Geochemistry of the Palaeocene‐Eocene Upper Kelalan Formation, NW Borneo: Implications on palaeoweathering, tectonic setting, and provenance

Abstract

The stratigraphic records of Palaeocene‐Eocene are studied with interest as they encompass significant high‐resolution information on the environmental and climatic signals. Here, we present whole‐rockgeochemistry, mineralogy, and petrography of the turbiditic sedimentary rocks of the Upper Kelalan Formation, NW Borneo, and constraints on palaeoweathering, tectonic setting, and provenance. These are fine‐medium‐grained, poor to moderately sorted, angular to sub‐rounded litharenites with lesser occurrences of arkose, wacke, and Fe‐sandstone. The dominant proportion of monocrystalline and polycrystalline quartz, followed by K‐feldspar and plagioclase and minor amounts of lithic fragments, zircon, etc., with nil‐appreciable quantities of clay occur in these rocks. Chemical weathering indices (CIA, CIW, and PIA) values and A‐CN‐K plot show that the source area has undergone a moderate to an intense degree of chemical weathering and also influenced by the recycling effect. The majority of the sediments are derived from the felsic source area (i.e., granites) with some minor input from the metasedimentary/metamorphic terrain. Based on the geochemical ratios and discriminant diagrams, it is determined that the Schwaner Mountains and its metamorphic group of rocks were the principal provenances with some input from West Borneo Group of rocks. Our data suggest the sediments were deposited initially in an active continental margin setting during the Palaeocene that may have shifted to a passive margin setting during the Eocene age.