Persistence of pyrite in mountain river sediments sourced by landsliding in southeastern Taiwan

Although pyrite (FeS₂) is highly reactive in oxygen-rich environments and is expected to be largely consumed through the weathering zone, observations from Taiwan indicate that pyrite grains can survive and be transported by fluvial systems. This rapidly uplifting island exhibits exceptionally high erosion rates driven by frequent earthquakes, typhoons, and pervasive landsliding.In this study, we examine the distribution and preservation of detrital pyrite in river sediments from southeastern Taiwan. Using petrographic, heavy-mineral, Raman spectroscopy and SEM-EDS data, we assessed pyrite abundance, grain morphology, and oxidation state across catchments spanning a range of erosion regimes. The results reveal that pyrite abundance and persistence scale with erosion rates: catchments eroding faster than 1 mm/yr export up to ~30% of the exhumed pyrite, accounting for more than 1% of the total sediment load, primarily as fresh fragments, whereas lower-relief catchments are dominated by oxidized pyrite grains. Fresh pyrite is particularly abundant in sands sourced from the Central Range, where erosion rates are highest and landsliding triggered by typhoons is widespread. These observations indicate that rapid erosion, rather than mineralogical resistance or external geochemical controls, is the primary factor governing pyrite survival in Taiwan’s river systems. Detrital pyrite can therefore bypass oxidative weathering in fast-eroding orogenic settings, with important implications for sulfur and carbon cycling and for the preservation of pyrite in the sedimentary record.