Pleistocene Loess-paleosol Sequence Research Articles

Geophysical sediment properties of a late Pleistocene loess–paleosol sequence, Chenarli, northeastern Iran

AbstractWe present stratigraphic, magnetic, diffuse reflectance spectrophotometric analyses, and chronologic data for the Chenarli loess–paleosol sequence in northeastern Iran. Eight loess units (LU) are identified, described, and constrained in time based on relative stratigraphy and luminescence dating from >130 ± 9.1 ka to ~9.8 ± 0.7 ka. Our data indicate that pedogenic magnetite/maghemite formation gives rise to magnetic enhancement in modern soil and paleosols. The top of LU 7 is demarcated by the well-developed last interglacial soil in which magnetic depletion occurred. We infer that magnetic depletion in this paleosol was produced by reducing conditions in a seasonally waterlogged soil during a warm and wet phase within Marine Isotope Stage (MIS) 5e. Units LU 6 to 1 record several episodes of dust accumulation and soil formation during the last glacial and Holocene. Increased dust accumulation rates occurred during middle-late MIS 3 and lasted into the late MIS 2, with a peak during the last glacial maximum (LU 2). These findings could be applicable to understanding magnetic enhancement/dissolution mechanism in the loess–paleosol sequences in study area. We infer paleoenvironmental changes in northeastern Iran relative to northern Iran, Eurasia, and China.

Revisiting Late Pleistocene Loess–Paleosol Sequences in the Azov Sea Region of Russia: Chronostratigraphy and Paleoenvironmental Record

Loess-paleosol sequences are the most intensively studied terrestrial archives used for the reconstruction of Late Pleistocene environmental and climatic changes in the Azov Sea region, southwest Russia. Here we present a refined chronostratigraphy and a multiproxy record of Late Pleistocene environmental dynamics of the most complete and representative loess–paleosol sequences (Beglitsa and Chumbur-Kosa sections) from the Azov Sea region. We propose a new chronostratigraphy following the Chinese and Danubean loess stratigraphic models that refines the subdivision of the Last Interglacial paleosol (S1) complex in two Azov Sea sites, resolve the uncertainty of the stratigraphic position of the weakly developed paleosol (L1SSm) in Beglitsa section, and allow for direct correlation of the Azov Sea sections with those in the Danube Basin and the Chinese Loess Plateau. More importantly, it may serve as a basis for better constraining local and regional chronostratigraphic correlations, and facilitate the interpretation of climatic connections and possible forcing mechanisms responsible for the climatic trends in the region. In addition, a general succession of environmental dynamics is reconstructed from these two vital sections, which is broadly consistent with other loess records in the Dnieper Lowland and Lower Danube Basin, demonstrating similar climatic trends at Glacial–Interglacial time scales. Furthermore, our results have important implications for the chronostratigraphic representativeness of Beglitsa as a key regional loess section and for the reconstruction of the temporal and spatial evolution of Late Pleistocene climate in the Azov Sea region.

The formation of iron oxides and magnetic enhancement mechanisms in northern Iranian loess-paleosol sequences: Evidence from diffuse reflectance spectrophotometry and temperature dependence of magnetic susceptibility

The magnetic properties of the loess-paleosol sequences from northern Iran provides a model for understanding pedogenic processes and their relationship to paleo-precipitation in this region. For the first time, we present diffuse reflectance spectrophotometry (DRS) analyses, color measurement analyses, and temperature-dependent susceptibility (χ-T) in argon from two late Pleistocene loess-paleosol sequences in northern Iran. Magnetic iron oxide minerals, principally magnetite, maghemite, hematite, and goethite were identified in the study sections. The results of DRS and color measurements show that a* values, the hematite to goethite ratio and the maghemite to hematite ratio, exhibit a significant positive correlation with the pedogenic process and paleosol formation and are superior to low-frequency susceptibility alone for estimating paleoprecipitation. Our data also indicates that pedogenic maghemite-magnetite formation and dissolution/reprecipitation are major contributors to the magnetic enhancement of loess-paleosol sequences and might indicate a seasonal aspect for pedogenic maghemite-magnetite formation. We propose the DRS-derived illite to chlorite ratio as a useful index for assessing the intensity of silicate mineral weathering in the northern Iranian loess-paleosol sequences. In addition, DRS can be used to discriminate between pedogenic and detrital hematite of loess-paleosol sequences. We also propose that the χ-T cooling and heating ratio model is a quantitative proxy for magnetic enhancement in soils and paleosols of loess-paleosol sequences.

Late Pleistocene loess-paleosol sequence at the Belovo section, south of Western Siberia, Russia: Preliminary results

Eurasian loess-paleosol sequences provide continuous records of global change in mid-latitude Northern Eurasia. The loess-paleosol sequence of West Siberia located in the central part of the mid-latitude Eurasian loess belt extending from West Europe to Yakutia is an outstanding paleoclimate archive in Northern Asia. The stratigraphy has been best documented on the left bank of the Ob River, in the so-called Ob Loess Plateau. This study focuses on the stratigraphy of the most complete Middle-Late Pleistocene loess-paleosol sequence at the Belovo section. The suggested high-resolution model of the Belovo Late Pleistocene stratigraphy is based on magnetic and sedimentological proxies and is correlated with other Eurasian loess records and with the global marine δ18O stratigraphy. The enviromagnetic signal at Belovo Loess-paleosol sequences shows a transitional pattern comparable with both typical Eurasian loess magnetic records. Detailed paleopedological interpretations of the magnetic and sedimentological data from the Belovo section have important implications for appropriate linking different Late Pleistocene climates and environments of other the well-known Eurasian loess provinces.

Multiple stages of plant root calcification deciphered by chemical and micromorphological analyses.

Rhizoliths, that is, roots fossilized by secondary carbonates, have been known for ages and are increasingly used for paleoenvironmental reconstructions. However, knowledge about their formation mechanisms remains limited. This study reports the mineralogical and chemical characterization of rhizoliths at different stages of mineralization and fossilization in the Late Pleistocene loess-paleosol sequence of Nussloch (SW Germany). Scanning electron microscopy coupled with elemental mapping and 13 C solid-state nuclear magnetic resonance were used to concomitantly characterize the mineral and organic matter of the rhizoliths. These joint analyses showed for the first time that large rhizoliths are not necessarily remains of single large roots but consist of numerous microrhizoliths as remains of fine roots, formed mainly by calcium carbonates with only low amounts of Mg and Si. They further revealed that the precipitation of secondary carbonates occurs not only around, but also within the plant root and that fossilization leads to the selective preservation of recalcitrant root biopolymers-lignin and suberin. The precipitation of secondary carbonates was observed to occur first around fine roots, the epidermis acting as a first barrier, and then within the root, within the cortex cells, and even sometimes around the phloem and within the xylem. This study suggests that the calcification of plant roots starts during the lifetime of the plant and continues after its death. This has to be systematically investigated to understand the stratigraphic context before using (micro)rhizoliths for paleoenvironmental reconstructions in terrestrial sediments.

Revisiting the chronostratigraphy of Late Pleistocene loess-paleosol sequences in southwestern Ukraine: OSL dating of Kurortne section

Revisiting the chronostratigraphy of Late Pleistocene loess-paleosol sequences in southwestern Ukraine: OSL dating of Kurortne section

Revisiting the chronostratigraphy of Late Pleistocene loess-paleosol sequences in southwestern Ukraine: OSL dating of Kurortne section

Due to the general lack of other high-resolution paleoclimate records, loess-paleosol sequences are crucial archives for disentangling past climate variability in southeastern Europe. Here we present results of a multi proxy sedimentological and geochemical investigation of Kurortne loess-paleosol section from southwestern Ukraine, coupled with detailed optically stimulated luminescence (OSL) dating. OSL investigations were carried out on quartz grains of different grain sizes (4–11 μm, 63–90 μm and 90–125 μm), using the single aliquot regenerative (SAR) protocol. The OSL dating results are in line with previous findings on dating loess-paleosol sequences along the Black Sea shore in Romania, as well as worldwide: (i) ages obtained on different grain sizes are in agreement for equivalent doses of less than 200 Gy, whereas for higher equivalent doses 4–11 μm ages underestimate the coarser fraction ages; and (ii) an inverse correlation between dated grain size fractions and saturation characteristics is reported.Our combined dating and sedimentological approach would confirm that the investigated uppermost 4.5 m at Kurortne cover the Last Glacial Cycle, adding important data in better constraining local and regional chronostratigraphic correlations. The application of the SAR protocol on 63–90 μm quartz grains on samples collected from the lower part of S1 soil (the Kaydaky unit) and from the Kaydaky/Pryluky units boundary produced ages of 123 ± 10 ka and 85 ± 6 ka, respectively. As the temporal range covered by these units in the Ukrainian Quaternary stratigraphic framework is still debatable, our results confirm the broad correlation of the Kaydaky-Pryluky paleosol units at Kurortne with the last interglacial (i.e., MIS 5). Dating the Uday and Bug loess units produced ages corresponding to MIS 4 and MIS 2, respectively, whereas the sample collected from the Vytachiv unit provided an age of 37.7 ± 2.4 ka, assigning this paleosol to MIS 3. On the basis of trends in the magnetic enhancement, the onset of pedogenetic processes likely commenced already around 20 ka, but the formation of the topmost S0 soil has begun after 13.8 ± 1.0 ka.

Radiocarbon dated malacological records of two Late Pleistocene loess-paleosol sequences from SW-Hungary: Paleoecological inferences

The two loess-paleosol sequences of Villánykövesd and Máza preserved specific paleoecological information of the Late Pleistocene environmental conditions in SW-Hungary. For malacological examinations, sampling of 12 cm intervals were used; homogenous amounts of sediment (ca. 5 kg) were collected. During the malacological examinations, more than 27,000 specimens were identified. Interpreting their environmental and climatic demands the paleoclimate and paleoenvironment of the last 80,000 years could be reconstructed. The results of the malacological investigations of Villánykövesd sequence indicated 5 malacological zones (MZs) by the snail species’ dominant occurrence. All of the 5 MZs indicate mild climatic conditions with only one cooling phase. The mild climatic conditions were reconstructed by the high dominance of thermophilous species, especially Pupilla triplicata. This warmth loving, xerophilous and open vegetation preferring species is present in the entire sequence, which indicates a refuge area of P. triplicata around Villánykövesd. At the Máza sequence, 9 MZs could be allocated with mainly dominance of cold resistant species, indicating cooler climatic conditions than at Villánykövesd. The reason of the high ratio of cold resistant species and the high number of MZs could be the geographic exposition of the Máza sequence. The Máza sequence is located in a bench between higher and lower reliefs on the northern pediment area of Mecsek Mountains. This indicates the presence of a fluctuation zone for the snail species in the area of Máza sequence. The Late Pleistocene sequences possess different climatic and environmental conditions during same timeframe, therefore we highlight that the previously reconstructed mosaic-like environmental patters in the Carpathian Basin are real properties in the region.

Evaluating the paleoclimatic significance of clay mineral records from a late Pleistocene loess-paleosol section of the Ili Basin, Central Asia

AbstractIn this study, we present clay mineral records from a late Pleistocene loess-paleosol sequence in the Ili Basin, Central Asia, and assess their significance for paleoclimatic reconstruction. The results show that the clay minerals are mainly illite (average 60%) and chlorite (28%), with minor kaolinite (9%) and smectite (3%). Illite was of detrital origin with no obvious modification to its crystal structure. Increases in illite content in the loess are ascribed to wind intensity rather than pedogenesis. High proportions of illite in the clay fraction, and of muscovite in the bulk samples of the paleosol units, may lead to an overestimation of the weathering intensity. Kaolinite was likely inherited from the sedimentary rocks, while chlorite might have been inherited from both sedimentary and metamorphic rocks. The paleoclimatic signals of kaolinite and chlorite were unclear, due to reworking by both fluvial and eolian systems. Smectite was more likely formed by the transformation of biotite and illite, and its variation in the loess sequence was also controlled by wind intensity; this was largely due to aggregation and is unlikely to reflect moisture changes. Although the interpretation of paleoclimate evolution may contain some uncertainties, clay mineralogy does provide the possibility of tracing dust provenance.

Pleistocene climate change inferred from multi-proxy analyses of a loess-paleosol sequence in China

The aeolian loess blanketing the Chinese Loess Plateau (CLP) is sensitive to climate change in monsoonal East Asia. Here, we present a multi-proxy climatic record from a Pleistocene loess-paleosol sequence from the Lantian Basin on the southern margin of the CLP. The measurements include magnetic susceptibility and related magnetic properties, bulk median grain-size, color reflectance, and the color-inferred hematite versus goethite ratio (Hm/Gt). A long-term aridification and cooling trend during the interval from ca 2.22–0.43 Ma is indicated by two magnetic grain-size proxies, corresponding to the global climatic cooling of the late Cenozoic. In addition, at least four intervals of climatic extremes are evident in the record of Hm/Gt ratio: at 1.71–1.65 Ma, 1.26–1.24 Ma, 0.94–0.86 Ma, and 0.62–0.48 Ma. These intervals are characterized by distinct regional climates, which contrast with the global climatic conditions represented in marine sediments. For example, a relatively arid climate is documented from 1.71 to 1.65 Ma, which was rapidly succeeded by a relatively humid climate which is associated with the earliest hominin (with an age of ca 1.63 Ma) in the Lantian Basin.

Disentangling interactions between microbial communities and roots in deep subsoil

Soils, paleosols and terrestrial sediments serve as archives for studying climate change, and represent important terrestrial carbon pools. Archive functioning relies on the chronological integrity of the respective units. Incorporation of younger organic matter (OM) e.g. by plant roots and associated microorganisms into deep subsoil and underlying soil parent material may reduce reliability of paleoenvironmental records and stability of buried OM. Long-term effects of sedimentary characteristics and deep rooting on deep subsoil microbial communities remain largely unknown. We characterized fossil and living microbial communities based on molecular markers in a Central European Late Pleistocene loess-paleosol sequence containing recent and ancient roots with ages of several millenia. The molecular approach, comprising free and phospholipid fatty acids (FAs), core and intact polar glycerol dialkyl glycerol tetraethers (GDGTs), as well as 16S rRNA genes from bacterial DNA, revealed the presence of living microorganisms along the sequence, with bacterial community composition comparable to that of modern topsoils. Up to 88% redundancy between bacterial genetic fingerprint and molecular signature of fossil microorganisms suggested a time-integrated signal of the molecular markers accumulated over a time span potentially lasting from sedimentation over one or more rooting phases until today. Free FAs, core GDGTs and DNA, considered as remains of fossil microorganisms, corresponded with ancient and recent root quantities, whereas phospholipid FAs and intact polar GDGTs, presumably derived from living microorganisms, correlated only with living roots. The biogeochemical and ecological disequilibrium induced by postsedimentary rooting may entail long-term microbial processes like OM mineralization, which may continue even millenia after the lifetime of the root. Deep roots and their fossil remains have been observed in various terrestrial settings, and roots as well as associated microorganisms cause both, OM incorporation and mineralization. Therefore, these findings are crucial for improved understanding of OM dynamics and carbon sequestration potential in deep subsoils.

A Review of Recent Advances in Red-Clay Environmental Magnetism and Paleoclimate History on the Chinese Loess Plateau

The red-clay sequence on the Chinese Loess Plateau (CLP) was deposited during the late Miocene-Pliocene and is encoded with important information of past climate changes. However, it has received much less study in comparison to the overlying Pleistocene loess-paleosol sequence. In this paper, we review recent progress in characterizing the environmental magnetic parameter-based paleoclimate history recorded by the red-clay sequence. Several key conclusions are as follows. 1) the red clay and the loess-paleosol sequences have similar magnetic enhancement mechanisms but magnetic minerals in the red clay sequence have experienced a higher degree of oxidation than in the loess-paleosol sequence. 2) The CLP experienced a cooling and wetting trend from 4.5 to 2.7 Ma, caused by ice sheet expansion and East Asian summer monsoon intensification, respectively. 3) The above conclusions benefit from backfield remanence curve unmixing and comparison of magnetic grain size/concentration records, which are particularly useful in separating the temperature from the precipitation signal. A clear need in future studies is to explore the concentration and the grain size variations of hematite and goethite in the red-clay sequence and their formation mechanisms. The payback would be a clear understanding of climate history during the late Miocene-Pliocene, a possible analog for future warmer climate.

Micromorphology of the lower Pleistocene loess in the Iranian Loess Plateau and its paleoclimatic implications

Abstract The loess deposits in Iran are a valuable archive of regional paleoclimatic and paleoenvironmental information. Extensive sedimentological and chronological studies have been carried out on the middle to upper Pleistocene loess successions during the past decades, but there is an absence of comparable research in the older loess deposits. Recently, a 19-m-thick loess-paleosol sequence was discovered in the central Iranian Loess Plateau (ILP), which was paleomagnetically-dated to ∼2.4–1.8 Ma and thus represents by far the oldest loess known in northern Iran. Here, we present the results of a detailed micromorphological investigation of these lower Pleistocene loess-paleosol sequences (“red sequence”) from the ILP. Our main findings are as follows: 1) The Agh Band red sequence deposits are an extremely thick soil complex comprising paleosols in different stages of development; 2) the micromorphological index of soil development (MISECA) suggests that the moderately- and well-developed paleosols in the red sequence formed in an environment with mean annual precipitation ranging from around 450 to 650 mm, respectively; and 3) MISECA suggests that the red sequence formed under a semi-arid to sub-humid climate and thus under wetter and more favorable conditions than the overlying late Pleistocene loess and modern soils.

Late Pleistocene loess of the Lower Rhine

From the Lower Rhine a compiled 25.7 m thick Late Pleistocene loess-paleosol sequence is differentiated into five lithostratigraphic units: the Rheingau Member (MIS 5), the Keldach Member (Weichselian Early Pleniglacial, GS-21.1–18, MIS 4), the Ahrgau Member (Weichselian Middle Pleniglacial, MIS 3) and the Hesbaye and Brabant Members (Weichselian Late Pleniglacial, MIS 2). It correlates well with climate fluctuations known from ice cores and deep-sea cores. The sequence was continuously sampled by 335 samples. It cuts through all essential layers and soils of the Late Pleistocene Upper Loess Formation. A continuous coarse silt index (CSI) curve shows a maximum in the Hesbaye Member (31–24 ka b2k) indicating the strongest wind conditions during the early Late Pleistocene. Further CSI highs lie in the Keldach and early Brabant Members. CSI lows are found the early and middle Rheingau Member (GI-25–?GI-22), the Jackerath-Spenrath Soils within the deeper Keldach Member (?GI-20–19), the early Ahrgau Member (GI-17–GI-12) and finally in the Elfgen Soil (GI-2) at the base of the Brabant Member. The organic carbon culminates in the Titz Humus Zone, presumably at the end of GI-21, indicating scanty oxidation during the following cold Lower Weichselian Pleniglacial period. The Garzweiler Solcomplex forming a prevailing period of soil formation between 130 and 78 ka BP (MIS 5e–a) is considered as interglacial complex (Rhine Interglacial Complex) continuing the style of the older interglacial complexes of MIS 7, 9 etc. The Ahr Interstadial Complex (MIS 3) is seen as immature complex of warm phases with fabric of the interglacial complexes. – Author's suggestion: The Rhine Interglacial Complex covers MIS 5e–a and restricts the Weichselian Glacial to MIS 4 through MIS 2. This procedure follows the style of the older interglacial complexes.

Radiocarbon dated malacological records of two Late Pleistocene loess-paleosol sequences from SW-Hungary: paleoecological inferences

The two loess-paleosol sequences of Villanykovesd and Maza preserved expressive paleoecological information of the Late Pleistocene environmental conditions of SW-Hungary. For malacological examinations sampling of 12 cm intervals were used and homogenous amounts of sediment (cca. 5 kg) were collected. During the malacological examinations more than 27,000 specimens were identified. Adjusting their environmental and climatic demands the paleoclimate and paleoenvironment of the last 80,000 years could be reconstructed

Deciphering magnetoclimatological patterns of late Early to early Middle Pleistocene loess–paleosol sequences in the western Chinese Loess Plateau

A detailed environmental magnetic investigation in conjunction with geochemical, bulk grain size and redness analyses of late Early to early Middle Pleistocene loess–paleosol sequences at the Jiuzhoutai and Caotan loess sections has been carried out, aimed to explore the reliability of magnetic parameters as paleoclimatic proxies in the western Chinese Loess Plateau (CLP). The results show that magnetic enhancement of early- to mid-Pleistocene loess–paleosol sequences at both sites is not solely due to the neoformation of ultrafine magnetic particles through pedogenesis, but in the case of several loess layers (e.g., L8 and L9) is more attributed to the significant input of coarse-grained magnetic minerals associated with the advance of desert margin and/or with significant changes in local sediment input. Since the magnetoclimatological signals studied here are obviously controlled by both pedogenesis and wind vigor, measurements of magnetic susceptibility (χ) and saturation isothermal remanent magnetization (SIRM), both of which are responsive to both ultrafine pedogenic magnetic particles and eolian coarse-grained pseudo-single domain/multi-domain magnetic particles, could not provide unambiguous interpretation of the magnetic response to the East Asian summer monsoon intensity. In contrast, anhysteretic remanent magnetization (ARM) and the percentage of frequency-dependent magnetic susceptibility (χfd%), which are notably responsive to ultrafine magnetic particles, can aptly trace changes in the concentration of pedogenic magnetic particles and can therefore be used as reliable proxies of pedogenic intensity. The magnetic grain size dependent proxies, e.g., ARM/χ and ARM/Ms (Ms, saturation magnetization), geochemical indices (e.g., chemical index of alteration, Zr/Rb and Al/Si ratios), and bulk grain size records all exhibit concordant variations and are more straightforward proxies for addressing the East Asian monsoon variability. Therefore the combination of multi-parameter mineral magnetic, geochemical and grain size analyses is very useful for distinguishing, delimiting and correlating loess sequences, and for accurately deciphering their paleoclimatic signals embedded in the weakly weathered loess. As the classical precipitation-driven pedogenic model for magnetic susceptibility enhancement is not entirely applicable to the early- to mid-Pleistocene loess developed in the semi-arid western CLP, considerable caution should also be warranted in using magnetic susceptibility measurements alone in the quantitative reconstruction of paleoprecipitation.

The dynamics of the Late Pleistocene loess formation, Lozhok section, Ob loess Plateau, SW Siberia

There are unique loess-paleosol sections that fully reflect paleoclimate changes during the Late Pleistocene in southern West Siberia. This record of climate shows a good correlation with the marine oxygen isotope curve and other global climate records, and consequently the loess-paleosol sequence of West Siberia is a detailed reference scale. Lozhok is a key section for the Late Pleistocene loess-paleosol sequence of the Novosibirsk Ob' Region. Average loess accumulation rates of each studied loess layer were calculated on the basis of previous 14C and TL dating results and on correlation of the loess-paleosol sequence of southern West Siberia with MIS and the Middle Siberia loess-paleosol sequence. The grain-size distribution data indicates intensification of environmental dynamics until the Last Glacial. Bulk chemical composition reveals the intensification of aridization from the Tulino to the Bagan loess, and that this trend was not constant. Greater accumulation loess activity during Bagan time (MIS-2) is also confirmed by loess accumulation rate calculations. Results of sand quartz grain morphoscopy show that loess layers were formed by aeolian processes in periods of deep cooling and aridization. The Late Pleistocene loess layers were formed in periglacial environments, in arid cold deserts.

Identifying depositional and pedogenetic controls of Late Pleistocene loess-paleosol sequences (Saxony, Germany) by combined grain size and microscopic analyses

Identifying depositional and pedogenetic controls of Late Pleistocene loess-paleosol sequences (Saxony, Germany) by combined grain size and microscopic analyses

Re–Os isotopic records in Pleistocene loess–paleosol sequences from the Yili Basin, northwestern China

The Re–Os isotope system is a potentially powerful tool for obtaining information on source regions and transportation processes of aerosols such as mineral dust. Re–Os isotopic systematics were studied in two Pleistocene loess–paleosols exposed at Kuerdenengbulake and Zeketai in the Yili Basin, northwestern China. In the late Pleistocene Malan Loess, 187Os/188Os ratios (0.90–1.45) varied inversely with Os abundances (28–61pg/g). In the middle Pleistocene Lishi Loess section, fluctuations in Os abundances (25–50pg/g) were accompanied by a limited range of variation in 187Os/188Os ratios (generally 1.21–1.40). Four samples of Malan Loess from the Kuerdenengbulake section had higher Os concentrations and less radiogenic 187Os/188Os, coupled with higher zoisite/tourmaline ratios but uncorrelated with abundances of other minerals, paleomagnetic parameters, grain-size characteristics, major-element composition, or Rb–Sr and Sm–Nd isotopic systematics. The correlation between Os and zoisite/tourmaline ratio suggests that the source material of the loess changed when these samples were deposited, but this change was not evident in the other data in this study. Depth profiles show how Re–Os isotopic compositions varied with age of deposition. By characterizing Os abundances and 187Os/188Os ratios of late Pleistocene loess–paleosol samples in the Yili Basin, local paleoclimatic changes occurring over intervals of several thousand years could be identified that had not been found by traditional paleoclimatic proxies.When the 143Nd/144Nd ratio alone cannot distinguish the provenance of global eolian sediments, a combination of 143Nd/144Nd and 187Os/188Os can sometimes be effective. However, for the Yili Basin's loess–paleosol, the range of 187Os/188Os overlapped with ratios in eolian sediments from other areas, offering no improvement over 143Nd/144Nd alone in this respect.

Lateral and depth variation of loess organic matter overprint related to rhizoliths — Revealed by lipid molecular proxies and X-ray tomography

Abstract Terrestrial sediments like loess are well known for their paleoenvironmental significance. Although organic carbon contents are commonly very low, loess and organic matter (LOM) thereof is regarded as important terrestrial archive for vegetation and climate during deposition. However, the LOM signal is prone to contamination by OM of other age and origin than the synsedimentary vegetation, e.g. by postsedimentary deep-rooting plants. We hypothesized that the influence of rhizosphere effects related to deep-rooting plants varies with depth in quality, quantity and distance to the former root. The 13 m thick late Pleistocene loess-paleosol sequence at Nussloch (SW Germany) contains rhizoliths (calcified roots) of Holocene age. With the carbonatic encrustation leading to preservation of former root deposits, rhizoliths allow for assessment of rhizosphere processes that occurred during the root's lifetime. Several horizontal transects comprising rhizoliths, surrounding loess (rhizoloess) up to a distance of 11 cm from rhizoliths, and root-free reference loess from different depth intervals, were analyzed for their carbon (C), alkane and fatty acid (FA) composition. Alkane proxies like carbon preference index (CPI), average chain length (ACL), as well as n-C27/n-C31 and n-C29/n-C31 ratios indicated grass vegetation as origin of LOM, while rhizoliths derived from woody vegetation. Several lipid molecular proxies, e.g. short chain/long chain alkanes, long chain alkane composition and long chain/very long chain FA, indicated the incorporation of considerable amounts of root and rhizomicrobial OM. The rhizosphere effect, i.e. postsedimentary overprint of initial LOM in the vicinity of roots, was not restricted to few mm around the former root, but notable to distances of at least 5 cm and possibly more. This was confirmed by X-ray tomography analyses enabling identification of small calcified root remains and non-calcified root channels in the former rhizosphere, which could not be identified under field conditions. In depth intervals with high rhizolith frequency, this entailed lateral overprint of large parts of loess, which in depths of 1.95 and 3.2 m below present surface can cover the whole loess due to extension of the former rhizosphere of > 5 cm. Regarding the high rhizolith frequency (maximizing at 200 m− 2 at ~ 2.6 m depth) at Nussloch, these findings raise the importance of deep-rooting plants as potential source for significant postsedimentary overprint of loess-paleosol sequences.