Origin of Sulfides and Associated Sulfates in Neogene Sediments along the Kitakami River Basin from Northeast Japan : Sulfur Isotopic Characterization and Implications for Land Consolidation

Abstract

Land consolidation on Neogene sedimentary rocks often results in strong acid sulfate weathering which constraints subsequent land uses. Sulfur isotopic composition of the sulfide and associated sulfate minerals from marine sediments along the Kitakami River Basin, northeast Japan was studied. Large sulfur isotopic fractionation between sulfide minerals and concomitant seawater sulfate was observed for marine sediments formed under open oceanic conditions, relative to those from inland bay. Similarly, smaller sulfur isotopic fractionation was observed for sulfide minerals from deep sea sediments than those from shallower sea sediments. Very limited sulfur isotopic fractionation was observed for both brackish and terrestrial sediments. The sulfide minerals from Neogene sediments along the Kitakami River Basin reserve their sedimentary environments when the minerals were formed. There could not be found a definite relationship between the sulfur isotopic composition and the development of acid sulfates upon air drying of sediments.