44-9 K-means clustering of Jeju Island beach sands: Provenance and mineralogy

Abstract:

Jeju Island, located on the continental shelf of the Yellow Sea off the southern coast of the Korean Peninsula, represents a unique geological setting. The island’s volcanic edifice, dominated by Mt. Halla (1,950 m), was constructed through multiple stages of eruption spanning approximately 1.8 million years. The volcanic activity produced a diverse suite of lavas ranging from alkali basalt to trachyte, creating a distinctive mineral assemblage in the coastal sedimentary systems.

Integration of XRF and XRD data, combined with PCA and k-means clustering (k = 3), reveals three geochemically and mineralogically distinct facies in Jeju Island beach sands. Facies A represents carbonate-dominated sediment derived mainly from biogenic material, with calcite and aragonite as the dominant mineral phases. Facies B reflects strongly weathered basalt-derived detritus supplied to the coast via fluvial and erosional processes, characterized by elevated Al₂O₃, Fe₂O₃, and TiO₂ contents. Facies C represents a transitional composition in which carbonate minerals coexist with primary basaltic silicates, indicating mixing between biogenic carbonate and volcanogenic detritus under moderate weathering conditions.

The spatial distribution of the three facies,  carbonate-dominated beaches on the northern coast, silicate-dominated beaches along the remaining coasts, and transitional compositions on the southwestern and eastern coasts demonstrates that sediment provenance on Jeju Island is characterized by the proximity to weathered basaltic source terrains and the local availability of biogenic carbonate. To quantitatively assess geochemical maturation, the Chemical Index of Alteration (CIA) was integrated with TiO₂ immobility systematics. CIA values reflect the mixed-provenance nature of the sediments, whereas the TiO₂ gradient provides a carbonate-insensitive proxy for weathering advancement, peaking in the residual volcanic assemblages of Facies B (2.30 ± 0.81 wt%). SEM-EDS analysis confirmed that Fe-Ti oxide phases serve as the primary mineralogical carriers of this elevated TiO₂. These results demonstrate that Jeju’s coastal sediments are a cumulative record of the island's transition from an active emergent stage to a currently quiescent, erosion and biogenic carbonate dominated terminal state. This study highlights the utility of unsupervised machine learning in decoding the complex provenance of high-energy volcanic coastal systems.

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