4:15 PM - 4:30 PM
[HQR06-04] Sediment transport revealed by residual luminescence signals of modern beach feldspar sands at the Kashimanada coast
Keywords:OSL, sediment transport, Kashimanada
Residual doses from luminescence signals of modern sediments reflect degrees of sunlight exposure during sediment transport and provides a clue to the history of sediment transport through repeated deposition and transport. This function of sediment luminescence has been demonstrated in coastal systems. However, most previous studies have dealt with coasts with large-scale sediment inflow and discharge, and there are few case studies on relatively stable coasts with modest sediment discharge. This study evaluated residual doses of surface sediments collected from the beach in the Kashimanada coast to examine sediment transport in a relatively stable coast. Residual doses were evaluated by measuring the IRSL and pIRIR of a K-feldspar rich grains 180-250 µm in diameter extracted from the samples.
Along the beach south of Kashima Port, residual doses tended to decrease southward. Doses from pIRIR50/290 decrease from about 15 Gy to 8 Gy, suggesting southward longshore sediment transport. Since residual doses of sediments from rivers are generally high, the southward decrease indicates negligible contribution of the Tone River at the southern end of the Kashimanada coast regarding the supply of sand grains 180-250 µm in diameter. North of Kashima Port, the residual dose is highest on the Oarai Sun Beach, the northern end of the Kashimanada coast, where pIRIR50/290 is about 15 Gy. The regisdual dose decreases southward to the Taiyo Beach with the minimum pIRIR50/290 residual dose around 9 Gy, south of which no clear decreasing trend is observed until Kashima Port. On the beach south of the mouth of the Naka River, located further north of the Oarai Sun Beach across Oarai port, the residual dose of pIRIR50/290 is as high as 18 Gy. These trends suggest that sediments with high residual doses flow into the Oarai Sun Beach beyond Oarai Port and are further drifted southward to the Taiyo Beach.
Along the beach south of Kashima Port, residual doses tended to decrease southward. Doses from pIRIR50/290 decrease from about 15 Gy to 8 Gy, suggesting southward longshore sediment transport. Since residual doses of sediments from rivers are generally high, the southward decrease indicates negligible contribution of the Tone River at the southern end of the Kashimanada coast regarding the supply of sand grains 180-250 µm in diameter. North of Kashima Port, the residual dose is highest on the Oarai Sun Beach, the northern end of the Kashimanada coast, where pIRIR50/290 is about 15 Gy. The regisdual dose decreases southward to the Taiyo Beach with the minimum pIRIR50/290 residual dose around 9 Gy, south of which no clear decreasing trend is observed until Kashima Port. On the beach south of the mouth of the Naka River, located further north of the Oarai Sun Beach across Oarai port, the residual dose of pIRIR50/290 is as high as 18 Gy. These trends suggest that sediments with high residual doses flow into the Oarai Sun Beach beyond Oarai Port and are further drifted southward to the Taiyo Beach.