Geochemical characteristics and environmental significance of Talede loess–paleosol sequences of Ili Basin in Central Asia

The loess–paleosol deposit in Central Asia is a sensitive indicator of the evolution of the quaternary paleoclimate in the Westerlies, providing insight into the quaternary climate history and its relationship with global climatic changes. Based on the geochemical analysis of elemental composition of densely sampled strata from Talede loess–paleosol sequence in the Ili Basin, the results showed that SiO₂ had the highest major elements content, followed by Al₂O₃. The order of compositional abundance of major elements was generally as follows: SiO₂ > Al₂O₃ > CaO > Fe₂O₃ > MgO > Na₂O > K₂O. Trace elements (i.e. Rb, Sr, Sc, Ni, Cu, Ga, Mo, Y, Pb, Th) in the paleosol layers (i.e. S ₀, S _m, S ₁) and the loess layer of L ₁ were enriched relative to underlain loess (L ₂) horizons, except for the contents of Zr, Cs, Nd, and La in paleosol layers. All of geochemical proxies, such as enrichment factor, Rb/Sr ratio, eluvial coefficient (K _i ) and chemical weathering index, display no obvious differentiation in the Talede loess–paleosol deposit. The results indicate that the weak chemical weathering, greater evaporation and low effective moisture in Ili Basin, are to a degree weaker than those in the China Loess Plateau and the climate was warm–dry during the interglacial period. In addition, the loess of Ili area is rich in schistose minerals and implies that the loess may come from the deserts of Central Asia and it may be closely related to the widespread aridification of Central Asia.     

Stable isotope chemistry of fossil bone as a new paleoclimate indicator

During fossilization, bone is thought to recrystallize and alter chemically on timescales of kyr to a few tens of kyr, i.e., similar to the timescale for formation of soils. Therefore, C- and O-isotope compositions of bone apatite should correlate with trends in soil water composition and aridity, and serve as paleoclimate indicators. This hypothesis was tested by analyzing C- and O-isotope compositions of the CO₃ component of fossil bone apatite from mid-Oligocene through late Pleistocene units in Oregon and western Idaho, including the John Day (19.4-30.0 Ma), Mascall (15.2-15.8 Ma), and Rattlesnake (7.2-7.8 Ma) Formations, whose paleosol sequences have been studied in detail, and the Juntura (10-11 Ma), Hagerman (3.2 Ma), and Fossil Lake (<23-650 ka) fossil localities. Tooth enamel δ¹⁸O values provide a baseline of meteoric water compositions. Stable isotope compositions of bone CO₃ do change in response to broad climatic trends, but show poor correlation with compositions of corresponding paleosol CO₃ at specific horizons. Instead, compositional deviations between bone and paleosol CO₃ correlate with compositional deviations with the next higher paleosol; this suggests that the timescale for fossilization exceeds one paleosol cycle. Based on stratigraphic evidence and simple alteration models, fossilization timescales are estimated at 20-50 kyr, indicating that bone CO₃ will prove most useful for sequences spanning >100 kyr. C-isotopes show negative and strong positive deviations during wet and dry climates respectively, and short-term trends correspond well with changes in aridity within the Mascall and Rattlesnake Formations, as inferred from paleosols. A proposed correction to δ¹⁸O values based on δ¹³C anomalies implies a small, ∼1.5‰ increase in meteoric water δ¹⁸O during the late Oligocene global warming event, consistent with a minimum temperature increase of ∼4 °C. A strong inferred decrease in δ¹⁸O of 4-5‰ after 7 Ma closely parallels compositional changes in tooth enamel, and reflects a doubling in the height of the Cascade Range.     

Reconstructing the response of C3 and C4 plants to decadal-scale climate change during the late Pleistocene in southern Illinois using isotopic analyses of calcified rootlets

The δ¹³C and δ¹⁸O values of well-preserved carbonate rhizoliths (CRs) provide detailed insights into changes in the abundance of C₃ and C₄ plants in response to approximately decadal-scale changes in growing-season climate. We performed stable isotope analyses on 35-40 CRs sampled at 1-cm intervals from an 18-cm-thick paleosol formed in southern Illinois during Wisconsin interstadial 2. Minimum δ¹³C values show little variation with depth, whereas maximum values vary dramatically, and average values show noticeable variability; maximum δ¹⁸O values vary less than the minimum δ¹⁸O values. These findings indicate that a diverse and stable C₃ flora with a limited number of C₄ grass species prevailed during this interval, and suggest that the maximum growing-season temperatures were relatively stable, but minimum growing-season temperatures varied considerably. Two general patterns characterize the relationships between the δ¹³C and δ¹⁸O values obtained from the 1-cm samples. In some cases, low δ¹³C values correspond to low δ¹⁸O values and high δ¹³C values correspond to high δ¹⁸O values, suggesting that cooler growing-season temperatures favored C₃ and warmer growing-season temperatures favored C₄ plants. In other cases, low δ¹³C values correspond to high δ¹⁸O values, likely suggesting that wetter growing-season conditions were favorable to C₃ plants. The high density of well-preserved CRs in this paleosol provides a unique opportunity to study detailed ecological responses to high-resolution variability in growing-season climate.     

陕西长武黄土剖面L3～S6土层渗透性研究

根据渗水实验、孔隙度、粒度、磁化率测定,研究了长武黄土剖面L₃～S₆土层的渗透性及其成因。研究结果表明,L₃,L₄,L₅和L₆黄土层渗透性较强,稳定入渗速率较高,它们的渗透系数变化在0.57～1.06mm/分之间,4层平均为0.75mm/分;S₃,S₄,S₅和 S₆古土壤渗透性较弱,稳定入渗率较低,它们的渗透系数变化在0.18～0.71mm/分之间,4层平均为0.44mm/分。红色古土壤达到稳定入渗率的时间一般比黄土层要长;   黄土层的平均空隙度比红褐色古土壤高,渗透性强,粒度成分较粗,黄土层比红褐色古土壤层更利于构成含水层;   红褐色古土壤层粒度成分细,空隙度低,渗透性弱,比黄土层利于形成隔水层。长武第4层古土壤厚度小,纵向裂隙发育强,入渗速率较大,不易形成隔水层。磁化率、粘粒含量资料表明红褐色古土壤层与黄土层渗透性、含水空间和隔水性的差异主要是当时气候冷干和温湿交替变化的结果。     

Reconstruction of the late Quaternary paleoenvironments of the Nussloch loess paleosol sequence,Germany, using n-alkane biomarkers

This study contributes to the paleoenvironmental reconstruction of the loess–paleosol sequence of Nussloch, Germany, by using n-alkanes as plant leaf-wax-derived lipid biomarkers. We found that n-alkane patterns and concentrations in the Saalian loess and the last interglacial Eemian paleosol of Nussloch point to very strong degradation and prevailing deciduous vegetation. Degradation effects in the overlying paleosols and loess layers are less pronounced and allow for the application of an end-member mixing model to estimate vegetation changes semi-quantitatively. Our findings highlight the potential for the interpretation of degradation-corrected n-alkane ratios. n-Alkane modelling results for loess layers, paleosols and an in-filled paleochannel dated to ~ 60–32 ka suggest that up to ~ 50% of the n-alkanes were derived from deciduous trees or shrubs. This finding is in agreement with the abundant occurrence of wood fragments and indicates a highly variable and dynamic landscape dominated by tundra shrubland. On the other hand, deciduous trees or shrubs did not contribute significantly to the soil organic matter in the late Weichselian loess layers and the intercalated Gelic Gleysols (~ 32–18 ka).     

Stratigraphy and paleoenvironmental changes in the Yangtze Delta during the Late Quaternary

The Yangtze Delta area may be subdivided into paleo-valley and paleointerfluves of the last glaciation. The postglacial transgressive sedimentary cycle (PTSC) on the front zones of the paleointerfluves is composed of marsh-nearshore and barrier-lagoon, shallow marine and nearshore-tidal flat units, with a basement in stiff clay. The PTSC in back zones of the paleointerfluves consists of lacustrine-marsh deposits. The PTSC in the incised valley contains river channel, floodplain-estuary, estuarine-shallow marine and deltaic units, with an erosional surface at its bottom. The stiff clay and the erosional surface constitute the PTSC lower boundary.The stiff clay, consisting of a paleosol, experienced deposition alternating with pedogenesis during the falling of sea-level during δ¹⁸O stage 3; ongoing pedogenesis in the sea-level lowstand of δ¹⁸O stage 2; and early diagenesis after paleointerfluve inundation by the sea-level rise of δ¹⁸O stage 1. The climate during the paleosol formation was temperate with more than 500-mm a⁻¹ rainfall and frequently fluctuating groundwater.The Yangtze River incised its course during falling sea level of stage 3, and a huge incised valley was formed during the sea-level lowstand (stage 2). The filling of the incised valley took place during the postglacial sea-level rise, and delta formation occurred at a late stage of PTSC development.     

A new Late Cretaceous crocodyliform from the western margin of Gondwana (La Rioja Province,Argentina)

The Cretaceous witnessed the greatest diversity of Gondwanan notosuchian crocodyliforms, which displayed high levels of diversity and a notable array of specialized forms that developed in different ecological niches. Among this diversity, the advanced notosuchians are a clade of mid body sized forms which displays a remarkable abundance but is restricted to two lithological units from the Late Cretaceous of South America, the Adamantina Formation in southeastern Brazil and the Bajo de la Carpa Formation in Patagonia (Argentina). The only exceptions known so far were the Late Cretaceous Labidiosuchus from the Marilia Formation in Brazil and Yacarerani from the Cajones Formation in Bolivia. Herein we report a new Cretaceous crocodyliform, Llanosuchus tamaensis gen. nov. et sp. nov., found in the Los Llanos Formation (Campanian?) in northwestern Argentina (La Rioja Province). The small specimen includes well preserved fragments of the cranium and mandible with an estimated skull size of about 9 cm lengths. This crocodyliform shares several derived characters with Notosuchus terrestris from the Bajo de la Carpa Formation (Patagonia) and it was found in a weakly developed sandy paleosol profile formed in wet local conditions but in a region characterized by semi-arid climate and active eolian sedimentation. The presence of a new advanced notosuchian in the Cretaceous of western Gondwana, and its intermediate geographical region between the known South American species (Brazil, Argentina and Bolivia), has interesting implications, and adds another record of an advanced notosuchian in deposits with inferred warm climates and semi-arid paleoenvironments. Finally, Llanosuchus tamaensis supports a Late Cretaceous age for Los Llanos Formation with important geological implications for La Rioja Province.     

Qualitative fatty acid and n-alkane stratigraphy of the Lake Turkana Basin,Kenya

In order to improve understanding of the stratigraphy of the Lake Turkana Basin, one of the important sites in the evolution of early man, this study evaluates the usefulness of organic biological marker compounds, n-alkanes and fatty acids, for correlation of isolated sedimentary strata.Eighty-five paleosol samples were collected from well-defined sedimentary horizons in two regions (Area 103 and Area 130) of the Koobi Fora area of Lake Turkana. Results indicate that most of the organic matter present was derived from terrestrial plant waxes. In sediments where extensive diagenesis has occurred, microbial input of organic matter may have been substantial. Algae were either not an important source of organic matter, or their marker compounds have been removed or altered by degradative processes.The fate of the original paleosol organic matter has been governed to some extent by weathering processes, especially in Area 130. Weathering decreased the amount of extractable lipids, particularly fatty acids and the low molecular weight alkanes (C₁₇C₂₀); produced or retained relatively large amounts of alkanes greater than C₂₁ within a unimodal distribution; and lowered CPI values. Consequently, stratigraphic correlation by unique alkane and fatty acid distributions has been confined to short distances (many meters).Both n-alkanes and fatty acids have been retained better by association with clay minerals than by sand matrices. The alkane distribution of sandstones differs from that of clay organics in having a narrower carbon chain length distribution and lower CPI values. In Area 103, where weathering was less severe, compositional variations with stratigraphic position indicate that lipid material has been retained within each of the facies examined.     

中原邙山黄土地层

位于黄土高原与华北平原过渡带上的中原黄土地层,以邙山赵下峪剖面为其典型代表。据光释光和热释光测年及磁性地层研究结果,该剖面从邙山塬面至黄河河床出露S₀-S₁₀黄土-古土壤序列,总厚度172.1m,B/M界线记录于S₈古土壤层顶部,以厚层晚更新世S₁古土壤(15.7m)和巨厚L₁黄土(77.3m)为其特色。赵下峪剖面上末次间冰期以来的平均沉积速率明显增大,其中以末次冰期晚冰阶L₁LL₁黄土的沉积速率最大,高达34.5mm/a。在邙山黄土堆积过程中,倒数第二冰期末(相当于L₂顶部),约150ka B P,发生了风尘沉积速率的突变,其原因是此时黄河贯通三门峡东流,给风尘源区带来丰富的物质。同时赵下峪剖面的磁化率曲线所示,黄土-古土壤的磁化率强弱,并不简单地反映夏季风强度,也要受到沉积速率变化的影响。      

Age of the fossil Dali Man in north-central China deduced from chronostratigraphy of the loess–paleosol sequence

Dali Man, an archaic type of early Homo sapiens, is of great significance to the origin of Homo sapiens. Achievements have been made during the past decades in the understanding of the fossil human skull as well as the accompanying mammalian fossils and stone artifacts. However, the absolute age of the fossil Dali Man still remains unclear. Based on the magnetic susceptibility of loess sediments and the relationship of terracing process with climatic condition, we correlated the loess sequence and the subjacent terrace alluvium at the Dali Man site with the well-studied loess–paleosol sequence at Luochuan in the central part of the Chinese Loess Plateau. The correlation indicates that the loess–paleosol sequence at the Dali Man site extends down to the paleosol S2, and the underlying fluvial deposits correspond to the loess L3. Because the Dali Man skull appears in the basal gravel layer of the terrace, and because the deposition of the terrace gravels would occur during the transition from S3 paleosol formation to L3 loess accumulation, the age of the fossil Dali Man is inferred to be ca 270 ka, which is equivalent to the age of the boundary between the loess L3 and paleosol S3 on the magnetic susceptibility time series of the Luochuan loess–paleosol sequence.     

临夏塬堡黄土地层S1古土壤中的正构烷烃及其古植被意义

运用GCMS,对临夏S₁古土壤剖面连续系统采集的18个有机地球化学样品进行分析研究的结果发现,所有样品的正构烷烃的高碳数部分均有显著的奇偶优势,CPI值达到5.0以上,并且以表征草本植物输入的正构烷烃C₃₁为主峰。结合不同植被区现代土壤样品的分析结果,研究区正构烷烃特征表明即使在第四纪的气候最适宜期的末次间冰期,在甘肃临夏附近的黄土高原发育了草原植被景观。     

Goethite, calcite, and organic matter from Permian and Triassic soils: carbon isotopes and CO2 concentrations

Pedogenic goethites in each of two Early Permian paleosols appear to record mixing of two isotopically distinct CO₂ components—atmospheric CO₂ and CO₂ from in situ oxidation of organic matter. The δ¹³C values measured for the Fe(CO₃)OH component in solid solution in these Permian goethites are −13.5‰ for the Lower Leonardian (∼283 Ma BP) paleosol (MCGoeth) and −13.9‰ for the Upper Leonardian (∼270 Ma BP) paleosol (SAP). These goethites contain the most ¹³C-rich Fe(CO₃)OH measured to date for pedogenic goethites crystallized in soils exhibiting mixing of the two aforementioned CO₂ components. δ¹³C measured for 43 organic matter samples in the Lower Leonardian (Waggoner Ranch Fm.) has an average value of −20.3 ± 1.1‰ (1s). The average value yields a calculated Early Permian atmospheric Pco₂ value of about 1 × PAL, but the scatter in the measured δ¹³C values of organic matter permits a calculated maximum Pco₂ of 11 × PAL (PAL = present atmospheric level). Measured values of the mole fraction of Fe(CO₃)OH in MCGoeth and SAP correspond to soil CO₂ concentrations in the Early Permian paleosol profiles of 54,000 and 50,000 ppmV, respectively. Such high soil CO₂ concentrations are similar to modern soils in warm, wet environments.The average δ¹³C values of pedogenic calcite from 9 paleosol profiles stratigraphically associated with MCGoeth (Waggoner Ranch Fm.) range from −6.5‰ to −4.4‰, with a mean δ¹³C value for all profiles of −5.4‰. Thus, the value of Δ¹³C between the pedogenic calcite data set and MCGoeth is 8.1 (±0.9)‰, which is in reasonable accord with the value of 7.7‰ expected if atmospheric Pco₂ and organic matter δ¹³C values were the same for both paleosol types. Furthermore, the atmospheric Pco₂ calculated for the Early Permian from the average measured carbon isotopic compositions of the paleosol calcite and organic matter is also analytically indistinguishable from 1 × PAL, with a maximum calculated atmospheric Pco₂ (permitted by one standard deviation of the organic matter δ¹³C value) of ∼5 × PAL.If, however, measured average δ¹³C values of the plant organic matter are more positive than the original soil organic matter as a result of diagenetic loss of ¹³C-depleted, labile organic compounds, calculated Permian atmospheric Pco₂ using these ¹³C-enriched organic values would underestimate the actual atmospheric Pco₂ using either goethite or calcite. This is the first stratigraphically constrained, intrabasinal study to compare ancient atmospheric CO₂ concentrations calculated from pedogenic goethite and calcite. These results demonstrate that the two different proxies record the same information about atmospheric CO₂.The Fe(CO₃)OH component in pedogenic goethite from a Triassic paleosol in Utah is significantly enriched in ¹³C relative to Fe(CO₃)OH in goethites from soils in which there are mixtures of two isotopic CO₂ components. Field-relationships and the δ¹³C value (−1.9‰) of the Triassic goethite indicate that this ancient paleosol profile experienced mixing of three isotopically distinct CO₂ components at the time of goethite crystallization. The three components were probably atmospheric CO₂, CO₂ from in situ oxidation of organic matter and CO₂ from in situ dissolution of preexisting calcite. Although mixing of three isotopically distinct CO₂ components, as recorded by Fe(CO₃)OH in goethite, has been described in modern soil, this is the first example from a documented paleosol. Its preservation affirms the need for careful, case-by-case assessment of ancient paleosols to establish that goethite in any particular soil is likely to be a valid proxy of atmospheric Pco₂.     

New Data on the Composition of Magnetic Minerals from Paleosols of Southern Tajikistan

A dependence of the magnetic susceptibility () on the alternation of paleosol and loess has been revealed for loess sections of southern Tajikistan: the value increases in paleosols and decreases in loesses. The magnetic signal intensification in the paleosol is caused by an elevated content of ferromagnetics. New electron-microscopic data on magnetic minerals from the paleosol have demonstrated that the principal ferromagnetic responsible for high values of the paleosol is biogenic fine-dispersed magnetite. Its particles vary from 0.0n to 0.n m in size and exhibit crystallochemical characteristics typical for this mineral. Under pedogenetic conditions and participation of Fe-reducing bacteria, the activity of biomineralization is controlled by paleoclimatic variations.     

陕西洛川地区全新世中期土壤与气候变化*

在洛川城东全新世中期古土壤剖面中采集了66块样品,利用气量法、磁化率测定、颗粒分析和显微镜观察方法,对土壤层中的CaCO₃含量、磁化率、颗粒成分、微结构进行了分析和鉴定。粒度成分显示洛川中全新世土壤可分为两层,中间为薄层黄土层。实验资料表明,洛川中全新世早期土壤CaCO₃含量低,平均为0.34 ％ ,具有显著淋溶土壤的特征; 小于0.005mm的粘粒含量比马兰黄土高约12 ％ 。粘化层(Bt层)中光性粘土胶膜有一定的发育,而且可见少量块状粘土胶膜存在,表明该层古土壤具有粘粒迁移和粘粒淀积的特征,指示中全新世早期发生的成壤作用比洛川现今成壤作用显著强。由此可以确定,中全新世早期土壤类型应为淋溶褐土, 当时夏季风活动增强,气候比现今明显温湿,年平均降水量至少比现今多100mm余。中全新世晚期古土壤CaCO₃平均含量为2.5 ％ ,淀积型粘土胶膜发育差,以残积粘土为主。中全新世晚期古土壤比早期土壤发育弱,但比该区现代土壤发育强,土壤类型应为典型褐土,当时气候也比现代温湿。中全新世中期6000~5000年间为气候冷干和沙尘暴活动加强的环境恶化期。研究结果对揭示黄土高原中部全新世中期土壤性质和气候变化具有重要意义。     

A pedogenic goethite record of soil CO2 variations as a response to soil moisture content

The terrestrial carbon cycle and the role of atmospheric CO₂ concentrations in controlling global temperatures can be inferred from the study of ancient soils (paleosols). Soil-formed goethite and calcite have been the primary minerals used as a geochemical proxy for reconstructing atmospheric pCO₂ from ancient terrestrial records. In the case of goethite, optimum sampling strategies for reconstructing pCO₂ focus on the portion of the soil profile that displays steep gradients in both soil CO₂ concentration and δ¹³C values of soil CO₂ such that a keeling plot can be developed for a given soil and atmospheric pCO₂ can be calculated from it. We report data from a Carboniferous paleosol that depart from the expected linear trends. The results indicate that pedogenic goethite is sensitive to variations in the isotopic composition of soil CO₂, over a range of timescales, and can record these variations in the carbon isotope composition and mole fraction of Fe(CO₃)OH in solid solution with goethite. We explore possible environmental conditions that can drive these changes as a function of either moisture controlled variations in soil respired CO₂ or in the residence time of carbon in soils. The implications of this result are overestimation of paleoatmospheric pCO₂ from pedogenic goethite.     

Climatic sub-cycles recorded by the fourth paleosol layer at Luochuan on the Loess Plateau

The Chinese loess–paleosol succession, deep-sea sedimentary sequences and ice cores are the three types of paleoclimatic records. Measurements were made of the ancient climatic proxies of magnetic susceptibility, median diameter of grain size and content >40 μm, and the CaCO₃ content of samples collected at 1 cm depth intervals in the fourth paleosol layer of the Luochuan loess-paleosol section on the Chinese Loess Plateau. Wavelet analysis of the data identified cycles of climate change, which were compared to the marine δ¹⁸O record of SPECMAP. The results showed that: (1) when the fourth paleosol layer was forming, the paleoclimate was relatively stable but five extreme climatic events were identifiable as occurring around 408, 381, 376, 368 and 361 kaBP; (2) two of these regional events differed from the global trend; (3) during marine isotope stage (MIS)11, the fourth paleosol layer of the Luochuan loess section recorded a regional quasi-19 ka climatic sub-cycle and (4) this sub-cycle was also reflected globally in the SPECMAP data indicating that, during MIS11, this sub-cycle was regionally and globally synchronized.     

Late Pleistocene and Holocene climate and geomorphic histories as interpreted from a 23,000 C yr B.P. paleosol and floodplain soils, southeastern West Virginia, USA

Field, micromorphological, pollen, whole soil (XRF), and stable isotope geochemical methods were used to evaluate the latest Pleistocene to Holocene climate record from a floodplain-terrace system in southeastern West Virginia. A late Pleistocene (22,940 ± 150 ¹⁴C yr B.P.) silt paleosol with low-chroma colors formed from fluviolacustrine sediment deposited during the last glacial maximum (Wisconsinan) and records a cooler full-glacial paleoclimate. Fluvial gravel deposited between the latest Pleistocene and earliest Holocene (prior to 6360 ± 40 ¹⁴C yr B.P.) was weathered in the middle Holocene under warmer, drier climate conditions, possibly correlated with the Hypsithermal and Altithermal Events of the eastern and southwestern United States, respectively. The glacial to interglacial climate shift is recorded by: (1) changes from a poorly drained landscape with fine-textured soil, characterized by high organic C and redoximorphic features related to Fe removal and concentration, to a well-drained, coarse-textured setting without gley and with significant argillic (Bt) horizon development; (2) changes from a high Zr and Ti silt-dominated parent material to locally derived, coarse fluvial gravels lower in Zr and Ti; (3) a shift from dominantly conifer and sedge pollen in the paleosol to a modern oak/hickory hardwood assemblage; and (4) a shift in δ¹³C values of soil organic matter from −28‰ to −24‰ PDB, suggesting an ecosystem shift from cooler, C3-dominated flora to one that was mixed C3 and C4, but still predominantly composed of C3 plants. A root-restrictive placic horizon developed between the late Pleistocene silt paleosol and the overlying fluvial gravel because of the high permeability contrast between the two textures of soil materials. This layer formed a barrier that effectively isolated the Pleistocene paleosol from later Holocene pedogenic processes.     

Stable isotopic evidence for Middle Pleistocene environmental change from a loess‐paleosol sequence: Kärlich,Germany

Loess‐paleosol sequences are important terrestrial archives of palaeoenvironmental change. Such sequences are rich in pedogenic carbonate, the oxygen and carbon isotopic values of which can provide important palaeoenvironmental information. Although some studies have pioneered the use of O and C isotopes in loess‐paleosol sequences, they are not routinely used as palaeoclimate proxies. In this study we analysed the sedimentology, micromorphology, geochronology and isotopic geochemistry of a Middle Pleistocene loess‐paleosol section, located at Kärlich, Germany. The section studied correlates with the Elsterian glacial (MIS 12) and Holsteinian interglacial (MIS 11). Embedded tephra layers yielded ⁴⁰Ar/³⁹Ar ages of 466±3 ka, 447±1 ka and 361±3 ka. The sedimentology and micromorphology of the sequence record a shift from accretionary loess accumulation (MIS 12) to prolonged pedogenesis at a stable land surface (MIS 11). Soil carbonate δ¹⁸O values record an enrichment of ～3‰ during the accumulation of the loess, reaching peak values comparable with those found in the MIS 11 soil. The δ¹⁸O signal is interpreted as reflecting temperature, highlighting the potential of δ¹⁸O analysis of European loess soil carbonates as a means of reconstructing palaeotemperature history.     

Paleosol at the Archean—Proterozoic contact in NW India revisited: Evidence for oxidizing conditions during paleo-weathering?

A number of fine-grained sericite bearing pelitic, schistose lithologies occur along the Archean (Banded Gneiss Complex)-Proterozoic (Aravalli Supergroup) contact (APC) in the Udaipur valley in NW Indian craton. These Al-rich lithologies (subsequently metamorphosed) have been described as ‘paleosols’, developed over a 3.3 Ga old Archean gneissic basement and are overlain by Paleoproterozoic Aravalli quartzite. The paleosol was developed between 2.5 and 2.1, coincident with the globally recognized Great Oxidation Event (GOE). In previous studies these paleosol sections were interpreted to have developed under reducing environment, however, the finding of a ‘ferricrete’ zone in the upper part of Tulsi Namla section (east of Udaipur) during the present study (in addition to earlier reported lithologies) has led to an alternative suggestion of oxygen-rich conditions during paleosol development. The Tulsi Namla paleosol section shows all the features characteristic of a complete paleosol section described from other Archean cratons. The paleosol includes sericite schist with kyanite as the prevalent Al-silicate in the lower part of profile while chloritoid and Fe-oxides typify the Fe-rich upper part. Alumina has remained immobile during the weathering process while Fe and Mn show a decrease in the lower part of the section and an abrupt rise in the upper part, in the ferricrete zone. The field and geochemical data indicate that the Tulsi Namla section is an in situ weathering profile and at least the upper part shows evidence of oxidizing conditions.