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Strontium isotopic composition in late Pleistocene mammal bones from the Yakutian region (North-Eastern Siberia)
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Quaternary International 179 (2008) 72–78
Strontium isotopic composition in late Pleistocene mammal bones from the Yakutian region (North-Eastern Siberia) M. Barbieria, T.V. Kuznetsovab, V.I. Nikolaevc,, M.R. Palomboa,d a
Universita` Roma ‘‘La Sapienza’’, 00185 Roma, Italy Moscow State University, 119899 Moscow, Russian Federation c Institute of Geography RAS, 119017 Moscow, Russian Federation d CNR Istituto di Geologia Ambientale e Geoingegneria, Italy b
Available online 24 August 2007
Abstract Isotopic strontium composition of several bones, for which 14C data are available, retrieved from latest Pleistocene deposits of the Yakutian region has been analysed. Three different groups have been detected, corresponding to samples from great maritime (YanaIndigirka interfluve, Kolymian lowland) lowlands covered by thick Pleistocene sediments, from areas where Palaeozoic and Precambrian complex and Mesozoic granites crop out, and from Arctic coasts and Siberian Islands. Preliminary results highlight the difficulty in discriminating among resident, temporary migrant or long-distance newcomers if the sampling is not consistent. Taking into account global changes of sea level, the Laptev Sea shelf was mainly drained during the sea level lowering in the Late Pleistocene. Herbivores, and especially mammoths, did not utilise this shelf pastures. Therefore, the results pose several questions: what is the reason for herbivores not visiting the shelf? Was the shelf occupied by other mammal populations whose remains lie on the sea bottom? Was the territory too boggy for large animals? Why did mammals prefer vegetation from inland over shelf landscapes? The ongoing research might clarify some issues. r 2007 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction The Late Pleistocene history of the woolly mammoth, Mammuthus primigenius, is much better known than any other extinct Eurasian species, possibly because the availability of abundant fossil specimens and radiocarbon data available from Europe and northern Asia (Stuart, 2005). On the other hand, in spite of long-term research, authors are far from reaching a consensus on environmental reconstructions of mammoth habitats, as well as on causes of extinction (see inter alios Verkhovskaya, 1988; Ukrainsteva et al., 1996; Stuart, 2005; Velichko and Zelikson, 2005). Actually, during the Last Cold Stage M. primigenius spread across Northern Eurasia, and it was generally accepted that mammoth populations inhabited open steppes, locally with trees and bushes under cryo-arid Corresponding author.
E-mail addresses: [email protected] (M. Barbieri), [email protected] (T.V. Kuznetsova), [email protected] (V.I. Nikolaev), [email protected] (M.R. Palombo).
climate conditions. Some authors suggested in some regions, e.g. in Siberia, at times the climate was similar to the modern one or even warmer and woodlands would be more important than generally supposed (Lazukov, 1973; Verkhovskaya, 1988). Moreover, if there is evidence that latest Pleistocene climatic changes produced habitat fragmentation, and population contraction promoting extinctions, on the other hand there is strong evidence (several radiocarbon dates from more than one laboratory) that M. primigenius populations inhabited North-Eastern Siberia (Taymyr Peninsula) about 9.6–9.9 ka BP (Sulerzhitsky and Romanenko, 1999; MacPhee et al., 2002) and survived on Wrangel Island to about 3.7 ka BP (Vartanian et al., 1995; Tikhonov and Vartanyan, 2001). Moreover, as any given ‘‘lowest’’ occurrence date is merely a provisional and minimum estimate of the true extinction date (MacPhee and Flemming, 2001; Palombo, 2005), the hypothesis that woolly mammoth lived in northern Asia during the early Holocene is not a trivial one. If climate contributed in minor amount, or not at all (see Fox et al., 2007, for a discussion) to the M. primigenius extinction, how and to
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which extent did climate fluctuation affect faunal dispersion and dispersal during the latest Pleistocene? Indeed, in the Taymyr region, it seems that some anomalous time intervals characterise the fossil record. Moreover, they occur at the same time in the chronometric records of other regions in which the target species existed (MacPhee et al., 2002). Thus, if ‘‘gaps’’ are recognised in any region, should they be explained by periodic occupancy of these territories by woolly mammoth populations? Along the Laptev Sea coast and New Siberian Islands, perennially frozen terrestrial deposits outcrop, whose fossiliferous content (diatoms, palinomorphs, macroflora remains, mammal bones, etc.), supplemented by 14C dating, provides excellent archives of past life and Pleistocene–Holocene environmental conditions. This contribution to the debate analyses isotopic strontium composition of several bones, for which 14C data are available, retrieved from latest Pleistocene deposits of the Yakutian region, and then compared with the isotopic ratio of substratum rocks. The aim is to trace the possible migratory routes followed by animals to reach the locality where fossiliferous beds accumulated. To reconstruct the geographical origin of fossiliferous remains, key information might be provided by strontium isotope ratios of fossil remains affected by limited or no exposure to diagenesis— as the bones preserved in Yakutian permafrost are—since they give information on the substratum of the area where the animals once lived. Herbivores maintain their Sr isotope ratios from the underlying soil and bedrock. It is possible to distinguish between resident and non-resident animals by comparing the Sr isotope ratio of skeletal remains with the ratios of the soils and bedrock where the fossils where found. This provides information on the possible transport and redeposition of the fossil remains (Sealy et al., 1991). 2. Palaeoenvironmental conditions in the Lena Delta area during the last 60 ka At the present time, the Lena Delta area, belonging to the northern tundra zone, is characterised by long (8 months), severe winters, and short, cold summers: temperatures range from 32 to 34 1C (January) to about 9 1C (July), and annual precipitation from 200 to 300 mm. Tundra-gley and peaty-gley (histosols and inceptisols) soils with an active-layer thickness of about 30–40 cm prevail (Atlas of Arctic, 1985), and permafrost has a thickness of 500–600 m (Grigoriev et al., 1996). Moss–grass–low shrub tundra dominates the vegetation, with vascular plant species such as Betula exilis, Dryas punctata, Salix pulchra, Cassiope tetragona, Oxyria digyna, Alopecurus alpinus, Poa arctica, Carex ensifolia, Carex rotundifolia, and Eriophorum medium, mosses such as Aulacomnium turgidum, Hylocomium alaskanum, Drepanocladus iniciatum, and Calliergon sarmentosum, and lichens such as Alectoria ochroleuca, Cetraria cuculliata, and Cetraria hiascus.
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During the Last Glacial six alternating climate phases can be detected on the basis of biogeochemical and paleontological data. The first phase, developed during the Late Zyryanian Stadial (Early Weichselian, Marine Isotope Stage (MIS) 4) about from 60 to 50 ka BP (Schirrmeister et al., 2002), was characterised by dry and cold summer with low bioproductivity, as confirmed by oxygen isotope composition of ice wedges indicating extremely low winter temperatures. Sediments had a prevalent fluvial origin. For the second phase (Early Karginsky Interstadial, Middle Weichselian, MIS 3, about 50 to 35–34 ka BP), pollen data suggest rather warm and wet climates (temperatures 0.5–1.5 1C warmer and precipitation 25–75 mm higher than today) for the Taymyr Peninsula, but treeless vegetation and rather cold and dry climate for Laptev Sea coast (Bykovsky Peninsula and Bol’shoy Lyakhovsky Island). In the third period (Late Karginsky, 33 to 23–22 ka BP) pollen records from the northern Taymyr Peninsula and Laptev Sea coast indicate a vegetation cover dominated by open steppe-like herb communities. Climatic conditions were rather severe (with temperatures 2–5 1C colder and precipitation 50–100 mm lower than today; Kuznetsova et al., 2003). During the following period (Last Glacial Maximum, MIS 2, between 22 and 15 ka BP) the most unfavourable environmental conditions can be detected. This phase has been interpreted as an extremely cold and dry one, characterised by sparse vegetational cover and low pollen productivity. Insects and mammals are documented by scanty remains, and only a few dates from woolly mammoth bones have been obtained (Kuznetsova et al., 2001). Between 15 and 12 ka BP, a remarkable change in environmental conditions can be inferred from both geochemical and paleontological data. Vegetation (macroflora and high pollen productivity) as well as insect remains indicate temperate-warm and humid climate conditions. The temperatures were 1.5 1C warmer and precipitation ca. 25 mm higher than today (Schirrmeister et al., 2002). A short climate improvement is particularly evident about 12 ka BP (Bølling-Allerød Interstadial). Possibly since ca. 20 ka BP to 11 ka, the precipitation source area changed as documented by stable isotope data from ice wedges. Moreover, during this phase, thermal erosion and thermokarst started, fluvial transport of clastic material began, and peaty soil formation took place. The climate and environment were the most favourable of all the Late Pleistocene for woolly mammoth. M. primigenius remains particularly are found in the area. Throughout the last phase, and until about 8 ka BP, the degradation of permafrost by thermokarst processes and the formation of new landscapes with a great number of thermokarst lakes are consistent with early Holocene climatic improvement. Moreover, gradual paleoenvironmental changes are visible since about 4.5 ka BP (Schirrmeister et al., 2002).
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3. Materials and methods Strontium isotope analyses were conducted for 26 M. primigenius tusks from Northern Yakutia Late Pleistocene deposits (Fig. 1), and 27 14C dated bones of M. primigenius from Bol’shoy Lyakhovsky Island (New Siberia Islands) (11 specimens), Lena River Delta (10 specimens) (Fig. 2). Single specimens from the Omoloy River and Omulyakhskaya Guba, as well as a few specimens of Equus ferus (Lena River Delta) and Bison priscus (Bol’shoy Lyakhovsky Island) have been analysed for comparative purposes. Accordingly, a total of 39 M. primigenius samples have been studied. Strontium isotope values have been obtained from solid rock (13 samples) and silt (2 samples) collected from Bol’shoy Lyakhovsky Island and in the Kolyma River area (3 silt samples). Tusk and bone samples for isotope analyses were mechanically cleaned. To avoid the diagenetic Sr, which can modify the 87Sr/86Sr ratios, samples of mammal bones and tusks were pre-treated with 1.0N acetic acid and then washed with bidistilled water. Hundred milligram of sample were dissolved in 2.0 N HCl, and Sr chemical separations were performed using standard ion-exchange chromatographic methods. Rock and soil samples were dissolved by HNO3 and HF acid solutions and strontium was obtained using the same methodology employed for the analyses of mammal bones and tusks. The Sr was deposited as Sr(NO3)2 on the W filament and the isotope 87Sr/86Sr ratios were measured by VG 54E mass spectrometry. The measured ratios were fractionation-corrected to an 86Sr/88Sr value of 0.1194. The determinations of 87Sr/86Sr on the NBS 987 strontium carbonate standard yielded values equal to 0.710247 0.00002 (2s).
Fig. 2. Location of Late Pleistocene mammals complex’ bones and samples of rocks studied. Mammal bones: 1: the Delta Lena River; 2: Bol’shoy Lyakhovsky Island (New Siberia Islands); 3: the Omoloy River area and 4: Omulyakhskaya Guba. Samples of rocks: I: Bol’shoy Lyakhovsky Island; II: Duvanny Yar (Low the Kolyma River area).
Table 1 Strontium isotope composition of mammoths’ tusks (location see Fig. 1) (s ¼ 70.00001) Samples no.
87
Sr/86Sr
2 14 15 18 42 70 77 101 104 125 139 141 151
0.71165 0.71102 0.71102 0.71072 0.71110 0.71241 0.71085 0.71230 0.71015 0.71091 0.71059 0.71137 0.71153
Samples no.
87
Sr/86Sr
160 167 190 211 212 216 219 221 226 245 256 266 278
0.71130 0.71088 0.71103 0.71370 0.71319 0.71087 0.71112 0.71106 0.71428 0.71156 0.71402 0.70976 0.70920
4. Results and discussion
Fig. 1. Location of mammoth’s tusks studied.
The results obtained for tusk samples from Northern Yakutia region (Table 1, Fig. 3) discriminate three M. primigenius groups. The first group includes samples from maritime lowlands (Yana-Indigirka interfluve, Kolymian lowland) covered by thick Pleistocene sediments (such as loess-like covering loam, lacustrine-swamp or alluvial deposits). Their 87Sr/86Sr values range from 0.70920 to 0.71130 (average value 0.7107570.00056, n ¼ 12). Unfortunately, only a few 87Sr/86Sr analyses were conducted from the Pleistocene sediments (‘‘Icy complex’’). The values 0.70998–0.71100 (Table 2) are in good
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Fig. 3. 87Sr/86Sr ratios in tusks of Late Pleistocene mammoths from Northern Yakutia.
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accordance with those obtained for the M. primigenius specimens (0.71072–0.71102). Moreover, the results fit with data available for mammoth tusks from valleys whose relatively small rivers (the Berelekh River, the Alazeya River, the Malaya Kuropatoch’ya River) drain only Pleistocene sediments (Berelekh River: 87Sr/86Sr ¼ 0.71085; Alazeya River: 87Sr/86Sr ¼ 0.71087; Malaya Kuropatoch’ya River: 87Sr/86Sr ¼ 0.71110). They are here considered as ‘‘standard’’ values for animals inhabiting territories where these deposits crop out. Accordingly, the strontium ratio obtained for M. primigenius samples from YanaIndigirka interfluve, Kolymian lowland regions could indicate resident populations. The second group consists of samples from areas where the Palaeozoic and Precambrian basement complex and the Mesozoic granites crop out. The values obtained for samples from Tommot massif area (87Sr/86Sr ¼ 0.71370), and the western periphery of Poluusny hills (87Sr/86Sr ¼ 0.71319) are consistent with the value obtained for basement complex rocks are 87Sr/86Sr40.71400 (Maslovskaya et al., 1980). Moreover, some specimens from Bol’shoy Lyakhovsky Island show a strontium ratio (87Sr/86Sr ¼ 0.71402–0.71428) similar to those obtained for sandstone, granite and silt deposits cropping out in this area (87Sr/86Sr ¼ 0.71320–0.71484) (Table 2). The scarcity of samples from Bol’shoy Lyakhovsky Island in this group prevents any hypothesis. On the other hand, values of M. primigenius samples from the Ozhogina River valley (left tributary of the Kolyma River) are intermediate (87Sr/86Sr ¼ 0.71241) between the first and second groups. Moreover, the
Table 2 Strontium isotope composition (87Sr/86Sr) of rocks cropping out in Nothern Yakutia (location see Fig. 2.) SE part of Bol’shoy Lyakhovsky Island (New Siberian Archipelago) Age (period)
87
200750 million years 200750 million years 200750 million years 200750 million years 200750 million years 200750 million years 200750 million years 200750 million years Jurassic Jurassic 115 million years 115 million years 115 million years
n.d. 0.71469 n.d. 0.71744 0.71320 0.71719 0.71744 0.71777 0.71043 0.71039 0.71369 0.71120 0.70730
Southern coast of Bol’shoy Lyakhovsky Island (New Siberian Archipelago) 46LYA-3TZ-1-5 Aleurite (silt) 126LYA-1TZ-5 Aleurite (silt)
54050+31302250 yearsa 35680+400390 yearsa
0.71484 n.d.
Low reach of the Kolyma River area (Dyvanny Yar) A42 Aleurite (silt) with low ice content A50 Aleurite (silt)
15,000–20,000 years 35,000–40,000 years
0.70998 0.71000
Sample no. 109 304/8 301/2 144/2 145/1 148/1 144/11 205/3 180/11 117/1 501/1 320/1 436/2
Argillite Sandstone Argillite Sandstone Sandstone Argillite Black argillite Argillite Gabbro-diabase Diabase Granite Diorite Diorite (granodiorite)
Sr/86Sr
The obtained values have not been correct because of the age of bones are to recent to affecting the obtained strontium ratio. n.d., not detectable. a Andreev, Schirrmeister et al. (personal communication).
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0.71350 0.71300 0.71250
87Sr/86Sr
0.71200 0.71150 0.71100 0.71050 0.71000 0.70950 60,000
50,000
40,000
30,000
20,000
10,000
0
Age, years Fig. 4. Evolution of strontium isotope composition in Late Pleistocene mammal bones from Northern Yakutian region.
strontium ratio is higher than that obtained for silt deposits from the Kolima River area (Table 2). Accordingly, the hypothesis that this sample belongs to ‘‘non-resident’’ individuals cannot be ruled out. To the third group have been ascribed samples from arctic coasts and islands (Bykovsky Peninsula, Omulyakhskaya Guba, southern coast of Dmitry Laptev strait ¼ Oiaygossky Yar, Bol’shoy Lyakhovsky Island, Makar Island, Ion Island) whose strontium ratios range from 0.70976 to 0.71294 (Tables 1 and 3), the highest values corresponding to samples from Bol’shoy Lyakhovsky Island (87Sr/86Sr ¼ 0.71294 for the M. primigenius sample GIN-10714, dated at about 39.6 ka; 87 Sr/86Sr ¼ 0.71203 and 0.71208 for two B. priscus samples dated, respectively, around 41.5 and 38.2 ka) (Fig. 4), even excluding the above mentioned ones (0.71402 and 0.71428). On the other hand, taking into account just the mammoth samples from the Lena Delta, dated from about 34 to 13 ka, the range of strontium ratio is less, ranging from 0.71055 to 0.71153 (Table 3). Marine surface sediments of the Laptev Sea in area between deltas of the Lena River and the Yana River and New Siberian Islands have values 87 Sr/86SrX0.71365–0.71651 (Eisenhauer et al., 1999), confirming the number of different rocks cropping out in the surrounding mainland. Accordingly, taking into account the great variability of bedrock supporting the vegetational cover, it is not a simple task to understand and explain the different use of shelf, continental and island pastures due to changes of sea level in the Late Pleistocene. For instance, did mammoths from Oiaygossky Yar and the Lena Delta prefer continental pastures? Were the high values (87Sr/86Sr40.71400) of mammoths from Bol’shoy Lyakhovsky Island caused by the exposure of ancient crystalline rocks? Did mammoths from Makar Island use both continental and shelf pastures (0.71230)?
In general, the results support the hypothesis that migrations of Yakutian mammoths (at least for individuals or populations) were limited to several hundred kilometres. This conclusion could be indicated by the high 87Sr/86Sr values of mammoth tusks included in the second group, due to relatively reduced exposure of crystalline rocks. Moreover, the different soil and pasture exploitation and migratory behaviour of M. primigenius populations inhabiting this area, is confirmed by the C and N stable isotope values measured in their hair. Indeed, seasonal variation can be inferred for the analyses (Iacumin et al., 2005 and unpublished data). Consequently, it is likely that different mammoth populations used different pastures, even in the relatively small Yakutian region, depending on typology of outcropping rocks, changes of sea level in Late Pleistocene or different temporary/permanent migrations. Moreover, the results obtained for 14C dated bones of M. primigenius (Fig. 4) indicate that the only animals inhabiting Bol’shoy Lyakhovsky Islands during 38,200–41,500 B.P. used shelf pastures. This indicates relatively low sea level in the Karginsky interstadial (MIS 3). Probably, mammoth from Bol’shoy Lyakhovsky Islands (22,500 BP) and one from the Lena River Delta (34,000 BP) visited the shelf occasionally. Conversely, it seems the Laptev Sea shelf between the delta of the Lena River and New Siberian Island (varying in present depth from 20 to 40 m) was not visited by herbivores during the Late Pleistocene sea level lowering. 5. Remarks The preliminary results highlight the difficulty of discriminating among resident, temporary migrant or long-distance newcomers if the sampling is not consistent, and limited radiocarbon dated bones and samples are available for the analysis.
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Table 3 Strontium isotope composition (87Sr/86Sr) of late Pleistocene mammals complex’ bones from Northern Yakutia (location see Fig. 2) 14
C date
7s infinite dates
Mammuthus primigenius 12,030 60 12,500 50 13,100 500 13,740 50 145,00 140 19,200 220 20,200 100 20,800 600 22,100 1000 24,300 200
Lab. no.
Region
Lat., 1N
Long., 1E
Object
87
Sr/86Sr s ¼ 70.00001
GIN-10713 GIN-10716 GIN-10242 GIN-12041 GIN-10240 GIN-10235 GIN-10236 GIN-10248 GIN-10707 GIN-10264
B.L.I. B.L.I. D.L.R. Omulyakh D.L.R. D.L.R. D.L.R. D.L.R. B.L.I. D.L.R.
73.32 73.33 71.79 73.40 71.79 73 71.79 71.79 73.32 71.79
141.39 141.33 129.40 141.50 129.40 128.50 129.40 129.38 141.37 129.40
0.71118 0.71102 0.71103 0.71153 0.71119 0.71132 0.71121 0.71080 0.71172 0.71104
27,400 28,000
800 180
GIN-10262 GIN-10706
D.L.R. B.L.I.
71.79 73.32
129.40 141.37
30,200 30,720 31,500 31,900 34,000 37,800 39,600 40,200 43,600 48,000 50,650
400 200 650 400 500 900 1000 900 1000 2000 1820
GIN-10719 GIN-12042 GIN-10249 GIN-12037 GIN-10261 GIN-10660 GIN-10714 GIN-10703 GIN-10717 GIN-10709 KIA-10681
D.L.R. Omoloy R. D.L.R. B.L.I. D.L.R. B.L.I. B.L.I. B.L.I. B.L.I. B.L.I. B.L.I.
72.90 70.65 71.78 72.30 71.79 73.34 73.34 73.34 73.34 73.34 73.28
123.35 133.35 129.42 144.25 129.40 141.28 141.31 141.31 141.31 141.31 141.82
ulna fr. tusk fr. pelvis fr. tusk fr. pelvis fr rib fr. scapuia fr. metacarpale II pelvis fr thoraic vertebra limb bone fr. ulna (with marrow) cranium tusk fr. metatarsale III tusk fr. limb bone fr. vetebra femur fr. humerus scapula fr. tusk fr. molar
Equus ferus 16,380 35,900
120 600
GIN-10233 GIN-10269
D.L.R. D.L.R.
71.79 71.79
129.38 129.40
radius femur
0.71132 0.71143
Bison priscus 38,200 41,500
700 1100
GIN-10663 GIN-10686
B.L.I. B.L.I.
73.34 73.33
141.31 141.33
radius Sacrum fr.
0.71208 0.71203
0.71081 0.71083 0.71132 0.71130 0.71055 0.70976 0.71168 0.71139 0.71294 0.71290 0.71122 0.71128 0.71132
B.L.I.: Bol’shoy Lyakhovsky Island (New Siberia Islands); D.L.R.: the Delta Lena River; Omoloy R.: the Omoloy River; Omulyakh: Omulyakhskaya Guba.
Taking into account global changes of sea level, the Laptev Sea shelf was mainly drained during the sea level lowering in the Late Pleistocene. Herbivores, and especially mammoths, did not utilise shelf pastures. Therefore, the results open several questions: what is the reason for not visiting the shelf? Was the shelf occupied by other mammal populations whose remains lie on the sea bottom? Was the territory too boggy for large animals? Why did mammals prefer vegetation from inland and not shelf landscapes? Ongoing research might clarify some issues.
Acknowledgements We would like to thank the people who gave us the opportunity to study samples of bones and rocks from Yakutia, in particular Drs. A. Kuzmichev and L. Schirrmeister. Investigations were supported by Agreement CNR–RAS and RFBR (Grant 04-05-65314).
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Quaternary International 179 (2008) 72–78
Strontium isotopic composition in late Pleistocene mammal bones from the Yakutian region (North-Eastern Siberia) M. Barbieria, T.V. Kuznetsovab, V.I. Nikolaevc,, M.R. Palomboa,d a
Universita` Roma ‘‘La Sapienza’’, 00185 Roma, Italy Moscow State University, 119899 Moscow, Russian Federation c Institute of Geography RAS, 119017 Moscow, Russian Federation d CNR Istituto di Geologia Ambientale e Geoingegneria, Italy b
Available online 24 August 2007
Abstract Isotopic strontium composition of several bones, for which 14C data are available, retrieved from latest Pleistocene deposits of the Yakutian region has been analysed. Three different groups have been detected, corresponding to samples from great maritime (YanaIndigirka interfluve, Kolymian lowland) lowlands covered by thick Pleistocene sediments, from areas where Palaeozoic and Precambrian complex and Mesozoic granites crop out, and from Arctic coasts and Siberian Islands. Preliminary results highlight the difficulty in discriminating among resident, temporary migrant or long-distance newcomers if the sampling is not consistent. Taking into account global changes of sea level, the Laptev Sea shelf was mainly drained during the sea level lowering in the Late Pleistocene. Herbivores, and especially mammoths, did not utilise this shelf pastures. Therefore, the results pose several questions: what is the reason for herbivores not visiting the shelf? Was the shelf occupied by other mammal populations whose remains lie on the sea bottom? Was the territory too boggy for large animals? Why did mammals prefer vegetation from inland over shelf landscapes? The ongoing research might clarify some issues. r 2007 Elsevier Ltd and INQUA. All rights reserved.
1. Introduction The Late Pleistocene history of the woolly mammoth, Mammuthus primigenius, is much better known than any other extinct Eurasian species, possibly because the availability of abundant fossil specimens and radiocarbon data available from Europe and northern Asia (Stuart, 2005). On the other hand, in spite of long-term research, authors are far from reaching a consensus on environmental reconstructions of mammoth habitats, as well as on causes of extinction (see inter alios Verkhovskaya, 1988; Ukrainsteva et al., 1996; Stuart, 2005; Velichko and Zelikson, 2005). Actually, during the Last Cold Stage M. primigenius spread across Northern Eurasia, and it was generally accepted that mammoth populations inhabited open steppes, locally with trees and bushes under cryo-arid Corresponding author.
E-mail addresses: [email protected] (M. Barbieri), [email protected] (T.V. Kuznetsova), [email protected] (V.I. Nikolaev), [email protected] (M.R. Palombo).
climate conditions. Some authors suggested in some regions, e.g. in Siberia, at times the climate was similar to the modern one or even warmer and woodlands would be more important than generally supposed (Lazukov, 1973; Verkhovskaya, 1988). Moreover, if there is evidence that latest Pleistocene climatic changes produced habitat fragmentation, and population contraction promoting extinctions, on the other hand there is strong evidence (several radiocarbon dates from more than one laboratory) that M. primigenius populations inhabited North-Eastern Siberia (Taymyr Peninsula) about 9.6–9.9 ka BP (Sulerzhitsky and Romanenko, 1999; MacPhee et al., 2002) and survived on Wrangel Island to about 3.7 ka BP (Vartanian et al., 1995; Tikhonov and Vartanyan, 2001). Moreover, as any given ‘‘lowest’’ occurrence date is merely a provisional and minimum estimate of the true extinction date (MacPhee and Flemming, 2001; Palombo, 2005), the hypothesis that woolly mammoth lived in northern Asia during the early Holocene is not a trivial one. If climate contributed in minor amount, or not at all (see Fox et al., 2007, for a discussion) to the M. primigenius extinction, how and to
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which extent did climate fluctuation affect faunal dispersion and dispersal during the latest Pleistocene? Indeed, in the Taymyr region, it seems that some anomalous time intervals characterise the fossil record. Moreover, they occur at the same time in the chronometric records of other regions in which the target species existed (MacPhee et al., 2002). Thus, if ‘‘gaps’’ are recognised in any region, should they be explained by periodic occupancy of these territories by woolly mammoth populations? Along the Laptev Sea coast and New Siberian Islands, perennially frozen terrestrial deposits outcrop, whose fossiliferous content (diatoms, palinomorphs, macroflora remains, mammal bones, etc.), supplemented by 14C dating, provides excellent archives of past life and Pleistocene–Holocene environmental conditions. This contribution to the debate analyses isotopic strontium composition of several bones, for which 14C data are available, retrieved from latest Pleistocene deposits of the Yakutian region, and then compared with the isotopic ratio of substratum rocks. The aim is to trace the possible migratory routes followed by animals to reach the locality where fossiliferous beds accumulated. To reconstruct the geographical origin of fossiliferous remains, key information might be provided by strontium isotope ratios of fossil remains affected by limited or no exposure to diagenesis— as the bones preserved in Yakutian permafrost are—since they give information on the substratum of the area where the animals once lived. Herbivores maintain their Sr isotope ratios from the underlying soil and bedrock. It is possible to distinguish between resident and non-resident animals by comparing the Sr isotope ratio of skeletal remains with the ratios of the soils and bedrock where the fossils where found. This provides information on the possible transport and redeposition of the fossil remains (Sealy et al., 1991). 2. Palaeoenvironmental conditions in the Lena Delta area during the last 60 ka At the present time, the Lena Delta area, belonging to the northern tundra zone, is characterised by long (8 months), severe winters, and short, cold summers: temperatures range from 32 to 34 1C (January) to about 9 1C (July), and annual precipitation from 200 to 300 mm. Tundra-gley and peaty-gley (histosols and inceptisols) soils with an active-layer thickness of about 30–40 cm prevail (Atlas of Arctic, 1985), and permafrost has a thickness of 500–600 m (Grigoriev et al., 1996). Moss–grass–low shrub tundra dominates the vegetation, with vascular plant species such as Betula exilis, Dryas punctata, Salix pulchra, Cassiope tetragona, Oxyria digyna, Alopecurus alpinus, Poa arctica, Carex ensifolia, Carex rotundifolia, and Eriophorum medium, mosses such as Aulacomnium turgidum, Hylocomium alaskanum, Drepanocladus iniciatum, and Calliergon sarmentosum, and lichens such as Alectoria ochroleuca, Cetraria cuculliata, and Cetraria hiascus.
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During the Last Glacial six alternating climate phases can be detected on the basis of biogeochemical and paleontological data. The first phase, developed during the Late Zyryanian Stadial (Early Weichselian, Marine Isotope Stage (MIS) 4) about from 60 to 50 ka BP (Schirrmeister et al., 2002), was characterised by dry and cold summer with low bioproductivity, as confirmed by oxygen isotope composition of ice wedges indicating extremely low winter temperatures. Sediments had a prevalent fluvial origin. For the second phase (Early Karginsky Interstadial, Middle Weichselian, MIS 3, about 50 to 35–34 ka BP), pollen data suggest rather warm and wet climates (temperatures 0.5–1.5 1C warmer and precipitation 25–75 mm higher than today) for the Taymyr Peninsula, but treeless vegetation and rather cold and dry climate for Laptev Sea coast (Bykovsky Peninsula and Bol’shoy Lyakhovsky Island). In the third period (Late Karginsky, 33 to 23–22 ka BP) pollen records from the northern Taymyr Peninsula and Laptev Sea coast indicate a vegetation cover dominated by open steppe-like herb communities. Climatic conditions were rather severe (with temperatures 2–5 1C colder and precipitation 50–100 mm lower than today; Kuznetsova et al., 2003). During the following period (Last Glacial Maximum, MIS 2, between 22 and 15 ka BP) the most unfavourable environmental conditions can be detected. This phase has been interpreted as an extremely cold and dry one, characterised by sparse vegetational cover and low pollen productivity. Insects and mammals are documented by scanty remains, and only a few dates from woolly mammoth bones have been obtained (Kuznetsova et al., 2001). Between 15 and 12 ka BP, a remarkable change in environmental conditions can be inferred from both geochemical and paleontological data. Vegetation (macroflora and high pollen productivity) as well as insect remains indicate temperate-warm and humid climate conditions. The temperatures were 1.5 1C warmer and precipitation ca. 25 mm higher than today (Schirrmeister et al., 2002). A short climate improvement is particularly evident about 12 ka BP (Bølling-Allerød Interstadial). Possibly since ca. 20 ka BP to 11 ka, the precipitation source area changed as documented by stable isotope data from ice wedges. Moreover, during this phase, thermal erosion and thermokarst started, fluvial transport of clastic material began, and peaty soil formation took place. The climate and environment were the most favourable of all the Late Pleistocene for woolly mammoth. M. primigenius remains particularly are found in the area. Throughout the last phase, and until about 8 ka BP, the degradation of permafrost by thermokarst processes and the formation of new landscapes with a great number of thermokarst lakes are consistent with early Holocene climatic improvement. Moreover, gradual paleoenvironmental changes are visible since about 4.5 ka BP (Schirrmeister et al., 2002).
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3. Materials and methods Strontium isotope analyses were conducted for 26 M. primigenius tusks from Northern Yakutia Late Pleistocene deposits (Fig. 1), and 27 14C dated bones of M. primigenius from Bol’shoy Lyakhovsky Island (New Siberia Islands) (11 specimens), Lena River Delta (10 specimens) (Fig. 2). Single specimens from the Omoloy River and Omulyakhskaya Guba, as well as a few specimens of Equus ferus (Lena River Delta) and Bison priscus (Bol’shoy Lyakhovsky Island) have been analysed for comparative purposes. Accordingly, a total of 39 M. primigenius samples have been studied. Strontium isotope values have been obtained from solid rock (13 samples) and silt (2 samples) collected from Bol’shoy Lyakhovsky Island and in the Kolyma River area (3 silt samples). Tusk and bone samples for isotope analyses were mechanically cleaned. To avoid the diagenetic Sr, which can modify the 87Sr/86Sr ratios, samples of mammal bones and tusks were pre-treated with 1.0N acetic acid and then washed with bidistilled water. Hundred milligram of sample were dissolved in 2.0 N HCl, and Sr chemical separations were performed using standard ion-exchange chromatographic methods. Rock and soil samples were dissolved by HNO3 and HF acid solutions and strontium was obtained using the same methodology employed for the analyses of mammal bones and tusks. The Sr was deposited as Sr(NO3)2 on the W filament and the isotope 87Sr/86Sr ratios were measured by VG 54E mass spectrometry. The measured ratios were fractionation-corrected to an 86Sr/88Sr value of 0.1194. The determinations of 87Sr/86Sr on the NBS 987 strontium carbonate standard yielded values equal to 0.710247 0.00002 (2s).
Fig. 2. Location of Late Pleistocene mammals complex’ bones and samples of rocks studied. Mammal bones: 1: the Delta Lena River; 2: Bol’shoy Lyakhovsky Island (New Siberia Islands); 3: the Omoloy River area and 4: Omulyakhskaya Guba. Samples of rocks: I: Bol’shoy Lyakhovsky Island; II: Duvanny Yar (Low the Kolyma River area).
Table 1 Strontium isotope composition of mammoths’ tusks (location see Fig. 1) (s ¼ 70.00001) Samples no.
87
Sr/86Sr
2 14 15 18 42 70 77 101 104 125 139 141 151
0.71165 0.71102 0.71102 0.71072 0.71110 0.71241 0.71085 0.71230 0.71015 0.71091 0.71059 0.71137 0.71153
Samples no.
87
Sr/86Sr
160 167 190 211 212 216 219 221 226 245 256 266 278
0.71130 0.71088 0.71103 0.71370 0.71319 0.71087 0.71112 0.71106 0.71428 0.71156 0.71402 0.70976 0.70920
4. Results and discussion
Fig. 1. Location of mammoth’s tusks studied.
The results obtained for tusk samples from Northern Yakutia region (Table 1, Fig. 3) discriminate three M. primigenius groups. The first group includes samples from maritime lowlands (Yana-Indigirka interfluve, Kolymian lowland) covered by thick Pleistocene sediments (such as loess-like covering loam, lacustrine-swamp or alluvial deposits). Their 87Sr/86Sr values range from 0.70920 to 0.71130 (average value 0.7107570.00056, n ¼ 12). Unfortunately, only a few 87Sr/86Sr analyses were conducted from the Pleistocene sediments (‘‘Icy complex’’). The values 0.70998–0.71100 (Table 2) are in good
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Fig. 3. 87Sr/86Sr ratios in tusks of Late Pleistocene mammoths from Northern Yakutia.
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accordance with those obtained for the M. primigenius specimens (0.71072–0.71102). Moreover, the results fit with data available for mammoth tusks from valleys whose relatively small rivers (the Berelekh River, the Alazeya River, the Malaya Kuropatoch’ya River) drain only Pleistocene sediments (Berelekh River: 87Sr/86Sr ¼ 0.71085; Alazeya River: 87Sr/86Sr ¼ 0.71087; Malaya Kuropatoch’ya River: 87Sr/86Sr ¼ 0.71110). They are here considered as ‘‘standard’’ values for animals inhabiting territories where these deposits crop out. Accordingly, the strontium ratio obtained for M. primigenius samples from YanaIndigirka interfluve, Kolymian lowland regions could indicate resident populations. The second group consists of samples from areas where the Palaeozoic and Precambrian basement complex and the Mesozoic granites crop out. The values obtained for samples from Tommot massif area (87Sr/86Sr ¼ 0.71370), and the western periphery of Poluusny hills (87Sr/86Sr ¼ 0.71319) are consistent with the value obtained for basement complex rocks are 87Sr/86Sr40.71400 (Maslovskaya et al., 1980). Moreover, some specimens from Bol’shoy Lyakhovsky Island show a strontium ratio (87Sr/86Sr ¼ 0.71402–0.71428) similar to those obtained for sandstone, granite and silt deposits cropping out in this area (87Sr/86Sr ¼ 0.71320–0.71484) (Table 2). The scarcity of samples from Bol’shoy Lyakhovsky Island in this group prevents any hypothesis. On the other hand, values of M. primigenius samples from the Ozhogina River valley (left tributary of the Kolyma River) are intermediate (87Sr/86Sr ¼ 0.71241) between the first and second groups. Moreover, the
Table 2 Strontium isotope composition (87Sr/86Sr) of rocks cropping out in Nothern Yakutia (location see Fig. 2.) SE part of Bol’shoy Lyakhovsky Island (New Siberian Archipelago) Age (period)
87
200750 million years 200750 million years 200750 million years 200750 million years 200750 million years 200750 million years 200750 million years 200750 million years Jurassic Jurassic 115 million years 115 million years 115 million years
n.d. 0.71469 n.d. 0.71744 0.71320 0.71719 0.71744 0.71777 0.71043 0.71039 0.71369 0.71120 0.70730
Southern coast of Bol’shoy Lyakhovsky Island (New Siberian Archipelago) 46LYA-3TZ-1-5 Aleurite (silt) 126LYA-1TZ-5 Aleurite (silt)
54050+31302250 yearsa 35680+400390 yearsa
0.71484 n.d.
Low reach of the Kolyma River area (Dyvanny Yar) A42 Aleurite (silt) with low ice content A50 Aleurite (silt)
15,000–20,000 years 35,000–40,000 years
0.70998 0.71000
Sample no. 109 304/8 301/2 144/2 145/1 148/1 144/11 205/3 180/11 117/1 501/1 320/1 436/2
Argillite Sandstone Argillite Sandstone Sandstone Argillite Black argillite Argillite Gabbro-diabase Diabase Granite Diorite Diorite (granodiorite)
Sr/86Sr
The obtained values have not been correct because of the age of bones are to recent to affecting the obtained strontium ratio. n.d., not detectable. a Andreev, Schirrmeister et al. (personal communication).
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0.71350 0.71300 0.71250
87Sr/86Sr
0.71200 0.71150 0.71100 0.71050 0.71000 0.70950 60,000
50,000
40,000
30,000
20,000
10,000
0
Age, years Fig. 4. Evolution of strontium isotope composition in Late Pleistocene mammal bones from Northern Yakutian region.
strontium ratio is higher than that obtained for silt deposits from the Kolima River area (Table 2). Accordingly, the hypothesis that this sample belongs to ‘‘non-resident’’ individuals cannot be ruled out. To the third group have been ascribed samples from arctic coasts and islands (Bykovsky Peninsula, Omulyakhskaya Guba, southern coast of Dmitry Laptev strait ¼ Oiaygossky Yar, Bol’shoy Lyakhovsky Island, Makar Island, Ion Island) whose strontium ratios range from 0.70976 to 0.71294 (Tables 1 and 3), the highest values corresponding to samples from Bol’shoy Lyakhovsky Island (87Sr/86Sr ¼ 0.71294 for the M. primigenius sample GIN-10714, dated at about 39.6 ka; 87 Sr/86Sr ¼ 0.71203 and 0.71208 for two B. priscus samples dated, respectively, around 41.5 and 38.2 ka) (Fig. 4), even excluding the above mentioned ones (0.71402 and 0.71428). On the other hand, taking into account just the mammoth samples from the Lena Delta, dated from about 34 to 13 ka, the range of strontium ratio is less, ranging from 0.71055 to 0.71153 (Table 3). Marine surface sediments of the Laptev Sea in area between deltas of the Lena River and the Yana River and New Siberian Islands have values 87 Sr/86SrX0.71365–0.71651 (Eisenhauer et al., 1999), confirming the number of different rocks cropping out in the surrounding mainland. Accordingly, taking into account the great variability of bedrock supporting the vegetational cover, it is not a simple task to understand and explain the different use of shelf, continental and island pastures due to changes of sea level in the Late Pleistocene. For instance, did mammoths from Oiaygossky Yar and the Lena Delta prefer continental pastures? Were the high values (87Sr/86Sr40.71400) of mammoths from Bol’shoy Lyakhovsky Island caused by the exposure of ancient crystalline rocks? Did mammoths from Makar Island use both continental and shelf pastures (0.71230)?
In general, the results support the hypothesis that migrations of Yakutian mammoths (at least for individuals or populations) were limited to several hundred kilometres. This conclusion could be indicated by the high 87Sr/86Sr values of mammoth tusks included in the second group, due to relatively reduced exposure of crystalline rocks. Moreover, the different soil and pasture exploitation and migratory behaviour of M. primigenius populations inhabiting this area, is confirmed by the C and N stable isotope values measured in their hair. Indeed, seasonal variation can be inferred for the analyses (Iacumin et al., 2005 and unpublished data). Consequently, it is likely that different mammoth populations used different pastures, even in the relatively small Yakutian region, depending on typology of outcropping rocks, changes of sea level in Late Pleistocene or different temporary/permanent migrations. Moreover, the results obtained for 14C dated bones of M. primigenius (Fig. 4) indicate that the only animals inhabiting Bol’shoy Lyakhovsky Islands during 38,200–41,500 B.P. used shelf pastures. This indicates relatively low sea level in the Karginsky interstadial (MIS 3). Probably, mammoth from Bol’shoy Lyakhovsky Islands (22,500 BP) and one from the Lena River Delta (34,000 BP) visited the shelf occasionally. Conversely, it seems the Laptev Sea shelf between the delta of the Lena River and New Siberian Island (varying in present depth from 20 to 40 m) was not visited by herbivores during the Late Pleistocene sea level lowering. 5. Remarks The preliminary results highlight the difficulty of discriminating among resident, temporary migrant or long-distance newcomers if the sampling is not consistent, and limited radiocarbon dated bones and samples are available for the analysis.
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Table 3 Strontium isotope composition (87Sr/86Sr) of late Pleistocene mammals complex’ bones from Northern Yakutia (location see Fig. 2) 14
C date
7s infinite dates
Mammuthus primigenius 12,030 60 12,500 50 13,100 500 13,740 50 145,00 140 19,200 220 20,200 100 20,800 600 22,100 1000 24,300 200
Lab. no.
Region
Lat., 1N
Long., 1E
Object
87
Sr/86Sr s ¼ 70.00001
GIN-10713 GIN-10716 GIN-10242 GIN-12041 GIN-10240 GIN-10235 GIN-10236 GIN-10248 GIN-10707 GIN-10264
B.L.I. B.L.I. D.L.R. Omulyakh D.L.R. D.L.R. D.L.R. D.L.R. B.L.I. D.L.R.
73.32 73.33 71.79 73.40 71.79 73 71.79 71.79 73.32 71.79
141.39 141.33 129.40 141.50 129.40 128.50 129.40 129.38 141.37 129.40
0.71118 0.71102 0.71103 0.71153 0.71119 0.71132 0.71121 0.71080 0.71172 0.71104
27,400 28,000
800 180
GIN-10262 GIN-10706
D.L.R. B.L.I.
71.79 73.32
129.40 141.37
30,200 30,720 31,500 31,900 34,000 37,800 39,600 40,200 43,600 48,000 50,650
400 200 650 400 500 900 1000 900 1000 2000 1820
GIN-10719 GIN-12042 GIN-10249 GIN-12037 GIN-10261 GIN-10660 GIN-10714 GIN-10703 GIN-10717 GIN-10709 KIA-10681
D.L.R. Omoloy R. D.L.R. B.L.I. D.L.R. B.L.I. B.L.I. B.L.I. B.L.I. B.L.I. B.L.I.
72.90 70.65 71.78 72.30 71.79 73.34 73.34 73.34 73.34 73.34 73.28
123.35 133.35 129.42 144.25 129.40 141.28 141.31 141.31 141.31 141.31 141.82
ulna fr. tusk fr. pelvis fr. tusk fr. pelvis fr rib fr. scapuia fr. metacarpale II pelvis fr thoraic vertebra limb bone fr. ulna (with marrow) cranium tusk fr. metatarsale III tusk fr. limb bone fr. vetebra femur fr. humerus scapula fr. tusk fr. molar
Equus ferus 16,380 35,900
120 600
GIN-10233 GIN-10269
D.L.R. D.L.R.
71.79 71.79
129.38 129.40
radius femur
0.71132 0.71143
Bison priscus 38,200 41,500
700 1100
GIN-10663 GIN-10686
B.L.I. B.L.I.
73.34 73.33
141.31 141.33
radius Sacrum fr.
0.71208 0.71203
0.71081 0.71083 0.71132 0.71130 0.71055 0.70976 0.71168 0.71139 0.71294 0.71290 0.71122 0.71128 0.71132
B.L.I.: Bol’shoy Lyakhovsky Island (New Siberia Islands); D.L.R.: the Delta Lena River; Omoloy R.: the Omoloy River; Omulyakh: Omulyakhskaya Guba.
Taking into account global changes of sea level, the Laptev Sea shelf was mainly drained during the sea level lowering in the Late Pleistocene. Herbivores, and especially mammoths, did not utilise shelf pastures. Therefore, the results open several questions: what is the reason for not visiting the shelf? Was the shelf occupied by other mammal populations whose remains lie on the sea bottom? Was the territory too boggy for large animals? Why did mammals prefer vegetation from inland and not shelf landscapes? Ongoing research might clarify some issues.
Acknowledgements We would like to thank the people who gave us the opportunity to study samples of bones and rocks from Yakutia, in particular Drs. A. Kuzmichev and L. Schirrmeister. Investigations were supported by Agreement CNR–RAS and RFBR (Grant 04-05-65314).
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