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Quaternary Research 57, 355–370 (2002)doi:10.1006/qres.2002.2322, available online at http://www.idealibrary.com on
Late Quaternary Stratigraphy, Glacial Limits, and Paleoenvironmentsof the Marresale Area, Western Yamal Peninsula, Russia
Steven L. Forman1
Department of Earth and Environmental Sciences, University of Illinois at Chicago, Chicago, Illinois 60607-7059
Olafur Ingolfsson
Earth Sciences Center, Goteborg University, Box 460, Goteborg, Sweden S-405 30
Valery Gataullin
Oil and Gas Research Institutes, Riga, LV 2006, Latvia
William Manley
Institute of Arctic and Alpine Research, University of Colorado, Boulder, Colorado 80309-0450
and
Hanna Lokrantz
Earth Sciences Center, Goteborg University, Box 460, Goteborg, Sweden S-405 30
Received August 1, 2001; published online April 23, 2002
Stratigraphic records from coastal cliff sections near theMarresale Station on the Yamal Peninsula, Russia, yield new insighton ice-sheet dynamics and paleoenvironments for northern Eurasia.Field studies identify nine informal stratigraphic units from oldestto youngest (the Marresale formation, Labsuyakha sand, Kara di-amicton, Varjakha peat and silt, Oleny sand, Baidarata sand, Betulahorizon, Nenets peat, and Chum sand) that show a single glacia-tion and a varied terrestrial environment during the late Pleistocene.The Kara diamicton reflects regional glaciation and is associatedwith glaciotectonic deformation from the southwest of the underly-ing Labsuyakha sand and Marresale formation. Finite radiocarbonand luminescence ages of ca. 35,000 to 45,000 yr from Varjakhapeat and silt that immediately overlies Kara diamicton place theglaciation >40,000 yr ago. Eolian and fluvial deposition ensuedwith concomitant cryogenesis between ca. 35,000 and 12,000 calyr B.P. associated with the Oleny and the Baidarata sands. Thereis no geomorphic or stratigraphic evidence of coverage or proxim-ity of the Yamal Peninsula to a Late Weichselian ice sheet. TheNenets peat accumulated over the Baidarata sand during much ofthe past 10,000 yr, with local additions of the eolian Chum sandstarting ca. 1000 yr ago. A prominent Betula horizon at the base ofthe Nenets peat contains rooted birch trees ca. 10,000 to 9000 cal yrold and indicates a >200-km shift northward of the treeline from
1 To whom correspondence should be addressed. E-mail: [email protected].
the present limits, corresponding to a 2◦ to 4◦C summer warmingacross northern Eurasia. C© 2002 University of Washington.
35
INTRODUCTION
The formation of high-latitude ice sheets in the Quaternaryhas led to fundamental shifts in the climate system. Continental-scale glaciation increases planetary albedo and globally altersplanetary wave structure (e.g., Kutzbach et al., 1994). In turn,ice-sheet freshwater inputs and associated isostatic and eustaticdriven changes of the bathymetry of continental shelf seas thatborder northern Eurasia can significantly alter global oceancirculation (Forman et al., 2000). The Eurasian ice sheet whichterminated in the Siberian lowland or adjacent shallowcontinental shelf modulated fresh water flux into the globalocean through direct input and potential blockage of 2 of the10 largest river systems in the world, the Ob and Yenisei rivers(Rudoy and Baker, 1993). Continental-scale proglacial lakesthat may have formed with ice-sheet damming of drainagesin northern Siberia would have rerouted fresh water from theArctic Ocean to lower latitude seas, potentially impacting NorthAtlantic deep-water formation (Weaver, 1995). Thus, theeastern limit of the Eurasian ice sheet and associated deglacialchronology is critical to assess whether the last glaciation
5 0033-5894/02 $35.00Copyright C© 2002 by the University of Washington.
All rights of reproduction in any form reserved.
356 FORMAN ET AL.
FIG. 1. (A) Late Weichselian and early/middle Weichselian–inferred ice-sheet limits in northern Eurasia from Svendsen et al. (1999), Forman et al. (1999),
and Polyak et al. (2000a). (B) Yamal Peninsula showing major rivers and spot elevations (meters). (C) Enlargement of Corona Satellite image 054 050 and 054051 taken on September 8, 1964, of western Yamal Peninsula, Russia. Kilometer-scale bar shows location of studied sections.
E
WESTERN YAMAL Presulted in continental-scale reorganization of Arctic hydro-logy.
Recent field-based research suggests that the maximumEurasian ice-sheet limit in the Pechora Lowland was reached> 40,000 yr B.P., with the last glacial maximum position 10 sto 100 km seaward in the southern Barents Sea (Polyak et al.,2000a; Svendsen et al., 1999). The presence of glacial flutesand till in the central Barents Sea is a definitive indicator that anice sheet was grounded at the seabed during the Late Weichselian(Gataullin et al., 1993). This ice sheet inundated adjacentSvalbard, expanded northward to the edge of the continentalshelf (Landvik et al., 1998), and filled the >500-m-deep FranzVictoria and Santa Anna troughs (Lubinski et al., 1996; Polyaket al., 1997). Studies of the postglacial emergence on Franz JosefLand and Novaya Zemlya indicate maximum ice-sheet loadingover the central Barents Sea and eastern Svalbard (Forman et al.,1997). This isostatic response within prescribed glacier limitsand coupled with refinements in modeling Earth rheology is thebasis for reconstructing a 2-km-thick ice sheet over the BarentsSea, with limited coverage over the Kara Sea (Lambeck, 1995;Peltier, 1996). Recent studies have identified deposits on low-lands adjacent to the southern Kara Sea that antedate the LateWeichselian and are one basis for inferring Late Weichselianice limits seaward of northern Siberia (Astakhov et al., 1996;Forman et al., 1999; Mangerud et al., 2001). One marine ge-ologic study places the Late Weichselian ice-sheet limit in theKara Sea east of the Novaya Zemlya Trough (Polyak et al.,2000b). Few observations constrain the eastern limit of lateQuaternary ice sheets in northern Eurasia (e.g., Forman et al.,1999; Moller et al., 1999). Thus, we present a detailed lithostrati-graphic record and associated radiocarbon and luminescenceages for western Yamal Peninsula (Fig. 1). This contribution ex-pands on a previous report (Forman et al., 1999) and gives newinsights on glacier coverage and changing paleoenvironmentsduring the past ca. 60,000 yr.
CHRONOLOGIC CONTROL
Primary age control is provided by accelerator mass spectrom-etry (AMS) radiocarbon dating of terrestrial organics (Table 1)and thermoluminescence and optically stimulated luminescenceages on fine-grained (4–11 µm) and coarse-grained (100–150 µm) extracts from sediment (Table 2). For many stratigra-phic units, the Varjakha peat and silt, the Oleny sand, theBaidarata sand, the Nenets peat, and the Chum sand plant ma-terial dated is in situ and often collected from growth position.Organic remains in the Marresale formation, the Labsuyakhasand, and the Kara diamicton are allochthonous and predate thedeposit.
Infrared-stimulated luminescence (IRSL) and thermolumi-nescence (TL) ages are determined on the polymineral fine-grained fraction from the Varjakha peat and silt, the Oleny sand,and the Baidarata sand by multiple aliquot additive dose proce-
dures (Forman, 1999). One coarse-grained quartz aliquot fromthe Baidarata sand (UIC656) was dated by green-stimulated lu-NINSULA, RUSSIA 357
minescence (Table 2). IRSL and TL ages are nearly identicalfor samples UIC649, UIC650, UIC652, and UIC653 (Table 2),indicating that the luminescence signal of the Oleny sand andVarjakha peat and silt is fully solar reset prior to deposition. Theconcordance between luminescence ages and corresponding cal-ibrated (“calendar”) radiocarbon ages gives added confidence inthe concluded chronology (Table 2).
THE STRATIGRAPHIC RECORD
Most of the Yamal Peninsula is covered by Quaternary sedi-ments, which overlie Mesozoic and Cenozoic deposits, exceed-ing 4 km in thickness (Rostovtsev, 1982). The pre-Quaternarydeposits are largely unlithified silts and clays. LithifiedPaleozoic rocks occur south and west of the Yamal Peninsulain the Polar Ural Mountains and adjacent highlands, VaygachIsland, and the Novaya Zemlya archipelago.
The coastal cliff sections of western Yamal Peninsula con-tain a rich record of late Quaternary environmental change.Previous studies have documented the continuity of lithostrati-graphic units and investigated the origin of ground ice (Astakhovet al., 1996; Kaplyanskaya and Tarnogradsky, 1986). Other stud-ies (Arslanov et al., 1986; Bolihovsky et al., 1989; Gataullin,1988; Krapivner, 1986) have included part of the YamalPeninsula sequence in regional stratigraphic assessments andprovide supportive stratigraphic observations and 14C ages(Table 1). Our field studies concentrated on the well-exposedQuaternary stratigraphic sections in coastal cliffs 10 to 25 m highwithin 5 km south of the Marresale Station (Fig. 1). The locationof sections (e.g., “2.51-km” section) was determined in kilome-ters measured from the south bank of Marresale River at the coast(N69◦43.27′ E66◦48.80′). We define nine informal stratigraphicunits, from oldest to youngest, which are presented below: theMarresale formation, Labsuyakha sand, Kara diamicton,Varjakha peat and silt, Oleny sand, Baidarata sand, Nenets peat,Betula horizon, and Chum sand (Fig. 2).
Marresale Formation
The Marresale formation underlies all other exposed strata onthe west coast of Yamal Peninsula. This formation is composedof >300-m-thick, rhythmically bedded, stratified and massiveclay silt and silty sands. Lithology and bedding characteristicstogether with remains of foraminifera, diatoms, pollen, and plantmacrofossils indicate that it was deposited in a prodeltaic marineenvironment (Gataullin, 1988). The thickness of the unit indi-cates that it was deposited during a period of subsidence. Thesource of sediments may be a prograding delta of the Ob Riversometime in the middle to late Pleistocene (Gataullin, 1988).
The most complete section of the Marresale formation is ex-posed in coastal cliffs that are 20 to 35 m high, extending 20 kmnorth and 3 km south of the Marresale Station (Fig. 1). The ex-posed strata are folded here into a large, complex anticline witha northwest–southeast strike over 150–200 m in amplitude and a
15-km folding wavelength (Gataullin, 1988). In the center of thisstructure, there are abundant low-angle folds with amplitudes
358 FORMAN ET AL.
TABLE 1Radiocarbon Ages for Quaternary Stratigraphic Units on Western Yamal Peninsula, Russia
Weight Depth Laboratory Age,Section location Reference Material dated (mg) (m) numbera 14C yr B.P.
Labsuyakha sandLabsuyakha River mouth This study Abraded wood 27,000 GX-21800 >41,910Yarayakha River mouth Gataullin, 1988 Plant remains LU-285 33,160 ± 550Station Ust’-Yuribei Gataullin, 1988 Peat LU-1166 40,930 ± 1580Kharasavey River mouth Gataullin, 1988 Peat Ri-284 35,404 ± 340
Gataullin, 1988 Peat Ri-281 >31,520Kharasavey borings Krapivner, 1986 Peat GIN-2810 35,100 ± 1000
Krapivner, 1986 Peat GIN-2811 >26,000Maresalle Station Zubakov, 1972 Wood LU-11 >55,500
Bolihovsky et al., 1989 Wood GIN-5199 31,100 ± 400Bolihovsky et al., 1989 Wood GIN-5198 42,000 ± 100
Kara diamictonKharasavey River mouth Gataullin, 1988 Wood Ri-299 35,973 ± 370Maresalle Station Arslanov et al., 1986 Log LU-1270 43,110 ± 1540
Varjakha peat and silt4.1 km site This study Peat plant 50 9.6 NSRL-10307 32,800 ± 390
This study Peat plant 250 9.3 AA-26940 32,700 ± 580This study Peat plant 106 8.1 NSRL-10308 33,400 ± 450This study Peat plant 237 6.5 NSRL-10309 32,400 ± 440This study Peat plant 105 5.7 AA-26939 32,400 ± 500
4.5 km site This study Plant fragment 6 7.1 AA-26937 29,860 ± 720from ice wedge
4.70 km site This study Peat plant 120 9.0 NSRL-10310 30,100 ± 260This study Peat plant 1000 8.0 AA-26941 27,980 ± 380This study Peat plant 750 7.0 AA-26942 28,560 ± 360
4.73 km site This study Peat plant 292 5.7 AA-26945 28,233 ± 3625.1 km site This study Peat plant 400 8.8 AA-26944 28,359 ± 327
Oleny sand4.70 km site This study Vascular plant 49 6.4 NSRL-10312 25,100 ± 560
This study Vascular plant 34 5.7 NSRL-10311 27,300 ± 4304.73 km site This study Vascular plant 27 5.5 AA-26946 28,280 ± 421
This study Vascular plant 18 4.9 AA-26947 27,450 ± 320This study Vascular plant 6 3.9 AA-26948 26,230 ± 260
Baidarata sand1.61 km site This study Vascular plant 42 5.2 AA-26949 15,025 ± 95
This study Vascular plant 104 4.7 AA-26950 14,280 ± 90This study Vascular plant 1540 2.6 AA-26951 13,225 ± 85This study Vascular plant 378 1.9 AA-26952 12,220 ± 75
2.04 km site This study Vascular plant 15.3 6.7 AA-26962 16,360 ± 120This study Vascular plant 20.0 6.6 AA-26961 15,020 ± 120This study Vascular plant 18.0 6.3 AA-26960 14,140 ± 100This study Vascular plant 15.9 4.0 AA-26959 13,845 ± 80This study Vascular plant 9.3 2.7 AA-26958 12,980 ± 80
2.51 km site This study Vascular plant 26.1 3.8 AA-26965 13,975 ± 953.39 km site This study Vascular plant 9.4 3.8 AA-26964 13,060 ± 100
This study Vascular plant 27 3.2 AA-26966 13,990 ± 100Marresale Station Gataullin, 1988 Moss Tln-1059 13,830 ± 260
Gataullin, 1988 Vascular plant Tln-1026 13,970 ± 140Gataullin, 1988 Moss Tln-1059 13,830 ± 260Gataullin, 1988 Vascular plant Tln-1026 13,970 ± 140
Marresale Station Bolihovsky et al., 1989 Moss GIN-5197 13,280 ± 150Bolihovsky et al., 1989 Moss GIN-5196 13,340 ± 200Gataullin & Forman, unpub. Vascular plant 47 4.5 AA-20496 14,160 ± 120Gataullin & Forman, unpub. Vascular plant 27 3.8 AA-20495 13,780 ± 190
Gataullin & Forman, unpub. Vascular plant 50 2.6 AA-20494 13,750 ± 110Gataullin & Forman, unpub. Vascular plant 40 1.6 AA-20493 13,265 ± 150
WESTERN YAMAL PENINSULA, RUSSIA 359
TABLE 1—Continued
Weight Depth Laboratory Age,Section location Reference Material dated (mg) (m) numbera 14C yr B.P.
Betula horizon1.61 km site This study Betula bark 487 1.29 AA-26967 8865 ± 65
This study Betula wood 70900 1.00 GX-23496 7990 ± 652.04 km site This study Betula twig 532 1.80 AA-26957 8345 ± 60
This study Betula bark 17000 1.20 GX-23495 8050 ± 80This study Betula bark 25900 1.15 GX-23943 8620 ± 70This study Betula bark 14000 0.70 GX-23494 8110 ± 90
Kharasavey River mouth Gataullin & Forman, unpub. Betula wood 21900 1.20 GX-21799 8780 ± 150Marresale Station Gataullin & Forman, unpub. Betula bark 20700 1.05 GX-21801 8610 ± 150
Bolihovsky et al., 1989 Betula wood RUH-5204 8240 ± 70Arslanov et al., 1986 Betula wood LU-1266 7820 ± 70
Nenets peat1.61km site This study Peat plant 14 0.20 P980087121 1153 ± 112.04 km site This study Peat plant 127 1.25 AA-26956 8195 ± 60
This study Peat plant 17.5 0.25 AA-26955 1015 ± 40This study Peat fragment 250 1.85 AA-26938 7165 ± 75
in ice wedgeMarresale Station Gataullin, 1988 Peat Ri-362 4640 ± 150
Arslanov et al., 1989 Peat LU-1266 7820 ± 70Arslanov et al., 1989 Peat LU-1267 9010 ± 100Arslanov et al., 1989 Peat LU-1268 6400 ± 250
Kharasavey River mouth Gataullin & Forman, unpub. Peat plant 28 4.0 AA-20490 9365 ± 100Gataullin & Forman, unpub. Peat plant 31.6 3.4 AA-20489 8945 ± 80Gataullin & Forman, unpub. Peat plant 306 1.7 AA-20488 5980 ± 80Gataullin & Forman, unpub. Peat plant 38 1.1 AA-20487 5785 ± 80
Chum sand2.04 km site This study Vascular plant 14.4 0.20 AA-26954 Post-bomb
This study Vascular plant 11.2 0.10 AA-26953 80 ± 402.90 km site This study Vascular plant 57 0.95 P98-08692A 620 ± 6
a Radiocarbon laboratories abbreviations: AA: NSF-Arizona AMS Facility, Univ. of Arizona, Tucson, AZ; GIN: Geological Institute. Russian Academy ofSciences, Moscow; GX: Geochron Laboratories, Cambridge, MA; LU Geographical Research Institute, St. Petersburg State University; NRSL: INSTAAR, Univ.
of Colorado, P: PRIME AMS Laboratory; Purdue University. Tln: Radiocarbon Institute of Science—Application Research, Riga, Latvia.of 10–50 m and wavelengths of 100–500 m (Fig. 3). Sharplyasymmetrical, commonly strongly compressed anticlinal foldsoccur, with overturning to the northeast. The magnitude of fold-ing and brecciation increases substantially near the contact withthe overlying Kara diamicton.
Labsuyakha Sand
The Labsuyakha sand occurs as shallow paleochannel fillson top of the Marresale formation. The infillings vary in widthfrom a few meters to ∼1 km and thicknesses range from a fewmeters to ∼50 m. Labsuyakha sand consists of two major litho-facies. A lower facies of predominantly planar and trough cross-bedded fine-to-medium sand and an upper facies of ripple andhorizontally bedded fine sand and silt. The lower facies con-tains abundant plant detritus including twigs and tree trunks;coal particles, granules of amber, occasional reindeer antlers(Rangifer sp.), shell fragments, and pebble gravel also occur.
This facies constitutes a basal and point bar sand of a braidedfluvial environment. The upper facies is characterized by rip-Laboratory, Institute of Geology at Tallinn Technical University, Estonia; Ri:
pled and horizontally bedded sand, with localized occurrence ofcentimeter-scale silt beds, some containing allochthonous clast-sized pieces of gytja and peat. This facies is interpreted as afloodplain deposit with overbank silts.
The age of the Labsuyakha sand is not well known; a numberof 14C analyses on preserved tree logs and other plant detritusyielded ages between >26,000 and 42,000 14C yr B.P. (Table 1).The occurrence of Rangifer sp. antlers in the Labsuyakha sandprovides additional, but broad age control. In the Europeanbiostratigraphic record, Rangifer sp. is a younger steppe faunafrom the Middle Pleistocene record at Sussenborn, Germany(Kahlke, 1969), and a correlative age for the Labsuyakha sandis <500,000 yr.
Kara Diamicton
The Kara diamicton is a complex unit containing large ice bod-ies and massive and stratified diamictons. Most notably, there are
a variety of m-to-km-scale glacial tectonic structures associatedwith the Kara diamicton that extensively deform the underlying
360
FORMAN ET AL.TA
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WESTERN YAMAL PENINSULA, RUSSIA 361
FIG. 2. Summary of stratigraphic sections for a 4-km length of coastal cliff exposures immediately south of the Marresale Station. Shown are associated
cumbent folds and low-angle thrusts defined by debris bands
radiocarbon (103 14C yr B.P.) and luminescence ages (103 yr B.P.).
Labsuyakha sand and Marresale formation (Fig. 3). Coastal sur-veys indicate that the Kara diamicton is widespread on westernYamal Peninsula, but has yet to be identified north of 70◦50′N.The diamicton ranges in thickness from <1 to >20 m in the sec-tions north of the Marresale Station. The diamicton is commonlyfrozen, containing ≤80% ice. The enclosed ice contains debrisbands, deformed sandy intraclasts, recumbent folds, and fine pli-cation of thin ice within bodies of massive ice. We concur withprevious interpretations that the ice structures indicate burial ofglacier ice originally associated with deformation of underlyingsediments and deposition of the Kara diamicton (Astakhov et al.,1996; Kaplyanskaya and Tarnogradsky, 1986). The basal contactof the Kara diamicton is highly erosive and tectonically discor-dant, with thrusts from the southwest forming numerous large(>10 m) nearly isoclinal, recumbent to gently inclined folds.Parallel and harmonic folds occur but large, overturned chevronfolds are most conspicuous. Close to the Marresale Station, thefolds are highly asymmetrical, with uniform vergence toward thenortheast, indicating deforming thrusts from the southwest. Theorientation of glaciotectonic structures indicates ice-sheet flowfrom the southwest emplaced the Kara diamicton and deformed
sediments on Yamal Peninsula.The Kara diamicton is a complex heterogeneous unit and issubdivided into three facies: stratified diamicton, massive-icediamicton, and clayey-silt diamicton. The lowermost facies isa stratified diamicton formed largely by intense shearing, fold-ing, and dislocation of underlying sediments, such that primarysedimentary structures are destroyed. A variety of deformationoccurs ranging from tight, low-angle thrust faults and recum-bent folds to small-scale boudinage structures, shear bands, anddisharmonic and intrafolial folds. Intense shearing is indicatedby truncation and brecciation of silt and sand beds. Locally, theunderlying Labsuyakha sand is drawn upward and sheared outalong thrust faults. Large chunks of the sand are also dislocatedand rotated, with primary sedimentary structures preserved anddeposited as intraclasts, with sharp contacts with the surround-ing diamicton (Fig. 4). This facies is interpreted as a subglacialdeformation till.
A dark, massive, debris-containing ice characterizes the Karadiamicton above the stratified facies. This massive-ice diamic-ton facies is composed up to 80% of ice, but it often has alayered appearance due to alternating debris-bands and ice. Re-
in the ice indicate flow towards the northeast, consistent with
362 FORMAN ET AL.
FIG. 3. Large-scale glaciotectonic overturning of the Marresale formation with asymmetrical compression and overturning of folds to the northeast. People in
the foreground are about 1.7 m tall.subdiamicton deformations. The massive-ice diamicton faciesshows subhorizontal fissility defining lens-shaped centimeter-thick plates. The diamicton is a mixture of clay, silt, and sandfractions, but the most prominent feature is the random occur-rence of pebbles and rare clasts in the sediment. Most clasts areangular or subangular and frequently show bullet-nosed formsand carry glacial striae. Pebbles occur also singularly in the ice.The stratified- and massive-ice diamicton facies contain sparseforams and shell fragments, indicating that the glacier mayhave advanced over the seafloor (Gataullin, 1988). The prove-nance of the diamicton matrix and pebble clasts shows enrich-ment in Paleozoic shale, sandstone, and limestone originatingfrom Ural Mountain sources and Cretaceous and Paleogene siltsand clays derived from the Kara Sea. The ice–diamicton faciesis interpreted as being derived from debris-rich glacier ice withglaciodynamic structures preserved.
The massive diamicton–ice facies is capped by up to 5-m-thickmassive to crudely stratified clayey silty diamicton. It differsfrom the underlying diamicton–ice facies with glaciotectonicstructures absent. Random pebbles and occasional sand horizons<1 cm thick occur. This facies also shows vertical jointing and
small-scale normal and reverse high-angle faults. This facies isinterpreted as a supraglacial meltout till formed by the release ofglacial debris from stagnant glacier ice. Alloctchonous terrestrialorganic matter from the Kara diamicton gave radiocarbon ages>36,000 14C yr B.P. (Table 1).
Varjakha Peat and Silt
The Varjakha peat and silt overlies the Kara diamicton in thesouthern part of the study area (Fig. 5). This deposit is most con-spicuous infilling of basins 5–20 m wide and 4–5 m deep in theKara diamicton. However, this unit, mostly composed of peatis also traced for nearly a kilometer, draping the paleosurfaceof the Kara diamicton. The sediment is thickest in basins andis characterized by subhorizontal centimeter-scale alternatingbeds of sandy silt and peat layers. Peat beds are more preva-lent in the basal 1–2 m of the deposits, with sandy-silt bedsdominant in the upper 1 m. The peat is well preserved, fibrous,and dominated by Sphagnum sp. moss with <20% mineralo-genic component. The sandy-silt beds can contain up to 20%peat and are traced laterally for 10 s of meters. Individual peatplants from the Varjakha peat and silt yielded radiocarbon ages ofca. 33,000–28,000 14C yr (Table 1). Corresponding fine-grained
polymineral extracts from the Varjakha peat and silt yieldedIRSL ages of ca. 36,000–45,000 yr (Table 2).
WESTERN YAMAL PENINSULA, RUSSIA 363
FIG. 4. Stratified facies of the Kara diamicton containing a large intraclast of Labsuyakha sand, with 1.7-m tall figure for scale.
FIG. 5. Stratigraphic sections immediately north and south of the Varjakha River. The Kara diamicton occurs at section location between 4.0 and 4.3 km and
is overlain by the Varjakha peat and silt. The Oleny sand occurs over the Varjakha peat and silt with ice wedges penetrating both units. The fluvial facies of theBaidarata sand caps the sequence. asl, above sea level.
364 FORMAN
Oleny Sand
Conformably overlying the Varjakha peat and silt is the Olenysand (Fig. 5), a well-sorted fine sand to fine sandy silt withmm- to cm-scale subhorizontal and undulatory stratification ofeolian origin. Bedding in the Oleny sand is graded, with topfiner grained laminae exhibiting a diffusive lower boundary andcontaining in situ rooted vascular plant remains that indicaterepeated brief periods of subaerial exposure and subsequentburial by eolian sand (Fig. 6). Coarser beds are composed of>95% fine and very fine sand with finer beds containing 65–85% sand and the balance dominated by fine and medium silt.Syngenetic and en echelon stacked frost-crack pseudomorphsoccur in locally deformed and truncated beds and terminateat the top of fine beds attest to active cryogenesis with eo-lian deposition (Fig. 6). Near the top of the Oleny sand, abun-dant meter-scale cryogenic convolutions are associated with ahorizon of buried 1- to 2-m-wide ice wedges that represents a
FIG. 6. Photograph of the Oleny sand showing fine sand and very fine sand–silt beds and associated cryogenic deformation. Well-preserved vascular plantsare associated with the finer beds. Grey and white bars are 10 cm long.
ET AL.
significant period of subaerial exposure. Well-preserved vascu-lar plant fragments from the Oleny sand yielded radiocarbonages of ca. 25,100–28,300 14C yr (Table 1) and correspond-ing IRSL ages of ca. 30,000–33,000 yr (Table 2). A radiocar-bon age of 29,860 ± 720 14C yr B.P. (AA-26937) on plant re-mains from the base of an ice wedge indicates initial formationca. 30,000 14C yr B.P. (Table 1; Fig. 2).
Baidarata Sand
The uppermost part of the stratigraphic sequence containsinterfingering eolian and fluvial sediments, referred to as theBaidarata sand (Figs. 5 and 7). The eolian facies containsmillimeter- to centimeter-scale subhorizontal and undulatorystratified fine sand to a fine sandy silt (Fig. 7). Beds pinch andswell and are graded with abundant rooted vascular plant re-mains in the finer grained beds. Granulometry of four bed cou-plets shows that coarser beds are composed of >85% fine andvery fine sand, whereas finer beds are 75 to 70% sand and theremaining particles are predominantly silt. En echelon stacked1- to 3-cm-wide syngenetic frost-crack psedomorphs are com-mon and vertically displace beds by 1 to 20 cm. Ice wedges fromthe surface or overlying sediments penetrate the Baidarata sandand deform the sediment. Well-preserved shoots and rhizomesof European beach grass (Ammophila arenaria) occur denselythroughout this unit.
Fluvial interbeds vary in thickness from <1 to 4 m and usuallyexhibit horizontal to low-angle stratification, contain pebble- tocobble-sized silty intraclasts, and have an erosive wavy basalcontact with eolian sediments. Higher energy fluvial faciesdominate at section elevations approximately >12 m above sealevel (asl) and are characterized by cross-bedded strata withclimbing ripples and trough stratification with erosive lowercontact. Vascular plant remains from the eolian facies of theBaidarata sand yielded radiocarbon ages between ca. 15,100and 12,200 14C yr B.P. from the base to the unit top. Green-stimulated luminescence on quartz grains from the top ofBaidarata sand yielded an age of 12,500 ± 1000 yr (UIC656);a fine-grained polymineral fraction from the unit base gave19,300 ± 1600 yr (UIC657). Reworked plant remains from flu-vial facies yielded a radiocarbon age of 13,060 ± 100 14C yr B.P.(AA-26965).
Nenets Peat and Betula Horizon
The Nenets peat caps the section in many localities (Fig. 2).This fibrous peat- and sphagnum-dominated unit is thickestwhere it fills basins 1 to 4 m deep in the Baidarata sand andthins to <1 m on higher landscape positions (Fig. 7). The peatlargely remains frozen and hosts ice wedges 1 to 2 m wide,and, during the summer, the upper 1–1.5 m thaws. In the lower10 cm of peat in filled basins well-preserved Betula sp. treeremnants are rooted. These trees are rooted into the subjacent
Baidarata sand, occur in clusters of three or more, and have akrumholtz form with heights of 1–2 m and diameters of 5–12 cm.
365
The pervasiveated with the Kar
WESTERN YAMAL PENINSULA, RUSSIA
et
FIG. 7. The Baidarata sand and the overlying NenBirch leaves and bark are abundant in the surrounding peat. Ra-diocarbon ages indicate that the Nenets peat accumulated fromca. 9400 to 1000 14C yr B.P. Trees from the Betula horizon,which overlap with early peat accumulation in some localities,date from ca. 8900 to 7800 14C yr B.P. (Table 1). In many places,0.5- to 1.0-m-wide ice wedges have formed from the top surfaceof the Nenets peat. A radiocarbon age of 7165 ± 75 14C yr B.P.(AA-26938; Table 1) on a peat fragment from the center of theice wedge indicates formation after 7200 14C yr B.P.
Chum Sand
Well-sorted fine to very fine sand often occurs on hilltops andslopes (Fig. 8). This sand noticeably thickens to >1 m at theupper edge of the coastal cliff. This unit contains millimeter-to centimeter-scale laminations disrupted by massive zones 5 to30 cm thick with abundant organics and secondary accumula-tions of pedogenic silt and/or clay. The coarsest beds containover 92% fine and very fine sand, with finer and organic richbeds containing 75 to 85% sand. This eolian sand is derivedlocally from cliff faces, fluvial channels, and denuded hilltopsassociated with overgrazing by reindeer. Radiocarbon dating ofburied vascular plant remains places deposition of this sand inthe past ca. 1000 14C yr (Table 1; Fig. 2).
Late Quaternary Paleoenvironments on Yamal Peninsula
and broad scale of glacial tectonism associ-a diamicton indicates basally erosive and sub-
s peat, topped by the Chum sand at 2.1-km section.
glacially deforming ice-sheet flow from the southwest. The pres-ence of Paleozoic shale, sandstone, and limestone erratics in theKara diamicton reflects ice-sheet flow onto the Yamal Peninsulafrom source areas from Novaya Zemlya or near the Ural Moun-tains. However, the configuration and limit of the ice sheet thatdeposited the Kara diamicton is unresolved. Gataullin (1988) fa-vored that the north–northeast paleoglacier motion inferred fromthe Kara diamicton reflects lateral expansion of a southward-moving lobate glacier margin into the southern Kara Sea from asource area on Novaya Zemlya. This hypothesized lobate mar-gin is inferred to have terminated on central Yamal Peninsula,although landforms associated with it have yet to be identified(Gataullin, 1988), Recent field studies along the southwesterncoast of the Kara Sea, however, indicate that there was glacierflow prior to the late Weichselian into the Kara Sea from northern(Manley et al., 2001) and southern sources (personal commu-nication, H. Lokrantz, 2001), potentially from highlands imme-diately southwest of the Ural Mountains. A lack of chronologicdefinition for diamictons on the Yamal and Yugorsky Peninsulasprecludes correlation of glacial events.
Radiocarbon ages of ca. 33,000 14C yr and corresponding lu-minescence ages of ca. 41,000 yr for the Varjakha silt and peatoverlying the Kara diamicton provide minimum limiting agesfor this glacial event (Fig. 9). We infer an early Weichselian ageof 60,000 to 70,000 yr or more for the Kara diamicton. Thisglaciation of Yamal Peninsula may be broadly correlative with
the Markhida limit in the Pechora Lowland dated at ca. 60,000 yr(Mangerud et al., 2001). Alternatively, the Kara diamicton may
366 FORMAN ET AL.
FIG. 8. The Chum sand, which accumulated during the past 1000 yr, reflects eolian sand contributions from cliff, fluvial, and hilltop sources. Pocketknife is
9 cm long.be penecontemporaneous with an even more extensive glacia-tion in Eurasia that formed a proglacial lake system, impound-ing numerous rivers west of the Ural Mountains ca. 100,000 yrago (Mangerud et al., 2001). Glacio-isostatically raised littoral
deposits on Novaya Zemlya that are >35,000 yr old and aretraced to at least 36 m asl reflect regional glaciation that ex-ceeded ice-sheet loading associated with the Late Weichselianglaciation (Forman et al., 1999). A similar raised-marine se-quence was identified up to 12 m asl on Vaygach Island wherein situ shells yielded radiocarbon ages of ca. >40,00014C yr
and luminescence ages on quartz grains of 45,000 yr providecloser constraining ages on deglaciation (Zeeberg, 2001). At the
WESTERN YAMAL PENINSULA, RUSSIA 367
FIG. 9. Composite stratigraphy, associated radiocarbon and luminescence chronologic control, inferred paleoenvironments and concluded calibrated ages(Stuiver et al., 1998; Kitigawa and van der Plicht, 2000) for western Yamal Peninsula, Russia.
western margin of the Barents Sea ice sheet on Spitsbergen, thepenultimate glacial event(s) occurred ca. 60,000 to 80,000 yr B.P.and exceeded Late Weichselian limits and glacioistatic response(Mangerud et al., 1998; Forman, 1999). The Kara diamicton re-flects regional glaciation of the Barents and Kara seas with ice-sheet advance across Yamal Peninsula probably late in marineoxygen isotope stage 5, stage 4, or earlier, with limits poten-tially compatible with maximum ice-sheet reconstructions (e.g.,Svendsen et al., 1999).
The accumulation of the Varjakha peat and silt over the Karadiamicton surface reflects landscape stability and amelioratedclimatic conditions ca. 45,000 to 30,000 yr ago (Fig. 9). Similarpeat deposits spanning ca. 50,000–30,000 yr B.P. and containingan abundance of boreal pollen are identified in the northern low-
lands of the Lena, Ob, and Yenisei Rivers (Ukraintseva, 1993;pp. 172–221). These peat deposits may demark the KarginskyInterstade, a distinct warm period (ca. 50,000–25,000) in cen-tral north Siberia between the Late Weichselian and an earlierglaciation characterized by pollen and diatom taxa similar to theHolocene with inferred summer temperatures warmer than today(Ukraintseva, 1993; pp. 172–221). Evidence for this warmingextends to the Bering Strait, where trees expanded to or beyondcurrent limits, with peak warming registered between 35,000and 33,000 yr B.P. (Anderson et al., 2001).
The occurrence of fluvial facies of the Baidarata sand up to16 m asl elevation in coastal cliffs indicates this river system wasgraded to higher level during the Late Weichselian. The YamalPeninsula during the last glacial maximum was ∼200 km fromthe ice margin, and thus local sea level was primarily con-trolled by the eustatic fall in sea level of about 115 m (Fairbanks
et al., 1989), exposing large areas of the Kara Sea. Rivers pro-graded across the shelf with reaches on Yamal Peninsula
N
368 FORMAaggrading. The eastern expansion of the ice sheet may havebeen limited by focused river discharge at the margin (Lammerset al., 2000). The intercalation of fluvial and eolian depositsin the Baidarata sand indicates that fluvial sediments exposedon bars or abundant channels were the prime source of eolianclastics. Eolian deposition was episodic with vascular plantsinhabiting stabilized surfaces and the rhizomes and shoots ofthe European beach grass enhancing the accumulation of eoliansand.
Our analysis of the stratigraphic record on western YamalPeninsula indicates active ice-wedge growth, eolian, and fluvialdeposition occurred during the Late Weichselian, ca. 25,000 to11,000 yr B.P. We found no geomorphic or stratigraphic evi-dence for glacier coverage or proximity to an ice sheet duringthe past 30,000 yr along the west coast of the Yamal Peninsula.Other chronologically controlled geomorphic and stratigraphicobservations constrained late Weichselian glaciation largely tothe Barents Sea with limited extension of the ice sheet intothe Kara Sea (e.g., Forman et al., 1997; Landvik et al., 1998;Mangerud et al., 2001; Zeeberg et al., 2001). Recent marine ge-ologic studies infer a limit of the Late Weichselian ice sheet ofeast of Novaya Zemlya Trough (Polyak et al., 2000b) (Fig. 1).Thus, we contend that Yamal Peninsula and much of Siberiaeast of the Ural Mountains was distal to moisture sources, asshown by the prevalence of sand sheets ca. 30,000–11,000 yr agoin the Marresale area. Other studies along the lowlands of theeastern Kara Sea support the nonglaciation of large areas, withPleistocene flora, mammals, and humans surviving throughoutthe Late Weichselian into the Holocene (e.g., Andreev et al.,1997; Ukraintseva, 1993; Sulerzhitsky and Romanenko, 1999).Thus, Late Weichselian glacier extent is characterized bydiminutive valley glaciers in the Ural Mountains (Astakhov,1997) and probably limited expansion of ice caps on SvernayaZemlya (Alexanderson et al., 2001), rather than by the large-scale continental glaciation of western Siberia envisioned inmany ice-sheet models (e.g., Peltier, 1996).
The occurrence of rooted birch trees in the uppermostBaidarata Sand that yielded radiocarbon ages between ca. 8800and 8200 14C yr B.P. indicates substantial warming on YamalPeninsula in the early Holocene (Fig. 9). This warming resultedin permafrost degradation and deepening of the active layer topermit the rooting of trees. This degradation in permafrost is rec-ognized across Eurasia and associated with substantially warmersummer temperatures (Anisimov and Nelson, 1996). The birchtrees recovered from the Nenets peat on Yamal Peninsula at-tained heights of 1 to 3 m, with a distinct krumholz form anddemarcate the northern extension treeline, which is presently200 km to the south. However, the Marresale area is probablynot the northern limit of early Holocene treeline, with one birchtree from 110 km north at the Kharasavey River mouth yield-ing a radiocarbon age of 8780 ± 150 14C yr B.P. (GX-21799;Table 1). This northward extension of treeline has been docu-
mented across Eurasia, reflecting a poleward shift of the borealforest and associated summer warming of 2 to 4◦C (MacDonaldET AL.
et al., 1999). Subsequently, the birch trees were subsumed bypeat starting at ca. 8200 14C yr B.P., reflecting a rising watertable with permafrost aggradation. Peat accumulation occurredthroughout the Holocene in 1- to 2-m-deep depressions in theBaidarata sand. Eolian sand accumulated on top of the Nenetspeat starting at ca. 1000 14C yr B.P. and continues today. De-nuded hilltops from reindeer overgrazing, cliff erosion, and flu-vial surfaces are the current sources for eolian sand.
CONCLUSIONS
1. The Kara diamicton reflects regional glaciation of theKara and Barents seas with the ice sheet overriding the YamalPeninsula >40,000 yr ago, possibly during the earlyWeichselian 80,000–60,000 yr ago, or possibly earlier. The ice-sheet configuration and limit associated with the deposition ofthe Kara diamicton remains unresolved but may approximatemaximum reconstructions. The Varjakha peat and silt accumu-lated on top of the Kara diamicton ca. 45,000–35,000 14C yr B.P.and reflects regional warming.
2. The Oleny and Baidarata sands on Yamal Peninsula revealeolian and fluvial deposition and ice wedge formationca. 30,000–12,000 14C yr B.P., during the Late Weichselian.There is no geomorphic or stratigraphic evidence to indicatecoverage or proximity of Yamal Peninsula to a Late Weichselianice sheet. The Late Weichselian ice-sheet margins lie betweenNovaya Zemlya and the Yamal Peninsula, with eastern expan-sion possibly limited by the 400-m-deep East Novaya ZemlyaTrough and concentrated river flow at the margin.
3. The discovery of birch trees 10,000–9000 cal yr old, rootedin the upper Baidarata sand, indicates at least a 200-km shiftnorthward of treeline from present limits, which reflects a 2–4◦Csummer warming across Eurasia (MacDonald et al., 1999). Thiswarming resulted in permafrost degradation and deepening ofthe active layer that permitted the rooting of the birch trees.
4. Peat accumulation occurred throughout most of the Holo-cene, with eolian sand deposition more conspicuous afterca. 1000 14C yr B.P., reflecting abundant sand sources fromdenuded hilltops associated with reindeer overgrazing, cliff ero-sion, and fluvial activity.
ACKNOWLEDGMENTS
The U.S. National Science Foundation (OPP-9796024) and Swedish NaturalSciences Research Council supported this study. We thank M. Leibman of theEarth Cryosphere Institute, Moscow for arranging logistics and our stay at theMarresale Station on Yamal. We acknowledge the reviews of J.-I. Svendsen andan anonymous reviewer.
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