Glacial History Of The Taymyr Peninsula And The Severnaya Zemlya Archipelago, Arctic Russia

Maximum glaciation in this region, when even the central Arctic Ocean was glaciated, took place during the late Saalian stage (ca. 140 ka BP, MIS 6). Glaci-isostatically depressed land areas were thereafter, during the Eemian/Kazanzevo (MIS 5e) interglacial, inundated by the marine ‘Boreal Transgression’. During the following Weichselian period, (MIS 5d-2) three glaciations, all with their culminating centres on the Kara Sea shelf, expanded over Taymyr. The oldest, peaking ca. 100 ka BP, reached south of the Byrranga Mountains, but the two younger stages (around 65 ka BP, and at the ‘Last Glacial Maximum’ (LGM) ca. 18 ka BP) reached only to the North Taymyr ice-marginal zone, near the peninsulas west coast. Glaciers from the ice-covered Severnaya Zemlya islands contributed to the Kara Sea centred ice sheets during the earlier periods, but not so during the LGM, when this archipelago was largely ice free. Keywords Siberia Pleistocene ice-sheet dynamics ice-margin extensions glacial chronologies 28.1 Introduction Since the late 1980s, there has been a re-assessment of the glacial history of the Russian Arctic, from the Kola Peninsula in the west to the Lena Delta and beyond in the east (e.g. Svendsen et al., 1999, 2004 ). In this context, work has been carried out from Lake Taymyr, south of the Byrranga Mountains, northwards to the Arctic coast of the Taymyr Peninsula and on the Severnaya Zemlya archipelago ( Fig. 28.1 ). The present contribution is a QUEEN member's summary, update and extension of the Taymyr Peninsula chapter ( Hjort et al., 2004 ) in the first edition of this book. Here, the authors review the results regarding the glacial and marine history of Taymyr and the Severnaya Zemlya islands in chronological order, with reference to previous as well as to contemporary Russian and other work. It should be noted that the Putorana Plateau at the southern base of the Taymyr Peninsula is not included. 28.2 The Middle Pleistocene Pre-Saalian History Summaries on the extensive Russian literature on the Quaternary stratigraphy of the west Siberian Plain and the Taymyr Peninsula, and critical reviews of these, have been provided by Arkhipov et al. (1986) and Astakhov (2001, 2004a,b) among others. In many regions, three to five diamict beds are identified, interbedded with terrestrial interglacial strata in subarctic areas and usually marine deposits within the arctic areas within or just outside the boundaries of the Late Pleistocene glaciations ( Astakhov, 2004a ). However, such stratigraphical successions are rarely observed in superposition but constructed from borehole correlations. The ‘pancake’ stratigraphy of the Ozernaya River sections on southern October Revolution Island in the Severnaya Zemlya archipelago, first briefly described by Bolshiyanov and Makeyev (1995) and later more comprehensively by Möller et al. (2007) , is thus unique for Arctic Russia in revealing at least four marine units intercalated with tills in superposition, two of which seem to be of Middle Pleistocene age ( Fig. 28.2 ). The two lowermost marine units, represented by deeper-marine to prograding deltaic sediment successions (marine unit M-I) and a glaciomarine/marine off-shore to shoreface sediment succession (marine unit M-II), are erosionally cut and overlain by tills (till units T-II and T-III; Fig. 28.2 ). Till fabrics and glaciotectonic structures within underlying marine sediment imply that the ice-movement direction was from a northern sector towards the south ( Fig. 28.2 ), thus suggesting that till deposition during the expansions for T-II–T-IV was from the local ice cap(s) ( Möller et al., 2007 ). From retrieved electron spin resonance (ESR) and green stimulated luminescence (GSL) ages of marine unit M-I (~ 300–400 ka), it is suggested that it possibly represents a marine isotope stage (MIS) 10–9 transitional phase with a deep-marine setting induced by isostatic loading from the previous glacial phase (T-I). Similar ages for marine deposits have been reported from a few localities on the Taymyr Peninsula ( Bolshiyanov et al., 1998 ; Fig. 28.1 ), such as along the Shrenk and Mamota Rivers, north of the Byrranga Mountains, at Labaz Lake, south of the Byrrangas and at the Novorybnoe Village, along the Khatanga River. The marine unit M-I could possibly correlate to the Tobol Interglacial ( Arkhipov, 1989 ) of the western Siberian lowlands, capped by till of the Samarovo glaciation (MIS 8) which forms the maximum glacial drift boundary in western Siberia. However, such correlations are highly speculative because of the poor age constraints; also older ESR and thermoluminescence (TL) ages have been presented for the Tobol Interglacial ( Volkova and Babushkin, 2000 ; as cited in Astakhov, 2004a ), suggesting an MIS 11 age, that is, a correlative of the Holsteinian Stage of western Europe ( Astakhov, 2004b ). The ESR and GSL ages recorded in marine unit M-II also suggest that this marine event is of a pre-Saalian age, most probably representing a deglacial sedimentary succession, formed at the transition from MIS 8 to 7 with a relative high sea level stand in excess of 71 m a.s.l. at deglaciation ( Fig. 28.2 ). A direct correlative on Taymyr for this marine event is not recorded. However, Molodkov and Bolikhovskaya (2002) report an ESR age cluster at around 220 ka for a number of raised marine deposits in northern Eurasia. The age envelope for the marine unit M-II possibly fits into the Shirta Interglacial (MIS 7), as dated on the north-western Siberian plain ( Astakhov, 2004a ), sandwiched between the Taz and Samarovo glaciations . 28.3 The Middle/Late Pleistocene Transition: The Saalian and Eemian Stages According to Svendsen et al. (2004) , the maximum glaciation of the Kara Sea shelf and Taymyr Peninsula, and merging of the ice caps over the Putorana Plateau and the Anabar Uplands, that is, when this whole north-eastern region was covered by an Eurasian ice sheet, took place during the late Saalian (MIS 6), with a maximum spread at ca. 140 ka and with deglaciation of the shelf at around 130 ka ( Lambeck et al., 2006 ). However, the absolute Eurasian ice sheet maximum in this area might have already occurred during MIS 8 (the Samarovo glaciation; cf. Astakhov, 2004a ), the Pleistocene maximum glaciation limit thus being spatially diachronous ( Astakhov, 2008 ). The Saalian is considered equal to the Taz glaciation of West and North Central Siberia. On Severnaya Zemlya, this glaciation is associated with the highest recorded (up to 140 m a.s.l.; Fig. 28.2 , marine unit M-III) beach–ridge complexes formed at deglaciation ( Möller et al., 2007 ), and this only 200 km from the shelf break to the deep Arctic Ocean. This implies an ice-sheet thickness in excess of 3000 m over the Kara Sea ( Lambeck et al., 2006 ) and concurs with possible ice-shelf grounding at 1000 m water depths on the Lomonosov Ridge in the central Arctic Ocean ( Jakobsson et al., 2001, 2008b; Polyak et al., 2001 ). On the southern flank of Taymyr, a number of wide ice-thrust/push-moraine ridges have been documented from earlier mapping, for example, by Kind and Leonov (1982) , and from recent LANDSAT satellite imagery interpretation and modelling of digital elevation (ASTER) data ( Möller and Sallaba, 2010 ) ( Fig. 28.1 ). If the suggestion in Svendsen et al. (2004) that the Jangoda–Syntabyl–Baikuronyora zone (the JSB line) marks the maximum Kara Sea Ice Sheet (KSIS) extent during an Early Weichselian glaciation is correct, then the Urdachsk (U), Sampesa (Sa) and Severokokorsk (K) ice-marginal zones ( Fig. 28.1 ) are older and might thus represent recessional phases of the Saalian/Taz glaciation after separation from the ice cap over the Putorana plateau. The deep isostatic depression of the land, caused by the thick Saalian ice load, led to widespread post-glacial marine inundation at deglaciation and subsequent deposition of marine sediments over large parts of Taymyr and Severnaya Zemlya. Such Kazantzevo Interglacial (equivalent to the Eemian Stage in the European terminology; ~ MIS 5e) sediments, typified by an arcto-boreal mollusc assemblage, are described from a large number of sites on the Taymyr Peninsula ( Urvantsev, 1931; Saks, 1953; Kind and Leonov, 1982; Möller et al., 2008 ) and from the Severnaya Zemlya archipelago ( Bolshiyanov and Makeyev, 1995; Möller et al., 2007 ) ( Fig. 28.1 ). Reported Eemian-age sediments range from deep-marine over shoreface and foreshore to beach-face sediment. The latter reach altitudes up to 130 m a.s.l. south of the Byrranga Mountains ( Möller et al., 1999a,b ) and as high as 140 m a.s.l. on Severnaya Zemlya ( Möller et al., 2007 ) and on Cape Chelyuskin, the northern tip of the Taymyr Peninsula ( Miroshnikov, 1959; Shneyder, 1989; Möller et al., 2008 ). 28.4 The Build-Up of KSIS: Changing Paradigms An early view of ice-sheet inception in north-western Siberia was that ice started to grow over mountains (e.g. the Byrranga Mountains, Ural Mountains, etc.), thereafter flowing into lowland areas (e.g. Urvantsev, 1931; Saks, 1953 ). From such a scenario, there has been a shift into a paradigm suggesting repeated build-up of thick ice sheets on the shallow shelves of the Barents and Kara Seas (e.g. Astakhov 1976, 1979, 1998; Grosswald, 1980, 1998; Kind and Leonov, 1982 ). The substantial loading from such continental-scale ice could explain the occurrence of high raised beaches, such as the ~ 140 m a.s.l. Saalian/Eemian-inundation shorelines on October Revolution Island, which are among the highest described from the Eurasian Arctic. Using such shoreline evidence and dated ice-marginal formations, the maximum KSIS thickness in the Saalian was estimated to 3000–3300 m by earth rheological inverse modelling ( Lambeck et al., 2006 ). More recent reconstructions of Eurasian Ice Sheet accumulations and decays have confirmed this latter paradigm (e.g. Möller et al., 1999a; Alexanderson et al., 2001, 2002; Hjort et al., 2004; Svendsen et al., 2004; Astakhov and Mangerud, 2005; Larsen et al., 2006 ). However, growing evidence suggests that the latter paradigm could be combined with the first. Structural and textural evidence from tills and sub-till sediments at a number of sites around the perimeter of the shallow Kara Sea, and within the Kara Sea itself, including Severnaya Zemlya ( Möller et al., 2007 ), at Cape Chelyuskin ( Möller et al., 2008 ), the north-western Taymyr Peninsula ( Hjort and Funder, 2008 ), the Yamal Peninsula ( Forman et al., 1999, 2002 ) and the Yugorski Peninsula ( Lokrantz et al., 2003 ) imply subglacial deformation and deposition during expansions of local ice caps and often suggesting ice-flow directions that are not compatible with ice flows that should have been generated from an ice sheet centred over the Kara Sea shelf (cf. review in Ingólfsson et al., 2008 ). However, such local ice caps could not have induced sufficient isostatic depression of the crust for explaining the high elevations documented for raised beaches. For resolution of this conflicting evidence, and based on an original concept of Hughes (1987) further modelled by Siegert et al. (2002) and Siegert and Dowdeswell (2004), Möller et al. (2007, Fig. 26) suggested that these peripheral sites were critical as nucleation centres for repeated initiations of large, coherent KSISs. These local ice domes in highland areas and along the perimeter of the Kara Sea were characterised by wet-based thermal regimes in their initiation phases, as indicated by deposition of deformation tills and plastic deformation of pre-existing sediment. They later gradually coalesced on the adjacent shelf with globally falling sea level. The latter facilitated the formation of a stable and thick sea-ice cover and later ice-shelf formation. Eventually, a large ice dome formed as a combination of ice flowing into the Kara Sea basin and snow accumulation on the grounded ice shelf, initiating redistribution of ice drainage and basal thermal regime. A fully developed KSIS preferentially drained towards the Arctic Ocean in the north as ice streams, such as those developed along the St. Anna and Voronin troughs. Towards the south, the ice flow reversed compared to the initiation phase north and west of the Byrranga Mountains, whereas south of these mountains the south-directed flow had already formed during the initiation phase. This continued, eventually leading to the terminal ice-margin positions of the individual glaciation phases in question. Such Kara Sea shelf-based ice sheets would have been sensitive to sea level changes; as global sea level rose when continental ice sheets disintegrated at terminations of glaciations, the KSIS rapidly lost mass, resulting in marine inundation and the deposition of marine sediments ( Ingólfsson et al., 2008 ). 28.5 The Early Weichselian—The Weichselian Glaciation Maximum on Taymyr From the southern foothills of the Byrranga Mountains and ~ 250 km southwards, at least eight moraine-ridge complexes have been recorded (e.g. Kind and Leonov, 1982 ; Fig. 28.1 ). However, their age of formation remains poorly constrained. Individual ridge complexes are up to 15 km wide and 100–150 m high and can be followed laterally for hundreds of kilometres. Some form distinct, sometimes complex morainic loops, others are more diffuse and ridge trends and connections are lost in large interlobate complexes. According to Kind and Leonov (1982) , the ridge complexes consist of active ice-thrust stacks of both Quaternary and pre-Quaternary strata, some ridges being glaciotectonic in origin, whereas others are more of ice disintegration type, lined with kame terraces and hummocky kame topography. Fossil ice is still present in many ridge complexes (e.g. Kind and Leonov, 1982; Siegert et al., 1999 ), a phenomenon that can also be seen from Landsat images, showing spatially concordant distributions of numerous thermokarst lakes. The glacial geomorphology, the direction of glaciotectonic deformation and the provenance of crystalline erratic boulders clearly indicate that these moraine-ridge complexes were constructed at KSIS marginal positions south of the Byrranga Mountains. Numerous suggestions have been proposed regarding which glacial stages and phases individual ridges represent ( Andreyeva, 1978; Andreeva and Isaeva, 1982; Kind and Leonov, 1982; Isayeva, 1984; Fisher et al., 1990; Siegert et al., 1999 ), varying from Saalian (Taz), Early Weichselian (Lower Zyryanka/Muruktin) to Late Weichselian (Upper Zyryanka/Sartan). The most recent compilation by Svendsen et al. (2004) suggested that the Jangoda–Syntabyl–Baikuronyora zone, the JSB line ( Fig. 28.1 ), should mark the maximum expansion of the KSIS in the Early Weichselian (unfortunately, the JSB line has been incorrectly drawn in Fig. 2 of Svendsen et al. (2004) , where it instead follows the Sampesa ridge (line Sa, Fig. 28.1 ), lying distal to the Syntabul ridge). Major argument for the JSB line being the maximum limit for an Early Weichselian KSIS is that marine deposits assigned to the Eemian/Kazantzevo interglacial are covered by a till north of the JSB ( Urvantsev, 1931; Saks, 1953; Kind and Leonov, 1982 ), but not south of it. However, it must be stressed that no direct age constraints exist for the JSB line as such. Based on the recently performed Landsat mapping ( Möller and Sallaba, 2010 ), the geomorphological connection between the Syntabyl and Baikuronyora ridge complexes seems less probable; the latter is readily traced into the younger Upper Taymyr ridge system (see below), and the former seems to continue into the wide Severokokorsk ridge complex (line K, Fig. 28.1 ). A connected Jangoda–Syntabyl–Severokokorsk moraine system (a connection already proposed by Isayeva, 1984 ) might thus be an alternative to the JSB line of Svendsen et al. (2004) for the Early Weichselian KSIS maximum. 28.6 Deglaciation from the Early Weichselian Maximal Position to the Byrranga Mountains The ice recession from the Early Weichselian maximum towards the Byrranga Mountains seems to have been halted at certain positions and/or interrupted by ice-margin readvances, as indicated from a number of ice-marginal formations, some of them with distinctly lobate planforms and with intricate patterns of secondary ridges and within-lobe younger ridges cutting off, or on-lapping to, older lobes (e.g. Fig. 28.3 ). Isayeva (1984) named these younger ice-marginal complexes the Mokoritto ridge system in the Pyasina River basin on the western Taymyr Peninsula and the Upper Taymyr Ridge system in the upper Taymyr River basin (ridge system M and UT in Fig. 28.1 , respectively). From Landsat imagery interpretation ( Möller and Sallaba, 2010 ), the latter system seems to link to the Baikuronyora ridge system along the southern shore of Lake Taymyr (line B, Fig. 28.1 ) which, however, was considered to be part of the terminal Early Weichselian ice-marginal zone by Svendsen et al. (2004) . The ice recession from the Early Weichselian maximum took place in a marine basin with water depths up to 100 m, as demonstrated from several localities with marine sediments within the Taymyr Lake basin and along the foothills of the Byrranga Mountains (filled circles, Fig. 28.1 ). These marine successions usually constitute off-shore glaciomarine to marine clayey–silty deposits. They continue in places into thick deltaic deposits, or at other places into shoreface and foreshore and sometimes also beach-face deposits and thus demonstrate more or less full isostatically driven regressional sediment sequences. The retrieved ages from mollusc shells and sediments from six investigated sites (26 ESR and 5 OSL ages) give a consistent age-frame of 95–70 ka. Radiocarbon dating of mollusc shells from the same localities all give infinite ages. The most prominent of the delta successions occurs in the Ledyanaya River valley, west of Lake Taymyr ( Fig. 28.1 ), the type locality for the ‘Ledyanaya Gravel Event’ ( Möller et al., 1999a,b ). Here, delta topset beds reach 100–120 m a.s.l. and the marine basin into which the deltas prograded probably reached 90–100 m a.s.l. This high, post-glacial marine limit, together with the huge accumulations of coarse sediments within the deltas, confirms the substantial glacioisostatic depression and indicate a substantial flow of sediment-laden glacial meltwater southwards through the Byrranga mountain valleys and into the marine basin. This meltwater must have emanated from an ice front which at that time stood along the northern slopes of the mountains. The marine event is probably the equivalent of the Karginsk marine transgression of Andreeva and Kind (1982) , in its earliest phase radiocarbon-dated to 50–39 14 C ka BP. However, these mollusc 14 C ages stem from conventional, that is, not accelerator mass spectrometry (AMS), dating and must be considered underestimates. There are no signs that glaciers regrowing during the Middle and Late Weichselian reached south of the Byrranga Mountains since this Early Weichselian deglaciation (e.g. Möller et al., 1999a ). The Taymyr Lake basin has thus been continuously ice free ever since. This is shown by a number of sites with ‘Cape Sabler-type’ sediment successions of laminated fine sand and silt, rich in organic detritus and also thick units of silt-soaked peat, deposited in a terrestrial setting with peat bog and aeolian deposition, interrupted by occasional lacustrine floods ( Möller et al., 1999a; Hubberten et al., 2004 ). AMS 14 C dates obtained from Cape Sabler and nearby sites (infilled squares, Fig. 28.1 ) suggest continuous deposition from before 40 14 C ka BP and into the Holocene. Lake sediment successions from both the Taymyr Lake itself and the adjacent Levinson-Lessing Lake ( Ebel et al., 1999; Hahne and Melles, 1999; Niessen et al., 1999 ) also indicate generally ice-free conditions in the Byrranga Mountains since at least the Middle Weichselian Substage time. The Early Weichselian KSIS also inundated the Chelyuskin Peninsula on north-easternmost Taymyr. This conclusion is based on till and glaciotectonic deformations overlying and affecting Eemian-age interglacial marine sediments, and from the occurrence of Kara Sea crystalline erratics found on the hilltops ( Möller et al., 2008 ). In addition, the glacioisostatic depression in this area (at least 80 m a.s.l.) resulted in post-glacial marine inundation, as indicated by ESR dating of mollusc shells in the marine sediments to ca. 93–80 ka and thus largely contemporaneous with that in the Taymyr Lake basin. 28.7 The North Taymyr Ice-Marginal Zone The north-westward retreat of the Early Weichselian ice front from the Byrranga Mountains seems to have proceeded largely by calving into a glacial lake filling the Shrenk, Trautfetter and part of the Lower Taymyr River valleys ( Fig. 28.1 ) and dammed towards the north-west by the ice itself. A new grounding line was reached on the north-western sides of the Shrenk and Trautfetter valleys, causing a temporary still-stand of the ice front and resulting in the formation of the North Taymyr ice-marginal zone, the NTZ ( Fig. 28.1 , NTZ 1). The NTZ is a complex of glacial, glaciofluvial and glaciolacustrine deposits, containing large amounts of redeposited Quaternary marine sediments and also glacially displaced, coal-bearing Cretaceous sands. It has now been dated for the first time and described in some detail by Alexanderson et al. (2001, 2002) but had already been broadly mapped and discussed by Kind and Leonov (1982) . When the KSIS front stood at this ice-marginal zone, it seems to have crossed the present coastline near the Michailova Peninsula at ca. 75 ° N. The NTZ can then be roughly ( Hjort and Funder, 2008 ) followed, first eastwards and then northwards for 700–750 km, mostly 80–100 km inland, and seems to recross the present coastline south of the Tessema River, around 77°N ( Fig. 28.1 ). It is best developed in its central parts, ca. 100 km north-east and south-west, respectively, of where it is today cut through by the Lower Taymyr River. The base of the NTZ in these central parts ( Alexanderson et al., 2001, 2002 ) is a series of ridges up to 100 m high and 2 km wide, mainly consisting of, or possibly only covered by, redeposited marine silts. The ridges are still ice cored, but in most parts of the zone, the present active layer only rarely reaches the ice surface. Associated with the NTZ are deltas, abrasion terraces and shorelines corresponding to two generations of ice-dammed lakes, with shore-levels at between 140 and 120 m and at ca. 80 m a.s.l. (Figs. 4 and 5 in Hjort et al., 2004 ). These lakes drained southwards into the Taymyr Lake basin, as recorded by current directions in fluvial sediment sequences along the Taymyr River valley where it passes through the Byrranga Mountains (today the river flows northwards). From the Taymyr Lake basin, the water continued either westwards to the south-eastern Kara Sea shelf or eastwards towards Khatanga Bay and the Laptev Sea. 28.8 The Early Weichselian NTZ Stage The NTZ is morphologically very complex and in its central part consists of three generations of ice-marginal deposits ( Alexanderson et al., 2001, 2002 ). The oldest is that formed as the ice front, largely through calving into its frontally dammed lake, had retreated north-westwards from its Byrranga still-stand position to the new grounding line. This stage is associated with the deepest glacial lake, reaching 140–120 m a.s.l. Two OSL dates from an ice-contact glaciofluvial sequence aggradated to the 140 m level gave ages of ca. 80 ka, which combined with the ESR ages obtained for the ‘Ledyanaya Gravel Event’, indicate its relationship with the Early Weichselian KSIS deglaciation process from its maximum stand south of the Byrrangas and the Taymyr Lake basin. 28.9 The Middle Weichselian NTZ Stage During the second NTZ generation, the ice front seems to have stood more or less at the same positions as during the older stage ( Fig. 28.1 : NTZ 2). This caused an overprinting on the previous morphology of a number of over-deepened lake basins and a new system of marginal moraine ridges, associated glacial lake deltas and shorelines, valley fills, etc. The ice-dammed lake was, however, shallower than the previous water body and reached only 80 m a.s.l. It has been OSL-dated at two localities; two delta samples gave an age of ca. 65 ka BP, and two dates from fluvial terrace deposits, connecting the ice front with the lake basin, gave ca. 70–55 ka BP. This stage of glacial lake sedimentation is further supported by three OSL dates of 60–55 ka from glaciolacustrine rhythmites in the Taymyr Lake basin, just south of the Byrranga Mountains, where the glacial damming in the north also led to a rising water level. The available dates thus indicate that an interval of at least 10,000 years occurred between the two oldest NTZ events, and data from the south-westernmost part of this ice-marginal zone indicate that the event around 70–60 ka was the last one to affect the whole NTZ ( Hjort and Funder, 2008 ). 28.10 The Late Weichselian NTZ Stage During the third NTZ generation, the KSIS affecting north-western Taymyr was much thinner than previously and inundated a much smaller area ( Alexanderson et al., 2001, 2002 ). Because it did not cross a 300–500 m high range of coastal hills ( Fig. 28.1 ), which were overridden during the two previous stages, its thickness near the present coastline could not have exceeded 500 m. Nonetheless, it penetrated 100 km inland on a 150 km broad front centred along the Lower Taymyr River valley and terminated at altitudes presently below 150 m a.s.l. ( Fig. 28.1 : NTZ 3). North-east of the valley the front abutted a system of bedrock cuestas, whilst to the south-west, it was in contact with the pre-existing NTZ 1–2 moraines and, in one case, formed an independent lobate moraine (Fig. 4 in Hjort et al., 2004 ). The area overridden by this ice sheet, the most recent to inundate the Taymyr Peninsula, is to a large extent covered by dislocated marine sediments, identifiable on satellite images by their dendritic erosional pattern. In a 5- to 10-km-wide zone behind the former ice front, where the ice contained most debris, the landscape is patterned by a multitude of shallow slides, exposing remnant glacier ice under a melt-out till cover of only about 0.5 m. (Fig. 6 in Hjort et al., 2004 ). Further north-west (up-ice), there are fewer indications of the former overriding. However, a boulder-lag on top of glaciolacustrine sediments at the Kara Sea coast ( Funder et al., 1999 ) may date from this glacial event. This youngest ice-sheet advance is pre-dated by two radiocarbon dates of ca. 20 14 C ka BP from mollusc shells ( Hiatella arctica , Astarte sp.), from glacially redeposited marine silt sampled ca. 2 km behind the former ice-front position ( Alexanderson et al., 2001, 2002 ). It is post-dated by a radiocarbon date of ca. 12 14 C ka BP from in situ terrestrial material just inside the present coast near the Taymyr River mouth ( Bolshiyanov et al., 2000 ). The glaciation thus dates from the Weichselian global Last Glacial Maximum (LGM). This brief advance (8000 years or less) of a thin ice sheet onto the present land, as marked by the NTZ 3 line, thus dates from the Weichselian Last Glacial Maximum (LGM). However, it is still unclear if the ice advanced from a regional ice cap on the very shallow, and for global eustatic reasons at that time mostly dry shelf in the northeastern corner of the Kara Sea, or if it was connected westwards to ice centred north of Novaya Zemlya, as suggested by Polyak et al. (2008). No evidence of any glacial lake dammed by this LGM ice sheet has been found north of the Byrranga Mountains, and it is therefore thought that its meltwater mainly drained southwards via the Lower Taymyr River valley into the Taymyr Lake basin ( Alexanderson et al., 2001, 2002 ). Indications of an increasing rate of sedimentation in the lake around 19 14 C ka BP ( Möller et al., 1999a, Hubberten et al., 2004 ) suggest a causal connection with a meltwater input. Neither have any raised marine shorelines, dated to the LGM or thereafter, been found on Taymyr. This is not surprising considering the thin, short-lived and thus isostatically insignificant ice, as well as the extremely low eustatic sea level at the time that persisted into the Holocene. 28.11 The Severnaya Zemlya Islands During the Weichselian Stage Eemian/Kazantzevo sediments in the Ozernaya River sections on southern October Revolution Island (MIS 5e; marine unit M-III, Fig. 28.2 ) form a regressional sequence, initiated by off-shore glaciomarine–marine sediments capped by shoreface to foreshore sands and gravels, in turn capped by till (till unit T-IV) of obvious Weichselian age ( Möller et al., 2007 ). This till is in turn at a number of sites overlain by marine unit M-IV sediments, forming a coarsening upwards succession from off-shore marine silty clays to foreshore/shoreface sands and gravels, starting well above 60 m a.s.l. Some M-IV sediments also consist of estuary/lagoonal sediment successions, at one site with a spectacular discovery of at least nine narwhal ( Monodon monoceros ) skeletons on the same depositional surface. These finds have been dated to ~ 50 ka. A number of 14 C ages on marine molluscs, which are finite but close to the analytical limit, suggest an age of 50–37 14 C ka BP. This age span is supported by some of the retrieved GLS ages, whereas others are significantly older. It is assumed that insufficient solar resetting of sediment in these cases is responsible for age overestimates. From all this, Möller et al. (2007) concluded that the M-IV sediments are of Middle Weichselian (MIS 3) age and, because no marine sediments of an undoubtedly interstadial MIS 5d–5a age have been identified, that October Revolution Island (and the whole Severnaya Zemlya archipelago) became glaciated during the initial phase of the Early Weichselian and remained so from MIS 5d to MIS 4. During the same period, the Cape Chelyuskin peninsula south of the islands became glaciated and thereafter deglaciated, experiencing no Middle Weichselian ice advance ( Möller et al., 2008 ). However, as previously described, the other parts of northern Taymyr experienced both an Early Weichselian ice retreat from the NTZ zone and thereafter a readvance to the NTZ in the Middle Weichselian. If ice persisted over Severnaya Zemlya throughout MIS 5a–d, then it could have acted as a nucleation area for the regrowth and expansion of the KSIS on the northern shelf during MIS 4. The studies on Severnaya Zemlya by Möller et al. (2007) revealed neither any sediments nor raised shorelines that could be tied to a Late Weichselian (MIS 2) glacial/deglacial event, and that Severnaya Zemlya was outside any KSIS during the LGM is further supported by a continuous sediment core from Changeable Lake on southern October Revolution Island. There 14 C and luminescence ages from the lake sediments suggest that the latest ice expansion occurred before 53 ka, followed by marine and lacustrine deposition during the LGM and into the Holocene ( Raab et al., 2003; Berger et al., 2004 ). A largely ice-free LGM on Severnaya Zemlya is further supported by mammoth remains that have yielded ages between 12 and 30 14 C ka BP ( Velichko et al., 1984; Bolshiyanov and Makeyev, 1995 ), and seemingly also by the submarine geology of the surrounding parts of the Kara Sea ( Polyak et al., 2008 ). 28.12 Summary of Results The main results of this study of the glacial and marine history of the Taymyr Peninsula, the Severnaya Zemlya archipelago and the Kara Sea shelf, as summarised in Fig. 28.4 , are as follows: • The so far documented maximum glaciation of this region seems to have taken place during the Late Saalian (MIS 6), when even the central Arctic Ocean was glaciated, with ice grounding on the Lomonosov Ridge. Thereafter followed the Eemian (Kazantzevo, MIS 5e) interglacial with, extensive marine inundation due to the isostatic effect of the preceding glaciation—the so-called Boreal Transgression. • During the Weichselian Stage, three phases of successively decreasing ice-sheet expanses and retreats have been mapped and dated. The most extensive glaciation dates from the Early Weichselian, culminating at ca. 100 ka, and a Middle Weichselian event of intermediate extent dates from 70 to 60 ka. The last and least extensive glaciation, contemporaneous with the global LGM, was short, lasting only 8000 years or less. It culminated after 20 ka and had largely disappeared from present onshore areas by 12 ka BP. • The main (culminating) ice sheets covering the Taymyr Peninsula during the Weichselian on all three occasions did emanate from the Kara Sea continental shelf, from where they advanced south-eastwards across the land. At most, the ice front reached some 400 km from the present coast, leaving a series of more or less distinct zones of ice-marginal features south of the Byrranga Mountains and the Taymyr Lake basin. In the south and east, the ice front reached the Laptev Sea drainage basin. • The KSISs dammed large glacial lakes, filling the lake- and river basins both north and south of the Byrranga Mountains (Fig. 5 in Hjort et al., 2004 ) and, during the final stages of the deglaciations, they also developed on the lowland areas along the coast. Water from north of the mountains drained southwards along the Taymyr River valley (where it flows northwards today) into the Taymyr Lake basin and, in most cases, thereafter probably westwards to the Kara Sea shelf. • An Early Weichselian marine inundation, following the regional Weichselian glaciation maximum, reached ca. 100 m above present sea level. 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