Abstract

<span style="font-size: 10.5pt; font-family: 'Times New Roman','serif'; mso-bidi-font-size: 10.0pt; mso-fareast-font-family: 宋体; mso-font-kerning: 1.0pt; mso-ansi-language: EN-US; mso-fareast-language: ZH-CN; mso-bidi-language: AR-SA;" lang="EN-US">Geochemistry of beach sand sediments collected from the Eastern San’in coast (n=17), Tango Peninsula (n=14) and Wakasa Bay (n=7) shorelines were investigated using XRF analyses for major and trace elements to characterize their composition, classification, maturity, provenance, tectonic setting and degree of weathering in source areas. Investigated sands from all sites were very similar showing depletion in all elements except SiO<sub>2</sub>, K<sub>2</sub>O and As relative to the UCCN and JUCN, suggesting a moderate geochemical maturation. Beach sand sediments from these locations can be classified as arkose, subarkose and litharenite that are chemically immature and formed under arid/semi-arid conditions with a tendency towards increasing chemical maturity suggesting that they are from multiple sources. The relatively low to moderate values of weathering indices of Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Chemical Index of Weathering (CIW), the beach sands from all sites in the source area have undergone low to moderate degree of chemical weathering. A-CN-K and A-CNK-FM plots, which suggest a granitic source composition, also confirm that the sand samples from these sites have undergone low to moderate degree of chemical weathering in consistent with CIA, PIA and CIW values. A plot of the analyzed beach sands data on the provenance discriminating function F1/F2 showed that most of the investigated beach sand sediments in all locations fall within mafic to intermediate ocean island arc source; similar to the tectonic setting discrimination diagrams based on major elements suggesting a passive margin.</span>

Highlights

  • The composition of coastal sediments is influenced by numerous components and processes, which contain important information about geochemical composition, weathering conditions and tectonic settings of the provenance and associated depositional basins

  • This study summarizes the results of an investigation on beach sand samples from Eastern San’in coast (Hyogo and Kyoto Prefecture), Tango Peninsula (Kyoto Prefecture) and Wakasa Bay (Fukui Prefecture), southwest Japan

  • Geochemical classification schemes of log (Na2O/K2O) versus log (SiO2/Al2O3), and log (Fe2O3*/K2O) against log (SiO2/Al2O3) show that the investigated beach sands from the Eastern San’in coast, Tango Peninsula, and Wakasa Bay are mainly arkose, subarkose and litharenite; suggesting that the sediments are from multiple sources

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Summary

Introduction

The composition of coastal sediments is influenced by numerous components and processes, which contain important information about geochemical composition, weathering conditions and tectonic settings of the provenance and associated depositional basins. The present study examines the geochemistry of sand samples collected from beaches on the Eastern San’in coast, Tango Peninsula and Wakasa Bay. The main purpose of the present is to determine their classification, maturity, sediment source area weathering, provenance and tectonic settings and to shed light on the source area paleo-weathering conditions in these sites. The main purpose of the present is to determine their classification, maturity, sediment source area weathering, provenance and tectonic settings and to shed light on the source area paleo-weathering conditions in these sites These factors were evaluated using elemental abundances, weathering indices and elemental ratios in comparison to the average Upper Continental Crust (UCC) and average Japan arc. This study summarizes the results of an investigation on beach sand samples from Eastern San’in coast (Hyogo and Kyoto Prefecture), Tango Peninsula (Kyoto Prefecture) and Wakasa Bay (Fukui Prefecture), southwest Japan

Sampling and Analytical Methods
Major and Trace Elements Geochemistry
Geochemical Classification
Normalized Compositions
Weathering Intensity and Chemical Maturity
Chemical Index of Alteration
Chemical Index of Weathering
Plagioclase Index of Alteration
A-CN-K Diagram
A-CNK-FM Diagram
Chemical Maturity
Provenance and Tectonic Setting
Conclusions

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