The Geological History of the Eastern Part of the Mongolian Geosyncline

Abstract

The biostratigraphy of the Khingan-Sungari area in Northeast China was greatly advanced very recently by Chinese geologists and palaeontologists. With the discoveries of Lower, Middle and Upper Cambrian and various Ordovician fossils it is now warranted that the Mongolian geosyncline was extended through the area already at the beginning of the Palaeozoic era. The silurian and later Palaeozoic sequence and its local variation are summarized and shown in two tables.
With reference to the geology of neighbouring areas the history of this part of the geosyncline is discussed. The intrageosynclinal vulcanism, mostly basic to intermediate, was often repeated there. During the Permian period sea retreated so extensively that the area turned out land completely by the end of the period. Land plants mostly of the Angara flora and Palaeomutela and other naiads are widely distributed there in the continental Upper Permian deposits. No Lower and Middle Triassic formation is as yet known from the area. In the eastern extension of the Lesser Khingan range in the Soviet Union, however, the marine Permian formation is overlain by the Skytic and Anisic formation conformably or disconformably.
Near the eastern border of Province Chilin as well as in East Transbaikalia the folded mountains of older rocks are overlain by the marine Upper Triassic formation with marked discordance. These Permian and older formations are widely intruded by the Permo-Triassic granites. Therefore the Mongolian orogenic zone is definitely younger than the Variscan or or Hercynian mountains of Europe. It is now well ascerained that its architecture was completed at about the same time with the Triassic Akiyoshi mountains in Japan.