Tephra Sequence with Mica Flakes

Abstract

In the northern half of Kitakami Mountains, some tephra sequences composed of micaceous clayey volcanic ashes and pumice layers without mica flakes are observed. These sections are situated at hill foots and presented within exposed regions of granitic rocks.Pumice grains fell and settled relatively in short time and, on the contrary, falling and settling of finer ash materials were slow or intermittent. So a certain part of clayey ashes with mica flakes derived from granitic rocks, was transported on slope and was coated with pumice layer. In addition to the mixture of materials at place in situ, relatively active movement of materials from considerable distances occurred during the stage of finer ash falling and weathering into clay.