Stratygrafia utworów ryfejsko-kambryjskich Północnej Mongolii

Ż. Biamba




The Riphean-Cambrian formatinos of North Mongolia are well developed. The area in study is situated at the contact of the Early Caledonian elements of West Trans-Baikalian reigon, East Saians and Tuwa, which stretch within the Soviet Union areas adjacent to Mongolia. The north-eastern region of the area under consideration adjoins the Baikalian elements of Chamar-Daban, and the southern parts of East Saians. In the south, and in the south-eastern area, it borders the Changai-Chentei zone and the Orchonu-Selengi volcanic zone (Fig. 1). Two complexes can be distinguished among the Riphean-Cambrian formations of North Mongolia. The first complex - which comprises the Lower Riphean and the Middle Riphean formations - resembles an old basement, the second one – which belongs to the Upper Riphean and the Middle Cambrian - is built up of gesynclinal formations of the early Caledonids. In the present paper the author discusses the stratigraphy of the second complex. The lower member of this complex is built up of the Darchak series (Tes-Subsugul area) and the Uliatogol series (Egyin-gol river basin), which begin the geosynclinals sedimentation. This sedimentation ends with the deposition of tuffaceous sandstones and the sandstone-tuff beds of the Uchutolgoi and Udjigin series referred to the Lena and Amigin stages (Figs 2-5, Table 1). A different character of the Riphean-Cambrian formations points to two various directions of geosynclinals development of the North Mongolia areas. Of decisive nature was here, in all likelihood, the character of the old basement, on which the geosyncline developed. The formations under discussion have been best examined in the region of the upper course of river Egyin-gol, on the western shore of the lake Chubsugul, and in the catchment area of river Shishkhid-gol. Here they reveal their greatest thickness.

Both the lithological composition and the age interval of the Riphean-Cambrian profiles are similar to the formations of this age, found to occur in the adjacent areas of the Soviet Union, and in the other regions of Mongolia. Terrigenous-carbonate farmations of the Tes-Chubsugul area are a continuation of the deposits of the Bokson-Sarchai graben in the East Saian area. The volcanogenic-sedimentary Riphean and Cambrian formations found to occur in the catchment areas of rivers Ider and Egyin-gol are in turn a continuation of the formations of the same age from the Dzida graben area in West Trans-Baikalian region. The same formations of the Ider river catchment area directly adjoin the areas of the Great Lakes Valley and the Dsabchan catchment area, where formations of the same age occur. A detailed correlation is shown in Table 1.

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