新疆阿勒泰变质的震旦系及其微古植物群

THE METAMORPHIC SINIAN SYSTEM IN ALTAI OF XINJIANG UYGUR AUTONOMOUS REGION, CHINA AND ITS THE MICROPALEOFLORA

在阿勒泰地区一些变质地层的多处剖面 近五十个样品中获得了比较丰富的微古植物和少量似几丁虫化石。将此区以往认识不一的哑地层确定为震旦系,并在前人工作基础上进行划分对比,提出了构造运动的新认识。

The Altai region is located in the frontier of the north part of Xinjiang, China and belongs to the Altai stratigraphic region of the Tianshan-Hinggan stratigraphic province, where the metamorphic strata are well developed with huge thickness and belong to shallow marine flysch deposits of gcosynclinal type. Owing to lack in biological fossils, the subdivision and correlation as well as the ownership of the age of the metamorphic strata in this region have been in confusion for long time. In recent years, we have studied the biostratigraphy in the Altai region, northern Xinjiang, and found more abundent micropaleoflora within many sections. According to micropalcoflora, authors ascertain the age of the metamorphic strata in this region belong to the Sinian system. The whole Altai stratigraphic region can be divided into three stratigraphic subregion: the Hanas, Nolt and Ertix. 1. The Sinian widely exposed at the Hanas subregion is called the Habahe Group. The original rocks are made up chiefly of sandstones and shales, the carbonate sediments are very little. The bottom of the Group is not exposed, but the Baihaba Group of the lower Silurian series overlies unconformably different horizons of the Habahe Group. The greatest thickness of the Habahe Group is about 7753m. The Group contains such micropaleofloras as Leiominuscula minuta, Leiopsophosphaera densa, Trematosphaeridium, Trachysphaer idium, Turuchania, Leiofusa naviculara, Conusmorpha brevis, Triangumorpha minor, Quadratimorpha, Polyedryxium, Pulvinosphaeridium, Paleamorpha punctulata and Micrhysiridium minimum, etc. 2. The Sinian exposed at the Nolt subregion is called the Mongdeqa Group, the lower part of which is made up of volcanic rocks, the upper part is composed of elastics with huge thickness belonging to flysch deposits. Both the top and bottom of the Group are not exposed. It is considered as a allochthonous nappe body. The appreciable thickness of the Mongdeqa Group is 6901-9462m. This Group yields such micropaleoflora as leiominuscula minuta, Margominuscula, Leiopsophosphaera densa, Trachysphaeridium simplex, T.cf. regosum, T.cf. dengyingense, Asperatopsophosphaera, Trematosphaeridium minutum, Monotrematosphaeridium, Turuchania, Leiofusa, Nephromorpha regularis, Conusmorpha brevis, Stictosphaeridium cf forenosum, Polyedryxium, Triangumorpha punctulata, Quadratimorpha, Archaeoellipsoides and Micrhystridium minimum, etc. 3, The Sinian widely exposed at the eastern part and northeastern part of the Ertix subregion is called the Kuwci Group. It represents a littoral to shallow-sea clastic formation. The original rocks arc made up chiefly of sandstones and shales, intercalated with some lens of carbcnate in some places. They have been metamorphosed to schists, gneisses, migmatites, granulitcs, phyllitcs and metamorphic sandstones, etc. The top and the bottom of the Group are not exposed. The greatest appreciable thickness is about 12000m. It contains micropalcofloras, such as Leiominuscula minuta, Margominuscula, Leiopsophosphaera densa, Trachysphaeridium, Archaeoellipsoides, Leiofusa, Nephromorpha, Conusmorpha brevis, Triangumorpha, Polyedryxium and Micrhystridium minimum, etc. The Habahc Group, Mongdcqa Group and Kuwei Group are all the products of elevation and folding of crust movement during the end of the late Proterozoic. They do not belong to the Caledonian tectonic level.