Sedimentary processes in transport-limited versus weathering-limited erosional regimes: Contrasting mineralogical and geochemical signatures of sand and mud in Hainan and Taiwan islands

Abstract

This study provides and discusses an integrated petrographic, heavy-mineral, clay-mineral, elemental-geochemistry and Sr-Nd isotope-geochemistry dataset on sand and mud transported by mountain rivers in Hainan Island, where sand composition is mainly feldspatho-quartzose to quartz-rich feldspatho-quartzose, with K-feldspar invariably prevailing over plagioclase. Illite associated with chlorite prevails in the west, whereas kaolinite prevails in the north and northeast, underscoring a gradient of eastward-increasing weathering intensity in close correspondence with the progressive eastward increase in monsoonal rainfall.

All sand samples are enriched in SiO₂ relative to the upper continental crust and consequently depleted in most other chemical elements. The order of element mobility indicated by α^Al values is Mg > Ca > Na > Sr > K ≈ Ba ≈ Rb. The ⁸⁷Sr/⁸⁶Sr ratio varies between 0.717 and 0.721, and εNd ranges from −6.7 to −9.6. Moderately negative εNd and relatively high ⁸⁷Sr/⁸⁶Sr point at a significant contribution from old crystalline basement, directly or through recycling of siliciclastic strata.

Two endmember types of short river systems can be distinguished in eastern Asia, one dominated by chemical weathering controlled by tropical monsoonal climate under a tectonically stable background and gentle topography (transport-limited regime, dominant in Hainan Island) and another dominated by provenance-controlled physical erosion under a tectonically active background and rugged topography (weathering-limited regime, dominant in Taiwan Island). Mineralogical and geochemical information obtained from river sediments in these contrasting regimes can be profitably used in paleo-climatic inferences and reconstructions.