Abstract
The Miocene Awa Group occurs in the eastern part of Iga City, Mie Prefecture, central Japan. We examined the geology and microfossils in detail. The Awa Group is composed of three formations (the Higashitanihata, Hiramatsu and Makino Formations). The Higashitanihata Formation unconformably overlies granite or gneiss of the Cretaceous Ryoke Complex and consists of basal conglomerate. The Hiramatsu Formation is composed of sandy conglomerate, sandstone and mudstone, and is divided into four lithofacies, suggesting two cycles of transgression-regression. The Makino Formation is composed of pebbly mudstone and unconformably overlies the Hiramatsu Formation. Relative sea-level lowering occurred at the boundary between the two formations. The Higashitanihata and Hiramatsu Formations in the central to northeastern areas strike E-W to NW-SE and dip about 10 to 20 ºS. Whereas those in the southern area vary by the development of a fault, a syncline and an anticline running NNE-SSW to NE-SW. Basin structure is developed only in the Makino Formation. Fossil foraminifers and calcareous nannofossils were examined to establish the biostratigraphy. The Hiramatsu Formation contains poorly preserved fossil planktonic foraminifers. The Makino Formation contains many index fossils showing the planktonic foraminiferal zones N.8 to N.9 of Blow (1969) and the calcareous nannofossil zone CN3 of Okada and Bukry (1980). Thus, the Makino Formation was certainly deposited between 16.4 and 15.6 Ma.
