MARINE TERRACES AND THEIR DEFORMATION IN NOTO PENINSULA, JAPAN SEA SIDE OF CENTRAL JAPAN

Abstract

Marine terraces in Noto Peninsula on the Japan Sea side of the central Japan were investigated with special reference to their geomorphic history and tectonic movements during the middle to late Pleistocene(Fig. 1). A large part of Noto Peninsula consists of a flight of marine terraces which have been classified into four groups, T, H, M and L in descending order of the elevation. The T terraces are further subdivided into T1 to T7, H into H 1 to H4 and M into M 1 to M3 (Figs. 2-8). The T terraces are very dissected, but their original surfaces are preserved as narrow flat tops of accordant heights which occupy extensive area of the inland of the peninsula. The H terraces surrounding the T terraces are continuously distributed, although they are smaller than the latter of width. The M1 terrace has the most well-preserved original surface consisting of thick marine sediments burying irregular bedrock reliefs at some places and is continuously developed throughout the study area. Thus, the Ml terrace can be correlated with the marine terrace formed ca. 120, 000-130, 000 y. B. P. during the Last interglacial transgression. It is inferred, therefore, that the formation of the oldest terrace (T group )of this area could go back to the early-middle Pleistocene and that the marine terraces would be resulted from a combined effect of continuous uplifts and eustatic changes of sea-level. Paleogeography of the three stages during the middle to late Pleistocene is reconstructed on the basis of marine terrace distribution (Fig. 9). It is obvious that progrssive emergence have occurred since the middle Pleistocene. The elevations of former shorelines of the Ml terrace range from 110 m (an average apparent rate of uplift ca. 1 m/l, 000 years) at the northernmost part to 20 m at the southeast, indicating marked southward tilting with a small component of eastward tilting. However, examing trends of the terrace heights in detail, the Noto Peninsula is not a single tilted block, but consists of several small blocks, each showing southward tilting (Fig. 10). The boundary of each block coincides with that of the mountains. Noticeable tilting, however, should have started after the M1 terrace formation, judging from the fact that there is no significant difference in the gradient of tilting between the M l terrace and the higher ones. Southward tilting seems to have continued to the present. In addition, many active reverse fault dislocating the marine terraces of various ages have contributed to the fragmentation of Noto Peninsula into smaller blocks.