Paleosol Profiles Research Articles

Paleosol geochemistry of the late Paleocene Goler Formation of Southern California

Abstract Paleosol (fossilized soil) geochemistry can provide a record of paleoclimatic conditions due to the relationships between pedogenic processes and climate. In this study, paleosols from the late Paleocene Goler Formation of Southern California were used to determine the paleoclimatic conditions active during pedogenesis. The enrichment and retention of soluble elements (Ca, Mg and Na) and the mobilization of Fe and Mn within the paleosol profiles suggest a climate with strongly seasonal precipitation. Similarly, variations in the Mn content and δ13C ratio of pedogenic carbonate nodules also reflect seasonal precipitation. Regional paleotopography was likely an important control on the paleoclimate of the Goler Formation due to rain shadow effects. Although the size and location of these ancient mountains are poorly constrained, the identification of climatic effects specifically associated with these variables provides new constraints.

The Permian Moradi Formation of northern Niger: Paleosol morphology, petrography and mineralogy

Three basic paleosol morphologies, named Type A, Type B and Type C, are described from the middle–upper Permian strata of the Moradi Formation, Tim Mersoi Basin, northern Niger. The Moradi Formation is a typical alluvial redbed succession dominated by red mudrocks with fine to coarse-grained pebbly channel sandstones and matrix-breccias. Type A paleosols are hosted by well-sorted fine to medium grained trough cross bedded and massive sandstones and preserve abundant vertical to horizontal micritic and microspar calcite tubules, interpreted as rhizoliths. Lateral variability of rhizoliths in Type A paleosols, and their close association with fluvial channel-fill sediments suggests they are the roots of grove stands of phreatophytic vegetation that grew within unstable anabranching stream systems. Type B paleosols are hosted by mudrocks and preserve well-developed ped structure, abundant micritic calcite nodules and vertically-stacked micritic calcite nodular bodies, as well as rare calcite with satin-spar texture interpreted as a pseudomorphic replacement of pedogenic gypsum. The morphology of Type B paleosols suggests they were formed in well-drained floodplain deposits on stable landforms. Type C paleosols are similar to Type B but preserve pedogenic structures indicative of soil volume expansion and contraction, as well as more abundant Stage II pedogenic carbonate nodules. The morphology of Type C paleosols suggests that they developed periodically rather than seasonally in poorly-drained deposits that nevertheless occupied a relatively stable part of the landscape such as the plains flanking ephemeral lakes or sabkhas.X-ray diffraction analysis of the <2μm fraction from the Moradi Formation strata indicates that paleosol phyllosilicates are composed of illite, smectite, and occasionally kaolinite and talc. Illite is likely a detrital mineral, whereas smectite and kaolinite are likely pedogenic weathering products. The presence of talc in the Moradi Formation paleosols is unusual. It is limited to paleosol horizons that also preserve evidence for pedogenic gypsum accumulation and is therefore most likely related to a pedogenic weathering process. It is possible that this talc is a relatively low-temperature (~50–100°C) diagenetic alteration product of pedogenic Mg–phyllosilicates such as sepiolite.The range of morphologies, petrographic textures and mineralogy of the paleosol profiles indicates semi-arid to hyper-arid climatic setting. This paleoclimatic reconstruction is in agreement with Middle and Late Permian conceptual paleoclimate models and quantitative general circulation models. Nevertheless, and in spite of an arid climate, Moradi paleosols and their host strata also indicate a relatively shallow groundwater table. Importantly, this shallow groundwater resource undoubtedly helped to support the moderately diverse fossil vertebrate assemblage and large-stature macrophytes preserved in the Moradi Formation.

Mineralogical evidence for a local volcanic origin of the parent material of Bermuda Quaternary paleosols

The alternation of carbonate deposits and paleosols compose the emerged part of the Bermuda archipelago. The pedological units present a complex and diversified mineralogy. Former studies demonstrated that the paleosols are not primarily a product of the unique dissolution of the surrounding carbonates, but contain a massive input of allochthonous non-carbonate detrital material. Researchers during more than the past three decades have attributed this flux of insoluble residues (IR) to Saharan dusts. We carried out systematic field and mineralogical analyses on the Quaternary paleosols from the Bermuda archipelago. Their mineralogical assemblage predominantly includes carbonates, clay minerals (kaolinite, chlorite and chlorite/vermiculite), phosphates, and aluminium and iron oxides/hydroxides. This assemblage is strikingly close to the mineralogy of the weathered volcanic substrate of Bermuda, but noticeably different from the mineralogy of Saharan dust. Moreover, we found volcanic lithoclasts in numerous paleosol profiles all over the archipelago and in all the recorded time intervals. We thus consider the volcanic seamount underlying Bermuda as the main source of non-carbonate minerals detected in the paleosols. This hypothesis further resolves the anomalous maturity of Bermudan paleosols compared to their southern counterparts in the Bahamas and Barbados.

Short chronosequences of paleosols from the Skvortsovka kurgans in the Buzuluk River valley of Orenburg oblast

Paleosols buried under kurgans of the Yamnaya (the third millennium BC) and Srubnaya (the 18th–17th centuries BC) cultures within the Skvortsovka group of kurgans in the Buzuluk River valley in Orenburg oblast have been studied. This is the area of the dry steppe zone. The changes in the paleosol properties make it possible to distinguish between relatively short-term chronointervals separately for the Yamnaya and Srubnaya cultures. The paleosol data and radiocarbon dating have been used for revealing the relative order of the construction of the kurgans within these chronointervals and for the paleoclimatic reconstruction. Quite definite changes took place in the soil formation from the beginning to the end of the particular chronointervals: the contents of humus and exchangeable bases and the portion of calcium ions in the composition of the exchangeable cations increased in parallel with the enhanced leaching of carbonates and the enhanced biological activity. These changes attest to the increasing amount of precipitation. In general, the climate of the Srubnaya cultural epoch was less continental, whereas the climate of the Yamnaya cultural epoch was relatively close to the modern climate. The 14C dates of the pedogenic carbonates in the upper meter of the paleosol profiles have been used as auxiliary data to confirm the sequence of the soil’s burial during the short chronointervals corresponding to the humid stages of the paleosol’s evolution, and the 14C dates of the diagenetic carbonates have been used to determine the dates of construction of the kurgans with due account for some time gap between the construction of the kurgans and the appearance of these carbonates in the buried soil profiles.

Late pleistocene paleosol sequences as an instrument for the local paleographic reconstruction of the Kostenki 14 key section (Voronezh oblast) as an example

A sequence of five paleosol units (with seven individual paleosol profiles) buried in the Late Pleistocene (20–40 ka) deposits was studied at the Kostenki 14 (K14) key section in Voronezh oblast with the use of a set of morphological, physicochemical, and instrumental methods. The upper-lying paleosols differed from the lower-lying paleosols in the less pronounced gley features, stronger aggregation of the soil material, more significant accumulation of carbonates, and higher percentage of calcium humates and fulvates. These features attested to the higher aridity of the paleoclimate and the development of the upper-lying paleosols under grassy vegetation. Within the studied paleosol sequence, the most developed profiles were typical of the soils that formed 27–32 ka ago during the Bryansk interstadial. The good aggregation, the presence of features left by the soil fauna activity, the high magnetic susceptibility, and the morphology of the secondary carbonates in the studied paleosols suggest that they were formed under meadow-steppe vegetation in well-drained positions and resembled modern cryoarid soils.

Factors of paleosol formation in a Late Cretaceous eolian sand sheet paleoenvironment, Marília Formation, Southeastern Brazil

The Marília Formation, which crops out in southeastern Brazil, is interpreted as a Late Cretaceous eolian sand sheet area. The sedimentary succession, ca 110 m thick, is characterized by alternating strata of eolian deposits and paleosols. The paleosols constitute more than 66% of the thickness, and are an important element in the interpretation of the paleoenvironmental controlling factors which affected the soil formation in this eolian sand sheet. In this paper six paleosol profiles are described and assigned to two pedotypes: Itaja and Apore. The Itaja pedotype is constituted of a sequence of five superimposed polygenetic profiles which show different phases of clay illuviation and carbonate precipitation, and it has been classified as Aridisol. The Apore pedotype overlies the Itaja pedotype. This pedotype shows an increase in leaching, CIA-K ratios, reddening, and illuvial clay features in respect to Itaja, and has been classified as Alfisol. The analysis of the factors which controlled the soil formation revealed that both pedotypes formed on a stable landscape probably covered by a community of low stature plants, in which the soils had sufficient time to develop very mature profiles. The changes in soil-forming processes were driven principally by variations in available soil moisture from precipitation. Using depth-to-carbonate functions from Bk and CIA-K proxy from Bt horizons of the Itaja pedotype, mean annual precipitation (MAP) estimates range from 240 to 1078 mm/yr, respectively. These contrasting climatic conditions resulted in the superimposition of arid or semi-arid with more humid climates and determined the considerable change in the pedogenic features, with many horizons showing the interlacing of calcite and clay features. In the Apore pedotype CIA-K proxy from Bt horizons estimates that averaged MAP was around 900 mm/yr, and the prevalent humid conditions can be attested by soil properties and abundance and depth of root traces. Our results show that the diversity in pedotypes is mainly attributed to differences in paleoclimatic conditions during Maastrichtian time, and that eolian sedimentation was restricted to periods of harsh arid conditions, as in semi-arid climates, with MAP estimates around 240 mm/yr, the formation of soils with well developed calcic horizons was possible.

Upper Permian paleosols of the East European Platform: Diagnostics of pedogenesis and paleogeographic reconstruction

A vertical sequence of seven buried paleosols composing the Klimovsk pedocomplex was studied in the basin of the Sukhona River (Vologda oblast). These paleosols were formed according to the accumulative model of pedogenesis (pedosedimentation model). They had monogenetic profiles with eluvial-gley, structural, and carbonate-illuvial types of differentiation. The set of elementary pedogenic processes responsible for the development of these soils included gleyzation in the surface horizon and around the roots, the inter- and intrahorizon translocation and segregation of iron, structuring, humification, weathering, lessivage, the migration and segregation of carbonates, and the synthesis of palygorskite and analcime. The studied paleosol profiles make it possible to reconstruct seven pedogenetic stages; each of them lasted for about n × 102–103 years. The paleosols were formed on a flat lacustrine-alluvial plain with drying lakes and temporary streams. The stages of inundation and water stagnation on the surface alternated with the stages of drying of the territory. The climate was warm, with well-pronounced wet and dry seasons. Against this general climatic background, arid climatic epochs marked by the development of calcic paleosols alternated with humid climatic epochs marked by the development of noncalcareous paleosols.

Interrelation of magnetic susceptibility, soil color and elemental mobility in the Pliocene–Pleistocene Siwalik paleosol sequences of the NW Himalaya, India

Apart from imparting color characteristics, the precipitation and dissolution of Fe-oxides (and hydroxides) during pedogenesis is coeval with transformation and translocation of major and trace elements. Based on rock magnetic and geochemical parameters for 27 paleosol profiles from three stratigraphic columns of Pliocene–Pleistocene Siwalik sequence in the NW Himalaya, we describe here the relationship amongst elemental mobility, Munsell color and low field mass normalized magnetic susceptibility ( χ lf). The study shows a consistent positive correlation of the rock magnetic parameters (principally magnetic susceptibility) with Munsell hue and Redness Rating (RR) index (Torrent et al., 1980, Blavet et al., 2000) of the soil profiles. The Late Miocene profiles show an increase of ~ 29% of Al 2O 3 concentration and that for the Pliocene and Pleistocene profiles show ~ 33 to 60% increase as a result of pedogenesis. Similarly the other immobile elemental oxide, Fe 2O 3 is increased by ~ 54% in the Late Miocene profiles and ~ 50 to ~ 63% in the Pliocene–Pleistocene profiles. Geochemical trends correlate with the χ lf, showing R 2 = 0.39 to 0.68 with Al 2O 3 and Fe 2O 3 and R 2 = − 0.40 to − 0.73 for SiO 2. Similarly the Munsell color parameters, especially the RR index display significant positive correlation where the magnetic mineralogy is dominated by hematite and goethite. These first order relationships amongst χ lf, RR index and elemental mobility demonstrate the potential use of magnetic susceptibility for rapid characterization of the widespread and heterogeneous pedogenic episodes within the dynamic sedimentary environments of the Himalayan foreland basin.

Paleosol profiles in the Shiohama Formation of the Lower Cretaceous Kanmon Group, Southwest Japan and implications for sediment supply frequency

This paper describes the pedogenic features of paleosols in the upper Lower Cretaceous Shiohama Formation, the lowest unit of the Shimonoseki Subgroup, in Yoshimi, Yamaguchi Prefecture, southwest Japan. The paleosol profiles in the Shiohama Formation are compound and complex, characterized by the presence of abundant calcrete horizons. An analysis of these profiles reveals that the floodplain upon which the Shiohama Formation was deposited was part of an unstable aggradation system characterized by the intermittent influx of sediments and occasional erosion. Furthermore, the mean annual range of precipitation was less than about 30 mm, suggesting only minor seasonal change between wet and dry conditions during deposition of the Shiohama Formation. The microstructures of the observed calcretes include dense microfabric, floating detrital grains, micronodules, circum-granular cracks, and complex cracks. These features formed by chemical precipitation under dry conditions, with little bioactivity. The calcrete horizons are classified into seven types (I–VII) based on their modes of occurrence. Two processes of carbonate accumulation can be identified based on the size and abundance of nodules: VI–V–III–(II)–I and VI–(V)–IV–II–I. These processes represent the development of calcrete horizons from the early to late stages of calcretization. Type I represents the most highly developed stage of calcretization. Calcretes within the Lower Member sequence of the Shiohama Formation show repetitions of type I and types II and III. Thus, it is interpreted that the frequency of sediment supply to the floodplain changed repeatedly over time.

Mycological complexes in Holocene and Late Pleistocene paleohorizons and in fragments of paleosols

Fragments of buried Late Pleistocene (30000-year-old) and Early Holocene (10000-year-old) paleosols contained viable complexes of microscopic fungi. The mycobiota of these paleosols represents a pool of fungal spores that is lower in number and species diversity as compared to that in the recent humus horizons and higher than that in the inclosing layers. The central part of the paleosol profiles is greatly enriched in microscopic fungi. In the intact humus horizons of the Late Holocene (1000–1200 years) paleosols, actively functioning fungal complexes are present. These horizons are characterized by their higher level of CO2 emission. The buried horizons, as compared to the recent mineral ones, contain a greater fungal biomass (by several times) and have a higher species diversity of microscopic fungi (including fungi that are not isolated from the recent horizons). Nonsporulating forms are also present there as sterile mycelium. The seasonal dynamics of the species composition and biomass of the fungal complexes were more prominent and differed from those inherent to the surface soil horizons. In the buried humus horizons, the dynamics of the fungal biomass were mainly due to the changes in the content of spores. The data on the composition of the fungal complexes in the buried soils confirm (due to the presence of stenotopic species) the results of paleobotanic analyses of the past phytocenoses or do not contradict them.

Multidisciplinary characterization of the middle Holocene eolian deposits of the Elsa River basin (central Italy)

In temperate regions, eolian deposits of different natures are often pedogenically-altered and mixed with underlying sediments. The research reported in this paper identifies for the first time the presence of eolian deposits in soils of central Tuscany and investigates the characteristics and origin. Five relict, polycyclic paleosol profiles were studied. P1 was situated in a natural dust trap, a doline on top of an isolated limestone hill; P2 and P3 were both situated on a limestone plateau, and P4 and P5 on a mid- and foot slope on schist. The profiles were sampled for routine analyses, iron forms, heavy minerals, major and trace elements, and pollen, spores and non-pollen palynomorphs. Undisturbed samples were taken for micromorphological and SEM analyses. Nine soil horizons were sampled for OSL dating. Eolian deposits were dominant or abundant in the first layers of P1, P2 and P3. OSL age determinations of soil horizons deriving from eolian parent material were middle Holocene. Chemical and heavy mineral analyses indicated different possible sources, including bare slopes, alluvial fans and wide channels, coming from the nearby streams that drain the Middle Tuscany ridge and the Mounts of Chianti; marginal contribution of volcanic ashes was only found in P1. The research demonstrated that wind soil erosion accompanied water erosion and colluvial deposition during the middle Holocene in the Elsa River basin. Pollen spectra, in particular, indicated that soil degradation occurred in an environment showing signs of incipient desertification, resulting from an increase of aridity in a land already strongly influenced by humans. Although central Italy is currently considered to be only marginally affected by wind soil erosion, a climate change, which would imply increased arid conditions, could trigger a new cycle of slope denudation, wind erosion and loess deposition.

Paleoclimatic interpretations from pedogenic calcretes in a Maastrichtian semi-arid eolian sand-sheet palaeoenvironment: Marília Formation (Bauru Basin, southeastern Brazil)

Stratigraphic and sedimentologic studies in continental successions do not always devote particular attention to the paleosols, in particular in arid or semi-arid paleoenvironments. The aim of this paper is to: (1) describe in detail the macro- and microscopic pedogenic features of four types of paleosol profiles with calcic horizons of the Marília Formation (Maastrichtian), and (2) elaborate paleoclimatic considerations based on the depth of the nodular calcic horizon and on the molecular weathering ratios of the main oxides. The Marília Formation, which crops out in the eastern portion of the Bauru Basin (São Paulo State, southeastern Brazil), usually contains profiles of calcic paleosols developed over sandstone deposits which formed in a eolian sand sheet paleoenvironment. The type of calcium carbonate accumulation in paleosol horizons varies from thin discontinuous coatings on ped surfaces trough faint filaments in soil matrix to massive accumulations between coalesced nodules, which are associated respectively to the stages I, II, and III of calcic soil development morphology classification. Four carbonate paleosol profiles with prominent calcic horizons (Bk and Ck) and secondary argillic horizons (Bt and Btk) have been studied in Marília Formation: two near the homonymous city and other two around the Monte Alto plateau. Field data and petrographic, geochemical, and clay mineralogy analyses allowed to classify these four paleosol profiles as Aridisols and define some paleoclimate considerations on their development. Molecular weathering ratios relative to calcification, hydrolysis, clay formation, salinization, and hydration of the paleosol profiles has been calculated to define the characteristic of the paleosols and the paleoclimatic proxies. Paleoprecipitations have been estimated by the application of an empirical equation that related this value to the depth of the Bk horizon.

Palaeoenvironmental reconstruction of the Late Cretaceous Sânpetru Formation (Haţeg Basin, Romania) using paleosols and implications for the “disappearance” of dinosaurs

Paleosols of the Late Cretaceous Sânpetru Formation (Haţeg Basin, Romania) are the subject of macroscopic, microscopic, and geochemical investigation in order to reconstruct the palaeoenvironmental and palaeoclimatic conditions in which dinosaurs lived. Study of overbank deposits present in an 860-m-thick stratigraphic interval of the Sânpetru Formation exposed along the Sibişel Valley reveals the presence of one facies and five different pedotypes: 1) finely laminated gray-green mudstones and siltstones interpreted as pond deposits; 2) bioturbated gray-green mudstones lacking macroscopic pedogenic features, interpreted as very poorly-developed hydromorphic paleosols; 3) bioturbated gray-green mudstones containing carbonate concretions, interpreted as poorly-developed hydromorphic paleosols; 4) mottled gray-green mudstones containing carbonate concretions and limited illuvial clay accumulation, interpreted as moderately-developed paleosols characterized by a high but fluctuating watertable; 5) bioturbated brown-red mudstones lacking macroscopic pedogenic features other than the occasional mottles, interpreted as poorly-developed paleosols that formed on the higher and better-drained floodplains; and 6) bioturbated brown-red mudstones containing carbonate nodules, interpreted as moderately-developed calcareous paleosols that formed on distal floodplain settings. Although limited exposure prevents the documentation of lateral relationships of pedotypes, the presence of paleosol profiles that display characteristics of two different pedotypes suggests that they represent a lateral continuum on the landscape related to local differences in hydrology and relief (i.e., catena). The pedotype assemblage reveals that the Sânpetru landscape was a mosaic of wetlands, seasonal wetlands, and better-drained floodplain habitats, similar to the present-day Indogangetic Plains. Pedogenic features and paleosol geochemistry indicate that the Maastrichtian climate of Romania was subhumid (< 1000 mm rain/year) and characterized by strongly seasonal precipitation. The distribution of pedotypes through the Sânpetru Formation reveals small- and large-scale palaeoenvironmental changes associated with the shifting of a complex mosaic of wet and dry habitats in response to shifts in river position on the alluvial plain. However, a major palaeoenvironmental change occurs in the upper Sânpetru Formation, where the region was transformed into extensive wetlands. Such dramatic changes coincide with river competence increase, change in palaeocurrent directions, and dearth of macrovertebrate remains, which had been previously misinterpreted as evidence for the disappearance of dinosaurs at the Cretaceous-Tertiary boundary. These palaeoenvironmental changes, induced by tectonism, are responsible for the shift from preservation of macrofossils concentrated by hydraulic processes into conspicuous lenticular bonebeds in the lower Sânpetru Formation to preservation of microfossil, and more rarely macrofossil, remains in hydromorphic calcareous paleosols in the upper Sânpetru Formation. The consequences of palaeoenvironmental changes on vertebrate preservation mode must be considered in the search for fossils and interpretation of the fossil record.

Paleoclimatic Implications of Crayfish-Mediated Prismatic Structures in Paleosols of the Paleogene Willwood Formation, Bighorn Basin, Wyoming, U.S.A.

Abstract Paleosols at Polecat Bench, northern Bighorn Basin, Wyoming, show prismatic structures not previously described in the Paleogene Willwood Formation. Prisms are densely spaced 15–50 mm diameter cylinders with vertical to slightly sinuous paths up to 400 mm long, subangular to rounded vertical faces, and slightly concave to convex tops. Prism exteriors are coated commonly by < 1-mm-thick clay films; exteriors also commonly show knobby and striated surficial morphologies. Prismatic structures are nearly exclusive to thin-bedded (< 1 m thick) compound paleosols composed of red to red-purple sandy mudrock overlying gray to green-gray heterolithic units composed chiefly of fine-grained sandstone. In addition to prismatic structures, these paleosols are characterized by large gray mottles, slickensides, and calcareous rhizocretions which crosscut or more typically follow prism exteriors. The architectural and surficial morphology of the soil prisms suggest strongly that these are pedogenically modified freshwater crayfish burrows of the ichnospecies Camborygma litonomos. At Polecat Bench, an ~ 40 m interval of the Willwood Formation records a transient episode of global warming known as the Paleocene–Eocene Thermal Maximum (PETM). The PETM interval is characterized by a series of predominantly red, cumulative paleosol profiles and increased soil carbonates. Prismatic soil structures and crayfish burrows are rare or absent in cumulic paleosols typical of the PETM, whereas they are locally abundant in red compound paleosols outside the PETM interval. The changes in paleosol morphology and a sharp decrease in crayfish burrows within the PETM interval suggest significantly improved soil-drainage conditions and lower water tables on the Willwood floodplain during the global warming event.

Spatiotemporal variations of Zr/Rb ratio in three last interglacial paleosol profiles across the Chinese Loess Plateau and its implications for climatic interpretation

The ratio of Zirconium to Rubidium (Zr/Rb) is suggested to be a better proxy for the East Asian winter monsoon strength than the widely-used grain size distribution. The rationale for the Zr/Rb proxy relies on the following assumptions: (1) Grain size fractionating characteristics during eolian dust transport should be archived in the Zr/Rb ratio records and this assumption is based on the premise that Zr is preferentially enriched in coarser grain size fraction while Rb tend to be enriched in finer grain size fraction; and (2) post-depositional weathering does not change the Zr/Rb ratio due to the immobility of these two elements. To examine these two assumptions, three last interglacial paleosols (S1) from Dingxi, Tianshui and Lantian, along a NW-SE transect across the Chinese Loess Plateau, were geochemically investigated. Our results show that the Rb concentration exhibits an increasing trend along the NW-SE transect both in the paleosol (S1) and the measured portions of the loess units (L1 and L2), being supportive to the assumption that Rb is enriched in the fine particles. But we also found that Rb loss did occur to some extent in the three profiles, contradicting to the presumption of Rb immobility during pedogenic processes. The Zr concentration exhibits an expected decreasing trend in the measured portions of the loess units and an unexpected increasing trend in the paleosol along the NW-SE transect. Moreover, the ratios of Zirconium to Hafnium (Zr/Hf) show different variation patterns between interglacial and glacial, implying that Zr-bearing minerals and their resident grain size fractions are probably not identical during interglacial and glacial. Thus, the assumption that Zr is enriched in coarse grain size fraction can no longer hold. We conclude that the final Zr/Rb value is not only dependent on grain size sorting processes but also on post-depositional alteration and source provenance. Under enhanced chemical weathering, especially when chemical index of alteration (CIA) is greater than 65, the Zr/Rb value loses its validity to be a reliable proxy for the winter monsoon strength. In addition, all the Zr/Rb value is constrained above 1.7, a minimum which is definitely modulated by all the three aforementioned factors.

Reconstructing in-situ vegetation dynamics using carbon isotopic composition of biopolymeric residues in the central Chinese Loess Plateau

Carbon isotopic compositions of total organic carbon (TOC) or leaf waxes in soils have been used to reconstruct past changes in the relative abundance of C 3 and C 4 plants. However, TOC contains organic matter of different source organisms (plants, animals, fungi, bacteria etc.) and its isotopic ratios could be modified during diagenesis since different organic fractions (e.g., carbohydrates, proteins, lipids etc.) have different isotopic ratios and degradation rates. Leaf waxes, on the other hand, are transported by wind and hence represent vegetation input from a large geographic area. We report in this paper a new approach to extract in-situ paleovegetation information from late Quaternary paleosols by determining carbon isotopic compositions of biomarkers derived from aliphatic bio- and geopolymers of plant origin. We show that C 9 to C 17 n-alkenes derived from aliphatic bio- and geopolymers are the dominant compounds released by flash pyrolysis of insoluble organic matter isolated from the late Quaternary paleosols in the Chinese Loess Plateau. Because the aliphatic polymeric substances are mainly derived from plant leaves, bark and roots, the isotopic signatures of these alkenes, determined using pyrolysis–gas chromatography–isotopic ratio mass spectrometry, reflect in-situ vegetation changes. Our down-core δ 13C data from the Xifeng loess–paleosol profile show significant coherence among biopolymer-derived n-alkenes, leaf wax n-alkanes, and TOC for the past 40 kyr. However, the different amplitudes of the temporal isotopic changes among these data sets are indicative of variability in in-situ and regional vegetation dynamics, organic sources and effect of diagenesis. Our data also imply that below-ground biomass is a major source of soil organic matter in the central China loess sediment.

Relationship of Floodplain Ichnocoenoses to Paleopedology, Paleohydrology, and Paleoclimate in the Willwood Formation, Wyoming, During the Paleocene-eocene Thermal Maximum

Vertical changes in distribution, abundance, and ichnodiversity of ichnocoenoses in alluvial deposits of the Willwood Formation suggest significantly drier moisture regimes in the Bighorn Basin, Wyoming, during the Paleocene–Eocene Thermal Maximum (PETM), a transient period of global warming. The Willwood Formation at Polecat Bench contains an abundant assemblage of ichnofossils, including various types of rhizoliths and invertebrate trace fossils, such as Naktodemasis bowni, Camborygma litonomos, Edaphichnium lumbricatum, cf. Cylindricum isp., cf. Planolites isp., cf. Steinichnus, and cocoon traces. These comprise six distinct ichnocoenoses, which are categorized as dominantly terraphilic, hygrophilic, or hydrophilic based on the inferred moisture regimes of their most abundant ichnofossil morphotypes and associated pedogenic features, including other trace fossils and rhizoliths. The interpreted moisture regimes correlate well with the paleoenvironments of their host lithofacies, as inferred from sedimentology and paleopedology. Outside the PETM interval at Polecat Bench, abundant avulsion deposits and thin, compound paleosols containing hygrophilic and hydrophilic ichnocoenoses suggest frequent depositional events and predominantly poor to imperfect soil-drainage conditions. Within the PETM interval, thick, cumulative paleosol profiles with abundant terraphilic to hygrophilic ichnocoenoses suggest significantly improved drainage conditions. Lithofacies and ichnocoenoses above the PETM interval are not significantly different from those below the interval, indicating a return to pre-PETM moisture regimes. These conclusions support previous studies that suggest the Bighorn Basin experienced transient drying during this interval. This study demonstrates that ichnocoenoses and their ichnopedologic associations can be used to refine paleohydrologic and paleoclimatic generalizations inferred from paleoclimate models.

Mineralogical composition of the clay fraction and micromorphology of the Middle and Late Pleistocene loesses and paleosols in the center of the East European Plain

The mineralogical composition of the clay fraction and microfabrics of the cryogenic soil-loess sequences of the Middle and Late Pleistocene ages have been studied near the northern boundary of loess sediments on the East European Plain. Poorly ordered mixed-layered mica-smectitic minerals with different portions of smectitic layers predominate in the clay fraction; di-and trioctahedral hydromicas occupy the second place. The clay fraction also contains chlorite, clay-size quartz grains, and feldspars. Individual smectite is present in some of the samples. Interstadial chernozem-like paleosols are specified by the higher content of clay, the maximum concentration of smectitic layers in the mixed-layered minerals, and the presence of individual smectite. The clay fraction in the profiles of interglacial paleosols is sharply differentiated: in the eluvial part, it is depleted of smectite and enriched in kaolinite, hydromica, and clay-size quartz. These features allow us to suppose that interglacial paleosols were subjected to podzolization processes. According to the mineralogical indices, Middle Pleistocene paleosols can be differentiated into those subjected to lessivage (the Kamenskii interglacial paleosol) and podzolization (the Inzhavin interglacial paleosol).

Paleosols, trace fossils, and precipitation estimates of the uppermost Triassic strata in northern New Mexico

This study provides a detailed pedogenic evaluation of two Upper Triassic (Late Norian through Rhaetian) stratigraphic intervals in New Mexico in order to assess the climate and ecology of the Latest Triassic, which ended in a mass extinction. The two study areas are located in north–central and east-central New Mexico and are separated by 200 km. Each section contains abundant paleosols of varying maturity with features that reflect an arid to semiarid climate. There is little pedogenic variation throughout the strata at each location, and a typical paleosol profile is about 1 m thick and has an AB–Bw–Bk–BC horizon succession. Bkm, Bss, Bssk, or Bssg horizons are present in some paleosols. Micromorphological features suggest dominantly well-drained sola (e.g., abundant carbonate nodules, illuviated clay) with minor periods of moist or saturated conditions (e.g., FeMn concretions, FeMn coatings and hypocoatings, sepic-plasmic fabrics). Trace fossils are abundant in these strata and are dominated by Taenidium serpentinum and root traces. Depth-to-carbonate functions estimate that mean annual precipitation was between 200 and 450 +/− 95 mm. Relative to location 1 (eastern New Mexico), location 2 (north–central New Mexico) produced higher paleo-precipitation estimates and has stronger and more abundant sepic-plasmic fabrics in thin sections. The presence of a gleyed paleosol, Camborygma eumnkenomos, and slickensides at location 2 also suggests conditions wetter than at location 1. Taxonomically, all of the paleosols in this study appear to be Entisols or Aridisols and can be grouped into seven representative pedotypes of varying maturity. By comparing these paleosols to modern soils, this study demonstrates that the Late Triassic Western Interior during the Late Norian to Rhaetian was arid to semiarid and supported a desert shrub environment that had localized and periodic moist or saturated soil conditions.

δ13C values of carbonate nodules across the Permian–Triassic boundary in the Karoo Supergroup (South Africa) reflect a stinking sulfurous swamp, not atmospheric CO 2

Paleosol macromorphology, petrography and stable isotope geochemistry of carbonate nodules from Permo–Triassic (P–T) boundary strata of the central Karoo basin, South Africa are presented in order to evaluate their utility as geochemical archives of Permian–Triassic paleoatmospheric chemistry and their potential to provide a terrestrial carbon isotope chemostratigraphy for correlation with contemporaneous global marine δ 13C records. Paleosol morphologies across P–T boundary strata of the central Karoo basin indicate the region was a poorly drained, seasonally to continuously flooded bottomland. Radiaxial calcite, microspar and micrite microtextures are observed in the calcite nodules associated with P–T paleosol profiles. Micritic calcite is typical of soil carbonate that forms in well-drained soils characterized by open-system gaseous diffusion between the soil and global atmosphere, whereas more coarsely crystalline textures and radiaxial calcite are more typical of crystallization in phreatic environments with limited gaseous diffusion between the soil and global atmosphere. In this regard, only those nodules composed of micritic calcite can be considered as a potentially reliable source of proxy information for paleoatmospheric δ 13C values across the P–T boundary. The δ 13C values of all carbonate nodules from two overlapping measured sections near Carlton Heights, South Africa range from − 24.4‰ to − 1.8‰, whereas micritic calcite nodule δ 13C values range from − 7.0‰ to − 21.3‰. Comparison of calcite δ 13C values with penecontemporaneous organic matter δ 13C values indicate that calcite δ 13C values < − 10.6‰ cannot provide a record of atmospheric δ 13C values. Rather, these more negative carbonate nodule δ 13C values likely reflect calcite crystallization under poorly drained, swampy conditions characterized by a semi-closed chemical system that evolved independently of Earth's troposphere. Therefore, previously reported negative carbon isotope shift(s) measured from carbonate nodules in the Karoo basin P–T strata do not provide a record of atmospheric δ 13C, and probably do not provide a viable carbon isotope stratigraphy that can be realistically correlated with global P–T marine carbon isotope stratigraphies.