Influence of different sedimentary environments on multi-elemental marine geochemical maps of the Pacific Ocean and Sea of Japan, Tohoku region

Abstract

(2017) Influence of different sedimentary environments on multi-elemental marine geochemical maps of the Pacific Ocean and Sea of Japan, Tohoku region. Bull. Geol. Surv. Japan, vol. 68 (3), p. 87-110, 9 figs, 5 tables. Abstract:The authors present comprehensive terrestrial and marine geochemical maps of the Tohoku region and examine how marine sedimentary environments affect the spatial distribution of elemental concentrations. Marine sediments from the Sea of Japan are relatively enriched in elements abundant in felsic igneous rocks such as K 2 O, Ba, and REEs. These elements are highly enriched in sediments around submarine topographic highs, and are products of the denudation of Neogene sedimentary rocks associated with dacitic tuff and barite nodules. The silt and clay in deep basins are abundant in elements such as MnO, Cd, and Pb because of early diagenetic processes. Silty sediments on the continental shelf are supplied by large rivers; however, their geochemical features are influenced not by the adjacent terrestrial materials but simply by the effects of grain size. The sandy sediments that extensively cover the seafloor of the Pacific Ocean in the study area were sampled from depths below wave base (100 -1,000 m). Their chemical compositions are homogenous and similar to those of stream sediments that originate from mafic volcanic rocks. Therefore, they are inferred to have been deposited as relict sediments under the influence of Quaternary mafic volcanic activity that have been transported from the shelf to the deep sea by gravity currents. Although 81% of the total terrestrial sediment yield is discharged into the Sea of Japan, the spatial distributions of elemental concentrations are not always continuous between land and sea. Similar findings are recognized for the Pacific Ocean side. Notably, coarse sands distributed offshore from Kamaishi are enriched in elements abundant in sedimentary rocks of the accretionary complexes and granitic rocks that crop out in adjacent terrestrial areas. Because the river system in this region is small and has low sediment yields, these coarse sands may have been produced via coastal erosion or denudation of parent rocks during past regression and transgression.

87Sr/86Sr Isotopic Ratio of Ferromanganese Crusts as a Record of Detrital Influx to the Western North Pacific Ocean

“…Based on the chemical compositions of sediments in the western North Pacific, a relative increase in volcanic components compared with aeolian dust after 2 Ma has been reported [19]. Volcanic rocks account for 38.4% of the Japanese land surface [59], and the average chemical composition of the stream and coastal marine sediments in NE Japan is similar to that of andesite, excluding highly incompatible elements, such as U and Rb [60]. Therefore, our results agree with the relative increase in volcanic components recorded in the sediments.…”

Complex factors contribute to the chemical composition of clastic sediments traveling from rivers to the ocean along island arcs: A case study of the Otsuchi area, Northeast Japan

“…They drew a geochemical map of Japan based on 53 major and trace element analyses of 3024 riverbed sediment samples and 4905 seabed samples. Using the geological database of AIST, Ohta et al (2017) discussed the influence of the sedimentary environment and found discontinuity in the special distribution of elemental concentrations between land and sea in some regions of Northeast Japan. Further detailed geochemical and sedimentary studies were needed in the region.…”