ニュ-ジ-ランドにおける第四紀研究の一断面--旧汀線の研究を中心に (外国における第四紀研究と日本における研究<特集>)

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In this paper, first, recent trends of Quaternary studies in New Zealand and their background are briefly reviewed. New Zealand is characterized as a mobile belt since Neogene and the present rugged landscape has been produced under the influence of the active tectonic movements which have continued to the Recent. Volcanic activities and repeated severe glaciations have also produced their peculiar topographies and sediments, and supplied abundant airfall deposits as volcanic ash and loess which were very useful as key beds for Quaternary chronology. Fig. 1 shows the principal influences on sedimentation during the Quaternary, and post-glacial tectonic regimes after SUGGATE, 1973 and LENSEN, 1975. (A: coastline mainly influenced by eustatic sea level changes, B: individual volcanic centres, C: Taupo volcanic zone, D: main areas of early Quaternary subsidence, E: glaciated areas, F: shoreline in the late Otira glacial, G: principal axes of orogenic uplift). Reflecting such an environments, special attention seems to have been paid to studies on the neotectonics, especially on active faults, tephrochronology and paleoenvironments including paleopedology, paleoclimatology, palynology and glacial chronology as represented in Table 1.The main part of this paper deals with the review of studies of sea-level records during the late Quaternary, with regard to the mode and rate of deformation and sea-level changes. Fig. 2 summarizes the height distribution of the last interglacial shorelines and their tectonic significance, after SCHOFIELD and SUGGATE, 1971, and other data. Figs. 3A-C show detailed data of the former shorelines after CHAPPELL, 1975, OTA, 1977 and SUGGATE, 1973. From these figures, remarkable differential uplift can be recognized, especially in the North Island. In the Bay of Plenty and Wellington areas (Figs. 3A, B-1 and B-2), progressive deformation during the late Quaternary is clearly noticed. Maximum rate of uplift reaches to approximately 1m/1, 000 years. Height data of a series of raised beach ridges on the southern tip of the North Island led to the detection of the rate of uplift and tilting due to active folding in the Holocene as shown in Fig. 4 and Table 2 (WELLMAN, 1967 and others). Maximum uplift rate in the Holocene is 4m/1, 000 years, which suggests an accelerated uplift in the Holocene compared to that in the late Quaternary.The amount of uplift in the South Island is not so great as in the North Island, and the mode of deformation in the post-glacial seems to be different from that of the older ones.The New Zealand sea-level curve during the last 10, 000 years is shown in Fig. 5. Maximum post-glacial sea-level of a little over 2m dated at about 4, 000 y. B. P. is inferred by SCHOFIELD and SUGGATE. Some other problems concerning the study of the former shoreline are also reviewed and discussed in this paper.

著者

太田陽子
横浜国立大学

ニュ-ジ-ランドにおける第四紀研究の一断面--旧汀線の研究を中心に (外国における第四紀研究と日本における研究<特集>)

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