149-173 Eiszeitalter und Gegenwart 55 Hannover 2005 4 Abb., 5 Tab.
Loess paleosol-sequences along a climatic gradient in Northern Iran
M K, R S, H A, M F A S*)
Keywords: loess, paleosol, luminescence, past cli- 7 or older interglacials. Th e pedocomplexes at Neka mate change, Pleistocene, Iran and Now Deh indicate polycyclic soil genesis includ- ing soil formation, truncation of the upper soil hori- Abstract: In Northern Iran, loess is found in diff er- zons, loess deposition and again soil formation. ent geomorphological settings along a climatic gradi- In the loess hills near Agh Band, 40 m thick homog- ent ranging from subhumid to semiarid conditions. enous loess covers a brown paleosol (Bw(t)), possibly Loess-paleosol sequences were investigated in detail correlating with the last interglacial soil. Th e loess at in three key sections located on the northern foot- Agh Band section has a high percentage of fi ne sand hills of Alborz mountains (sections at Neka and at and coarse silt and contains signifi cant amounts of Now Deh) and in the loess hills north of Gonbad-e gypsum. Kavus (section at Agh Band). Th e loess-paleosol sequences indicate pronounced At the section at Neka, two pedocomplexes consist- climate changes from dry and cool to moist and ing of moderately to strongly developed Bwk, Bt or warm conditions with loess deposition and soil AhBt horizons are intercalated in fi ne textured loess. formation, respectively. Th ey are excellent terrestrial Luminescence age estimates indicate that the upper archives of Quaternary climate and environment paleosol was formed during OIS 5a or 5c, whereas change in Northern Iran. the lower pedocomplex might represent OIS 5e or older interglacial periods. [Löss-Paläobodensequenzen entlang eines Kli- Nine light or dark brown paleosols (CBk, Bwk and magradienten in Nordiran] Btk horizons) are intercalated in the loess at the sec- tion at Now Deh indicating diff erent weathering intensities most likely during interglacial and inters- tadials periods of the Middle and Upper Pleistocene. Zusammenfassung Th e upper Bt horizon of Now Deh likely correlates with OIS 5e. Th e lower Bt horizons join to form a Im südlichen Kaspischen Tiefl and und seinen strong pedocomplex possibly correlating with OIS umliegenden Gebieten treten Lösse in verschie- denen geomorphologischen Positionen entlang * Anschrift der Verfasser: Dr. M. K und Prof. eines rezenten Klimagradienten von subhumi- Dr. A. S, INRES-Soil Sciences, Univer- den zu semiariden Verhältnissen auf. Drei Löss- sity of Bonn, Nußallee 13, 53115 Bonn, Germany, Paläobodenabfolgen werden beschrieben, die Email: [email protected], Prof. Dr. R. S, im nördlichen Vorgebirge des Alborz (Profi le Department of Geography, Shahid Beheshti Univer- sity, Tehran, Iran, Prof. Dr. H. A, College of Neka und Now Deh) und im Lösshügelland Natural Resources, University of Tehran, Karaj, Iran, nördlich Gondbad-e Kavus (Profi l Agh Band) Prof. Dr. M. F, Leibniz Institute for Applied aufgeschlossen sind. Geosciences (GGA-Institut), Geochronology and Das Profi l Neka besteht aus feinkörnigem Löss, Isotope Hydrology, Stilleweg 2, 30655 Hannover, der von zwei kräftig entwickelten Paläoboden- Germany komplexen aus Bwk-, Bt- und AhBt-Horizon- 150 M K, R S, H A, M F A S ten durchzogen wird. Erste Lumineszenzda- ern foothills of the Alborz mountains between tierungen weisen darauf hin, dass der obere Sari and Minoodasht (N I O Pedokomplex während der Sauerstoff -Isotopen- C 1978; G S Stadien (OIS) 5a und/oder 5c gebildet wurde, M E I) and locally während der untere das OIS 5e oder ein älteres occurs, for instance, on fl uvial terraces of Se- Interglazial repräsentieren könnte. fi d-Rud and Chalus River (N I Neun hell braune oder dunkel braune bis röt- O C 1978; E 1971; P & lich-braune Paläoböden (CBk-, Bwk- und Bt- D 1980) or in the Gharatikan watershed Horizonte) des Lösses bei Now Deh spiegeln (O & A, 2001). Th ough T unterschiedliche Verwitterungsintensitäten von (1877), S (1923) and B (1937) al- Interglazialen und Interstadialen des Mittleren ready mentioned loess deposits in Northern bis Oberen Pleistozäns wider. Während der obe- Iran, little information about the nature, origin re Bt-Horizont von Now Deh wahrscheinlich and chronology of the loess has ever been pub- mit dem OIS 5e korreliert, bilden die unteren lished. Bt-Horizonte einen Pedokomplex, der das In- B (1960) gave a short description of terglazial des OIS 7 repräsentiert. Die Pedo- loess in the Sefi d-Rud valley and correlated komplexe in Neka und Now Deh weisen jeweils these deposits with the Holocene. Following auf polyzyklische Bodenentwicklung hin, die this view, E (1971) suggested that brown Bodenbildung, Bodenabtrag, Lössaufwehung paleosol horizons intercalated in the loess from und erneute Bodenbildung umfasste. Sefi d Rud and also in loess deposits near Neka In den Lösshügeln bei Agh Band bedeckt ein 40 formed during moist periods of the Holocene, m mächtiges, weitgehend homogenes, gipshal- whereas loess deposition took place during dry tiges und feinsand- sowie grobschluff reiches periods. L (1988) described loess deposits Lösspaket einen braunen Paläoboden (Bw(t)), with intercalated brown paleosols near Now der vermutlich in das letzte Interglazial zu stel- Deh, which are likely identical to the “folded len ist. loess” described by R (1966). L Die beschriebenen Löss-Paläobodenabfolgen (1988) supposed that the brown paleosols dokumentieren den mehrfachen Wechsel von represent the last interglacial period and that trocken-kalten zu feucht-warmen Klimaverhält- loess deposition took place during glacial times. nissen mit Lössablagerung bzw. Bodenbildung. Paleosols as markers of interglacial periods have Sie stellen ausgezeichnete terrestrische Archive widely been used in the pedostratigraphical des quartären Klima- und Umweltwandels correlation of loess-paleosol sequences with the Nordirans dar. global climatic record (e.g., B, 2002). Soil formation requires moist and warm climat- ic conditions during interglacial or interstadial times. A vegetation cover is needed to supply 1 Introduction organic matter for accumulation of soil humus and to protect the soil against erosion. In con- In Northern Iran, loess is found in hilly areas trast, the deposition of loess took place dur- along the rivers Aras in East Azerbaijan prov- ing periods of low temperature and increased ince (Fig. 1), bordering the Gorgan and Atrek aridity, when production of silt-sized grains rivers in Golestan province and west of the Hari was intensifi ed by frost-shattering and glacial river in Khorassan province (B, G activity (e.g., W 2001). Mainly silt-sized & S 1990). Loess also covers the north- sediments were defl ated from the fl ood plains Loess paleosol-sequences along a climatic gradient in Northern Iran 151 and accumulated again by trapping through available including radiocarbon, luminescence shrub or grass vegetation. In Southern Iran, dating, amino acid racemisation and paleo- loess and loess-like sediments were deposited in magnetic measurements. Th e infrared optically the Basin of Persepolis located in the Southern stimulated luminescence method (IRSL) has Zagros mountains. Th ere, the loess formation been shown to be highly suitable for the dat- pathway is explained by intensifi ed production ing of loess in Tajikistan and to determine loess of silt-sized material during the Last Glacial mass accumulation rates in Europe (F maximum, fl uvial transport to the alluvial & D 1998; F, O & K- plains, defl ation, aeolian deposition and fl uvial 2003). displacement (K et al. 2005). In this paper we give fi rst detailed descriptions Cyclical climate changes like those of the Qua- of three key sections of Northern Iranian loess ternary can result in the formation of stacked and its paleosols. From these sequences eight loess-paleosol sequences as observed in the samples were taken for a fi rst luminescence study area. Th e grey, brown, reddish-brown dating approach to investigate the suitability of or mottled paleosol horizons of loess-paleosol loess from Northern Iran and to set up a more sequences likely correlate with diff erent weath- reliable chronological framework. Th e high po- ering intensities depending on temperature tential of Iranian loess as terrestrial archives of and precipitation during the period of forma- climate and environment change is indicated. tion (e.g., B, W & H 1998). Furthermore, several other physical properties of loess-paleosol sequences are suit- able as indirect proxy measures of past climate. 2 Materials and methods Th ese so-called climate proxies include grain 2.1 The study area size, colour, mineral assemblages, the content of organic carbon, CaCO3 or iron fractions, Th e loess-paleosol sequences are located at Neka micromorphological features, major and trace and Now Deh on the northern foothills of the element composition, isotope signatures or Alborz mountains east of Sari and east of Gor- magnetic susceptibility (e.g., T et al. gan, respectively, and at Agh Band in the loess 1985; B & H 1989; B, hills north of the city of Gonbad-e Kavus (Fig. W & S 1998; D, K 1). Th e loess hills near Agh Band are part of the M 1997; H et al. 2001; D et al. so-called Iranian loess plateau. Th e coordinates 2002). Furthermore, biological indicators like and altitudes of the sections of interest are given pollen or mollusc assemblages proved very use- in table 1. ful as climate proxies (e.g., K & S Modern mean annual precipitation ranges from 1995). ~750 mm/a to ~350 mm/a in the vicinity of the Absolute age determinations are required to sections at Neka and Agh Band, respectively. correlate loess deposits with those from diff er- Th is gradient refl ects the decline in precipita- ent areas and with the global marine or ice core tion from west to east along the southern coast record (oxygen isotope stages, OIS) in order to of the Caspian Sea. In addition, rainfall also study the impact of climatic changes on the ter- decreases from south to north with increas- restrial environments in a transect from west to ing distance from the Alborz mountains as east, from more oceanic to more continental indicated in annual mean rainfall data of Now driven climate. Several methods for relative and Deh and Agh Band. Mean annual temperatures absolute age assessments of loess deposits are are about 17 °C (Tab. 1). Th e wind regime of 152 M K, R S, H A, M F A S
Northern Iran is mainly driven by pressure dif- which might transport large quantities of dust ferences between the Caspian Sea basin and the and sand towards the Turkmen deserts (M- Central Iranian Highlands. During summer a 1986). strong heat depression forms over hot Central With the southward shift of the paleo-Mon- Iran resulting in north-westerly to north-east- soon during the Last Glacial Maximum (LGM, erly air-mass fl ows from the cooler Caspian Sea S et al. 1991) it might be assumed that basin and from the Turkmen steppe. In winter, paleowind directions in Iran at that time were winds can blow in the opposite directions from also dominated by north-westerly to north- the high-pressure area over cold Central Iran to- easterly equatorial currents. However, T wards the low-pressure over the comparatively et al. (1997) gave evidence for south-eastern warm Caspian Sea. Strong foehn type winds wind directions in the Central Iranian High- called “garmsil” can occur on the northern lands during the LGM. faces of Alborz and Kopet Dagh mountains, Little detailed information has been published
Fig. 1: Geomorphological map of Northern Iran showing the occurrence of loess hills and the location of sections described in the text. “Dasht” is a regional name for bajadas and alluvial plains whereas “qavirs” are claypans (playas) with a naturally high salt content in the endhoreic basins of the highlands.
Abb. 1: Geomorphologische Karte Nordirans mit der Verbreitung von Lösshügelländern (loess hills) und der Lage der im Text beschriebenen Lössprofi le. „Dasht“ ist eine regionale Bezeichnung für Fußfl ächen und fl uviale Aufschüttungsebenen (Bajadas und alluvial plains), während „Qavir“ für die salzreichen Tonpfannen (Playas) der endhoreischen Becken des Hochlandes steht. Loess paleosol-sequences along a climatic gradient in Northern Iran 153
Tab. 1: Coordinates, altitude and climatic data of the sections under investigation.
Tab. 1: Koordinaten, Höhenlage und klimatische Kenngrößen der beschriebenen Lössprofi le.
Mean annual Mean annual Location Latitude Longitude Altitude precipitation* temperature* [m above sea level] [mm/a] [°C]
Neka 36° 39’ 53’’ N 53° 23’ 46’’ E 116 ~750 ~17.0 Now Deh 37° 05’ 50’’ N 54° 12’ 58’’ E 172 ~600 ~17.5 Agh Band 37° 37’ 18’’ N 55° 09’ 39’’ E 150 ~350 ~17.0
* Estimates based on precipitation and temperature data for meteorological stations at the cities of Babolsar, Gorgan and Gonbad-e Kavus about Quaternary climate change and its eff ect ised in the fi eld according to the instructions on landscape evolution in the southern Caspian of AG B (1994). Grain size spectra were lowland and its vicinity. Attempts to reconstruct determined by wet sieving and the pipette climate history based on fl uvial and marine ter- method after destruction of soil organic mat- races (e.g., E 1971) are affl icted with large ter with H2O2 and dispersion with (NaPO3)6 uncertainties because of high rates of tectonic and Na2CO3. Gypsum was leached by repeated uplift in the Alborz mountains and of subsid- washing with deionised water prior to grain size ence of the Caspian basin. According to pollen analysis. spectra, isotope composition and other climate Inorganic carbon was measured with the gas proxies derived from sediments of Lake Zeribar volumetric method (S, B
(see inlet of Fig. 1), the LGM in the Western S 1995) and expressed as CaCO3 equiva- Zagros Mountains was dominated by a dry and lent. Organic carbon (OC) was calculated by cool climate ( Z & B 1991; substracting the total amounts of carbon before S, W I 2001) and followed by and after dry combustion of organic C (OC) for slowly increasing temperature and rainfall until 5 h at 550 °C (S, B S 6 000 a (6 ka) before present (B.P.), when the 1995). In both cases total carbon was measured comparatively warm and moist conditions of with a C/N/S analyzer (Forno EA of Fisons modern climate was attained. It might thus be Instruments, Italy). Total carbon after dry com- hypothesised that similar climate changes also bustion yielded slightly higher CaCO3 equiva- ocurred in other parts of Iran. However, reliable lents than by using the gasvolumetric method. climate reconstruction based on the analysis of Gypsum was extracted with water and selec- terrestrial or marine climate archives other than tively precipitated with acetone as described by the Lake Zeribar cores are still lacking. V R (1995). For micromorphological investigations, thin sections were prepared for samples marked in Tab. 2, 4 and 5. Th e denomination of soil ho- 2.2 Sedimentological and rizons widely follows the instructions of FAO paleopedological analysis (1998). However, loess layers with pedogenic accumulation of calcium carbonate and sharp Th e loess-paleosol sequences were character- upper boundary towards the B horizons were Tab. 2: Lithological properties of the loess-paleosol sequence at Neka. 154
Tab. 2: Lithologische Eigenschaften der Löss-Paläoboden-Abfolge bei Neka. M S, K,R HA,M F AS
b b b b b b b b b b b ID Depth Hor. Color (moist) CaCO3 OC cS mS fS vfS cU mU fU S U T vfS + Kd TC cU (cU/T) (m) ————————————————— g kg-1 ———————————————— —— (-)——
Nk 1a 0.80Ah 7.5 YR 3/2 1 10.00005 15124913955404551560.3 Tu2 Nk 2a 1.20 Bt1 7.5 YR 3/2 1 4.30005 17825016455914041830.4 Tu3 Nk 3a 1.70 Bt2 7.5 YR 3/4 2 3.00005 16027818156193761650.4 Tu3 Nk 4a 2.90 C(t)k 10 YR 4/6 229 <1.0 15 33 10 15 172 276 197 74 644 282 187 0.6 Lu Nk 5 5.60c C 10 YR 4/3 181 <1.0 5 5 8 18 266 339 185 35 789 177 283 1.5 Ut4 Nk 6 6.10c C 10 YR 4/3 160 <1.0 5 0 8 17 238 333 203 30 773 198 254 1.2 Ut4 Nk 7 7.90c C 10 YR 5/3 185 <1.0 0 5 10 15 294 337 184 30 815 156 309 1.9 Ut3 Nk 8 9.00c C 10 YR 5/3 158 <1.0 5059 224343208207742062331.1 Ut4 Nk 9a 9.50 CB 10 YR 5/3 192 <1.0 0 0 5 10 233 316 195 15 745 240 243 1.0 Ut4 Nk 10 10.40 C 10 YR 5/3 158 1.3 0 5 10 15 273 334 178 3 785 188 288 1.5 Ut4 Nk 11a 10.85 1Bwk 10 YR 4/3 42 1.8 10 8 5 10 155 321 197 33 673 294 165 0.5 Tu4 Nk 12a 11.35Bw(t)1 7.5 YR 4/3 17 2.25505 135286194156153701400.4 Tu3 Nk 13 11.75 Bw(t)2 7.5 YR 4/3 7 1.83300 14928217956103851490.4 Tu3 Nk 14a 12.15 Bt 7.5 YR 4/4 6 2.83303 16927316086013911710.4 Tu3 Nk 15 12.20 Ck1 10 YR 5/4 354 <1.0 43 28 13 20 149 246 229 104 623 273 169 0.5 Lu Nk 16a 12.60 Ck2 10 YR 6/4 347 <1.0 62 39 16 21 180 261 200 138 641 220 201 0.8 Lu Tab. 2 continued
b b b b b b b b b b b ID Depth Hor. Color (moist) CaCO3 OC cS mS fS vfS cU mU fU S U T vfS + Kd TC cU (cU/T) Loess paleosol-sequencesalongaclimaticgradientinNorthern Iran (m) ————————————————— g kg-1 ———————————————— —— (-)——
Nk 17a 13.30 Ck3 10 YR 5/3 153 <1.0 4869 177291210286792941870.6 Tu4 Nk 18a 13.80 CBk 10 YR 5/4 82 1.0 4859 168281212266613131770.5 Tu4 Nk 19a 14.20 2Bwk 10 YR 4/4 42 <1.0 10 10 8 10 144 287 209 38 641 322 154 0.5 Tu3 Nk 20a 14.75AhBt1 10 YR 3/4 11 3.25033 148271161105814091510.4 Tu3 Nk 21a 15.20AhBt2 7.5 YR 3/3 6 2.85303 174271171106163741740.5 Tu3 Nk 22a 15.75Bw(t) 10 YR 3/4 9 1.68833 169286181206363441710.5 Tu3 Nk 23a 16.05 Ck 10 YR 5/4 214 <1.0 45 33 13 23 171 270 218 113 659 228 193 0.8 Ut4 a Th in sections investigated b S, s: sand, sandy; U, u: silt, silty; T,t: clay, clayey; L, l: loam, loamy; cS (0.63-2.0 mm), mS (0.2-0.63 mm), fS (0.125-0.2 mm), vfS (0.063-0.125 mm), cU (0.02-0.063 mm), mU (0.0063-0.02 mm), fU (0.002-0.0063 mm), T (<0.002 mm in diameter); 2: low, 3: moderate, 4: high amounts of S, U, L, or T as subdominant particle size fraction c Sampling depth, all other depths are lower boundaries n.d.: not determined 155 156 M K, R S, H A, M F A S classifi ed as Ck horizons and not as Bk hori- fi ne-grained material (4-11µm) was prepared zons. CB horizons show clear signs of browning for the measurements, as described by F, and formation of secondary structure but still S & Z (1996). Th e material contain abundant grains of primary calcite. brought on discs were irradiated by a 90Sr beta Th ey are transitional horizons between loess (C source in at least seven dose steps with fi ve discs horizon) and Bw horizons. Th e latter are free of each and a radiation dose up to 750 Gray (Gy). primary calcite grains and have well developed All discs were stored at room temperature for at structure. BC horizons as defi ned by B, least four weeks after irradiation. Th e irradiated W H (1998) were not identi- samples were preheated for 1 minute at 230°C. fi ed. Bw(t) horizons have weak clay illuviation, Equivalent dose values were determined us- which is not suffi cient to classify as Bt horizons, ing infrared optically stimulated luminescence because less than 1% of pores contain illuvia- (IRSL) and the Multiple Aliquot Additive Dose tion argillans. Soil color names and notations Protocol (MAAD). A Schott BG39/Corning 7- were determined based on the revised edition 59 fi lter combination was placed between pho- of Munsell soil color charts (OYAMA & TAKE- tomultiplier and aliquots for the measurements. HARA 1992). Each aliquot was hold at a temperature of 50°C during 10 seconds of IR decay. Equivalent doses were obtained by integrating the 1 - 10s region of the IRSL decay curves. An exponential 2.3 Experimental details for growth curve was fi tted to the data and com- luminescence dating pared with the natural luminescence signal to estimate the equivalent dose. Th e reproducibil- Aeolian sediments like loess and dune sands ity of the measurements were excellent so that are particularly suitable for the application of normalisation was not applied. Alpha effi ciency luminescence dating techniques to determine was estimated to 0.08±0.02 for all samples. the “deposition age” of the sediments (F Dose rates for all samples were calculated from D 1998; L et al. 2003; W potassium, uranium and thorium contents, P 1988; Z et al. 1994). Lumines- as measured by gamma spectrometry in the cence is the light emitted from crystals such as laboratory, assuming radioactive equilibrium quartz, feldspar or zircon when they are stimu- for the decay chains. Cosmic dose rate was cor- lated with heat or light after receiving a natural rected for the altitude and sediment thickness, or artifi cial radiation dose. Th e equivalent dose as described by A (1985) and P is a measure of the past radiation energy ab- H (1994). Th e natural water content of sorbed and, in combination with the dose rate, the sediment was estimated to 15±5 %. yields the time elapsed since the last exposure to sunlight. An important assumption of lumi- nescence dating techniques is that the mineral 3 Loess-paleosol sequences grains were exposed to sunlight suffi ciently long enough prior to deposition. 3.1 Section at Neka Eight loess samples were taken in light-tight tubes about 250 g each in the fi eld. Further- East of the city of Sari, loess with a maximum more, about 1 kg of sediment was sampled for thickness of approximately 20 m covers Jurassic gammaspectrometry to determine the amount limestone of the Alborz front hills. At the sec- of radioactivity in the sediment. Polymineral tion at Neka (Tab. 2, Fig. 2), the uppermost Loess paleosol-sequences along a climatic gradient in Northern Iran 157
a) b) 0 0 Now Deh m m
2 2 Neka (23.0 ± 2.2 ka) Agh Band 0 m 4 a) b) 0 0 m m
2 20.5 ± 2.0 ka 6 2 2 (35.2 ± 3.2 ka) 4 8 4
6 10 6
8 12 c) 14 37.8 ± 3.6 ka 10 14 48.7 ± 4.7 ka 16
12 41.3 ± 3.9 ka 91.2 ± 8.8 ka 16 42 debris, m 34.7 ± 3.3 ka 14 (not sampled) 18 44
16 20 Legend
Ap, Ah AhBt 22 AB CB, CBk
Bw, Bwk Ck, (Ckm)
24 Bw(t) Cy
Bt, Btk C (loess)
Fig. 2: Loess-paleosol sequences at the sections at Neka, at Now Deh and at Agh Band. Please refer to text for further description.
Abb. 2: Löss-Paläobodenabfolgen bei Neka, Now Deh und Agh Band. Weitere Erläuterungen im Text. 158 M K, R S, H A, M F A S loess deposit is about 10 m thick and more or nescence age estimates are required to solve the less homogenous with a dull yellowish brown chronostratigraphical problem.
(10 YR 5/4, 10 YR 4/4) color and a CaCO3 Th e loess deposit above the two paleosols cor- equivalent ranging from 158 to 185 g kg-1. Th e relates probably with OIS 3 to OIS 2. An IRSL grain size modus is in the medium silt fraction age estimate of 37.8 ± 3.6 ka (sample NK2 of and clay contents range from 156 to 240 g kg- Tab. 2) was determined for the CB horizon at 1. Weak signs of soil formation including iron 9.5 m depth. A sample taken 20 cm from be- oxide mottling and light browning were found low the modern Bt horizon gave an IRSL age in a layer denominated as CB horizon at 9.5 estimate of 20.5 ± 2.0 ka indicating that the m depth. Underneath this horizon a strongly uppermost loess was deposited during the late developed brown (7.5 YR 4/3) paleosol with glacial maximum (LGM). Bw(t), Bt horizons at a depth of about 12 m Th e modern soil can be classifi ed as Typic Ar- and a very strong, brownish black (7.5 YR 3/2) gixeroll (S S S 1999) or Luvic paleosol (AhBt, Bw(t) horizons) at 15 m depth Phaeozem (FAO 1998) characterised by a thick including horizons of carbonate enrichment Ah horizon covering a strongly developed Bt (Ck) are exposed. Both paleosols have well-de- and a Ck horizon. Th e modern soil resembles veloped nut-shaped to angular blocky structure. the AhBtk horizon between 14.10 and 15.80 m Clay skins are apparent in the lower horizon of below surface rather than the Bw(t) and Bt of the fi rst paleosol and in the strongly developed the upper strong paleosol. AhBtk horizons of the lower paleosol. White patches of secondary calcite and some carbon- ate concretions show some re-calcifi cation from 3.2 Section at Now Deh the overlying loess. However, the CaCO3 equiv- alents of the paleosol horizons do not exceed 17 g kg-1 (Tab. 2). On top of both paleosols, About 20 km southeast of Gonbad-e Kavus, weakly developed light brown (10 YR 4/4) and the Now Deh river (R 1966) dissects a carbonate enriched Bwk horizons occur. Th ese more than 25 m thick sequence of dull yellow- horizons are genetically not related to the Bw(t) ish brown (10 YR 5/4) loess covering weathered or AhBt horizons of the two strongly developed limestone that dips to the northwest. Nine pale- paleosols. Th e Bwk horizons thus indicate a osols are intercalated in the loess exposed in two polycyclic soil genesis including soil formation, steep vertical undercut slopes, which parallel the truncation of the upper soil horizons, loess anticlinal shape of the bedrock. Since there is no deposition and again soil formation. Th erefore, dislocation of the paleosols or other indication the paleosols represent at least two and possibly of modern tectonic activity, the term ‘recent four periods of soil formation interrupted by folded loess’ of R (1966) is confusing. It loess deposition. is more likely that the anticlinal shape of the According to luminescence measurements, loess-paleosol sequence results from mantling a samples NK3 and NK4 taken from above and pre-existing land surface. below the fi rst paleosol gave IRSL age estimates At the northernmost cut of the river the loess of 48.7 ± 4.7 ka and 91.2 ± 8.8 ka (Tab. 3), is divided by four weakly to moderately devel- respectively. It is likely that this paleosol cor- oped and three strongly developed paleosols relates with OIS 5a or 5c. Th e lower paleosol represented by CBk, Bwk and Bt horizons with AhBtk horizons might therefore correlate (profi le a in Fig. 2). At the top of the sequence, at least with the last interglacial but more lumi- a Ck horizon is exposed, similar to Ck horizons Tab. 3: Dosimetric and chronological results.
Tab. 3: Dosimetrische und chronologische Ergebnisse. Loess paleosol-sequencesalongaclimaticgradientinNorthern Iran
Sample Lab-Id. Depth Uranium Thorium Potassium Cosmic H2O Dose rate Palaeodose IRSL Age m [ppm] [ppm] [%] [µGy/a] [%] [Gy/ka] [Gy] [ka]
NK1 LUM-634 2.0 2.36±0.04 9.07±0.10 1.70±0.03 183±9 15±5 3.63±0.32 74.5±2.5 20.5±2.0 NK2 LUM-635 9.3 3.06±0.05 11.00±0.11 2.03±0.03 140±7 20±5 4.08±0.38 153.9±3.2 37.8±3.6 NK3 LUM-632 10.3 3.35±0.06 12.25±0.12 2.06±0.03 131±7 20±5 4.33±0.41 211.0±4.4 48.7±4.7 NK4 LUM-633 12.5 2.09±0.05 6.98±0.09 1.23±0.02 120±6 20±5 2.63±0.25 239.4±5.0 91.2±8.8
ND1 LUM-636 2.0 2.81±0.07 9.65±0.10 1.80±0.03 189±1 15±5 3.97±0.36 91.2±2.5 23.0±2.2 ND2 LUM-637 7.0 2.79±0.06 9.13±0.11 1.86±0.03 136±7 15±5 3.90±0.35 137.3±2.4 35.2±3.2
AB1 LUM-644 15.0 2.87±0.06 9.13±0.11 1.82±0.03 86±4 15±5 3.84±0.36 158.7±3.1 41.3±3.9 AB2 LUM-645 16.0 2.78±0.05 9.85±0.11 1.79±0.03 81±4 15±5 3.86±0.36 134.0±2.6 34.7±3.3
Alpha effi ciency 0.08±0.02 Cosmic dose attenuation calculated with half thickness of sediments above sample. 159 160 M K, R S, H A, M F A S of modern soil in the area under study. Th e cumulation of carbonate. Leaching intensity modern soil has been sampled at profi le b of and/or time of soil formation were apparently Fig. 2, located about 200 m south of profi le a not suffi cient to decalcify the paleosols com- and on the backward site of the river cut shown pletely as a precondition for clay illuviation. in Fig. 3. Th e modern soil at profi le b is under Accordingly, comparatively thin Ck horizons rainfed agriculture and appears to be truncated are found below the CBk and Bwk horizons, by soil erosion. However, Bt horizons were not whereas the Ck horizons underneath the Bt ho- found and the soil classifi es as Typic Calcixeroll rizons exposed at 13.5, 20 and 24 m below sur- (S S S 1999) or Calcic Chernozem face are considerably thicker owing to a much (FAO 1998). According to fi eld observation in higher amount of carbonate enrichment. Th e a nearby location with an altitude of about 350 (reddish) dark brown Bt horizons (7.5 YR 3/4) m and possibly higher mean annual rainfall, the display a strong fi ne to coarse angular blocky to modern soil has a Bt horizon covered by a thick prismatic structure and clear clay coatings. Th ey Ah horizon. Th is soil resembles the modern soil have higher clay contents (Tab. 4) and accord- at the section at Neka. However, clay cutans are ing to fi eld evidence also higher bulk densities less clear and appear to be less well-developed than the CBk or Bwk horizons. Th e two upper likely owing to lower annual precipitation in Bt horizons are thin compared to the lower one. Now Deh. As their thickness does not correspond to the Below the Ck horizon of profi le a about 8 m of ones of the related Ck horizons the truncation homogenous loess are exposed, which has the of the upper part of the Bt horizons by erosion same color as the uppermost loess of Neka. Th e is very likely. grain size distribution shows slightly higher clay Below the Bt horizon at 24 m depth a further percentages and higher portions of very fi ne strongly developed paleosol (possibly a Bt hori- sand and coarse silt (vfS+cSi in Tab. 2, 4) in zon) was not accessible for description and sam- Now Deh. Accordingly, the coeffi cient of coarse pling (not shown in Fig. 2, Tab. 4). Th is paleosol silt/clay is slightly lower. At Now Deh some is found at a depth of about 27 m below surface loess layers contain pseudomycelia of secondary and forms a thick pedocomplex with the CBk calcite possibly indicating a weak synsedimen- horizon at 18.75 m and the two Bt horizons at tary soil formation. Th e Ck horizons found 20 m and 24 m depth about 20 m downstream immediately below CBk, Bwk or Bt horizons of the profi le a. Th is pedocomplex is also vis- described below have abundant carbonate con- ible in the left half of Fig. 3 showing a river cut cretions and nodules and/or patches of second- about 200 m upstream of the described section. ary calcite. Locally, calcite enrichment causes a In this cut, a strongly developed Bt horizon moderate cementation like in the Ck horizon (9th paleosol, not sampled) is exposed at 2.5 m directly beneath the lowermost Bt horizon. depth below the latter pedocomplex (Fig. 3). In profi le a, fi ve weakly to moderately devel- Two IRSL samples were taken in a profi le about oped dark brown to brown paleosols (10 YR 3/ 30 m north of profi le a from 2 and 7 m below 3 to 10 YR 4/4) are exposed at about 9.5, 11.5, surface and above the fi rst Bwk horizon to set 13.0, 16.0 and 18.75 m below surface. Th e up a fi rst chronological frame. Th e samples CBk and Bwk horizons of these paleosols have ND1 and ND2 gave IRSL age estimates of 23.0 massive to weak subangular blocky or weak ± 2.2 ka and 35.2 ± 3.2 ka, respectively (Tab. angular blocky structure and black manganese 2). Th ese results are in agreement with IRSL or humus mottles. Pseudomycelia and patchy age estimates of loess from the section at Neka. carbonate accumulations show secondary ac- However, in the river cut 200 m upstream of Tab. 4: Lithological properties of the loess-paleosol sequence at Now Deh.
Tab. 4: Lithologische Eigenschaften der Löss-Paläoboden -Abfolge bei Now Deh. Loess paleosol-sequencesalongaclimaticgradientinNorthern Iran b b b b b b b b b b b ID Depth Hor. Color (moist) CaCO3 OC cS mS fS vfS cU mU fU S U T vfS + Kd TC cU (cU/T) (m) —————————————————— g kg-1 ——————————————— —— (-) ——
Profile a ND 1 0.45 Ah 10 YR 2/2 101 19.568328 298247142456872683261.1 Tu4 ND 2 1.35 Ck 10 YR 5/4 208 9.213429 285253170367082563141.1 Tu4 ND 3 1.75 C 10 YR 5/4 176 6.613525 320282151347532133451.5 Ut4 ND 4 2.45 C 10 YR 5/4 166 <1.003428 318258143347202463461.3 Ut4 ND 5 3.40 C 10 YR 5/3 160 1.012321 294272148277142583151.1 Tu4 ND 6 6.30 C 10 YR 5/3 160 1.214423 308257145307102603301.2 Tu4 ND 7 7.80 C 10 YR 5/4 162 <1.003421 30327314887242483241.2 Ut4 ND 8 8.40 C 10 YR 5/3 151 1.004417 331286165257831923481.7 Ut4 ND 9 8.90 C 10 YR 5/3 139 2.002211 295311182157881973061.5 Ut4 ND 10 9.35 C 10 YR 5/3 134 <1.024526 352328153378331303792.7 Ut3 ND 11a 9.65 1CBk 10 YR 4/3 101 4.20127 188357174107192711950.7 Tu4 ND 12a 10.10 Bwk 10 YR 3/4 57 3.913311 202351120186733102130.7 Tu4 ND 13a 10.65 CBk 10 YR 4/4 145 1.9 8 18 9 19 234 259 173 53 666 281 252 0.8 Tu4 ND 14 11.30 Ck 10 YR 6/4 267 <1.0 1 15 10 23 242 267 190 49 700 251 266 1.0 Tu4 ND 15a 11.70 2CBk1 10 YR 4/3 155 2.317511 200294203236972792110.7 Tu4 161 162 M K, R S, H A, M F A S b TC Kd (cU/T) cU vfS + vfS b T b U b S b fU b ——————————————— —— (-) -1 mU b cU b vfS b fS b mS b 059618 236242144376223412540.7 Tu3 Tu3 236242144376223412540.7 059618 019517 223273187336832842400.8 Tu4 Tu4 223273187336832842400.8 019517 OC cS 3 11.95 CBk2 10 YR 3/3 71 3.118511 184274185256443321950.6 Tu3 Tu3 Tu3 Tu3 Tu3 Tu3 Tu3 184274185256443321950.6 207267172196453362180.6 3.118511 171260178216093701800.5 71 3.214410 3/3 34 242252144226373402520.7 207214126215484312150.5 1.916410 YR 3/4 67 2.38418 10 YR 4/4 13 <1.045311 10 YR 3/4 CBk2 84 Bwk 10 YR 4/4 249184110225434362570.6 YR 11.95 7.5 Bt 12.20 10 12.40 Ck1 <1.07528 8 10 YR 5/4 13.353Bwk 3/4 13.80 256 <1.0 14.05 YR Ck1 25 14.30 Ck2 41 15.80 10 YR 4/6 14C 16.50 4CBk 10 YR 5/4 26 206 220 7.5 241 <1.0 18.755CBk1 206 10 YR 5/4 10 YR 4/4 191 34 <1.0 19.00 106 160 27 43 147 CBk2 19.25 652 <1.0 24 1.3 242 Ck 9 10 YR 4/4 23 28 17 7 246 193 12 14 120 20 20.20Bt 0.9 10 YR 5/4 237 210 <1. 7 171 Ut4 5 226 357 17 87 163 19 182 <1.0 259 601 94 242 248 16 312 169 156 599 39 307 59 67 211 18 593 0.6 663 230 30 347 270 Tu3 215 0.7 251 200 Tu3 278 189 0.5 1.0 103 Tu3 Tu4 656 241 246 0.9 Ut4 a a a a a a a a a a a a a ND 29 (m) —————————————————— g kg ID Depth Hor. Color (moist) CaCO ID DepthColor Hor. ND 16 ND 21 ND 31 19.906Bw(t)k 10 YR 4/6 71 <1.047612 207226171286043672190.6 Tu3 Tu3 207226171286043672190.6 <1.047612 71 4/6 YR 10 ND 17 ND 18 ND 19 ND 20 12.60 Ck2 13.05ND 22 C ND 23 10 YR 5/4 sampledND 24 265 10 YR 5/4 ND 25 <1.0ND 26 200 25not 18.45 <1. 35 C ND 27 15 19.906Bw(t)k ND 28 33 31 225 253ND 30 165 108ND 19.55 644ND 32 248 C 258 0.9 10 YR 5/4 Lu 242 <1.0 8 32 14 23 197 248 188 78 633 288 221 0.7 Lu Tab. 4 continued Tab. Loess paleosol-sequences along a climatic gradient in Northern Iran 163 b TC Kd (cU/T) cU vfS + vfS b T b U b S b fU b ——————————————— —— (-) -1 mU b cU b vfS b fS b mS b OC cS 3 23.507CBk 10 YR 4/4 71 1.659614 214239192346463202280.7 Tu3 Tu3 Tu3 Tu3 Tu3 214239192346463202280.7 226243140216093692340.6 223231131225843942300.6 1.659614 <1.05639 71 <1.08527 17 4/4 13 3/4 3/4 YR 256223137336163512780.7 YR YR 10 7.5 7.5 19.743322 Bt1 21 21.40 Ck 2/3 23.507CBk 24.00 10 YR 6/4 YR 24.60Bt2 412 1.0 10 24.90 59 Ck 80 26 10 YR 6/4 30 181 0.55Ah 365 166 180 <1.0 0.70 194 AB 82 1.10 526 CBk 56 280 18 10 YR 3/3 211 10 YR 4/4 31 207 103 0.7 229 298 12.0 Lu 171 12 3.2 186 39 607 7 207 23 4 238 9 28 262 1.0 39 208 245 Lu 132 220 161 52 109 602 626 345 265 291 283 0.8 0.9 Tu3 Lu a a a a a a a a cf. to footnotes of Tab. 2 (m) —————————————————— g kg ID Depth Hor. Color (moist) CaCO ID DepthColor Hor. ND 33 a, b ND 34 ND 35 22.90ND 36 C ND 37 ND 38 10 YR 6/4 ND 39 24.70 237 Ckm Profile b 1.6ND 40 10 YR 5/4 32ND 41 10 458 0.25ND 42 <1.0 3 Ap ND 43 215 6 ND 44 97 185 10 YR 2/2 31 255 195 2.00 31 150 67 51 Ck 149 20.2 635 154 314 374 10 10 YR 5/4 452 191 7 173 292 0.6 4 <1.0 181 Tu3 27 25 0.9 266 226 21 Ls2 148 11 48 32 242 640 239 312 169 293 88 0.9 651 261 Tu3 274 0.9 Tu4 Tab. 4 continued Tab. 164 M S, K,R HA,M F AS
Btk of OIS 5 Discontinuities
Pedocomplex of OIS 7
Btk (9th paleosol)
Fig. 3: Strongly and moderately developed paleosols (Bt and Bwk horizons) intercalated in loess at the section at Now Deh. In the uppermost loess layer two straight lines indicate discontinuities and/or short phases of sand accumulation during the deposition of this Late Quaternary loess. In the lower half on the left side of the picture, a strong pedocomplex is exposed, most likely correlating with OIS 7. Th e sequence shown in Fig. 2 was described at a river cut about 200m downstream. In that profi le the pedocomplex sequence splits into four diff erent paleosols.
Abb. 3: Stark und mäßig entwickelte Paläoboden (Bt- bzw. Bwk-Horizonte) im Profi l Now Deh. Das obere Lösspaket wird von zwei geraden Linien durchzogen, die Diskontinuitäten und/oder Sandlagen in dieser jungquartären Lössablagerung anzeigen. In der linken unteren Hälfte der Abbildung ist der stark entwickelte Pedokomplex aufgeschlossen, der vermutlich in das OIS 7 zu stellen ist. Die Profi lskizze von Abb. 2 wurde an einem etwa 200m fl ussabwärts gelegenen Prallhang aufgenommen. Dort teilt sich der Pedokomplex in vier einzelne Paläoböden. Loess paleosol-sequences along a climatic gradient in Northern Iran 165 the section at Now Deh, two discontinuities are Th e section at Agh Band was investigated in intercalated in the loess above the fi rst paleosol three diff erent profi les (profi le a, b and c in horizon (Fig. 3). Th ese discontinuities were not Fig. 2). Th e loess hills are composed of more or observed in profi le a (Fig. 2). less homogenous dull yellowish brown (10 YR According to these fi rst age estimates and based 5/3) to yellowish brown (2.5 Y 5/3) loess rich on loess-paleosol stratigraphy in Europe, it is in chlorite, mica and gypsum. Th e loess has a very likely that the fi rst Btk horizon at 13.5 m grain size maximum in the coarse silt fraction, depth correlates with the last interglacial (OIS high amounts of very fi ne sands and maximum 5e), whereas the moderately developed brown Kd values > 10. It is considerably coarser than Bwk horizons from above the Btk represent the loess at Neka or Now Deh. Profi le a of interstadials of OIS 3 to 5d and the one from the section at Agh Band was described along below this Btk of OIS 6. Th e paleosols of the a steeply inclined southward facing slope (in- pedocomplex, at 18.75, 20 and 24.5 m below clination about 50°) of one of the loess hills. surface, are tentatively correlated with the pe- About 40 m thick loess deposits cover a brown nultimate and antepenultimate (OIS 7 and OIS paleosol with well-developed Bwy (10 YR 4/4) 9) or older interglacial periods. and Bw(t) (10 YR 5/4) horizons superimposing an older loess that resembles the upper loess deposit. Th e paleosol has moderate subangular blocky structure, patches of secondary gypsum 3.3 Section at Agh Band and few calcite pseudomycelia and concretions. Based on the resemblance to subsoil horizons of In the vicinity of the section at Agh Band Typic Calcixerepts that were mapped as mod- steeply sloping loess hills rise about 50 to 70 m ern soils of the area (SWRI 2000), the paleosol above the valley fl oors forming the picturesque possibly correlates with the last or penultimate landscape of the so-called Iranian loess plateau. interglacial soil, most likely OIS 5e. However, Th ese hills are covered by grassland with small independent age control is not available and shrubs mainly situated on the northward facing we did not fi nd an undisturbed modern soil for slopes. Overgrazing in connection with intense comparison yet. rainfall causes serious erosion by episodic sur- About 300 m to the east of the fi rst profi le (a), a face runoff and piping. Th e strong dissection of road cut exposes the loess of profi le b. Here the the plateau by deep valleys raises the question, loess is intercalated by several horizons with sec- whether the drainage system of the plateau was ondary gypsum (Cy horizons) or characterised formed during a period of higher precipitation, by weak iron oxide mottling indicating initial e.g., in early Holocene time. Finely laminated to weak soil formation during deposition of the lake deposits more than 8 m thick cover some of apparently homogenous thick loess deposit. At the valley fl oors between the loess hills. Th e lake the top of profi le b a weakly developed modern sediments have been subsequently eroded and soil with Ah (10 YR 4/2) and weak Bw (2.5 Y incised at least during Holocene times. Th ese 4/3) horizons superimposes the loess. It is most sediments give evidence for the existence of a probable that this soil formed after erosion of lake for many hundreds or thousands of years the modern climatic climax soil. Profi le b is after loess deposition had ceased. Th e lake sedi- located stratigraphically above the tentatively ments correlate most likely with a pluvial period last interglacial paleosol of profi le a and about including a signifi cant higher groundwater ta- 100 m north of profi le c, which was sampled for ble than today. IRSL dating (Fig. 5). Th e samples AB1 and AB2 166 M S, K,R HA,M F AS
Tab. 5: Lithological properties of the loess-paleosol sequence at Agh Band.
Tab. 5: Lithologische Eigenschaften der Löss-Paläoboden -Abfolge bei Agh Band.
b b b b b b b b b b b ID Depth Hor. Color CaCO3 OC Gypsum cS mS fS vfS cU mU fU S U T vfS + Kd TC (moist) cU (cU/T) (m) —————————————————— g kg-1 ————————————————— —— (-) ——
Profile a AB 1 1.80c C 10 YR 4/3 150 1.1 86.8 0 0 4 39 604 161 76 44 840 116 643 5.2 Ut2 AB 2 5.20c C 10 YR 4/3 113 1.3 35.6 0 0 5 99 681 94 36 104 811 85 779 8.0 Ut2 AB 3 7.40c C 10 YR 5/3 104 <1.0 38.1 0 0 5 47 661 164 29 52 853 95 708 7.0 Ut2 AB 4 14.00c C 10 YR 5/3 113 <1.0 47.0 0 0 5 95 689 106 24 10 818 82 784 8.4 Ut2 AB 5 30.00c C 10 YR 5/3 106 <1.0 41.4 0 0 3 23 571 248 61 26 880 94 594 6.1 Ut2 AB 6 38.50c C 10 YR 5/3 121 <1.0 63.2 0 0 7 30 544 221 76 37 842 121 574 4.5 Ut3 AB 7 a 41.50 Cy 10 YR 5/3 101 <1.0 84.0 0 0 3 76 539 186 77 79 802 119 547 4.5 Ut2 AB 8 a 41.90 C 10 YR 4/3 126 1.4 10.5 2 3 2 21 413 249 121 27 783 190 415 2.2 Ut4 AB 9 a 42.40 1Bwy 10 YR 4/4 44 2.7 113.1 5 2 4 17 316 252 147 28 715 258 317 1.2 Tu4 AB 10 a 42.70 Bw(t) 10 YR 4/4 38 1.7 8.6 4 3 1 12 390 247 111 20 748 232 391 1.7 Ut4 AB 11 a 43.00 Ck1 10 YR 5/4 202 <1.0 3.7 4 5 2 38 425 213 117 48 755 197 429 2.2 Ut4 AB 12 a 43.45 Ck2 10 YR 6/4 179 <1.0 4.8 5 4 1 38 446 222 104 48 772 180 450 2.5 Ut4 AB 13 a 45.00 C 10 YR 5/3 153 <1.0 1.0 7 8 6 33 478 229 90 53 797 149 482 3.2 Ut3
Loess paleosol-sequences along a climatic gradient in Northern Iran 167 b TC Kd (cU/T) cU vfS + vfS b T b U b S b fU b mU b ————————————————— —— (-) -1 cU b vfS b fS b mS b OC Gypsum cS 3 CaCO (moist) (moist) 0.75 CB 1.05 C 2.5 Y 3/3 176 2.5 Y 4/3 1.4 160 <1.0 0.1 3.15 Cy 0.0 3.75 0 C 0 2.5 Y 4/3 3 107 5 3 2.5 Y 5/3 <1.0 58 3 103 5.60 602 103.0 56 <1.0 Cy 141 6.00 638 101.7 3 C1 61 121 2.5 Y 5/3 63 54 3 0 804 116 63 2.5 Y 4/3 132 36 3 813 <1.0 660 116 124 25 31 576 693 <1.0 88.6 93 4.5 605 174 Ut3 64.4 5.1 140 63 0 Ut3 44 40 0 0 154 813 789 147 3 0 579 57 28 0 614 679 3.9 49 10.6 132 Ut3 636 Ut2 47 145 28 45 859 52 113 827 682 122 641 6.0 Ut2 5.2 Ut3 a a a a a a cf. to footnotes of Tab. 2 AB 16 AB 17 AB 18 1.70AB 19 Cy 2.25AB 20 C 2.40AB 21 2.5 Y 4/3 Cy 2.75AB 22 158 C 2.5 Y 5/3 AB 23 <1.0 2.5 Y 5/3 109 AB 24 79.3 105 <1.0 2.5 Y 5/3 4.35AB 25 <1.0 105.7 Cy1 4.80 111 0 112.2 AB 26 Cy2 <1.0 5.25 0 0AB 27 2.5 Y 4/3 109.8 3 C 14 2.5 Y 4/3 AB 28 118 6 14 9 3 <1.0 116 55 618 91 2.5 Y 5/3 <1.0 7.00 656 3 77.2 6 133 C2 114 122 31 59.6 59 574 0 <1.0 47 3 61 166 43 119 2.5 Y 5/3 589 3 811 46.4 816 3 61 129 163 122 64 3 46 673 5 74 6 665 <1.0 800 41 5 154 4.8 51 14 10.2 558 13.2 577 826 38 Ut3 Uu 174 585 123 9 3.7 594 58 164 1 53 Ut3 663 54 51 4.8 3 790 149 48 Ut3 158 803 51 2 562 149 82 67 589 542 862 3.5 219 56 Ut3 3.9 668 65 Ut3 11.9 73 826 Uu 101 549 5.4 Ut2 (m) —————————————————— g kg ID Depth Hor. Color Hor. ID Depth Profile b AB 14 AB 15 0.20 0Ah 10 YR 4/2 139 9.5 0.0 5 5 5 41 587 144 73 57a, b 803 140 628 4.2 Ut3 Tab. 5 continued Tab. 168 M K, R S, H A, M F A S were taken with a vertical distance of 1 m and area, whereas long-distance transport might yielded age estimates of 41.3 ± 3.9 ka and 34.7 have contributed the fi ne component in Now ± 3.3 ka, respectively (Tab. 2) indicating that Deh and Neka. Long-distance transport from deposition of this loess layer took place dur- valleys, fl ood plains and deserts of Central Asia ing OIS 3 of the last glacial. Th e two IRSL age was made responsible for loess deposition in estimates are in agreement within the 1-sigma Uzbekistan and Tajikistan that occurs up to an standard deviation. Both samples were taken altitude of 2,500 m above sea level (D from below a fault line dipping to the northeast, 1991). Th e loess cover on the foot hills near the most likely owing to a small land slide follow- section at Now Deh does not exceed an altitude ing heavy rain-fall or a much higher water table of 500 m (L 1988). during a pluvial time or earthquakes. Recent It is thus likely, that most of the dust in North- small and shallow land slides are often found on ern Iran derived from local fl oodplains of the the steeply inclined slopes of the loess hills. rivers Atrek and Gorgan. Unlike in Tajikistan, dust transporting winds possibly did not attain high altitudes. Assuming a paleowind direction from north to south, dry areas emerged dur- 4 Discussion ing Caspian Sea lowstands might have been a dust source, as well. During regressions of the Th e three loess-paleosol sequences show diff er- Caspian Sea, the gain in land surfaces along its ences in thickness, grain size distribution and southern coast was probably low, because the numbers and types of paleosols (Fig. 2, 4). Th e southern lowlands are narrow and have a steep uppermost unweathered loess deposits in Neka, slope towards the interior lake basin. West of Now Deh and Agh Band are about 10 m, 13 the present Turkmen shoreline a large shelf area m and 40 m thick, respectively, suggesting emerged during the Yenotaevian regression (24- diff erent mass accumulation rates during the 17 ka), though (M 1988). However, it last glacial. Mean grain size decreases in a N- is not clear, whether the lake fl oor was dry to al- S direction from Agh Band to Now Deh (and low dust entrainment or was covered by vegeta- Neka) as already observed by L (1988). tion as assumed for emerged continental shelves Th e granulometric composition of Agh Band in the coastal oasis model (F, W & loess resembles the one of loess deposits at the G 2002). northern footlopes of Kopet Dagh in north- Th e unweathered loess layers of each section eastern Iran (O A 2001). Th e are texturally and in relation to the calcium much fi ner loess facies at Neka and Now Deh carbonate content also mineralogically more compares to the fi ne loess facies accumulated in or less homogenous. Also, the sequences do not the piedmonts of Tien-Shan and Pamir-Alay in show any indication of groundwater infl uence. Tajikistan, e.g., in the uppermost loess deposits Th e degree of soil development refl ected in the of the key section at Darai Kalon (F diff erent types of paleosol horizons depends D 1998). Th ickness and mean grain on climatic conditions and duration of soil size of loess are functions of dust availability in formation during interstadial and interglacial the source areas, proximity to the dust source periods, only. Th ese paleosols can be defi ned area, maximum wind velocities and dust trap- as climaphytomorphic, which allows us to use ping effi ciency of the vegetation. Th e high them for paleoclimatic reconstructions. Th e content of fi ne sand and coarse silt in Agh Band morphology of modern soils at the diff erent indicates the close proximity to the dust source sections refl ect the recent climatic gradient. Th e Loess paleosol-sequences along a climatic gradient in Northern Iran 169
Neka Now Deh 0 0 m m Agh Band
0 m 2 2
2 4 4 OIS 2, 3 OIS 2, 3 6 6
OIS 2 to 5 d 8 8
10 10 OIS 3 or 5a-d
12 OIS 5a-d 12
42 OIS 5e m OIS 5e 14 14 OIS 5e 44 OIS 6 OIS 6 16 16 OIS 6 debris, (not sampled) 18
Legend 20 Ap, Ah AhBtk
AB CB, CBk 22 t OIS 7 Bw, Bwk Ck, (Ckm)
Bw(t) Cy
24 Bt, Btk C (loess)
Fig. 4: A pedostratigraphical framework for loess-paleosol sequences of Northern Iran.
Abb. 4: Pedostratigraphische Einordnung der Löss-Paläobodenabfolgen Nordirans. 170 M K, R S, H A, M F A S tentatively last interglacial paleosol has strongly well preserved in Uzbekistan and Tajikistan. developed AhBtk horizons at the section at According to B, W H Neka, moderately to strongly developed Bt ho- (1998) the Karamaydan section in Tajikistan rizons at Now Deh and moderately developed does not contain interstadial paleosol horizons Bw(t) horizon at Agh Band. Th is indicates simi- of the last glacial, partly because the uppermost lar climatic gradients during the past. However, loess is lacking. At the section at Darai Kalon, an undisturbed Holocene soil in the loess hills weak carbonate accumulation horizons but not near Agh Band has not yet been found and fur- complete paleosols were correlated with the last ther studies to establish mineralogical homoge- glacial (F D 1998). Correla- neity of the parent materials are necessary. tion of the 3rd or even 4th pedocomplex with As A horizons were not found, all paleosols were OIS 5e (L 1984, D 1991) truncated before loess deposition started again. would place the fi rst two or three pedocom- Instead, weakly developed brown paleosols plexes into the last glacial. Th ese correlations are (Bwk) were found on top of strongly developed likely invalid, as recent absolute age assessments Bw(t), Bt or AhBt horizons. Th is leads to the have shown (Z, D S hypothesis that soil genesis was polycyclic, 1996, F D 1998). which is well documented in the pedocomplex A fi rst chronstratigraphic framework of loess of OIS 7 at Now Deh that splits in distinct deposition and paleosols formation for the paleosol horizons and intercalated loess layers sections under study is presented in Fig. 4. Sys- at the section described. Paleosols up to 4 m tematic absolute age determinations are needed thick and pedocomplexes of the same thickness to verify the chronostratigraphic position of were described for loess sections in Uzbekistan the diff erent paleosols. Th e strongly developed and Tajikistan (L 1984; M, AhBt horizons in Neka might be good strati- K S 1987; D graphic markers because of their dark color. 1991; B, W & H, , According to additional fi eld observations near F D ). It appears that Neka, the loess record in Northern Iran prob- the Central Asian sequences are more detailed ably reaches far into the Middle Pleistocene. In than the Chinese loess-paleosol sequences with a quarry not accesible for sampling during this pedocomplexes in Central Asia representing study at least eight strongly developed brown or single paleosol horizons in China (B, dark brown paleosols or pedocomplexes divide a 2003). Th e loess-paleosol sequences of North- 25 m high loess deposit. In Northern Iran, there ern Iran then rather resemble the Central Asian might thus be the potential to study consider- than the Chinese sequences. ably longer loess records than described here. Th e loess deposits at Neka and Now Deh are much thinner including less pedocomplexes and paleosols than key sections in Uzbekistan or Tajikistan, the latter reaching a thickness up 5 Conclusion to 200 m and likely encompassing the whole Pleistocene. However, the Iranian sequences During the Late and Middle Pleistocene pro- might allow at least an equally good pedostrati- nounced changes from dry and cold to more graphic resolution of the last glacial/interglacial or less humid and warm climatic conditions cycle, because they include several weakly to occured in Northern Iran. Th e section at Now moderately developed paleosols. Paleosols of Deh gives evidence for at least nine periods of the last glacial/interglacial cycle are likely not loess accumulation interrupted by interglacial Loess paleosol-sequences along a climatic gradient in Northern Iran 171 and most probably also interstadial phases of B, R. (1960): Découverte de loess et soil formation. d’une ancienne vallée remblayé dans le cours Th e uppermost loess deposit probably formed inférieur du Séfi d-Roud (versant nord de during the last glacial. Paleosol horizons likely l’Elbourz, Iran). – C. R. Acad. Sc. Paris, testify interglacial and interstadial phases of 250: 1097-1098; Paris. soil formation. In many cases paleosol horizons B, H. (1937): Die Rolle der Eiszeit in Nord- group to form pedocomplexes, the latter repre- westiran. – Z. Gletscherk., 25: 130-183, 13 senting polycyclic soil genesis. Abb., 17 Photos; Berlin-Zehlendorf. Th e paleosols refl ect a trend of increased B, A. (2003): Correlation of loess-pale- paleoweathering intensity from the now semi- osol sequences in East and Central Asia with arid loess plateau at Agh Band to the subhu- SE Central Europe: towards a continental mid foothills of Now Deh and Neka. Rates of Quaternary pedostratigraphy and paleocli- loess deposition likely experienced an opposite matic history. – Quat. Int., 106/107: 11-31, trend. 7 Fig.; Oxford. Th e loess-paleosol sequences of Northern Iran B, A. & H, T. (1989): Paleosol are excellent archives of climate and environ- sequences as witnesses of Pleistocene climat- ment change for the time period of the Middle ic history. – Catena Suppl., 16: 163-186, 6 and Upper Pleistocene. Systematic absolute age Fig.; Gießen. assessments are needed for further correlation B, A., W, R. & H, T. of Northern Iranian loess with loess deposits of (1998): Pleistocene climatic history of East Central Asia and SE Europe and with the global and Central Asia based on paleopedologi- climatic record. cal indicators in loess-paleosol sequences. – Catena, 34: 1-17, 10 Fig.; Amsterdam. B, A., W, R. & S, S. (1998): Weathering and clay mineral formation in 5 Acknowledgment two holocene soils and in buried paleosols in Tajikistan: towards a Quaternary paleocli- We thank the University of Tehran and the Sha- matic record in Central Asia. – Catena, 34: hid-Beheshti University (Tehran) for help in 19-34, 11 Fig.; Amsterdam. logistic aff airs. Th is is part of an ongoing study B, D., G, J. & S, R. funded by the German Research Foundation (1990): Iran Geomorphologie. – Tübinger (Deutsche Forschungsgemeinschaft, DFG-Gz. Atlas des Vorderen Orients (TAVO), A III Ke 818/4-1 and Fr 877/9-1). 3, 1 Map; Tübingen. D, E., K, R.A. & M, X. (1997): Climate change, loess and palae- osols: proxy measures and resolution in 6 References North China. – J. Geol. Soc., 154: 793-805, 7 Fig.; London. AG B (1994): Bodenkundliche Kartieran- D, Z.L., R, V., Y, S.L., F, A., leitung. – 4. Anfl ., 392 S., 33 Abb., 91 Tab.; H, J.M. & W, G.A. (2002): Th e loess Hannover (E. Schweizerbart). record in southern Tajikistan and correlation A, M.J. (1985) : Th ermoluminescence with Chinese loess. – Earth and Planet. Sci. Dating. – 359 S., 42 Abb., 62 Tab.; Oxford Lett., 200: 387-400, 7 Fig., 1 Tab.; Amster- (Oxford University Press). dam. 172 M K, R S, H A, M F A S
D, A.E. (1991): Loess of Central Asia. – Pleistocene, based on loess malacofauna in GeoJournal, 24: 185-194, 8 Fig.; Dordrecht. Hungary. - GeoJournal, 36: 213-222, 3 Fig.; E, E. (1971): Südkaspisches Tiefl and Dordrecht. (Nordiran) und Kaspisches Meer. Beiträge zu L, A., H, C., R, D.D., A- ihrer Entwicklungsgeschichte im Jung- und , P., F, M., Z, L. & Postpleistozän. – Tübinger Geogr. Stud., 44, H, U. (2003): High-resolution 184 S., 54 Fig., 29 Photos; Tübingen. chronologies for loess: comparing AMS 14C FAO - F A O and optical dating results. – Quat. Sci. Rev., U N (1998): World 22: 953-959, 3 Fig., 2 Tab.; Amsterdam. Reference Base for soil resources. – World L, A.S.A. (1988): Distribution, prov- Soil Resources Reports, 84, 88 S.; Rome. enance, age and paleoclimatic record of the FAURÉ, H., WALTER, R.C. & GRANT, D.R. loess in Central North Iran. – In: E, (2002): Th e coastal oasis; ice age springs D.N. & F, R J. (Eds.): Loess – Its on emerged continental shelves. - Global distribution, geology and soils. Proc. of an Planet. Change, 33: 47-56. Internat. Symp. on Loess, New Zealand, F, M. & D, A.E. (1998): Loess 14.-21. Feb. 1987, 93-101, 6 Fig.; Rotter- chronology of the Middle and Upper Pleis- dam (Balkema). tocene in Tajikistan. – Geol. Rundsch., 87: L, A.A. (1984): Th e loess of Central 2-20, 12 Fig., 2 Tab.; Berlin. Asia. – In: V, A. A., W, H. F, M., O, E.A. & K, K.E. E. J. B, C. W (Eds.): Late Qua- (2003): Loess in Europe – mass accumula- ternary environments of the Soviet Union. tion rates during the Last Glacial Period. 125-131, 2 Fig., 1 Tab.; Minneapolis (Univ. – Quat. Sci. Rev., 22: 1835-1875, 6 Fig., 2 Minn. Press). Tab.; Oxford. M, G.A., K, S.M. S- F, M., S, U. & Z, A. , M.S. (1987): Th e Uzbekistan loess, (1996): Improvements in sample prepara- genesis and distribution. - GeoJournal, 15: tion for the fi ne grain technique. – Ancient 145-150, 3 Fig., 1 Tab.; Dordrecht. TL, 14: 15-17, 2 Fig., 1 Tab.; Clermont- M, A.V. (1997): Th e late Pleistocene- Ferrand. Holocene history of the Caspian Sea. – G S M E- Quat. Int., 41/42: 161-166, 6 Fig.; Oxford. : Geological Map 1 : 100 000, Sheet M, N.J. (1986): A geography of dust No. 6763 Behshar. – Tehran. storms in south-west Asia. – J. Climatol., 6: H, C., A, P., F, M., L, 183-196, 5 Fig., 2 Tab.; London. A., R, D.-D. & Z, L. (2001): N I O C (1978): Delta 13C of loess organic matter as a po- Geological map of Iran at the scale of 1: tential proxy for paleoprecipitation. – Quat. 1 000 000, Sheet No.1: North-West Iran. Res., 55: 33-38, 3 Fig., 1 Tab.; New York. – 1 Map with explanations; Tehran. K, M., F, M. S, A. O, R. & A, A. (2001): Characteris- (2005): Paleosols derived from loess and tics and provenance of the loess deposits of loess-like sediments in the Basin of Persepo- the Gharatikan watershed in Northeast Iran. lis, Southern Iran. – Quat. Int., 140/141: – Global Planet. Change, 28: 11-22, 6 Fig., 135-149, 3 Fig., 5 Tab.; Oxford. 3 Tab.; Amsterdam. K, E. & S, P. (1995): Palae- O, M. T, H. (1992): Revised oecological reconstruction of the Late standard soil color charts. – 13 pp, 10 Fig., Loess paleosol-sequences along a climatic gradient in Northern Iran 173
2 Tab., 13 Plates; Japan. T, D.S.G., B, M.D., M- P, A. & D, E.T. (1980): Das , D. & O’H, S.L. (1997): Devel- Quartär des Kaspischen Küstenvorlandes opment and environmental signifi cance of – Kartierung im Iran. – Mitt. Geol.-Paläont. an eolian sand ramp of Last-Glacial age, Inst. Univ. Hamburg, 49: 61-134, 38 Fig., 3 Central Iran. – Quat. Res., 48: 155-161, 5 Tab., 5 Plates; Hamburg. Fig., 2 Tab.; New York. P, J.R. & H, J.T. (1994): T, E. (1877): Über Lössbildung und über Cosmic ray contributions to dose rates for die Bildung von Salzsteppen. – Verh. k. u. k. luminescence and ESR dating: large depths geol. Reichsanstalt, 15: 264-268; Berlin. and long-term time variations. – Radiation T, L., Z, A., B, Y. Measurements, 23: 497-500, 2 Fig., 2 Tab.; & J, H. (1985): Th e loess-paleosol New York. sequence in China and climatic history. R, E.H. (1966): Geological observations – Episodes, 8: 21-28, 8 Fig., 1 Tab., 1 Photo; on alluvial deposits in Northern Iran. – Ge- Beijing. ological Survey of Iran, Report No. 9, 40 S., V R, L.P., Ed. (1995): Procedures for 10 Fig., 1 Plate; Tehran. soil analysis. –105 pp; Wageningen. S, E., B, H.-P. & S, K. V Z, W. B, S. (1991): Late (1995): Bodenkundliches Praktikum. – 295 quaternary vegetation of the Near East. S, 46 Abb., 60 Tab.; Wien (Blackwell). – Beihefte zum TAVO, Reihe A 18, 155 S., S, F., S, M., L, H., E- 49 Abb., 6 Tab.; Wiesbaden (Dr. Ludwig , H. (1991): Atmospheric sum- Reichert). mer circulation and coastal upwelling in the W, A.G. & P, S.C. (1988): Th er- Arabian Sea during the Holocene and the moluminescence ages for three sections in last glaciation. – Quat. Res., 36: 72-93, 13 Hungary. – Quat. Sci. Rev., 7: 315-320, 2 Fig., 2 Tab.; New York. Fig., 1 Tab.; Oxford. S S S (1999): Keys to Soil Taxon- W, J. S. (2001) “Desert” loess versus “gla- omy. – 8th Ed., 600 pp, 3 Fig.; Blacksburg, cial” loess: quartz silt formation, source areas Virginia (Pocahontas Press). and sediment pathways in the formation of S, A.F.v. (1923): Zur Frage der Lößbil- loess deposits. – Geomorphology, 36: 231- dung. – Z. dt. geol. Ges., 74: 320-325; 256, 12 Fig.; Amsterdam. Stuttgart. Z, L.P., D, A.E. & S, S, L., W, H.E. I, E. (2001): N.J. (1996): Th ermoluminescence dating of Proposed changes in seasonality of climate the Orkutsay loess section in Tashkent re- during the Lateglacial and Holocene at Lake gion, Uzbekistan, Central Asia. – Quat. Sci. Zeribar, Iran. – Th e Holocene, 11: 745-755, Rev., 14: 721-730, 5 Fig., 3 Tab.; Oxford. 5 Fig., 2 Tab; London. Z, L., O, E.A. & MC, W.D. SWRI – S W R I (1994): Towards a revised chronostratig- (2000): Soil Resources and use potential- raphy of loess in Austria with respect to ity map of Iran (1:1 000 000). – 6 sheets; key sections in the Czech Republic and in Tehran. Hungary. – Quat. Geochron., 13: 465-472, 6 Fig., 4 Tab.; Oxford.