Chita Movements, the Tectonic Movements Preceding the Quaternary Rokko and Sanage Movements

Abstract

Neotectonics in Southwest Japan had been hitherto exemplified by "Rokko Movements" and "Sanage Movements". Recently, it has been recognized that the Rokko and Sanage Movements are the Quaternary tectonic movements under the stress field with latitudinal compression. In the Chita Peninsula, gently undulated hilly lands are widely distributed over the whole area. The hilly lands are composed of two kinds of geologic series. Thus, the upper constituents of the hill are of the middle Pleistocene Taketoyo Formation, and the lower constituents are of the Pliocene Tokoname Group. The Tokoname Group is a partial component of the Tokai Group, the name of which is given to the fillings of Lake Tokai of the Pliocene to early Pleistocene time. Relationship between the Taketoyo Formation and the Tokoname Group is represented by clino-unconformity. This unconformity is recognized everywhere in and around the Ise Bay, between the Tokai Group and the correlatives of the Taketoyo Formation. Differences observed between the upper and lower constituents of the hill are distinctly recognized in lithology, rate of sedimentation, size and structure of the sedimentary basins and geological ages. As for the mode of tectonic movement, it is also recognized clear differences between depositional stages of both constituents. Accordingly, both geological series have different backgrounds from a geological point of view. Hereupon, two kinds of tectonic movement can be distinguished from each other, the "older movement" which deposited the Tokai Group, and the "younger movement" which deposited the Taketoyo and correlative Formations. The "older movement" does not fall in the category of Rokko and Sanage Movements. This is the reason why the "older movement" must be distinguished from the Quaternary tectonic movements. The name of Chita Movements is given to the "older movement". The Chita Movement is defined as the tectonic movement which caused the Tokai Group to deposit, deform and dislocate mainly during the Pliocene time. Regime of the Movement covers the Ise Bay and the surrounding area. Duration of the Movement is designated as the Pliocene and the former half of the early Pleistocene. The chief characteristic of tectonic movement is down-warping. It is suspected that the Chita Movement was generated under other stress condition which is different from the horizontal compressive one with latitudinal trend in the Quaternary Movement. The Chita Movement had emerged in the Lake Biwa and Osaka Bay districts.