ctf northwestern SiberiaNCO
elemenwestern Siberia were analysed to determine profiles of geochemical uniformity, element mobility andthe release and build-up of extractable Fe and Al. The scope of this study involves weathering processes
ents that yield importantinformation on profile chemical uniformity and the movement
The field area is drained by the Ob Estuary and borders the KaraSea along the Siberian Arctic coast (Fig. 1) (Mahaney et al.,1995). The flat to gently undulating land surface has a
JOURNAL OF QUATERNARY SCIENCE (2010) 25(2) 178189Copyright 2009 John Wiley & Sons, Ltd.Published online 21 July 2009 in Wiley InterScience(www.interscience.wiley.com) DOI: 10.1002/jqs.1290* Correspondence to: W. C. Mahaney, Quaternary Surveys, 26 Thornhill Ave.,Thornhill, Ontario, Canada, L4J 1J4.Low-temperature soils and palaeosols (Cryosols) are subject tocryoturbation (Fedorova and Yarilova, 1972; Ellis, 1980;Mahaney and Fahey, 1988; Mahaney et al., 1995; Jakobsenet al., 1996; Earl-Goulet et al., 1998), and to accumulations ofextractable Fe and Al linked to present and past soil-formingenvironments (Mahaney and Fahey, 1988; Mahaney, 1990;Mahaney and Hancock, 1996; Earl-Goulet et al., 1998;Mahaney et al., 1999). They are among the least understoodsoils in terms of the degree to which palaeoclimate affectedchemical weathering processes. Extractable Fe and Al havebeen used to classify soils (Blume and Schwertmann, 1969;Lutwick and Dormaar, 1983; Mahaney and Fahey, 1988); todate deposits (Mahaney and Sanmugadas, 1985; Birkelandet al., 1989; Mahaney, 1990; Mahaney et al., 1991, 1999); toanalyse pedogenesis in tundra podzols (Pereverzev, 2007); andto determine perched water tables (Mahaney and Fahey, 1988).The neutron activation analysis of soils not only provides totalconcentrations of Fe and Al, but also the concentrations of other
of soluble chemical elements. Only rarely have low-temperaturesoils been analysed for geochemical trends using instrumentalneutron activation analysis (INAA) (Earl-Goulet et al., 1997).
This study expands on previous stratigraphic and pedologicalresearch of Mahaney et al. (1995) in the YamalGydan area,and seeks to analyse distributions of total elements andextractable Fe and Al, to determine parent material uniformity,as well as leaching and weathering histories. In particular, thisinvolves the interpretation of oxihydrite levels, and behaviourof Fe and Al. As the distribution and concentration of rare earthelements (REEs) in Arctic soils are in general poorly understood(McLennan, 1989), the geochemical profiles of light and heavyREEs are used to assess parent material uniformity.
Field areathe age of a profile by its physical characteristics. However, it appears possible to determine broad ageranges from the isotopic composition of water in soils. Copyright # 2009 John Wiley & Sons, Ltd.
KEYWORDS: Arctic climatic optimum (Hypsithermal) palaeosol; FeAl extractions; chemical/geochemical indices of Cryosol pedogenesis.relative to total Fe increases in the AhBw horizons compared with the lower horizons, whereoxidation is weaker. Low total Fe reflects reworked felsic deltaic and shallow marine deposits fromthe Permian to the early Tertiary, thereafter emplaced by episodic flooding of glacial meltwater fromthe Arctic Urals and/or the Kara Sea Ice Sheet. Organically complexed Al (Alp), uniformly low in allsoils, nevertheless shows trends indicating some downward movement, a rather unique occurrence inArctic tundra soils. As indicated by the slow increase of oxihydrites, it may not be realistic to estimate
Introduction major, minor and trace elemextracts are investigated to elicit information regarding profile ag
over all or part of the Lateglacial to the Holocene Epoch (
In areas of ice-rich permafrost and massive ground ice(Astakhov, 2006), thermokarst modification is extensive to
ice wedges, in places, extend to within 12 m of the surface (forpermafrost extent see http//www.iiasa.ac.at/Research/FOR/
SIBERIAN CRYOSOLS 179incised the coastal plain to depths of 15 m a.s.l. Massive groundice bodies, which are believed to have an origin either assegregated ice or glacier ice (Trofimov et al., 1975; Astakhov,2006), have been significantly affected by thermokarstprocesses due to human impact and global warming (Popovaand Shmakin, 2009). The mean annual air temperature (MAAT)over Russia has risen by18C in the last 20 years (Shmakin andPopova, 2006). Pleistocene ice sheet limits reported by Formanet al. (2002), Ehlers and Gibbard (2004) and Svendsen et al.(2004) shown in Fig. 1 indicate the area has been ice-free sinceearly Weichselian time, and under periodic lacustrine andalluvial flooding (Forman et al., 2002) since at least the lastinterstade (ca. 45 ka). This interpretation is compatible with theage and origin of sediments reported in this study. Vasilievskayaet al. (1986) stress that the vegetation cover is highly dependenton the radiation/energy balance, which is
University for oxygen isotope analysis by mass spectrometry atn
180 JOURNAL OF QUATERNARY SCIENCErefers to C (subsoil) horizons with a brown colour that is at least10YR 5/4 or darker (see Mahaney, 1990, for an outline ofhorizon designations). The Cu designation refers to unweath-ered, unconsolidated and undifferentiated parent material(Hodgson, 1976). The soils all formed in fluvial deposits ofpresumed Holocene age, with minor airfall influx deposits ofsilt, and all are situated in topographic high positions with grass/herb tundra vegetation representative of the region. Parentmaterials are a mix of quartz and feldspar-rich sedimentsderived from crystalline basement rock; airfall sediments have asimilar source lithology. The three profiles are representative ofCryosols selected from among a suite of profiles studied acrossGydan and Yamal.
Organic samples collected for radiocarbon dating werehandled with metal implements and stored in aluminium foil,kept cool, and dated within two weeks of collection. Sampleswere dated at the University of Waterloo RadiocarbonLaboratory. Despite the presence of suitable minerals foroptically stimulated luminescence dating (OSL) quartz, albiteand orthoclase replicate dating of these beds for comparisonwith radiocarbon was not possible given funding constraints.Other sections in the general area were dated by OSL (seeMahaney et al., 1995).
The soil samples were air-dried and analysed for hygroscopicmoisture. The air-dried equivalent of 50 g oven-dried soil waslater subsampled for particle size analysis following proceduresoutlined by Day (1965). The coarse material (2 mm to 63mm)was separated by wet sieving. The fine material (
Taxonomically, the soil is a Regosolic Static Cryosol as definedin the Canadian Soil System.
The YAM9 profile (Fig. 3) contains a highly deformed surfacesoil over a buried peat showing only minor deformation,indicating a pedostratigraphic complex with frost heavingconfined to percolating meteoric water rather than from melt inthe active layer. The degree of deformation of horizons in thesurface pedon is consistent with classification as a BrunisolicDystric Turbic Cryosol. The surface peat contains anabundance of silt and fibrous brownish-black (10YR 2/3)organic material. Minor variations in colour occur with depth inthe surface epipedon, texture coarsens slightly down-profilewhile structure remains a fine grade of granular; both the Ah1and Ah2 horizons have friable consistence and lack plasticityand stickiness. Despite similar particle size characteristics inthe epipedon and subsurface B horizon, the structure becomesweak angular blocky and the material is slightly sticky andplastic.
Below the Bw horizon, clay increases in the Cox horizon,though with insufficient concentration to warrant a tdesignation. The matrix material is massive, with a firmconsistence, non-sticky and non-plastic. Below the ground soil/buried soil contact, the Lb horizon has a black (10YR 1/1)colour and is of loam texture with finely disseminated organicmaterial (unfortunately we lacked sufficient sample to analysethe organic carbon content; see under Soil chemistry). Theburied peat (Lb horizon) rests on frozen silty sand beds ofalluvial origin, weathered to a dull yellowish-brown (10YR 5/4)colour, with a silt loam texture, massive, friable consistenceand non-sticky and non-plastic. The lowermost Coxb horizonmakes a sharp contact with an ice wedge below.
The surface soil consists of wavy horizons and disjunct Ah/
Figure 2 GYDAN4 profile. This is a Fluvisol formed in stream sedi-ment overlying massive ground ice
Figure 3 YAM9 profile over an ice wedge. A surface Inceptisol with A/B/C hoburied L horizon, (b) the whole profile
Copyright 2009 John Wiley & Sons, Ltd.
SIBERIAN CRYOSOLS 181Bw/Cox horizons that are highly deformed and indicative offrost heaving. Whereas similar massive frost heave has beenreported elsewhere (Mahaney and Fahey, 1988), the soil
rizons formed over a buried peat (L horizon). Part (a) shows details of theJ. Quaternary Sci., Vol. 25(2) 178189 (2010)DOI: 10.1002/jqs
stratigraphic relationships suggest that the horizons that spilledon the surface were removed by wind and water erosion prior tothe build-up of the surface peat. Thus the peat may reflect acooling (Neoglaciation?) that occurred in the latter part of theHolocene, resulting in lower microbial activity. Frost heavingof subsurface horizons onto the surface is far more commonthan the infilling of surface material into melted frost/icewedges, as reported previously in Yamal by Vasilievskaya et al.(1986).
Certainly the development of a Bw horizon representssignificant weathering and pedogeneisis relative to GYDAN4,sufficient in effect to produce an Ah/Bw/Cox profile prior tofrost heaving and the later emplacement of the surface peat. Thecharacter of the deformed beds indicates that the soil formed inplace prior to a deformation in the sub-boreal climatic coolingfollowing the Climatic Optimum, which correlates well withwork carried out by Koshkarova and Koshkarov (2004) inCentral Siberia. While no 14C dates are available, the lessnegative 18O composition of the clays and bulk soils suggeststhat the surface soil represents weathering during the HoloceneClimatic Optimum.
Ice wedges, common on Yamal and Gydan, are alsocommon further southwest in taiga and forest communitieswhere ice wedge casts contain surface soil materials (ABhorizons) that have spilled downward (see Vasilievskaya et al.,1986), the opposite of the process described above. In southernexposures newly formed organic-rich horizons in topographicdepressions have started to reform in upper pseudo-ice wedge
the taiga and mixed taigaforest communities to the southwest,soil depth reaches to1.0 m and more (see Vasilievskaya et al.,1986).
increase in clay that is marginally below that required for a Bt,although the extractable Fe reported below and the field colourmight equivocally support a B horizon designation.
182 JOURNAL OF QUATERNARY SCIENCEcasts, presumably in response to cooling during the latter part ofthe Holocene (see Fig. 9 in Forman et al., 2002, for ananalogous situation). Mineral soils in the south contain organic-rich horizons approximately one-third to one-fifth the depth,and correspondingly of much younger age, than soils in Yamaland Gydan (see p. 56 in Vasilievskaya et al., 1986).
The YAM10 profile (Fig. 4) at Khalev Lake, a Gleysolic StaticCryosol with a thin Bw horizon, overlies C horizons withvariable weathering effects including significant gleyingcommon in Siberian soils (Federova and Yarilova, 1972).The original alluvial stratification, still pronounced as in the
Figure 4 YAM10 profile at Khalev Lake. Peaty Inceptisol with a thincolour B horizon (Bw) in a lacustrine terraceCopyright 2009 John Wiley & Sons, Ltd.Oxygen isotopes
The isotopic composition of pore waters and ground ice reflectsthe composition of the source water and provides informationon the freezing history of the ice (Michel and Fritz, 1978, 1982;Vasilchuk and Trofimov, 1988; Michel et al., 1989). Isotopicanalysis of ice wedges is particularly useful for determiningtemperature conditions during the period of their growth(Vasilchuk, 1987, 1992; Konjachin, 1988; Michel, 1990;Vasilchuk and Vasilchuk, 1996, 1997); thus wedges of varyingages can be of aid in assembling a climatic record oftemperature variations through time. Within the seasonallyfrozen active layer overlying permafrost, the isotopic compo-sition of pore ice can help to identify freezing processes relatedto the upward and downward migration of water due to strongtemperature gradients (Michel, 1982).
Samples collected at the three sites reported here andadditional sites in the area included pore ice, large and smallsegregated ice lenses, ice wedge ice, massive banded andParticle size
The analysis of sand, silt and clay, shown as depth distributionsin Fig. 5, are intended to illustrate the degree of modification ofthe original parent materials. All three profiles show an upwardincrease in silt, with an increase of silt between 15% and 60%compared with lower horizons suggesting airfall influx (similarto data interpretations of Forman et al., 2002). In one case(YAM10), this trend is mirrored by an upward increase in clay.The textures of these soils range from silty clay loam, silt loamand sandy clay loam in the Ah horizons, to silty clay loam andsandy loam in the Cox/Cg horizons. The Lb horizon in YAM9has a loam texture overlying a Cub horizon with a silt loamtexture. The texture of the Cox horizon in YAM9 shows anGYDAN4 profile, indicates only slight turbation duringpedogenesis (despite the presence of a Bw horizon). Hencethe texture (Fig. 5) reflects mainly the original depositionalvariation commonly associated with detrital effects. The Cghorizon, intensively gleyed, indicates periodic water saturationthat is supported by the ferrihydrite distributions reported laterin the paper. The profile, possibly of a similar age comparedwith the ground soil in YAM9, lacks an Ah horizon and containsa Bw horizon that is massive with a very friable to looseconsistence, non-sticky and non-plastic material. Rootspenetrate into the C horizon, which is a medium sandy loam,massive material with loose consistence, non-sticky and non-plastic.
Perched water above the massive ground ice has led togleying represented by the greyish olive colour, similar to whathas been previously recorded by Fedorova and Yarilova (1972)in soils of western Siberia. Periodic gleying in soils of Yamaland Gydan contrasts with extensive gleying in soils further tothe southwest, where soils are under strong reducing conditionsclose to the surface, often in the B horizons. Along transects intoJ. Quaternary Sci., Vol. 25(2) 178189 (2010)DOI: 10.1002/jqs
modern summer precipitation, and heavier than local surface
SIBERIAN CRYOSOLS 183massive segregated ice and ice-rich clay sediments. Oxygenisotope data for the three sites are compiled in Table 1. Modern...