The relationship between major element concentration and grain size within sandstones from four turbidite sequences in Japan

There are few systematic investigations of variation in major element concentration with varying grain size in sandstone. In this study we examine the relationship between grain size and major element composition for four suites of sandstone, each with different modal composition and SiO2 content. The sandstones are sampled from Permian, Cretaceous and Paleogene turbidite sequences in Japan. We found that the effect of grain size on sandstone chemistry is related to the mineral composition of the sandstone itself. In commonly occurring sandstones that are composed mainly of quartz, feldspar and felsic (intermediate) volcanic rock fragments, a decrease in grain size is accompanied by a gradual decrease in SiO2 content and increase in TiO2, Al2O3, Fe2O3⁎, MgO, K2O and P2O5. The relationships can be largely explained by relative increases in the abundance of illite and chlorite in the fine-grained sediments. In contrast, sandstones that are derived mainly from basic volcanic rocks and that contain a high proportion of mafic minerals show different major element trends in response to grain size variation. In this group SiO2 and K2O contents increase gradually with decreasing grain size, whereas TiO2, Fe2O3⁎, MgO, CaO and P2O5 decrease. The major element trends observed in these sandstones are related to syn-depositional hydraulic sorting of heavy mafic minerals from light felsic minerals such as quartz and feldspar.