Earth Sediments Research Articles

L-chondrite body breakup in Ordovician strata in China - A time tie point globally and across the inner solar system

More than a quarter of all meteorites falling on Earth today originate from the breakup of the L-chondrite parent body (LCPB) ∼470 Ma ago, the largest documented asteroid breakup in the past ∼3 Ga. The event had a profound impact on the inner Solar System, resulting in an orders-of-magnitude increase in L-chondritic material in mid-Ordovician sediments on Earth. Here we show based on Ordovician strata at Puxi River, China, and Hällekis, Sweden, that the first arrival of LCPB dust to Earth can be used for global high-resolution correlation. The approach unravels a remarkable parallelism in facies development between distant paleocontinents and environmental perturbations on a global scale, possibly related to cooling of Earth by LCPB dust. In the Puxi River section, the first L-chondritic dust coincides with volcanic ash zircons, allowing U-Pb dating of the LCPB breakup. Ages determined from both sedimentary ash and recent L chondrites are consistently close to 470 Ma. A more precise age assessment is method-dependent, but the dual and independent dating options allow unique calibration possibilities. A similar increase in LCPB-derived dust as in Earth's sediments may exist in coeval layered deposits on Mars, the Moon, and large asteroids and may be used as a chronostratigraphic tie point on an astronomical scale.

Аккумуляция наносов мелкозема гидротехническим сооружением в виде запруды в условиях Ростовской области

Purpose: to study the ability to accumulate fine earth sediments delivering with surface runoff of melt and rainwater, a hydraulic structure in the form of a retaining dam in combination with reclamation protective forest planting in Rostov region. Materials and methods. The object of research is a hydraulic structure in the form of a retaining dam, laid in 1982 under the leadership of Professor E.V. Poluektov on one of the branches of the Bolshoi Log gully near the Stepnoy village, Aksai district, Rostov region. The experimental design included observing the accumulation of volume and mass of sediment in the retaining dam and comparing them with the runoff at a stationary runoff site. Surface slope was 2–3°. The generally accepted research methods by G.V. Dobrovolsky and the methodology of the Russian Scientific Research Institute of Land Improvement Problems were used. Results. The studies were conducted in 1982–2023 over three periods: 1982–1995, 1996–2004 and 2004–2023. Archive observations by Professor E.V. Poluektov for the first and second periods were used, and research was carried out in 2023. Indicators of the volume and mass of fine earth were determined, and dependencies reflecting their delivery into the retaining dam for observation periods of 1982–1995, 1996–2004 and 2005–2023 were obtained, the sediment accumulation rate in the retaining dam over the observation periods was determined. Conclusions. Long-term studies have shown that the simplest hydraulic structures in the form of retaining dams are effective and are capable of retaining sediment runoff in the amount of 15.59 tons per 1 ha of watershed, which is 61 % of the sediment runoff at a stationary runoff site of 25.63 t/ha, i.e. the amount of sediment decreased by 39 %. The obtained dependencies are planned to be used in the development of a computer program for calculating the flow of sediment into the retaining dam, and the research results can be used in the design of such hydraulic structures.

Terrestrial paleoclimate changes recorded by Pleistocene red earth deposits at the Gaolingpo Paleolithic site, Bose Basin, South China

The Quaternary river sediments at Gaolingpo, Bose Basin, Guangxi Province contain stone hand adzes and microliths of Paleolithic and Neolithic ages, providing information about the effect of climatic and environmental changes on hominin and early modern human activities. Gaolingpo is a representative Paleolithic site in the Bose Basin, containing numerous stone artifacts of different ages in the red earth sediments. We examined the clay mineralogy and geochemistry of the Gaolingpo profile using X-ray diffractometry (XRD), diffuse reflectance spectroscopy (DRS), and X-ray fluorescence (XRF) spectroscopy with the goal of reconstructing paleoclimatic and environmental changes in the study area since the late Early Pleistocene. Within this soil profile, kaolinite and vermiculite increase and illite decreases gradually up section. The red earth sediments exhibit uniform chondrite-normalized rare earth element (REE) distribution patterns, which are similar to those of upper continental crust (UCC), post-Archean Australian shale (PAAS), loess and paleosol of the Chinese Loess Plateau (CLP), and Yangtze River deposits. These confirm that the Gaolingpo red earth sediments originated from fine materials of well-mixed weathered continental crust within the upper Pearl River drainage basin. The chemical index of alteration (CIA) of the Gaolingpo sediments is 86.4–92.1, indicating that the sediments have undergone intense chemical weathering. Based on changes in clay mineral contents and geochemical compositions through the profile, the paleoclimatic evolution of the Gaolingpo area since the late Early Pleistocene can be divided into two stages with four sub-stages: (1) a generally humid climate prevailed during stage I can be further divided in two sub-stages. Sub-stage Ia was temperate with an alternating dry and wet climate, while sub-stage Ib was a transition to a warmer temperate climate. (2) A subtropical humid climate prevailed during stage II and transitioned to a cooler climate in the later stage. In this episode, sub-stage IIa was the warmest and the most humid period since the late Early Pleistocene in Bose Basin, and Stage IIb was a transition to a relatively cooler subtropical climate. This climate pattern is compatible with the regional palynological record at Chongzuo, south Guangxi and is in general agreement with the δ18O records from cave stalagmites in southern China, but is inconsistent with the δ18O record at ODP Site 1148 in the northern part of the South China Sea, though the age constraints limit a precise correlation. This reflects the predominant influence of Qinghai-Tibetan Plateau uplift on East Asian climate since the late Early Pleistocene. The development of warm, humid, and only weakly fluctuating climate conditions in the Bose Basin was favorable for early hominin settlement.

Toward a sociology of evolution in the Anthropocene-Shared intentionality and cooperation through understanding minds.

Sociology has a long tradition of diagnosing contemporary societies, but little theoretical and empirical instruments for analyzing the long-term evolution of human coexistence. This goes hand in hand with a bias to disregard insights of evolutionary theory and research. The main argument here to develop is that a sociology of evolution should enter at the core of our discipline. This becomes even more important in the era of the Anthropocene as a new geo-chronological period of the planet's evolution that is characterized by substantial human influencing of planetary ecological mechanisms and could be found in earth sediments. If human intervention in the planet has reached such a scale that its future fate is no longer shaped mainly by natural cosmological laws, but by human intervention, then sociology has to broaden its temporal and substantive perspective; it should reflect more explicitly on the relationship between nature, culture, and technology. In what follows, we plead for giving evolutionary sociology, especially the long-term evolution of human coexistence between nature and culture, a greater place in sociology. To this end, we address three points. First, we ask why sociology is not concerned with the co-evolution of other creatures, but almost exclusively focused on the development and social change of humans over the short period of the last few centuries. Second, we argue that, with respect to the nature-culture relationship, sociology has essentially followed a questionable scientific division of labor, according to which the natural sciences deal with natural phenomena and sociology with sociocultural phenomena. Finally, we address the debate on the Anthropocene and distinguish between two ways of responding to the challenges it poses, namely with more technology or with more culture.

Absolute Configuration of Aliphatic Hydrocarbon Enantiomers Identified by Gas Chromatography: Theorized Application for Isoprenoid Alkanes and the Search of Molecular Biosignatures on Mars

Acyclic saturated hydrocarbon enantiomers were resolved by gas chromatography using a β-cyclodextrin-based chiral stationary phase. The stereospecific synthesis of single enantiomers of 4-methyloctane allowed to assign the absolute stereochemical configuration to the resolved enantiomers. Data show that the (S)-4-methyloctane shows higher chromatographic retention as compared to the (R)-4-methyloctane due to stronger van der Waals interactions with the β-cyclodextrin chiral selector. This introductive research presents future prospects for the separation of stereoisomers of larger branched hydrocarbons. We discuss the importance of chiral hydrocarbons, more precisely the stereochemistry of the isoprenoid alkanes pristane and phytane, as potential biosignatures stable on geological timescales. The origins of pristane and phytane in Earth sediments are presented, and we detail the implications for the search of extinct or extant life on Mars. The data presented here will help to systematically investigate the chirality of hydrocarbon enantiomers in biological and nonbiological samples and in samples to be analyzed by the ESA’s ExoMars rover to trace the chiral precursors of life in 2023.

Organic biomorphs may be better preserved than microorganisms in early Earth sediments

Abstract The Precambrian rock record contains numerous examples of microscopic organic filaments and spheres, commonly interpreted as fossil microorganisms. Microfossils are among the oldest traces of life on Earth, making their correct identification crucial to our understanding of early evolution. Yet, spherical and filamentous microscopic objects composed of organic carbon and sulfur can form in the abiogenic reaction of sulfide with organic compounds. Termed organic biomorphs, these objects form under geochemical conditions relevant to the sulfidic environments of early Earth. Furthermore, they adopt a diversity of morphologies that closely mimic a number of microfossil examples from the Precambrian record. Here, we tested the potential for organic biomorphs to be preserved in cherts; i.e., siliceous rocks hosting abundant microbial fossils. We performed experimental silicification of the biomorphs along with the sulfur bacterium Thiothrix. We show that the original morphologies of the biomorphs are well preserved through encrustation by nano-colloidal silica, while the shapes of Thiothrix cells degrade. Sulfur diffuses from the interior of both biomorphs and Thiothrix during silicification, leaving behind empty organic envelopes. Although the organic composition of the biomorphs differs from that of Thiothrix cells, both types of objects present similar nitrogen/carbon ratios after silicification. During silicification, sulfur accumulates along the organic envelopes of the biomorphs, which may promote sulfurization and preservation through diagenesis. Organic biomorphs possessing morphological and chemical characteristics of microfossils may thus be an important component in Precambrian cherts, challenging our understanding of the early life record.

Декоративна накладка з зображенням лева з розкопок неподалік села Міжгір’я (Волинська область)

The article is explaining a unique bronze application, which was discovered during the excavation season 2017 on Mizhgirya-3 site – two-layered settlement of Early Iron Age and Age of Principalities. This item was uncovered amid the upper earth sediments, largely destroyed by plowing, thus making it impossible to determine the exact chronological interpretation. Based on the analysis of creative stylistics and technological features of this piece of craftsmanship, an excessive pursuit was commenced for the parallels in the imageries and designs of decorative ornaments, particularly inherent to Ancient Rus culture. It includes various examples of zoomorphic motifs, lion’s pictures as well, in the church architectural décor and on similar samples of ornamented jewelry. The closest stylistic equivalence to the application’s image from Mizhgirya-3 site was found among decorative ceramic tiles collected during the excavations of ancient Halych hill-fort, some of them holding the image of a lion or a lioness. Particular attention was turned towards the searches of analogies among jewelry, applying specific techniques of openwork metal casting, like some items from the excavations of the Ancient Rus’ major cities of Halych and Novgorod, found inside cultural sediments from the 12th – to the 15th centuries. Comparative analysis of various objects, either depicting similar visual motifs or applying the distinctive metal casting technique, made it possible to verify the application’s origin at the later stages Age of Principalities cultural evolution, especially the one determined by the advance of Galicia and Volhynia state. Henceforth, the discovery of the items became more relevant with the upper chronological layer of Mizhgirya-3 site, which was dated by the 12th – 13th centuries after the evaluation of supplemented materials. Key words: bronze decorative application, openwork metal casting, Age of Principalities, zoomorphic motif, «lion passant».

Study of organic-matter intercalated vermiculitic phases in the hydromorphic red earth sediments

Al-hydroxy intercalated vermiculitic phases have been widely observed in pedogenic environment, but soil organic intercalations have rarely been reported. In the present study, mixed-layer illite–vermiculite (I/V) with organic matter (OM) intercalation under hydromorphic conditions in the Xuancheng red earth sediments was investigated in order to better understand the interlayer components occurring in mixed-layered clay minerals and the formation of this unusual OM interlayered mixed-layer clay species. Selective extraction of organic fillings by ammonium ethylene diamine tetraacetic acid (EDTA) and acid ammonium oxalate (NH4OX) showed that the components associated with organic complexes in the interlayer space of the 2:1 clays are mainly Fe- and A1-(oxy)hydroxides, which block substantial swelling after ethylene glycol solvation and complete collapse after heating. The OM interlayer filling contains CH3(CH2), CO, COO-, and NH functional groups and are resistant to H2O2 extraction although the binding intensity to the interlayer surface may change. Upon heating to ~300 °C the OM filling escapes from the interlayer space which causes the collapse of the 2:1 clay species. Alteration of primary illite during pedogenesis causes release of K and intercalation of hydrated cations in the interlayer space, and also leaching of Al and Fe. There is accumulation of exchangeable cations and Al and Fe oligomers in the interlayer region, which affects the behavior of I/V clays on glycolation and heating. Hydromorphic conditions favor the transformation of organic polymers into small size organic acids, and thus, favor the intercalation of interlayer OM filling into the 2:1 clays. Pedogenesis processes involves both the weathering of clay minerals and the decomposition of OM, leading to formation of interlayer clay-organic complexes in a hydromorphic soil.

Diversity analysis and metagenomic insights into antibiotic and metal resistance among Himalayan hot spring bacteriobiome insinuating inherent environmental baseline levels of antibiotic and metal tolerance

ObjectivesMechanisms of occurrence and expression of antibiotic resistance genes (ARGs) in thermophilic bacteria are still unknown owing to limited research and data. In this research, comparative profiling of ARGs and metal tolerance genes among thermophilic bacteria has been done by functional metagenomic methods. MethodsShotgun metagenomic sequence data were generated using Illumina HiSeq 4000. Putative ARGs from the PROKKA predicted genes were identified with the ardbAnno V.1.0 script available from the ARDB (Antibiotic Resistance Genes Database) consortium using the non-redundant resistance genes as a reference. Putative metal resistance genes (MRGs) were identified by using BacMetScan V.1.0. The whole-genome sequencing for bacterial isolates was performed using Illumina HiSeq 4000 sequencing technology with a paired-end sequencing module. ResultsMetagenomic analysis showed the dominance of Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes in two hot springs of Sikkim. ARG analysis through shotgun gene sequencing was found to be negative in the case of thermophilic bacteria. However, few genes were detected but they showed maximum similarity with mesophilic bacteria. Concurrently, MRGs were also detected in the metagenome sequence of isolates from hot springs. Detection of MRGs and absence of ARGs investigated by whole-genome sequencing in the reference genome sequence of thermophilic Geobacillus also conveyed the same message. ConclusionThe study of ARGs and MRGs (Heavy metal resistance gene) among culturable and non-culturable bacteria from the hot springs of Sikkim via metagenomics showed a preferential selection of MRGs over ARGs. The absence of ARGs also does not support the co-selection of ARGs and MRGs in these environments. This evolutionary selection of metal resistance over antibiotic genes may have been necessary to survive in the geological craters which have an abundance of different metals from earth sediments rather than antibiotics. Furthermore, the selection could be environment driven depending on the susceptibility of ARGs in a thermophilic environments as it reduces the chances of horizontal gene transfer.

Fe-oxide mineralogy of the Jiujiang red earth sediments and implications for Quaternary climate change, southern China

Diffuse reflectance spectrophotometry (DRS) is a new, fast, and reliable method to characterize Fe-oxides in soils. The Fe-oxide mineralogy of the Jiujiang red earth sediments was investigated using DRS to investigate the climate evolution of southern China since the mid-Pleistocene. The DRS results show that hematite/(hematite + goethite) ratios [Hm/(Hm + Gt)] exhibit an upward decreasing trend within the Jiujiang section, suggesting a gradual climate change from warm and humid in the middle Pleistocene to cooler and drier in the late Pleistocene. Upsection trends toward higher (orthoclase + plagioclase)/quartz ratios [(Or + Pl)/Q] and magnetic susceptibility values (χlf) support this inference, which accords with global climate trends at that time. However, higher-frequency climatic subcycles observed in loess sections of northern China are not evident in the Jiujiang records, indicating a relatively lower climate sensitivity of the red earth sediments in southern China.

Synthesis of 26-methyl cholestane and identification of cryostanes in mid-Neoproterozoic sediments

The biomarker distributions of mid-Neoproterozoic sediments (800–717 million yr, Ma) from various locations are characterized by the occurrence, besides cholestane isomers, of a novel series of C28 steranes, whereas classical C-24 alkylated steranes are absent. These unusual C28 steranes, termed cryostanes, seem to be restricted to pre-Snowball Earth sediments. We report their conclusive identification as 26-methyl cholestanes based on comparison of gas chromatographic (GC) behavior and mass spectrum of the last eluting cryostane isomer with those of a 26-methyl 5α(H),14α(H),17α(H),20R-cholestane standard obtained by way of synthesis. Sterols methylated at C-26 seem to be restricted to some demosponges and, based on molecular clock estimates, demosponges may have emerged in the time interval 800–700 Ma. A sponge origin of cryostanes is thereby conceivable, making cryostanes the oldest molecular markers for animals. However, other biological sources need to be explored, including the wide variety of eukaryotic protists.

Geochemical and detrital zircon U-Pb geochronological constraints on provenance of the Xiaomei red earth sediments (Bose Basin, Guangxi Province, southern China)

The Bose Basin in southern China is within a region influenced by the winter westerly monsoon and, thus, potentially subject to eolian dust accumulation. A red earth sequence developed on terraces of the Youjiang River (a branch of the Pearl River) records information about climate variation during the Pleistocene and its relationship to contemporaneous global climate changes. In this study, geochemical characteristics and U-Pb geochronology of detrital zircons of the red earth sequence at Xiaomei were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), inductively coupled plasma mass spectrometry (ICP-MS), thermal ionization mass spectrometry (TIMS), and detrital zircon U-Pb dating analyses. Our results show that the red earth sediments are composed of quartz and clay minerals (kaolinite, illite, and mixed-layer illite/vermiculite) with minor hematite and goethite. Mobile elements such as CaO, MgO, Na2O, K2O, Sr and Ba are depleted and immobile elements such as TiO2, Al2O3, Fe2O3(t) and Zr are enriched in comparison with loess-paleosols of the Chinese Loess Plateau (CLP), the upper continental crust (UCC), and post-Archean Australian shale (PAAS). These data indicate that the Xiaomei red earth sediments have experienced intense chemical weathering, similar to that of the Xuancheng and Jiujiang red earth sections on the middle to lower reaches of the Yangtze River. The Xiaomei sediments have similar La/Th ratios, U/Pb vs. Th/Pb relationships, and rare earth element (REE) distributions to the CLP, UCC, and PAAS, and their low εNd(0) values are indicative of an upper crustal origin. The 147Sm/144Nd and 87Sr/86Sr ratios of the Xiaomei sediments are different from loess-paleosols of the CLP but similar to those of well-mixed river sediments. U-Pb dating of detrital zircons in the Xiaomei sediments shows that crystals from different units have slightly different age distributions. The full Xiaomei section yields a distribution similar to that of Upper Permian-Triassic clastic rocks in the Youjiang area, and the distribution of the middle to upper Xiaomei section additionally shows similarities to upper crust of the South China Craton. Our results indicate that the Xiaomei red earth sequence, which dates to the late Early to early Middle Pleistocene (~1.0–0.6Ma), accumulated predominantly from fluvially transported, locally weathered materials and, therefore, that the sediment-carrying capacity of the East Asian winter monsoon has been overestimated in previous provenance studies of red earth sediments in South China.

Monsoonal climate evolution in southern China since 1.2 Ma: New constraints from Fe-oxide records in red earth sediments from the Shengli section, Chengdu Basin

Southern China has experienced a dominantly monsoonal climate since the early Quaternary, owing to the influence of Asian monsoons from several directions during that period. Pedogenic Fe-oxides (hematite and goethite) are regarded as sensitive indicators of monsoonal paleoclimates. To obtain a better understanding of monsoonal climate changes in the subtropical zone of southern China, samples from the Shengli section (Chengdu Basin) were investigated using diffuse reflectance spectroscopy (DRS), high-resolution transmission microscopy (HRTEM), X-ray diffraction (XRD), X-ray fluorescence (XRF), and inductively coupled plasma-mass spectrometry (ICP-MS). TEM results show that both hematite and goethite occur as fine particles with an irregular morphology. Most hematite grains have low crystallinity and nanoporous structure, suggesting that they formed from a ferrihydrite precursor. Uniformity of trace-element and REE distribution patterns, Eu and Ce anomalies, and (La/Yb)N ratios throughout the section suggests that the Shengli deposits were probably well mixed in the source area prior to transport and deposition, and that there has been little change in the source areas of primary materials since 1.2Ma. The high chemical index of alteration (CIA) of the red earth (79–88) reflects strong chemical weathering processes in southern China. Besides, DRS analyses of Fe-oxides show that most red earth samples at Shengli contain more hematite than goethite, which is opposite to typical loess-paleosol profiles from northern China. These results confirm that southern China generally experienced more intense weathering processes than northern China since 1.2Ma.Large fluctuations in major-element oxide concentrations and clay-mineral assemblages in the lower part of the section indicate climatic fluctuations between perennially humid and seasonally humid conditions in the mid-Pleistocene. Monsoonal climate evolution, as proxied by the hematite/(hematite+goethite) [Hm/(Hm+Gt)] ratio, shows a long-term but stepwise cooling and drying pattern in the Chengdu Basin with major transitions at ~1.0, 0.45, and 0.1Ma. These transitions were probably triggered by episodes of tectonic uplift of the Tibetan Plateau and global climate change, with consequent effects on the Asian monsoons. The transitions in our paleoclimate proxy records for southern China match well with shifts in the marine oxygen and carbon isotope records since the mid-Quaternary, providing evidence of strong teleconnections between global and regional climates, terrestrial weathering, and the global carbon cycle.

Three-component mixed-layer illite/smectite/kaolinite (I/S/K) minerals in hydromorphic soils, south China

To understand clay mineral transformations in hydromorphic conditions in the red earth sediments in Xuancheng, south China, clay mineralogy was investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). The XRD results indicated that clay minerals in the hydromorphic soils were illite, kaolinite, smectite, vermiculite, and mixed-layer illite/smectite and illite/smectite/kaolinite. Changes of the kaolinitic reflections under the various conditions suggested that the kaolinitic phase is a mixed-layer structure having kaolinite layers randomly interstratified with illite and smectite layers. HRTEM observation showed that 10 A illite layers interstratified with both 15 A smectite layers and 7 A kaolinite layers in clay particles, confirming the occurrence of illite/smectite/kaolinite (I/S/K) three-component mixed-layer clays. The lattice fringes of the I/S/K clays appeared corrugated and vanishing, and also exhibited variable thickness along a lattice fringe, which were consistent with changes from illite to smectite, from smectite to kaolinite, and from illite to kaolinite, respectively. Hydromorphic conditions in the Xuancheng soils led simultaneously to the direct transformation of illite to kaolinite and the transformation of illite to smectite to kaolinite in the pedogenic processes, and the formation of I/S/K three-component mixed-layer clays as intermediate products of these processes.

Atmospheric record in the Hadean Eon from multiple sulfur isotope measurements in Nuvvuagittuq Greenstone Belt (Nunavik, Quebec)

Mass-independent fractionation of sulfur isotopes (S-MIF) results from photochemical reactions involving short-wavelength UV light. The presence of these anomalies in Archean sediments [(4-2.5 billion years ago, (Ga)] implies that the early atmosphere was free of the appropriate UV absorbers, of which ozone is the most important in the modern atmosphere. Consequently, S-MIF is considered some of the strongest evidence for the lack of free atmospheric oxygen before 2.4 Ga. Although temporal variations in the S-MIF record are thought to depend on changes in the abundances of gas and aerosol species, our limited understanding of photochemical mechanisms complicates interpretation of the S-MIF record in terms of atmospheric composition. Multiple sulfur isotope compositions (δ(33)S, δ(34)S, and δ(36)S) of the >3.8 billion-year-old Nuvvuagittuq Greenstone Belt (Ungava peninsula) have been investigated to track the early origins of S-MIF. Anomalous S-isotope compositions (Δ(33)S up to +2.2‰) confirm a sedimentary origin of sulfide-bearing banded iron and silica-rich formations. Sharp isotopic transitions across sedimentary/igneous lithological boundaries indicate that primary surficial S-isotope compositions have been preserved despite a complicated metamorphic history. Furthermore, Nuvvuagittuq metasediments recorded coupled variations in (33)S/(32)S, (34)S/(32)S, and (36)S/(32)S that are statistically indistinguishable from those identified several times later in the Archean. The recurrence of the same S-isotope pattern at both ends of the Archean Eon is unexpected, given the complex atmospheric, geological, and biological pathways involved in producing and preserving this fractionation. It implies that, within 0.8 billion years of Earth's formation, a common mechanism for S-MIF production was established in the atmosphere.

Pedogenic alteration of illite in subtropical China

AbstractPedogenic alteration of illite from red earth sediments in Jiujiang in subtropical China was investigated using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM). Illite, hydroxy-interlayered vermiculite (HIV), kaolinite and mixed-layer illite-HIV (I-HIV) are present in the soils. The characteristic reflections of the clay phases were 14 Å, 10–14 Å, 10 Å, and 7 Å, respectively. After Mg-glycerol saturations, the 14 Å peak of the samples did not expand, and after heating at 350°C and 550°C it shifted to 13.8 Å and 12 Å respectively, with no residual 14 Å reflection, suggesting the occurrence of hydroxy-interlayered vermiculite. The randomly interstratified I-HIV clays were characterized by a broad peak at 10–14 Å, which did not change its position after Mg-glycerol saturation, but collapsed to 10 Å after heating at 350°C and 550°C. HRTEM analysis showed different lattice fringes of 12 Å, 10 Å and 7 Å . Mixed-layer I-HIV, HIV-K and illite-kaolinite (I-K) were observed in the HRTEM images which represented the intermediate phases during illite alteration. The merging of two 10 Å illite layers into a 12 Å HIV layer, lateral transformation of one HIV layer into one kaolinite layer and alteration of one illite layer into two kaolinite layers illustrated the mechanisms of illite-to-HIV, HIV-to-kaolinite and illite-tokaolinite transformation, respectively. The proposed pedogenic alteration of illite and the weathering sequence of the clay minerals in Jiujiang is illite → I-HIV → HIV → HIV-K → kaolinite. In addition, illite may transform directly to kaolinite.

Characterisation of the hydroxy-interlayered vermiculite from the weathering of illite in Jiujiang red earth sediments

The clay mineralogy and formation of hydroxy-interlayered vermiculite (HIV) in the Jiujiang red earth sediments were investigated using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and inductively coupled plasma-atomic emission spectrometer (ICP-AES) analyses. The 1.4-nm peak of HIV did not change after Mg2+ saturation and glycol solvation, but it exhibited partial collapse to 1.0 nm after K+ saturation followed by heat treatment at successively higher temperatures. HIV was also characterised by FTIR adsorption bands at ~3485 cm–1 and ~3415 cm–1, which did not change with increasing temperature. DSC analysis revealed that the dehydroxylation of hydroxides in the interlayer of HIV began at ~400°C, and a further dehydroxylation was confirmed by the XRD of the sample heated to ~600°C. The ICP-AES analysis of sodium citrate extracts showed that the Al concentration was higher than that of Fe, indicating that the Al was probably present as hydroxy-Al in the interlayer of HIV. The presence of hydroxy-Al polymers in the interlayer influenced both expandability and thermal properties of HIV clays from Jiujiang red earth sediments.

Randomly interstratified illite–vermiculite from weathering of illite in red earth sediments in Xuancheng, southeastern China

Mixed-layer illite–vermiculite (I/V) clays of the Xuancheng red earth were investigated using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectrometer, and high-resolution transmission electron microscopy (HRTEM) methods. The XRD results indicated that the mixed layer I/V clays were characterized by the broad 10–14Å peak with a maximum intensity at ~12Å in air-dried sample, which decomposed into two peaks at 10Å and 14Å peaks respectively after ethylene glycol treatment. After K+ saturation, the 14Å peak changed to 10Å, which reverted back to 14Å after saturation with Mg2+ with a notable decrease in intensity of the 10Å peak. The broad 10–14Å peak collapsed to 10Å on heating to 400°C. These suggested that the broad 10–14Å peak resulted from randomly interstratified illite–vermiculite clays together with discrete illite and also vermiculite. HRTEM observation showed that straight 10Å illite layers were interstratified with 12Å vermiculite layers, suggesting that transformation of illite to vermiculite involves an exchange of K+ by hydrated cations associated with a swelling of the illite. The (060) spacing of I/V clay is 1.50Å, indicating a dioctahedral precursor of illite and thus reinforcing the transformation from illite to vermiculite. FTIR analysis suggested that most band positions of vermiculite and illite in mixed-layer I/V did not change in comparison with those of the discrete clay species, indicating that the basic crystal structure of mixed-layer illite–vermiculite remains the same as the discrete clays. The interlayer cations in the interlayer region of vermiculite layers of the I/V clays are mainly Ca and minor Mg, Al, and Fe. The abundant Ca makes the I/V clays to behave like I/S on glycolated and thermal treatment, while the Mg, Al, and Fe complex ions in the interlayer region cause the vermiculite layer to lose its expandability and to behave like chlorite. The mixed-layer I/V clays were widely formed in late Quaternary alluvial fans in subtropical to tropical areas, where the sediments experienced synchronous pedogenic modification. The syndepositional pedogenesis process leads to an incomplete transformation of illite to vermiculite and causes the formation of metastable intermediates of mixed-layer illite–vermiculite.

Geochemical constraints on provenance of the mid-Pleistocene red earth sediments in subtropical China

The source of mid-Pleistocene red earth sediments in the middle to lower reaches of the Yangtze (Changjiang) River was investigated based on their geochemical characteristics. The Xuancheng and Jiujiang red earth sediments have similar major and trace element distribution patterns. Compared to the loess and paleosol deposits of the Chinese Loess Plateau, the upper continental crust (UCC), and the post-Archean Australian average shale (PAAS), the sediments display notable depletion of CaO, MgO, Na2O, and accumulation of TiO2, Al2O3, and Fe2O3(t). The trace element distribution patterns of the red earth sediments are also different from those of loess and the PAAS, but are similar to those of the loess deposits, except for lower values of mobile trace elements Sr, Ba, and Ni, and higher values of Zr and Y. The red earth samples have uniform La/Th ratios of ~2.8, compatible with those of the UCC, loess, and paleosol. They also have similar chondrite-normalized REE patterns, characterized by enriched LREE and relatively flat HREE profiles, and consistent negative Eu anomalies, similar to those of the UCC, the loess and paleosol, and the Yangtze deposits. These results suggest that the red earth sediments have been subject to considerable mixing prior to deposition and strong subsequent chemical weathering. The sediments have very uniform 143Nd/144Nd and 147Sm/144Nd ratios, this points to well-mixed and multi-recycled sediments. The 143Nd/144Nd and 87Sr/86Sr values of the red earth sediments match well with those of the deposits in the middle to lower reaches of the Yangtze River, but are different from those of the loess and paleosols. This suggests that the red earth sediments are derived from the drainage basins of the middle to lower Yangtze River and might have experienced more intense chemical weathering relative to the Yangtze deposits, as reflected by their higher Rb/Sr ratios, intense depletion of mobile elements and accumulation of immobile elements, as well as their well-developed net-like structure.

Hydroxy-interlayered vermiculite genesis in Jiujiang late-Pleistocene red earth sediments and significance to climate

To understand the paleoclimatic significance of the red earth sediments in Jiujiang, southern China, hydroxy-interlayered vermiculite (HIV) in the deposits was investigated using X-ray diffraction (XRD), chemical extraction, and high resolution transmission electron microscopy (HRTEM). The XRD results indicated that the clay mineral assemblages of the sediments are mainly illite, kaolinite, HIV, vermiculite, with minor illite-HIV mixed-layer clays. The 1.41-nm reflection did not expand after Mg saturation and glycerol solvation, but it shifted to 1.38nm and 1.20nm when the samples were heated to 350°C and 550°C, respectively. The 1.41-nm spacing showed partial collapse after K+ saturation at 80°C in association with the reinforcement of the 1.0nm reflection. Collapse of the HIV (001) spacing was related to the release of Al, Mg, and Ca from the interlayer after KCl extraction. The Al was probably present as hydroxy-Al in HIV interlayers before being released. The HRTEM image revealed 1.4-nm lattice fringes interstratified with illite 1.0nm fringes and two illite lattice fringes merged into one HIV fringe. This suggests that the HIV clays in Jiujiang soils resulted from illite weathering. The shift of a small X-ray diffraction reflection between 1.0 and 1.4nm for an air-dried and glycerol-solvated sample to 0.997nm after heating at 550°C indicated the presence of an irregularly interstratified illite–HIV mineral. The common occurrence of HIV minerals in the Jiujiang red earth sediments suggests a climate with frequent wet and dry cycles prevailed during late-Pleistocene time.