Some lithological characters of Cretaceous sandstones in the Sanchu district, central Japan.
Lawsonite, pumpellyite and jadeitic pyroxenc have been found as forming clastic materials in lower Cretaceous formation of the Sanchu district, near Tokyo. These materials are confined to the lower Cretaceous sandstones and can never been found in middle or upper Cretaceous formations. K-feldspar and biotite are very common as elastic materials in sandstones of lower, middle and upper Cretaceous formation of the Sanchu district. Amounts of K-feldspar as well as of biotite regularly increase from lower to upper stratigraphical sequence. Lawsonite, pumpellyite and jadeitic pyroxene must have been derived from Sanbagawa metamorphic belt widely exposed in northern side of the Sanchu district. However, K-feldspar as well as biotite flakes are believed to have come from granitic rocks and their associated metamorphic rocks in Ryoke metamorphic belt exposed in northern side of the Sanbagawa metamorphic terrain.