In this decade, the geological and paleontological investigations in the Andean region distributed in Colombia, Peru, Bolivia, Chile and Argentina of South America have been greatly progressed by Japanese specialists. It may have special significance for the developments of paleontology in our country through the comparative study between the Andean and Japanese regions. From the point of view, the Paleontological Society of Japan planned a Symposium of “Geology and Paleontology in the Andes” on the occasion of the annual meeting held at Chiba University on January of 1982. Fifteen articles were communicated and they cover various branches of paleontology, namely, plants (pollen, leaves, woods) and animals (foraminifers, corals, bryozoans, brachiopods, molluscs, mammals), and also the sedimentary environments. The more detailed paleontological study in South America is necessary to evaluate the relationships between the South America and East Asia. In this paper, the summaries of each speakers in the symposium are described for themselves. More details will be published on another occasions.
Minami-Iwo volcano is located at the southern end of Izu-Bonnin volcanic chain, 1300km south of Tokyo. It consists of three major volcanic edifices; older volcano I (OV1), older volcano II (OV2), and younger volcano (YV). At the boundaries between OV1 and OV2 and OV2 and YV, pyroclastic materials are characteristically observed; scoria fall deposit between OV1 and OV2, and scoria fall deposit and pyroclastic flow deposit between OV2 and YV. Older volcanoes, OV1 and OV2, are wholly composed of lava flows with both aa and pahoehoe surface textures. Younger volcano (YV), on the other hand, consists mainly of scoriaceous agglutinate which made up the steep slope of the main Minami-Iwo volcano. The older volcanoes are cut by numerous dikes (115 all told) which are dominant at the south and southwest sea cliffs. Four specimens collected from OV1, OV2 and dikes show normal thermoremnant magnetic orientation suggesting the oldest age less than a few hundred thousand years. Rocks of Minami-Iwo volcano are ankaramite, olivine basalt, augite-olivine basalt and plagioclase phyric basalt. The petrographic features and the chemical composition show that the rocks of Minami-Iwo volcano are of alkali rock series. The basalt of alkali rock affinity is the first discovery for volcanoes located at the volcanic front in Japan.