Tracing highly oxidized events and its response to peat dynamic from the northwest Kapuas coastal wetlands, Indonesia

Peat deposits are highly sensitive to environmental changes and are well-suited to palaeobotanical investigations. Therefore, we assess the integration between organic petrology, palynology, and microcharcoal distributions to provide a robust interpretation on peatland dynamic and paleoenvironmental reconstruction. In addition, we propose a peat characterization using a quantitative color coordinate (CIELAB) to reduce biases while characterizing peat via qualitative comparisons to the Munsell soil color chart. This study was conducted in low-lying mires in the northwest Kapuas coastal plain, West Kalimantan, Indonesia. Five types of peat were identified: sapric muck, sapric shorts, sapric wood, coarse hemic, and fine hemic. The quantitative color coordinate analysis successfully recognizes the peat physical properties but is not directly related to the peat type. Higher values of the red-green chromaticity index (a*) indicate a greater preservation of plant material. Conversely, lower values represent charcoal or an oxidized layer of organic matter. Higher contents of inertinite or oxidized organic matter are comparable to the microcharcoal abundance, showing the presence of severe fires. At least eight fire events were reported, with decreasing intensity towards top of the core. Variation in microcharcoal abundances led to a degree of preservation changes, nutrient status and paleovegetation shift in the studied area. Four phases of peat dynamics were identified: initiation, early ombrogenous, late ombrogenous, and topogenous phases. In general, past vegetation shows an alternation community of mixed-riparian forest and open vegetation to present day mangrove low-lying topogenous mire. Our findings refer to the vulnerability of vegetation changes and peat dynamics concerning on highly oxidized events related to the fire intensity as an important driver in the northwest coastal wetlands of Kalimantan Island. • Peat deposits studied from the northwest Kapuas Coastal Wetlands, Indonesia. • Abundant microcharcoal shows fire as an important event of mire ecology. • Positive relationship is associated with inertinite content and microcharcoal distribution. • Fire occurrences influence the maceral assemblages and vegetation changes.