Cryogeochemical features of Holocene and Late Pleistocene syngenetic ice wedges at the mouth of the Seyakha (Zelenaya) River, East Yamal Peninsula

Vasil'chuk Yurii Kirillovich ORCID: 0000-0001-5847-5568 Doctor of Geology and Mineralogy Professor, Lomonosov Moscow State University, Faculty of Geography, Department of Landscape Geochemistry and Soil Geography 119991, Russia, Moscow, Leninskie Gory str., 1, of. 2009 vasilch_geo@mail.ru Other publications by this author

Introduction

    Cryogeochemical studies in the tundra of Western Siberia of a vast and poorly populated territory were constructed in such a way that it was possible to identify the features of the chemical composition of re-vein ice from different temperature zones contained in sediments of different ages and genesis. It is important to note that samples from re-vein ice were taken not only along a vertical or horizontal line^[1], but also along a "grid" (to detect changes in chemical composition along the entire cross-section and length of the veins). It was found that the ice veins are often differentiated into zones of unequal mineralization, located in the form of wedges of different lengths and cross-sections nested into each other. This phenomenon is especially pronounced in sections with a higher degree of salinity of ice veins.^[2,3] The configuration of wedges with different salinity in the body of veins is not always correct, they are often significantly asymmetrical. Wedges appear as a result of successive changes of facies and hydrochemical conditions during the formation of ice veins.^[3]

    One of the mandatory conditions for the formation of wedges with different salinity in the body of one vein should be the relative localization of the area of cracking of ice veins for a long time, sufficient for the formation of a wedge of a certain salinity. If such localization is not observed, then zones with a clear differentiation in salinity are not formed, and newly formed elementary veins either "pickle" the ice veins throughout the volume (if they are more fresh), or increase its salinity as a whole.

    Most of the published data^[4-9] indicate a low degree of salinization of re-vein ice, which gave rise to the conclusion that their ubiquitous low mineralization does not exceed 0.1 g/l. Our results indicate that this is not always the case. Indeed, the main part of the re-vein ice is relatively poorly saline. However, in a number of sections, syngenetic re-vein ice is mineralized much more significantly.

    The probability of encountering re-vein ice in the north of Western Siberia with a total mineralization value of more than 0.2 g/l exceeds 10%^[10,11]. Interestingly, in 28% of the samples studied, the chlorine ion content exceeds 0.02 g/l, and in 8% it is more than 0.1 g/l. These two indicators – high mineralization and high chloride content – are perhaps the most convincing indicators of paleofacial conditions for the formation of re-vein ice. For the remaining components (the distribution of which is also heterogeneous and quite interesting), the indication of the facies conditions for the formation of re-vein ice is more complex and less definite. The data on the content of sodium and potassium ions are indicative in this regard, which in more than 80% of the studied samples contain less than 0.02 g/l.^[10,11]

    Despite the relatively rare occurrence of saline differences in re-vein ice, they should not be neglected, since these veins are direct indicators of the marine or lagoon-marine sedimentation regime during their formation. Interestingly, the ratio of more saline and less saline ice in syngenetic Pleistocene and Holocene veins is somewhat different.

    The powerful Late Pleistocene syngenetic re-vein ice lying in sections of the second and third marine and lagoon-marine (Guba) terraces of the north of Western Siberia, as a rule, are characterized by a low degree of salinity. According to the classification of Yu.K. Vasilchuk ^[12], all of them belong to fresh, most often bicarbonate or sodium chloride. There is a tendency to increase the mineralization of ice from 0.02–0.1 g/l in veins enclosed in the strata of lagoon-marine sediments to 0.1–0.5 g/l in the strata of marine sediments. It should be noted that in relatively little saline Late Pleistocene syngenetic veins, zones with different mineralization can be isolated. When evaluating these data, it is necessary to keep in mind the features of direct field study and sampling of ice from relict Late Pleistocene syngenetic veins. It is well known that most often in the field of observations (in outcrops, wells and especially in pits) it is this upper "desalinated" part of the veins.

    The salinity of re-vein ice contained in Holocene strata is generally somewhat higher. It is quite different in the ice veins formed in alluvial deposits, on the one hand, and marine and lagoon-marine – on the other. When studying syngenetic Holocene veins on floodplains and the first terraces of rivers, the author found that they are fresh in the upper reaches of rivers, their mineralization does not reach 0.1 g/l. When moving downstream of rivers to the sea (or to the lip), mineralization sometimes increases significantly. In the strata of the first terraces of the laids and floodplains in the estuaries of rivers, the mineralization of ice veins often exceeds 0.2 g / l, and in some cases reaches values of the order of 0.8–1.2 g / l, i.e. the veins pass into the category of slightly saline, according to the classification of the author.^[12]

    There are many reasons preventing the formation of highly mineralized syngenetic re-vein ice. It is noteworthy that, despite all these reasons, sufficiently saline (with a mineralization greater than 0.2 g/l) syngenetic re-vein ice is found in a number of Late Pleistocene and Holocene re-vein ice in the north of Western Siberia.^[13] The presence of mineralized veins unambiguously allows us to identify the genesis of these strata as marine or lagoon-marine and indicates very harsh climatic conditions during the accumulation of soils (otherwise subaqual growth of veins would be impossible).

Fig. 1. Location of the research area

       We were lucky to be the first to study the cryolithological, isotopic and geochemical features of the Seyakhinsky syngenetic re-vein complex on the east coast of Yamal in 1978 (70.166° s.w., 72.5666° v.d.) Initially by the author (together with A.Vasilchuk)^[14] the riverine (Seyakha-Zelenaya River) edom outcrop of this complex was studied in more detail, in the next 2 years the work was focused on the outcrop that revealed Holocene and Late Pleistocene re-vein ice on the shore of the Gulf of Ob (70.1667°S., 72.5083° V.D.). Subsequently, the outcrop was investigated by I.D. Danilov^[15] and V.F. Bolikhovsky^[16,17].

Research objects

Holocene re-vein ice on the floodplain of the Seyakha River (Green)

Deposits of the high floodplain of theSeyakha (Green), studied in detail in outcrops and wells of the floodplain of the Seyakha (Green) river, 4.1 km northwest of the village. Seyakha, top-down opened:

0,0-0,3 m. Peat desalinated slightly decomposed brown sedge-sphagnum.

0.3-0.5 m. The sand is frozen, gray fine-grained with detaching spots indistinctly layered.

0.5-2.0 m. Frozen gray fine-grained sand with thin layers (0.2-0.3 cm) of peat.

2.0-2.3 m. Layering of light-gray quartz sand and gray-brown sand torn off, the thickness of the interlayers is 1 cm.

2.3-3.0 m. The ice is re-vein, at a depth of 2.8 m, the content of mineral impurities is high in the ice.

3.0-3.60 m. Oblique interlayers of quartz sand ozheleznennogo dark gray and brown sand torn off, the thickness of the interlayers is 0.5 cm the distance between the interlayers is 1.5 cm.

3.6-4.7 m. The sand is light gray frozen with interlayers of sand of highly hardened ochreous.

4.7-5.5 m. Thin layering of weakly silted dark gray and black sand, as well as white quartz sand, the thickness of the interlayers is 0.1-0.2 cm, in the range of 4.7-5.2 m 107 interlayers

5.5-6.0 m. The sandy loam is dark gray, with obliquely inclined layers of gray sand.

6.0-7.5 m. Gray sand with thin layers of white quartz sand.

In the upper part of the section there are relatively small re-vein ice up to 1.5 m wide and about 3 m high.

Holocene re-vein ice in the peat bog on the third terrace

Several interesting fragments of Holocene cryolithogenic outcrops were studied within the Seyakhinsky section, among them: syngenetic re-vein ice in paragenesis with peat veins continuing ice veins (Fig. 2) and syngenetic re-vein ice in paragenesis with peat veins lying parallel with ice veins (Fig. 3). Peat the vein extending the ice vein from below in the second fragment was dated to 9300 ± 100 years (GIN-2472), i.e. 11080-10198 caliber. years, an average of 10492 caliber. years.

Fig. 2. Cryogenic structure, radiocarbon dating and sampling scheme of relatively narrow re-vein ice in paragenesis with peat veins (pseudomorphoses): 1 - vertically striped ice of syngenetic re-vein ice; 2 – peat; 3 – sand; 4 – sandy loam; 5 – sampling sites: organics for radiocarbon analysis (a), re-vein (b) ice for hydrochemical and enzymatic analyses.

Syngenetic re-vein ices in paragenesis with peat veins lie almost parallel with peat veins (Fig. 3, 4). The heads of both are located at the same depth - about 0.5-0.7 m. Ice veins here reach 2-2.5 m in height, they are represented by pinkish-brownish ice, the width of the head veins is more than 1.6 m, white sugary ice is marked on the lateral contacts of the veins (approximately 0.1 m wide). The ice of the veins is pinkish-brownish, the width of the head of the vein is more than 1.6 m, white sugary ice is marked on the lateral contacts (approximately 0.1 m wide). Peat veins reach 2 m vertically, they are composed of frozen desalinated peat slightly decomposed with twigs and preserved bark, leaves of dryads, saxifrage and dwarf birch. The deposits containing the veins are represented by yellowish fine detached sand with inclusions of twigs and nests of separation.

                A sample of peat with small twigs in a peat vein in the second fragment (see Fig. 4) in the upper part of the section at a depth of 1.6 m, dated to ¹⁴ with 9280 ± 140 years (Hel-4031), i.e. 11176-9926 caliber. years, an average of 10486 caliber. years, and peat at a depth of 0.5 m is dated 6560 ± 150 years (Hel-4068), i.e. 7865-6980 caliber. years, an average of 7458 caliber. years. Thus, peat ground veins were actively formed in the initial phase of the Holocene optimum, determined for Yamal from 9.0 to 4.5 thousand years ago^[13]. Moreover, peat veins were formed, obviously, as a result of significant drying of the seasonal thawing layer at the beginning of the Holocene optimum.

Grayish-brown detached thin-layered sand lies directly above the head of the veins (the thickness of the interlayers is 0.3-0.03 m), the layering is expressed by fluctuations in the degree of separation and changes in the granulometric composition. Above lies a layer of brown frozen peat, which is similar to the peat that, together with sand, performs ground veins. The lower boundary of this layer is uneven karma-like (the thickness of the interlayer is 0.3 m). The ice vein most likely developed syngenetically to the accumulation of an underground peat vein. This is evidenced by the upward bending of the layers of the enclosing layered sands at the lateral contact with the ice vein.

Fig. 3. Syngenetic re-vein ice is brown-pink in paragenesis with peat veins, in the southern part of the peat bog located on the surface of the third 24-meter terrace at the mouth of the river.Seedling (Green). Photo by A.K. Vasilchuk

Fig. 4. Holocene syngenetic re-vein ice is brown-pink in paragenesis with peat veins, in the southern part of the peat bog located on the surface of the third 24-meter terrace at the mouth of the river.Seedling (Green): 1 – re-vein ice; 2 – fringe ice; 3 – organic residues in deposits: a – peat, b – shrub branches; 4 – sand; 5 – sandy loam, 6 – sampling: a – for ¹⁴ S and age, caliber. years, b – for hydrochemical analysis

Severe winter conditions caused the freezing of accumulated lake and marsh sediments and the growth of re-vein ice.

Late Pleistocene re-vein ice in Edom on the third terrace

As a result of the study of this section during a number of field seasons, a fairly complete picture of its cryolithological structure has developed. The length of the outcrop along the coast of the Gulf of Ob is more than 4 km, the height ranges from 22 to 24 m. In the cryolithological structure, 2 parts are clearly distinguished - the lower: 12 -15 m with polygonally vein ice up to 3 m wide and the upper: 9-12 m with narrow ice veins up to 1 - 1.5 m wide (Fig. 5).

Fig. 5. Late Pleistocene syngenetic re-vein ice in the edom of the third 24-meter terrace at the mouth of theSeedling (Green). Photo by A.K. Vasilchuk

         In the thickness of the edoma of the third terrace with a height of up to 22-24 m, the largest re-vein ice known for the north of Western Siberia has been uncovered.^[18,19,20] Repeated field survey performed by the author allowed us to identify three main cryostratigraphic horizons. The lower 11 m thicknesses are represented by a “puff": frequent layering of sandy loam and allochthonous compacted peat. Deposits accumulated, most likely, in variable subaqual-subaerial conditions: interlayers containing organic matter in the form of roots, stems and leaves belong to subaerial horizons, sandy loam interlayers without organic inclusions belong to subaqual. There are ice veins 3 m wide, stacked with pure ice. In the middle part of the section (with a thickness of about 10 m), narrower veins up to 1-1.5 m wide and vertical layers of mineral inclusions were studied. The host sediments are represented by layered sandy loams with a small amount of organic matter (see Fig. 5). The upper horizon (2-3 m thick) is represented by layered yellow sand, presumably accumulated in subaqual conditions during the higher level of the Gulf of Ob, which was subsequently proved by the presence of well-preserved in situ brackish foraminifera: Elphidium subclavatum Gudina, Pninaella pulchela Parker, Protelphidium parvum Gudina, etc. Ice veins 1.5 m wide were found here^[21].

In 2016, the marginal part of the edoma with a height of about 17 m was investigated (Fig. 6).

Fig. 6. Late Pleistocene syngenetic re-vein ice in the edom of the third 24-meter terrace at the mouth of theSeedling (Green). Photo by N.A. Budantseva

In the cryostratigraphy of the outcrop in this part of Edoma, 2 fragments were identified: at a height of 5-6 m above the edge of the Gulf of Ob, a paragenetic combination of an ice vein and a layer of segregation ice was revealed. In the upper 5-meter part of the outcrop, in the range of absolute heights of 11.5-16.5 m, a thickness of grayish-yellow fine powdery sand with an admixture of organic matter was uncovered, including veins 1-1.5 m wide in the upper part, about 5 m high.^[20]

Late Pleistocene syngenetic re-vein complex

In the upper part of the outcrop, a powerful bundle of yellow layered sand attracts attention (see Fig. 5), indicating the possible higher relative position of the Ob Bay (or river, or other body of water) during its accumulation.

                To link the thickness, the most informative ¹⁴ From the date were obtained at a height of +0.2 m above the edge of the Gulf of Ob - 36800 + 3300/-2100 years, i.e. 42426 caliber. years and at an altitude of +21.2 m - 11620 ± 90 years, i.e. 13486 caliber. years, which makes it possible to date the entire period of accumulation of syngenetic veins in the Seyakhinsky late Pleistocene ice complex in the range from 35 to 11 thousand years, i.e. from 42 to 13 thousand caliber. The date of 17 thousand years, i.e. 20904 caliber, is also extremely important. years obtained from the upper subaqual stratified strata, which indicates the continued subaqual sedimentation in the Gulf of Ob at this time (it is during this period that the lowest level of the World Ocean is usually reconstructed). The completion of the accumulation of the "puff" (as well as wider and more massive veins of the lower tier) dates back about 22 thousand years ago ^[18], i.e. 26 thousand caliber. years.

 Chemical composition of re-vein and texture-forming ice

 The chemical composition of all types of ice encountered and the sediments containing them has been determined:

a) in Holocene re-vein ice in the thickness of the floodplain of the Seyakha River, Green (Table. 1), b) in syngenetic frozen sediments (fine and fine sand) in the thickness of the floodplain of the Seyakha River, Green (Table. 2), c) in segregational and re-vein and texture-forming ice of Holocene deposits in the lake-marsh tab in the upper part of the section of the third terrace (Table. 3), d) in late Pleistocene re-vein ice in the thickness of the third terrace (Table. 4), e) in syngenetic frozen sediments of the 25-30 meter Late Pleistocene terrace (Table. 5 and 6).

Chemical composition of Holocene re-vein ice and their host deposits on the floodplain

                Mineralization in Holocene re-vein ice in the thickness of the floodplain of the Seyakha River, Green varies markedly from 24 to 176 mg/l, the chemical composition of water-soluble salts is dominated by bicarbonates, ranging from 6.1 to 36.6 mg/l (Table 1, Fig. 7).

                Mineralization in syngenetic Holocene frozen sediments (fine and fine sand) in the thickness of the Seyakha River floodplain, Green at depths from 2.3 to 6.8 m varies little, the dry residue content varies from 0.071 to 0.113%, sulfates predominate in the ionic composition of water-soluble salts - ranging from 0.09 to 0.022% (Table 2).

Table 1. Mineralization (Min.), chemical composition of water-soluble salts in Holocene re-vein ice in the thickness of the floodplain of the Seyakha River (Green), 4.1 km northwest of the village. Seyakha, East Yamal. Sampling 1978

Fig. 7. Ionic composition of water-soluble salts in Holocene re-vein ice in the thickness of the floodplain of the Seyakha River (Zelenaya), 4.1 km northwest of the village. Seyakha, East Yamal. Sampling 1978

Table 2. Composition and content of water-soluble salts in syngenetic frozen sediments (fine and fine sand) in the floodplain of the Seyakha River (Green), 4.1 km northwest of the village. Seyakha, East Yamal. Sampling 1978

Chemical composition of Holocene re-vein ice and their host deposits of the lake-marsh tab in the upper part of the section of the third terrace

Mineralization in re-vein ice in Holocene sediments in the lake-marsh tab in the upper part of the section of the third terrace is insignificant - 24-27 mg/l, but in the segregation and texture-forming ice of Holocene deposits in the lake-marsh tab in the upper part of the section of the third terrace, a somewhat unexpected effect was noted, high salinity in the lower part and its decrease up the section of the peat bog: in the bottom parts of the peat deposit, the mineralization of ice sluices is 570-430 mg/l, in the middle part - 189 mg/ l, and in its near-surface parts - 76-18 mg/l (Fig. 8).

Table 3. Mineralization (Min.), chemical composition of water-soluble salts and enzymatic activity in segregation and re-vein and texture-forming ice of Holocene deposits in the lake-marsh tab in the upper part of the section of the third terrace.

Notes: The definitions were made in the chemical-analytical laboratory of the V.V. Dokuchaev Institute of Soil Science

       The data on the chemical composition and mineralization of segregation texture-forming ice in a powerful peat bog turned out to be very interesting. A very consistent change in mineralization with depth is noted here. The mineralization of ice sluices in the bottom parts of the peat deposit is 570-430 mg/l, in the middle part of the deposit - 189 mg/l, and in its near-surface parts - 76-18 mg/l. At the same time, the content of hydrocarbonates decreases from 470-340 to 24-2 mg/l just as naturally from the bottom up. Attention is drawn to the stable low content of sulfates (4-6 mg / l), the noticeable presence of calcium ions (3-56 mg / l) and magnesium (1-33 mg / l), and the content of the former also naturally decreases from the bottom up. The change in pH with depth is also very remarkable: in the bottom parts of the peat bog, segregation ice is characterized by a pronounced alkaline type, in the middle part it is close to neutral, and in the upper part it is acidic.

 Chemical composition of Late Pleistocene re-vein ice

and the deposits of the third terrace containing them

                The mineralization of Late Pleistocene re-vein ice varies quite widely from 17 to 309 mg/l (Table. 4), bicarbonates almost always dominate, but the presence of chlorides, sulfates and calcium ions is noticeable in the most mineralized ice (Fig. 8).

In late Pleistocene re-vein ice in the thickness of the third terrace, ice mineralization increases from bottom to top, amounting to 17-80 mg/l in the veins of the lower tier, up to 140 mg/l in the veins of the middle tier and up to 230-309 mg/l in the veins of the upper tier. The composition of anions is dominated by HCO ₃^- (average value 50 mg / l), among the cations Ca ²⁺ (average 12 mg / l).

In the veins of the middle and upper tier, increased values of the content of the remaining ions are noted at some horizons (see Table 4). This distribution of mineralization suggests that the role of the waters of the Gulf of Ob is more noticeable at the final stage of the formation of ice veins (as will be shown later, this is reflected in the biochemical activity of ice veins).

Table 4. Mineralization (Min.), chemical composition of water-soluble salts and enzymatic activity in late Pleistocene re-vein ice in the thickness of the third terrace. Sampling of 1980 - 279-YuV and 1996 - 363-YuV

Note: n/a - not measured

8. Mineralization, chemical composition of water-soluble salts and enzymatic activity in late Pleistocene re-vein ice in the thickness of the third terrace. Sampling of 1980 - 279-YuV and 1996 - 363-YuV

         In general, we note a rather low mineralization of Late Pleistocene syncreogenic vein-containing sediments in the Seyakhinsky section (Table. 5), it is 0.04-0.13%, sodium bicarbonates predominate in the composition of salts (from 0.007 to 0.05%), however, in the middle part of the section, the culmination of sodium chlorides also attracts attention, since their number in ice veins increases in parallel with their increase in sediments. In the composition of other components of the chemical composition from the Seyakhinskaya strata, the content of sulfate ions ranges from 0.006% in the upper part of the section to 0.03% in the middle part, their content decreases again down the section, the calcium content is insignificant (less than 0.01%); pH varies from 8.4 in the upper part of the section to 6.4 in the lower. The mineralization of ice veins increases from bottom to top, amounting to 40-70 mg/l in the veins of the lower tier, and up to 140 mg/l in the veins of the middle tier.^[11] This means that the role of the waters of the Gulf of Ob is more noticeable at the final stage of the formation of ice veins (as will be shown later, this is reflected in the biochemical activity of ice veins).

Table 5. Composition and content of water-soluble salts in syngenetic frozen sediments of a 25-30-meter Late Pleistocene terrace near the village. Seyakha (East Yamal)

Table 6. Mineralization (Min.), chemical composition of water-soluble salts and enzymatic activity in segregational schlier ice of the Seyakhinsky Late Pleistocene section (Eastern Yamal). Sampling 1996 - 363-YuV

The mineralization of texture-forming ice (Table 6) is quite low in the lower part of the section (40-120 mg/l), increases sharply in the middle part (up to 820 mg/l) and decreases slightly in the upper part of the section (up to 470-510 mg/l). The ionic composition is dominated by HCO ₃^- (23-628 mg/l) and Na⁺ (1-84 mg/L), however, in the middle part of the section, where maximum mineralization is observed, Ca ²⁺ and Mg ²⁺ ions culminate among the cations, which probably indicates that deposits of this tier were formed in conditions of a heavily desalinated pool.

Discussion

   Mineralization and ionic composition of water-soluble salts in re-vein ice of different ages near the village. The seeds differ markedly (Table 7).

Table 7. Range of variability of mineralization (Min.) and ionic composition of water-soluble salts in re-vein ice of different ages near the village. Seyakha (Eastern Yamal).

        The Holocene PPLS in the lake-marsh tab are the most fresh in general - their mineralization varies in a narrow range from 24 to 27 mg/l, the content of anions and cations also varies slightly from 1 to 10 mg/l. Holocene PPLS in the floodplain of the Seyakha River (Green) are close to them in mineralization and ionic composition of water-soluble salts.) - in them, the total mineralization varies markedly from 26 to 176 mg/l and late Pleistocene PPL in the thickness of the third terrace, in which the total mineralization is even more variable from 17 to 309 mg/l. In the ionic composition of water-soluble salts, chlorides vary very widely in floodplain Holocene PLL from 4.2 to even 47.9 mg/l (in the tail of the vein), and in late Pleistocene PLL from 4 to 24 mg/l, the great variability of sulfates also draws attention: in floodplain Holocene PLL from 3.7 to 25.5 mg/l, and in late Pleistocene PPL from 0.1 to 46 mg/l.

The change in the mineralization of texture-forming ice in the thickness of the Holocene peat bog - its regular gradual decrease from bottom to top (from 576 to 18 mg/l) indicates that the cause of the formation of the lake-marsh basin was the extraction of large masses of highly mineralized segregational and pore ice contained in the upper part of the section of the lagoon-sea terrace (of course, it is impossible to exclude a splash of highly mineralized Guba water in the initial stage of the formation of lake-marsh basins). This is indicated, first of all, by the close qualitative nature of the segregation texture-forming Holocene and Late Pleistocene ice in the upper part of the section in those fragments of the terrace that did not experience any transformations in the Holocene. Its mineralization ranges from 470 to 810 mg/l, magnesium and calcium carbonates predominate, the ice is highly alkaline - the pH is more than 9. Although these values are somewhat higher than those observed in Holocene segregation texture-forming ice in the lower part of the peat bog, this is easily explained by the participation of precipitation in the composition of the seasonally thawed ice layer already at the first stage of the formation of the peat bog. In the future, the role of precipitation increased and at the final phase of ice formation in the upper part of the peat deposit, precipitation completely dominated.

         In the upper parts of the peat bog, as well as in modern veins, low mineralization is noted in Holocene syngenetic veins - 24-27 mg/l, the ionic composition is dominated by bicarbonates (6-10 mg/l), chlorides (7-8 mg/l) and calcium (2-4 mg/l). A slight increase in the proportion of chlorine in the ionic composition of the ice veins may indicate the direct influence of precipitation, the chemical composition of which was formed over the water area of the slightly saline Gulf of Ob.

           Most of the published data^[4,5,6,22] indicates a low degree of salinization of re-vein ice, which gave rise to the conclusion that their ubiquitous low mineralization does not exceed 0.1 g/l.^[6] The results obtained by the author indicate that this is not always the case. Indeed, the main part of the re-vein ice is relatively poorly saline. However, in a number of sections, syngenetic re-vein ice is mineralized much more significantly.

                Analysis of all data on the chemical composition of ice shows that the probability of meeting in the north of Western Siberia of re-vein ice with a total mineralization value of more than 0.2 g/l exceeds 10%.^[10,11] Interestingly, in 28% of the samples studied, the chlorine ion content exceeds 0.02 g/l, and in 8% it is more than 0.1 g/l. These two indicators – high mineralization and high chloride content – are perhaps the most convincing indicators of paleofacial conditions. For the remaining components (the distribution of which is also heterogeneous and quite interesting), the indication of the facies conditions for the formation of re-vein ice is more complex and less definite. The data on the content of sodium and potassium ions are indicative in this respect, which in more than 80% of the studied samples contain less than 0.02 g/l.^[10,11]

                Despite the relatively rare occurrence of saline differences in re-vein ice, they should not be neglected, since these veins are direct indicators of the marine or lagoon-marine sedimentation regime during their formation. Interestingly, the ratio of more saline and less saline ice in syngenetic Pleistocene and Holocene veins is somewhat different.

                The powerful Late Pleistocene syngenetic re-vein ice lying in sections of the II–IV marine and lagoon-marine (Guba) terraces of the north of Western Siberia, as a rule, are characterized by a low degree of salinity. There is a tendency to increase the mineralization of ice from 0.02–0.1 g/l in veins enclosed in the strata of lagoon-marine sediments to 0.1–0.5 g/l in the strata of marine sediments. It should be noted that in relatively little saline Late Pleistocene syngenetic veins, zones with different mineralization can be isolated. As shown above, in a powerful ice vein located in the thickness of organomineral deposits of late Pleistocene age near the village of Seyakh, mineralization varies from the bottom up from 0.04–0.08 to 0.11–0.14 g / l, which probably indicates a slight increase in the influence of salty Guba waters at the final stages of the formation of ice veins. This is also evidenced by the analysis of the water extract from the organomineral deposits containing the veins. Their mineralization increases from the bottom up from 1.02 to 1.18–1.60 g/kg, and to a large extent its increase is due to an increase in the content of sodium and potassium chlorides – typical salts of marine waters.

                Among the Late Pleistocene, veins with low ice mineralization are quite widely developed. Often, even syncryogenic re-vein ice in the strata of marine terraces is mineralized slightly – the amount of dry residue in them does not exceed 0.05 g/l. Mineralization is especially low in the uppermost parts of the veins, in the addition of which, along with the ice of the relict late Pleistocene vein, epigenetic Holocene ice, which was introduced later, also participates.^[11] When evaluating these data, it is necessary to keep in mind the features of direct field study and sampling of ice from relict Late Pleistocene syngenetic veins. It is well known that most often in the field of observations (in outcrops, wells, and especially in pits) it is this upper "desalinated" part of the veins.

       The salinity of the re-vein ice contained in Holocene strata is generally somewhat higher. It is quite different in the ice veins formed in alluvial deposits, on the one hand, and marine and lagoon-marine – on the other. When studying syngenetic Holocene veins on floodplains and the first terraces of rivers, it was found that they are fresh in the upper reaches of rivers, their mineralization does not reach 0.1 g/l. When moving downstream of rivers to the sea (or to the lip), mineralization often increases significantly. In the strata of the first terraces of laids and floodplains in the estuaries of rivers, the mineralization of ice veins often exceeds 0.2 g/l, and in some cases reaches values of the order of 0.8–1.2 g/l.  The possibilities of cryohydrochemical analysis are particularly convincing when comparing the mineralization of re-vein ice on floodplains and on the laids of the north of Western Siberia. The number of samples analyzed by the author from the veins of these two types of Holocene soil strata is approximately the same. The author revealed that the occurrence of re-vein ice with a dry residue value of 0.2 g/l or more in the alluvial Holocene strata of floodplains is close to zero, whereas in the lagoon-marine and marine Holocene strata of the lade they are noted in 22% of the analyzed samples, and in 16% of the samples of veins in the lade strata the total mineralization exceeded 0.4 g/l.^[10,11]

        Undoubtedly, the mineralization index of more than 0.2 g / l should be considered a direct sign of participation in the formation of veins of marine or Guba waters. However, quite often, even in relatively saline marine Holocene sediments, there are quite fresh syngenetic re-vein ice. The explanation of this phenomenon should be sought in the mechanism of formation of syngenetic veins in the subaqual mode. The key to solving this issue may also be a comparison of the mineralization of syngenetic ice veins currently forming on floodplains and laids with the composition of possible sources of water flowing into frost-breaking cracks. From the analysis of the data obtained, it follows that: 1) the mineralization of ice veins filling modern frost-breaking cracks (of the current year) on floodplains and laids is often very close and in most cases does not exceed, according to testing data, 0.02 g/l. It is obvious that veins with greater mineralization are also formed, but they have not yet been tested by us; 2) the mineralization of the water of rivers and lakes ranges from 0.05 to 0.15 g / l, it rises slightly in the estuaries of the valleys, where salt lakes can occur on floodplains, and in the river the water can be heavily salted during high tide. The salinity of the water of the Kara Sea, even near the coast, is 7-16 g/ l; 3) the salinity of the ice cover in the coastal parts of the Kara Sea and the lips is always less than the salinity of the source water – it almost never reaches a value of 1 g/ l. The explanation for this is given in the monograph of B. A. Savelyev^[23]. It should be noted that we sampled ice in summer – during its destruction, possibly at the stage of ice formation in autumn, its salinity is slightly higher in the lower part of the ice sheet; 4) the chemical composition of the permafrost waters of the seasonal thawing layer is characterized by fairly close mineralization values – from 0.07 to 0.14 g/l. However, sometimes, although quite rarely, lenses of water with a salinity of up to 3.5 g/l are found on the sole of the seasonal thawing layer (for example, on the watershed surface in the upper reaches of the Pemakodayakha River, Northern Yamal ^[10]).

                We emphasize that the amount of water-soluble salts in vein-containing sediments is, as a rule, significantly higher than that of vein ice. It often reaches 1-2 g/kg in alluvial and lagoon-marine soils and 2.5-5, less often up to 10-20 g/kg in marine (coastal–marine) soils^[10].

                The above facts allow us to present the general features of the formation of the salt composition of re-vein ice in various facies conditions as follows. On high terraces and watershed plains, only atmospheric water is involved in the formation of ice veins (epigenetic type). Ice syngenetic veins developing on the surface of high floodplains and laids also owe their origin mainly to the flow of atmospheric moisture into frost-breaking cracks (if the crack is open to the daytime surface) or waters of the seasonally thawed layer (in the case of intra-ground frost-breaking cracks). Only in rare cases, saltier waters can get into the cracks here: if there is a salt lake nearby, or as a result of an extremely active tide, or more often a surge. Note that such tides and surges can occur only in summer, when the surface of the sea or the lip is free of ice, and during this period most of the frost-breaking cracks (although, according to our observations, not all) it's already closed.

                The cryohydrochemical material obtained by the author also testifies to the possibility of the formation of syngenetic re-vein ice in subaqual conditions.^[10] In the northern regions of Yamal and Gydan Peninsula, we have repeatedly observed polygonal relief under water at the bottom of shallow lakes, less often it was observed on the littoral of the lips and seas and only in isolated cases - in shallow water, in riverbeds. Of course, the same pattern was observed in the past (in the Pleistocene and Holocene). Of course, the polygonal relief under water can also be inherited, formed after the flooding of a polygonal-vein array formed in subaerial conditions. But this does not exclude the possibility of subaqual vein growth. The complex structure of syngenetic veins in saline marine (lagoon-marine) soil strata, the differentiation of their total mineralization into separate wedges and the increased content of water-soluble salts (among them chlorides) compared with veins of subaerial origin indicate the possibility of their formation in the subaqual conditions of the upper littoral of the lips and seas.

                Of course, the question is legitimate then, why are syngenetic veins lying in marine saline soils often poorly mineralized? When discussing this issue, it should be emphasized that the cracking of veins located in shallow sea conditions occurs in winter when the water layer above them freezes. The formed ice also cracks above the veins, and through cracks are formed, open to the daytime surface. This leads to the fact that the cracks are clogged with ultra–fresh snow, which, on the one hand, makes it extremely difficult for seawater to penetrate into the cracks, and on the other hand, it greatly decompresses it. However, this does not completely exclude the possibility of salt seawater entering the body of veins through cracks. It is known that the cover sea ice contains a significant amount of brine. It is important to take into account that the lowest solidification temperature, equal to -55 ° C, has CaCl ₂^[23], the relatively low solidification temperature of NaCl is -22.6 °C. In the process of ice metamorphism during the year, brine filtration is quite intensive in it. According to B. A. Savelyev^[23], an increase in the temperature of the ice cover in spring (in March – April) leads to an increase in the liquid phase and the formation of through capillaries in the ice, through which intensive brine infiltration begins downwards. Moreover, chlorine compounds should migrate first of all. If there is a snow plug in the frost crack, the brine mixes with the snow and often significantly decompresses. Getting below, into the vein, in conditions of lower temperatures, the water freezes in the form of an elementary vein having a salinity 10-15 times less than the salinity of sea (source) water and 3-4 times less than the salinity of the cover ice. However, its mineralization is often one or two orders of magnitude greater than the mineralization of moisture filling frost-breaking cracks in subaerial conditions (even after water flows down the walls of frost-breaking cracks in relatively salty soils).^[10]

Interesting data were obtained by a joint analysis of the chemical composition of ice and its enzymatic activity. Different types of ice have demonstrated different activity: in the veins of the lower part of the Late Pleistocene section of the Seyakhinskaya edoma, which are somewhat fresher than the upper ones (salinity from 17 to 80 mg/l), proteolytic activity varies from 44 to 154 f.u./l. In the veins of the middle tier (salinity 110-140 mg /l), the distribution of activity is quite mosaic, it varies from 48 to 180 f.u. / l., in the veins of the upper part of the section (with a noticeable admixture of sand in the ice), formed 11-20 thousand years ago, (they are saltier - mineralization from 130 to 300 mg/l) proteolytic activity varies from 100 to 200 f.units / l. Interestingly, in small veins of the upper tier, where high mineralization was noted, the activity values turned out to be quite low – about 70 f.u./ l. Nevertheless, there is a general trend of increasing proteolytic activity in veins from the bottom up from more fresh to more salty. Thus, the ice of veins formed with a slightly greater participation of the Guba waters has a noticeably higher salinity and higher enzymatic activity.^[21]

In textural schlier ice in the edom thickness, the distribution of activity is most clearly consistent with the distribution of mineralization. In the texture-forming ice of the lower tier, the activity increases from the bottom up from 40 to 320 f.u./l, reaches a maximum value of 350 f.u./l in the middle part (where the highest mineralization is noted) and decreases slightly in the upper part of the section to 150 f.u./l. ^[21]

          These data confirmed that the formation of the lower part of the Seyakhinsky polygonal-vein complex occurred in the conditions of the high laida of the Gulf of Ob, and its upper part - rather on the low laida or even on the beach.^[21]

The Seyakhinsky polygonal-vein complex, judging by the inclusions of sand in the body of veins in the form of vertical tracers, clearly visible especially in the upper part of the outcrop, was formed in subaqual conditions. This is also confirmed by the data on the chemical composition of sand and ice veins and on the activity of enzymes in the ice. Most likely, this active formation of veins occurred nevertheless in conditions of shallower waters, closer to the conditions of the supralithoral or the beach. After a certain period when there was accumulation of mineral strata with little saturated organic matter, the subaqual regime was replaced mainly by a subaerial one (most likely due to a local change in the level of the reservoir or local elevation of the shore) and the growth of re-vein ice resumed. During this period there was an intensive accumulation of organic matter and, therefore, it can be well dated to 14C. Thus, by examining the coastal strata, it is possible to trace the fluctuations of the sea in the past. In addition to global trends of sea level decline or rise, there are no less (and often noticeably more) active changes in the level of the coast, due to geocratic movements. It is with them that such an active sedimentation can be associated on the eastern coast of Yamal (and probably on the western coast too) at the end of the Late Pleistocene cryochron - i.e. at a time when deep regression of the Arctic basin is assumed according to many paleoceanological reconstructions (as previously noted in ^[13]). Obviously, this regression was not as widespread and not as deep (as is commonly believed).

               In the last 2-4 years, interest in hydrochemical studies of re-vein ice has increased, as evidenced by publications in highly rated journals [24-26, etc.]

         But.Pisisyuk and co-authors investigated the geochemical characteristics of the re-vein ice of the eastern coast of the Faddevsky Peninsula.^[24] The predominant part of solutes in the studied samples is represented by Na⁺ and Cl^- ions, ranging from 3.5 to 141.1 mg/l for Na+ and from 6.1 to 146.4 mg/l for Cl^- (Table 8). The highest concentrations are observed in the samples of schlier ice and the "tail" of the Holocene vein concentrations of Cl^- (146.4 and 100.5 mg/l) and Na⁺ (141.1 mg/l). and 51.3 mg/l), respectively.^[24]

SO ₄ ^{2- prevails in the composition of solutes of the Late Pleistocene PLL of the Faddevsky Peninsula}, although the values are distributed unevenly over the ice massif, ranging from 4.2 to 131.6 mg/l. Late Pleistocene PPLS show enrichment with non-marine SO ₄ ^2-, while data on SO ₄ ^2- obtained at other sites reflect the "marine" signal.

Among Holocene veins, the content of SO ₄ ^2- does not exceed 7.49 mg/l, with the exception of a sample from the "tail" of the vein, where the value reaches 22.3 mg/l. SO ₄ ^2- in schlier ice fully reflects the "marine" composition with a concentration of 28 mg/l. Ca2+ is mainly represented in components that do not contain sea salt, with the exception of schlier ice. Ca ²⁺ is evenly distributed between samples from 1.1 to 6.3 mg/l. A similar range was recorded for K⁺ and ^Mg2+ ions, reaching 3.4 mg/l and 8.75 mg/l, respectively. Schlier ice (A1) demonstrates a peak value of K+ (9.1 mg/l) and a high content of Mg ²⁺ (6 mg/l).^[24]

Table 8. Average ratio of the main ions of the re-vein ice of the eastern coast of the Faddevsky Peninsula From ^[24]

                V.Butakov ^[9] having investigated the geochemical composition of the re-vein ice of the Kara region: in the Arctic tundra with marine influence (O. Bely, Sibiryakova, village Dixon), in the northern tundra (Gyda village, Karepovsky village in the west of Taimyr), in the typical tundra (Yamal Peninsula in the area of Marre-Sale lake, Sokhonto Lake and in the valley of the Yuribey River) and in the southern tundra (in the north of the Pur-Taz interfluve), came to the conclusion that the main the source of the chemical composition of re-vein ice is atmospheric winter precipitation with marine or continental aerosols. Another source may be the permafrost waters of the seasonally thawed layer. Their composition is formed mainly due to sediments drained by surface and atmospheric waters. The third source is surface water, which enters the veins when the water level rises during sea surges or floods of river and lake waters. The chemical composition of re-vein ice differs from texture-forming ice primarily by lower concentrations of chemical elements. The composition of ice can also be influenced by organic matter that sorbs chemical elements due to the structure of organic molecules.^[9] He noted that chloride and sodium ions entered the veins of the Arctic islands together with marine aerosols as part of atmospheric precipitation. At the same time, the re-vein ice of the Arctic islands of Bely and Sibiryakova and the ice of the settlement area . Dixon in Western Taimyr is characterized by low mineralization – less than 50 mg/l. The re-vein ices studied on Bely Island have ultra-fresh (34-43 mg/l) bicarbonate-chloride, sodium-magnesium and calcium-magnesium-sodium composition (previously, Yu.K. Vasilchuk, A.K. Vasilchuk and V.T.Trofimov ^[2,3] studied highly mineralized re-vein ices on Bely Island). The re-vein ices studied on Sibiryakova Island have ultra-fresh (38-40 mg/l) chloride, magnesium-sodium and sodium composition.

        The re-vein ice of the area of P. Dixon has an ultra-fresh (25-49 mg/l) bicarbonate, chloride-bicarbonate, chloride, magnesium-calcium, magnesium-sodium-calcium, sodium, calcium-magnesium-sodium composition. In the area of the village . Dixon, both in the upper and lower tiers of ice veins located on a slope high above sea level, Ca ²⁺ and HCO ₃^{- ions predominate}. The veins opened in the valley floor are dominated by Cl- and Na+ ions, which came from flooding the lowlands with sodium chloride waters during the formation of Holocene veins.^[9]

At the same time, V. Butakov and co-authors^[8] note that the chemical composition of the re-vein ice studied in the coastal zone of the key sites of Bely Island, Sibiryakova Island, Western Yamal and Western Taimyr was influenced by marine and continental aerosols. Syngenetic re-vein ice, fresh and ultra-fresh in mineralization, formed during the freezing of meltwater, contain snow-sorbed marine aerosols. Re-vein ice in a remote area of the lake from the sea. Sohonto have no signs of marine influence on the ratio of basic ions. Re-vein ices with mineral inclusions were formed not only due to thawed snow waters with aerosols of continental origin, but also due to super-frozen waters. The mineralization of syngenetic re-vein ice without the participation of segregation ice formation does not depend on the degree of salinity of the host sediments.^[8]

                K. Holland and co-authors^[25] considered the geochemical composition (Cl^- , Na⁺, Br, SO ₄ ^2-, Mg ²⁺, Ca ²⁺, K⁺) of the re-vein ice of the Taktayaktak coast in northern Canada (69,409°s.w., 133,124° w.d.). Depletion values of SO ₄ ^2- indicates that the geochemistry of re-vein ice is predominantly of marine origin, mainly from near-surface seawater. A linear decrease in bromine enrichment and, to a lesser extent, Mg ²⁺, Ca 2⁺ and K⁺ relative to Na₊ and d ^exc and the values of ?18 ^O (?2 H) up to 2800 thousand years b2k (in calendar years up to 2000) suggests the presence of some systematic factor leading to such a strong trend, possibly, due to the contribution of deep frost during the early growth of the ice vein, although this has been little proven so far. Throughout the record, there has been a long-term increase in sea salt concentrations in the period from 4600 to 700 years b2k, which may indicate a reduction in the distance to the coast of the studied area in the late Holocene, caused by the retreat of the coast due to the high rate of coastal erosion and minor changes in RSL. This study is a good step towards understanding the factors influencing the ionic geochemistry of coastal re-vein ice during the Holocene.^[25]

J. Iizuka and co-authors^[26] conducted a study of re-vein ice exposed by the Cape Barrow outcrop (Northern Alaska, 71°18's.w., 156°40' s. d.). Ca ²⁺, Na⁺, SO ₄ ^2-, NO ₃^-, Cl^- and other ions, which are part of the re-vein ice, had a marine and continental origin. The ratio of concentrations of the same ions of marine and continental origin indicates the different role of seawater in the formation of the macronutrient composition of re-vein ice. Researchers have found that all Na+ is of marine origin. Ca ²⁺ and SO ₄ ^{2- ions were of continental origin}, contained in an amount of 0.022 mmol/l and 0.06 mmol/l, respectively. It was found that the macro-component composition of the re-vein ice was formed under the combined influence of the ice-containing soils (Ca ²⁺, SO ₄ ^2-) and the waters of the Beaufort Sea (Na⁺, Cl^-, Br^-).^[26].

          E.V. Bezrukova and co-authors^[27] showed that the variations of macronutrients in the thickness of the bottom sediments of the lake. Cascade-1 in the Eastern Sayan indicate that the content of almost all petrogenic elements exhibit their maxima between 13,200-12,800 cal. l.n. in the thickness of gray clays. Between about 12,800-12,000 cal. years ago (biogenic-terrigenous silty layer, LGZ 3a) the values of Na, K, Ca, Mg, Al, Si, Ti, Mn, Sr and Zr decrease, and LOI increases. Between 12,000 and 7,500 cal. l.n. the contents of all the main elements remain almost constant, and the concentrations of only Na, Mg, Al and Si increase slightly. After 7,500 cal. l.n., the contents of all elements seem to increase, while the LOI value tends to gradually and noticeably decrease. The P value reaches its maximum in the uppermost 2 cm of the core.^[27]

                Conclusions

1. Comparison of the range of variability of mineralization and ionic composition of water-soluble salts in re-vein ice of different ages near the village. Seyakha (East Yamal) showed:

a). Holocene PPLS in the lake-marsh tab are the most fresh in general - their mineralization varies in a narrow range from 24 to 27 mg/l, the content of anions and cations also varies slightly from 1 to 10 mg/l;

b). Holocene PLL in the lake-marsh tab are close to Holocene PLL in the thickness of the floodplain of the Seyakha River (Green) - the total mineralization varies markedly from 26 to 176 mg/l and Late Pleistocene PLL in the thickness of the third terrace, in which the total mineralization is even more variable from 17 to 309 mg/l. In the ionic composition of water-soluble salts, chlorides vary very widely in floodplain Holocene PLL from 4.2 to even 47.9 mg/l (in the tail of the vein), and in late Pleistocene PLL from 4 to 24 mg/l, the great variability of sulfates also draws attention: in floodplain Holocene PLL from 3.7 to 25.5 mg/l, and in late Pleistocene PPL from 0.1 to 46 mg/l.

2. Despite the relatively rare occurrence of more saline differences of re-vein ice, they should not be neglected, since it is these veins or fragments of veins that are direct indicators of the marine or lagoon-marine sedimentation regime during their formation.

3. In general, we can talk about mainly atmospheric nutrition of both Holocene and Late Pleistocene re-vein ice of this site.

4. The noticeable role of atmospheric nutrition in the texture-forming ice of the sediments containing veins is sometimes complicated by the participation of salts dissolved from the host sediments, for example, during the development of a lake-marsh basin on the surface of the third terrace or by the influx of Guba waters during the run-up increase in the level of the lip and water in the estuary of the river to the surface of the floodplain.

Thanks

The author is deeply grateful to Dr. A.Vasilchuk and Ph.D. N.Budantseva for their participation in field work and L. Bludushkina for the design of schedules.