On the Formation of Coal-Bearing Strata of the Tataurovskoye and Chernovskoye Deposits in the Chita-Ingoda Depression

L. A. Pukhlyakov

(Presented by Professor A. V. Aksarin)

The surfaces separating beds of various rocks in the Tataurovskoye and Chernovskoye brown-coal deposits are very uneven. For example, on the eastern side of one of the sections of the Chernovskoye open pit (Fig. 1), the coal beds have a horizontal occurrence

Fig. 1. Structure of the eastern side of one of the sectors of the Chernovskoye open pit (sketch). The vertical scale is exaggerated by a factor of 1:5. 1 — brown coal; 2 — earthy coal; 3 — coaly clay; 4 — aleurite; 5 — collapsed rocks that prevented tracing changes in the structure of the bed in the meridional direction; 6 — place from which rocks were removed during overburden operations.

over a distance of only about 300 m; then, in the southern direction, it rises at an angle of about 5°, while in the northern direction it dips (in Fig. 1 the ratio of scales is 1:5, and therefore these angles appear somewhat larger).

Similar phenomena are observed here very often, which creates certain difficulties in working the deposit and has given rise to the view that the tectonic history of this area was complex [1, p. 45]. Some facts, however, compel us to abandon this view. In particular, the rise of the floor of the bed in the southern direction in the sector shown in Fig. 1 corresponds to a facies transition of brown coal first into earthy coal, and then into coaly clay. In the northern direction, as the floor of the bed dips, its thickness decreases from two meters to several centimeters. It follows from what has been said that the irregularities considered existed at the time the bed was formed,

Otherwise (if these irregularities had been produced by tectonic movements that followed the formation of the seam), the facies changes in them would not be connected with these irregularities.

The beds of other rocks behave in an analogous way. When they occur horizontally, they are well sustained in thickness and are homogeneous in facies. When the soil rises or subsides, they increase or decrease in thickness and are replaced facies-wise by other rocks. All this leads to the conclusion that the irregularities of the surfaces separating the various rocks were formed

Fig. 2. Distribution of the results of granulometric analysis of sands of the Tataurovskoye deposit on L. B. Rukhin’s diagram. I — field of channel sands, II — field of lacustrine sands, III — field of uncertainty

as a result of the activity of flowing waters, and by no means of tectonic forces. Incidentally, disjunctive disturbances in the Chernovskoye section were not found by the author, despite careful searches for them.

It is not yet possible to study the surfaces of the boundaries between individual rock beds at the Tataurovskoye deposit to the same extent as at Chernovskoye, since it has not yet been put into development. In this connection, a study was made of the loose sands underlying and overlying the coal seams of this deposit, according to the method of L. B. Rukhin [3, 4], certain aspects of which were refined by the author in the study of loose sands of the Irsha-Borodino brown-coal deposit of the Kansk-Achinsk basin [2], as well as of the Dolgomostovskoye deposit of the same basin. The results of the study are given in Table 1, from which it is evident that the majority of the samples (31 out of 56) fell within the field of uncertainty of L. B. Rukhin’s diagram (Fig. 2), 20 were concentrated in the field of channel sands, and only 5 in the field of lacustrine sands. For comparison, it may be noted that among the sands of the Dolgomostovskoye deposit of the Kansk-Achinsk basin, which were studied by the same method in 1963–64, lacustrine sands predominated.

The predominance of river deposits among the rocks of the formation under consideration is also acknowledged by M. S. Nagibina [1, p. 44].

Thus, during the epoch of formation of the coal-bearing strata of the deposits of the Chita-Ingoda depression, that is, in Jurassic time, here

Table 1

Results of granulometric analysis of sands from the Tataurovskoye deposit

Continuation of Table 1 (p. 2 of the table)

a river regime predominated. At the same time, the river channel shifted from one side of the valley to the other. Otherwise, this was approximately the same regime that exists here at the present time.

Further, since the coals of the area under consideration are brown coals, it may be assumed that the layer of sediments above them during the period of their existence as a whole remained the same as it remains at the present time. From what has been said it follows that no tectonic movements occurred in this area either in Jurassic time or after it.

REFERENCES

1. M. S. Nagibina. Upper Mesozoic continental deposits of Transbaikalia, their composition and conditions of formation. Transactions of the Institute of Geological Sciences, issue 128. Geological Series (No. 49). Publishing House of the USSR Academy of Sciences, 1951.

2. L. A. Pukhlyakov. Some remarks on the tectonics and paleogeography of the Irsha-Borodino brown-coal deposit. Proceedings of TPI, vol. 166, 1969.

3. L. B. Rukhin. The granulometric method of studying sands. Publishing House of Leningrad University, 1947.

4. L. B. Rukhin. Granulometric analysis of loose and weakly cemented sedimentary rocks. Article in the collection Methods for Studying Sedimentary Rocks, vol. 1, Gosgeoltekhizdat, 1957.