Lithology of Upper—Middle Pleistocene Tills in the Far Northeast of European Russia L. N. Andreicheva Institute of Geology, Komi Scientific Center, Ural Branch, Russian Academy of Sciences, ul. Pervomaiskaya 54, Syktykvar, 167982 Russia email: [email protected] Received May 11, 2010
Abstract—Detailed lithological study of tills was carried out at exposures along the Adz’va, Bol’shaya Rogovaya, and Seida rivers—northern tributaries of the Usa River—in the northeasternmost area of the Timan–Pechora–Vychegoda region. The results of grain size, mineralogical, and petrographic analyses cou pled with measurements of orientation of elongated clasts in tills made it possible to substantiate the presence of three moraine horizons. Lithological features of the Pechora (Dnieper) and Polyarny (Ostashkovo) hori zons of tills testify to the input of terrigenous material from Novaya Zemlya. The upper (middle Pleistocene) till, which is also as defined as the Vychegoda (or Moscovian) till, represents clastic material derived from the Polar and Subpolar Urals. Lithological properties have been defined for the stratification and correlation of tills. A chart of lithological criteria has been compiled for the subdivision and correlation of middle and upper Pleistocene tills in the Far Northeast of European Russia. DOI: 10.1134/S0024490212020022
The geological setting of Quaternary sediments and the age of separate Pleistocene horizons in a spacious northeastern area of European Russia are highly debatable issues. The number of glacial horizons in the middle Pleistocene and their stratigraphic affiliation are actively discussed in literature. A substantiated identification of different middle Pleistocene— Dnieper (Pechora, according to the regional scheme) and Moscovian (Vychegoda)—tills also remains a debatable issue. The stratigraphic position of the Shk lovsky (Rodionovo)—the former Odintsovo intergla cial sequence—is also actively discussed so far due to different interpretations of the stratotype section near Station Odintsovo in the Moscow region (Velichko, 1981; Konovalenko, 1985; Maudina et al., 1985; Chetvertichnye …, 1987; Duryagina and Konovalenko, 1993; and others). Therefore, our study of the middle Pleistocene section along the Seida River is very important. This study included the lithological exam ination of tills and the analysis of spore–pollen assem blages from the Rodionovo lacustrine–boggy sedi ments containing a meterscale layer of peats, which were formed under climatic conditions no less warm than at present and are correlatable with the Shklovsky sediments (Andreicheva and Duryagina, 1999). The Rodionovo interglacial sediments are sandwiched between till horizons, suggesting the existence of two middle Pleistocene glacial epochs in the study region. The Moscovian (Vychegoda) till formation in this region is also controversial. According to A.S. Lavrov (Gosudarstvennaya …, 1999), two glaciation centers existed in the Vychegoda time. He identified Novaya
Zemlya as the second center that was synchronous with the Fennoscandinavian one. According to this author, the Moscovian till also represents various gla cial provenances: the Fennoscandinavian provenance for tills in the northwestern and central parts of the Timan–Pechora–Vychegoda region; the Polar and Subpolar Urals for tills in the Far Northeast of Euro pean Russia (Andreicheva, 1987, 1992, 2009; Andreicheva and Duryagina, 1999). Dispute over stratigraphy and paleogeography of late Pleistocene, particularly its postMikulino (post Sulino) segment, as well as timing and boundaries of the Valdaian (Weichselian) glaciers in European Rus sia, has not also ended so far. Several different and suf ficiently controversial models have been proposed for the last glaciation in the Russian Arctic (Astakhov, 1999; Astakhov et al., 1999; Grosval’d, 1999; Man gerud et al., 1999; Pavlidis, 1992; Velichko et al., 2000; and others). The main question is to identify the cul mination period of the last terrestrial glaciation (early or late Valdaian), i.e., to establish which of the two upper Pleistocene glaciers—Podporozh’e or Ostashk ovo (Laisky or Polyarny)—moved further southward. This problem is among the most debatable ones, because some researchers are extremely committed to geochronometric data for the timing of sedimentary bodies. However, they ignore publications devoted to the comprehensive study of sediments by other (palynological, paleomicrotheriological, and litholog ical) methods. The results of our studies related to Valdaian glaci ations in the Timan–Pechora–Vychegoda region
agree with the opinion in (Chebotareva and Makary cheva, 1974) suggesting very insignificant scales of the early Valdaian sheet glacier development. In the Laiskian time, this area accumulated alluvialperigla cial pebblestones and sand with numerous pseudo morphoses, which were formed after the frostshat tered wedges, and other cryogenic structures, as well as fauna of small mammals (hoofed lemmings) with the evolution level index ranging from 17 to 24. The rodent fauna composition (Kochev, 1993) indicates that the paleoclimate was similar to the modern climate: the northern area was occupied by the typical shrubby tundra. The later Laiskian cooling period was marked by a more sever climate and development of the Arctic tundra. The cold climate in the early Valdaian (Laiskian) time did not lead to sheet glaciation in the region. The Laiskian tills have not been detected in numerous sections with the lower Valdaian periglacial sediments dated on the basis of small mammal fossils. We believe that the upper reliefforming and till dominated glacial complex was accumulated in the late Valdaian (Ostashkovo or Polyarnoe) time: the northwestern part of the Timan–Pechora–Vychegoda region was covered with the Fennoscandinavian gla cier, while the northeastern part was occupied by the Paikhoi–Novaya Zemlya glacier. The aim of our investigation was to elucidate the stratigraphic affiliation of till horizons in the Far Northeast of European Russia, reveal the number of glaciations in the middle and late Pleistocene, and determine the positions of provenances during glacia tions based on study of the lithology of tills. METHODS During field works, we made the layerbylayer description of sections and selection of till samples for their examination by various lithological (grain size distribution, mineralogical, and petrographic) meth ods. Spacing of sampling sites was governed by the thickness of sediments and variation of their struc turaltextural features due to the affiliation of tills with a certain facies type. In addition, till samples were taken in places unsubjected to glaciodynamic defor mations and secondary processes. Lithological data are sufficiently informative and reliable for the stratigraphic positioning of tills and their correlation. However, since lithology of tills is closely related to the composition of the underlying rocks, which have a strong influence on the composi tion of local moraines, such lithostratigraphic data were compiled only for the major till sequences. The grain size composition of tills was studied to determine their structural characteristics: average par ticle size (dav) and sorting coefficient (Sс). The sorting coefficient of sediments was expressed via the normal ized entropy, which depends only on the weight of fractions and does not depend on grain size (Belkin and Ryazanov, 1972). The carbonate content in tills
was determined during the preprocessing of samples with 10% hydrochloric acid. The results of grain size analysis were interpreted with bar charts, cumulative plots, and various (ternary, pair, and genetic) dia grams. The mineral composition of fine soil (melkozem) in tills was determined in 0.25–0.1 mm fraction, which is a good proxy in terms of weight and prove nance composition (distal, transit, and local). In order to scrutinize the mineral composition of tills, particu larly to identify minerals of light fraction and micro texturalmicrostructural features of tills, we studied the petrographic thin sections. To identify the provenances, we studied the petro graphic composition of clastic material taken from tills 0.25 m3 in volume (Lavrov, 1976). The content of coarseclastic material (more than 1 cm in size) in the tills commonly does not exceed 5 or 6%. To correlate the major tills, we distinguished the petrogenetic rock groups (Gaigalas, 1979) and then identified the differ entaged horizons of tills based on the quantitative relationships between rock groups. Orientation of elongate boulders was measured in undisturbed sites of tills, i.e., generally in the central parts of a till horizon, to determine the direction of glacier movement. However, numerous observations of the orientation of clasts in the major till sequences show that the orientation is usually constant within a single sequence from its top to bottom. We measured the orientation of long axes in no less than 50 rock clasts at each observation point. The results obtained were presented as rose and pole diagrams. Comparison of maximums of the dominating orientation of rock clasts with the petrographic features of boulders and pebbles makes it possible to pinpoint the glaciation centers during different Pleistocene epochs. RESULTS AND DISCUSSION In coastal exposures along the northern tributaries of the Usa River (Adz’va, Bol’shaya Rogovaya, and Seida), we can distinctly identify three till horizons (Fig. 1). The lower horizon (apparent thickness no more than 20 m) is exposed usually at the base of coastal outcrops. Thickness of the overlying till is as much as 25–30 m. The upper portions of coastal sec tions include an additional (certainly younger) till horizon not more than 10 m thick. All till horizons are composed of apparently indistinguishable bouldery loam: dense, unsorted, nonlayered loam with coarse clastic (usually nonrounded) material of different pet rographic compositions and shapes, as well as clasts of fossil wood and shell detritus redeposited from the underlying primary rocks. The till horizons alternate with layers of the subaqueous clay, silt, and sand char acterized by the development of layered textures and moderate or high degree of material sorting. In some places, the differentaged till horizons are overlapped.
LITHOLOGY AND MINERAL RESOURCES
LITHOLOGY OF UPPER—MIDDLE PLEISTOCENE TILLS
ay aR .
Ro go v a ay
431 K olv
Sh Pechora R.
11 15 22 418 24 27 R. Usa
ap ki n
Fig. 1. Schematic location of sections studied at coastal exposures and their numbers.
The till horizons were subdivided and correlated on the basis of lithological data: grain size composition of melkozem, mineral composition of the fine sand frac tion, orientation of the elongated rock clasts, and pet rographic composition of the coarseclastic material. Based on various lithological characteristics obtained for each till, we determined their stratigraphic affilia tion: we assign the lower glacial sequence to the middle Pleistocene Pechora horizon (pc); the middle sequence, to the middle Pleistocene Vychegoda hori 4 zon ( Q II vc); and the upper sequence, to the late Val 4
daian (Polyarny) horizon ( Q III p). Lithological characteristics of the differentaged till horizons are given below. Grain Size Composition Table 1 shows the grain size composition of tills in the northeasternmost part of the Timan–Pechora– Vychegoda region. 2 The Pechora till (Q IIpc). Coastal outcrops along the Adz’va River show three till horizons separated by intermoraine sediment piles (Fig. 2). LITHOLOGY AND MINERAL RESOURCES
The grain size composition of the Pechora horizon, which is exposed only at the base of sections exposed along the lower 80kmlong river segment, is marked by a high clay content (average): <0.01 mm fraction 43.7%, silt fraction 32.8%, and gravel–sand fraction 23.5%. The average diameter (dav) of melkozem in the Pechora till is 0.014 mm and the average sorting coef ficient (Sc) is 0.16. The average content of carbonates, i.e., material soluble in 10% HCl, is 2.9 %. The high clay content in the Pechora till can be related to the following process: the Pechora glacier actively assimi lated Upper Jurassic (Callovian) clay, which is locally developed as underlying rocks in the lower course of the Adz’va River. This process is also suggested by the presence of numerous outliers of Mesozoic sandy– clayey rocks at the base of coastal outcrops in the lower course of the river. This suggested is supported by the fact that the Pechora till in some sections is marked by a very dark (almost black) color that was inherited from the Callovian clay. However, the high clay con tent in the Pechora till can also be inherited from the Mesozoic sandy–clayey sediments that are wide spread in the Bol’shaya Zemlya tundra (rocks of prox imal redeposition). No. 3
Table 1. Average grain size composition of tills in the Far Northeast of European Russia Area (River)
Carbonate content, %
Average content of fractions, %, size, mm >1.0
Average Sorting diameter, dav, coefficient, Sc mm
Q II pc
Q II pc
Q II vc
Q II vc
Q II vc
Q III p
Q III p
In the Bol’shaya Rogovaya River valley, the seg ment extending from its upper course to the mouth of the Bol’shoe Pyatomboiyu River lacks the Pechora till and includes only two other till horizons (Fig. 3). This is likely caused by the fact that the Pechora horizon commonly occurs at the base of coastal exposures in the lower course of rivers over the entire northern area of the Bol’shaya Zemlya tundra. In sections exposed along the Seida River, the Pechora till occurs as sandy loam characterized by vir
tually constant composition within the horizon. This till represents the coarsest, very dense, and unsorted (Sc = 0.10, dav = 0.038 mm) material in the study region. The content of clasts of the graveltofine peb ble dimension is anomalously high (11.5%); the sand fraction makes up 22.8%, the silt fraction, 38.4%; and the clay fraction 27.3%. The very high density of till is likely related to the anomalously high carbonate con tent (average 12.7%, as much as 17.5% in some places). Pleistocene sediments in the Seida River basin
Fig. 2. Schematic geological section across the Adz’va River valley. (1) Clay; (2) sand; (3) gravel with pebble; (4) till; (5) peat; (6) clasts of mollusk shells; (7) outcrops of Permian polymictic sandstones; (8) outliers of preQuaternary (Jurassic and Cretaceous) rocks. The shape of outliers between sections 415–424 is out of scale. LITHOLOGY AND MINERAL RESOURCES
LITHOLOGY OF UPPER—MIDDLE PLEISTOCENE TILLS Altitude, m 125 120 115 110 105 100 95 90 4 vc 3 QII 85 80 75 70 27
1 s QIII
1 QIII s
4 vc 3 QII
4 p QIII
4 vc QII
4 QII vc
12 10 11
Section no. 35
50 55 60 65 70 Distance from the estuary, km
Fig. 3. Schematic geological section across the Bol’shaya Rogovaya River valley. Legend as in Fig. 2.
overlie the Lower Permian coarsegrained sandstones and gritstones, probably, governing the grain size com position of the Pechora till in the region. 4
The Vychegoda till ( Q IIvc). At exposures along the Adz’va River, this till is everywhere composed of sandy loam with almost equal contents of the gravelsand, silt, and clay fractions (30.6, 33.6, and 35.9%, respec tively). The rock is unsorted (average diameter of par ticles 0.021 mm, Sс = 0.11). The average content of material, which is soluble in 10% HCl, is 2.3%. In the Bol’shaya Rogovaya River basin, the Vyche goda till was studied in 13 sections. The till is marked by highly variable grain size composition and repre sented by sediments ranging from sandy loam to heavy loam with a high carbonate content (as much as 7.9%). Moreover, the till composition shows close cor relation with the underlying sediments: the gravel sand fraction is higher in tills overlying the alluvial and marine sediments, while the finegrained composition is typical of till overlying the lacustrine and lacustrine glacial sediments. In the Seida River valley, the Vychegoda till is char acterized by a significantly lesser carbonate content, relative to the Pechora till: (6.9 and 12.7%, respec tively). This is likely related to its lesser density. The Vychegoda till is composed of loam with a very low degree of sorting (Sc = 0.10) and medium diameter of particles (0.02 mm); i.e., as compared to the Pechora till, the Vychegoda till has a finer grain size composi tion. The average content of the gravelsand, silt, and clay fractions is 23.2, 40.0, and 36.8%, respectively. 4
The Polyarny till ( Q III p). The grain size composi tion of the Polyarny till in the Adz’va River basin is LITHOLOGY AND MINERAL RESOURCES
variable in different sections. The carbonate content is not high (4.2%). The average content of the gravel sand, silt, and pelite fractions is 24.6, 32.0, and 43.4%, respectively. The average diameter of particles (dav) is 0.015 mm. The sediments are marked by a low sorting coefficient (Sс = 0.12). In the Bol’shaya Rogovaya River valley, the Pol yarny till is represented by poorly sorted loam (Sс = 0.16) with significant contents of the silt (47.0%) and pelite (36.9%) fractions. Therefore, the average diam eter of grains is 0.018 mm. The average content of material soluble in 10% HCl is 7.8% in the Polyarny till. Mineral Composition Table 2 presents the mineral composition of the fine sand fraction in tills from the coastal exposures along the Adz’va, Bol’shaya Rogovaya, and Seida riv ers. 2
In the Adz’va River basin, the Pechora till ( Q II pc was studied only in two sections at the lower course of the river. The composition of heavy minerals here is variable. In some places (outcrop 431), the heavy frac tion (average yield 0.41%) is represented by the ilmenite (10.6%)–amphibole (11.1%)–garnet (18.7%)–epidote (33.5%) mineral assemblage. In other places (e.g., out crop 437), the average content of heavy minerals is 0.52% and represented by the amphibole (10.6%)– pyrite (11.2%)–siderite (18.5%)–epidote (20.6%) mineral assemblage enriched in ilmenite (9.4%) and garnets (9.1%). This can be explained by the glacial assimilation of both underlying Jurassic rocks and Tri No. 3
Table 2. Average mineral composition of tills in the Far Northeast of European Russia, %
Note: (–) Mineral was not detected.
assic gravellysandy sediments that are developed in the northeastern glacier migration area. The heavy fraction of both rocks is dominated by minerals of the epidote–zoisite group. Moreover, pyrite and siderite are abundant. Relative to the younger moraine hori zons, the Pechora till shows the following distinction: the light fraction is enriched in glauconite, which is typical of Mesozoic sediments. Significant assimila tion of glacier bedrocks is indicated by outliers and xenoclasts of Mesozoic rocks in the Pechora till, which was produced by active glaciodynamics of the glacier and intense glacial exharation. In the Pechora till confined to the Seida River val ley, the heavy fraction (yield 0.86%) is characterized by the siderite (22.4%)–epidote (26.3%)–pyrite (27.3%) mineral assemblage with low contents of gar nets (5.1%) and amphiboles (3.2%). Very high pyrite and siderite concentrations are likely related to the assimilation of Mesozoic rocks, which are developed northward of the Seida River valley, by the Pechora glacier. 4
The Vychegoda till ( Q II vc). In sections in the lower course of the Adz’va River, the Vychegoda till is char acterized by the stable amphibole (10.6%)–ilmenite
(10.8%)–garnet (16.6%)–epidote (36.3%) assem blage. Yield of these heavy minerals is 0.51%. In some places, the till includes abundant titanium minerals (average 11.3%) probably redeposited from the Mid dle and Upper Jurassic rocks that are enriched in these minerals. High epidote and garnet concentrations are caused by the influence of both metamorphosed greenstone (garnetcontaining) rocks in the Urals and the Permian terrigenous rocks that are widespread in the eastern area (basins of the Bol’shaya Rogovaya and Seida rivers) and characterized by high contents of minerals of the epidote–zoisite group (up to 60%) in the heavy fraction (Chalyshev and Varyukhina, 1968). Upward the river course, yield of the heavy fraction is 0.74%. The epidote and garnet contents decrease to 25.4 and 14.6%, respectively, due to a drastic increase in siderite (28.7%). This can be related to increase of the role of adjacent transit (Upper Triassic) rocks, which are enriched in siderite grains and nodules, in the process of glacial assimilation. The Vychegoda till at coastal outcrops along the Bol’shaya Rogovaya River is marked by still higher epi dote content: it reaches onehalf of the total weight of the whole heavy fraction, which makes up 0.61%. As in sections exposed along the Adz’va River, the high
LITHOLOGY AND MINERAL RESOURCES
LITHOLOGY OF UPPER—MIDDLE PLEISTOCENE TILLS
epidote content in the Vychegoda till is likely related to the influence of the Uralian rocks and the Upper Permian terrigenous rocks that underlie Quaternary sediments in the Bol’shaya Rogovaya River valley. The leucoxene content clearly increases downward the river course from 4 or 5 to 13–17%. Its average content in the Vychegoda till from the Bol’shaya Rogovaya basin is 8.1%. In general, the total content of pyrite and siderite in the studied river segment is 22.1%. In the northern Seida River basin, the content of heavy minerals in the Vychegoda till is 0.76%. Here, the Vychegoda till is characterized by the ilmenite (11.1%)–siderite (14.8%)–pyrite (15.1%)–epidote (30.3%) mineral assemblage. 4
The Polyarny till ( Q III p). The mineral composition of the fine sand fraction of the Polyarny till in the Adz’va River valley is characterized by a stable compo sition of heavy minerals (yield 0.6%). The till is marked by the garnet (12.3%)–pyrite (14.6%)–sider ite (17.9%)–epidote (21.3 %) mineral assemblage with a high content of the Tibearing minerals (10– 12.6%). In sections along the Bol’shaya Rogovaya River, the Polyarny till is characterized by very low yield, (0.26%) and siderite (13.2%)–garnet (14.6%)– ilmenite (14.6%)–pyrite (14.8%)–epidote (18.8%) mineral assemblage. Petrographic Composition Study of the petrographic composition of the clas tic material in tills revealed a wide spectrum of sedi mentary, igneous, and metamorphic (erratic, transit, and local) rocks. Their compositions are presented in Fig. 4. 2
The Pechora till ( Q II pc). Relative to other rocks, the petrographic composition of coarseclastic mate rial from the Pechora till in the Adz’va River sections is characterized by a higher content (average 38%) of clasts of carbonate rocks, including local Devonian and Carboniferous light gray and white limestones that make up the Chernyshev Range. About onethird of clasts in this rock group is represented by the darkcol ored limestones and dolomites delivered from distal provenances. Proximal rocks (23.9%) are represented by the Paikhoi–Ural Complex: various quartzites and quartzitic sandstones (Devonian and Lower Ordovi cian rocks included) coupled with metamorphic and igneous rocks. The Pechora till includes rare clasts of alien rocks—dark gray and black limestones (with numerous corallites and frequent calcite veinlets), dolomites, pink marbletype crinoid–bryozoan lime stones of the Ordovician or probably Early Silurian age (determination by L.V. Nekhorosheva), which are key rocks from Novaya Zemlya, as well as violet and pink Devonian–Ordovician quartzitic sandstones and quartzites coupled with siliceous rocks of the Lemva LITHOLOGY AND MINERAL RESOURCES
zone. Local rocks (hard greenish gray and gray sand stones, gritstones, and conglomerates of the Per mian–Triassic age, as well as basalt clasts exposed in the Mt. Tal’bei area in the Chernyshev Range) make up 15.7%. Clasts of the transit Mesozoic terrigenous rocks make up 22.4%. Long axes of rock clasts are usu ally N to Soriented (NNW–NNE 34010°). In the Seida River valley, the coarseclastic mate rial of the Pechora till is dominated by carbonate rocks (41.1%). As in the Adz’va River valley, carbonate rocks here are mainly observed as lightcolored varieties (29%) transported from the proximal provenances. Local rocks are also represented by Permian and Tri assic terrigenous rocks, which make up 17.7% of the total content of all clasts in the till complex. The distal Jurassic and Lower Jurassic terrigenous rocks (clasts of dark gray and brown sandstones with ammonites and belemnites), light gray and greenish gray glauconitic sandstones, as well as pebblestones with wellrounded pebbles, make up 23.4%. Igneous and metamorphic rocks, as well as basic and intermediate rocks that are alien for the Seida River basin (basalt, gabbro, diabase, diorite, various schists, quartzites, and quartzitic sandstones) make up 17.8%. Boulders are oriented along 0–60°. 4
The Vychegoda till ( Q II vc). In sections exposed along the upper and lower courses of the Adz’va River, the Vychegoda till is characterized by significant dif ferences in the petrographic composition of rock clasts: high contents (up to 38.2%) of Mesozoic rocks (light and brownish gray sandstones with occasional inclusions of plant detritus, siltstones, and mudstones, as well as coaly–clayey gritstones) in the till developed at the upper course of the river. Sections exposed downward the river course are dominated by rocks of the Polar and Subpolar Urals: violet–pink quartzites and quartzitic sandstones (Devonian sequence and Lower Ordovician Tel’pos Formation), green lava breccia, quartz–epidote rocks, gabbro diabases, amphibolites, peridotites, pyroxenites, and various schists (phyllites included). Their average content is 39.2%. The share of hard Permian–Triassic greenish gray and gray polymictic sandstones and gritstones increases to 30.1%. The Vychegoda till of the entire Adz’va River basin is marked by depletion in carbon ate rocks (19.9–25.9%). Lower Paleozoic dark gray or black limestones and dolomites delivered from the dis tal provenances are subordinate. Orientation of long axes of rock clasts (80–105°) suggests a nearly latitudi nal (E–W) input of clastic material during the till for mation in the Adz’va River valley. In contrast, the Vychegoda till in the Bol’shaya Rogovaya River valley is enriched in carbonate rock clasts (35–45%). Their content decreases to 26–30% in some sections and increases to 51–58% in other sections. The average content of carbonate rock clasts in the till is 40.4%. In terms of the ratio of dark and lightcolored varieties, the first rock group predomi No. 3
a Vychegoda Horizon
b Vychegoda Horizon
c Vychegoda Horizon
1 2 3 4 5 6
Fig. 4. Petrographic composition of clastic material in tills in the Far Northeast of European Russia. (a) Adz’va River, (b) Bol’shaya Rogovaya River, (c) Seida River. (1) Dark limestones and dolomites; (2) light gray and white limestones; (3) Jurassic and Lower Jurassic terrigenous rocks; (4) Permian and Triassic terrigenous rocks; (5) igneous and metamorphic rocks; (6) quartz ites and quartzitic sandstones.
nates in most sections; the ratio is almost equal in some places; and light gray and white limestones pre vail in rare cases. Local rocks are represented by the Permian polymictic sandstones, mudstones, silt stones, and mustard sandstones. Their average content in the till is usually insignificant (9.4%). The Vyche goda till is marked by a sufficiently high concentration of the Uralian igneous and metamorphic rock clasts, which are similar to those in the till of sections exposed along the Adz’va River, as well as quartzites and quartzitic sandstones that are alien to the Bol’shaya Rogovaya River basin. Their content is variable (30– 37% in some sections, average 26.2%). The nearly lat itudinal and NE orientation of elongated clasts in the till (ENE 45–90°) confirms the involvement of Ura lian rocks in its formation. As in sections along the Adz’va River, the Vyche goda till in the Seida River basin is depleted in carbon ate rocks (25.7%). However, relative to the Pechora
till, the former variety is slightly enriched (22.8%) in the Permian and Triassic rocks (clasts of greenish gray and mustard sandstones, siltstones, mudstones, grit stones, normal and coaly–siliceous shales). These rocks can be considered local and mediumscale tran sit rocks, because the Permian rock terrane occupies a sufficiently large area and underlies the Pleistocene sediments on both northern and eastern sides of the study region. This till is enriched in clasts of igneous and metamorphic rocks, as well as quartzitic sand stones and quartzites from the Uralian provenance, relative to the Pechora till (28.2 and 17.8%, respec tively). Input of clastic material from the Urals is also suggested by the orientation of long axes of boulders (40–60°). 4
The Polyarny till ( Q III p). The petrographic compo sition of the coarseclastic material from the Polyarny till in sections of the Adz’va River is dominated by car
Pink crinoid–bryozoan lime stones of Novaya Zemlya
Pink crinoid–bryozoan lime stones of Novaya Zemlya
Rocks of the Polar and Subpolar Urals
Pink crinoid–bryozoan lime stones of Novaya Zemlya
Reference boulders, other typical rocks
Note: (I) Carbonate rocks; (II) local terrigenous rocks; (III) distal terrigenous rocks; (IV) distal igneous rocks.
Table 3. Lithological criteria for the subdivision and correlation of upper–middle Pleistocene tills in the Far Northeast of European Russia
LITHOLOGY OF UPPER—MIDDLE PLEISTOCENE TILLS 261
bonate rocks (average 48.3%). As in the Pechora till, Lower Paleozoic limestones and dolomites account for onethird of all clasts in this group; Mesozoic ter rigenous rocks make up 20.4%; and metamorphic rock clasts account for 20.5%. Permian and Triassic sedi mentary rocks are subordinate (10.8%). In the Polyarny till, long axes of clasts are oriented along 35020°. It includes rocks transported from the Paikhoi–Novaya Zemlya region: Paleozoic dark gray or black lime stones and dolomites, as well as episodic boulders of reference rocks (Ordovician–Early Silurian pink crinoid–bryozoan limestones) derived from Novaya Zemlya. These facts suggest that the Polyarny till accumulated terrigenous material transported from the Paikhoi–Novaya Zemlya glaciation center. This petrographic composition of clasts is also typ ical of the Polyarny till in the Bol’shaya Rogovaya val ley. The coarseclastic material is mainly composed of carbonate rocks (42.1%). Clasts of igneous and meta morphic rocks, as well as quartzites and quartzitic sandstones, make up 27%, on the average. The share of Mesozoic rocks and Permian–Triassic sedimentary rocks is almost equal (16.1 and 14.7%, respectively). Long axes of rock clasts are oriented along 330–350°. The till includes rock clasts from the Paikhoi–Novaya Zemlya provenance, which are similar to those in the Polyarny till from the Adz’va River basin. These facts indicate that the Polyarny till in the Bol’shaya Rogovaya valley is also related to the Paikhoi–Novaya Zemlya glaciation center. Lithological similarity of the Polyarny till in the Adz’va and Bol’shaya Rogovaya valleys suggest a single provenance of terrigenous material during the formation of the Polyarny moraine horizon. CONCLUSIONS The results of comprehensive lithological study o f differentaged till horizons at coastal exposures of the Adz’va, Bol’shaya Rogovaya, and Seida rivers—right tributaries of the Usa River in the Far Northeast of European Russia made it possible to accomplish the lithostratigraphic subdivision of sections and elucidate the specific lithological features of tills (Table 3). Cor relation of these features with the glacial provenances has been unraveled. Coastal exposures of the Adz’va River show three till horizons that are sufficiently discernible in lithol ogy. The segment extending from the upper course of the Bol’shaya Rogovaya River to the estuary of the Bol’shoe Pyatomboiyu River lacks the Pechora till. The Seida River valley lacks the Polyarny till. The middle Pleistocene glacial complex distinctly show two differentaged (Pechora and Vychegoda) tills separated by a lacustrine–boggy sediment pile assigned to the Rodionovo Horizon based on palyno logical data. Lithological discrepancies in the till com position suggest their formation during the changeover of glacial provenances and confirm the autonomous
evolution of continental glaciers that produced the tills. Horizons of the Pechora and Polyarny tills are characterized by restrictive development in the study region. Input of the terrigenous material of tills from the Paikhoi–Novaya Zemlya glaciation center is indi cated by nearly meridional orientation of long axes of clasts, the presence of pebbles and boulders of Paleo zoic rocks (dark gray and black limestones and dolo mites derived from the Paikhoi–Novaya Zemlya region), clasts of reference rocks (Ordovician–Early Silurian pink crinoid–bryozoan limestones derived from Novaya Zemlya), as well as significant contents of pyrite and siderite in the mineral assemblages. The Vychegoda till is most widespread in Adz’va, Bol’shaya Rogovaya, and Seida river valleys. The heavy fraction of the till is marked by high concentra tions of epidote and garnet. They could be derived from the Uralian greenstones and metamorphosed garnetbearing rocks, as well as from Upper Permian terrigenous rocks that are widespread in the study region. The heavy fraction of these rocks contains as much as 60% minerals of the epidote–zoisite group. In general, orientation of the elongated rock clasts in the Vychegoda till is nearly latitudinal. In addition, pebbles and boulders in the till demonstrate high con centrations of Uralian igneous and metamorphic rocks. These facts suggest that the till was formed by glaciers of the Polar and Subpolar Urals. ACKNOWLEDGMENTS This work was supported in part by the Earth Sci ence Division of the Russian Academy of Sciences (Program of Fundamental Researches no. 14). REFERENCES Andreicheva, L.N., Lithological Control of the Correlation of Principal Moraines in the Adz’va River Valley, in Strati grafiya i paleoekologiya paleozoya i kainozoya SeveroVos toka evropeiskoi chasti SSSR (Paleozoic–Cenozoic Stratig raphy and Paleoecology of the Northeastern European Soviet Union), Syktyvkar, 1987, pp. 64–70. Andreicheva, L.N., Osnovnye moreny evropeiskogo severo vostoka Rossii i ikh litostratigraficheskoe znachenie (Princi pal Moraines in Northeastern European Russia and Their Lithostratigraphic Significance), St. Petersburg: Nauka, 1992. Andreicheva, L.N., Lithological Composition of Pleis tocene Sediments in the Bol’shaya Rogovaya River Basin, in Geologiya i mineral’nye resursy Evropeiskogo severovostoka Rossii (Geology and Mineral Resources in Northeastern European Russia: New Results and Perspectives), Syk tyvkar: Geoprint, 2009, pp. 89–92. Andreicheva, L.N. and Duryagina, D.A., New Data on Stratigraphy of the Middle Pleistocene in the Pechora Low land, in Geologiya i mineral’nye resursy evropeiskogo severo vostoka Rossii: novye rezul’taty i novye perspektivy (Geology and Mineral Resources in Northeastern European Russia:
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