The Geology of Upper Baleh River, Kapit, Sarawak

Geological mapping of the proposed Baleh National Park, Sarawak was conducted during the Heart of Borneo Expedition in Mid November 2015 with Institute of Biodiversity and Environmental Conservation, Universiti Malaysia Sarawak. A geological map of the study area is compiled together with maps of the previous studies. The proposed Baleh National Park is made up of plateau and mountain chains. The topography of the study area is closely related to the geology. The plateau is underlain by the volcanic rocks which consists predominantly of tuff and dacitic rocks with scattered agglomerate, while the mountain chains are the ridges which striking east-west direction are underlain by slate interbedded with siltstone, sandstone and mud clast conglomerate of the Layar Member. The Layar Member of the Belaga Formation is suit of deep ocean marine deposits during the Late Cretaceous [100.5–66 million years ago (ma)]. The plateau of the Bukit Tiban was formed as a result of the volcanic eruption during the Late Miocene (11.6–5.3 ma). Several interesting geoheritage sites were observed in the study area. Keywords: Bukit Tiban, columnar joints, dacite, geoheritage, Layar Member