Landfonn Analysis, Vo/. 3:47-61 (2002) The granulometric properties of contemporary aeolian sands in a taiga-steppe area of Eastern Siberia Tadeusz Szczypek Valerian A. Snytko Faculty ofEarth Sciences, Inslilule o/Geography University o/Silesia. Russian Academy a/Sciences, Siberian Bratlch, Bfdziliska St.• 60. 41w200 Sosnowiec. Poland Ulanbutorskaya St., J, 6640331rku/sk. Russia e-mail: [email protected] e-mail: [email protected] Abstract: The grain size dislribution and quartz grain (1.0-0.8 mm) abrasion degree for the contemporary aeolilln sands occurring in a zone oflaiga and steppe in the neighbourhood of Lake Baileal, in Eastern Siberia, is compared LA with similar features in other aeolian sediments. Five sites in a taiga zone, one in a forest-steppe lone and one in a steppe zooe: have been investigated. Whereas the morpho-fonning influence: of the wind is obvious in lIle area --- investigated, the role of the wind is important only in respect of grain size distribution and is not an imponant foctor in determining in quanz grain abrasion size. Kty word)': Eastern Siberia, modem aeolian processes, aeolian landfonns, aeolian sands Introduction sites lie in the BaikaI rift zone; in the Tunka Basin 00 the wcslern margin ofBaikal; on the wcstcmshorcofOIkhon Aeolian sands in Eastern Siberia area fonn part of Island on Baikal and onthe shores ofthe Bratsk Reservoir genetically quite different sand~gravel deposits, somc on the River Angara. The following sites ofacolian sands ofwhich arc widespread. Such areas have local names have been investigated: oftaiga -1-Rassvc( OD Bratsk - ..tukulans", ,,kuytuns" or "badars" (preobrazhenski, Reservoir, U- Great Khuzhir on Olkhon. ill - Sandy 1961; Pavlov, 1981; Krcndelev, Nasyrova, 1985 and Bay, IV -the terrace ofthe lrkut River, V -thc slope of others) and may usually occur on the floors of largc Mt Kbayrkhan in the Tunka Basin, vegetated by forest­ faulted depressions. Other sandy areas are smaller and steppe: Vl- tbe valley ofthe Tunka in the Tunka Basin these reflect particular local lithological conditions. and of steppe: VII - lhe Seven Pincs area on Olkbon Thanks to it, the aeolian sands in the area above­ (Fig. I). mentioned seem to be rather popular, although they The area analysed is characterised by very strong usually occupy relatively small areas. Whatever they continental climatic conditions with large mean tcmpe­ originate, the aeolian sands are now covered by taiga ratures variations between Summer and Winler, vegetation (dark and light taiga - Baikal, 1993). reaching an amplitude 3Q-40Q or more; the precipitation Seasonally, these areas are affccted by powerful, usually is also very low here, the annual sums fluctuating undirectiona~ winds, especially in early Spring and between 200 mm on Olkhon and 450-500 mm in the Autumn(Vyrkin, 1986; LublSOva, 1994). Whereas tbese Tunka Basin (Baikal, 1993; Szczypck, 1995). deposits are widespread, such mechanical properties as: grain size distribution and quartz grain abrasion, are almost complelc1yunknown. Fwther. very little is known Anemological conditions about Ihc sources of these scdiments. The purpose of the research described here was to detemline the The anemological conditions in the area investigated influence of aeolian processes in the study area by are very variable, In this study it is necessary to know analysing selected aeolian sands and by a review ofthe the directions ofprevailing winds as well as the annual literature concerning such scdirnents. Most ofthe study distribution ofdays with very strong winds, i.e. blowing 47 Tadeusz Szczypek, Valerian A. Snytko The granulometric properties ofcontemporary aeolian sands in a taiga-steppe area ofEastern Siberia 30 60ka more complicated, because, in the vicinity of degree of deposits - u have been calculated (Folk o . , Balagansk, the south-westerly and southerly winds and Ward, 1957); alternate with an easterly air flow. FUJ1her, in the b) quartz grains (1.Q-{).8 mm) abrasion degree, neighbourhood of the Rass\fet Station, westerly and applying (1) the mechanical method by Krygowski north·westerly winds prevail (Ovchinnikov, 1998). (1964) - from this the abrasion coefficient Wo, the With regard to the average number ofdays with strong content of well·rounded grain') of r type, mcdium­ winds per year, Olkbon has 27 sueh days (mostly in rounded grains off3 type and angular grains ofa type Autumn and in the beginning of Winter, and least of have been calculated, and (2) morphoscopy by Cailleux ~ all, in Summer); Sandy Bay has 43 (these being fairly (1942) - from this the content of mat-rounded grains VII evenly distributed through the year); although it is also ofRM type, polished rounded grains EL, intetmediate + possible to distinguish an Autwnn and early Winter EM aDd angular NU have been calculated. air flow as well as one in Spring. In the Twtka Basin Taiga sites ID ... lbere are significantly fewer (the westcrn part has 18, IRKllTSK similarly with a seasonal distribution; the eastern part has only 13, the Spring and early Swnmcr air flows predominating. Asat Olkhon and in the Angara vallcy, • Main geomorphological features. Holocenc the mean number ofdays with strong winds is 26, but wind·blown aeolian sands occur along the shores of Fig. J. Location of sites investigated against a here Spring air flows are strongest, the minimum flows Bratsk Reservoir, on the margins of or only partly background of main vegetation fonnations \I are in Summer and Winter (Fig. 2B). The significantly overlapping the area of taiga (Owczinnikow, 1996; 1 - Rusvet, 11 - G"'~l Khu~.hir, III _ SllIdy 8.ty, IV - Imn larger number ofdays with strong winds at Baikal is lmace, V- t.1l Kha)'fkhan. V1- Tunh nUey, V11- Seven Ovchinnikov, 1998). They lie at 400 m a.s.1. or more. Pmea; t - taiga. 2- Slqlpl: presumably a result ofthe intensive local atmospheric The source deposits are dry lake sands and unconsol· circulation over this lake and its neighbourhood. idated river deposits. The aeolian forms in the study with velocities> 15 mxs·l (Spravochnik po klimatu..., 1992). By contrast. in the western part of the Tunka in Nonnally there are large differences atmospheric area appear to be produced by abrasion processes 1967). In this respect. the shores ofBaikal and Olkbon Basin.. westerlywinds oVefWhelmingly predominate. but pressure between these areas (Galaziy, 1987 and which occur in the reservoir, especially at times of fundamentally differ from the Tunka Basin. On Olkhon, in the eastern part- casterlyones with a certain influence others). The same is probably true for the Bratsk fluctuating water level, when widespread sandy de­ westerly and nonh-westcrly winds clearly predominate of morpho-fonning westerly winds (Fig. 2A). In the Reservoir. posits become uncovered and dry out (Owczinnikow, although northerly winds are also important; a similar comparatively short section ofthe Angara valley in the 1996; Ovchinnikov, 1998). wind regime is observed in Sandy Bay (Szczypek, Wach, neigbbowhood ofthe Bratsk Reservoir the situation is Characteristics of aeolian sands Owing to the intensive influence ofwesterly and north-westerly winds, those sandy deposits which are o 30 60km Research methods uncovered at times oflow water level become blown , .. __ . clearofthe reservoir shores. Thick aeolian covers have ';,) • . Laboratory analyses ofthese deposits included: "2 .••. thereby been created on the beach, whereas at the edge , , a) standard grain size distribution, following of the reservoir, irregular dunes are present, which "J.tU.~. which the mean grain size diameter Mz and sorting gradually migrate towards the south..east (Fig. 3). A " • • *~ ~ \=SRATSK W ATE R RESERVOIR= .-·····:::::l·i.:·~·-• ~ ,s .-.-.-.-· .. _.. ""la ': . ':s . .. --~ "\Q~ c....:..= A Q ....:\ 7: :r~:::; B "- ;. *...;:;:::.-:.-·.:::: •••••• ~-{> •• I ... • I ,..~~.V- .:'L:W:b:i:tL::I- I. wind rose for Rassvet station (R) Fig. J. Morphological sketch-map ofaoolian landfonns in lhe neighbourhood of Rassvet (after Ovchinnikov, (998) Fig. 2. Wind regime in the area investigated I - edieof~ JhoR: in t996, 2 - alllMal-dduvW depo$iu, ) -1Kulcrinc ~rl$,.-1KustriIM: MI'dy cleI-ltI. ~ - KOI....sands(-''I A - ...."Id rtISO, B - melJI cbys nwnbn wi:h wind,:> I Sin. r dllllfe'.1Id ~). 6-d'reciolI of<ldlation processes. 7 - forest 48 7- Landf<>rm... 49 Tadeusz Szczypek, Valerian A Snytko The granufometric properties ofcontemporary aeolian sands in a taiga-steppe area ofEastern Siberia The river /bankJ­ • Properties ofthe deposits. Mz=0.326 mm (0.188-0.807 mm): the average With respect to the abrasion degree, the wind­ they are moderately sorted (a= 0.45). The Ncogene sands are characterised by having signjficant fine content of material >0.5 mm is 12.7% (2.5--61.5%) blown sands do not differ from the source material. deposits are slightly finer, because the value of fraction. On average, they contain 4.6% of coarse and the finest - 3.9% (0.3-11.0%). These deposits The Wo value amounts to 614 (497--673): they contain Mz = 0.403 mm; they are composed of30.1% coarse grains (0.5 mm) and 38.4% of silt/clay particles are less well sorted than these ofthe beach - a= 0.77 0% ofgrain of rtype; a-73.5% (61.2-81.1%), RM grains and 3.5% ofthe frnest particles. They are also «0.125 mm). Therefore mean grain diametcr in (Ovch;nn;kov, 1998) (F;g, 4 I), - 1.8%, NU - 2.7% and EM - 94.3% (Ovchinnikov, sorted to a moderatc degree, although less well so lhe~e weakly sorted deposits (s = 1.05) is relati­ With respect to the quartz grains abrasion, the 1998) (F;g, 4 I1), than the beach sands (0= 0.89). Thegranitoid regolith vely small and the Mz is 0.137 nun (0.100­ fluvial deposits are characterised by. a mean value of (missing the coarsest parts) is coarse-grained: 69.2% 0,210 mm), abrasion coefficient Wo = 628: they are devoid of Great Khuzhir of grains are >0.5 mm in diameter there are no silt/ The beach deposits are clearly well-washed and, grains of rtype, but they contain 73.5% of angular clay panicles, so the value of Mz ::, 2.250 mm.