Accretionary Process of the Tertiary Setogawa and Mikasa Groups, Southwest Japan

The Middle Eocene to Lower Miocene Setogawa Group consists of pelagic, hemipelagic, and terrigenous sediments with volcanic intercalations. The sediments were deposited in and below the lower bathyal zone. The Setogawa Group is a wedge-shaped volcano-sedimentary pile, deformed by reverse faults and asymmetric folds at the landward edge, and constitutes a subduction complex. The reverse faulting and asymmetric folding took place abruptly, accompanied by tilting, uplifting, and gravity sliding of strata, and dewatering and consolidation of sediments. This was followed by the Lower Miocene Mikasa group, which consists of (in ascending order) debris flow deposits, terrigenous, and volcano-terrigenous sediments. The basal debris-flow deposits were mostly derived from the upper part of the Setogawa Group. They buried the structural depressions formed by the reverse faulting and asymmetric folding and eroded the underlying strata over the short timespan included in the Stichocorys delmontensis Zone. The Mikasa G...