DOI / # 2007 Taylor & Francis CLAS HÄTTESTRAND, VASILI KOLKA AND ARJEN P. STROEVEN

Transcription

1 The Keiva ice marginal zone on the Kola Peninsula, northwest Russia: a key component for reconstructing the palaeoglaciology of the northeastern Fennoscandian Ice Sheet CLAS HÄTTESTRAND, VASILI KOLKA AND ARJEN P. STROEVEN BOREAS Hättestrand, C., Kolka, V. & Stroeven, A. P (October): The Keiva ice marginal zone on the Kola Peninsula, northwest Russia: a key component for reconstructing the palaeoglaciology of the northeastern Fennoscandian Ice Sheet. Boreas, Vol. 36, pp Oslo. ISSN One of the key elements in reconstructing the palaeoglaciology of the northeastern sector of the Fennoscandian Ice Sheet is the Keiva ice marginal zone (KIZ) along the southern and eastern coast of Kola Peninsula, including the Keiva I and II moraines. From detailed geomorphological mapping of the KIZ, primarily using aerial photographs and satellite images, combined with fieldwork, we observed the following. (1) The moraines display ice contact features on both the Kola side and the White Sea side along its entire length. (2) The Keiva II moraine is sloping along its length from c. 100 m a.s.l. in the west (Varzuga River) to c. 250 m a.s.l. in the east (Ponoy River). (3) The KIZ was partly overrun and fragmented by erosive White Sea-based ice after formation. From these observations we conclude that the KIZ is not a synchronous feature formed along the lateral side of a White Sea-based ice lobe. If it was, the moraines should have a reversed slope. Rather, we interpret it to be time transgressive, formed at a northeastward-migrating junction between a warm-based Fennoscandian Ice Sheet expanding from the west and southwest into the White Sea depression, and a sluggish cold-based ice mass centred over eastern Kola Peninsula. In contrast to earlier reconstructions, we find it unlikely that an ice expansion of this magnitude was a mere re-advance during the deglaciation. Instead, we propose that the KIZ was formed during a major expansion of a Fennoscandian Ice Sheet at a time pre-dating the Last Glacial Maximum. Clas Hättestrand ( classe@natgeo.su.se) and Arjen P. Stroeven, Department of Physical Geography and Quaternary Geology, Stockholm University; Vasili Kolka, Geological Institute, Kola Science Centre RAS, Apatity; received 20th March 2006, accepted 21st February The evolution of the Fennoscandian Ice Sheet (FIS) since the Last Glacial Maximum (LGM) is reasonably well constrained for its southern and western sectors (Kleman et al. 1997; Boulton et al. 2001; Ehlers & Gibbard 2004). However, the glacial history of the northeastern sector of the ice sheet, including the Kola Peninsula, is more poorly understood. Reconstructions of ice cover in the area are of particular interest because the FIS here was close to its maximum eastwards extent during the Weichselian (Fig. 1; Svendsen et al. 2004; Demidov et al. 2006) and the White Sea depression was a primary location for ice streams in the FIS (Punkari 1995; Boulton et al. 2001). Hence ice centred on the Kola Peninsula and ice lobes draining through the White Sea may have played an important role in nourishing the Barents Sea Ice Sheet and, later, in influencing Arctic Ocean circulation during deglaciation. Despite the fact that the Kola Peninsula displays a dense and complex pattern of glacial landforms (Fig. 2; Hättestrand & Clark 2006b), many aspects of the icesheet history of the region remain elusive. For example, the overall deglaciation pattern is under debate. Three general glaciation models and patterns of deglaciation have been proposed: (1) deglaciation of the east-central part of the peninsula whilst ice lobes still occupied the surrounding depressions and straits (Apukhtin & Ekman 1967; Niemelä et al. 1993; Yevzerov 2001); (2) the existence of a dynamically independent ice cap, the Ponoy Ice Cap, centred on eastern Kola Peninsula in post-lgm time (Strelkov 1976a; Ekman & Iljin 1991), possibly interacting with ice lobes in the White Sea basin; (3) ice marginal retreat inwards from the coast, east to west across the peninsula, towards the area of final deglaciation in northern Sweden (Punkari 1993; Kleman et al. 1997; Hättestrand & Clark 2006a). One of the most prominent landscape features and a key element in reconstructing the history and dynamics of the northeastern part of the FIS is the Keiva ice marginal zone (KIZ), which parallels the Tersky coast along southern and eastern Kola Peninsula, from Varzuga River in the west to Lumbovka in the northeast (Figs 2, 3). This zone of ice marginal landforms is commonly interpreted to have formed during the last deglaciation (c kyr BP; Svendsen et al. 2004), partly along the margin of an ice lobe filling the White Sea depression and partly along the margin of a Ponoy Ice Cap (e.g. Ekman & Iljin 1991). However, currently there is no consensus regarding its precise formation and age. In an attempt to resolve these issues, we have mapped the geomorphology of the entire 300-km length of the KIZ in detail using aerial photographs and satellite images. Specifically, we have reviewed and discussed formation theories in view of recent glacial DOI / # 2007 Taylor & Francis

2 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 353 Fig. 1. Location map. Ice marginal positions and dates from Svendsen et al. (2004) and Demidov et al. (2006). geomorphological mapping (Hättestrand & Clark 2006b) of Kola Peninsula that has shown that the KIZ has, in many places, been overrun by regional ice flow from the southwest, indicating that it pre-dates the last major ice cover of the area during the Late Weichselian. Palaeoglaciological setting The glacial geological and geomorphological record of the Kola Peninsula displays a distinct patchy pattern (Krasnov et al. 1971; Strelkov 1976b; Niemelä et al. 1993; Hättestrand & Clark 2006b), indicating that different areas retain the imprint of different glacial regimes. In the western part of the Kola Peninsula region there are generally thicker and more extensive glacial deposits than in the east (Niemelä et al. 1993), and glacial lineations are the dominant landform type (Fig. 2), indicating deposition by warm-based ice. In the area south of the central Kola mountains and in the area between Kandalaksha Bay and the Finnish border, densely spaced drumlins with high elongation ratios indicate the location of a palaeo-ice stream draining into the White Sea from the west (e.g. Punkari 1982, 1993; Boulton et al. 2001; Hättestrand & Clark 2006b). In contrast, tills and subglacial morphology are absent in much of the east-central part of the Kola Peninsula. This led Ramsay (1898), Apukhtin & Ekman (1967) and Krasnov et al. (1971), among others, to suggest that the FIS did not cover eastcentral Kola Peninsula during the LGM. However, not recognized by these authors, eastern Kola Peninsula has an abundance of lateral meltwater channel series (Fig. 2A), and these prove the former presence of a deglaciating ice sheet. Because such channel series form through ice surface melting and runoff alone, they indicate cold-based conditions of the ice sheet during deglaciation (Dyke 1993; Hättestrand & Clark 2006a). The absence of subglacial features further indicates that the glaciations prior to the last deglaciation were cold-based over east-central Kola Peninsula as well. Moreover, the lateral meltwater channels can be used to derive the ice-surface slope direction (and, therefore, ice-flow direction) during the deglaciation, thus allowing for reconstruction of the ice marginal retreat (Fig. 2B). Hättestrand & Clark (2006a) argued that there cannot have been a separate Ponoy Ice Cap on eastern Kola Peninsula in Lateglacial time, because all ice masses, even those entirely cold-based, leave a meltwater record when retreating. However, on Kola Peninsula there are no landforms indicating a westfacing ice margin during deglaciation. The largest coherent glacial landform system in the area is the KIZ (Fig. 3). The most prominent features of the KIZ are two moraine belts: Keiva I, a smaller moraine belt situated 1020 km from the coast, between Strelna River and Sosnovka River, and Keiva II, a larger moraine system situated approximately 20 km further inland from Keiva I, and extending from Varzuga River to Ponoy River. These moraines were already recognized in the early 1900s by Grigoryev (1934), Vvedenski (1934) and Richter (1936), and the names Keiva I and Keiva II were introduced by Lavrova (1960). In the following, we refer to the Keiva moraines (Keiva I and Keiva II) when discussing the moraine ridges, whereas we label the entire ice marginal system, from Varzuga to Lumbovka, the KIZ. Previous interpretations Considering its large dimensions, comparable in size to the Salpausselkä moraines in Finland, and therefore its potential importance for regional ice-sheet reconstructions, there are surprisingly few comprehensive studies that consider the KIZ as a coherent feature. Palaeoglaciological reconstructions of the KIZ are either based on detailed descriptions of individual key sites or are included in general studies of the palaeoglaciology of the eastern Baltic Shield. Hence detailed geomorphological maps and stratigraphical descriptions representative of the entire length of the KIZ are essentially lacking. Probably because of this absence of comprehensive studies, no conclusive theory regarding depositional processes and the events

3 354 Clas Hättestrand et al. BOREAS 36 (2007) Fig. 2. A. Key glacial geomorphological elements of the Kola Peninsula (simplified from Hättestrand & Clark 2006b). B. Ice marginal retreat pattern (extended from Hättestrand & Clark 2006a).

4 C a m po ha a its al Py R T e r s k y IIa c o a s t Ke iva sa R. Pu l noy Po a iv Ke Ib I Sosnov ka R. er R iv A' Lumbovka The Keiva ice marginal zone on the Kola Peninsula, NW Russia Fig. 3. The glacial geomorphology of the southeastern Kola Peninsula (extracted from Ha ttestrand & Clark 2006b). The insert profile shows the westward slope of the Keiva II moraine. A iver Very large meltwater channel Hummocky moraine St re lna R Large meltwater channel km. R End moraine belt (larger deposit) y no Po A' Esker 200. R End moraine (single ridge) s So a vk no Delta and outwash Legend. R Ib Ke i va I ga n lo Pu 150. R S a ln tre. Ke i va I ga. R Ke i va I I a C n va ha. R Lineations (drumlins, flutings) ga 50 km 0 zu r Va R. er Riv 66 N m asl A 40 E I 67 N 36 E a zug Var iv it al Py K R. e ga on a BOREAS 36 (2007) 355

5 356 Clas Hättestrand et al. BOREAS 36 (2007) leading to the formation of the KIZ has emerged. However, based on available data, a number of widely different formational theories can be recognized (Fig. 4). Throughout the paper, published radiocarbon ages have been converted to thousands of calendar years before present (kyr BP) using the IntCal04 calibration curve (Reimer, 2004). Original investigations describing the KIZ mainly used geomorphological field observations, and the moraines were considered to be ice-contact deposits, formed between a lobe of the FIS in the White Sea depression and a stagnant sector of the FIS covering Kola Peninsula (Grigoryev 1934; Richter 1936). Vvedenski (1934) correlated Keiva I and II with the Salpausselkä formations, and considered them to be of Younger Dryas age. Lavrova (1960), who compiled the first map of the Quaternary geology of the Kola Peninsula region, also correlated the Keiva moraines with the Salpausselkä ridges, and concluded that the Keiva moraines were formed along the southeastern margin of a more or less stagnant part of the FIS, centred over the Kola Peninsula (Fig. 4A). In contrast, Apukhtin & Ekman (1967), Apukhtin & Yakovleva (1967) and Krasnov et al. (1971) argued, based partly on the lack of till on east-central Kola Peninsula, that there was no Kola-based ice in Fig. 4. Previous reconstructions of the formation of the Keiva moraines.

6 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 357 Lateglacial time, and hence that the moraines were built by White Sea ice lobes alone (Fig. 4B). Krasnov et al. (1971) interpreted the northern part of Keiva II to represent the LGM ice marginal position. Apukhtin & Ekman (1967) and Apukhtin & Yakovleva (1967) linked the Keiva moraines to other ice-marginal formations, in a northwest direction from Varzuga, via the central Kola Mountains and up to the Barents Sea coast east of Murmansk, and they argued for a formation during the Neva/Older Dryas stage ( kyr BP). Many formation theories for the Keiva moraines include the presence of a Ponoy Ice Cap/Ice Sheet, suggested to have been an independent ice sheet located over eastern Kola Peninsula in Lateglacial time. For example, Armand (1960), Armand et al. (1964) and Armand (1965) all argue that the Keiva moraines were formed between a White Sea-basin ice lobe and a Ponoy Ice Cap (Fig. 4C). This hypothesis has been adopted in many later publications (e.g. Yevzerov 1990; Ekman & Iljin 1991). Strelkov (1976a, b) held a slightly different view and suggested that the section of the Keiva moraines west of Strelna River was deposited between White Sea-based ice and FIS ice over the peninsula, whereas the eastern part was deposited between the White Sea lobe and a stagnant Ponoy Ice Cap. Keiva II is normally considered to be older than Keiva I, but Rainio et al. (1995) and Svendsen et al. (2001) suggested that Keiva I was older and that Keiva II was formed entirely by a Ponoy Ice Cap during the Younger Dryas. Bakhmutov et al. (1991, 1992, 1993) conducted detailed stratigraphical studies of a number of sections along Ust-Pyalka River, a tributary to Pyalitsa River, just north of the Keiva I moraine. They counted 606 clay varves (Kolka 1996) in distal sediments in a delta deposited north of the Keiva I moraine. Palaeomagnetic data of the varved clay deposits indicated an age of kyr BP (Older Dryas or beginning of Alleröd) and they therefore concluded that Keiva I formed at the Neva stage. Further, they suggested that Keiva II formed at the Luga stage (c kyr BP). Based on satellite imagery mapping of glacial lineations, eskers and ice-marginal formations, Punkari (1985, 1993, 1995) and Boulton et al. (2001) suggested that the Keiva moraines formed as an interlobate complex formation. Punkari (1993, 1995) argued that the White Sea depression should have been the location for effective draw-down of ice, and faster ice retreat than on land, rather than a site of persistent ice lobes. Hence, in contrast to most previous studies, in their reconstruction the Keiva moraines were formed at a high-angle interlobate intersection (Fig. 4D). Yevzerov & Nikolayeva (1997, 2000) incorporated the Keiva moraines into a moraine-forming model of general applicability to the Kola region. In this model, end moraine pairs formed during climateinduced oscillations of the ice sheet margin. A warm stage during deglaciation is represented by a dump moraine, while ice margin advances form push moraines during cold stages. Following this scheme, Yevzerov & Nikolayeva (2000) suggest that Keiva II is a dump moraine belt deposited during the warm period preceding Oldest Dryas, while Keiva I was formed as a push moraine during Oldest Dryas. Both moraines are considered to have formed at the margin of an ice lobe in the White Sea basin. The formational model of Yevzerov & Nikolayeva (1997, 2000) does not require a Ponoy Ice Cap, and they state that if present it was morphologically inactive. Saarnisto et al. (2000), Lunkka et al. (2001), Svendsen et al. (2001, 2004) and Demidov et al. (2004) conducted palaeoglaciological studies on Kola Peninsula within the QUEEN framework. They emphasized that Keiva I consists of a minor discontinuous belt of end moraines, while Keiva II is a complex of glaciofluvial formations (including esker-type ridges that are feeding the Keiva II from both sides, outwash and interlobate formations). Keiva II is interpreted to reflect the interplay between a White Sea-basin ice stream and the inactive Ponoy Ice Cap between 16 and 12 kyr BP. The eastern part of Keiva II is suggested to be an interlobate formation between the ice cap and the White Sea ice stream. The central and western parts of Keiva II are proposed to have formed solely at the margin of a Ponoy Ice Cap. Based on optically stimulated luminescence (OSL) dates from glaciofluvial deltas, Svendsen et al. (2001) concluded that Keiva I formed no later than 16 kyr BP while Keiva II formed at 1213 kyr BP. In sharp contrast to the above are interpretations of the KIZ by Grosswald (1998) and Grosswald & Hughes (2002), who recognized the fact that the Keiva moraines slope from northeast to southwest, a fact that is rarely mentioned in other formation models. They argued that, because the slope of the Keiva moraines reflects the slope of the ice-sheet surface, the ice flow came from the northeast (Fig. 4E). Furthermore, they argued that the ice lobe that deposited the Keiva moraines belongs to a general Younger Dryas expansion of ice from the Barents Sea that invaded large parts of northern Kola Peninsula. Methods The glacial geomorphology was mapped using satellite images, aerial photographs and fieldwork. The entire Kola Peninsula was mapped in Landsat 7 ETM/ images with a 15-m resolution (Figs 5, 6; Hättestrand & Clark 2006b). Key areas of the KIZ were also mapped in detail using aerial photographs at the scale of 1: (1.3-m resolution), interpreted in stereo using a Zeiss Jena Interpretoscope with up to 16/magnification. Field-based mapping and verification of the image interpretation were conducted in 2004, during a

7 358 Clas Hättestrand et al. BOREAS 36 (2007) Fig. 5. False-colour Landsat 7 ETM satellite image composed of bands 5, 4 and 3 of Keiva IIa (extending from left/west to right/ east) around the Strelna River (centre of image). The geomorphological interpretation of this area is shown in Fig. 8. North to the top. helicopter field survey along the KIZ between the Varzuga and Ponoy rivers. Description of the Keiva ice marginal zone General characteristics The KIZ extends for about 300 km, in a wide arc paralleling the White Sea and southernmost Barents Sea coasts, from Varzuga River in the southwest to Lumbovka in the northeast. The ice marginal zone consists of the Keiva I and II moraines, hummocky moraine, meltwater channels and outwash sediments (Figs 3, 7, 8), all indicating the presence of a former ice margin. The western limit of the KIZ is ambiguous. Ekman & Iljin (1991) argued that the Keiva II moraine can be recognized as far west as Lake Vyalozero-Munozero, northeast of Umba (c. 358E, not on map). However, a coherent belt of ice-marginal deposits only occurs east of Varzuga River. There is a ridge deposit that extends further west from Varzuga, but it is a much smaller single ridge (c. 100 m wide and B/20 m high) that branches in places, runs partly on the floor of large meltwater channels and has a winding course, clearly different in character from the kilometre-wide moraine complexes east of Varzuga River. Because of its morphological characteristics, we tentatively classify the ridge west of Varzuga River as an esker (Fig. 3). The Keiva I moraine The Keiva I moraine is small and subdued compared with Keiva II, and consists of a 40-km long chain of elongated moraine segments orientated northeast southwest between the lower reaches of the Pyalitsa and Pulonga rivers. Another 10-km long linear moraine ridge occurs to the south of the mouth of Ponoy River, and this may be a northern continuation of Keiva I. Keiva I is mostly a few hundred meters wide and less than 10 m high, and slopes down towards the northeast. Its westernmost segment, however, is a multi-crested ridge complex, up to 2 km wide and 50 m high. Deltaic deposits with feeding eskers from the southsoutheast occur in gaps between individual segments of the Keiva I moraine. One such delta with associated ice-lake sediments, in the Ust-Pyalka river valley (tributary of Pyalitsa river), was studied in detail by Bakhmutov et al. (1991, 1993). They concluded that the glaciofluvial palaeodrainage was directed towards the north and that an ice lake existed on the northern side of Keiva I for up to 600 years. The Keiva II moraine The Keiva II moraine consists of two segments (which we refer to as Keiva IIa and Keiva IIb), which overlap over a c. 25-km distance between the Strelna and Pyalitsa rivers (Fig. 3), with the eastern segment (Keiva IIb) being shifted 810 km towards the coast (Fig. 8). Each segment is characterized by a well-developed moraine belt, only cut where crossed by rivers. The moraine is km wide and is typically multicrested (cf. Fig. 9B). Between the Varzuga and Strelna rivers, Keiva IIa is particularly distinct and 3060 m high. North of Strelna River, the Keiva IIb moraine topography decreases gradually, becoming only a few metres high near Ponoy River (Fig. 9D). Along its entire length, Keiva II is much wider than high and, therefore, it has an overall plateau-like cross-section (Fig. 9D). Its surface is often hummocky or composed of several closely stacked ridge crests

8 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 359 inner Kola Peninsula is always sharp and relatively steep, while the margin facing the White Sea coast is usually more gradual and diffuse, and in places merges into irregular hummocky moraine. The Keiva II moraine is sloping consistently, from c. 100 m a.s.l. in the west at Varzuga River to c. 250 m a.s.l. in the northeast where it crosses the Ponoy River. Taking into account that, at the time of formation, western Kola Peninsula was likely to have been glacioisostatically depressed, the slope of the Keiva II was probably even more pronounced at the time of formation. Both Keiva IIa and Keiva IIb are sloping at the same rate, about 1 m/km. Keiva II has a series of feeding eskers on both sides along its entire length. The feeding eskers on the southeastern side are commonly 530 km long and branching, clearly indicating subglacial water flow directed towards the moraine from White Seagrounded ice (e.g. at Sosnovka River; Fig. 3). The feeding eskers on the northwestern side are fewer and shorter, up to 23 km long, but they clearly show that some material was transported towards Keiva II also from Kola-based ice (Fig. 9C). There are extensive traces of meltwater drainage both across and parallel to the Keiva moraines (Fig. 10B, D). Most of these traces indicate meltwater drainage across the moraines towards the south and southeast (Fig. 8). The northern part of Keiva IIb is in places cut by deeply incised canyons, indicating drainage parallel to the moraine towards the north (Fig. 10D). Fig. 6. False-colour Landsat 7 ETM satellite images composed of bands 5, 4 and 3. A. Drumlinized end-moraine ridges south of Lumbovka. B. Keiva IIb north of Pulonga River. C. Very large meltwater channels north of the Tersky coast, west of Strelna River. See Fig. 3 for place names. North to the top. (Fig. 9B), indicating collapse of the moraine margins and melting of buried ice during final ice retreat from the area. In more detail, the northwestern side facing Other ice-marginal landforms Apart from the short feeding eskers, there are no landforms that appear connected to the KIZ on the inner northwestern side of the Keiva II. The zone between the Keiva II moraine and the coast, on the other hand, has extensive areas of hummocky moraine (Fig. 3). There are also a number of very large meltwater channels running subparallel to the coast indicating meltwater drainage towards the east and northeast. These channels are up to 1 km wide and 50 km long (Figs 3, 6C). In addition, there are numerous medium-sized and smaller channels indicating drainage in the same direction. Many of these channels have outwash fans or deltas at their distal end. The vast majority of the channels display distinct characteristics of having formed in an icemarginal environment: (1) they run subparallel to contours, which indicates that ice must have constrained the water flow on at least one side of the channel; (2) they often have a meandering course and they slope consistently towards lower ground along their entire length, indicating that they were formed in a subaerial environment where water was guided by gravity alone; and (3) smaller channels often occur on slopes in parallel series, a situation analo-

9 360 Clas Hättestrand et al. BOREAS 36 (2007) Fig. 7. A. Glacial geomorphology of western Keiva IIa in the Varzuga area. B. Interpreted sequence of events in the Varzuga area.

10 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 361 Fig. 8. A. Glacial geomorphology of eastern Keiva IIa and western Keiva IIb in the Strelna River area. B. Interpreted sequence of events in the Strelna River area.

11 362 Clas Hättestrand et al. BOREAS 36 (2007) Fig. 9. Oblique views of the Keiva II moraine. A. Keiva IIb, where cut by Sosnovka River, looking southeast. B. Keiva IIa, south of Ozero Verkhneye Ondomozero, looking west. Note the multicrested ridge crest. The moraine ridge has a sharp edge to the flat landscape to the north (right), while it is grading into a hummocky moraine on the southern (left) side. C. A flat-crested feeding esker (from lower left to centre of photo) joining Keiva IIb (linear feature from left to right) from the interior of Kola Peninsula just north of Sosnovka River. D. Keiva IIb just south of Ponoy River looking south. The ridge here has a typical plateau-like cross-section. gous to channel series observed in front of many cold-based glaciers in the Arctic (e.g. Dyke 1993). In contrast, a limited number of channels (e.g. close to the mouth of the Ponoy River; Fig. 3) display clear characteristics of a subglacial origin, where water was guided by the overburden ice-pressure gradient; they are more or less straight (and typically follow bedrock weakness zones), have canyon-like appearances with low width-to-depth ratios, and cut through bedrock obstacles independently of local topography. The zone of hummocky moraine and northwards orientated meltwater channels continues north of Ponoy River, all the way to the peninsula of Lumbovka at 67850?N, which is particularly rich in meltwater channels and outwash. Moraines are also an integral part of this zone, but they are smaller and less distinct than those of Keiva II south of Ponoy River and they are extensively drumlinized. Relict lake shorelines are found in many basins on the northwestern side of Keiva II. Around Ozero Babozero (Fig. 7) and the Ondomozero lakes (Fig. 8), numerous shorelines occur at c. 160 m a.s.l., which is 1020 m above the present-day lake levels. Furthermore, some lake basins on the interior Kola side of Keiva IIb, between the Pulonga and Sosnovka rivers, are encircled with series of relict shorelines up to a few metres above the present lake levels. There is a notable absence of major spillways associated with these lake levels, except for the present-day outlet drainage routes from the lakes. The KIZ area is rich in glacial lineations, such as drumlins and smaller scale drumlinization features. One set of drumlinization features has lineations

12 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 363 Fig. 10. Field photographs of Keiva II. A. A sandy deflation surface south of the Lake Ozero Verkhneye Ondomozero (just visible in the right background), looking west. B. Section of Keiva IIb between the Sosnovka and Ponoy rivers, where the moraine ridge is composed of till. Boulders have accumulated at the surface as a lag deposit, because of meltwater channel incision across the ridge. The channel floor slopes from west (far distance in the centre of the photograph) to east (lower right). C. Bouldery surface of Keiva IIa south of the Lake Ozero Babozero. The boulders are almost entirely (c. 90%) of local Tersky sandstone (Seliverstova 1999), which dominates the bedrock geology between Keiva II and the White Sea coast (Pozhilenco & Lyubtsov 2002). D. Meltwater canyon between the Sosnovka and Ponoy rivers that parallels Keiva IIa, looking north. parallel to the feeding eskers from the White Sea side of the moraines, indicating ice flow at a high angle to the Keiva II moraine. Good examples of these are located south of the Ponoy and Sosnovka rivers. In addition, many ice-marginal landforms are drumlinized by ice flow from the southwest. This drumlinization covers the entire KIZ and is superimposed on moraine ridges, hummocky moraine, eskers and channels and their associated outwash sediments. For example, the belt of parallel moraine ridges south of Lumbovka is heavily drumlinized (Fig. 6A). In general, the Keiva II moraine is markedly continuous, but between Lake Babozero and Varzuga River the moraine is broken up into segments that appear displaced northwards, and some of these are strongly drumlinized (Fig. 7). Stratigraphy As part of this study, we investigated the surficial stratigraphy of the KIZ. The surface material of Keiva II varies from coarse bouldery material with numerous erratics to sandy compositions with infrequent erratic boulders on top (Fig. 10AC). The surface material of the Keiva I moraine appears to be mostly till. There are few stratigraphical observations of the Keiva I and II moraines, although some sites have been studied in detail (e.g. Bakhmutov et al. 1991, 1992, 1993). However, it has not been shown conclusively that these sites can actually be directly tied to the formation of the KIZ. For example, the delta located near the village of Varzuga (Fig. 7) has been investigated in several studies (e.g. Yevzerov et al. 2000; Svendsen et al. 2004) and has been used to infer

13 364 Clas Hättestrand et al. BOREAS 36 (2007) formational conditions and age of the Keiva II moraine. However, this delta displays a 200-year long varved clay sequence overlain by cross-bedded sand indicating northeastwards palaeo-water flow, and shows no signs of having been distorted by subsequent ice overriding. This observation stands in sharp contrast to the Keiva II moraine, which in the same area is strongly drumlinized and distorted by later ice flow from the southwest. Moreover, the upper surface of the delta is located at about 40 m a.s.l., which matches the highest post-glacial shorelines of the Belomorian Periglacial Lake in the area (Fig. 7; Kolka et al. 2000; Kolka & Korsakova 2005). This indicates that the Varzuga delta was built after final ice retreat from the area, at the time of incursion of the Belomorian Periglacial Lake in the area between the Keiva II moraine and the Tersky coast. When set against the extensive evidence that ice was present on both sides of the Keiva II moraine when it was built (see above), our conclusion is that the formation of the Varzuga delta must postdate the formation of the Keiva II moraine. The sand in the Varzuga delta has an OSL age of 12 kyr BP (Svendsen et al. 2004) and, although this seems like a possible deglaciation age for the region, it is only a minimum constraint for the true age of the Keiva II moraine. Discussion Observational constraints Given the described characteristics of the KIZ, it is pertinent that any credible theory of its formation must be compatible with, and be able to explain, the following observations. 1. The Keiva II moraine displays ice-contact features (e.g. feeding eskers and collapsed ice-contact slopes) on either side along its entire length. 2. The Keiva II moraine is sloping along its length from c. 100 m a.s.l. in the west (Varzuga River) to c. 250 m a.s.l. in the east (Ponoy River). 3. After formation, the KIZ was overrun and fragmented by ice flow from the southwest, as shown by drumlinization and partial destruction of several moraine segments, particularly east of Varzuga River and north of Ponoy River. 4. There is widespread morphological evidence for subglacial melting conditions on the White Sea side of the moraines (eskers, drumlins and flutings) but very little on the Kola side. 5. There is ubiquitous evidence of massive meltwater discharge eastwards, in the form of large lateral drainage channels, all along the coastal lowlands between the Varzuga River in the southwest and Lumbovka in the northeast. Formational conditions Observation 1. The ice contact features along the Keiva II clearly show that it was formed between two ice masses, located on the interior Kola Peninsula and in the White Sea depression, respectively. We consider it highly unlikely that the moraine was formed by ice from only one side and that the eskers on the other side were deposited at a later (or earlier) stage and by chance stopped right at the moraine ridge. Observation 2. The slope of the Keiva II moraine clearly indicates that it could not have been formed as an isochronous lateral feature at the margin of a White Sea lobe extending from the FIS in the west. A lateral moraine is inherently sloping in the direction of ice flow, as the ice-surface slope is controlling iceflow direction. Hence the moraine must be a timetransgressive formation and, considering observation 1, is interpreted to have formed at an advancing junction between Kola Peninsula-based ice and a White Sea-based ice-sheet lobe. The inference of a formation during a White Sea-based ice-sheet lobe advance rather than during an ice-sheet retreat is based on the fact that the feeding eskers are meeting the Keiva II at a nearly perpendicular angle from the White Sea side. The interpretation of this pattern is that the White Sea ice lobe was highly active, having a distinctly lobate ice-margin outline throughout the formation of the KIZ. It is unlikely that the ice sheet maintained a strongly lobate ice margin throughout the deglaciation of the southern Barents Sea and the eastern White Sea basin, because during steady icemarginal retreat in a partly subaqueous environment we expect the ice margin to retreat faster in water, because of calving, than on dry land (Punkari 1995). It could still be argued that the KIZ was formed during a deglacial re-advance (which would also induce a lobate ice margin). However, the KIZ is a continuous feature for more than 300 km and, because it is shown to be a time-transgressive feature, it must therefore represent ice advance over a long time period. Moreover, numerous lateral channels at c. 200 m a.s.l. at the northern end of the KIZ near Lumbovka clearly mark the left-lateral side of an ice lobe invading the southernmost Barents Sea basin from the south. This provides a firm restriction on the permissible outline of the ice margin at this time. Any realistic configuration of the ice lobe flowing north out from the White Sea (acknowledging the need for a symmetric cross-section of the ice lobe) must have had a corresponding rightlateral margin close to the coastline on the other side of the basin, i.e. on Kanin Peninsula. Because the Late Weichselian maximum ice margin extended no further east than just off the west coast of the Kanin Peninsula (Fig. 1; Demidov et al. 2006), the ice advance that resulted in the formation of the northernmost parts of the KIZ must have occurred when the ice sheet was

14 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 365 close to its Late Weichselian maximum position or during an earlier glaciation of similar extent. Observation 3. This observation indicates that the formation of the KIZ was not the last glacial event in the area. This is because sections of Keiva II, the hummocky moraine and the channels were overridden by uniform ice flow from the southwest subsequent to formation. The overriding of Keiva II east of Varzuga (Fig. 7) could have been achieved by a relatively minor (1020 km) re-advance after formation. However, the extensive drumlinization of the moraine segments north of Ponoy River (Figs 3, 6) indicates regional ice flow from the southwest, and this can only have been achieved after a change of the ice-flow regime over eastern Kola Peninsula after the formation of the moraines. Hence observation 3 corroborates the interpretation that the KIZ was formed before the onset of the last deglaciation. Observation 4. This observation indicates that the White Sea ice-sheet lobe was warm-based throughout the area of the KIZ and that the Kola Peninsula-based ice was probably cold-based. The latter is indicated by the lack of glacial sediments and subglacial landforms, but most convincingly shown by the existence of numerous lateral channels north and west of the Keiva II moraine (Figs 2, 7, 8; Hättestrand & Clark 2006b). The feeding eskers to the Keiva II moraine that do occur on the interior Kola side are only a few kilometres long, and such short near-marginal eskers have also been shown to exist in predominantly cold-based areas of former glaciation (Dyke 1993; Hättestrand & Stroeven 2002). Although observation 3 indicates that the whole eastern Kola Peninsula was subjected to regional ice flow from the southwest subsequent to the formation of the KIZ, this appears to have been a transient condition of relatively short duration because it did not manage to thaw the basal ice in the central part of the peninsula. Similarly, although the White Sea-based ice flow seems to have been predominantly warm-based, it cannot have been particularly erosive (or was a shortlived transient condition) because of the presence of numerous pre-lgm deposits south and east of Keiva II, for example Eemian marine sediments (Lavrova 1960) and fluvial sediments of mid- to early Weichselian age (Lunkka et al. 2001). The relict lake shorelines that occur around lakes on the northern and western side of the Keiva II moraine show that these lakes were previously larger. Because the palaeo-lakes seem to have used the same outlets as the current lakes, it is likely that the shorelines reflect higher lake levels before the outlet rivers had cut through the Keiva II moraine to the current channel depth. Hence there appears to be no need to invoke a damming ice margin in the south and east to explain these relict shorelines. Observation 5. This observation indicates that there has been substantial drainage of meltwater along an ice margin that was sloping from west to east and from south to north in the coastal areas of southern and eastern Kola Peninsula. The meltwater channels run at an oblique angle to contours, and hence their course must have been guided by blocking ice to the south. The relative age of these channels compared with the other morphological elements is ambiguous. Around Varzuga (Fig. 7) there are large ice-marginal channels that underlie both eskers and moraine segments. On the other hand, some of the very large ice-marginal channels are cut into the drumlinized surface (Fig. 6C; Hättestrand & Clark 2006b). The interpretation is that there are several generations of channels belonging to both the advance of the FIS through the White Sea and to deglaciation stages. Formation model The formation of the KIZ is conditioned by the critical observations presented above and is interpreted to involve several steps, outlined below (Figs 11, 12). During expansion, the FIS was advancing from the west into the White Sea basin. At the time of FIS expansion into the western White Sea basin, ice is likely to have also covered eastern Kola Peninsula, either as a separate ice cap, similar to the proposed Lateglacial Ponoy Ice Cap, or as an eastward extension of the FIS over the continental water divide (Fig. 11A). This Kola-based ice must have been almost entirely coldbased (Fig. 12A) because of the lack of glacial sediments and subglacial landforms over east-central Kola Peninsula (Fig. 2). As the FIS entered the White Sea depression it advanced over subaqueous soft sediments, and its deformation potential may have promoted fast ice flow, or even ice-streaming, to occur, and the formation of a distinct White Sea ice lobe. The cold-based ice body located over eastern Kola Peninsula was much more restricted because it was located in a precipitation shadow behind the main FIS ice divide in the west, and hence expanded more slowly. As the White Sea lobe advanced with its left lateral margin onto the Tersky coast, it dammed the meltwater routes from the Kolabased ice, and water was rerouted along its margin eastwards (and later northeastwards) and large meltwater channels formed (Figs 11B, 12B). At the point where the White Sea ice-lobe margin merged with the Kola-based ice margin, sediments brought northwards by the warm-based ice flow were trapped at this junction and a moraine was formed (Figs 11B, 12C). As the White Sea ice lobe continued to advance, the junction gradually shifted towards the northeast, thus forming new segments of the moraine, while previously deposited segments were overrun and, where subjected to warm-based ice flow, drumlinized and partly destructed (Figs 7B, 12D). Finally, this junction reached

15 366 Clas Hättestrand et al. BOREAS 36 (2007) Fig. 11. Formation model for the Keiva ice marginal zone. Thick line indicates moraines. Thick arrows indicate glacial meltwater drainage and formation of marginal channels. Present-day sea level is used in all panels. Late Weichselian maximum ice margin from Demidov et al. (2006). the northeastern tip of Kola Peninsula (Figs 11C, 12E), at which time the eastern FIS margin was located near its maximum position. When the entire Kola Peninsula was overrun by ice flow towards the northeast, the northern parts of the KIZ were drumlinized (Figs 11D, 12F). There is no evidence that the ice sheet build-up occurred without interruptions. Indeed, the overlap between the two main sections of the Keiva II moraine at Strelna River (Figs 3, 8A) may be evidence of an interruption and that build-up and ice expansion in the White Sea occurred during two phases. A possible scenario is that the Keiva IIa formed during the initial White Sea ice lobe advance. A temporary climatic amelioration or specific glaciodynamic control may have induced a relatively quick response (retreat) of the dynamic White Sea-based lobe, whereas the Kolabased ice continued to respond to the overall growth of the FIS towards the coast across the already deposited Keiva IIa moraine. During renewed ice expansion in the White Sea basin, the eastern section of the KIZ and Keiva IIb formed (Fig. 8B). Keiva I is shown in some maps (e.g. Ekman & Iljin 1991) as a continuous moraine belt that parallels the Keiva II over much of the length of the KIZ. However, we concur with Lunkka et al. (2001) and Svendsen et al. (2004) that Keiva I is a short and discontinuous belt of moraine segments. Also, it is commonly assumed that Keiva I and Keiva II are related in time and formation. However, in contrast to Keiva II, there is no morphological evidence (e.g. feeding eskers) of supporting ice on the northwestern side of the Keiva I moraine. Hence this moraine was probably formed purely along the lateral side of a White Sea ice lobe. This is consistent with Bakhmutov et al. s (1991, 1992, 1993) interpretation

16 BOREAS 36 (2007) The Keiva ice marginal zone on the Kola Peninsula, NW Russia 367 Deglaciation During the last deglaciation, the ice margin generally retreated westwards (Hättestrand & Clark 2006a). There are numerous lateral meltwater channels that show the direction of ice-marginal retreat over the Kola Peninsula, and these unanimously indicate an icesurface slope, and hence ice-flow direction, out from the central parts of the peninsula towards the northern, eastern and southern coasts (Figs 2, 11E). There is little direct evidence for the deglaciation of the White Sea basin, but it is conceivable that the ice margin retreat was interrupted by re-advances and that individual ice marginal landforms along the Tersky coast (such as Keiva I) may be of deglacial age. Although this paper presents a hypothesis for the detailed sequence of events leading to the formation of the KIZ, a firm absolute chronology is lacking. There are too few radiometric constraints (e.g. radiocarbon, cosmogenic nuclide or OSL dates) from eastern Kola Peninsula to provide a solid chronostratigraphic framework, and those that exist can rarely be tied firmly to the morphostratigraphy. Indeed, considering that pre- Late Weichselian deposits are frequently found along the peripheral parts of eastern Kola Peninsula (e.g. Grave & Koshechkin 1969; Molodkov & Yevzerov 2004) and the non-glacial character of the landscape in the interior of the peninsula (e.g. Niemelä et al. 1993; Kolka & Korsakova 2005; Hättestrand & Clark 2006b), it appears that the last ice cover in the region was ineffective in reshaping its bed. Hence, until more dating is available, it remains undetermined whether the KIZ in its entirety belongs to the Late Weichselian. Within the field campaign for this study, we collected samples for cosmogenic nuclide dating and we expect to provide additional constraints on both the deglaciation chronology and possible age of the KIZ in forthcoming publications. Fig. 12. Formation model for the Keiva ice marginal zone shown as a profile from the central White Sea to the southern Barents Sea trough. For location of profile, see Fig. 11A. Arrows indicate ice-flow direction. Encircled crosses in D and E denote ice flow into the picture. Black area indicates Keiva moraines (in crosssection). that an ice-dammed lake existed north of Keiva I for up to 600 years (Kolka 1996) during its formation, and with the observation that Keiva I is sloping in the opposite direction to Keiva II. Because Keiva I is not as clearly overprinted by cross-cutting fluting as Keiva II, it is uncertain where it belongs in the regional morphostratigraphy, but available dates suggest that Keiva I is of deglaciation age. Bakhmutov et al. (1991) date the distal ice-dammed lake to kyr BP and, if the existence of the lake is indeed tied to the formation of the moraine, this would also be the age of the moraine. Comparison with previous models Given the characteristics of the Keiva II moraine system described above, we argue that alternative formation hypotheses for the KIZ are hampered by the following observations. Formation by Kola-based ice (either FIS or separate Ponoy Ice Cap) (Fig. 4A). The ubiquitous evidence of ice flow directed towards the moraine on its southeastern side (feeding eskers and drumlins/fluting) clearly defies formation by Kola ice alone. Formation by White Sea-based ice lobe of the FIS (Fig. 4B). There are two major lines of evidence that argue against formation along the lateral side of a White Sea ice lobe alone. First, there are feeding eskers, albeit few, joining the Keiva II moraine on its northwestern side, indicating the presence of ice also on this

17 368 Clas Hättestrand et al. BOREAS 36 (2007) side of the moraine when it was built. Second, the slope of Keiva II, downwards from east to west, is a particularly strong argument against formation by a White Sea-based FIS lobe alone. A lateral moraine formed by an ice lobe flowing towards the northeast in the White Sea basin would have been sloping in the opposite direction. Formation by an ice lobe originating in the Barents Sea (Fig. 4E). All available ice-flow directional evidence (glacial striations, drumlins/flutings, eskers and marginal meltwater channels), without exception, indicates ice flow from southerly directions, at a high oblique angle to the former ice margin (the moraines). This is in direct conflict with general ice flow from the north. Formation in some parts by White Sea ice lobe(s) and in other sections by Kola-based ice (Saarnisto et al. 2000; Svendsen et al. 2001). Evidence for ice contact on both sides of the Keiva II moraine (i.e. feeding eskers and a consistent longitudinal rising slope of the moraines towards the northeast) strongly suggests that ice was present on both sides throughout the formation of the moraines. Formation as an interlobate deposit formed during Lateglacial ice marginal retreat (Fig. 4C, D). The Keiva II moraine, feeding eskers and ice-marginal meltwater channels bear signs of glacial overriding, drumlinization and partial destruction by a regionalscale ice flow from the southwest, in parts at right angles to the KIZ itself. Post-formational overriding is a common feature in interlobate complexes from the last deglaciation (Punkari 1997) but usually not of the regionally consistent scale as is the case across eastern Kola Peninsula, indicating pervasive ice flow across the peninsula also after the formation of the KIZ. Because of its regional scale, it cannot be argued that this glacial overriding occurred during smaller re-advances during the deglaciation. Instead, the drumlinization of the KIZ indicates ice flow across the entire southeastern Kola Peninsula towards the northeast, requiring an ice sheet extent of LGM proportions (Fig. 1). In addition, linear interlobate glaciofluvial complexes usually have feeding eskers at right angles only on one side, whereas the eskers (and other ice-flow features) on the other side are parallel to the interlobate ridge (e.g. Punkari 1997). The feeding eskers of the Keiva II moraine are at right angles on both sides of the ridge along most of its length. Palaeoglaciological implications Although there is no morphological evidence of a Ponoy Ice Cap during the deglaciation (Hättestrand & Clark 2006a,b), we do not rule out the possibility that an independent ice cap was centred over eastern Kola Peninsula before the formation of the KIZ. One characteristic feature of the KIZ is the zone of hummocky moraine that extends from Varzuga River to Lumbovka. The formation history of this hummocky moraine remains undetermined, but we tentatively relate it to the expansion of a warm-based sedimentloaded White Sea ice-lobe margin towards the marginal areas of the cold-based Kola Peninsula-based ice. When applying a Kola-scale perspective, the distribution of hummocky moraine is characterized by a well-defined zone westward from the KIZ, making a semi-circle over the central Kola Mountains and up to the northern coast east of Murmansk (Fig. 13). This pattern may reflect the outline of an ice cap that was already in existence when the FIS expanded eastwards towards its LGM position. This would be an equivalent to the earlier proposed Lateglacial Ponoy Ice Cap, but being in existence much earlier than previously proposed. Because an independent pre-lgm Kola Ice Cap would have been dynamically incorporated in the FIS, it is the retreat of the FIS that is reflected in the deglaciation landform record, not the retreat of an independent ice cap. The fact that Kola-based ice appears to have been slow-growing compared with the White Sea-based ice may indicate that little precipitation reached eastern Fennoscandia, possibly because moisture was blocked by the FIS ice divide area over the Bothnian Bay. Hence a strong contrast in advance and retreat between the White Sea lobe and Kola Peninsula ice may have resulted if the FIS advance occurred because of ice advection from the higher ice divide areas in the west, while continental starvation characterized the slow response in mass balance in the east. 200 km Fig. 13. Distribution of hummocky moraine (black) on Kola Peninsula (extracted from Hättestrand & Clark 2006b).