Last interglacial climate changes and environments of the Lesser Kuril arc, north-western Pacific

Quaternary International 241 (2011) 35e50

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Last interglacial climate changes and environments of the Lesser Kuril arc, north-western Pacific N.G. Razjigaeva a, *, L.A. Ganzey a, T.A. Grebennikova a, N.I. Belyanina a, V.Yu. Kuznetsov b, F.E. Maksimov b a b

Pacific Institute of Geography, FEB RAS, Vladivostok, Russia Saint-Petersburg State University, Saint-Petersburg, Russia

a r t i c l e i n f o

a b s t r a c t

Article history: Available online 17 February 2011

Last Interglacial Age deposits were studied in detail with radiocarbon and 230Th/232Th and 234U/232Thdating on Zelenyi and Tanfil’ev Islands. The deposits of two transgressions were distinguished (MIS 5e and 5a). The deposits of maximal transgression include warm marine diatom assemblages with subtropical species. The climate was warmer than modern. On Tanfil’ev Island, marine deposits were deposited under cooler conditions (MIS 5a), covered by lacustrine and peat bog deposits. 230Th/232Th and 234 232 U/ Th-data (interval of 69.4 þ 8.2e7.0 ka and 73.0 þ 5.3e4.8 ka) were obtained from this terrestrial unit. Pollen spectra established some stages of vegetation development that reflect progressive cooling. The surface peat record shows pronounced cooling that correlates with the Late Pleistocene Glacial (MIS 4). During warming in the second half of the Late Pleistocene (MIS 3), the climate was similar to modern or slightly cooler, and forest vegetation occupied the land bridge that connected the Lesser Kurils with surrounding islands. The Last Interglacial Maximum caused considerable changes to landscape zones on the Southern Kurils. The specific paleolandscape changes on small islands depended upon significant changes in the configurations of land during oscillations in sea level. Volcanic activity was another regional factor influencing different landscape components. Ó 2011 Elsevier Ltd and INQUA. All rights reserved.

1. Introduction The Last Interglacial Maximum represents an important phase in landscape development, during which zonal systems throughout northern Eurasia were fundamentally reorganized. This warming period was accompanied by marine transgression as sea levels fluctuated, thus markedly changing the configuration of coastlines (Chappell and Shackleton, 1986; Kaplin and Selivanov, 1999; Svitoch, 2002 and others). Paleoreconstruction in the southern Russian Far East: Primorye (Aleskeev and Golubeva, 1980; Pavlyutkin and Belyanina, 2002; Korotky et al., 2005, 2006) and Sakhalin Island (Aleksandrova,1982; Korotky et al.,1997; Pushkar’ and Cherepanova, 2001; Svitoch, 2002) has been undertaken for this period. Biostratigraphic data are the primary basis for this reconstruction. Data for oceanic islands in the northwest part of the Pacific Ocean during the Last Interglacial Maximum are unavailable (Melekestsev et al., 1974) and information on deposit ages for the Kuril Islands is contradictory. Several papers date the 30e40 m marine terrace deposits as Late Pleistocene (Melekestsev et al., 1974, and others). Further stratigraphic study of these deposits on Kunishir and Iturup

* Corresponding author. E-mail address: [email protected] (N.G. Razjigaeva). 1040-6182/$ e see front matter Ó 2011 Elsevier Ltd and INQUA. All rights reserved. doi:10.1016/j.quaint.2011.02.002

Islands dated them to the Middle Pleistocene (Pushkar’ and Cherepanova, 2001; Razjigaeva et al., 2005). Of the marine deposits found in the south of the Greater Kuril Ridge, only beach facies, for which biostratigraphic data have not been obtained, are tentatively assigned to the Late Pleistocene. Late Pleistocene peat bogs have been discovered here and radiocarbon dating is at the method’s threshold, which makes it impossible to determine their exact age (Razjigaeva and Ganzei, 2006). Use of 234U/232Th-dating of Late Pleistocene peat bogs offers a new opportunity to study this age boundary (Kuznetsov and Maksimov, 2003; Kuznetsov et al., 2003). The objective of this article is to reconstruct climate changes in the southern Kuril Islands in the Last Interglacial, to correlate these changes with global climate change patterns, and to analyze evolutionary features of paleolandscapes on small islands as land surfaces changed during transgression and regression cycles. Material obtained from multifacies and Late Pleistocene deposits on Zelenyi and Tanfil’ev Islands in the southern Lesser Kuril Ridge serves as the basis for the reconstruction (Fig. 1). 2. Regional setting The Lesser Kuril Ridge is located at the south end of the Kuril Islands, separating the Sea of Okhotsk from the Pacific Ocean, and

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Fig. 1. Location of study area.

stretches from the Kamchatka Peninsula in the north to Hokkaido Island in the south (Fig. 1). The Lesser Kuril Ridge includes Shikotan Island and a group of small islands located near Nemuro Peninsula on Hokkaido Island. Their extension is the submarine Vityaz Ridge that stretches in a northeast direction parallel to the Greater Kuril Ridge. The deep water Kuril-Kamchatka Trench flanks the Pacific Ocean side of the ridge. The Southern Kuril Strait, which is 48.1 km wide and reaches 200 m in depth, separates the Lesser Kuril Ridge from Kunashir Island. Shallow straits 1.85e11 km wide and 10e54 m deep separate the islands. The strait separating the Lesser Kuril Ridge from Hokkaido Island is 0.7 km wide and 89 m deep. The Lesser Kuril Ridge is older than the Greater Kuril Ridge and has a different geologic history. The islands consist primarily of Late Cretacerous and Paleogene volcanogenic and volcanogenic-sedimentary rocks. Zelenyi and Tanfil’ev Islands have a depressed relief and represent terrace-like surfaces that are 10e15 m high, and up to 25 m on southeast Zelenyi Island. Most of the land surface is wetland on whose edges grassland communities have developed. Woody vegetation is absent (Chernyaeva, 1977; Barkalov and Eremenko, 2003). The landscape structure is mosaic and the territory types are differentiated by the degree of wetting. The climate on the islands is oceanic with warm winters (average January temperature 5.3 S, minimum 20 S) and cool

summers (average August temperature þ16.1 S, maximum þ28 S). The sum of temperatures during the growing season (>10  C) is 1563  S, the average annual temperature is 5.2 S, and the average annual precipitation is 1020 mm (Reference Book of USSR Climate, 1968, 1970). Fog and strong winds are typical and these prevent the formation of a stable snow cover. Ocean currents play a particularly important role in regulating regional climate patterns in the Southern Kuril Islands. The Pacific Ocean Oyashio Current borders the islands on the east and the Southern Kuril Strait on the west. The Oyashio Current draws cold water from north to south in the Kuril region. The warm Soya Current is very important as it warms the southern part of the Sea of Okhotsk and Southern Kuril Strait. 3. Materials and methods Expeditions undertaken in 2004e2005 studied a series of sections of Late Pleistocene deposits on Zelenyi and Tanfil’ev Islands (Fig. 1). Section elevation was determined through alignment. The biostratigraphic study includes diatom and pollen analysis. Three pollen sums were calculated: total arboreal pollen, total non-arboreal pollen, and total spores. The percent of each taxon is calculated for these groups. Numerical age determination using radiocarbon (Geological Institute RAN, Moscow) and uranium-thorium methods (St. Petersburg State University, St.

N.G. Razjigaeva et al. / Quaternary International 241 (2011) 35e50 Table 1 Results of radiochemical analysis and

230

37

Th/U-age of buried peat, Tanfil’ev Island (total dilution sample method).

Lab no

Intervalm

Mineral mix %

238

197-TA 198-TA 199-TA 200-TA 201-TA

3.40e3.50 3.35e3.40 3.30e3.35 3.20e3.30 3.10e3.20

27.35e33.55 26.67 22.03 18.86e21.21 19.65e20.17

0.453 0.412 0.424 0.438 0.508

U (decay/min$g)     

0.016 0.014 0.014 0.013 0.021

234

230

U (decay/min$g)

0.516 0.489 0.517 0.503 0.581

    

0.017 0.016 0.016 0.014 0.023

Th (decay/min$g)

0.481 0.447 0.440 0.437 0.517

    

0.014 0.013 0.012 0.009 0.018

232

Th (decay/min$g)

0.443 0.447 0.454 0.460 0.525

    

0.014 0.013 0.012 0.010 0.018

230

Th/234U

0.931 0.906 0.851 0.870 0.891

    

0.042 0.040 0.035 0.031 0.047

234

U/238U

1.141 1.188 1.218 1.147 1.143

    

0.048 0.048 0.047 0.036 0.055

Comments: Age of peat in the interval 3.10e3.40 me73.0  5.3/4.8 ka.

littoral species dominate. Rare, redeposited valves (Coscinodiscus marginatus var. fossilis, Neodenticula kamtschatica, Pyxidicula zabelinae, Actinocyclus ochotensis var. fossilis), that became extinct in the Pliocene and Pleistocene are found in the deposits. Four assemblages are identified that reflect the sequence of climate and environment changes (Fig. 4).

Petersburg) were applied to date peat bogs. Two analytical models for separating uranium and thorium isotopes in each sample internally within in a vertical section of peat were used for dating. Peat samples were leached with a mix of HCleHNO3, using the total dilution sample method HCl e HNO3 e HF. Complete radiochemical analysis of the solution was obtained (Kuznetsov and Maksimov, 2003; Kuznetsov et al., 2003). The isotopic ratios 230Th/232Th and 234 232 U/ Th used in calculating the final age differ insignificantly in various samples (Table 1 and 2). This requires using a time contour method (Ivanivich and Harmon, 1992; Heijnis, 1992). The so-called Geyh Approximation was not used to estimate age (Geyh, 2001). The weighted mean values for isochronic ages and errors (1s) were calculated (Maksimov et al., 2006). The deposits include numerous volcanic ash layers. Chemical composition for volcanic glass was determined through microprobe analysis (V. G. Khlopin Radium Institute, St. Petersburg, Russia). Grain size composition of marine deposits and volcanic ash was studied using am “Analysette 22” (Pacific Institute of Oceanology FEB RAS, Vladivostok, Russia) and by sieving. The ash content of peat was determined.

4.1.1. Assemblage 1 (interval 3.40e3.55 m from the surface) Sub-littoral benthic dominate: boreal Cocconeis scutellum, Diploneis smithii var. pumila, Nitzschia granulata, cosmopolitan Dimerogramma minor, and planktonic taxa include Paralia sulcata, Thalassiosira bramaputrae and thermophilic Cyclotella striata. The abundance of benthic flora indicates a coastal shallow zone. The role of open marine diatoms (Thalassiosira gravida, Thalassiosira oestrupii, Coscinodiscus perforatus and others) is insignificant. The high content of freshwater species (58%) entering the littoral zone from the coasts is a feature of these deposits. Among them are epiphytic Fragilaria construens f. venter, F. construens f. subsalina, benthic Amphora ovalis, A. pediculus and planktonic Cyclotella meneghiniana, C. krammeri, C. distinguenda, and Aulacoseira granulata characteristic of lakes. It is not out of the question that an open lake existed, and freshwater flora may have been transported. Rare species from the genera Eunotia and Pinnularia are also encountered, indicating wetland development.

4. Results Marine and terrestrial multi-facial deposits on Zelenyi and Tanfil’ev Islands embedded in eroded surfaces from the Upper Cretaceous belong to the Late Pleistocene. Marine deposits are represented by beach, lagoon and marsh facies. Terrestrial deposits (up to 3.6 m thick) with well pronounced cryogenic structures (involutions) overlie the marine unit.

4.1.2. Assemblage 2 (interval 2.80e3.40 m) A reduction in the content of plankton species (up to 8%) is observed. Against a preponderance of Cocconeis scutellum, Dimerogramma minor, D. minor var. nana and Paralia sulcata a variety of benthic species of the genus Nitzschia increases, a feature of warm shoals with aquatic vegetation. Warm water species Achnanthes brevipes, Navicula granulata, Lyrella lyra, Campylodiscus echeneis, C. hibernicus, Zygoceros rhombus reach 30%. Boreal Odontella aurita, Grammatophora oceanica appear in the upper part. The assemblage indicates a shallow, warm lagoon. Content of neritic and ocean diatoms increases to 12%. The content of freshwater diatoms decreases to 37%, of which the leading planktonic species are Aulacoseira granulata, A. ambigua and the epiphytic are Rhoicosphenia abbreviata, Rhopalodia gibberula. Species from genus Cyclotella are rare. The role of wetland species from the genus Eunotia and Pinnularia increased.

4.1. Zelenyi Island The most informative section (5304) is located on the eastern coastline of Zelenyi Island (43 31.0640 N, 14611.2480 E). Here, at the base of a coastal bench, dense, light gray clay (up to 1.4 m thick) with indistinct, undulating horizontal stratification, is laterally transitional to interbedded greenish-gray, small grain well sorted sands with small, well rounded pebbles and gravel (Fig. 2). The deposit top is 4 m above sea level. The grain size composition of the deposits indicates gentle sedimentation conditions in which silty mud accumulated (Fig. 3). Deposits feature unimodal, bimodal and polymodal curves that have particles sizes ranging from 1e3 m, the second with a well expressed mode of 80e110 m. A total of 94 marine and brackish-water diatom and 91 allochthonous freshwater taxa were encountered. Marine subTable 2 Results of radiochemical analysis and

230

Lab no

Intervalm

238

197-T 198-T 199-T 200-T 201-T

3.40e3.50 3.35e3.40 3.30e3.35 3.20e3.30 3.10e3.20

0.247  0.240  0.293  0.250  0.318 

4.1.3. Assemblage 3 (interval 2.60e2.70 m) The species diversity decreases and many warm water forms disappear. Cocconeis scutellum remains the dominant species.

Th/U-age of buried peat, Tanfil’ev Island (leach sample method).

U (decay/min$g) 0.009 0.008 0.013 0.009 0.011

234

U (decay/min$g)

0.315 0.286 0.347 0.310 0.412

    

0.010 0.009 0.015 0.010 0.013

Comments: Age of peat in the interval 3.10e3.40 me69.4  8.2/7.0 ka.

230

Th (decay/min$g)

0.212 0.220 0.228 0.181 0.284

    

0.010 0.006 0.005 0.004 0.009

232

Th (decay/min$g)

0.185 0.188 0.213 0.177 0.259

    

0.009 0.005 0.005 0.004 0.009

230

Th/234U

0.675 0.769 0.657 0.585 0.691

    

0.039 0.031 0.031 0.024 0.031

234

U/238U

1.275 1.194 1.181 1.236 1.295

    

0.056 0.048 0.065 0.052 0.050

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Fig. 2. Sections of Late Pleistocene marine deposits of Zeleniy and Tanfil’ev Island. Zeleniy Island: A, B, C e eastern coast 2.3 km south of Valton Cape (section 5304, 5504), D e coast of Voeikov Strait (section 2504); Tanfil’ev Island: E  southern coast, marine sands, covered Cretaceous rocks (section 27105); F e northern coast between Bolotniy and Dozor Capes (section 25805).

Boreal species such as Odontella aurita, Thalassiosira bramaputrae, Detonula confervacea, Cocconeis californica, Delphineis surirella and Diploneis suborbicularis, Nitzschia acuminata increase. The presence of Achnanthes hauckiana, Nitzschia sigma, Navicula peregrina, Rhopalodia musculus and others is a feature of brackish, clear waters. The assemblage indicates slight cooling and an increase in freshwater supply, demonstrated by a high content of freshwater diatoms (52%). Among neritic and ocean diatoms (16%), the arctic-

boreal Thalassiosira gravida, T. nordenskioldii, and northern boreal Thalassiosira eccentrica show cooler conditions. 4.1.4. Assemblage 4 (interval 2.25e2.60 m) The species diversity of diatoms increases. Cocconeis scutellum and Odontella aurita dominate, and benthic boreal Dimerogramma minor, Diploneis smithii, Navicula glacialis appear. In the upper part, planktonic species increase (up to 8%), including Paralia sulcata,

N.G. Razjigaeva et al. / Quaternary International 241 (2011) 35e50 5

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G Fig. 3. Grain size composition of marine coastal and lagoon deposits of Last Interglacial of Zeleniy Island (section 5304). A-G e intervals (from top): 2.30e2.35; 2.45e2.50; 2.65e2.70; 2.80e2.85; 3.00e3.05; 3.30e3.35; 3.40e3.45 m.

Trachyneis aspera, Cyclotella striata, and Actinocyclus octonarius. A variety of benthic species from the genus Nitzschia and Navicula marina, N. forcipata, Melosira moniliformis, and M. lineata are present. This assemblage is similar to Assemblage 2. Neritic and

ocean species (up to 34%, 22 taxa) are represented by arctic-boreal Thalassiosira gravida, T. nordenskioldii, northern boreal Thalassiosira eccentrica, T. decipiens, Rhisozolenia hebetata, and southern boreal and subtropical Thalassiosira leptopus, Thalassionema nitzschioides,

Fig. 4. Percentage diatom diagram of Late Pleistocene deposits of Zeleniy Island (section 5304). 1 e silt and silty clay, 2 e loam, 3- pebbles, 4 e san, 5 e rubbish, 6 e soil.

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Stephanopyxis nipponica, Rhizosolenia calcar-avis. Their presence in a lagoon assemblage is most likely associated with strong and frequent storms. The abundance of warm water, including tropical and subtropical species (15.5%) demonstrates the high marine water temperature of the time. Among the freshwater species (total 30%), the planktonic Aulacoseira granulata and epiphytes Fragilaria exigua, Cymbella gracilis, and Rhoicosphenia abbreviata dominate. 4.1.5. Pollen zone Zln-1 (interval 2.75e3.33 m) Rich pollen spectra are found in deposits. There are three pollen zones within these deposits (Fig. 5). Pollen zone Zln-1 (interval 2.75e3.33 m) is distinguished by a greater concentration of arboreal pollen, in which broadleaved pollen (up to 55%) dominate: Quercus, Ulmus, Juglans, and rare Corylus, Tilia, Carpinus, Fagus, and Acer. Small-leaved pollen (up to 40%) is represented by Alnus, Betula, Duschekia, and Salix. A high content of Myrica pollen was noted. Pollen discovered in the middle part of the interval morphologically resembles shrub birch pollen (15.8%). The content of the conifers Picea and Abies increased higher up in the interval. Pinus s/g Haploxylon, P. s/g Diploxylon, Tsuga, and rare Cryptomeria, Cupressaceae, Araliaceae, and Viburnum are present. The nonarboreal group includes pollen of wetlands and moist depressions, mixed meadows plants, rare Myriophyllum, and Nymphaea pollen, plants that are typical for lakes. Among the spores, ferns (Polypodiaceae, Osmunda cinnamomea, Ophioglossaceae, Coniogramme) and Sphagnum dominate, a high content of Lycopodium is noted, and rare Selaginella selaginoides is found. 4.1.6. Pollen zone Zln-2 (interval 2.6e2.75 m) This zone has reduced arboreal pollen content, among which Picea and Betula dominate. There is a sharp reduction in the content of broadleaved pollen (10%). The growth of Myrica in combination with an increase in the content of Cyperaceae, Sphagnum may serve to demonstrate expanded wetland areas. The amount of fern and moss spores decreased. Selaginella helvetica and S. selaginoides (2%) are noted. 4.1.6.1. Pollen zone Zln-3 (interval 2.25e2.6 m). This zone features an increase in the content of non-arboreal pollen and spores. Smallleaved pollen dominate (up to 46%) in the lower part of the interval (Betula sect. Albae, B. sect. Costatae, Betula sp., and shrub birch e up to 16.5%). The content and diversity of broadleaved taxa (Quercus, Ulmus, Juglans, Tilia, Corylus, Fagus) increases. The amount of conifer pollen reaches 33.9%. Species characteristic of wetlands (Cyperaceae, Ericaceae) and coastal meadows (Asteraceae, Chenopodiaceae, Apiaceae, Poaceae) dominate, and in the upper part of the section Artemisia appears. Ferns dominate the spores. In the lower part of the interval the Sphagnum content is high, with proportions decreasing in the overlying bed of marine deposits.

The composition of the pollen spectra demonstrates that climatic conditions in the first and third phases of development of vegetation were warmer than today. The second phase indicates a short-term, minor cooling, and possibly an increase in humidity. Marine beach deposits (thickness up to 2 m) suspected to be the same age are encountered on Zelenyi Island in sections of beach scarp on the side of Voeikov Strait and around Utinoe Lake (Fig. 1). They are represented by gray well sorted medium and coarse sands and round pebbles. Rare valves of marine sub-littoral diatoms are noted in the sands: planktonic Actinocyclus octonarius and benthic Campylodiscus echeneis, common in lagoons. 4.2. Tanfil’ev Island Shallow deposits have been studied in detail in the northern part of Tanfil’ev Island (section 25805) where interbedded yellowgray well sorted sands of various grain sizes, and gravels with well rounded pebbles and layers of black heavy mineral concentrates are exposed in the section of the cliff (Fig. 2). The overlying bed of the deposits rests at 6.2 m above sea level. Reddish volcanic ash of dacitic composition, with particles 20e30 m dominant, is present in the upper part of the section (Fig. 6). The volcanic glass has a high K2P content (Table 3). Diatom flora found in marine sands includes 12 marine and brackish forms. Littoral species dominate, such as southern-boreal Hyalodiscus obsoletus (36.1%), and northern boreal benthic and tychoplanktonnic Plagiogramma staurophorum (13.3%), Cocconeis scutellum (12%), Grammatophora oceanica (6%), Paralia sulcata (4.8%), Diploneis subcincta (2.4%), Arachnoidiscus ehrenbergii, and Nitzschia acuminata. The neritic southern-boreal species Thalassionema nitzschioides is encountered. There is an abundance of sponge spicula in several layers. The diatom assemblage, along with the well sorted deposit with an abundance of heavy minerals and lamination features, indicate inshore environments. Sands are replaced with gravels (up to 1 m thick) in the cliff from Cape Dozor to Groznaya Bay. Peat bog sediment with numerous ash layers resting on marine gravels are also found along the northern coast of the island (section 25905) (Fig. 7). Deposits in the low part of the section (interval 3.60e3.93 m) are heavily mineralized (33.6e45.7%). Three layers of volcanic ash are encountered, with the lowest the thickest. The volcanic glass has a low content of TiO2 (0.27%) and K2O (0.76%) (Fig. 8). In the interval 2.93e3.20 m, the peat is minimally mineralized (13.4e20.9%). A 14S-date of 46800  1200 BP (GIN-13462) obtained from deposits is considered as too young (Table 4), as other dates obtained from the upper peat include 230Th/234U-dates of 69.4 þ 8.2/7.0 ka and 73.0 þ 5.3/4.800 ka, and a 14S-date >49.5 ka (GIN-13463). The lower volcanic ash is of sand size (mode

Fig. 5. Percentage pollen diagram of Late Pleistocene deposits of Zeleniy Island (section 5304). Legend as Fig. 4.

N.G. Razjigaeva et al. / Quaternary International 241 (2011) 35e50

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Fig. 6. Grain size composition of volcanic ashes from Late Pleistocene deposits section of Tanfil’ev Island. Samples: A e 12/25805; B e 40/25905; C e 49/25905; D e 51/25905; E  52/25905; F e 53/25905.

0.16e0.2 mm). Within the 2.65e2.93 m interval (Fig. 6), in the middle of the layer, the size of the material increases (mode 0.2e0.25 mm). The TiO2 and K2O contents in the volcanic glass are close to tephra KRP-III, from the Kutcharo Volcano (Okumura, 1991). The amount of organic material reaches 4.62%. In interval 2.25e2.20 m, there is volcanic ash with an average grain size of well sorted sand (mode 0.315e0.4 mm). The chemical content (Fig. 8) is also close to the tephra from KRP-III Kutcharo Volcano (Okumura, 1991). Volcanic ash is well exposed along the cliff, in section 26405, located 1 km to the west of 25905. Woody material within a peat layer with interbedded ash produced a 14S-date of

43400  1100 BP (GIN-13467, Table 4). The upper part of the peat bed (1.62e2.20 m) is heavily mineralized (64.5e90.7%). In interval 2.19e2.20 m a layer of sand-sized volcanic ash is found. In interval 2.06e2.14 m, silt-sized (20e30 mm) dacitic volcanic ash is encountered. The significant thickness of the layer (up to 8 cm) and the well sorted material demonstrates that the eruption was large. The volcanic glass has a high content of TiO2 (0.64%), FeO (3.09%) and Na2O (4.58%), and contains 1.69% K2O (Table 3), which distinguishes it from the well-known Late Pleistocene ash on Hokkaido Island (Fig. 8). A 14S-date of 31200  450 BP (GIN-13467) was obtained from enclosing peat (Table 4).

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Table 3 Chemical composition of volcanic glass from tephra layers of Late Pleistocene deposits, Tanfil’ev Island, Lesser Kurils (%) #

Sample

Interval m

SiO2

TiO2

Al2O3

FeO

MnO

MgO

CaO

Na2O

K2O

Total

1 2 3 4 5 6 7 8 9 10 11

52/25905 51/25905 49/25905 45/25905 43/25905 40/25905 37/25905 26/25905 25/25905 5/25905 12/25805

0.98e1.02 1.53e1.58 1.65e1.67 1.83e1.86 1.91e1.98 2.14e2.16 2.40e2.45 2.73e2.81 2.81e2.93 3.81e3.87 1.27e1.33

75.16 76.09 75.59 71.41 73.02 72.31 76.52 76.66 77.37 77.23 77.61

0.54 0.30 0.32 0.58 0.61 0.64 0.36 0.34 0.28 0.27 0.19

13.52 14.30 13.67 15.26 14.27 14.68 13.48 13.80 12.60 13.17 12.83

2.19 1.46 2.19 3.15 2.96 3.09 1.97 1.54 1.46 1.93 0.90

nd nd nd 0.06 nd nd nd 0.13 nd nd nd

nd nd 0.28 0.25 nd nd nd nd 0.28 0.27 nd

1.96 1.54 2.33 2.87 2.73 2.52 1.91 1.26 1.26 2.05 0.82

4.45 4.10 4.49 4.45 4.11 4.58 4.45 4.38 4.63 3.95 3.29

1.99 1.81 1.00 1.54 1.87 1.69 1.04 1.87 1.76 0.76 4.41

99.76 99.82 99.89 99.58 99.54 99.53 99.71 99.97 99.64 99.65 100.05

nd e less than limit of detection.

Two layers of volcanic ash mixed with sand (modes 0.2e0.25 mm; 0.315e0.4 mm) with silt (17%) is encountered above. Volcanic glass is of the pumice type and has a characteristically high content of TiO2 (up to 0.61%), FeO (up to 3.15%) and K2O (up to 1.87%). Their source is unknown. Wood from the peat enclosing the

second layer was 14S-dated at 27000  6300 BP (GIN-13465), but the date may be too young. An overlying volcanic ash is deposited with silt and clay particles (modes 1e2 mm and 20e30 mm) (Fig. 6). It features bubble-wall volcanic glass with a low content of TiO2 (up to 0.32%), FeO (up to

Fig. 7. Section of Late Pleistocene peat bog of Tanfil’ev Island (25905). A e overview; B e lower part; C e all section.

N.G. Razjigaeva et al. / Quaternary International 241 (2011) 35e50

Fig. 8. Chemical composition of volcanic glass from the sections of Tanfil’ev Islands. Hokkaido (data by K. Okumura, 1991).

2.19%), and K2O (up to 1.00%), that is characteristic of the tephra of Kutcharo Volcano (Okumura, 1991). Peat covers a thick layer of volcanic ash (1.62e0.52 m). In the lower part, the material is better sorted, a mode of 20e30 mm is well defined and a mode 1e2 mm is weakly evident (Fig. 6). In the upper part of the layer, the material is less well sorted. The chemical composition of the glass from the lower layer resembles the KPI-KSr tephra from volcano Kutcharo (Fig. 8). Bubble-wall volcanic glass from the central part of the layer is distinguished by a high content of TiO2 (0.54%) and FeO (2.19%). It Table 4 14 C-dates and Kuril Islands. Sample

230

Th/U-dates of Late Pleistocene deposits of Tanfil’ev Island, Lesser

Interval m

Material

14

Sedate Th/U-date*

Lab. index, GIN-

230

1/25905

3.87e3.89 3.10e3.40

Peat Peat

3/25905 7/25905 1/26405 1/26405 1/26405

2.93e2.98 1.62e1.65

Peat Peaty clay Wood Wood Wood

*

46800  73000 þ 69400 þ >49500 36700  27000  31200  43400 

Refers to U/Th dates as indicated in table.

1200 5300/e4800* 8200/e7000* 400 630 450 1100

13462

13463 13464 13465 13466 13467

43

is not out of the question that this layer includes ash from several eruptions, possibly from various sources. A 14S-date of 36700  400 BP (GIN-13464, Table 4) was obtained from the upper part of the peat under the ash. The diatom assemblages of the deposit from section 25905 can be divided into two parts (Fig. 9). In the lower interval (3.60e3.93 m) are found 28 forms (99.4%) of marine diatoms with a small amount of freshwater species. The upper interval (0.30e3.60 m) has only freshwater diatoms (195 species), among which the most representative genera are Pinnularia (35), Eunotia (35), Navicula (24), Cymbella (19) and Gomphonema (12). Eleven taxa from the genera Aulacoseira and Stephanodiscus are present. The composition of freshwater flora reflects a very shallow lake with aquatic vegetation. At the same time during the development of the lake, periods of inundation and swamping are identified. In Assemblage 1, at the base of the section, rare marine sublittoral Cocconeis scutellum, C. verrucosa, Diploneis smithii, Paralia sulcata and freshwater species from Pinnularia and Eunotia genera are found. A rich diatom assemblage was present in the sand layer (interval 3.89e3.91 m), where marine species reach 99.4%. Sublittoral diatoms such as Paralia sulcata, and benthic Grammatophora oceanica, Cocconeis scutellum, and C. verrucosa prevail. Northern boreal plankton Trachyneis aspera, and the benthic cosmopolite Cocconeis costata, and rare southern-boreal Navicula marina, Lyrella hennedyi, Auliscus sculptus and others were present. The assemblage indicates semi-open bay environments and climate similar to the present. In the upper deposits (interval 3.87e3.89 m), the content of marine species decreases (55%). Cocconeis verrucosa and Paralia sulcata dominate, and the moderately warm water neritic Actinoptychus senarius and benthic cosmopolites Cocconeis dirupta, Rhabdonema arcuatum, Campylodiscus clypeus were found. Freshwater species are represented mainly by Pinnularia borealis, and the assemblage includes high contents of Eunotia praerupta and Hantzschia amphioxys, typical for intermittent wet environments. These changes in the diatom assemblage could be connected with sea level drop and intensive supply of freshwater diatoms from coastal areas. A rich diatom assemblage with marine species prevalent was found in interval 3.75e3.81 m. Paralia sulcata dominates, with warm water species Delphineis surirella, Auliscus sculptus, and Hyalodiscus obsoletus and neritic Actinoptychus senarius. The assemblages reflect a higher sea level. The deposits from interval 3.66e3.74 m include rich freshwater diatom flora, epiphites Aulacoseira aff. crassipunctata dominate, and tychoplanktonic Aulacoseira alpigena is subdominant. Species from Pinnularia are abundant. The assemblage indicates a shallow oligotrophic lake. In interval 3.60e3.65 m, marine species reach 29%, and Cocconeis scutellum dominates. Among freshwater species, Pinnularia viridis, P. isostauron, and Fragilaria construens f. venter prevail. The presence of Cymbopleura naviculiformis, Cymbella ehrenbergii, Gomphonema angustatum, G. helveticum, Navicula elginensis, and N. elginensis var. cuneata indicates river flow input. In general the assemblages reflect a shallow semi-enclosed bay environment. Similar assemblages of diatoms were identified for tidal zones and marshes on Eastern Hokkaido (Sawai, 2002). Assemblage 2 (interval 3.20e3.60 m) is characterized by rich species diversity. An abundance of Aulacoseira aff. crassipunctata, Aulacoseira alpigena, Fragilaria construens f. venter, Pinnularia viridis, Diploneis ovalis, species from the genera Cymbella (C. aspera, C. gracilis, C. ehrenbergii, C. hebridica), and Gomphonema (G. trunctatum, G. clavatum, G. gracile and others), and Cymbopleura naviculiformis reflects conditions of a shallow oligotrophic lake with diatoms derived from temporary streams. In this interval, the degree of peat mineralization declines from 41.6% to 18.9%. Assemblage 3 (interval 2.93e3.20 m) is distinguished by low species variety and content of diatoms. Pinnularia viridis, P.

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Fig. 9. Percentage diatom diagram of Late Pleistocene deposits of Tanfil’ev Island (section 25905). 1 e peat, 2 e peaty silt, 3 e volcanic ash of silt size, 4 e volcanic ash of sand size, 5 e pebbles, 6 e rubble, 7 e loam, 8 e soil.

isostauron and species of the genus Eunotia (E. fallax, E. glacialis, E. nymanniana and others) dominate. This assemblage is typical of overgrown lakes and wetland development. Assemblage 4 (interval 2.65e2.93 m) includes a thick volcanic ash layer in interval 2.73e2.93 m, with planktonic Stephanodiscus rotula and S. minutulus, characteristic of large, deep water lakes (Davidova, 1985). Rare Cocconeis neodiminuta, Fragilaria ulna, and Diploneis elliptica are present. Diatom valves are for the most part broken. In interval 2.65e2.73 m, an abundance of bottom flora is observed, dominated by Cavinula cocconeiformis, Amphora veneta, Caloneis bacillum, Nitzschia perminuta, Navicula cincta and Pinnularia lundii. Among the epiphytes, Achnanthidium minutissimum and Achnanthes helvetica prevail. The assemblages characterize a shallow, quiet pool with weakly acidic water. Assemblage 5 (interval 2.20e2.65 m) is characterized by high species diversity and a large quantity of diatom valves. In the lower part of the assemblage, Aulacoseira aff. crassipunctata, Aulacoseira alpigena, Tabellaria flocculosa and benthic Anomoeoneis brachysira dominate. Species from the genera Eunotia, Pinnularia, Cymbella are rare. In the upper part, the content of Fragilaria constricta, F. exigua, Eunotia praerupta, E. glacialis, E. serra, Pinnilaria stauroptera, Pinnularia viridis increases significantly. The assemblage indicates a shallow, gradually overgrown and swampy lake environment. Assemblage 6 (interval 2.06e2.20 m) is distinguished by a high diversity of species from the genus Eunotia, characteristic of oligotrophic-dystrophic pools with reduced conductivity and pH. Acidophilous epiphytes such as Eunotia pectinalis, E. exigua, E. incisa, E. monodon, E. sudetica and benthic Navicula soehrensis var. muscicola, N. soehrensis var. hassiaca, N. festiva, Anomoeoneis brachysira dominate. The assemblage reflects a wetland environment. Assemblage 7 (interval 0.52e2.06 m) is dominated by Aulacoseira aff. crassipunctata. In the lower part of the interval, benthic species such as Pinnularia viridis, P. brevicostata, P. nodosa,

Pinnularia streptoraphe and planktonic Aulacoseira crenulata, Aulacoseira alpigena are encountered, with Diploneis ovalis. In interval 1.71e1.77 m the species diversity of diatoms decreases sharply, and a high content of Pinnularia viridis together with Eunotia exigua, E. praerupta, E. serra and others that are characteristic of wetland conditions are observed. In the interval 0.98e1.71 m, the predominance of Aulacoseira aff. crassipunctata, Diploneis ovalis and species from the genus Pinnularia, and species from the genera Eunotia, Cymbella and Fragilaria constricta reflect water with low pH. The assemblage is characteristic for a shallow lake with shortterm oscillating water levels. This interval has frequent redeposited marine ocean and neritic diatoms, both from extinct PliocenePleistocene taxa (Coscinodiscus marginatus var. fossilis, Pyxidicula zabelinae, Stephanopyxis sp.) and those that exist today (C. oculusiridis, C. perforatus). Assemblage 8 (interval 0.30e0.44 m), identified from the base of the Holocene soil is characterized by a very low content of diatoms. More frequently encountered are circum-neutral Pinnularia borealis, Hantzschia amphioxys, Diadesmis contenta, and Luticola mutica, characteristic of weakly inundated surfaces and soils. The study of the distribution of pollen in peat bogs on Tanfielva Island makes it possible to identify the following pollen zones (Fig. 10). Pollen Zone T-1 (interval 3.66e3.93 m) features a high content of non-arboreal pollen (Fig. 11). The group is dominated by coniferous pollen (Picea sect. Omorica, P. sect. Eupicea, Abies, Pinus s/g Haploxylon) and Tsuga is present. Among the narrow-leaved, there is a high content of Alnus and hybrid birch pollen. A relatively high content of broadleaved pollen is noted. Among non-arboreal pollen, in a background of the dominance of wetland vegetation pollen (Cyperaceae, Ericales, Drosera), a high content of Poaceae and mixed grass pollen is noted. Among the spores, Sphagnum dominates.

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45

Fig. 10. Percentage pollen diagram of Late Pleistocene deposits of Tanfil’ev Island (section 25905). 1 e peat, 2 e peaty silt, 3 e volcanic ash of silt size, 4 e volcanic ash of sand size, 5 e pebbles, 6 e rubble.

In Pollen Zone T-2 (interval 2.93e3.66 m), Picea dominates and the role of alder and birch pollen decreases. Viburnum and Euonymus pollen is encountered. The predominance of non-arboreal pollen, and spores from Sphagnum moss, demonstrates the broad development of wetland landscapes on the coast, where a significant content of Cyperaceae and Ericaceae, represented by various genera (Ledum, Rhododendron, Menziesia) are noted. Pollen Zone T-3 (interval 2.45e2.65 m) differs in an increase in the content of arboreal pollen, among which Myrica dominates. The content of broadleaved taxa and spores decreased. Among nonarboreal taxa, Cyperaceae and Ericaceae dominate and the content of Poaceae increases. Pollen Zone T-4 (interval 2.35e2.45 m) features an increase in the content of Pinus s/g Haploxylon. The dominant small-leaved vegetation is Duschekia and shrub birch pollen appears. Rare broadleaved

pollen is present. Non-arboreal pollen includes Cyperaceae, Ericaceae, and rare Drosera. The content of Sphagnum increases, and Selaginella selaginoides is encountered in significant quantities. Pollen Zone T-5 (interval 1.86e2.35 m) is distinguished by an increase in Picea. The content of Pinus s/g Haploxylon and Duschekia declines sharply and the content of broadleaved pollen grows (up to 5.9%). Rare Larix appears. Among the non-arboreal pollen, the appearance of Lysichiton is characteristic. In the upper part of the zone, there is an abundance of Asteraceae and Poaceae. Among the spores, along with a large content of Sphagnum, ferns appear in increasing content upwards, including Osmunda cinnamomea. In Pollen Zone T-6 (interval 1.62e1.86 m), arboreal pollen dominate. The amount of Abies increases, with the content of Picea remaining large, Tsuga reappears, and Larix is rare. The content of birch and Myrica pollen decreases. Broadleaved pollen is rare.

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Fig. 11. Sections of Late Pleistocene deposits of Tanfil’ev Island (Groznaya Bay) with cryogenic structures (A) and traces of solifluction (B, C).

Among non-arboreal plant pollen, taxa typical for wetlands -Cyperaceae, Ericaceae, Sphagnum, Drosera e dominate, and Menyanthes appears. At the base of the zone, Lysichiton and Osmunda continue to play a significant role, with mixed grass pollen (Asteraceae, Polygonaceae, Fabaceae, Apiaceae) in the upper half. In the upper part of the zone, the content of arboreal pollen decreases. The content of Alnus, Duschekia, and non-arboreal Ericaceae increases. Peat is exposed in the section of the cliff over around 1 km, increasing in thickness to the west. In the upper part of the peat, numerous tree remains are found, from which 14S-dates were obtained (Table 4). In the peat and higher deposits, involution textures are observed. The overlying yellow-brownish loam has cryogenic textures. 5. Discussion The data obtained from multi-facial deposits exposed in coastal cliffs on Zelenyi and Tanfil’ev Islands made it possible to conduct stratigraphic partitioning of sections, recognizing specific periods of marine and continental deposit accumulation, conditions and factors leading to a shift of conditions, and assessment of climatic and paleolandscape situations. 5.1. Age determination The zonal diatom scale is useful for determining the age of marine deposits for the Pleistocene of the Pacific Ocean Region (Pushkar’ and Cherepanova, 2001). From the zonal species of diatoms in the studied deposits, Actinocyclus ochotensis var. fossilis, Coscinodiscus marginatus var. fossilis, Neodenticula kamtschatica, Pyxidicula zabelinae, and Stephanopyxis sp. are encountered. Valves are poorly preserved and are probably redeposited from ancient marine deposits. Despite the absence of the zonal species Proboscia curvirostris, marine deposits can be attributed to the late

interglacial because the diatom assemblages include a large component of warm water neritic and ocean species, including subtropical. The absence of P. curvirostris may be associated with the fact that this species is not encountered in large numbers even in deep water deposits in the zone of the same name (Pushkar’ and Cherepanova, 2001). Data from spore and pollen analysis demonstrating the distribution of temperate polydominant forests indicates the formation of deposits in interglacial conditions. On Tanfil’ev Island, the 14S-date of 46800  1200 BP (GIN13462) obtained from marine deposits in section 25905 can be interpreted as too young, as an overlying peat has yielded an infinite 14C date (GIN-13463) and 230Th/U series dates of 69.4 þ 8.2/ 7 ka (leaching method) and 73.0 þ 5.3/4.8 ka (full solution method). According to the biostratigraphic analysis, the deposits were formed in the concluding stage of the warm epoch at the beginning of the Late Pleistocene. The 230Th/U results correspond well with data for 230Th/234U dating for deep water deposits of the northern part of the Pacific Ocean, where the warm phase at the close of the late interglacial period dates to around 80.4 ka (Pushkar’ and Cherepanova, 2001). A 230Th/234U-date of 80600  2900 (K-171) was obtained for marine deposits of the Golubkovskaya Formation of Southern Primorye, with thermophylic pollen spectra (Pavlyutkin and Belyanina, 2002). The lower part of the peat that covers marine deposits probably accumulated at the end of the Last Interglacial period, and the upper part formed in the first glacial period and in the warming in the second half of the Late Pleistocene (14S-dates from 43400  1100 BP (GIN-13467) to 27000  630 BP (GIN-13465)). The well expressed cryogenic structure in the upper part of the section and other sites (Fig. 11) demonstrates that deposits were subjected to cryosolic deformations in the Last Glacial Maximum. Similar structures were identified both on eastern Hokkaido Island and on northern Honshu Island (Koaze et al., 1974). Such structures are not observed in the deposits for the Holocene in the Lesser Kurils.

N.G. Razjigaeva et al. / Quaternary International 241 (2011) 35e50

47

5.2. Sedimentary environments and sea level changes

5.3. Climatic changes and palaeolandscapes

The marine deposits accumulated in the transgression period of the Last Interglacial period in various coastal and marine conditions. The transgression had a complex structure and is divided into three phases identified as MIS 5e, 5s, 5a, with the maximum increase in sea level (up to 10e12 m) in the early phase with the warmest climate (Zubakov, 1990; Bilinsky, 1996; Kaplin and Selivanov, 1999). In the region of the Lesser Kurils, the maximum transgression accumulated lagoon deposits for Zelenyi Island and beach deposits up to 10 m, and formed an abrasion platform 10e15 m high, the remnants of which are today Zelenyi and Tanfil’ev Islands. Apparently, most of the islands in the south of the Lesser Kuril Ridge existed as shallow water shoals. Small islands were present in the eastern part of Zelenyi Island and Yurii, Anuchin, and Demin islands. The structure of the diatom assemblages identified in lagoon deposits indicate a shift in conditions from marine shallow water shoals to lagoons. Grain size composition of the deposits reflects the calm conditions of the sedimentation in which silty mud accumulated. In the development of the lagoon, phases associated with the lowering of sea level during minor cooling show an increase in the content of sub-littoral benthic species and an increase in the content of cold water diatoms that entered from the open ocean. At that time there was an active loss of freshwater diatoms from wetland areas of the coastline. Data from spore and pollen analysis shows a slight cooling. Breaks in sedimentation are apparent. Most likely, the lowering of the sea level was not great (in the range of MIS 5e) since a cardinal restructuring in the diatom assemblages and the planktonic spectra did not occur. A short-term regression during the transgression, correlated to MIS 5e, is recognized in marine terraces on Primorye (Korotky et al., 2006). The following rise in sea level again led to the formation of lagoons. The diatom assemblage reflects warm water conditions but, on the whole, the climate at this time was cooler than in the previous warming. The water exchange of the lagoon with the ocean became more active, indicated by the high concentration and variety of neritic and oceanic diatoms. Marine deposits from the lower part of the peat bog section on Tanfil’ev Island are represented by sub-littoral or marsh sediments, accumulated during cooler conditions, most likely in the concluding phase of the transgression comparable to MIS 5a. The overlying bed of the marine deposits is 5 m higher than the modern sea level. Sharp transitions of diatom assemblages with a predominance of marine or freshwater species are probably associated with an abrupt lowering of the sea at the beginning stage of the regression, during which the formation and subsequent destruction of a barrier occurred. A stable barrier formed later, after which a broad (greater than 1 km) lake formed. The absence of rheophils in the composition of the diatoms shows that temporary streams flowed into the waterbody, redepositing valves of freshwater and marine diatoms of various ages. 230 Th/U-dating indicates that the lake arose around 80e70000 years ago, and data identify four phases of flooding and three stages of shallowing and bog formation. At the beginning phase of formation, the rates of sedimentation in the waterbody were rather high. Probably the shift of lake-wetland conditions shown in the upper part of the peat succession developed in response to the formation of several freshwater bodies, and breaks are observed in sedimentation. The lake body received atmospheric precipitation, and the bog flooding phases were connected with a change in moisture content of the climate, during which the fall of volcanic ashes of various grain size composition may have played a role.

Warming at the start of the Late Pleistocene, which had a global character, led to significant changes in the zonal structure of landscapes across all of Northern Eurasia (Velichko et al., 2002), including the mainland shorelines of the southern Russian Far East (Aleskeev and Golubeva, 1980; Korotky et al., 2005, 2006). This warming had specific features on islands. The spore and pollen assemblages corresponding to the warmest climatic condition obtained from lagoon deposits, for example, on Zelenyi Island, apparently mark the final stage of the optimum for the late interglacial period. At this time in the Southern Kurils Southern temperate polydominant and mixed coniferous broadleaved forests were distributed. The change in pollen complexes allowed identification of three vegetation development phases: 1) southern temperate polydominant and mixed coniferous broadleaved forests, with wetland areas on the coastline; 2) dark coniferous and mixed spruce-fir forests with a mix of birch, broad development of wetland associations on the coastline; 3) park-like birch forests and thin mixed coniferous broadleaved forests with fern ground cover, broad development of meadows and meadow-wetland landscapes on areas adjacent to the coast. Climatic conditions during the first and third phases were warmer than today, and the second reflects a short-term, minor cooling and possibly an increase in humidity. Cooling is marked by the disappearance of warm water diatoms and an increase in the content of arctic forms entering the lagoon from the open ocean. The warming marked in the third phase is less well expressed than in the first. The trend toward cooling at the end of this warm period appeared as a reduction in warm water diatoms. In the epochs correlated to MIS 5e and 5c, southern temperate forests were broadly distributed on central Hokkaido Island (Igarashi, 1994). Similar forests currently occupy southwestern Hokkaido. On the northern and eastern coastlines of Hokkaido in the Late Pleistocene optimum, spruce and fir-spruce forests with a mix of broadleaved species developed (Sakaguchi and Okumura, 1986; Ooi et al., 1996). During the formation of marine deposits of the concluding stage of the Late Pleistocene transgression (MIS 5a), the dry land landscapes in the area of the Lesser Kurils experienced a significant restructuring. Climatic conditions became colder and closer to contemporary. On the coastline there was a distribution of dark coniferous taiga with elements of Southern Temperate flora as well as grassland and grassland-wetland landscapes with alder thickets. Later, during the regression, wetland landscapes had a broader distribution on the coastline and a phase of spruce-fir forests with southern temperate elements, with Euonymus and Viburnum is identified ca. 70e80,000 years ago. Pollen spectra from lacustrine deposits overlying the ash layer correlated with marker ash KP-II-III of Kutcharo Volcano (Hokkaido Island) reflect development of fir (Abies) forests. The nemoral plant role decreased, and the climate became cooler. Ericaceae-Cyperaceae swamps with Myrica were widespread on the coasts. Well pronounced cooling is recorded in the deposits of Pollen zone T4 (Pinus s/g Haploxylon-Duschekia-Selaginella), which correlated with the first glacial stage of the Late Pleistocene (MIS 4). Pinus pumila grew with Duschekia, swamp and wet grasslands with Selaginella selaginoides developed in the coasts, and dark conifer forests occupied the inner part of the islands. Modern analogues of such landscapes are typical for the Central Kurils (annual T 1.6 S, meat TJane6.3 S, sr. TAug. 10.9 S, annual precipitation 1213 mm) (Reference Book of USSR Climate, 1968, 1970). Pollen spectra with abundance of Selaginella selaginoides with pollen of Pinus pumila are typical for deposits of the Late Pleistocene glacial stages of Hokkaido (Heusser and Igarashi, 1994; Igarashi, 1994). The pollen zone distinguished for Tanfil’ev Island is similar to pollen spectra of

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terrestrial deposits of southeastern Hokkaido ca. 50e55 ka (Sakaguchi and Katon, 1993). This period is characterized by heavy snowfalls, and temperature was low, but higher than during the Last Glacial Maximum (Ono, 1991). Cooling in Lesser Kurils was less significant than at the Last Glacial Maximum. Tundra and forest tundra with permafrost developed in this area (Razjigaeva et al., 2005). On Hokkaido, cooling of the Last Glacial Maximum was strong: the climate was significantly cold and dry (Ono, 1991; Sakaguchi and Katon, 1993; Igarashi, 1994), and discontinuous permafrost existed (Koaze et al., 1974; Ono, 1991). In the upper part of the peat on Tanfil’ev Island, the pollen spectra reflect the development of spruce forests with fern understory. Larch was present, also characteristic for the pollen spectra at the end of the Late Pleistocene on Hokkaido Island (Igarashi et al., 1990; Igarashi, 1996). Along the shores of paleolakes there existed sphagnum shrub wetlands and mixed grass oversaturated meadows. Lysishiton camtschatcense (L.) Schott was present. The climate conditions were close to modern or slightly colder. Sea level was lower than modern, and dry land was significantly more extensive. There existed a dry land bridge uniting the Lesser Kurils with adjacent islands that also facilitated the development of forest vegetation. The warming correlates with the warm epoch of the second half of the Late Pleistocene. Similar forests existed at this time on eastern Hokkaido, when the climate was somewhat cooler and drier than today (Igarashi et al., 1990). The concluding stage of the formation of the buried peat bog was accompanied by spruce-fir forests with fern understory. Local vegetation was moisture-loving, mixed grass meadows and sphagnum bush wetlands. Open larch forest existed on the coastal wetland. A comparison of the development of landscapes in warm epochs of the Late Pleistocene with modern ones shows that the landscapes are only partially conditioned by climate. Paleoclimatic characteristics were not entirely similar to what had existed earlier. A significant factor controlling the direction and the irreversible development of landscapes in island conditions, aside from climate changes, was a change in the contours and sizes of the dry land in various epochs. Subdividing of the large land bridge into some small islands during transgressions hindered forest development, and straits limited migration of plants. As a rule, grasslands and peatlands became the main landscapes on small islands. 5.4. Volcanic and tectonic activity Analysis of the position of volcanic ash layers indicates that volcanic eruptions occurred irregularly during Late Pleistocene within the region. The sources of volcanic ashes in deposits of Lesser Kurils were Hokkaido and Kunashir Volcanoes. Higher volcanic activity took place at the end of the transgressive phase of Late Pleistocene Optimum, but the maximum activity of volcanic eruptions took place in the second half of Late Pleistocene. Mineral content of the peat strongly increased, reaching 67%. Diatom analysis showed that volcanic ash fall had a large impact on the ecologic condition in freshwater bodies. Apparently, the shift of diatom assemblages was connected not only with a change in humidity but also with the volume of pyroclastic material entering the water bodies, its grain size, and chemical composition. As a rule, inundation phases came after the ash fall of strong eruptions, especially if the pyroclastic material was silt and clay-sized. The introduction of microelements from volcanic material facilitated the large scale development of diatoms. For example, in a diatom assemblage from ash in section 25905 (interval. 2.66e2.93 m), Stephanodiscus rotula and S. minutulus appear in large numbers, characteristic of large, deep lakes (Davidova, 1985). These species are present in several lacustrine diatom assemblages of Kunashir (Cherepanova and Grebennikova, 2001) and Armeniya

(Golovenkina, 1981), where the onset of their development was associated with the influence of volcanism. Volcanic ash fall from strong eruptions had an influence on the irreversible path of landscape development. The fall of a thick layer of volcanic ash with a fine grain size composition in the late Pleistocene covered almost all relief forms on Zelenyi and Tanfil’ev Islands. This led to a long period of water saturation and to the development of weltand landscapes that have existed on small, depressed islands since the late glacial period. Data on the relief of marine deposits of the late interglacial period makes it possible to evaluate the neo-tectonic situation in the southern Lesser Kuril Ridge. The cover of marine deposits in all the sections studied are at a height of 8e10 m, and do not exceed the rise of sea level for the late Pleistocene transgression (MIS 5e), þ10 to þ12 m a s l. (Bilinsky, 1996; Kaplin and Selivanov, 1999). On the Nemuro peninsula, the territory of Hokkaido Island that is closest to islands studied, work on correlating and evaluation of the deformation of marine terraces showed that marine deposits formed in the transgression belong to MIS 5e, and do not occur above 10 m (Okumura, 1996). On this basis, a conclusion was drawn on the relative tectonic stability of the territory. Measurements with the help of exact, contemporary geodesic methods show that the area of Nemuro peninsula has in the last 50 years subsided at a rate of up to 0.8e0.9 cm/year (Ozawa et al., 1997). The sections of Holocene deposits on Zelenyi, Yurii, and Tanfil’ev Islands also demonstrate the tendency for subsidence of this territory throughout the Holocene. On the other hand, in the late Holocene and in historic time episodically strong earthquakes have been accompanied by sharp, coseismic movements leading to the rise of the territory from 0.5 to 2 m (Sawai, 2002; Atwater et al., 2004). Therefore, there is a contradiction between the data indicating the great rate of modern movement and evaluations of the limited cumulative effect of neo-tectonic movements in the late Pleistocene-Holocene. 6. Conclusion Multifacies marine and continental deposits that accumulated in the Last Interglacial Age were discovered in the southern Lesser Kuril Ridge. Detailed study of a series of sections made it possible to identify deposits from two phases of transgression that tentatively belongs to MIS 5e and the concluding phase of MIS 5a. The cover of the marine deposits is located no higher than 8e10 m above modern sea level. The deposits of the maximal phase of transgression that corresponds to the optimum of the Late Pleistocene include warm water assemblages of marine diatoms, including subtropical species. Most of the islands at that time were shallow water shoals with small islands. The climate was warmer than today. The following three phases of development of vegetation are defined: 1) southern temperate and mixed coniferous broadleaved forests, wetlands areas on the coast that correspond to the optimum of the Late Pleistocene; 2) dark coniferous and mixed spruce-fir forests with areas of birch, broad distribution of wetland associations caused by a small cooling and, possibly, an increase in precipitation; 3) park-like birch and spotty mixed coniferous broadleaved deciduous forests with fern cover, broad development of meadow and meadow-wetland coastal landscapes that correspond to a warming but that was less expressed than in the optimum. Marine deposits that accumulated in cooler climatic conditions correspond to a transgression phase correlating to MIS 5a. The cover of marine deposits is 5 m higher than modern sea level.

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Marine deposits without an apparent break are covered by lake deposits and peat, dated by 230Th/U dating in the interval 69.4 þ 8.2/7 ka and 73.0 þ 5.3/4.8 ka. The pollen spectra from marine and lake-wetland deposits make it possible to identify the following three phases (4e6) of development of vegetation reflecting progressing cooling: 4) dark coniferous taiga with elements of southern temperate flora and meadow-wetland landscapes with spotty patches of alder on the coastline; 5) spruce-fir forests with southern temperate elements, with Euonymus and Viburnum, and broad development of wetland landscapes on the coast; 6) spruce-fir forests, development on the coastline of EricaceaeCuperaceae wetlands with a significant area of Myrica tomentosa. 7) Significant cooling correlates with the first Late Pleistocene glacial phase (MIS 4) marked in the overlying peat. The vegetation phase included Pinus pumila groves with Duschekia on the coasts and development of swamps and wet grasslands with Selaginella selaginoide. Coniferous forests occupied the inner part of islands. In the consequent warming that correlates with the warm epoch of the second half of the Late Pleistocene, the climate was close to modern or slightly cooler. Forest vegetation existed on the extensive dry land uniting the Lesser Kuril Ridge with adjacent islands. Two vegetation phases are distinguished: 8) Abies forests with fern cover (Osmunda cinnamomea dominate), larch appears, Sphagnum-Ericaceae swamps with Lysishiton and wet grasslands were widespread on the coasts; 9) Abies forests, wet grasslands and Sphagnum-Ericaceae swamps with open larch forests on the coasts. Thus, in the Last Interglacial Age, a significant restructuring of landscape zones took place in the south of the Kurils: an expansion of the zone of broadleaved forests in the optimal phase of the beginning of the Late Pleistocene that displaced varied species dark coniferous forests. The specifics of the paleolandscape shifts on small islands were determined by a significant change in the configuration and area of dry land during fluctuations of sea level that caused the separation or uniting of island territories. Another factor having a regional character is volcanic activity, which exerts a large impact on various landscape components. Acknowledgments The authors wish to express their gratitude to M.M. Pevzner and L.D. Sulerzhitskii (Geological Institute RAS, Moscow, Russia) for carrying out the radiocarbon dating, to Yu. L. Kretser (V.G. Khlopin Radium Institute, St. Petersburg, Russia) for the study of the composition of volcanic glass, to A.I. Botsul (Pacific Institute of Oceanology FEB RAS, Vladivostok, Russia) for carrying out grain size analysis, to N.P. Domra (Institute of Biology and Soil Sciences FEB RAS, Vladivostok, Russia) for assistance in processing materials, and to A.A. Kharlamov (P.P. Shirshov Institute of Oceanology RAS, Moscow, Russia) for participation in research expeditions. This work was carried out through a grant from the RFFI 06-05-64033, 09-05-00003, and FEB RAS 09-I-ONZ-19. References Aleksandrova, A.N., 1982. Pleistocene of Sakhalin. Nauka, Moscow. Aleskeev, M.N., Golubeva, L.V., 1980. About stratigraphy and palaeogeography of late Pleistocene of south Primorye. Bulletin of USSR Quaternary Study Commission 50, 96e107.

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