Loessoids and other indications of the northern periglaciation1

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This is a review of research in the structure of the Late Pleistocene periglacial zone of northern formerly glaciated Russia obtained during the last 40 years. The discussion concerns sediments and landforms of flatlands formed in the last 60 ka after the disintegration of regional ice sheets of the early Late Pleistocene. A special emphasis is on poorly studied phenomena of subaerial sedimentation which in the north before 1990-s, unlike in southern Russia, was commonly disregarded in geological and geographical papers in favour of glacial and aqueous processes. However, presently a wide distribution of subaerial sediments including dune sand, niveo-aeolian sand and various loess-like silts is established. Monotonous silty formations are now mapped as associations of different subaerial sediments called `loessoids`. This term embraces equally the classical steppe loess, loess-like silts of the forest zone and icy aeolian silts of the yedoma type. Together with these indications of harsh continental climate in the northern periglacial environment related products of permafrost development such as ice wedges, solifluction sheets, sandy hillocks formed by topographic inversion of thermokarst sinkholes are considered. Also in this context the specific alluvium and cryoarid biota characteristic for the continental climate аre discussed. The obtained results do not support the popular reconstructions of forested landscapes of the modern type for the MIS3 interval. According to the new results jointly with the reinterpreted old data, treeless and forest-tundra landscapes are inferred for this time. This allows to consider the periglaciation of northern Russias a counterpart of the Central European Pleniglacial.

Sobre autores

V. Astakhov

Saint-Petersburg University; VSEGEI; Institute of Geography RAS

Autor responsável pela correspondência
Email: val-asta@yandex.ru
Rússia, Saint-Petersburg; Saint-Petersburg; Moscow

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2. Fig. 1. Location map: discussed sites are lettered. Thick lines are limits of different glaciations.

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3. Fig. 2. Cryogenic aeolian sediments of the Arcctic. (а) — typical striped Yedoma formation of loess-like silts with bands of segregated ice and moss seams penetrated by syngenetic ice wedges at Bol. Lyakhovsky Island, 73.5°N (photo by V.Ye. Tumskoy). (б) — dated sequence at the Syo-Yakha river mouth (C in fig. 1) by (Vasilchuk, Vasilchuk, 1998), simplified. 1 — fine sand, 2 — coarse silt, 3 — silt with peaty seams, 4 — syngenetic ice wedges. ¹⁴C dates not calibrated.

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4. Fig. 3. Upper Pleistocene periglacial sediments interrelated in north-eastern European Russia (principal profile, modified after (Astakhov, Svendsen, 2011)).

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5. Fig. 4. Subaerial deposits of the Upper Pleistocene near Akis settlement on the western bank of the Pechora River (65°50ʹ N; А in fig. 1). (а) — loess-like silt with ferruginous smears changing upwards into coversand; (б) — aeolian sand (А) with a tongue of soliflucted diamicton (Б) and dessication cracks of the palaeosol (В).

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6. Fig. 5. Section of sandy coastal lowland on Timan Beach (67°50ʹ N., 49°10ʹ E; TБ in fig. 1). Characteristic sequence of postglacial Pleistocene of the Lower Pechora: dominant aeolian sands underlain by limnic silts and sands with wisps of solifluction sediments by (Mangerud et al., 1999). 1 — peat; 2 — аeolian dune sands; 3 — pebble lag; 4 — аeolian horizontally bedded sands; 5 — solifluction diamicton; 6 — limnic laminated sands; 7 — cobble gravel; 8 — disturbed silts and sands; 9 — marine silt and clays; 10 — till; 11 — ice-wedge casts; 12 — OSL dates; 13 — ¹⁴C dates.

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7. Fig. 6. Aeolian landforms in the lower reaches of the Pechora River. (а) — overgrown dune on Kuya River east of Naryan-Mar city (K in fig. 1); (б) — sandy residual hillocks armoured by cobbly gravel west of the Pechora mouth; (в) — wind-eroded tiny residual cones on the crest of a glaciotectonic ridge at Vashutkiny Lakes (68°5ʹ N., 61°38ʹ E; В in fig. 1) (Astakhov, Svendsen, 2011).

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8. Fig. 7. Niveo-aeolian sands. (а) — western beach of the Korovinstaya Estuary at the Pechora River mouth (68°25ʹ N., 53°22ʹ E; Ko in fig. 1), (б) — sand pit in Aksarka, southern bank of the Ob River (Polar Circle; Ak in fig. 1) (Astakhov, 2014). Note the sharp boundaries between thin bands of fine sand and dark silt, tiny frost cracks (a), droplet disturbances and weed rootlets (б).

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9. Fig. 8. Finely stratified, dense coversand (А), overlain by diagonally bedded loose dune sand (Б) on Kuya River near the bridge (67°33ʹ N, 53°20ʹ E; K in fig. 1).

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10. Fig. 9. Section of Palaeolithic site Byzovaya on the eastern bank of the Pechora River (65° N; Б in fig. 1). Interstadial soliflucted diamicton with mammoth bones and tools of early Late Palaeolithic overlain by subaerial sequence of arid periglacial after (Svendsen et al., 2008; Heggen et al., 2012). ¹⁴C dates not calibrated.

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11. Fig. 10. Mirrorred pattern of periglacial landscapes in airphotos of 1:50 000 scale after (Astakhov, 1998). (а) — modern thermokarst lakes (black) and their dry floors (gray) on the perennially frozen lowland along the Barents Sea coast 68°30ʹ N, 55°20ʹ E; (б) — thawed Pechora River terrace 240 km to the south: flatbread-like forested hummocks 5—10 m high (dark gray) built of fine limnic sand resultant from thermokarst inversion of shallow lakes; (в) — similar inversion topography of the thawed sandy plateau in the Siberian Uvaly (63° N, 82°E).

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12. Fig. 11. Section of the 2nd terrace of Usa River at the Palaeolithic site Mamontovaya Kurya (Polar Circle, MK in fig. 1). Evidence of postglacial fluvial and aeolian sedimentation in periglacial environment 40 to 14 ka BP after (Svendsen, Pavlov, 2003). 1 — small ice-wedge cast; 2 — rippled silt; 3 — horizontally bedded sand; 4 — cross-bedded dune sand; 5 — cross-bedded gravel; 6 — bones and tusk; 7 — stone tools; 8 — silty lumps; 9 — OSL date (ka BP)×10³; 10 — radiocarbon date ¹⁴C (BP)×10³.

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13. Fig. 12. Pollen diagram of the Mamontovaya Kurya (МК in fig. 1) sequence indicating tundra-steppe landscapes along Usa River at 40 to 24 BP in modern northern boreal forest (Halvorsen, 2000).

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14. Fig. 13. Periglacial sediments exposed on the northern bank of the Ob River, Mega channel, 61°4ʹ N., 76°20ʹ E, in the downstream part of section fig. 14 (а – loess-like silt, б — ice-wedge cast, в — fine sandy sediment of a thermokarst pond). Greenish colour of the massive silt (“wet loess”) indicates reducing environment of the aeolian sedimentation.

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15. Fig. 14. Sections of Late Pleistocene periglacial formations on the Transverse Ob River, 61° N. (а) — downstream part of the Mega sequence at 13 km upstream of the town of Megion (Astakhov, 1989), (б) — generalized profile of sections along Mega channel by (Astakhov, 2006). 1 — loess-like silt; 2 — sandy rhythmite; 3 — sand and clay intercalated; 4 — clay; 5 — peaty rhythmite; 6 — crudely laminated sand; 7 — peaty soils; 8 — ice-wedge casts. Radiocarbon dates by (Arkhipov et al., 1980). ¹⁴C dates not calibrated.

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16. Fig. 15. Periglacial formations of the Transverse Ob River along profile Lokosovo–Mega–Agan (Astakhov, 1989) (61° N; Л-М-Аг in fig. 1). ¹⁴C dates not calibrated.

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17. Fig. 16. Sedimentary sequence of the 2nd terrace of Tobol River on eastern bank near settlement Lipovka (57°50ʹ N; Ли in fig. 1) simplified after (Kaplyanskaya, Tarnogradsky, 1974). 1 — oxbow-lake clay cut by ice-wedge casts, 2 — conterminal unit: massive silts with tundra paleosols and a horizon of rooted larch stumps (П), 3 — sandy silt with interlayers of fine sand, 4 — laminated fine sand with silt seams.

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