Palaeoclimate characteristics in interior Siberia of MIS 6–2: first insights from the Batagay permafrost mega-thaw slump in the Yana Highlands

Abstract

Abstract. Syngenetic permafrost deposits formed extensively on and around the arising Beringian subcontinent during the Late Pleistocene sea level lowstands. Syngenetic deposition implies that all material, both mineral and organic, freezes parallel to sedimentation and remains frozen until degradation of the permafrost. Permafrost is therefore a unique archive of Late Pleistocene palaeoclimate. Most studied permafrost outcrops are situated in the coastal lowlands of northeastern Siberia; inland sections are, however, scarcely available. Here, we describe the stratigraphical, cryolithological, and geochronological characteristics of a permafrost sequence near Batagay in the Siberian Yana Highlands, the interior of the Sakha Republic (Yakutia), Russia, with focus on the Late Pleistocene Yedoma ice complex (YIC). The recently formed Batagay mega-thaw slump exposes permafrost deposits to a depth of up to 80 m and gives insight into a climate record close to Verkhoyansk, which has the most severe continental climate in the Northern Hemisphere. Geochronological dating (optically stimulated luminescence, OSL, and 14C ages) and stratigraphic implications delivered a temporal frame from the Middle Pleistocene to the Holocene for our sedimentological interpretations and also revealed interruptions in the deposition. The sequence of lithological units indicates a succession of several distinct climate phases: a Middle Pleistocene ice complex indicates cold stage climate. Then, ice wedge growth stopped due to highly increased sedimentation rates and eventually a rise in temperature. Full interglacial climate conditions existed during accumulation of an organic-rich layer – plant macrofossils reflected open forest vegetation existing under dry conditions during Marine Isotope Stage (MIS) 5e. The Late Pleistocene YIC (MIS 4–MIS 2) suggests severe cold-stage climate conditions. No alas deposits, potentially indicating thermokarst processes, were detected at the site. A detailed comparison of the permafrost deposits exposed in the Batagay thaw slump with well-studied permafrost sequences, both coastal and inland, is made to highlight common features and differences in their formation processes and palaeoclimatic histories. Fluvial and lacustrine influence is temporarily common in the majority of permafrost exposures, but has to be excluded for the Batagay sequence. We interpret the characteristics of permafrost deposits at this location as a result of various climatically induced processes that are partly seasonally controlled. Nival deposition might have been dominant during winter time, whereas proluvial and aeolian deposition could have prevailed during the snowmelt period and the dry summer season.

Past climate and continentality inferred from ice wedges at Batagay megaslump in the Northern Hemisphere's most continental region, Yana Highlands, interior Yakutia

“…The middle part of the unit was dated to 142.8 ± 25.3 and > 123.2 kyr by optically Ashastina et al (2017) and Murton et al (2017) and this study. Photograph taken by Alexander Gabyshev in 2015. stimulated luminescence (OSL) and to 210.0 ± 23.0 kyr by infrared stimulated luminescence (IRSL) (Ashastina et al, 2017), pointing to its deposition during MIS 6. This age is supported by palaeo-ecological data (Ashastina et al, 2018).…”

“…Photograph taken by Alexander Gabyshev in 2015. stimulated luminescence (OSL) and to 210.0 ± 23.0 kyr by infrared stimulated luminescence (IRSL) (Ashastina et al, 2017), pointing to its deposition during MIS 6. This age is supported by palaeo-ecological data (Ashastina et al, 2018). An organic-rich unit of silty sand with abundant wood and plant remains (in lenses up to 3 m thick) overlies a distinct erosional surface near the top of the lower sand unit.…”

“…Neither study site has been glaciated during at least the last 50 000 years, and the Batagay megaslump provides access to permafrost formations starting from the Middle Pleistocene (Ashastina et al, 2017;Murton et al, 2017). The present mean annual air temperature at Batagay is −15.4 • C (mean of the coldest month: −47.7 • C; mean of the warmest month: 15.4 • C) and the mean annual precipitation is 170 to 200 mm (Ivanova, 2003).…”

“…The Batagay megaslump (67.58 • N, 134.77 • E), close to the city of Batagay on the east bank of the Yana River, is the world's largest known thaw slump (Fig. 2) (Ashastina et al, 2017;Murton et al, 2017). It is located on a hillslope in the taiga landscape (328 m above sea level for the highest part of the headwall) and exposes a sequence of permafrost deposits at least 60 m thick, with underlying bedrock cropping out in places (Kunitsky et al, 2013).…”

“…The slump exposes Pleistocene and Holocene permafrost formations ranging in age from MIS 6 (or older) to MIS 1 (Ashastina et al, 2017(Ashastina et al, , 2018Murton et al, 2017). Above slate bedrock and a basal diamicton, four major cryostratigraphic units contain ice wedges and/or composite wedges ( Fig.…”