アンデス南部の地質・古生物学的研究

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Under close international cooperation the research was carried out from early September in 1970 to early January in 1971 to the Andes situating between Chile and Argentina. The purposes of our research are as follows : A) To collect fossil molluscas is and plants in the field work in various localities from the stratigraphical point of view. B) To make clear what is common and what is different between the fossils in Japan and those in the Andes through the comparative study with both of them. C) To make clear the geographical distribution of fossils in Pacific region including Japan and the Andes. D) To make clear the relation between the crustal movement and the change of fossils in the geological age. The Andes is so wide that we divided the area for our research into five districts : Copiapo-Antofagasta, Santiago, Concepcion and its southern part (Madre de Dios), Mendoza, Patagonia and Sierra Australes, where we had the bases for the field work. The headquarters for whole research was located at Santiago, the capital of Chile. The materials collected by us in these districts were gathered at the headquarters in Santiago, and they were sent to Japan from Valparaiso harbour in Chile. Although the materials are being examined now, the results of the study already known are as follows : 1) In the Cerritos Bayos near Calama, Northern Chile, the Jurassic system which was reported by BIESE in 1956, 1957 and 1961, ranging from Sinemurian to Tithonian, was clarified stratigraphically, but we could not confirm in detail BIESEs fossil zones. 2) Limon Verde area located about 20 km south from Calama forming high plateau, are occupied by the Palaeozoic or pre-cambrian and Mesozoic groups and igneous rocks. The Jurassic system mainly consisting of the alternation of medium to coarse-grained sandstone, black shale and grey limestone, yields such molluscan fossils as Frenguelliella sp., Weyla alata (van Bum), Mactromya n. sp., Chlamys cf. textoria (Schlotheim) . Judging from the molluscan fossils, the alternation is probably lower Jurassic in age. 3) Domeyko range is situated at the west of the Andes. The west slope of the range crops out the alternation of sandstone and shale. It was extremely folded by the crustal movement. The alternation contains such fossils as Cardinia sp., Protocardia n. sp., Astarte sp. and Thracia sp.. From these fossils it is thought that the alternation is lower Jurassic. The eastern slope of Domeyko range near Sal de Punta Negra consisting of the alternation of sandstone, shale and limestone, occurs the molluscas such as Eopecten sp., Pinna sp., Minetrigoniinae gen. and sp. nov. etc. 4) In Concepcion area there were found many kinds of deposits such as Palaeozoic or pre-cambrian, Mesozoic and Cenozoic groups. There is also a broad distribution of the Palaeozoic granitic rocks forming coastal range. The Triassic formation along the Bio Bio river consisting of clayslate, greywacke, arkose sandstone and conglomerate is marine and non-marine deposits. From the northern area of the river many plants were collected. And some specimens of Halobia were found at the point of about 2km south of Unihue. The upper Cretaceous Quiriquina formation which is distributed in the Quiriquina island, is well exposed in the western and eastern sides of the island. Many molluscan fossils including Pacitrigonia were collected in the western side of the island. On the contrary, in the eastern side, many Cretaceous plants including Dicotyledoneae were newly founded in the upper part of the Quiriquina formation close with “Eocene” marine deposit.
社団法人東京地学協会の論文

アンデス南部の地質・古生物学的研究

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