PROVENANCE OF THE KANTU FORMATION SANDSTONES, NANGA KANTU AREA,KETUNGAU BASIN, WEST KALIMANTAN

摘要

This research aims to study the provenance of the Kantu Fm. sandstones. Seventeen samples were taken from Nanga Kantu area, Ketungau Basin, West Kalimantan Province during geological mapping by Center of Geological Survey (CGS) Ketungau Team.This study has been conducted through petrography and modal composition analysis, using point-counting-method following Gazzi-Dickinson. The calculated modal composition is then plotted in Q-F-L, Qm-F-Lt, and Qp-Lv-Ls diagrams.Based on its lithology characteristics, the Kantu I'ormation can be divided into Sandstone Unit and Sandstone - Claystone Unit. The Kantu Fm. sandstones are very fine to medium sand grain (0.0625 - 0.4 mm), consisting of quartz (36 -59%), feldspar (2 - 4%), mica (4 - 8%), lithic fragments (9 - 19%), opaque material (1 - 3%), with matrix (7 -17%), and cement (4 - 7%) present between grains. Zircon, epidote, and tourmaline (sums up to approximately 1%) and organic materials (5 - 8%) are occasionally present. Kantu Fm. sandstones are classified as sublitharenite, lithic greywacke, and litharenite.Based on petrographic analysis and modal composition plotting in the diagrams, the main source of the Kantu Fm. sandstones is most likely the Kapuas Complex / Lubok Antu Melange (Late Jurassic - Early Cretaceous) and Rajang Group (Early Cretaceous - Middle Eocene) located north -northeast of Ketungau Basin. The Kapuas Complex and Rajang Group was deformed and uplifted by the end of Eocene during Sarawak Orogeny. The sediment materials eroded from the uplifted lundmasses were transported and deposited in the adjacent basin to form the Kantu Fm. sandstones.