STRATIGRAPHY OF PRECAMBRIAN ROCKS OF THE WESTERN SECTION OF THE SANGILEN HIGHLAND (TUVA)

The stratigraphic sequence of the Precambrian complex of the western Sangilen Highlands, Tannu Tuva, include schists, schistose sandstones, fine-gravel conglomerates, micaceous and ferruginous quartzites, graphitic marbles, and gneisses of the Teskhem, Mugur, Balyktyghkem, Chartyss, and Naryn formations, which grade upward into one another without break. Deposits containing Lower Cambrian fossils are also known in the area. The ferruginous quartzites, associated with the upper Mugur, mark the principal boundary in Precambrian sedimentary accumulation and indicate the change from terrigenous sediments to calcareous marine sedimentation.

The degree of metamorphism varies considerably, both horizontally and vertically. Terrigenous deposits correspond to the green-schist facies. Local variations in the metamorphism of calcareous deposits apparently result from the variability of original components. Also important is the superimposed injection metamorphism associated with Proterozoic intrusions. --Editor.