Geological Structure of the Middle Anuy Region of Northwestern Altai (Based on the 1931 Survey)

I. Preface

The Middle Anuy geological-prospecting party worked under my direction during the summer of 1931 in the Middle Anuy area of the Northern Altai (northwestern part of sheet 14, row X, of the ten-verst map), funded by and on assignment from the West Siberian Geological Prospecting Trust. The party’s task was to cover an area of 1,100 sq. km with geological survey and prospecting, and to establish the industrial value of the region.

The topographic base for the party’s work was a 5-verst map, photographically enlarged two and a half times. The map has no contours and in places suffers from inaccuracy.

The office processing was carried out in the Department of General Geology of the Siberian Geological Prospecting Institute, under the constant direction of Prof. M. A. Usov, to whom I offer my sincere gratitude. I am also very grateful to I. K. Bazhenov, as the technical director of the Charysh group, who assisted us with his advice and instructions both in the field and during the course of the office work.

II. Orographic and Hydrographic Sketch

1. In orographic and hydrographic terms, the region is of interest in that along its northern boundary runs the face of the Altai; to the north of it stretches a broad, slightly hilly steppe plain, while to the south the Altai Mountains begin. The face of the Altai is not very sharply expressed in the area studied; moreover, the relative difference in elevation between the adjoining undulating plain and the hills of the front part of the mountains reaches only 250 m, with the absolute elevation, for example, of Karaulnaya hill being 470 m. The appended profile from the summit of Butachikha hill to the steppe river Kudrikha (Fig. 1) illustrates this situation. In places there is not even a sharp boundary between the Altai and the plain—namely, where ridge-like, swell-shaped spurs, composed to a significant extent of bedrock and covered by a mantle of proluvial-deluvial deposits, extend from the Altai into the steppe.

Furthermore, the direction of the face is by no means rectilinear; on the contrary, it either forms deep embayments or sends high, swell-shaped projections far out into the steppe, and the sections of the face projecting into the mountainous part of the Altai are associated precisely with those places where rivers break out from the mountains onto the steppe plain. Finally, if one analyzes the geological structure of the adjoining parts of the face and the plain, it proves that both are composed of the same formation of green-violet shales, which crop out repeatedly on the plain, and only along the valleys of small rivers do we observe thicknesses of post-Pliocene unconsolidated deposits.

Let us trace the details of this northern boundary of the Altai. Near the village of Mikhailovskoye, where the Yegorshikha River emerges from the mountains onto the steppe plain, we encounter a steep scarp of the mountainous part, represented here by the Butachikha hill, with an absolute elevation of 200 m. This scarp extends westward to the place where the Slyudyanka River, having already come out onto the plain, again enters the mountains.

The northern slope of the mountainous part here is covered by a train of proluvial-deluvial deposits, which are now also being eroded by the Yegorshikha River.

From the place where the Slyudyanka River enters the mountains, the line of the mountain façade sharply changes its direction from east to north, then smoothly bends around Karaulnaya hill, with an absolute elevation of 470 m, and farther on again runs eastward as far as the village of Solovykha, having a somewhat sinuous character; moreover, these bends are confined to the places where small rivers emerge from the mountains onto the steppe plain. Thus, at the outlets of the Ganin spring and the Solovykha River, the façade naturally forms recesses projecting into the valleys of these streams. At the same time, here and there, as a result of selective erosion, residual hills and capes occur in such recesses—for example, at the confluence between the mouth of the Slyudyanka River and the Anuy River.

From the village of Solovykha the line of the façade runs generally in a NE direction, passing beyond the limits of our map sheet, where it smoothly turns westward. But here too, in detail, the façade line has a sinuous character. Thus, near the village of Kamyshenka, where the Medvedevka, Revnevka, and Kamyshenka rivers flow out of the mountains, we encounter something like a recess with a fairly steep scarp of the mountain façade, which ends east of the village of Kamyshenka; farther on the mountain façade, as if advancing onto the steppe plain, projects into the steppe and extends as far as the village of Solonovka.

When viewed generally from the mountain façade toward the north, there opens before us a picture of an even, slightly hilly steppe receding northward. On closer examination it proves to be rather dissected, and here and there individual hills rise above its general surface. Thus, 10–12 km north of the village of Mikhailovskoye, a rounded hill composed of eruptive rock rises above the steppe plain, and northeast of the same village, far out on the steppe plain, other mountain remnants can be seen.

Other characteristic elements of the dissection of the steppe plain are ridge-like watershed crests. They begin directly from the mountain façade, stretching far northward into the steppe and aligning with the general direction of the drainage arteries.

We observe such ridge-like watershed crests along the left side of the Anuy River from Karaulnaya hill; here this ridge is covered by loose eluvial-deluvial deposits, for here and there along the road from the village of Antonyevskoye to the village of Mikhailovskoye small gravel of lilac shales and greenish-gray sandstones is occasionally encountered on it. Then, we encounter the same kind of ridge on the watershed section between the Solovykha and Kamyshenka rivers and their tributaries—the Medvedevka and Revnevka rivers. Finally, most distinctly expre—

we observe a grassy ridge on the interfluve of the Kamyshenka and Solonovka rivers.

To characterize the geological structure of the steppe plain, we shall first of all present the factual observational data from the route from the village of Mikhailovskoe, situated at the facies, to the Kudrikha River, located 12 km north of the village of Mikhailovskoe. Here the steppe plain is composed of greenish-gray metamorphic and strongly kaolinized shales, whose age we determine as Lower Silurian, since they differ in no respect, either in their composition or in the elements of their occurrence, from the corresponding metamorphic sequence that we record in the mountainous part. The Kudrikha River has cut deeply into these metamorphic shales, and it is evident that in this place they are covered only by a soil layer 20–30 cm thick. Then, at the village of Kamyshenka, in the First Department of the Engels Commune, according to the words of a peasant of this commune, I. S. Nechushkin, who took part in drilling a well for water in 1930, the plain at this place is composed of the following loose deposits, from top to bottom: 1) peat with small shells, thickness up to 30 m; 2) blue clay, thickness up to 30 m; 3) fine gruss (thickness unknown); 4) yellow clay; 5) bluish-white, very greasy clay, thickness 9 m; 6) fine pebble gravel; 7) red clay, thickness up to 50–60 m; 8) very fine gruss.

Summing up the foregoing, we may say that the present-day facies of the Altai has an erosional character; if V. A. Obruchev, in Altai Studies (vol. II, pp. 28–30), writes that “above the steppe plain on the southern horizon the Altai Mountains rise like a wall, to a height of several hundred meters,” this is only a general impression. In reality, sharp and large ledges of the foothills are observed only in places where rivers emerge from the mountains, where the rivers, eroding the bedrock, form as it were troughs, which introduce a sharp contrast between the steppe plain and the mountainous part. Such erosional troughs we encounter near the village of Mikhailovskoe, near the village of Solov’yikha, and near the village of Kamyshenka. But the watershed ridges described above do not give a sharp contrast in the transition from the mountainous part to the steppe plain; on the contrary, they soften the northern slopes of the mountains.

1. In the relief of the mountainous part of the Altai we find traces of an ancient peneplain. Namely, if one disregards the rare sharp knolls, which are represented by metamorphic shales, to a greater or lesser extent silicified and therefore well resisting erosion, then the watershed spaces and the summits of the hills are smoothed, and their general enveloping surface seems more or less level. Into the body of this hilly peneplain numerous streams and springs are incised in the form of canyons or, in general, deep valleys, and these have created the modern dissected relief. Moreover, in the southern part of the plateau another, more highly uplifted peneplain is discernible, of which small watershed platforms have been preserved, very convenient for arable fields.

Thus, the modern relief of the mountainous part on our plateau, in all its details, is conditioned by a fairly prolonged and very complex—

history of the hydrographic network, i.e., the relief is conditioned purely by erosional processes. The differing lithological composition of the mountain areas introduces great variety into the existing forms of relief, which is connected with the processes, and hence also with the forms, of selective weathering and denudation.

The possible participation of glacial phenomena in the creation of relief forms is not excluded, since the occurrence, in the headwaters of the Talovka River, of a large granite boulder, which is foreign to the rocks of the basin of this stream, and the absence of nearby granite bodies, allow one to think that this boulder is erratic. However, no other traces of former glaciation could be found on the plateau, unless one counts the small and rarely occurring cirque-like funnels, which are embryos of cirques and, under favorable conditions, could have developed into cirques. Such funnels are encountered along the Talovka River, in its headwaters, on the NE slope, up to 100 m in diameter and up to 20 m deep; in them, on June 14, large patches of snow lay. We also encounter similar cirque-shaped funnels on the watershed of the Solovykha and Kamyshenka rivers in the headwaters of the Berdich spring.

1. The entire investigated plateau is taken up by the system of the Anuy River with its numerous tributaries; the left and principal ones among them are the rivers Tatarka, Talovka, Vyatichkha, and the most interesting, the Slyudyanka River, while the right tributaries are the rivers Solovykha, Berezovka, and Kamyshenka. Thus, the main water artery in the region is the Anuy River, flowing in a meridional direction, in accordance with the prevailing strike of the sedimentary sequence widely distributed on our plateau.

Throughout the extent of the plateau the Anuy River has a rather sinuous character, and the bends not infrequently assume the fairly regular form of square brackets, which is caused by selective erosion by the river: it flows now along the strike of the sedimentary rocks, in accordance with the schistosity, and now across their strike. The valley of the Anuy River is rather deep and well developed by lateral erosion, reaching a width of 1.5 km; its slopes are steep and stony; often they descend to the river as cliffs, precisely where the erosive activity of the river is manifested in a lateral direction.

Throughout the extent of our plateau the Anuy River is accompanied by the first terrace, its width being 1.5 km and its height 2–3 m; however, in places it is replaced by a pseudo-terrace of erosion of deluvial deposits. Beneath a soil layer of 20–30 cm, this terrace is composed chiefly of gray, sandy material, which is irregularly interbedded with layers of well-rounded pebbles of various sizes. In some of its sections, owing to the recent manifestation of bottom erosion by the Anuy River, the terrace has assumed an island-like character, is densely overgrown with willow thickets, and represents a convenient place for apiaries; beautiful meadows also spread out upon it, and after haymaking it is turned into pasture.

In addition to this meadow terrace, we also record higher erosion terraces. Thus, along the left side of the Anuy opposite the village of Berezovka, south of the mouth of the Vyatichkha River, an erosion terrace is visible, with a height of

above the level of the Anuy by 14 m. Somewhat above the village of Berezovka, where the Kalmyk Cape projects, composed of a marly-sandy sequence, this cape consists of two erosion terraces; the height of the first terrace above the level of the Anuy is 70 m, and the elevation of the second above the first is 10–15 m. Still farther downstream from the village of Sibiryachikha, the so-called Sibiryachikha Cape likewise presents two such erosion terraces; we were unable to measure their heights, but one must think that they are approximately the same as at the Kalmyk Cape. It is interesting that here, on the right side of the river, at a height of 70 m above the level of the Anuy, on the eroded surface of the limestone, we encountered well-rounded river gravel.

As for the tributaries of the Anuy River, all of them, with rare exceptions, flow approximately in a latitudinal direction, cutting across the strike of the sedimentary sequence. Their common characteristic features in their lower reaches are narrow, almost canyon-like valleys, with steep, often rocky slopes of 20–30°, whereas the upper reaches of these tributaries are usually broad, with low and gentle slopes, often swampy. Consequently, the new cycle of erosion has affected only the lower parts of the tributaries of the Anuy River.

The southern slopes of the tributary valleys are, as a rule, extremely steep, and at their bases are heaped cones of dejection of deluvial-proluvial material coming from dry ravines, which come to life during heavy downpours; moreover, the cones of dejection, undercut by the stream, create a false impression of terraces. The northern slopes, gentler, are often accompanied by accumulation terraces composed of grayish-yellow loam.

There is no need in what follows to dwell on the description of all the tributaries of the Anuy River, since in their essence and character they do not differ from one another; among them the most typical and interesting are the Slyudyanka and Berezovka rivers.

The Slyudyanka River must be considered separately, since it is of interest in that, emerging from the mountains near the village of Mikhailovskoye, it flows in the steppe along the face directly eastward, then, at the end of the village, turns sharply to the south, cuts into the mountains and, rounding the Karaulnaya hill, with an absolute elevation of 460 m, emerges again into the steppe, where it flows into the Anuy River at the very face, somewhat above the village of Antonyevskoye.

Such remarkable behavior of the Slyudyanka River may be explained by the fact that in the past the river, apparently, flowed in the same direction as it does at present, but in younger rocks, which in the course of geological time were destroyed by denudation; at the same time it must be assumed that the country underwent gradual uplift, thanks to which the river had the opportunity not only to saw through the young formation, but then also to cut into the more ancient sequence, thereby preserving its original direction, and, as we see, it succeeded in doing this. If this kind of explanation is recognized as correct, then it follows that the Slyudyanka River is older, and its valley younger, than those tectonic movements which conditioned the river’s cutting through the more ancient sequence. Thus, the valley of the Slyudyanka River in the described

...in the area has an epigenetic character. It is possible, however, that it belongs to antecedent formations, since we find no clear remnants of loose strata here.

The Berezovka River flows from E to W, across the strike of the strata. In its upper part the river valley has comparatively gentle slopes covered with a grassy mantle. The valley of the river, both in its upper and in its middle course, is considerably swampy, especially in the headwaters, and along its entire length is accompanied by a floodplain terrace averaging 1.5 m in height. This terrace consists essentially of dark-gray silty material, with an admixture of fine rubble from the rocks of the river basin (green-violet shales). From the confluence of the Petrushkin and Listvenny springs to Poruchinskaya Hill, along the left slope of the valley, a second longitudinal terrace is clearly visible, rising 8–10 m above the first. It consists chiefly of grayish-yellow loess-like loam without signs of bedding. At present this terrace is being eroded by the river, and after spring floods the local population from time to time finds bones of post-Pliocene vertebrates in the side of the terrace. Beginning from the mouth of Denisov Spring, the right tributary of the Berezovka River, and down to the very mouth of this river, on the terrace that widens at this point and passes into an alluvial fan, the village of Berezovka is situated. Near the creamery this fan is dissected by a deep and narrow ravine, in which we see the following section from top to bottom:

1) yellowish-gray, loess-like loam, without noticeable bedding, with a fauna of freshwater mollusks. Individual interbeds of loess-like loam are wave-like bent; decayed plant remains are encountered in places. Thickness of the bed up to 15 m;

2) a bed of coarse angular rubble from the rocks of the Berezovka River basin, with an admixture of loess-like material mixed with fine pebbles. Thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.5 m;

3) a bed of coarse angular rubble from the same rocks . . . 0.3 m;

4) loess-like loam, interbedded with fine and coarse rubble up to 20%, thickness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1.5 m;

5) approximately up to 48% sandy-clayey material, up to 50% fine rubble and up to 2% coarse rubble, consisting predominantly of limestone and igneous rock composing Poruchinskaya Hill. Among these beds there occur small lenses up to 10 cm thick of loess-like loam.

On the basis of all the foregoing, we may say that in the area studied by us two later cycles of erosion are clearly outlined; moreover, the last cycle is still in its first phase, and all the rivers are working to deepen their channels. It is interesting to point out that at the end of the preceding erosion cycle the area was under conditions of a dry climate, marked by the wide development of loess-like loams.

III. Green-Violet Formation ($S_1$).

The oldest and most widely developed formation in our area is a sedimentary metamorphosed unit of b. or m. homo-

similar in its lithological composition. It consists chiefly of green, greenish-gray, lilac, reddish-brown shales and sandstones, sometimes somewhat calcareous. Much more rarely we encounter in it now beds, now lenses of marbled limestone, fairly homogeneous in composition, usually light-colored, at times coarsely and at times more finely bedded, and containing no fauna. Fairly characteristic are the sporadically occurring interbeds and lenses of silicilites in the formation. The presence of rare sill-like bodies of metamorphosed basic igneous rocks in this sequence indicates that, at the time of its deposition, there was some volcanic activity.

The green-violet formation in the western part of the sheet may be characterized by the following normal section along the Tatarka River, beginning from its headwaters upward through the formation: 1) green calcareous sandstones with interbeds of sandy shales; 2) gray-green argillaceous-siliceous shales with interbeds of sandstones; 3) green chlorite-sericite platy shales; 4) a horizon of light-gray marbled limestone (15 m); 5) lilac-green-gray chloritized shales with interbeds of green calcareous sandstones; 6) green-gray sandstones with interbeds of green and lilac shales, passing into brownish-red arkosic sandstones.

From this section it is evident that the calcareous element in the formation is subordinate and appears in it either as an admixture of calcium carbonate in the green sandstones, or, still more rarely, as separate beds or lenses of marbled limestone. For example, such a limestone bed was traced by us from the Tatarka River below Glinyany Spring northward: it extends in a meridional direction, crosses Karaulnaya Hill, and farther on passes into the steppe plain, disappearing beneath loose proluvial-deluvial deposits, with a thickness of 10–15 m. In another place, namely in the southwestern part of the sheet, at the confluence of the Kamenushka and Bolshoy Sibiryachenok rivers, we also record a lens of marbled limestone: in a northwestern direction it reaches the headwaters of Poperechny Sibiryachenok Spring, where it apparently pinches out, since farther on we do not encounter it; and to the southwest this lens extends almost to the headwaters of Avdyushkin Spring, a left tributary of the Sibiryachikha River, where it likewise pinches out. Looking at the map, we see that this lens bends along its strike, sharply deviating toward the northwest from the dominant meridional strike of the entire metamorphic sequence.

The limestones of the metamorphic sequence are distinguished by a greater or lesser homogeneity of composition and are readily exploited here by the local population for burning lime.

Furthermore, the metamorphic formation is characterized by the presence within it of silicilites (quartzites), encountered rather frequently. Usually they occur as bedlike lenses or veins of the most variable thickness, from several centimeters to 10 m, and contain magnetite and pyrite in small quantities. This is partly

primary sedimentary rocks of sealing-wax-red color, and partly metasomatic formations. They will be described in detail below.

A characteristic feature of the metamorphic green-violet formation is the presence in it of a large number of quartz lenses and veins. In this formation they occur literally at every step, being completely barren with respect to mineralization, with the rare exception of 3–4 quartz veins located not far from the igneous bodies. All these vein-lenses follow the schistosity, and are often pinched out both horizontally and vertically. It is not superfluous to note that the enclosing shales or sandstones seem to flow around such lenses (Fig. 2). These quartz veins are very inconstant both in strike and in thickness; the latter is measured from cm to 3–5 m. In parallel with this it must be noted that the entire sequence has undergone weak hydrothermal or metasomatism, namely—fine pyritization, calcitization, silicification, and partly epidotization and chloritization. All these metamorphic processes are due to intrusions, some of which are exposed, while others still remain not revealed by denudation.

The upper horizons of the green-violet formation in the western part of the sheet are replaced by coarser-grained, often pudding sandstones, and we enter another formation, which differs rather sharply from the one just described both in its lithological composition and in the presence of organic remains, widely distributed in it. According to a preliminary determination of the fossils, we assign this formation to the lower Devonian; this will be discussed in greater detail in the corresponding chapter. But here it is necessary to note that the relationship of these two formations at this place has not been definitely established by us, since no obvious signs of angular unconformity could be found, and only on the basis of indirect considerations can one admit the possibility of an unconformity, which may have remained unnoticed by us owing to the extremely intense dislocation of both formations along the Tatar section.

The Lower Devonian formation, which in general has a meridional strike, on the eastern side is truncated by a clear tectonic line, along which an upthrust of the green-violet formation onto the Devonian formation took place. The tectonic line runs approximately in a meridional direction, having a somewhat curved character; in the north, near the village of Solovikha, this line turns rather sharply to the northeast, passing beyond the limits of our sheet.

To the east of the tectonic line we again enter the green-violet formation, which also extends as a broad belt in a meridional direction. This part of the formation differs in no way from the western part of the metamorphic sequence characterized by us, preserving the homogeneity of lithological composition, and also maintaining the elements of bedding characteristic of it. In essence, here we have a repetition of the western part of the metamorphic sequence, owing to the indicated dislocation of the upthrust type.

But at the headwaters of the Solovyshenok River, a tributary of the Solovikha, along the spring

To the east we encounter limestone which, beginning from the head of the Pryamoi Chapyzhnyi spring, extends southward to the watershed area and, gradually widening, disappears beneath loose soil formations. We were unable to establish precisely the relationship of this limestone to the green-violet formation because of the heavy turf cover of this locality. But judging by the character of the limestone, it differs from the limestone we encountered in the western part of the green-violet formation, being distinguished by a considerably greater extent, lesser marbleization, and an irregular, moreover weak, schistosity. In addition, farther south, in the upper branch of the Yurtnaia River, opposite the settlement, we encountered fossils in this limestone which make it possible to assign it to \(D_1\).

Tracing the green-violet sequence farther east, we gradually enter its upper horizons, which at first consist essentially of the same material, with the only difference that the sandstones here are coarser-grained. In addition, metamorphism is manifested somewhat more weakly here, since in places one can observe separate irregular bands of relatively fresh rocks, which, apparently, is explained by weaker or entirely absent contact metamorphism in these localities.

On the western slope of Kolpak Hill, along a small spring flowing in on the right into the Revnevka River, it is evident how the rocks of the green-violet formation gradually pass into gray, in places grayish-black marly shales and sandstones with meridional strike and a dip to the E of \(60^\circ\); they are interbedded with small lenses of limestone containing the fauna Calopoecia anticostiensis Bill and Favosites Krasnikovi n. sp., assigned by K. V. Radugin to the upper part of the Lower Silurian.

Thus, in the upper parts of the green-violet formation there appears a marly horizon containing a fauna that quite definitely indicates the Lower Silurian age of this entire formation, which Altai geologists generally assign to the Cambro-Silurian.

Above the horizon of Kolpak Hill described by us, we encounter mylonitized blocks, and then also bedrock outcrops of strongly crushed, breccia-like limestone, with abundant coral and crinoid fauna, of which the whole hill is composed. It must be noted that in the system of the Kamyshenka River, in individual places of this area, we also encounter small fields of the Siluro-Devonian formation preserved from denudation.

Farther east, approximately from the middle course of the Berezovka River, a tributary of the Kamyshenka, to its headwaters, there stretches a belt of steeply dipping Lower Devonian formation, consisting of limestone, marls, and conglomerates. This formation is apparently cut off by a steep tectonic line, along which the green-violet sequence was thrust over the Siluro-Devonian.

For the petrographic characterization of the green-violet formation we shall give here the microscopic description of only some of its most widespread elements.

1. Clayey-siliceous sericite schists. The main mass in this rock is represented by clayey sericitized material—the cement—and by angular grains of quartz, not infrequently grouped into separate accumulations. Black specks of organic matter in the form of graphite are scattered through the rock in rather large quantity. The rock is cut by a system of fissures filled with quartz showing cloudy extinction. More siliceous rocks are encountered occasionally, in which the rounded outlines of radiolarian shells are visible.

2. Chlorite-sericite pyritized siliceous schist. The mineralogical composition of this rock is quartz with ragged outlines, cemented by finely clayey material, chlorite, sericite, and black specks of graphite, unevenly distributed through the rock.

3. Lilac siliceous-clayey schist. The main mass in this rock consists of fine clayey material of a brownish-lilac color, with a large amount of finely disseminated organic matter. In addition, the rock is cut by a system of fissures running in the most varied directions and often intersecting one another. These fissures are filled with quartz showing cloudy extinction. Along these same fissures calcite penetrated, as though deposited upon the quartz. It is quite evident that both the quartz and the calcite in this rock are not products of recrystallization, but are minerals of hydrothermal formation.

4. Brownish-gray calcareous chlorite-sericite sandstone. This sandstone consists of angular grains of quartz and feldspar, often with ragged outlines and with clearly expressed polysynthetic twinning. The cement consists of fine-grained quartz-feldspar material, calcite, chlorite, and sericite. Grains of an ore mineral are frequently encountered.

5. Marbleized limestone. As already indicated, limestone in the green-violet sequence occurs now in the form of beds, now in the form of lenses. It is usually of a fine-grained variety. Its color is either dirty gray or milky white, with a greenish tint, and it has a saccharoidal structure. Under the microscope the limestone shows its homogeneous fine-grained structure. As impurities it contains grains of quartz with noticeable cloudy extinction and black specks of organic matter.

6. Schistose diabase. The rock was encountered along the Tatarka River below the mouth of the Pashin spring. It is characterized by a fine-crystalline structure of secondary origin; in it, separate areas of albitized polysomatic plagioclase have been preserved. In general, the rock, besides albite, includes: 1) titanite, formed at the expense of decomposed titaniferous augite, 2) green hornblende in irregular prisms with split edges, 3) chlorite, 4) epidote, 5) sericite. The rock has not retained its original appearance and structure, having been strongly altered as a result of lateral pressure and subsequent recrystallization, apparently under the influence of emana-

tions. In any case, it can be established that it was formed from diabase, which apparently constitutes a sill in the given formation.

7. Ferruginous silicilite. This rock is one of those characteristic of the green-violet sequence; it occurs in it rather often in the form of interbeds or veins of the most varied thickness, generally conforming to the direction of schistosity of the formation; it has a jasper-like appearance and is usually colored sealing-wax red.

Under the microscope the rock consists predominantly of quartz, now of fine-grained, now of coarse-grained structure. The quartz grains have undergone cataclasis, possessing undulatory extinction oriented in one direction. This is especially clearly visible in the large quartz grains. In addition to quartz, the rock is enriched to a greater or lesser degree in ore minerals of the magnetite and hematite type; in one of such veins, encountered by us on the watershed ridge at the heads of Denisov and Listvenny creeks, which are right tributaries of the Berezovka River, visible gold was found during processing of the material, though in a small quantity. In general, from a number of specimens it can be definitely established how the primary, undoubtedly sedimentary, very fine-grained ferruginous silicilite is gradually cut by quartz veinlets, with parallel recrystallization of hematite, and then is transformed into a poor quartz-hematite ore, part of the ore minerals of which partly entered with emanations either from the lower parts of the same horizon or from magma. After its formation this rock was subjected more than once to pressure, which—among other things—broke it up into lens-shaped bodies.

The entire metamorphic green-violet formation was repeatedly subjected to intensive dislocations, as a result of which it was assembled into steep folds of several orders. The beds of the formation are set almost on end, are intensively schistose in the direction 320–350° with a predominant dip to the E at an angle of 70–90°, so that the general strike of the formation remains meridional. Along with intensive and repeated dislocation, the green-violet formation was subjected to varying degrees of metamorphism, both regional and contact, as evidenced by the presence in it of intrusions of granite and diorite, as well as small extrusive bodies of other rocks, which caused one or another contact alteration. In addition, the presence in this sequence of fairly frequently occurring silicified areas, pyritized and in general metasomatized to one degree or another, allows one to think that at depth in this sequence we also have magmatic bodies which apparently caused both silicification and other metasomatic phenomena, as well as pyritization, but which have not yet been exposed by denudation. Under the influence of regional metamorphism the green-violet formation underwent now a rather fine, almost slaty, now a coarser and irregular schistosity, depending on composition; moreover, on the planes of schistosity we usually encounter new formations in the form of chlorite and sericite, more rarely and in lesser amounts epidote, po-

as a result of which the shales acquired a silky-ribbed appearance on the cleavage planes.

Along with the more regular vertical cleavage, the green-violet sequence also underwent other types of dislocation, in the form of horizontal shear fractures that cut the quartz veins, whereas the crumpled cleavage, which broke the shales into powder along individual zones, passes around these quartz veins, indicating its more recent origin. The more regular vertical cleavage, together with horizontal shear fractures in the massive sandstones, produces a typical rectangular jointing, which is especially well expressed in the greenish-gray and lilac sandstones so well developed in the middle and upper reaches of the Solovykha River.

In addition to all the above, the green-violet formation is characterized by the presence within it of peculiar tectonites (Figs. 3 and 4), with excellently expressed slickensided surfaces, turned, in most cases, with their convex side toward the SW, which also indicates the direction of the tectonic forces that acted from the SW. The quasi-pebbles of the tectonites are widespread in the green-violet formation and may sometimes produce a false impression of conglomeratic horizons. At the same time, in this ancient formation we rather often encounter microthrusts, usually of small amplitude, measured in centimeters.

Given the complex tectonics of the area, it is very difficult and probably even impossible to establish the thickness of the formation described, since it is broken by several systems of cleavage cracks that have obscured the elements of its bedding. In any case, it must be supposed that, since in moving from W to E we encounter ever newer—namely, higher—horizons of the green-violet formation, its thickness is very considerable, measured in kilometers.

IV. Siluro-Devonian formations.

The next major formation in age in our area is the Lower Devonian, which is fairly widely distributed, having been encountered within the field of development of the green-violet sequence in the form of broad belts elongated in a meridional direction.

For some convenience, we give each of these belts a separate name. Thus, the far western belt, extending along the Anuy River, beginning at the village of Sibiryachikha to the village of Berezovka, then including almost the whole of Denisov Creek (right tributary of the Berezovka River) and a considerable upper part of Ganin Creek (tributary of the Anuy), and continuing farther north through the village of Solovykha, is named the Anuy-Ganin belt. The eastern belt, situated in the system of the Kamyshenka River and, chiefly, in the upper course of its right tributary—the Berezovka River, is named the Kamyshenka belt.

It should be said that both belts, on the west and on the east alike, are bounded by zones of disturbance, to one degree or another by us

established, apparently representing grabens formed as a result of rupture of continuity, probably during a repeated plicative process that folded this sequence together with the underlying green-violet formation, already rigid by that time. Let us dwell on the characteristics of each of these belts.

a) The Anuy–Kaninskaya belt, elongated in a meridional direction, has the following section along the right bank of the Anuy near the village of Berezovka (from bottom to top): 1) reddish-brown, ringing sandstones, with interbeds of green-gray shales, up to 1 km thick¹; 2) green marly shales—40 m; 3) gray, thin, marbled limestones with rare fauna; 4) greenish-gray marls; 5) conglomerates with pebbles of silicified rocks up to 15 m; 6) green marly shales with interbeds of green-gray sandstones—280 m; 7) green-gray calcareous sandstones with interbeds of marls—200 m; 8) massive limestones (reefs) with abundant fauna of corals and crinoids.

The entire sequence of the belt was subjected to repeated tangential pressure, although less sharply than the Lower Silurian sequence. In any case, it is gathered into steep folds of almost meridional direction, often of an isoclinal order, with the beds set steeply, almost on end, with a prevailing dip to the east at an angle of 70–90°. Alongside folds of the first order, we also encounter smaller folds in it, and sometimes one may observe disharmonic folding with peculiar fine cleavage and corrugation, which is quite natural, since this sequence is not homogeneous in its lithological composition. Limestones and sandstones, in the form of more or less thick deposits, undoubtedly played the role of those competent beds that forced the marly formations into the indicated fine cleavage and corrugation, as a more yielding mass.

Alongside folding, the Lower Devonian sequence underwent sufficiently pronounced, though not as complex as in the Lower Silurian formation, jointing close to a meridional direction; this jointing manifests itself differently in different cases: sometimes it is finely and regularly lined, observed in clayey shales; sometimes coarser and more irregular, corresponding to more coarse-grained sandy formations. We often encounter pencil-like parting, for example, along the left bank of the Anuy below the village of Sibiryachikha, in a rocky exposure of dark-gray calcareous sandstones and shales. Elsewhere, on the right bank of the Anuy, near the village of Berezovka, lilac-brown sandstones, alongside the general strike of the jointing NW 345°, give a classic ribbed surface. Such pencil-like, and sometimes also ribbed, parting is caused by the noncoincidence of bedding with jointing. It should also be noted here that for this formation, as for the Lower Silurian one, the presence in it of tectonites with quasi-

pebble rock consisting essentially of smoothed fragments of sandstone and limestone. The sizes of such tectonitic fragments vary greatly—from 0.5 cm to tens of cm in cross-section, and in limestones they are sometimes measured even in meters (Fig. 5).

The origin of the tectonites is as follows. In the mass we have rocks with differing resistance to pressure, as a result of which the clayey shales were finely schistose, whereas individual interbeds of sandstone within these shales, being less yielding, were crushed into fragments, which were displaced and at the same time rounded. The same thing occurred with individual limestone beds. Such a picture, complicated moreover by an innumerable number of micro-overthrusts, sometimes creates the impression of conglomeratic horizons.

Let us dwell further on the description of the limestones and their relations with the marly rocks. Limestones in this formation often occur in the form of more or less rounded or lens-shaped blocks, which appear as if pressed into the marly shales. Sometimes the limestone seems to lie discordantly upon the marly shales. In reality, we have a single formation in a varied lithological expression. We observe such a picture, for example, along the right bank of the Anuy, a little below the village of Sibiryachikha, where on the crests of the green marly shales (very similar in appearance to the Lower Silurian ones), and also within them, separate limestone areas occur, the fauna of which is identical with that of the shales containing limestone. From Fig. 6 it is evident that here we apparently have remnants of the cores of small synclines with an axis plunging northward, as well as tectonite. That not only limestone but also sandstone could have been pressed into the marly shales here is indicated by Fig. 7.

In another case, in this formation the limestone appears either as beds or as lenses, and in both cases their thickness varies greatly; everywhere the alternation of limestones with marls is noticeable.

In a third case, the limestone appears in the form of rather large fields, now widening, now narrowing, but in general oriented in a meridional direction; we refer them to reef formations. They are most widely developed in such areas as the village of Sibiryachikha, near the village of Berezovka, and then farther north and east of the Gannin spring in the area of the village of Solovykha. The boundaries of such fields shown on the map cannot claim precision, since we did not carry out their special outlining. Incidentally, it should be noted that the above-mentioned areas of limestone distribution are characterized by the presence in them of karst phenomena, although small in size. The presence of karst funnels was established by us in the area of the village of Berezovka, somewhat south of Poruchinskaya Hill,^1 and then almost at the very boundary of the facies, west of the village of Solovykha. Along with karst phenomena it is also necessary to point out the presence—

^1 According to the inhabitants of the village of Berezovka, in 1930 a collapse occurred here, accompanied by a rather strong rumble.

similar caves in the limestones developed near the village of Sibiryachikha, which we were unable to examine, and also in the limestones near the village of Berezovka south of Poruchinskaya Hill, where these caves reach 20 cubic meters in volume.

Further, let us dwell on the description of the section of the formation along Gannii Creek, since it is of interest in that here we have a well-expressed brachiopod horizon. The section along Gannii Creek is given by us from west to east, approximately from the place where the creek makes a sharp turn to the east and up to the head of this creek, and has the following form (from bottom to top): 1) grayish-green calcareous sandstones and shales; 2) grayish-white limestones with rare remains of crinoid columnals; 3) green sandstones with interbeds of shales; 4) yellow-brown sandstones with brachiopod fauna; 5) green-gray marly shales; 6) limestones containing coral fauna; 7) yellow-brown sandstones with a large amount of brachiopod and algal fauna; 8) light-gray limestones, apparently cut off by a fault fissure.

From the section presented we see that the rocks composing the basin of Gannii Creek, in their general aspect, do not differ especially from the rocks given in the section along the Anui and apparently are only the higher horizons of the same Lower Devonian formation. The degree of dislocation of this area remains approximately the same as in the entire sequence, with the sole difference that at the very head of the creek the yellow-brown brachiopod sandstones have a schistosity strike of 330° with a dip to the east at an angle of 80°; farther down the creek the schistosity sharply changes its strike direction to 25–35°, which is maintained as far as the place where the creek turns sharply eastward. This kind of change in the direction of schistosity can be explained by purely local conditions of the manifestation of dislocation, since in another place, in the lower reaches of the Solovikha River (left), we encounter the same brachiopod sandstones, but already with a meridional direction of schistosity.

b) The Kamyshen belt differs somewhat from the Anui–Gannii belt just described; its most essential distinction is the absence of yellow-brown sandstones with brachiopod fauna, very characteristic of the uppermost horizons of the above-mentioned belt, and also the fact that in this belt there is a considerable quantity of conglomerates containing limestone pebbles with abundant fauna, chiefly corals and bryozoans; among them Halysites was encountered.

In the further description of the Kamyshen belt we shall have to distinguish the Kamyshen belt proper and its western sector, which will include Kolpak Hill and other small outliers of the Upper Silurian formation.

The Kamyshen belt proper, being elongated almost in a meridional direction, represents a complex syncline, complicated in its marginal parts by disjunctive disturbances. True, we were unable to observe clear tectonic boundaries here, but the sharp change of the rocks composing this belt with the surrounding rocks,

belonging to the Lower Silurian formation, permits such an assumption to be made.

Lithologically, the Kamyshenka belt proper is composed chiefly of whitish-gray and dirty-gray limestones with a rarely occurring coral fauna, green and greenish-gray marly shales, lilac-brown and greenish-gray sandstones and conglomerates.

The limestones in this belt behave rather inconsistently. In places we encounter their strong development. For example, beginning from the fork of the Berezovka River and up to its middle course, where apparently the western tectonic boundary passes, the limestone sequence widens, assuming a somewhat elongated form close to the meridional direction. Here the limestone is recrystallized, rarely contains a fauna of favosites and remains of crinoid columnals, and is often healed along fractures by secondary calcite veinlets. Elsewhere the limestones are thinly interbedded with yellowish-green-gray and lilac-gray shales. The strike of such beds is NW 345°, dipping to the E at an angle of 40°. Finally, 3–4 km east of the village of Kamyshenka, on the northern slope of the Altai facies, we observe a coarser interbedding of limestone with grayish-yellow sandstones, often conglomerate-like, striking NE 10° and dipping to the E at an angle of 80°. The thickness of the limestone beds here reaches 100 m. We did not encounter fauna in them. Such beds are repeated here quite often, which may serve as some indication of fine folding in this sector.

Let us turn to the description of the conglomerates, which occur most frequently above the fork of the Berezovka River. They are especially well represented along the left branch of the Berezovka River opposite the Verkhne-Berezovsky settlement, by the road itself, where we encounter large outcrops of conglomerate. It consists chiefly of pebbles of gray sandstone, up to 20 cm across, of subrounded pebbles of reddish and gray limestone, with an abundant coral fauna of Favosites and Halysites and other forms, as well as of well-rounded pebbles of silicified rocks colored green, gray, black, and red, with pebble sizes from 0.5 to 1–2 cm in diameter. The cement of the conglomerate is gray, sandy, ranging from fine- to coarse-grained in structure; the grains of the cement consist of the silicified rocks mentioned above. Interbedded with the conglomerates is sandstone, gray and green in color when weathered. The strike of the bedding is NE 15°, dipping to the W at an angle of 75°. The thickness of the conglomerates is about 20 m.

Proceeding farther east, 0.5 km from this outcrop, we again encounter a bed of conglomerate, whose cement is more greenish in color, while fauna is more rarely found in the limestone pebbles. The attitude elements of this bed remain the same.

Fifty meters to the east there is again a bed of conglomerate, of approximately the same character, but its attitude elements have changed, namely the strike here is NE 30°, dipping to the E at an angle of 35°. It is also characteristic of the latter conglomerate bed to note that along the strike it passes into conglomerate-like sandstones.

An interesting question is the age and conditions of formation of the conglomerates described. A limestone pebble from the first outcrop contains Halysites. It must be said that B. F. Speransky, in an adjacent part of the Altai, found in the marls of the upper horizon of the Upper Silurian a large quantity of Halysites and other fossils¹). Therefore our conglomerates are younger than the marly horizons established by Speransky and may signify the Lower Devonian.

c) Western sector of the Kamyshenka belt. This sector may be characterized as follows. On the western slope of Kolpak Hill there occur marly horizons containing the fauna Calopoecia anticostiensis Bill and Favosites Krasnikovi n. sp.²), which indicates the Lower Silurian age of these marly shales. As for the limestones, strongly developed in the upper part of the hill, which contain a rich coral fauna, in general appearance they are assigned to the Upper Silurian. The presence of mylonitized blocks of this same limestone and, in general, the strong fragmentation and breccia-like character of this limestone in its bedrock outcrops, which are in contact with the Lower Silurian formation, as well as the sharp bending of the marly shales at this place, allow us more or less definitely to trace here a crumpling zone between these formations, formed as a result of disharmonic folding.

Eastward, the limestone of Kolpak village is replaced by a greenish-gray, coarse-textured sandstone, fairly fresh in general appearance, with clearly expressed bedding of 10–20° and with a dip to the NW at an angle of 40°, indicating a comparatively gentler attitude of this formation. In the sandstone there are fairly gentle joint surfaces, along which slipping took place from S to N, with the strike of the slip planes 360° and a dip to the E at an angle of 70°. Both from the west and from the east this sandstone is underlain by strongly fractured and recrystallized limestones, so that in this displacement we apparently have the remnant of the core of a syncline of the formation under consideration.

Farther along the Kamyshenka River, somewhat below the mouth of the Berezovka River (a tributary of the Kamyshenka), on the western slope it is visible how the same limestone rests unconformably on the heads of green-violet shales. In the limestone, bedding is observed with a strike of 340° and a dip to the E at an angle of 70°. It is characteristic to note that in the lower part of the slope, almost above the very channel of the Kamyshenka River, in a steep exposure, a rock crops out consisting by 50% of pieces of quartz, rounded to one degree or another, while the remaining mass—the cement—is represented by red-brown sandy material. Under the microscope the quartz pieces are strongly fractured. Fig. 8 indicates the relationships of the limestone and mylonite with the green-violet formation. It is possible that it is an ancient deluvium, upon which

¹) B. F. Speransky. Preliminary report on investigations in the NW 1/4 of sheet 14, row X, 1929 (manuscript).
²) Determination by K. V. Radugin.

then the Upper Silurian–Middle Devonian sea transgressed. This question remains open for the time being, since we do not have sufficient data for its final resolution.

It must also be noted that in the system of the Kamyshenka River, in certain places within this area, we encounter small fields of the Silurian–Devonian formation that have been preserved from denudation. Thus, according to the data of collector O. E. Novitsky, who traversed a route along the Izvestkovyi Creek, a left tributary of the Kamyshenka, it is evident from the outcrops he described that the summits of the hills in this place are composed of limestones, while beneath them appear sandstones characteristic of the green-violet series. In another place, somewhat above the mouth of the Bolshoi Creek, a right tributary of the Kamyshenka, in an outcrop we encounter a cap of limestone with a sparse coral fauna, from beneath which, lower down the slope, there first appear fragments of green-violet shales, and then bedrock exposures of the same shales. Such a picture clearly indicates the overthrusting of limestone of the Upper Silurian formation onto the Lower Silurian, with disruption of the natural boundary between these formations.

In conclusion, we emphasize that both the western Anui–Ganin belt and the eastern Kamyshenka belt, as well as the middle wedge-shaped area, which we assign to the Lower Devonian, underwent intense and, moreover, repeated dislocation, as a result of which this formation was gathered into steep folds, not without ruptures of continuity, along which structural grabens formed in individual sectors.

V. Intrusive Formations

On the surveyed map sheet, among the sedimentary formations described, there occur bodies of igneous rocks strictly subordinate to one or another formation. Their different composition and structure, as well as the different forms of occurrence of these intrusive rocks, make it possible to divide them into three groups and distinguish the following formations: 1) granite, 2) quartz-albite porphyry, and 3) monzonite.

1. Granite Formation

This formation is located in the SE corner of the surveyed map sheet and consists, as it were, of two bodies which, beyond the limits of the sheet, apparently merge into a single body.

The southern body is represented by porphyritic granite, the main mass of which is veiled by mattress-like blocks of aplite-like granite.

In terms of landforms, and also hypsometrically, this area differs from the relief of the sedimentary green-violet series, which the intrusive body cuts through. This is quite understandable, since granite, being more resistant to the agents of weathering and erosion, yielded more slowly to their action and thus acquired a relatively higher position above the sedimentary series. The varied weathering forms of the Altai granites, which have not once found their ...

its description in the literature on the Altai, allow us not to dwell on this question in detail, and we shall confine ourselves to indicating only that our granite is characterized chiefly by a mattress-like, sometimes lenticular jointing, not infrequently crowned by tower-like remnants. It should be noted that the slopes of the Lukovaya and Malaya Rassypnaya hills, composed of granite, are covered by large talus accumulations of blocks of aplite-like granite and, as a rule, are wooded, which makes the area rather inaccessible for investigation.

The porphyritic granite is light-colored, of medium- to coarse-grained texture, with porphyritic segregations of gray, sometimes smoky quartz, the grains of which reach \(1 \times 0.5\) cm, and of feldspar, of approximately the same dimensions as the quartz. Among the dark-colored minerals, biotite is essentially present; its flakes attain small sizes, measured in tenths of a centimeter. Muscovite is admixed with the biotite in much smaller quantities.

Under the microscope, the principal mass is uneven-grained, consisting of quartz and plagioclase, with orthoclase entirely indistinct owing to the metamorphism of the rock. Quartz appears as small isometric grains that are the product of crushing and recrystallization of larger grains. In general, the rock has undergone fairly strong pressure, as indicated by the fragmentation of the quartz grains, as well as by the undulatory extinction of its larger individuals. Plagioclase (oligoclase-andesine) is strongly altered, becoming covered with a dusting of saussurite. A large part of the biotite is represented by a fine-flaky aggregate of secondary origin, the fine biotite sometimes being associated with fine-grained quartz and plagioclase. Sometimes, in the larger flakes of biotite, pleochroic halos are noticeable, although the mineral itself that caused these halos is not visible. Of the ore minerals we encounter only pyrite in the form of small grains, partly altered to limonite.

It should be noted that this granite body is cut by aplite veinlets and dikes of the most varied thickness. These aplites are the product of additional intrusions of the same granitic magma. Aplite-like granite is particularly developed; it is light in color and has a fine and uneven-grained texture with segregations of dirty-white feldspar and quartz. The rock contains a rather large amount of a dark-colored component, accumulating in irregular fine-grained patches. There is a little muscovite in the form of small flakes, distributed rather uniformly through the rock.

Under the microscope, the aplite-like granite shows a panidiomorphic-granular structure with a small number of phenocrysts of alkaline feldspar and quartz. Quartz is usually observed in the form of isometric grains, with noticeable undulatory extinction. The microcline present in small quantity, in the corresponding sections, shows a clearly expressed cross-hatched structure. Plagioclase appears as small laths with fine twin striation, occurring both independently and

and in grains of alkaline feldspar, and also, at times, quartz. Biotite is observed in irregular groups, having passed into chlorite and partly into muscovite. The magmatogenic components are: quartz, microcline, oligoclase-albite, and biotite. Among the new formations that appeared as a result of the pneumatolytic phase of autometasomatism should be included tourmaline, with weak pleochroic colors, in irregular, as it were corroded, columnar crystals, and muscovite. To the thermal phase belong sericite, zoisite, and pyrite, at whose expense limonite was formed as a product of weathering.

The northern part of this formation is likewise represented by the peripheral part of an intrusive body that goes westward beyond the limits of the sheet and was not traced further by us.

It is characteristic to note the difference in relief between the southern and northern parts of this formation. If, in describing the southern part, we pointed to relatively elevated landforms as compared with the sedimentary sequence, then in the northern part we have precisely the opposite phenomenon: namely, the northern part, occupied by intrusive rock, constitutes a lowered area in the form of a basin, the margins of which consist of sedimentary rocks of the green-violet sequence, hardened to one degree or another and therefore hypsometrically occupying a higher position than the intrusive rock.

The composition of the formation of the northern part includes porphyritic granite and its hybrid variety, as well as quartz diorite. Unfortunately, we can say nothing about the contact boundaries of these rocks, nor about the dimensions of their bodies, since this area, owing to the lowered forms of the relief, is masked by a soil cover and is entirely under arable fields. And only the small distances between the outcrops from which samples of these rocks were taken make it possible to say that the hybrid variety of granite, as well as the quartz diorite, are apparently comparatively small intrusive bodies, being situated in the peripheral part of the porphyritic granite, which is the principal rock in the formation described.

The porphyritic granite does not differ from the rock described above. The hybrid granite is macroscopically distinguished from the porphyritic granite by a darker coloration, owing to a noticeable amount of biotite, which is grouped into separate accumulations. In the phenocrysts there is feldspar. Under the microscope the porphyritic character of the rock is conspicuous, the phenocrysts being rather large prisms of zonal plagioclase, corroded along the periphery. The groundmass consists of quartz with undulatory extinction, plagioclase, and slightly perthitized orthoclase, with a more or less noticeable quantity of biotite flakes, usually corroded and containing pleochroic halos, and also gathering into accumulations which, evidently, give the rock a melanocratic appearance, having formed, one must suppose, at the expense of assimilation of the country rocks. This rock, like the preceding ones, underwent slight cataclasis with subsequent metasomatic changes, here—however—not sharply expressed.

Under the microscope, quartz diorite appears to consist essentially of plagioclase laths and hornblende prisms, the latter having everywhere recrystallized into pale actinolite, not infrequently with ragged forms, with the separation of a small amount of fine-grained ore; in the interstices there is a little xenomorphic quartz, with slight undulatory extinction. As a metasomatic manifestation, besides the actinolitization of the amphibole, slight saussuritization of the plagioclase should be noted.

From the description of the rocks of the granite formation it is evident that they underwent metamorphism, expressed first in cataclasis, and then in recrystallization, as well as in metasomatism caused by certain emanation processes.

The contact zone around the granite intrusion has a width of 1.5–2 and more km. The contact effect near the granite intrusion was expressed in the recrystallization of green-gray schists and sandstones, with the formation of black, dense biotite hornfelses, while with increasing distance from the contact the degree of recrystallization of the rocks decreases. Sometimes in the hornfelses one can observe banding, which may have been due to the primary heterogeneity of the structure of the original rock, undoubtedly of sedimentary origin. It is also necessary to note the widespread occurrence in the hornfelses of a fine-spotted and sometimes nodular texture.

A typical hornfels under the microscope appears as a fine-grained quartz-biotite mass with grains of ore or graphite, and also with a large number of prismatic segregations of feldspar, forming homogeneous crystals in these prisms, strongly, however, veiled by the finest inclusions of quartz grains and dark pigment. In places these formations have more or less rounded outlines, and they might be taken for chiastolite or cordierite, but transitional forms, and sometimes distinct polysynthetic striation, indicate the feldspathic composition of these original crystalline forms, which impart to the rocks a macroscopically nodular character.

It must be supposed that the contact zone extends more widely than is shown on the map, but here we find ourselves in a difficult position, since at times it becomes impossible to distinguish the processes of contact action of this intrusion from the hydrothermal metamorphism caused by a later intrusion, because in both cases the rocks become darker and more compact.

2. Quartz-albitite-porphyry formation.

The rocks of this formation deserve special attention, since with their intrusions, in our opinion, are connected the quartz veins and ferruginous formations so widespread among the green-violet formation. Quartz albitite-porphyries occur in various parts of the green-violet sequence, being represented in the form of dikes and stocks. Thus, at the head of the Berezovka River (right tributary of the Anuy), we recorded 4 dikes of quartz albitite-

porphyry. They occur in green-violet schists and sandstones, fully conforming to the direction of schistosity and being elongated in the meridional direction. In this direction they can be traced for up to 2–3 km and more, reaching a thickness of from 10 to 30 m. They are usually divided by two jointing cracks: one of them runs in a vertical direction, coinciding with the direction of schistosity, while the other jointing passes in a horizontal direction.

Macroscopically, a typical quartz albite porphyry is a light grayish-green, fine-grained rock in which small phenocrysts of quartz and feldspar can be seen. The rock, apparently, has been subjected to pressure, for the hydrous oxides of heavy metals, spreading along cracks, give it a banded appearance.

The microscope shows that the most widespread representative of this formation is indeed quartz albite porphyry. The main mass of this rock consists of a rather fine-grained aggregate of quartz and feldspar; the phenocrysts are also represented by them, with quartz standing out especially, sometimes forming regular crystals of various sizes. It is interesting that the small quartz phenocrysts are surrounded by a rim of granophyre. The rock has undergone distinct pressure and subsequent intense sericitization, which especially affected the feldspar, recognizable as albite only in a few preserved areas.

Varieties of quartz albite porphyry are occasionally encountered that contain, among their segregations, a noticeable number of stacks of biotite flakes, usually bleached.

Finally, there is a variety of the rocks of the formation that consists essentially of albite and has a bostonitic character.

This intrusion took place after the principal schistosity of the green-violet formation, according to which its bodies are oriented, and undoubtedly after the granite intrusion, for the dikes of albite porphyry are found now near the contact zone of the granite massif, now at a considerable distance from it, while having an entirely different facies character.

Let us note that quartz veinlets occur in the bodies of this formation.

3. Monzonite Formation.

The eruptive rocks of this formation are represented essentially by quartz and quartz-free monzonite porphyries and by quartz augite diorite porphyrite. These rocks are widely distributed among the sedimentary sequence of the Lower Devonian formation, which forms part of the Anui–Kanin belt. Cutting through it, they form bodies, sometimes fairly large and sometimes smaller, in the form of stocks and dikes. Not infrequently such bodies, as is evident from the geological map, are grouped together, forming, as it were, clusters representing a series of pipe-like bodies closely situated relative to one another.

Bodies of the monzonite formation are the product of comparatively young tectonic movements in the Altai, since in the area studied they cut through Lower Devonian deposits.

The monzonite formation is represented by the following rocks.

Quartz monzonite porphyry is, macroscopically, a grayish-green, fine-grained rock, often of compact structure. Within the groundmass, in the form of elongated columns and in large quantities, a dark-colored component is present. Schlieren-like formations of the same composition are often encountered in the rock; their dimensions are usually small, reaching \(1 \times 2.4 \times 5\) cm.

Under the microscope the groundmass of the rock is fine-grained, consisting of completely altered feldspar and grains of quartz, and is usually filled with zoisite, calcite, and a chlorite-biotite mass. Within the groundmass, in the form of elongated laths and narrow prisms, there is plagioclase with fine polysynthetic twinning striation, strongly affected by calcite and sericite; there is also hornblende, altered into chlorite, and rhombic pyroxene, which has begun to be replaced by a biotite mass preserving the outlines of the dark-colored mineral; there was also biotite, completely chloritized.

The rock is characterized by the following strongly developed secondary minerals: a) pyrite, which is quite abundant; it occurs either as small cubes or fills cleavage cracks, apparently of pyroxene, as well as of biotite. b) A chlorite-biotite mass, observed in large quantities; it is finely smeared over the thin section and is most often concentrated along the periphery of the dark-colored component; the chlorite probably formed at the expense of hornblende and biotite, since in some cases it preserves the cleavage of biotite. c) Clinozoisite, most often occurring as elongated grains grouped in separate parts of the thin section, occupying the places of formerly existing dark-colored components. d) Calcite, as a rule, in fairly large quantity; under the action of hydrochloric acid on the rock it effervesces; it also, chiefly, fills either the dark-colored component or grains of feldspar. e) Rarely occurring grains of apatite, which are somewhat rounded and are associated with feldspar.

In other bodies of this formation, according to microscopic analysis, some rocks contain no quartz, while otherwise preserving the same composition and structure as the quartz monzonite porphyries; we call them quartz-free monzonite porphyries.

Quartz augite-diorite porphyrite was encountered by us along the Berezovka River (a tributary of the Anuy); it composes Poruchinskaya Hill, situated on the left side of the Berezovka River. On the opposite side of the valley of this stream we encounter the quartz monzonite porphyry described above. Macroscopically, the quartz augite-diorite porphyrite differs from the quartz monzonite porphyry only by its grayer coloration. Under the microscope it is established that the groundmass of the rock is fine-grained, consisting, apparently, of feld-

of this spar, being heavily filled with biotite mass and calcite. Within the main mass there are observed, as it were in the form of clusters, grains of water-clear quartz with corroded edges. Among the dark-colored minerals, abundant augite and hypersthene are present, with optical properties clearly expressed for them. An extremely large place in the rock is occupied by zoisite, in the form of short-prismatic crystals with the porcelain-like tint characteristic of this mineral, which appears upon darkening of the mirror. The rock has undergone rather strong autometasomatism, which found expression in zoisitization, chloritization, calcitization, and saussuritization, with the formation of ilmenite probably at the expense of titanite.

Summing up the brief description of the monzonite formation, we arrive at the following conclusion.

a) The bodies of the monzonite formation, cutting through the Anui–Ganin belt of the Lower Devonian, are probably the product of comparatively young tectonic movements in Altai.

b) The intrusions of the monzonite formation were not formed in a single episode, as is evidenced by the different differentiation of the monzonite magma, which found expression in quartz and quartz-free monzonite porphyries and in quartz augite-diorite porphyrite.

c) The strong autometasomatism of these rocks is due in part to the pipe-like form of their bodies, along which emanations moved upward with particular ease, altering the rocks of the formation often beyond recognition.

d) The possibility is not excluded that, in the sector of the Anui–Ganin belt of the Lower Devonian, we have the development of diatremes, some of which at one time managed to break through to the ancient surface, while others only approached close to it, forming the original breccias of sedimentary rocks encountered here.

VI. Stratigraphy and Tectonics

In describing the geological formations, we have already indicated the relationships among them, and the presence of fossils in them made it possible to establish their geological age. As a result, the relations of the intrusive rocks to one or another sedimentary formation make it possible to judge also their relative age.

The oldest formation of the area studied is the sedimentary Lower Silurian (green-violet) formation, extending in a WNW—nearly meridional—direction. In its lower horizons it is composed essentially of argillaceous-siliceous shales, then of chlorite-sericite pyritized siliceous shales, marbled limestones of small thickness, lilac-green-gray chloritized shales, green-gray and brownish-gray calcareous-chlorite-sericite sandstones, and also, rarely, of sill-like bodies of basic igneous rocks. In its very uppermost horizons the formation is crowned by gray and grayish-black marly shales and sandstones containing Calopoecia anticostiensis Bill. and Favosites Krasnicovi

n. sp., whose fauna, according to K. V. Radugin, characterizes the upper part of the Lower Silurian. This sequence, as is evident from geological reports—some published, some remaining in manuscript—is widely distributed in Altai and, according to the descriptions of Altai geologists, including V. P. Nekhoroshev¹, has until now been conventionally assigned to the upper part of the Cambro-Silurian. We can now state more definitely that here we are dealing with the Lower Silurian, characterized faunistically.

As regards the thickness of this formation, it remains for us not precisely determined, since the entire formation is intensely dislocated, extremely strongly fractured and schistose, which presents a major obstacle to determining its true thickness. But it may be assumed, if all the disturbances in this formation are taken into account, that its true thickness may prove to be three times less than its apparent thickness, i.e., approximately 5–6 km.

Thus, in the SW corner of the surveyed sheet, the green-violet formation is cut by an intrusion of granite. The presence of cataclastic phenomena in the minerals composing the granite indicates with complete obviousness that the granite body was subjected to strong tangential pressure after its formation. We find it difficult to speak of the form of the granite body, since it enters our sheet only by its eastern peripheral part, but we must note that the contact of this body with the enclosing sedimentary sequence is very steep.

The contact zone formed by the granite intrusion, and reaching a width of 1.5–2 km and more, testifies to the large scale of the intrusive body. This contact effect of the intrusion on the sedimentary sequence was expressed in its complete recrystallization near the contact and in simple hornfelsing away from the intrusive body, with an almost constant manifestation of the spotted and nodular textures of the hornfelses.

It is necessary to emphasize the circumstance that the Lower Silurian green-violet formation was repeatedly subjected to tangential pressure, as a result of which it is extremely strongly fractured and schistose in a NNW—almost meridional—direction, evidently under the influence of E. or W. pressure, which produced both plicative and disjunctive dislocations in this formation. In accordance with the constant change in the mechanical properties of the formation, it reacted in different ways to the repeatedly recurring pressure, as a result of which four types of schistosity were produced.

The first type of schistosity is expressed in the form of very regular and thin, almost sheet-like, schistose parting with a vertical dip. The second type finds its expression in cleavage cracks close to the horizontal direction. This type of schistosity is most often and most effectively encountered in sand—

... in them, forming blocky jointing. To the third type we assign shell-like schistosity, which has crushed the schists into powder along separate zones. And, finally, to the fourth type we assign tectonites. We have dwelt on their more detailed description in the corresponding chapters.

Along with the above-described types of schistosity, the Lower Silurian formation also underwent other forms of disjunctive dislocation, manifested in the form of micro-faults, whose observed amplitude is not great. The fractures of such throws, as a rule, dip steeply to the E.

Next we shall indicate the interrelations of the types of schistosity. These interrelations in the various parts of the given formation appear as follows. Parallel to the vertical schistosity there run quartz veins and lenses, which are enveloped by shell-like schistosity and are cut by horizontal shear cracks. This circumstance makes it possible to outline the following sequence in the order of formation of the schistosity. The first—the most ancient—schistosity will be the vertical one, often finely foliated, and the quartz veins are confined to it. Second in time of formation will be the shell-like schistosity, which goes around the quartz veins. It was followed by schistosity manifested in the form of shear cracks close to the horizontal direction.

By the geological moment when the folded green-violet formation was subjected to denudation processes, probably in connection with new tectonic movements along the jointing that existed by that time, there occurred intrusion of quartz-albite-porphyry magma, which produced small bodies in the form of dikes from 10 to 30 m thick and stocks. With them we associate the formation of quartz veins, lenses, and poor ferruginous quartzites, so well developed in the Lower Silurian formation and described in detail in the appropriate place.

Onto the denuded Lower Silurian formation transgressed the Upper Silurian sea, leaving a predominantly limestone formation, faunistically characterized; it has been preserved only in a few small troughs in the middle part of the sheet, and its fauna is not entirely clear, for which reason this formation is distinguished somewhat conditionally.

Undoubtedly younger is the formation preserved in grabens and consisting of gray-yellow sandstones with a rich brachiopod fauna, as well as of massive reef limestones with a rich coral fauna, interbedded with marls.

We assign to this formation a Lower Devonian age on the basis of the fauna collected by us in this series. This is evident from the following list of fauna, collected at various points of the formation and determined by K. V. Radugin, except for the section along the Ganin spring: Favosites proximus Hall, Siringopora cf. bifurcata Lonsd., Favosites sp., Stromotopora florida var. prima n. var., Cyathophyllum hexagonum, Favosites aff. polymorphus Goldf., Cyathophyllum clarki Schwartz, Cyathophyllum ex gr. C. hexagonum, Heliolites aff. de-

cipiens M. Coy, Favosites Forbesi var. eifeliensis (?) Nich., Favosites sp., close to F. intricatus Barr., Cyathophyllum sp., Coenites lunata Nich. and Hinde, var. major n. var., Striatopora sp., Acervularia luxurians, var. altaica n. var., Pycnostylus (?) sp., Heliolites aff. Nicholsoni Eth., Neofavosites Ussovi n. gen. et sp., Clathrodictyon vesiculosum var.

Moreover, the decisive significance belongs to the brachiopod fauna. This fauna, collected along the Ganin spring, was provisionally determined by L. L. Khalfin, who gives the following list: Strophonella planuscula n. sp., Atrypa reticularis L., Cyrtina heteroclita Defr., Camarotoechia sp., Leptaena Baueri Barr., Spirifer togatus Barr. On the basis of comparison with the richer and more diverse fauna of Medvedev Log¹, he indicates that the deposits of the Ganin spring belong to the upper part of the Lower Devonian.

The transgression of the Upper Silurian, and then of the Lower Devonian sea onto the surface of the Lower Silurian formation, which by that time had been abraded, produced a thick sequence of sediments. Their deposition did not take place in a quiet geological setting, but under probable epeirogenic movements, as evidenced by the rapid alternation of various rocks—shales, sandstones, limestones, and intraformational conglomerates—without noticeable angular unconformities between them.

The next phase of dislocations, the age of which cannot be established from our materials, gathered this entire sequence into steep folds of the same NNW strike as in the Lower Silurian. This is what should have occurred, since by that time the Lower Silurian formation had fully consolidated and thus, during plicative processes occurring in the soft Silurian–Devonian sequence, imposed upon it its own form and direction.

The lateral pressure that resumed after this folding complicated the structure of the Silurian–Devonian sequence, causing in it folding, cleavage, and schistosity of approximately the same character as in the Lower Silurian sequence, with the sole difference that all these processes manifested themselves in it much more weakly. In addition, during the contortion of the formations, the boundary horizons between the lower and upper divisions of the Silurian underwent fragmentation; such interformational disturbances morphologically resemble zones of nappe dragging.

In all probability, the large disjunctive dislocations should also be assigned to this same time; as a result of them structural grabens were formed, now occupied by the Silurian–Devonian. Their meridional direction clearly indicates a W. or E. direction of the corresponding tangential forces.

The reverse-fault disturbances that bounded the grabens on the eastern side were expressed most distinctly. In particular, the eastern boundary of the Anuy–Ganin graben is traced quite clearly

almost throughout its entire extent; moreover, the northern part of the boundary is even expressed in the relief as a result of selective denudation. The angle of dip of the fault cannot be established, but since the line of disturbance in general follows the relief, it may be thought that the thrust is not especially steep. As for the western boundaries of the grabens, as well as the outline of the middle field with the Silurian-Devonian sequence, they are marked only by an abrupt change of formations.

In conclusion it should be noted that, in the Lower Devonian sequence, composed of rocks with different mechanical properties, folding and the subsequent cleavage acquired a disharmonic character; namely, the horizons of flexible and yielding marls underwent the greatest dislocation, in the form of sharp folding and strong cleavage, whereas the limestones preserved a comparatively calm attitude.

Let us turn to the question of the age of the intrusions.

The granite intrusion was studied by us over a small area, so that the form of its body is unknown. If one proceeds from the fractured character of the marginal part of the body, then a Taconic age could be assigned to the granite; but it is more probable that it is Variscan, as everywhere in Altai, where these granites are in places fractured. As for the intrusion of monzonite-porphyries, it may also be of Devonian age.

In the subsequent period there was a series of epirogenic movements in Altai. Of these, the latest were manifested in the creation of the modern Altai Mountains, as well as in the formation of a number of terraces and corresponding deposits described by us.

The tectonic life of Altai is still continuing, being manifested, among other things, in earthquakes¹, which recur here relatively often; thus, during one summer of 1931, namely in the first half of August, we observed two earthquake events: the first on August 11 at 4 a.m. near the village of Solonovka, expressed in a wave-like oscillation of the earth’s surface, and the second—on August 16 at 8 p.m. in the village of Mikhailovskoye, which manifested itself more strongly than the first and was accompanied, again, by wave-like oscillation so strong that a hanging lamp swayed violently, the walls of the house cracked, and it was difficult to stand on the floor; there was great fright among the population and animals. Thus, in terms of intensity the latter earthquake may be assigned to class II on the Rossi–Forel scale. Unfortunately, we cannot say anything about the direction of oscillation of these earthquakes. V. P. Nekhoroshev, giving a summary of earthquakes in Altai, sees the cause of the seismicity “in the uneven block displacement of the ancient folded block—the foundation of Altai—broken into separate sections. Some sections of this block are at present exposed at the surface, while others are concealed beneath a cover of later Paleozoic strata, but the movement of the latter is in direct dependence on the movement of the foundation underlying them.”

General Conclusions

The geological history of the Middle Anuy district and its features in stratigraphic-tectonic terms may be briefly characterized as follows.

1. The most ancient formation of the district is the Lower Silurian metamorphic green-violet sequence, the upper horizons of which have been faunistically characterized.

2. In one of the phases of the Taconic diastrophism it was folded into NNW-trending folds.

3. Subsequent tangential pressures, repeated more than once, produced four types of schistosity in this formation.

4. By the time the formation had been somewhat denuded, renewed movements, whose age in the district could not be established, led to intrusions of quartz albitite-porphyry, in the form of small stocks and dikes that penetrated along the vertical foliation and produced a large number of quartz veins, mostly barren from an ore standpoint, and also caused a fairly considerable metasomatic alteration in the rocks of the formation.

5. The transgression of the Upper Silurian, and then of the Lower Devonian, sea produced a sequence of sediments with a strong development of reef formations in them and with a rich fauna.

6. The next phase of dislocations folded the Silurian-Devonian sequence into steep folds of the same NNW direction as in the Lower Silurian, which, having already hardened by that time, forced the overlying Silurian-Devonian sequence, as the more yielding one, to assume during this dislocation the general character of its structure.

7. In the subsequent period, with the renewal of tangential pressure, alongside foliation, ruptures of continuity occurred in the sedimentary formations, with the formation of structural grabens, in which chiefly the Siluro-Devonian was preserved.

8. The meridional schistosity of the Lower Silurian and Siluro-Devonian formations and the meridional direction of the grabens indicate the constancy of the W. or E. direction of the main mountain-forming movements in the district.

9. With repeated twisting of the sedimentary formations of the Silurian, movements took place between them that disrupted the contact between the formations, which led to forms resembling nappes.

10. The age of the intrusions of granites and monzonite-porphyries could not be precisely established; the most probable age is Variscan for the granites and Devonian for the monzonite-porphyries.

11. Later, significant epeirogenic movements took place in the Altai, which in recent times led to the formation of a mountainous country and, in particular, of various terrace formations.

12. The tectonic life of the Altai continues today, as is evident from the frequent earthquakes occurring in it and sometimes reaching considerable intensity.

Summary

The geologic history of the Middle-Anuy region in the Altai, investigated by the author in 1931, may be characterized as follows:

1. The most ancient formation of the region is composed of the Lower Silurian metamorphic green-violet series, the upper horizons of which contain a fauna characterizing them.

2. During one of the phases of the Taconic diastrophism it was gathered into folds of NNW strike.

3. The subsequent tangential pressures, occurring repeatedly, have caused four types of schistosity in this formation.

4. Toward the time when the formation had been somewhat denuded, repeated disturbances, the age of which could not be determined, led to intrusions of quartz albitite porphyry forming small stocks and dikes. These intrusions penetrated along the vertical schistosity and caused the occurrence of a great quantity of quartz veins, which were for the most part barren, and a considerable metasomatic alteration in the rocks of the formation.

5. A transgression of the Upper Silurian and later of the Lower Devonian seas formed a series of sediments with a great development of reef limestones having a rich fauna.

6. The next phase of dislocations gathered the Siluro-Devonian series into steep folds of the same NW strike as in the Lower Silurian, which had solidified by this time and forced the overlying Siluro-Devonian series, being weaker during this dislocation, to take on the general character of its structure.

7. In the subsequent period, when tangential pressure was renewed, breaks of continuity occurred in the sedimentary formations in addition to lamination, and structural grabens were formed, the Lower Devonian being chiefly preserved in them.

8. The meridional schistosity of the Lower Silurian and of the Siluro-Devonian formations, as well as the meridional trend of the grabens, show the constancy of the west–east directions of the principal mountain-forming movements in the region.

9. During the repeated warping of the Silurian sedimentary formations, disturbances occurred between them and broke the contact between the formations, this being favorable to the development of forms resembling carriages.

10. The age of the granite and monzonite porphyry could not be precisely defined; the most probable is the Hercynian age of granites and the Devonian age of monzonite-porphyries.

11. Later on, considerable epeirogenic movements took place in the Altai, which led in recent times to the formation of a mountainous country and particularly to that of different terraces.

12. The tectonic life of the Altai still continues at the present time, this being evident from frequent earthquakes reaching at times a considerable intensity.

Translated by B. Gootovskaja.

Fig. 1. Schematic profile of the Altai mountain massif from the Butachikha River to the Kudrikha River.
(Constructed from barometric leveling.)

Labels on the profile: r. Butachikha; r. Egorishka; r. Slyudyanka; r. Kudrikha; C.
Scale: vertical; horizontal.
Reference horizon: 300 m above sea level.

Fig. 2.

Fig. 3.

Fig. 4.

Fig. 5.

Fig. 6.

Fig. 7.

Explanation of the figures.

1. A broken quartz veinlet compressed by metamorphic schists.

3–4. Compressed fragments of sandstone in metamorphic schists.

1. A large limestone fragment among marly schists.

2. A large limestone mylonite in a block with schists: (a) limestones, (b) schists.

3. Silicification of coarse mylonite in sandstone (a) and schist (b).

GEOLOGICAL-LITHOLOGICAL MAP

of the Middle Anuy region of Northwestern Altai
(part of sheet 14, row X, of the ten-verst map,
compiled from the data of the geological survey of 1931
by geologist P. F. Krasilov)

Scale: 0 1 2 3 4 5 km

Legend

Section along line A–B–V–G.

1. V. P. Nekhoroshev, Earthquakes in Altai and Their Connection with the Geological Structure.—Vestnik G.K., No. 7, 1927. ↩↩↩↩