Formation Deposition, Based on Palynological Data from Siung Malopot, Central Borneo

Abstract

The northern part of Barito basin is exposed around Siung Malopot area (Central Kalimantan), showing the late cretaceous basement of andesite lavas and granite intrusion. The basement is unconformably overlied by the rocks of Tanjung formation at middle to late Eocene age. Compressive phase during Miocene and Plio-Pleistocene folded and uplifted all existing rocks, made the rocks become relatively north-south structurally oriented. The exposed Tanjung formation consists of sandstone, mudstone, siltstone with intercalation of coals and thin layers of limestone. These lithologies may represent the upper parts of Tanjung formation. Palynology quantitative study is an approach to identify the palaeoclimate and palaeoecology of a certain sedimentation system. Analyses from 18 samples taken from lithologies of Tanjung formation show the presence of palinomorph fossils associated in Proxapertites operculatus zonation indicating the P18-P20 age intervals, or late eocene age. The ratio of spore and non-spore percentage, as well as the comparison between arboreal pollen (AP) and non-arboreal pollen (NAP) show the significant change of environment from time to time during the deposition of the Tanjung formation, also indicating the climate humidity that became more stabile to the younger ages. From 52 observed taxa in the samples, the ratio of marine versus non-marine taxon indicates the influence of sea-water influx in the sedimentation system, explaining the possible presence of thin limestone intercalations at the upper parts of Tanjung formation. Palynology quantitative study on Tanjung Formation indicates the sedimentation of this formation was in backmangrove environment that tends to become more influenced by marine conditions.