2001 Volume 110 Issue 5 Pages 708-724
The Plio-Pleistocene Mitoyo Group along the northern flank of Asan Mountains, central Kagawa Prefecture, mainly comprises the Saita and Yakeo Formations, unconformably underlain by Cretaceous basemant rocks of the Ryoke Granitoids and Izumi Group. The Saita Formation contains clasts of sedimentary rocks from the Izumi Group, and granitoids, as well as schist from the Sambagawa Metamorphic Rocks underlying the Shikoku Range. The formation crops out in the southern Ayakami area with a narrow longitudinal distribution. Clast fabric in the Saita Formation generally indicates a northward to westward paleocurrent direction. The Paleo-Doki River northerly flowing across the Asan Mountains formed the Saita Formation in the Early to Middle Pliocene.
The Yakeo Formation unconformably underlain by the Saita Formation is composed of clasts from the Izumi Group and Ryoke Granitoids. The formation crops out over the Kagawa, Ayakami, and Konan areas, and underlies the gently tilted hills with dissected flat summits. Clast fabric in the Yakeo Formation generally indicates northward to westward paleocurrent direction. The Paleo-Goto River northerly flowing within the Asan Mountains formed the Yakeo Formation as an alluvial fan deposit in the Early Pleistocene, adjacent to the northern flank of the mountains. The Median Tectonic Line and Northern Flank fault group of the Asan Mountains had been active since Middle Pliocene. The uplift of the mountains resulted in a relative height of a few hundred meters and the disappearance of the northward flowing river.
