東北地方太平洋沖地震にょる岩手，宮城，福島県沿岸域における津波堆積物の供給源 -TOC/TN比おょび安定硫黄同位体(δ~(34)S)を指標として-

摘要

Geochemical analyses （total nitrogen: TN,total organic carbon: TOC，total sulfur： TS，and stable sulfur isotope ratio: δ~(34)S) were performed on tsunami deposits by the 2011 off the Pacific coast of Tohoku Earthquake obtained from Iwate, Minamisanriku, Kesen-numa, and Sendai Bay areas for a total of 133 samples. Although TOC/TN ratios ranged widely (0.7-90), most of the samples (more than 80% of samples) ranged from 10-30,which were similar results to those for marine surface sediment in the Pacific coast area. Low δ~(34)S values （from - 29.6‰ to - 11.3‰） from Iwate, Minami Sanriku,and Sendai Bay tsunami deposits were observed. Generally, such low δ~(34)S values result from large isotope fractionation caused by the activity of sulfate-reducing bacteria in marine sediment under a sulfate (SO_4~(2-) ) rich environment. These results suggest that the tsunami deposits were mainly derived from marine sediment. High correlations between TS and As contents (r = 0.958) were observed in tsunami deposits from the Kesen-numa area. Furthermore, the high δ~(34)S values （from - 3.1‰ to — 0.7‰） in the tsunami deposits from the Kesen-numa area correspond well with those of hydrothermal ore samples from the Kesen-numa area. These results indicate that sulfur and arsenic in tsunami deposits from the Kesen-numa area originated in slag from the mines.