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

Kseniia Ashastina,Frank Kienast,Margret Fuchs,Lutz Schirrmeister

doi:10.5194/cp-13-795-2017

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.

Highlights

During Late Pleistocene marine regression stages, ice-rich deposits several dozen metres in thickness – the Yedoma Ice Complex (YIC), formed on the now-inundated Laptev and East Siberian Sea shelves and on the coastal lowlands of Published by Copernicus Publications on behalf of the European Geosciences Union.K
Differences in the thawing rates along the outcrop provide a variety of conditions on the bottom and along the margins of the thaw slump
The western, northwestern, and southwestern parts of the outcrop consist of nearly vertical walls that are eroding most actively (Fig. 6), while the southeastern side is a gentler slope with a gradient of up to 45◦ (Fig. 4b)

Summary

Introduction

Ashastina et al.: Palaeoclimate characteristics in interior Siberia of MIS 6–2 northern Yakutia (Romanovskii et al, 2000a; Schirrmeister et al, 2013) Because they contain syngenetically frozen sediments and well-preserved fossil remains, YIC deposits provide a unique Late Pleistocene palaeoenvironmental archive. The concept of a purely aeolian origin of the mostly silty and fine-sandy, ice-rich deposits has become a widely accepted view in recent time (Zimov et al, 2012; Astakhov, 2014; Murton et al, 2015), but the assumption that loess covered the whole area during the Late Pleistocene contradicts cryolithological studies (Schirrmeister et al, 2011b) For this reason, the hypotheses of nival formation (Kunitsky, 1989), proluvial and slope genesis (Slagoda, 2004), and alluvial (Rozenbaum, 1981), or polygenetic genesis (Konishchev, 1981; Sher, 1997) are noteworthy

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