Sedimentology and geochemistry of the Pleistocene-Holocene fluvial-lacustrine colluvial sedimentary sequence in the Pegalan River section, NW Borneo: Implications for regional tectono-climatic conditions and landscape evolution

Sedimentary archives preserve records of prevalent tectonic, climatic, depositional, and diagenetic conditions, which can be deciphered through integrated analyses of facies, mineralogy, and geochemistry. These records can also be correlated with local-to global-scale equivalents when reliable stratigraphic age constraints are available. This study documents a fluvial-lacustrine-colluvial sedimentary sequence deposited during the Middle Pleistocene-Holocene in northwestern Borneo, recording the pre­vailing tectono-climatic and geomorphic dynamics of the region. The inferred environmental conditions and landscape evolution indicate the presence of a low-gradient river channel controlled by seasonal flow variations, which underwent episodic changes in stream course under the combined influences of tectonics and climate. Facies characteristics, geochemical discriminant diagrams, and stratigraphic variations in mineralogy and geochemistry suggest alternating hot-arid and wet-humid conditions, presumably corresponding to the H1 and H2 events. Available age data from the present and previous studies in the region indicate that the sedimentary sequence and the interpreted tectono-climatic-geomorphic evolutionary events likely occurred between 37,900 BP and the present. The findings of this study provide an important basis for constraining regional to global tectono-climatic models.