The Atsumi Peninsula is situated in the southern part of Aichi Prefecture, Central Japan. Geologically, this peninsula is mainly composed of the relatively thick marine Pleistocene sediments about 100m in thickness which is called the Atsumi formation, exclusive of the inlier Paleozoic mountainland in the west. In this paper, the authors intend to induce the mode of crustal movement during the Quaternary in this peninsula on the basis of the distribution, character and altitude of the marine terraces. The results are summarized as follows: 1) In the Atsumi Peninsula, there are five groups of the marine terraces which indicate the existence of the former high sea level. They are the higher terraces, Tempakuhara terrace, Fukue terrace, the lower terrace and the alluvial plain in the descending order and their distribution is shown in Fig. 1. The higher terraces are the fragmentary abraded rocky surfaces and subdivided into two levels, both of them represent the high sea level during the early Quaternary before the deposition of the Atsumi formation. Tempakuhara terrace can be considered originally, as the accumulation terrace of the Atsumi formation, as pointed out by Kuroda, Kaizuka and Tsuchi's previous studies. At present, this surface shows the undulated hilly topography, dissected densely by many small rivers. Fukue terrace is developed as the typical marine terrace which has the distinct back scarps and flat terrace plains composed of marine beach gravels overlying unconformably the Atsumi formation. This terrace can be thought to correlate with Shimosueyoshi terrace in Kanto district, according to the resemblance of geological and morphological characteristics in the both terraces. Consequently, it is probable that Fukue terrace has been formed during the period of the high sea level at the last interglacial stage. The lower terrace is generally fluvial one along the rivers, but some places such as near the mouth of the River Shio, it has the characters of marine origin. The alluvial plain, which is several meters in height above the present sea level at its inner edge, seems to show the postglacial transgression. 2) The height of former shoreline of each level varies considerably with locality as shown in Fg. 1. For example, that of Fukue terrace varies from 8m at the southwestern part to 42m at the northeastern. To know the general tendency of the altitude distribution, Fg. 2 is drawn in which the heights of former shorelines higher than Fukue terrace are projected to the direction parallel to the long axis of the peninsula. From this figure, it is recognized that in every terrace the altitude is increasing toward the northeast by east, excepting minor irregularities. Moreover, in the higher terraces and Tempakuhara terrace the mean gradient of altitude seems to be nearly same (1.75×10-3 in the latter), while in Fukue terrace it is only about 4.72×10-4 along the Atsumi Bay and 9.41×10-4 along the south coast. Accordingly, the mode of the crustal movement deforming the marine terraces of this region is characteristic of an upwarping movement, axis of which runs from WSW to ENE dipping towards NNW. And it is inferred that the main activity of this upwarping began during and after the deposition of the Atsumi formation and has been continued at least after the formation of Fukue terrace. As to whether this movement is still continued or not up to the Recent, however, the authors would like to consider in future.
The attitude of the climatic and sea-level changes inferred from the Pleistocene geology of South Kanto offers a standard scheme on those of Japanese Islands (Fig. 1). In this paper the writer attempts to establish the time-stratigraphic division of the Japanese Pleistocene based on the Quaternary geology of Tokyo-Yokohama area, and gives some consideration on the stratigraphic problems of the area, then lists up the paleoclimatic data of the area by plant remains, pollen, molluscs, foraminifers etc. (Tab. 1). The age of the Shimosueyoshi stage is discussed in comparison with climatic and sea-level curves given by de Vries, Emiliani, Fairbridge, and Broecker (Fig. 2).
Equations of the Shannon-Wiener information theory and the MacArthur's type I distribution, which are fully shown in the text, are applied to synecologic analysis of chydorid thanatocoenosis in Lake Nojiri. Indices of the specific diversity and the equitability (ε) were very low in the late glacial disproportionate population (Hutchinson's type IV distribution). It took about 5, 000 years from the end of the late-glacial period to establish a maximum equitable chydorid population. Two volcanic ash falls seriously disturbed the chydorid biocoenosis in the lake; the first volcanic ash fall (ca. 5, 600 B. P.) led to an extinction of Eurycercus lamellatus and a sharp decrease of the ε value (from 1.0 to 0.47), and the second volcanic ash (ca. 4, 600 B. P.) to a temporary decrease of Alona affinis and of the ε value (from 0.71 to 0.66). Two peaks of Monospilus dispar are also resulted from these disturbances. Agricultural activities intensified at around 1, 500 B. P. led to an increase of the productivity of the lake, without reducing significantly the equitability of chydorid population.