Soil Formation, Subaerial Sedimentation Processes and Ancient Cultures during MIS 2 and the Deglaciation Phase MIS 1 in the Baikal–Yenisei Siberia (Russia)

Abstract

The time of Sartan glaciation in the Baikal–Yenisei Siberia, is comparable with that of MIS 2 and the deglaciation phase MIS 1. Loess loams, aeolian–colluvial sands and sandy loams represent subaerial sediments. There are four subhorizons (sr¹, sr², sr³ and sr⁴) in the Sartan horizon (sr). Sedimentary and soil-forming processes at different stratigraphic levels are considered. Differing soil formation types of cold periods are distinguished. Soils of the interstadial type with the A-C profile are represented only in the Early Sartan section of this paper. The soils of the pleniglacial type are discussed throughout the section. Their initial profile is O-C, TJ-C and W-C. Plant detritus remnants or poor thin humus horizons are preserved in places from the upper horizons. We propose for the first time for the interphasial soil formation type of cold stages to be distinguished. This is represented in the sections by the preserved BCm, BCg, Cm and Cg horizons of 15–20 cm thick. The upper horizons are absent in most sections. According to the surviving fragments, these were organogenous (O, TJ and T) and organomineral (AO and W) horizons. The sedimentation and soil formation features are considered from the perspective reconstruction of the Sartan natural and climatic conditions. Buried Sartan soils often contain cultural layers. Soil formation shows a well-defined periodicity of natural condition stabilization, which allowed ancient populations to adapt actively to various situations. Archaeologists’ interest in fossil soils is based on the ability of soils to “record” information about the natural and climatic conditions of human habitation.

1. Introduction

The Baikal–Yenisei Siberia, is a territory located between Lake Baikal in the east and the Yenisei River valley in the west, located at 52°–56° N and 93°–109° E. The southern border runs along the foot of the Eastern Sayan Mountains (Figure 1).

The Baikal–Yenisei Siberia, belongs to the extra glacial zone in the geographical framework under study. During the cold stages of the Pleistocene, glaciers existed only in the mountains and did not descend further than their foothills.

The cold stage preceding the Holocene, within the regional (Siberian) climatic–stratigraphic scale, is regarded as the Sartan (sr) glacier, the stratigraphic analogs of which are the final stages of the last glacials (Late Wurm, Late Vistula, Late Valdai, Late Wisconsin, Late Weichsel). The Sartan glaciation covers the chronological interval of ~24–10.3 ¹⁴C ka BP or ~27–28–11.7 ka cal BP, which is correlated with MIS 2 and the deglaciation phase MIS 1.

In Greenland, ice core records [1] MIS 2 synchronized with Greenland Stadiums 3-1. The beginning of MIS 2 is defined as the Last Glacial Maximum (LGM) or the time when the continental ice sheets reached their maximum total mass during the last ice age. Maximum ice sheet size coincides with a minimum in global sea level [2,3].

The chronological beginning of LGM is still subject to discussion [2,3,4,5]. However, according to Philip Hughes and Philip Gibbard, the compromise in determining the LGM age is to rely on the NGRIP curve records [1] and correlate them with Greenland Stadium 3 in the range of 27.54–23.34 ka cal BP [5].

The deglaciation phase MIS 1 is identified with the retreat of a glacier of 14.7–11.7 ka cal BP, under conditions of changing climatic waves of warming–cooling: Oldest Dryas (16.9–14.7 cal ka BP), Bölling (14, 7–14.1 cal ka BP), Older Dryas (14.9–12.91 cal ka BP), Allerød (12.9–12.71 cal ka BP) and Younger Dryas (12, 7–11.71 cal ka BP).

The LGM concept is relevant both for paleoclimatology [4] and archaeology. Archaeologically, MIS 2 is a time of major cultural change. The depopulation of territories is explained by the peculiarities of the natural LGM conditions, highlighting cultural breaks, migrations, technological innovations and changes. The impact of the LGM on the culture of ancient humans is actively discussed in the literature [6,7,8,9,10,11,12,13,14,15,16,17,18,19].

The urgency of the climate change problem has forced the scientific community to pay special attention to Lake Baikal, in the bottom sediments of which an archive of paleo climatic data of tens of millions of years old are stored.

Based on the results of Lake Baikal bottom sediment drilling by an international team of scientists using various research methods, records of global climate changes over the past 1–8 million years have been obtained [20,21,22,23,24].

Nevertheless, these records do not contain enough detailed information about the natural environment during MIS 2. In general, MIS 2 is defined as a period with steppe and tundra landscape in a cold, extremely continental arid climate and permafrost.

In more detail, climatogenic changes in the natural environment have been revealed during palynological studies of the bottom sediments of Lake Kotokel and peatlands, located on the Lake Baikal eastern coast [25,26,27,28,29,30].

According to palynological data, the Sartan period is characterized mainly by tundra, tundra-steppe and steppe vegetation. The appearance of woody vegetation has been recorded from 15.5 ka cal BP [26].

Currently, an active interdisciplinary study of terrestrial deposit sections is ongoing in the region (including geoarchaeological sites) in the multi-proxy records (MPR) system [31,32,33].

It is crucial to note that all of these studies have only scratched the surface of problems of soil formation during cold periods. At the same time, the terrain and climatic reconstruction obtained by various methods during the studies of bottom sediments and peatlands and the MPR materials do not contradict the conclusions previously made from pedolithological data [34,35] and presented in this article.

Soil formation processes in the cold Pleistocene epoch, including the Sartan (sr) glaciation, which is the closest to our time, is understudied [36,37,38].

Sartan subaerial deposits are exposed by conventional soil sections from a depth of 40–60 cm from the surface. They are located in the root zone and have a significant impact on the appearance, properties and profile structure of ”modern” soil [39].

The article presents a detailed study of the structure and properties of Sartan subaerial deposits, the soil formation process based on the reference geoarchaeological sites in the Baikal–Yenisei Siberia, and identifying the impact of harsh environmental conditions on ancient cultures.

2. Materials and Methods

2.1. Study Area

The Central Siberian Plateau occupies the main part of the Baikal–Yenisei Siberia, its altitudes varying from 550 to 800 m a.s.l. in the south to 1000 m in the north. Its ridges (1000–1700 m a.s.l.m) stretch along Lake Baikal western shore, with a natural lake level of 455 m. In the northeast, the ridges rise to 2500 m [40].

The main waterways of the Baikal–Yenisei Siberia, are the Yenisei River, the Lena River (its upper course) and the Angara River, with major tributaries Irkut, Kitoi, Belaya, Oka, Kuda, etc.

There are Paleozoic marine sedimentary rocks mainly in the territory of the Baikal–Yenisei Siberia. Carbonate rocks represent the deposits: limestones, dolomites, calcareous sandstones and siltstones. Continental, predominantly carbonate-free sandstones and siltstones with coal interlayers partially cover Paleozoic marine rocks. These are Jurassic deposits in the south of the region, and Permian–Carboniferous rocks in the extreme west [41].

Loose Quaternary cover sediments in the Baikal–Yenisei Siberia, are different. There is an eluvium of insignificant thickness (less than 1 m) at the tops of watersheds. On slopes, there is colluvium, increasing in thickness towards the foot to 4–5 m and above. The alluvium is formed on the bottoms of river valleys. Regional loess-like deposits are found only along the sides of large river valleys, covering above floodplains terraces and adjoining parts of the slopes. It is known that loess-like sediments do not form significant homogenous covers even on terraces. They are often mixed with colluvial, aeolian and aeolian–colluvial deposits. The total thickness of such formations can reach up to 10 m. The earliest loess-like loams have been found in regional areas since the beginning of the Pleistocene [42,43].

The climate of the Baikal–Yenisei Siberia, is distinctly continental in general due to its location in the center of Asia. The annual average monthly temperature amplitude ranges from 38 °C in the south to 48 °C in the north. The daily amplitude reaches 20–30 °C. The average temperatures in January, the coldest month, range from −15 °C in the south to −33 °C in the north. July is the warmest month. Its average air temperature is +18 °C. The average annual rainfall ranges from 380 to 450 mm. Although it is insignificant, the atmospheric humidity coefficient is slightly higher than 1, due to low evaporation [44].

The Baikal–Yenisei Siberia, was a periglacial area in the Pleistocene. Cover glaciers were located at a great distance—on the Arctic Ocean coast and in the north of Western Siberia. Glaciers in the region were mountainous (in the south—the Eastern Sayan mountain range, to the northeast of Lake Baikal—the North-Baikal and Patomskoye Uplands).

At the same time, the studied region was a zone of permafrost distribution, with significant thickness. The modern Baikal–Yenisei Siberia, inherited large cold reserves from permafrost. Active permafrost degradation began in the Holocene (Preboreal).

At present, only isolated islands with a permafrost thickness of up to 80–100 m have survived the continuous permafrost in the south of the region. There are also permafrost lenses with a thickness of 15 m in the wetlands of rivers in the taiga zone. In the north of the Baikal–Yenisei Siberia, permafrost is more widespread and better preserved.

Taiga landscapes dominate in the region, where the main species are light Coniferous species of larch (Larix sibirica) and pine (Pinus silvestris). Cedar (Pinus sibirica) is found in high mountainous areas. In the southern plain, agricultural lands occupy significant areas. The forests here are mainly secondary—pine and small-leaved (Betula sp., Populus tremula). In the southeastern part of the Baikal–Yenisei Siberia, there are small islands of steppes. Meadows and swamps cause vegetation in relief depressions.

Luvisols, Cambisols and Retisols represent the modern soil cover under Coniferous forests and Chernozem in the steppe areas.

2.2. Archaeological Background

For the Baikal–Yenisei Siberia, until recently, the cultural completeness of Sartan was problematic, since for a long time it was believed that there was a large chronological break in the cultures of this time [45,46,47,48]. As a result of recent research, the list of Sartan archaeological sites has significantly expanded. Among the determining factors was the detailed study of the stratigraphic sequence of the Sartan deposits, which allowed us to revise the age of many archaeological complexes and to search for new objects.

Currently, approximately 50 archaeological sites are known on the territory of the Baikal–Yenisei Siberia, the materials of which are associated with the Sartan deposits. The age of some complexes is determined by their stratigraphic position and morphotypological characteristics of lithic assemblages.

At 20 sites, a team of authors conducted detailed interdisciplinary studies using radiocarbon dating, the results of which are presented in this article.

The territorial spreading of the Sartan archaeological sites is uneven. This is due, first, to the specificity of research traditions, which was expressed by the insufficient knowledge of the territory. Archaeological sites of this period are mostly concentrated in the valleys of the major tributaries of the Angara River. In the flood zones of its four reservoirs (Irkutsk, Bratsk, Ust-Ilimsk and Boguchany), in contrast to the Yenisei River valley, targeted searches for Sartan archaeological sites have not been carried out. Due to excavation in the area of the future Angara reservoir cascade, the list of Sartan archaeological objects was practically not expanded. Five such objects are known in the area of the Bratsk reservoir. Several more sites have been found in the Ust-Ilimsk and Boguchany reservoirs, but there are not enough data on them. On the Baikal coast, the Sartan complexes have been studied only in the north. In other areas, single Late Upper Paleolithic sites are known only by individual surface collections.

The known archaeological sites of Sartan occupy the middle and lower tiers of the relief with relative elevations in the range of 9–30 m. In these areas, archaeological materials are usually in situ, since the cultural-containing deposits of this period are a variety of soil formations, except for the Early Sartan sections with the soliflucted soils. Many of the Sartan archaeological sites can be defined as multilayered or microlayered [49], which allows the continuous natural and cultural evolution to be traced with a reliable geochronological timeline of events.

2.3. Methods

2.3.1. Interdisciplinary Pedolithological Method

A stratigraphy, structure and composition investigation of Sartan deposits and soils in the Baikal–Yenisei Siberia, was carried out using the pedolithological method at numerous geoarchaeological sites, including the reference (Figure 1) with radiocarbon, archaeological dating and paleontological material.

The pedolithological method was developed by the Galina Vorobieva based on studying the sections of “modern” soils, “soil-forming” rocks, buried heterochronous fossil soils and loose sediments separating them [35].

The method has been tested on many hundreds of soil sections, geoarchaeological objects (excavations of multilayered and single-layered sites and burial grounds), as well as on objects of a wide age range—from sediment sections of the final Miocene and lower Pliocene to the historical urban cultural layer in Irkutsk city [42,43,50].

Large volumes of geological and archaeological workings and huge areas of outcrop walls require replacing the usual method of description adopted in soil science with other methods that would make it possible to easily encode and clearly demonstrate extensive information. These requirements are most consistent with large-scale color drawings of section walls (sometimes bottoms), with indications of the numbers of lithological layers, levels of cultural horizons, deposits genesis, information on the figure (in the form of various icons and indexes) about the shape and nature of new formations, inclusions, granulometric composition, structural features, deformations, etc. A stratigraphic scale bar accompanies the figure. The explanatory note of the figure is given in the form of a description of the composite section and transcript of this description, indicating the genesis of each layer [50]. In addition, materials on the photo-fixation of the structure of the excavation sites walls and bottoms are provided. The fundamental difference with the pedolithological approach is that the research is based on fieldwork on the section’s structure, and therefore, conclusions made directly in the field form the basis of all information; analytics only clarifies their correctness.

Thus, the pedolithological method allows us to consider sections of subaerial deposits as a laminated stratum, in which traces of various natural events, caused by climate and landscape changes, seismotectonics, exogenous geological processes, anthropogenic and other factors, are encoded.

The pedolithological method was used in studies in the 1980s and 1990s. In the 20th century, it allowed a detailed stratigraphic division of the Sartan subaerial formations in the Baikal–Yenisei Siberia, data to be conducted [39,40]. Four stratigraphic subhorizons are distinguished in their structure: sr¹–~28–22 ka cal BP (divided into two phases: sr¹₁(sol)–~28–25 cal ka BP and sr¹₂–~25–22 ka cal BP; sr²–~22–19 ka cal BP; sr³–~19–15 ka cal BP; sr⁴–~15–11.7 ka cal BP. Its own climate, sedimentation and pedogenesis processes characterized each stage of the Sartan period (Figure 2 and Figure 3A,B).

The increased number of dating methods and their improvement in recent decades have led to the clarification of the chronological intervals of the Sartan subhorizons. Herein, for the reference geoarchaeological objects, new radiocarbon dates, recalculated to calendar dates, are given.

2.3.2. Radiocarbon Dating

This study analyzes data only from geoarchaeological sites where interdisciplinary studies have been conducted using paleopedology and geoarchaeology methods and for which reliable radiocarbon dates corresponding to MIS 2 have been obtained.

The author’s team carried out detailed interdisciplinary studies using radiocarbon dating on 20 reference geoarchaeological sites (Figure 1). Most of them—that is, 15 sites—are located in the Southern Angara region; 3 sites are located in the Lena-Baikal region; 1 site is located in the Kan-Yenisei region.

The description of some of the objects is presented in this article; the others are described in the Appendix A.

The list of radiocarbon dates represented in

Table A1. Radiocarbon dates for the Sartan geoarchaeological sites of the Baikal–Yenisei Siberia (sorted by layers, from bottom to top).

#	Site	Layer	Dated Material	Lab #	14C date, BP	Age, Mean HPD cal BP	References
Southern Angara region
1	Malta	8	Mammuthus bone	OxA-39087	21,860 ± 130	26,130 ± 140	This paper
2	Malta	8	Rangifer tarandus bone	OxA-6191	21,700 ± 160	26,010 ± 160	[90]
3	Malta	8	Bison bone	GIN-8475	21,600 ± 170	25,900 ± 160	[75]
4	Malta	8	Mammuthus bone	GIN-9509	21,400 ± 110	25,750 ± 120	[75]
5	Malta	8	Mammal bone	OxA-6193	21,340 ± 340	25,620 ± 360	[69]
6	Malta	8	Mammuthus bone	GIN-7702	21,300 ± 110	25,630 ± 150	[75]
7	Malta	8	Mammuthus bone	GIN-7704	21,300 ± 300	25,580 ± 310	[75]
8	Malta	8	Mammuthus bone	GIN-7703	21,100 ± 150	25,450 ± 170	[75]
9	Malta	8.1	Mammuthus bone	GIN-8888	22,900 ± 240	27,180 ± 280	[75]
10	Malta	8.2	Mammuthus bone	GIN-7708	21,600 ± 200	25,910 ± 200	[75]
11	Malta	8.3	Mammuthus bone	GIN-7706	21,000 ± 140	25,360 ± 180	[75]
12	Malta	8.4	Mammuthus bone	GIN-7710	20,800 ± 140	25,070 ± 210	[75]
13	Malta	8–9.1	Mammuthus tooth	GIN-9510	21,000 ± 110	25,360 ± 160	[75]
14	Malta	8–9.1	Mammuthus tusk	GIN-9508	20,800 ± 120	25,070 ± 180	[75]
15	Malta	8–9.1	Mammal bone	OxA-6192	20,340 ± 320	24,510 ± 400	[87]
16	Malta	9.1	Mammal bone	GIN-8887	20,440 ± 240	24,600 ± 320	[75]
17	Malta	9.1	Mammal bone	GIN-7705	19,900 ± 800	24,120 ± 920	[75]
18	Malta	9.2	Bovinae bone	GIN-8476	14,720 ± 190	17,950 ± 260	[75]
19	Malta	10	Charcoal	AA-37473	12,490 ± 90	14,680 ± 230	[75]
20	Malta	10	Charcoal	AA-37186	12,400 ± 90	14,550 ± 230	[75]
21	Malta	10	Charcoal	AA-37186	12,140 ± 90	14,040 ± 170	[75]
22	Malta	10	Charcoal	AA-20930	12,015 ± 85	13,900 ± 100	[75]
23	Buret	1	Mammal bone	SOAN-1680	21,190 ± 100	25,520 ± 140	[72]
24	Igeteiskii Log 1	4	Mammal bone	LE-1592	23,508 ± 250	27,690 ± 250	[34]
25	Igeteiskii Log 1	4	Mammal bone	LE-1590	21,260 ± 240	25,550 ± 240	[73]
26	Igeteiskii Log 2	n/n	Soil	LU-6515	22,500 ± 980	26,930 ± 1030	[74]
27	Malta-Strelka	n/n	Soil	LU -6529	21,740 ± 480	26,100 ± 520	[91]
28	Krasnyi Yar 1	6	Mammal bone	SOAN-7780	19,975 ± 170	24,030 ± 200	[74]
29	Krasnyi Yar 1	6	Mammal bone	SOAN-7779	19,760 ± 230	23,750 ± 300	[74]
30	Krasnyi Yar 1	6	Mammal bone	GIN-5330	19,100 ± 100	23,040 ± 130	[74]
31	Krasnyi Yar 1	3	Mammal bone	SOAN-7778	15,880 ± 240	19,220 ± 270	[74]
32	Ust-Oda	2	Mammal bone	SOAN-8848	18,250 ± 190	22,160 ± 220	[92]
33	Novyi Angarskii Most	below 5	Mammal bone	SOAN-5180	18,510 ± 220	22,480 ± 240	[92]
34	Novyi Angarskii Most	5	Mammal bone	SOAN-5181	14,840 ± 125	18,120 ± 170	[92]
35	Malta-Most 1	3	Equus sp. bone	OxA-39082	15,167 ± 59	18,470 ± 110	This paper
36	Malta-Most 1	3	Mammal bone	GIN-9511	14,680 ± 100	17,970 ± 160	[93]
37	Kitoiskii Most	1	Mammal bone	UCIAMS-207544	14,970 ± 70	18,330 ± 150	[94]
38	Kitoiskii Most	1	Mammal bone	UCIAMS-207545	14,620 ± 60	17,920 ± 140	[94]
39	Cheremushnik 2	2	Rangifer tarandus bone	OxA-39085	15,651 ± 63	18,920 ± 60	This paper
40	Cheremushnik 2	1	Equus sp. bone	OxA-39084	12,602 ± 46	15,000 ± 110	This paper
41	Badai 5	3	Equus sp. bone	OxA-39083	12,081 ± 44	13,940 ± 80	This paper
42	Sosnovyi Bor	5	Rangifer tarandus bone	OxA-39086	12,390 ± 45	14,520 ± 190	This paper
43	Sosnovyi Bor	4	Mammal bone	AA-38038	12,090 ± 110	13,990 ± 180	[95]
44	Sosnovyi Bor	3b	Mammal bone	GIN-5328	12,060 ± 120	13,960 ± 180	[34]
45	Ust-Belaya	17	Bison bone	GIN-5835	11,810 ± 90	13,670 ± 110	This paper
46	Ust-Belaya	16	Charcoal	SOAN-4016	15,300 ± 800	18,690 ± 1000	[96]
47	Ust-Belaya	16	Large mammal bone	UCIAMS-157872	12,140 ± 30	14,030 ± 60	[97]
48	Ust-Belaya	16	Large mammal bone	UCIAMS-157873	12,035 ± 30	13,910 ± 70	[97]
49	Ust-Belaya	16	Charcoal	GIN-9514	11,300 ± 600	13,350 ± 830	[98]
50	Ust-Belaya	14b	Charcoal	AA-36951	11,765 ± 70	13,630 ± 80	[75]
51	Ust-Belaya	14	Capreolus pygargus bone	UCIAMS-165555	12,165 ± 45	14,060 ± 80	[97]
52	Ust-Belaya	14	Cervidae horn	OxA-27120	11,800 ± 55	13,660 ± 70	[99]
53	Ust-Belaya	14	Mammal bone	OxA-27123	12,090 ± 60	13,950 ± 90	[99]
54	Ust-Belaya	14	Mammal bone	UCIAMS-144528	11,995 ± 45	13,900 ± 70	[99]
55	Ust-Belaya	14	Bison bone	GIN-5329	11,930 ± 230	13,900 ± 340	[65]
56	Ust-Belaya	14	Charcoal	AA-36914	11,840 ± 75	13,690 ± 100	[65]
57	Ust-Belaya	14	Mammal or bird bone	UCIAMS-157874	11,670 ± 30	13,530 ± 40	[97]
58	Galashikha	5	Large mammal bone	UCIAMS-157876	11,935 ± 25	13,840 ± 90	[75]
59	Galashikha	4	Large mammal bone	UCIAMS-157875	11,650 ± 25	13,520 ± 40	[75]
Lena-Baikal region
60	Shishkino 8	1	Mammal bone	AA-8882	21,190 ± 175	25,510 ± 190	[99]
61	Shishkino 2	3	Mammal bone	GIN-5634	13,900 ± 200	16,860 ± 290	[66]
62	Makarovo 2	4	Charcoal	GIN-481	11,950 ± 50	13,860 ± 100	[66]
63	Makarovo 2	3	Charcoal	GIN-480	11,860 ± 280	13,860 ± 400	[66]
64	Makarovo 2	3	Charcoal	GIN-480	11,400 ± 500	13,450 ± 650	[66]
65	Berloga	lower	Soil	SOAN-4006	14,100 ± 250	17,160 ± 380	[100]
Kan-Yenisei region
66	Strizhovaya Gora	18	Mammal bone	GIN-5326	14,000 ± 1500	17,270 ± 2110	[68]
67	Strizhovaya Gora	14–16	Sharcoal	GIN-5823	13,160 ± 960	15,910 ± 1340	[101]
68	Strizhovaya Gora	16	Mammal bone	GIN-5822	12,090 ± 120	14,000 ± 200	[68]
69	Strizhovaya Gora	15	Mammal bone	GIN-5821	12,000 ± 150	13,910 ± 210	[68]
70	Strizhovaya Gora	14	Mammal bone	GIN-5820	12,250 ± 150	14,350 ± 310	[68]
71	Strizhovaya Gora	13	Mammal bone	GIN-58190	11,890 ± 60	13,740 ± 100	[68]
72	Strizhovaya Gora	13	Mammal bone	IM SOAN-406	10,850 ± 300	12,730 ± 370	[68]
73	Strizhovaya Gora	12	Mammal bone	GIN-5819	11,350 ± 100	13,250 ± 90	[68]
74	Strizhovaya Gora	10	Mammal bone	GIN-5816	17,400 ± 300	21,110 ± 410	[68]

does not include data for which the context, sample material, or laboratory data are unknown.

Most of the dates (46 definitions) were obtained by liquid scintillation counting (LSC) in the Soviet and Russian laboratories of Geological Institute RAS (GIN), Institute of Geology and Mineralogy SB RAS (SOAN), Permafrost Institute SB RAS (IM SOAN), Institute of the History of Material Culture RAS (LE) and St Petersburg State University (LU). At the University of Arizona AMS Laboratory (AA); Oxford Radiocarbon Accelerator Unit, University of Oxford (OxA); Keck-CCAMS Group, University of California, Irvine (UCIAMS), the AMS method was used to obtain the other dates (28 definitions).

Radiocarbon dates were calibrated using the program OxCal 4.4.2 [51], atmospheric curve IntCal2s0 [52]. At almost all sites, the layers in the section were numbered from top to bottom, except at the Malta site, where they are numbered from bottom to top.

3. Results

3.1. The Sartan Chronology

To determine the chronological framework for the stratigraphic subdivisions of Sartan in the Baikal–Yenisei Siberia, we analyzed the collected radiocarbon dates. As a result, dates with large values of the root-mean square deviation (≥500 years) are excluded.

The AMS dates are the most reliable, especially those obtained in recent years in the laboratories of the University of Oxford and the University of California, Irvine. At the same time, it should be noted that in general, many LSC dates are relatively consistent with the AMS data, especially with the GIN index, so they can be considered relatively accurate.

The results of the analysis of radiocarbon dates for the geoarchaeological sites of the Baikal–Yenisei Siberia (

Table 1. Summary data on the age of Sartan sediments and cultural complexes of the Baikal–Yenisei Siberia, according to stratigraphic subdivisions.

	Stratigraphic Subdivision	Site	Layer	Range, Mean HPD cal BP	Geographical Coordinates
Early Sartan	Sartan 1—sr11(sol) from 27,690 ± 250 to 24,510 ± 400	Igeteiskii Log 1	4	from 27,690 ± 250 to 25,550 ± 240	53°34′50.0″ N 103°25′41.0″ E
		Malta	8–9.1	from 27,180 ± 280 to 24,510 ± 400	52°51′06.6″ N 103°30′53.4″ E
		Malta-Strelka	n/n	26,100 ± 520	52°49′28.3 N 103°33′00.3 E
		Buret	1	25,520 ± 140	52°59′03.6″ N 103°31′27.8″ E
		Shishkino 8	1	25,510 ± 190	54° 0′52.88″ N 105°40′43.56″ E
	Sartan 1—sr12 from 22,480 ± 240 to 22,160 ± 220	Krasnyi Yar 1	6	from 24,030 ± 200 to 23,040 ± 130	53°36′53.23″ N 103°28′45.20″ E
		Novyi Angarskii Most	below 5	22,480 ± 240	52°15′20.17″ N 104°16′26.88″ E
		Ust-Oda	2	22,160 ± 220	52°27′40.28″ N 103°45′5.69″ E
Middle Sartan	Sartan 2—sr2	no radiocarbon data
	Sartan 3—sr3 from 19,220 ± 270 to 16,860 ± 290	Krasnyi Yar 1	3	19,220 ± 270	53°36′53.23″ N 103°28′45.20″ E
		Cheremushnik 2	2	18,920 ± 60	52°53′55.8″ N 103°37′11.0″ E
		Malta-Most 1	3	from 18,470 ± 110 to 17,970 ± 160	52°49′40.23″ N 103°32′31.98″ E
		Kitoiskii Most	1	from 18,330 ± 150 to 17,920 ± 140	52°28′40.2″ N 103°46′26.7″ E
		Novyi Angarskii Most	5	18,120 ± 170	52°15′20.17″ N 104°16′26.88″ E
		Malta	9.2	17,950 ± 260	52°51′06.6″ N 103°30′53.4″ E
		Berloga	lower	17,162 ± 375	53° 1′55.36″ N 106°51′12.06″ E
		Shishkino 2	3	16,860 ± 290	54° 0′22.39″ N 105°40′50.03″ E
Late Sartan	Sartan 4—sr4 from 15,000 ± 110 to 13,250 ± 90	Cheremushnik 2	1	15,000 ± 110	52°53′55.8″ N 103°37′11.0″ E
		Malta	10	from 14,680 ± 230 to 13,900 ± 100	52°51′06.6″ N 103°30′53.4″E
		Sosnovyi Bor	5, 4, 3b	from 14,520 ± 190 to 13,960 ± 180	52°50′06.9″ N; 103°35′37.7″ E
		Ust-Belaya	17–14	from 14,060 ± 80 to 13,530 ± 40	52°55′15.54″ C 103°39′7.86″ B
		Badai 5	3	13,940 ± 80	52°51′56.8″ N 103°37′27.4″ E
		Galashikha	5–4	from 13,840 ± 90 to 13,520 ± 40	52°54′40.61″ N 103°38′54.93″ E
		Makarovo 2	4, 3	from 13,860 ± 400 to 13,450 ± 650	54° 0′26.40″ N 105°47′35.59″ E
		Strizhovaya Gora	16–12	from 14,000 ± 200 to 13,250 ± 90	56°12′52.96″ N 95°46′50.12″ E
	YD—Sartan 4—sr4	no radiocarbon data

), allow us to determine a chronological framework for the Early Sartan as a whole from 27,690 ± 250 to 22,160 ± 220 µ HPD cal BP; for the Middle Sartan—from 19,220 ± 270 to 16,860 ± 290 µ HPD cal BP; for the Late Sartan—from 15,000 ± 110 to 13,250 ± 90 µ HPD cal BP.

Sartan subaerial deposits are represented by different genesis and granulometric compositions (from sands to heavy loads). Geoarchaeological sections are characterized by interbedded loess-like loams with aeolian sands and sandy loams, and less often with interlayers of colluvium or solifluction where the average total power of loess layers is 0.5–0.8 m. The total thickness of all Sartan loose deposits rarely exceeds 1.5–2 m. Only on sands, did it significantly rise to 3–4 m and above (Kitoiskii Most site; Figure 4).

According to the lithological features in the structure of the Sartan deposits of the Baikal–Yenisei Siberia, it is possible [35] to distinguish 4 stratigraphic units (subhorizons sr¹, sr², sr³ and sr⁴). In general monotonous (cryoarid) background Sartan time, each of the subhorizons differs in peculiarities, including the presence of soils with different degrees of development and preservation; cryogenic process peculiarities; a certain sequence of changes in the composition, structure and genesis of sediments (Figure 2 and Figure 3).

In the studied sections, the Sartan soils are horizons (layers) of small thickness (rarely more than 12–15 cm), located parallel to the ancient day surface and differing from the host deposits in their color (Figure 3A). At the top of the horizons, a darker color is sometimes observed, due to a slight increase in the organic matter content (Figure 4). In some horizons, the color becomes lighter closer to the top due to carbonate distribution. In several sections (Shishkino, Makarovo 4, etc.), the top of the horizons of Sartan soils is broken by a fine network of drying cracks.

Almost all of the Sartan soils have been beheaded. The few remaining fragments of the upper horizons of Sartan soils have a low humus content (less than 1%) and a humate-fulvate or fulvate composition.

The preserved mineral part of the soil profile has a slightly heavier granulometric composition than the host deposits, which are highly diverse and represented in sections from sand and sandy loam to heavy loam. Visually, the soil structure is very poorly expressed. In the medium- and heavy-loamy soil thin sections, the ooid organization of the microstructure is visible, due to the colloid coagulation under the calcium ion influence.

All soils are carbonated and have a pH > 7. Carbonates are usually dispersed in the soil and concentrated at the surface. These carbonates are sinlitogen to the soil formation. Carbonates and ferrum hydroxides accumulated on the walls of the cracks cut through the soil are postpedogenic.

To designate the soil horizons, the indices adopted in the Russian Soil Classification [53] were used: Organogenic horizons: O—litter-peat; T-peat; TJ—dry peat. Organomineral: AO—coarse humus; W— underdeveloped humus; humus horizons: A and A1. Mineral horizons: BC—transitional to the parent rock and C—loose soil-forming rock. Indices of genetic traits indicate the features of soil formation processes: h—humus formation; m—metamorphic transformations, giving the horizons a brownish color; g—gleying, which gives the horizons bluish and greenish tones.

During the archaeological excavations, paleontological material from the sections was extracted and analyzed. However, the reconstruction of landscapes based on paleontological material is very difficult, since the species that lived in the Baikal region in the Sartan period can be characterized as “disharmonious” faunas when representatives of various biotopes are met—from dry steppes to tundra [54], which indicates the mosaic nature of the region’s landscapes.

Unfortunately, spore–pollen analysis gives a very small yield of pollen and spores from subaerial deposits and soils.

3.1.1. The Early Sartan Deposits and Soils

The Early Sartan deposits (sr¹) include two lithological units. The lower unit (sr¹₁(sol) ~28–25 ka cal BP) is represented by solifluction and colluvial–solifluction formations, which are almost ubiquitous and have different thicknesses—from 0.1–0.2 m to 1 m and above (Figure 5C).

Bone remains of Mammuthus primigenius, Coelodonta antiquitatis, Bison priscus, Rangifer tarandus, Equus caballus, Ursus arctos, Canis lupus, Vulpes vulpes, Gulo gulo, Lepus timidus, Alopex lagopus and Lagurus lagurus were found in the Early Sartan deposits.

The low unit of the Early Sartan deposits, usually painted in bright stripes, is represented by alternating sands and silty loams with fragments of humus (A) and illuvial (B) soil horizons formed in the preceding warmer epoch (Karginian megainterstadial; MIS 3). Judging by the pedosediments, well-developed soils were subjected to solifluction. They were destroyed and buried in early Sartan (sr¹₁sol) solifluction and colluvial solifluction formations.

In situ soils of the Early Sartan age are extremely rare, only in the depressions of the paleorelief, where they were quickly buried under colluvial deposits. Similar soil in the Igeteiskii Log 2 section (22,500 ± 980 cal BP, LU-6515) is represented by the AY-Cm profile. The redness of soils and sediments in this section is inherited from the red rocks of the Upper Cambrian (Figure 6). The humus horizon AY has a thickness of 15–20 cm and contains 1–1.2% humus. The slightly altered parent rock (Cm) has a thickness of approximately 40 cm (Figure 4). We consider this soil as interstadial [55].

The upper unit (sr¹₂~25–22 ka cal BP) is composed of aeolian–colluvial sandy loess deposits (sr¹₂), which have poor preservation and low thicknesses (up to 0.2–0.3 m) due to deflation. Traces of soil formation were not revealed, which indicates very unfavorable climatic conditions and can be considered as the climatic pessimum of Sartan.

3.1.2. The Middle Sartan Deposits and Soils

The Middle Sartan deposits include two units—sr² (22–19 ka cal BP) and sr³ (19–15 ka cal BP). Bone remains in sr²-deposits belong to Bison priscus, Rangifer tarandus, Equus caballus, Ursus arctos, Vulpes vulpes and Microtus oeconomus. Equus hemionus, Ovis nivicula, Ovis ommon, Cervus elaphus, Capreolus pygargus, Saiga tatarica and Lepus timidus are added into sr³-deposits.

The lower unit (sr²) is composed of loess loams, usually poorly gleyed; the thickness of the deposits rarely exceeds 0.3 m.

Some climate warming at the sr² time (~22–19 ka cal BP) activated soil formation. Soils of different degrees of gleying formed in the Baikal–Yenisei Siberia. Essentially, these are the remains of the Cg horizons of poorly developed gley soils. The thickness of the Cg horizons is up to 10–12 cm.

The upper soil horizons are not preserved or partially preserved. In a number of sections (Igeteiskii Log 1, Shebuteika), there are traces of humus and organogenic horizons in the soils. These may have been sod-gley (W-Cg), peat-gley (T-G) and/or silt-gley (O-Cg; O-G) soils. Sometimes, the gleyed Cg horizons in their upper part contain an increased amount of humus (up to 0.6–0.8%). The section Krasnyi Yar 3 site contains two thin soils. The soils contain carbonate pedotubules, syngenetic to sr² soil formation, at the roots, presumably of shrub vegetation.

The upper unit (sr³~19–15 ka BP) is represented by sandy loess-like loams, sometimes by alternating sands and sandy loams of aeolian–colluvial genesis; the thickness of sediments can reach 1–1.5 m and above (Figure 3B). Changes in the composition of deposits indicate that most of the sr³-period was characterized by a more arid climate, in which aeolian processes have been activated.

In sr³-sediments, there are several levels of surface stabilization with traces of immature soils, presumably with a TJ-C or W-C profile (Sosnovyi Bor, Mount Igetei, Shishkino, Makarovo IV and Lokomotiv-kotlovan).

During the sr³ period, an immature soil called Malta (ML) was formed. The Malta soil (Figure 7) is widely distributed in the Baikal–Yenisei Siberia, where it occupies strict stratigraphic positions in sections, but may have a different appearance. Brownish or pinkish horizons BCm or Cm represent the thickness of loess loams. Their color indicates the oxidative conditions of soil formation. It is likely that the oxidative environment of soil formation contributed to the humus mineralization. There is no humus horizon. The average thickness of the preserved soil profile is 12–15 cm with variations from 5 to 25 cm (Figure 3A).

Ancient humans best preserved this soil at site Malta-Most 1, where it is preserved under large dolomite slabs (18,470 ± 110 cal BP, OxA-39082; 17,970 ± 160 cal BP, GIN-9511) brought to the archaeological site. The soil has a brownish color and a dwarf profile, AJca-BCm-Cm, where the thickness of horizon AJca is 1.5–2 cm, BCm is 2–5 cm and Cm is 3–9 cm. The formation of horizon AJ with such a low thickness is impossible. It is likely that the current state of the upper horizon is the result of the organogenic horizon W transformation due to organic matter mineralization.

In geoarchaeological site sections composed of sandy deposits (Kitoiskii Most, Sosnovka-karier, etc.), in some areas, this soil is split into three (sometimes four) thin (4–5 cm) grayish horizons. The soils have a cohesive sand composition and a low humus content (0.30–0.35% humus; in the separating cohesive sands, the humus content is significantly lower—0.12–0.20%). In the Kitoiskii Most section (Figure 4), the middle horizon is cultural (18,330 ± 150 cal BP, UCIAMS-207544; 17,920 ± 140 cal BP, UCIAMS-207545). The surface level of the habitat is marked with small charcoal inclusions.

3.1.3. The Late Sartan Deposits and Soils

The Late Sartan deposits (sr⁴~15–11,7 ka cal BP) are represented by strongly carbonated loess loams (Figure 3), with an average thickness of approximately 0.5 m, broken by deep frost-breaking structures (Figure 5A,D). We compare this evidence of rapid cooling at the end of the last glaciation with the Younger Dryas (YD).

From the sr⁴-deposits top, several crack generations are laid: from small shrinkage cracks with a depth of 10–12 cm to medium-sized cracks with a depth of 0.5–0.8 m and large, deep (up to 2 m or more) cryogenic cracks. The largest frost structures are represented in the sections by wide wedges, tearing apart the entire thickness of the Sartan and even the upper part of the Karginian (MIS 3) sediments (Figure 5A,B,D).

The remains of Bison priscus, Rangifer tarandus, Equus caballus, Eohemionus, Capreolus pygargus, Cervus elaphus, Alces alces, Canis lupus, Lepus timidus and Myospalax sp. are found in the Late Sartan deposits.

The age of soil formation traces corresponds to the Bølling-Allerød warming; therefore, this stratigraphic level is called the Bølling-Allerød (BA) level of soil formation. At this stratigraphic level, soils can be split into a series of embryonic (immature) soils depending on the depositional characteristics. The largest number of embryonic soils is noted in deposits of colluvial–aeolian or alluvial–aeolian genesis. Thus, in the section in the Ust-Belaya site, there are up to 5–10 embryonic soils with 11 ¹⁴C dates from 14,060 ± 80 to 13,530 ± 40 cal BP (Figure 8).

In areas where deposition is uniform, embryonic soils can be combined into one or two soils (Figure 4). The thickness of the soils varies from 5–7 cm to 10–12 cm. Most of the sections (Novyi Angarskii Most, Makarovo 2, Sosnovyi Bor, etc.) contain two close horizons, which are indexed as Ch, Cm or Cg. Locally, they united into one horizon and then disappeared. The soils of the Makarovo 2 section were formed on loamy-clayey colluvium—products of the disintegration of Upper Cambrian red-colored siltstones and mudstones. There are radiocarbon dates for these soils: 13,860 ± 400 cal BP (GIN-480); 13,860 ± 100 cal BP (GIN-481).

Cultural horizons 3b (13,960 ± 180 cal BP, GIN-5328) and 3d in the Sosnovyi Bor section of aeolian sands (Figure 8) are confined to soils. The AJ-Cm profile in wet soil is clearly visible. Soil horizon coloring is as follows: AJ—grayish; Cm—brownish. There are changes in insect activities in soils. When soil drying, their cementation occurs due to the abundance of carbonates. In the open section, the drained soils are highlighted by a white color and large solidity compared to the enclosing loose sands. The soil with cultural horizon 3b is better preserved, the thickness of horizon AJ is up to 5 cm, Cm is approximately 10 cm, the granulometric composition is sandy loam and the humus content in horizon AJ is 1.2%.

Thus, well-defined Bølling–Allerød soils can be considered interphasial soils.

3.2. Cryogenic Deformations in the Sartan Deposits of the Baikal–Yenisei Siberia

3.2.1. Solifluction

The most active solifluction processes developed in the Early Sartan (sr¹₁sol–28–25 ka BP) (Figure 5B,C), although relict solifluction of a different age can occasionally be found in limited areas. The solifluction development in the region was promoted by the dissected topography and increased soil and ground moisture, due to the low evaporation of atmospheric moisture in the initial cryohumid phase of the Sartan glaciation.

The thickness of the Early Sartan solifluction and colluvial–solifluction sediments on the floodplain terraces usually does not exceed 0.3–0.5 m. Accumulations of solifluction are confined to ancient logs and depressions, as well as to the bends of the slopes, where their convex part turns into a concave one. Despite the almost ubiquitous manifestation of Early Sartan solifluction, the solifluction forms of paleorelief are preserved almost nowhere.

Analysis of the composition and structure of the loose strata of the Quaternary deposits of the Baikal–Yenisei Siberia [34], strongly suggests that none of the other denudation processes provided such an effect in terms of the scale, speed and degree of relief flattening as that achieved during the Early Sartan solifluction. Solifluction slides, removing the seasonally thawed layer, exposed permafrost rocks, which contributed to their melting. The multiple processes led to a rapid denudation of the tops and upper parts of the slopes, as they lost a significant part and sometimes the entire thickness of loose deposits, developed before Sartan.

Solifluction was a collector of heterochronous paleolithic material, bone remains and soil sediments of the Karga megainterstadial (MIS-3). Solifluction is probably the main cause of ancient soil destruction, especially that of the Karginian period (kr², Osa soils os¹ and os²), since the Early Sartan solifluction directly followed the Karginian soil formation process.

3.2.2. Frost-Breaking Structures

The Sartan period in the Baikal–Yenisei Siberia, developed in cryoarid climate conditions. Traces of cryogenic cracking can be found at any stratigraphic position of the Sartan section (Figure 2). Among the frost-breaking structures, initially, ground veins predominate, which do not go beyond the seasonally frozen layer. Their vertical dimensions are 0.2–0.4 m up to 0.5 m. The smallest cracks are very narrow (tongued), almost not opened. It is likely that they also functioned as drying cracks in the summer period in the tundra-steppe landscapes of the Sartan period.

In the upper seasonally frozen layer, in spring and summer, cracks were “healed” by water suspensions penetrating here (thawed and rain moisture with products of soils and subsoils surface erosion) and turned into ground veins. In winter, cracking was restored.

Frost-breaking crack formation also developed under the conditions of the cryohumid climate of the Early Sartan period, but its traces are rarely found in solifluction deposits, since they quickly disappeared, as the cracks were filled with liquefied soil that flowed down the slope. Only a few of them had a chance to survive, mostly directed along the slope, but they soon took the form of gills, through which there was a discharge of excess moisture (Figure 7, Malta site).

The thickest cryogenic structures can be traced in the areas of the distribution of Cambrian carbonate-bearing rocks. They are confined to the polygonal network nodes. In modern relief, they have the appearance of well-defined rounded depressions with a diameter of 5–7 m or more. The vertical dimensions of such wedges are up to 3–4 m, and sometimes up to 5 m.

The most powerful frost structures were formed in the final phases of the Pleistocene (YD). Deep cracks penetrated into the permafrost layer, forming in it ever-widening and deepening ice–soil veins and ice veins. After the ice melted in the Holocene, the ice veins were transformed into pseudomorphs along the ice wedges.

Large frost-breaking structures (depth—2–3 m; width in the top of sr⁴-deposits—up to 2.5–3.5 m) and medium frost-breaking structures (depth—2–1 m; width—1–1.5 m) are widely distributed on terraces and slopes covered with a blanket of loess deposits (Figure 5A,B,D). At present, the lower and middle parts of the frost-breaking structures with a depth of more than 1.2–1.5 m are pseudomorphs, which are mainly filled with a Sartan mineral substrate; the upper part is filled with material from Holocene soil horizons.

In the Holocene, in the areas of deep frost-breaking structures distribution, the development of the bumpy-depression relief took place during the thawing process of ice veins. The average elevation of bumps over depressions is rarely more than 1–1.5 m (Figure 9A,B).

Younger Dryas cryogenesis determined the modern structure of the soil cover of the Baikal–Yenisei Siberia. Large polygons are manifested in the modern relief almost everywhere in the form of the bumpy-depression relief and polygonal-block microrelief. Usually, the excess of bumps over the depressions is 1–1.5 m; the excess of flat blocks over the hollow-like kettles is 0.2–0.5 m (Figure 10A).

In the areas of indigenous carbonate-bearing rock development, as well as carbonate-bearing loose deposits of considerable thickness at cryogenic crack intersection nodes, the kettles are often transformed into deep (3–5 m or more) karst craters.

Polygons that are less than 10 m in size are almost not pronounced in the modern terrain. In areas under natural vegetation, they are visible in the form of a polygonal microrelief. The prepared surface of the smallest polygons has the appearance of a cobblestone pavement.

Polygonal-block structures are visible on arable lands as light, low-humus spots surrounded by a darker soils network. Light spots are formed due to the cutting of a part of the humus horizon during the surface technogenic leveling. Often, the light spots on the fields are Sartan carbonate loess loams exposed to the modern surface.

The territory of the Baikal–Yenisei Siberia, was covered with a network of cracks with different sized cells from 0.3 m to 80–90 m across (Figure 10A,B).

According to the scale of frost-breaking cracking of soils and subsoils, the Younger Dryas, short-term but very deep cooling (YD) had no analogs in the Late Neo-Pleistocene. Powerful frost-breaking structures similar to those of Sartan were only recorded [42,43] in the Upper Eopleistocene sediments (the second half of the Early Pleistocene).

3.3. Sartan Archaeological Complexes

The materials of the Sartan archaeological sites in the Baikal–Yenisei Siberia, are associated with soil formations of deposits of different geneses: proluvial (Makarovo 2), aeolian (Krasnyi Yar 1, Sosnovyi Bor), mixed aeolian–colluvial (Kitoiskii Most) and colluvial–alluvial (Ust-Belaya, Galashikha), most with loess deposits with a predominance of the colluvial component. Many geoarchaeological sites are multilayered (microlayered); from 2 (for example, Cheremushnik 2) to 10 cultural levels (Ust-Belaya) of the Sartan age have been recorded.

Among the archaeological complexes, several cultural and chronological groups can be correlated with the climate–stratigraphic chart of Sartan on the territory of the Baikal–Yenisei Siberia (Figure 11).

The earliest group consists of complexes of Early Sartan. The materials of seven archaeological sites with the Malta-Buret core are associated with solifluction formations. M.M. Gerasimov first identified the materials of Malta as Aurignacian [56]. They are characterized by the presence of bone structures, bone items and art objects (anthropomorphic and zoomorphic sculptures, ornaments and symbolic products): flat bipolar, single-platform fan-shaped, carinated and terminal (edge-faceted) cores; various tools on blades with dorsal, nibbling and regular retouch; end-scrapers; chisel-like tools; side-scrapers; points; bifaces. The Western origin of the “classic Malta” complexes is now confirmed, in addition to the technical and morphological characteristics of the subject material, by the results of anthropological [57] and genetic studies [58]. Late Moustierian complexes coexist in parallel with them with characteristic quartzite technoforms (Malta-Strelka): side-scrapers, points, burins on flake, pebble-cores and choppers.

Cultural transformation takes place in Sartan. At the end of Early Sartan, complexes with classical terminal-edge microknapping are fixed. G.I. Medvedev introduced the concept of terminal edge knapping [59]. In East Asia, it is traditionally understood as the technique of wedge-shaped core [60] and/or edge-faceted [61] cores in different preparation systems. The complexes of this time are scarce and are represented by materials from cultural layers 7 and 6 of the multilayered site Krasnyi Yar 1. Most of these materials have been lost. They are characterized by terminal-edge knapping, mainly of the carinated shape. Yubetsu is the earliest core. The industry also includes flat and amorphous cores, side-scrapers, end-scrapers, points, burins, borers, choppers and abrasives. In addition, bone pendants, beads made from ostrich eggshells, bone needles and bonfires with coal were found [46,62,63,64].

For Sartan 2, there are no radiocarbon dates as yet, and the presence of cultures can be determined as flickering. It is possible that the complexes of the Belsk-Zalog geoarchaeological site have this age according to stratigraphy, in which complexes in the core pre-forms in the Horoko technique are recorded, as well as cultural layers 5 and 4 of the Krasnyi Yar 1 site with a few featureless findings.

Figure 11. Archaeological materials from the Sartan complexes of the Baikal–Yenisei Siberia: 1–6, 10–14, 21–26—Malta (layers 8–9.1); 7–9, 15–20—Krasnyi Yar 1 (layer 6); 27–30—Igeteiskii Log 1 (layer 4); 31–35, 39–43—Malta-Most 1 (layer 3); 48–50—Kitoiskii Most (layer 1); 36–38, 44–47—Krasnyi Yar 1 (layer 3); 51–52—Shishkino 2 (layer 3); 53–56—Sosnovyi Bor (layer 4); 57–58, 64–65—Sosnovyi Bor (layer 5); 59–63, 66–69—Ust-Belaya (layer 16); 70–73—Badai 5 (layer 3); 74–76—Makarovo 2 (layer 2); 77—Makarovo 2 (layer 4); 78–79—Strizhovaya Gora (layer 14); 80–85—Galashikha (layer 4). Unpublished drawings and photos: 48–50, 53–54, 70–76 by Dmitry Zolotarev; 1–6, 10–14, 21–26 by Ekaterina Lipnina; 31–35, 39–43 by Natalia Berdnikova. Other drawings and photos adapted from the following: 44–47 [62]; 77 [65]; 59–63, 66–69, 80–85 [66]; 78–79 [67,68]; 57–58, 64–65 [69]; 1–6, 10–13, 21–25 [70]; 55–56 [71]; 7–9, 15–20, 27–30 [72,73,74]; 51–52 [34].

Figure 11. Archaeological materials from the Sartan complexes of the Baikal–Yenisei Siberia: 1–6, 10–14, 21–26—Malta (layers 8–9.1); 7–9, 15–20—Krasnyi Yar 1 (layer 6); 27–30—Igeteiskii Log 1 (layer 4); 31–35, 39–43—Malta-Most 1 (layer 3); 48–50—Kitoiskii Most (layer 1); 36–38, 44–47—Krasnyi Yar 1 (layer 3); 51–52—Shishkino 2 (layer 3); 53–56—Sosnovyi Bor (layer 4); 57–58, 64–65—Sosnovyi Bor (layer 5); 59–63, 66–69—Ust-Belaya (layer 16); 70–73—Badai 5 (layer 3); 74–76—Makarovo 2 (layer 2); 77—Makarovo 2 (layer 4); 78–79—Strizhovaya Gora (layer 14); 80–85—Galashikha (layer 4). Unpublished drawings and photos: 48–50, 53–54, 70–76 by Dmitry Zolotarev; 1–6, 10–14, 21–26 by Ekaterina Lipnina; 31–35, 39–43 by Natalia Berdnikova. Other drawings and photos adapted from the following: 44–47 [62]; 77 [65]; 59–63, 66–69, 80–85 [66]; 78–79 [67,68]; 57–58, 64–65 [69]; 1–6, 10–13, 21–25 [70]; 55–56 [71]; 7–9, 15–20, 27–30 [72,73,74]; 51–52 [34].

Sartan 3 complexes are more numerous (approximately 14 registered sites). The most representative sites are Krasnyi Yar 1, Malta-Most 1, Kitoiskii Most, Shishkino 2 and Cheremushnik 2. They are characterized by a combination of several techniques of terminal-edge knapping: Saikai, Campus and burin spall techniques. They are combined with flat cores with an oblique platform for the removal of large blades. The industry includes microblades, retouched blades and tools with end-scrapers, borers, notched tools, chisel-like tools, burins, points and bone items (needles, rods, awls and anthropomorphic sculptures). Habitat spaces are marked with bonfires; small pits of unclear functional purpose are marked. These complexes contain coal and ocher (mineral pigment) [46,75,76].

Archaeological sites with Sartan 4 complexes make up the largest group (16 objects were taken into account, among which up to 2–10 layers of this age were recorded). The main objects are Sosnovyi Bor, Ust-Belaya, Galashikha, Strizhovaya Gora, Cheremushnik 2 (1), Badai 5 and Makarovo 2 [65,75,76]. For these sites, there is a variety of knapping techniques. The Yubetsu technique with a sharp flaking angle is widely used in the traditional system of platform trimming. Bifaces, unifaces, flakes, platy partings and pebbles were the preforms. There are forms in the Rankosi technique, as well as in the earlier Saikai and Campus techniques. Terminal-edge cores are combined with a variety of prismatic and fan-shaped forms. The industry includes end-scrapers, burins, knives, retouched blades, chisel-like tools, points, reamers, borers, bifaces, side-scrapers, chopping and chopper tools, stone pendants and bone tools (needles, points, composite inset tools, harpoons and fishing hooks). Habitat spaces are marked with bonfires. Large fish remains (sturgeon, taimen and pike) are often found.

Archaeological complexes of the Younger Dryas in the Baikal–Yenisei Siberia, have not yet been identified.

4. Discussion

4.1. Types of Soil Formation in the Pleistocene Cold Epochs

Despite the significant duration of glaciations, the study of soil formation in the cold intervals of the Pleistocene is still insufficient; the issues of morphology, genesis, evolution, classification and nomenclature of soils remain unresolved.

For cold periods, A.A. Velichko and T.D. Morozova [55] distinguish two types of soil formation: (1) interstadial and (2) pleniglacial.

According to A.A. Velichko and T.D. Morozova, interstadial soils were formed in the initial glaciation stages and formed complexes with interglacial soils, and there are two main groups of interstadial soils: (1) soils with a predominance of humus-accumulative processes of soil formation (profile A-C); (2) soils with a predominance of permafrost-gley processes (profile A1g-Cg).

The time of pleniglacial soil formation [55] corresponded to that of the most unfavorable cryoarid conditions of glaciations (pessimums) when biochemical and biophysical trans-formations actively developed only in microzones around plant root systems, and the leading place was occupied by cryogenesis and cryomorphism processes. In such conditions, only specific sinlitogen soil could develop, including loess. Pleniglacial soil formation was manifested in the weak humus accumulation, microaggregating, accumulation and redistribution of secondary carbonates without their leaching.

In the Sartan deposits of the Baikal–Yenisei Siberia, in most cases, interstadial soils are extremely rare and are confined only to the Early Sartan (sr¹₁sol) subhorizon (Figure 6). A possible reason for this is the solifluction processes that denuded loose sediment and soil. The widespread solifluction processes had the maximum activity in the Early Sartan period (Figure 3).

In addition to the interstadial and pleniglacial types, we propose that the interphasial type of soil formation should also be distinguished.

Interphasial type refers to soil formation that took place with some improvements in natural conditions and a weakening of the sedimentation intensity, lasting for a relatively long time (approximately more than 500 years).

This relative warming duration could lead to a noticeable transformation of the mineral substrate and, although it was not sufficient for the formation of medial soil horizons, it contributed to the development of processes of biochemical weathering and horizon formation Ch, Cm, Cg or even BCm and BCg. The description of the horizons is as follows: Ch—grayish soil-forming rock, relatively enriched with humus; Cm and BCm—pinkish or brownish horizons, differing in weathering degree; Cg and BCg—bluish, greenish or tobacco-gray gleyed horizons.

Beheaded interphasial soils in sections are fixed in the form of sustained interlayers with a thickness of up to 10–15 cm (rarely more) and differ from the host deposits in color. Previously, we considered them [34] as “weathering horizons” (Figure 3A).

Most interphasial soils did not preserve the upper horizons, but they were probably represented by organogenic or organomineral formations (O, TJ, T, AO and W), in rarer cases—thin humus horizons AJ and AY. (AJ horizon—light humus, characteristic of arid soils; AY horizon—gray humus (turf), characteristic of forest soils.)

We could consider the Malta soil (Figure 3A) as an example of interphasial soil in the sections of the Baikal–Yenisei Siberia, which is present in the Middle Sartan deposits of many sections. The Malta soil has a greater profile among other soils; this is an indicator of the significant duration of its formation compared to other Sartan buried soils. At the same time, there is a rather weak manifestation of the soil horizons, which can be explained by unfavorable climatic conditions.

Analyzing the stratigraphic structure of climate change during the last ice age [1], the stratigraphic position of the Malta soil can be attributed to the GS-2.1 stage, within which the GS-2.1b substage is distinguished, characterized by a less severe climate and a longer duration (3,400 years). The substage was dated in the range of 20.9–17.5 ka cal BP.

The dating obtained for the cultural layers from Malta soils in the Malta sections (layer 9.2), Malta Most 1 (c.l. 3), Novyi Angarskii Most, etc., perfectly coincide with this time. Therefore, for the Malta soil of sites Kitoiskii Most and Malta Most 1, there is a series of dates in the range of 17.6–18.6 ka BP.

According to the dates, the time of the Malta soil formation fully corresponds to the chronological interval of the substage GS-2.1b.

In general, traces of pleniglacial soil formation type are presented by two groups of objects in Sartan subaerial deposit sections in the Baikal–Yenisei Siberia: (1) immature soils, retaining only the soil formation levels, and (2) separating them with soil-rocks (loess and non-loess formations) that perform a soil function in the coldest stage of the Sartan period.

The immature soils with organogenic horizons traces (O—underlayer; TJ—dry peat; W—slightly humic) on the unchanged rock (horizon C) probably had the original O-C, TJ-C and W-C profile, which can be traced by a thin 1–2 cm layer of a darker color. In sandy–sandy loam strata, the brown remains of organogenic detritus diagnose this level of soil formation (sites: Badai 5, Sosnovyi Bor and Kitoiskii Most). In sections composed of loam, a humus layer marks the level of embryonic soil formation process with a thickness of 1–2 cm or a series of such layers (sites: Novyi Angarskii Most, Malta and Zalari).

4.2. Comparative Analysis of the Last Glacial Paleosols in Different Regions

Unfortunately, in many regions of the Asian part of Russia, soil scientists have not studied sections of subaerial deposits; therefore, information on the paleosols of the last glacial period is either absent or very scarce.

In this case, the southern forest-steppe part of Western Siberia [77] is better studied where there are several levels of soil formation in the sections of Sartan soil–loess deposits.

Suminsk soil (sm), whose formation period is within 19.6–16.3 ka BP [38,77], attracts the most attention. This soil, which is 20–30 cm thick, is located between two interlayers of Sartan loesses (Yeltsovsk and Bagan).

In different geomorphological positions, the Suminsk soil can have different morphology and properties: in some areas, it is represented as a poorly developed chernozem, or as soil with a preserved brownish weathering horizon, in others, as a gley horizon. The soil usually contains carbonates. Small polygonal fracturing of its surface, cracks up to 12 cm, is a soil feature. Such cracks indicate a strong drying out of the soil surface. V.S. Zykina believes that the Sumy soils formed in dry steppes [77].

In the parts of Western Siberia, the Sumy soil is a stratigraphic analog of the Malta soil of the Baikal–Yenisei Siberia. Both soils are morphologically similar; the differences are that there are no drying cracks on the surface of the Malta soil.

This indicates a high moisture content in the soils of the Baikal–Yenisei Siberia, probably associated with the reduced evaporation of soil moisture in colder climates.

In the southeast of Western Siberia, in the Bagan loess, stratigraphically higher than the Suminsk soil [43], there are two soil formation levels of the Bølling-Allerød age (14,934 ± 993 cal BP; SOAN-9707; 12,388 ± 774 cal BP, SOAN-9792). Humus interlayers represent these underdeveloped soils of 5 to 10 cm thickness. Similar double humus horizons (Ch) are also very typical for the Late Sartan soils of the Baikal–Yenisei Siberia.

On the East European Plain, in loess sediments, in which extreme cryoarid environments of the Late Valdai periglacial (MIS 2) were recorded, A.A. Velichko [78] identified Trubchevsk soil. It is located between the Desninsky and Altynovsky loesses and represents weak interstadial soil formation—the gleying horizon associated with insignificant warming, climate humidization and weakened loess accumulation.

The Trubchevsk soil was studied in more detail in the Cheremoshnik key section (Yaroslavl Volga region). It is a thin dark, humus–gley paleosol (Agb–Gb profile), dated 19,790 ± 490/560 cal. kyr BP, IGAN [79].

South of the Middle Don basin (Voronezh region), the Late Paleolithic site Divnogorye is known. A complex of underdeveloped soil enclosing and separating sediments is called the Divnogorsk pedolithcomplex. The lower, most developed paleosol (Rendzic Chernozem) is related to Bølling warming, and the medium (Rendzic Leptosol) and upper (Cambisol) paleosols to Allerød warming. The paleosols were developed during periods of climate warming at the late-glacial period in periglacial forest-steppe conditions [80].

Soil–loess deposits in the central and southern regions of Western Europe are widespread. Loess formed in the final LGM, and the deglaciation stages are located in the upper part of their section. Researchers, in general, were directed to a comprehensive study of loesses. At the same time, there is insufficient information about soils aged 24–11.7 ka cal BP, enclosed in loesses. Researchers note that the presence of buried soils at different stratigraphic levels indicates a weak development of soil formation processes, but do not give these soils the status of a stratigraphic marker [81,82].

In Northern Europe, soil formation began with the stage of deglaciation [83]. These soils are called Usselo and Finow. The sandy composition of the parent rocks and the humid climate determined the features of soil formation. Under these conditions, in some provinces, Finow soils were formed, in which only the weathering horizon (Bw), characterized by a brownish color, or the horizon enriched with iron hydroxides (Bv), remained. It is likely that the soils were eroded due to the active development of aeolian processes. Such buried Bølling-Allerød soils are classified as Brunic Arenosols and as Podzols. In other provinces, Usselo soils were formed with thin humus (Ah) and eluvial horizons (E), which are classified as Albic Arenosols or Podzols. Charcoals belonging to Pinus silvestris, Salix sp. and Populus tremula are often found on the soil surface, which indicates strong forest fires. Usselo paleosols are also found in Central Europe, where they are confined to aeolian sands [84,85].

Bølling-Allerød soils on sands are quite widespread in the Baikal–Yenisei Siberia, but have a completely different structure. Usually, this is a series of thin, weakly humified gray interlayers, sometimes merged, and considered as the Ch. The dry continental climate of the region did not favor the development of forest landscapes or eluvial processes in soils.

Last Glacial loess is widespread in the conterminous United States and is thicker, on average, than at most other localities in the world. Loess strata in different regions have specific features. This is probably why they are given the names Peoria Loess and Bignell Loess. Late Wisconsin loess is widespread and thick, especially Peoria Loess (10–48 m thick). Loesses have been altered by soil formation and weathering. Loess strata contain underdeveloped soils and weathering horizons at different levels. Cycles of loess–soil formations in the structure of loesses are distinguished. The cyclic structure determines the presence of underdeveloped soils and weathering horizons in the loess at different levels, which are difficult to date due to the low content of organic matter [86].

Elements of the proximity of the structure of the sections (LGM, MIS 2) for the Baikal–Yenisei Siberia, and North America are solifluction textures present in the lower part of Peoria Loess and indicating the presence of permafrost at the early stages of loess formation (~21.0–16.5 ka BP).

4.3. The Problem of Dating the Early Sartan Deposits

The beginning of the Last Glaciation Maximum (LGM) dates back to 28 ka cal BP. Therefore, it could be expected that the earliest sediments of the Sartan age, which in our region are represented by the Early Sartan solifluxium, should have the same dates. However, the numerous radiocarbon dates obtained from solifluxium are much older, 28–25 ka cal BP.

This discrepancy in dating has the following explanation. Solifluction developed under conditions of a sharp cooling of the climate (beginning of MIS 2). It carried down the slopes of the loose sediments and soils that had formed before the Sartan. Thus, the early Sartan solifluxium was a collector of various materials (fragments of soils, fauna and artefacts) from more ancient subaerial formations.

In particular, the soils of Karginian megainterstadial (MIS 3) were destroyed in places by solifluction and in places redeposited on lower relief elements. Karginian pedo-sediments in the composition of solifluxia are 35–25 ka cal BP and above.

In connection with the indicated problem of dating the earliest layers of the Sartan age, we propose that the beginning of the Sartan glaciation should be correlated with the beginning of the LGM (beginning of MIS 2), i.e., with the date 28–27 ka cal BP, and the interval 28–25 ka cal BP should be considered as the age characteristic of the material redeposited by solifluction.

Soils carried down the slope by solifluction were mainly formed during the previous 1–4 ka cal BP in different conditions at the end of the Karginian mega-interstadial.

Thus, the nature of the environment of the reconstructions made based on the study of solifluxium cannot be reliable indicators of the conditions of Early Sartan, but they can serve as additional information about the natural conditions of the final stages of the Karginsky mega-interstadial (MIS 3).

The main reason for the development of the early Sartan solifluction on the slopes, where it had not developed before, was a strong cooling of the climate at the beginning of the Sartan, which led to permafrost and deforestation of the territory. Low evaporation provided high soil moisture, giving it fluidity over the slippery surface of the frozen underlying layer.

At present, we are unable to assess the discussed problem of the discrepancy between the radiocarbon dating of the soliflucted deposits and the validity of natural and climatic reconstructions. Is the problem typical for the Baikal–Yenisei Siberia, or does it have wider areas? The lack of information on the presence of solifluxium in the sediments of the last glacier may be due in some cases to its actual absence, in others, to the poor knowledge of the sections.

In any case, the problem of the discrepancy between the dates of the glacial beginning requires attention and additional discussion.

4.4. The Development of Sartan Cultures in the Baikal–Yenisei Siberia

In the development of Sartan cultures in the territory of the Baikal–Yenisei Siberia, there is an unequal provision of the selected subdivisions with archaeological materials, which allowed us to state the fact of some discreteness (breaks) in the cultural development or the flickering cultures manifestation in the ranges of 22.2–19.2 ka cal BP, 16.9–15.0 ka cal BP and 13.2–11.7 ka cal BP.

The idea of the influence of climate and, above all, LGM on the reduction in or complete absence of human populations in the territories neighboring the Baikal–Yenisei Siberia, is very popular. For Mongolia, three cultural breaks were defined—before LGM (31–29 ka cal BP, coincides with cold Heinrich Events 3), LGM (23–21 ka cal BP) and post-LGM (17–14 ka cal BP, coincides with Heinrich Events 1) [17]; for the Transbaikalia—in LGM (24.8–22.7 ka cal BP) [14]; for the Yenisei River valley—also in LGM (24.8–20.7 ka cal BP) [6,8].

The small number or absence of cultural complexes on the territory of the Baikal–Yenisei Siberia, in the so-called breaks cannot be explained only by the cold climatic conditions that led to the depopulation of the territory. This situation is caused by several factors. Among them are the insufficient information on the territory and the existence of certain stereotypes in search of archaeological sites. It turned out that the Sartan 3 archaeological sites occupied special areas in the terrain, which ensured the protection of the residential territory from winds. It is likely that there were other types of adaptation to difficult climatic conditions. Another factor is the incomplete identification of some cultural complexes, both stratigraphically and chronometrically. In addition, an important factor is the proximity to the tectonically active Baikal Rift. Due to geoarchaeological studies, various traces of tectonic activity in Sartan deposits were recorded: local mudflows; existence and descent of lakes; flooding and erosion of individual sections of the valley; landslides [87,88,89]. The extraordinary natural situations of the Sartan period also had an extraordinary adaptive response in the ancient population, expressed in the peculiarities of the geographical and topographical disposition of habitats at different times. The same natural events and situations also had a certain influence on the cultural content of various Sartan chrono-intervals.

Sartan soil formation suggests that it is unlikely that depopulation caused by natural situations could have occurred on the territory of the Baikal–Yenisei Siberia. This demonstrates a well-defined periodicity of natural condition stabilization, which allowed ancient populations to actively adapt to various situations.

5. Conclusions

Sartan subaerial formations in the Baikal–Yenisei Siberia, are up to 1.5–2 m thick. Alternating deposits of various genesis, composition and properties characterize their structure: loess-like loams; colluvial–aeolian and aeolian sands and sandy loams; colluvium of different granulometric compositions. Solifluxium is usually present at the bottom of the sections; loess-like formations are best represented in the upper part (sr⁴).

The extraordinary adaptive response was reflected in the Sartan deposits: (1) the cryogenesis of the Young Dryas (YD), which manifested itself in the polygonal network of significant frost cracks; (2) cryogenesis of early Sartan, which manifested itself in solifluction and denuded the slopes and transported the demolished material to gentle or negative forms of relief (to above-floodplain terraces, hollows and depressions).

Sartan deposits, as a rule, are strongly carbonated. The reason for this is a widespread occurrence in the region of bedrock carbonate rocks of the Paleozoic, carbonate loess-like formations, the cryoarid climate of the Sartan time and low (350–450 mm) modern atmospheric humidity, insufficient for the active leaching of carbonates.

All Sartan deposits in the Baikal–Yenisei Siberia, have been transformed by weak and specific soil formation. In the sections of Sartan subaerial formations, the following are diagnosed: interstadial soils (very rarely), interphasial soils (weathering horizons or gleying horizons), soil formation levels and sandy–sandy loam or loess-like soil, which served as soils under conditions of an increased rate of aeolian and colluvial cryogenic deposition against the background climate.

Among the Sartan soils, the most visible are interphasial soils, distributed at the following stratigraphic levels: sr²~22–19 cal ka, sr³~19–17 ka cal BP and sr⁴ (BA)~15–13 ka cal BP. We associate the activation of soil formation with the phases of some improvement in the climatic situation. Among the interphasial soils in the sections, the most common is the Malta soil, which formed 18 ± 0.5 ka cal BP.

In short, interphasial soils in the sections are represented by horizons of only the lower part of the profile, which have a brownish-pinkish color (BCm and Cm horizons), grayish-tobacco (BCg horizon), or greenish-blue (Cg horizon) color. The color of the soil horizons of subaerial sections represents redox processes, mainly due to different ice content and permeability of permafrost located at a shallow depth from the day surface. The absence of the upper horizons does not allow these soils to be named precisely but gives reason to assume that predominantly organogenic or organomineral horizons existed in the soil profile.

Pleniglacial pedogenesis traces are found at all stratigraphic levels. Their appearance is caused not only by climatic fluctuations but also by the conditions of temporary stabilization of the surface with a weakening of sedimentation at the location site.

Archaeological sites of the Sartan age are often located on low terraces above the floodplain in the valleys of major rivers in the region and on slopes adjacent to terraces. Most of the complexes tend to the estuarine areas of the valleys. The cultural layers are confined to the horizons of interphasial and pleniglacial soils, which mark certain stratigraphic levels in aeolian, loess or colluvial deposits.