Abstract
Abstract We investigated the origin of marine sediments and their transfer by water currents using the spatial distribution patterns of multi-elements in terrestrial and marine areas of Kyushu, western Japan. Quaternary volcanic material covers Cretaceous granitic rock and Jurassic–Paleogene sedimentary rock of an accretionary complex in this region. Cluster analysis based on chemical compositions identified the origin of marine sediments from stream sediments originating from the above lithologies. Pyroclastic-flow deposits associated with caldera formation, particularly that of the Kikai Caldera (7.3 ka), were characterized by low Cr/Ti and La/Yb ratios. In contrast, the La/Yb ratio was very high in sediments derived from granitic rock and sedimentary rock of the accretionary complex. The spatial distributions of low Cr/Ti and La/Yb ratios suggest that marine sediments containing pyroclastic materials, which are found within an 80 km radius of the Kikai Caldera, were distributed on the shelf and transported northeastwards by a branch of the Kuroshio Current. The continuous distribution of the medium Cr/Ti and high La/Yb ratios from the land to the coast, slope and deep basin on the Pacific Ocean side suggests that sediments supplied from the terrestrial area were transferred by gravitational transport from the shelf to the deep basin.
Highlights
IntroductionThe Kyushu region, southwestern Japan, was selected as a study area in which sandy sediments containing pyroclastic deposits supplied by largescale eruptions from the Kikai Caldera (7.3 ka) (Maeno and Taniguchi 2007; Fujihara and SuzukiKamata 2013) are widely distributed in the southern marine area of Kyushu Island (Ikehara 2014) (Fig. 1)
The Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), has created geochemical maps showing the spatial distribution patterns of the concentrations of multiple elements throughout the country based on stream and marine sediments (Imai et al 2004; Imai et al 2010)
The chemical compositions of the stream sediments were determined by the lithology dominantly distributed in the watershed area
Summary
The Kyushu region, southwestern Japan, was selected as a study area in which sandy sediments containing pyroclastic deposits supplied by largescale eruptions from the Kikai Caldera (7.3 ka) (Maeno and Taniguchi 2007; Fujihara and SuzukiKamata 2013) are widely distributed in the southern marine area of Kyushu Island (Ikehara 2014) (Fig. 1). In this region, there are various bedforms such as subaqueous sand dunes, sand ribbons and ripples (Ikehara 1988, 1993; Ikehara and Kinoshita 1994). Geochemical maps of sediments in Kyushu, Japan and adjacent terrestrial materials; (2) the dispersion processes of volcanic materials erupted by very large eruptions; and (3) and the transportation of granules and sandy sediments by water currents
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