Atmospheric dust plays multiple significant roles in the Earth system, and its quantitative data are vital for an in-depth understanding of paleoclimate changes. However, the lack of coal-derived atmospheric dust data from the Paleogene–Neogene periods of the Cenozoic restricts comprehensive research on the paleoclimate system. Based on the hypothesis that the average content of inorganic components in coal throughout regional geological history is primarily supplied by atmospheric dust, this study systematically collected and supplemented measurements of coal ash yield, which serves as a proxy indicator for the content of inorganic components in coal during the Paleogene and Neogene sedimentary periods worldwide, and established a global database of coal ash yield. By applying the long-term rate of carbon accumulation (LORCA) method, global atmospheric dust deposition rates for both periods were estimated, thereby characterizing their spatial-temporal distribution patterns and transport pathways. The results indicate that compared with the Paleogene period, the atmospheric dust emission intensity in the Neogene period was higher and its spatial distribution was more extensive, with its high-value areas mainly concentrated in southeastern East Asia and central–eastern Europe. Driven by prevailing winds (e.g., the westerlies, the northeast trade winds), atmospheric dust deposition rates decreased significantly with increasing distance from arid source areas, and exhibited a clear negative correlation. From the perspective of latitudinal variation, global atmospheric dust deposition rates exhibit an overall increase from the Paleogene to Neogene periods; however, the subtropical belt (20°N–30°N) records an inverted pattern, with Paleogene period atmospheric dust deposition rates exceeding Neogene period values. The analysis suggests that the transition of global temperatures from the Paleogene period greenhouse climate to the Neogene period icehouse climate governs the periodic variations in dust flux. Meanwhile, the continuous movement of global plates (including subduction, collision, and separation) altered regional paleogeomorphology and atmospheric circulation, significantly influencing the spatiotemporal differentiation patterns of atmospheric dust deposition.
Zircon petrochronology provides key insights into the sedimentary evolution of ancient terranes. We analyzed ∼470 detrital zircons from two Upper Frasnian–Lower Famennian and one Upper Famennian–Visean sections of the South Armenian Block (SAB) using U–Pb geochronology, Lu–Hf and O isotopes, and trace-element geochemistry. These successions document the final episodes of siliciclastic deposition along northeastern Gondwana. All sandstones are highly quartz-rich (>90%), reflecting long-distance transport. About 350 concordant U–Pb ages define older clusters (∼19%), Neoproterozoic (∼63%), and Paleozoic (18%), with peaks at ∼2.5 Ga, ∼910 Ma, ∼600 Ma, and ∼350 Ma, consistent with eastern Gondwanan provenance. Zircon ɛHf(t) (up to –30) and δ18O data (up to 12) for the 600–500 Ma and 900–700 Ma groups indicate derivation from highly evolved sources. Trace-element proxies (U/Yb, LREE/HREE, Ce/Y) display bell-shaped distributions peaking at 700–500 Ma, further pointing to a mixture of evolved and mildly juvenile sources. Zircon petrochronological constraints suggest that the main contributors were likely the sedimentary cover of the Arabian–Nubian Shield, supplemented by more distal Pan-African basement domains such as the Saharan Metacraton and Mozambique Belt. A relative scarcity of 600–500 Ma age zircons, together with recycled ɛHf(t) values, indicates only minor input from the Cadomian arc. The increase in zircon ɛHf(t), together with the marked decrease in U/Yb, LREE/HREE, and Ce/Y after 500 Ma, indicates a shift toward more oceanic-like geochemical signatures, reflecting attenuation of the continental contribution during the early rifting of northern Gondwana terranes. Taken together, the high maturity, peripheral Gondwanan setting, stratigraphic facies, age spectra, and isotopic signatures of the SAB sandstones support their interpretation as very distal representatives of the eastern Gondwana super-fan system.
During the Paleocene–Eocene Thermal Maximum (PETM), global temperatures rose, negative carbon isotope excursion (CIE) occurred and widespread oceanic deoxygenation happened, leading to biotic turnover. Moreover, a Pre-Onset Excursion (POE) has been documented globally and claimed to be more similar to ongoing anthropogenic emissions. Understanding how these two events have affected the macrobenthic tracemaker community (e.g., polychaetes, crustaceans, echinodermata, mollusks) provides crucial information for modern and past marine benthic ecology. Here we present an ichnological analysis of both events along a continental–marine transect. The POE had a variable impact at coastal environments while a decrease in trace fossil abundance is observed at platform environments. The PETM onset marked the macrobenthic tracemaker community extinction. However, during the PETM core, abundant root trace fossil beds appeared at coastal areas, probably associated with accelerated hydrological cycles. Then, on the platform, before the CIE recovery starts, the trace fossil assemblage is reestablished, while in the deep-sea, even after the excursion is over, trace fossil abundance only partially recovers. Our study unveils a protracted recovery of the PETM, suggesting that the macrobenthic tracemaker community was under stress for a much longer period in the deep-sea environments of the Pyrenean Basin. Finally, our results indicate that the PETM had a more dramatic impact on the tracemaker community than the POE.
Ancient oncoid structures serve as important archives of past environments, providing significant insights into early ecosystems and the role of cyanobacteria in shaping Earth's early history. The Cambrian Series 2 oncoids from the Jianchang and Mantou formations in the Fuzhou-Bay section, Liaotung Peninsula, North China, are particularly noteworthy due to their distinct features. These include centimeter-scale, spherical to ellipsoidal grains, with a matrix enriched in clots and microclots of filamentous cyanobacteria, and composed of dense micrite and microspar that form heterogeneous and laminated structures. The presence of calcified cyanobacteria sheaths, especially those of the Hedstroemia group, suggests a strong connection with modern nitrogen-fixing Rivularia species, which occur in both the cortices of the oncoids and their surrounding matrix. This association provides valuable insights into the development of oncoids within photosynthetic biofilms and microbial mats. Despite the abundance of fossilized cyanobacterial filaments, interpreting the formation processes of these oncoids remains challenging due to diagenetic alterations. Significant uncertainties persist regarding the exact mechanisms of calcification in cyanobacteria-dominated biofilms and microbial mats. However, the presence of cyanobacterial filaments resembling Hedstroemia, Apophoretella, and Acuasiphonoria, which are analogous to modern nitrogen-fixing Rivulariaceae, sheds light on the early occurrence of complex cyanobacterial communities during Cambrian Series 2 (∼521–509 Ma). In conclusion, this study highlights the unique characteristics of Cambrian oncoids, their relationship with cyanobacteria, and the challenges in interpreting their formation. It provides valuable insights into the early evolution of high-order cyanobacteria and the calcification processes within microbial mats.
Coal pore structure fundamentally controls coalbed methane (CBM) storage and seepage capacity, yet the governing role of the sedimentary paleoenvironment remains inadequately constrained. This study investigates the Late Permian Longtan Formation coals in southwestern Sichuan Basin, a transitional marine–continental deposit, utilizing proximate analysis, maceral identification, vitrinite reflectance, low-temperature nitrogen adsorption (LP–N2A), X-ray fluorescence (XRF), and inductively coupled plasma mass spectrometry (ICP–MS). Results reveal that the coals accumulated in a warm, humid, and productive reducing paleoenvironment. During the depositional period, increasing weathering intensity and more reducing conditions in the water body contributed to higher concentrations of pyrite and clay minerals, while reducing those of carbonate minerals and quartz. This resulted in a gradual decrease in the average pore size of the coal and an increasing complexity of the total pore system, including non-microporous structures. This study elucidate the mechanistic links between paleoenvironmental conditions and coal reservoir properties, providing a critical geological basis for CBM exploration.
Since the middle of the 20th century, the origin of the Hirnantian deposits of North Africa and the Arabian Peninsula have been interpreted as evidence of large-scale glaciation. In spite of this long held interpretation, a summary of documented data from this area indicates no evidence of full scale glaciation, but rather a more spasmodic or catastrophic origin of the geologic features, possible with outflow of subsurface water similar to what has been interpreted at our neighbour planet Mars. The evidence is of massive flows of water and sediment gravity flows (SGFs) connected to tectonics. The origin and transport of hydrocarbons in the area may be spasmodic, and there is no evidence of connection to continental-wide glaciation. A Diamict origin table is used to sum up the evidence of geologic features which have been interpreted to be from glaciation, and if these are better explained by glaciation or other geological processes.
Travertine has been found to originate from various source rocks, especially carbonates and granitoids, but little is known about those derived from mafic or intermediate volcanic rocks. Therefore, detailed hydrochemical, sedimentological, and isotopic characteristics of the Xiabiaoyuan travertine system (Tengchong, SW China), which developed on Quaternary olivine trachybasalt and basaltic trachyandesite substrata, were investigated here. The travertine build-up is confined within an area approximately fifty-five meters wide and thirty-five meters long, with a height of about seven meters. The spring water is of meteoric origin and exhibits a relatively low water temperature (between 23.6 °C and 29.5 °C) and exceptionally high [Mg2+]/[Ca2+] (varying from 16.6 to 46.3) ratio, which is attributed to olivine-rich aquifer rocks. Four depositional environments were identified from the vent to the distal area (vent pool, discharge pool, gentle smooth slope, and terraced slope), with travertine deposition occurring in the latter three. The travertine was composed entirely of aragonite and five lithotypes were identified, including reed travertine, crystalline crust, paper-thin raft travertine, coated bubble travertine, and filamentous boundstone. Changes in depositional environments led to the formation of these diverse lithofacies. Travertine formation is primarily driven by CO2 degassing, while the exclusive presence of aragonite is attributed to the high [Mg2+]/[Ca2+]. Our isotopic analyses indicate 1) a thermogene origin of the travertine, with parent CO2 mainly of magmatic origin, and 2) a mixed Sr origin from mafic–intermediate volcanic rocks and their underlying Cretaceous–Paleogene granitoids. Based on these, a formation model, from subsurface fluid circulation to surface travertine deposition, was constructed. Overall, this study suggests that mafic–intermediate volcanic source rocks strongly influenced the characteristics of travertine, particularly in terms of its mineralogical and 87Sr/86Sr characteristics. This first comprehensive sedimentological and isotopic study of travertine linked to mafic–intermediate volcanic source rocks may offer new insights into travertine genesis in similar settings and into the reconstruction of (paleo-)hydrogeological aquifer lithology in (paleo-)spring systems.
Abundant carbonate concretions in Early Silurian Longmaxi Formation shales of the Upper Yangtze archive key palaeoenvironmental and diagenetic information. In this study we integrate petrography, inorganic geochemistry and carbon–oxygen isotopes to constrain their origin. The concretions are dominated by low-Mg calcite with minor dolomite, pyrite and diagenetic barite. Moderately 13C-depleted carbonate (δ13C = −10.7‰ to −14.7‰) and palaeotemperatures of 64–66 °C indicate early-diagenetic formation at shallow burial within the sulfate reduction zone (SRZ) and overlying sulfate–methane transition zone (SMTZ). These signatures and associated geochemical data show that dissolved inorganic carbon (DIC) was mainly supplied by organoclastic sulfate reduction (OSR) and sulfate-driven anaerobic oxidation of methane (SD-AOM). Core–rim elemental zoning records dominantly concentric growth with subordinate pervasive pore-filling cementation. Rare-earth element (REE) patterns distinguish volcanic Eu anomalies in Hirnantian–Rhuddanian host shales from subtler Eu–Yb anomalies in Aeronian concretions, consistent with modification by reducing, Fe-rich pore fluids rather than by basin-wide hydrothermal overprint. High Ba and 34S-enriched barite document internal Ba recycling in a paleo-SMTZ. Enhanced Hirnantian–Rhuddanian productivity and anoxia, followed by more oxygenated Aeronian conditions and greater carbonate–clay input, together with sustained OSR and SD-AOM, controlled concretion nucleation and cementation. Overall, these concretions offer a useful record of how ancient marine environments, carbon cycling and early burial processes interacted in organic-rich sediments.
Syn-sedimentary liquefaction-fluidization-induced soft-sediment deformation structures (SSDS) triggered by seismic and aseismic processes often infer about the ancient hydrodynamics condition, tectonics, while, compressive understanding of seismic and aseismic processes in sedimentation is constrained. The study explores several SSDS beds preserved in the multiple stratigraphic intervals of 1.75Ga to 0.75Ga Vindhyan sediment succession, India. Sedimentological study conveys that the studied carbonate to siliciclastic sediment has deposited in marine shelf to lagoon, with an exception of aeolian environment. The laterally continuous-extensive, recurrent SSDS preserved in carbonate succession of 1.6Ga and 0.9Ga infer that SSDS are possibly seismites. The change of depositional dynamics from lagoon to open marine at onset of seismites confirm the seismicity origin. The shallow marine shelf siliciclastic and lagoonal carbonate succession records multiple SSDS as topmost deposition of meter-scale coarsening up sequence which are the imprint of repetitive basin subsidence and followed by sedimentation in influence of intrabasinal rift tectonics. The open marine carbonate shelf preserving meter-scale fining-up cycle with SSDS at base is the record of tempestite. Tidal shelf records overturned cross-bedding, convolute laminations are the highlights of tidalites. Tsunami waves ingress in the costal dune field imprint as convolute lamination, and thick muddy sediment decode as the tsunamites. This study infers that the seismicity, tsunami can modify depositional regime, while storm, tide, intrabasinal rift continue similar sedimentation. Origin of earthquake may be linked to northern and southern Indian block assemblage-drifting with Vindhyan Basin tectonics vs. sedimentation, while detailed sedimentation age and tectonics is the future perspective of study.
The Neoproterozoic Oxygenation Event (NOE) is widely regarded as a crucial stage for the significant increase of atmospheric and shallow marine oxygen levels, impacting early environmental and biological evolution. However, our current understanding of redox evolution in the Xuhuai Basin during this critical period remains fragmentary. In this study, we conducted petrological and geochemical investigations on the Wangshan Formation (ca. 950 Ma–890 Ma) at the southeastern margin of the North China Craton (NCC). The results show that the Wangshan Formation is widely developed with stromatolites, recording the evolution of shallow water carbonate depositional environments from intertidal to subtidal zones. The geochemical data reveal a slightly negative Ce anomalies, elevated Mo/Ca and U/Ca ratios, persistently high δ13C values (∼5‰), and δ34Spy increasing to +36.05‰, collectively indicating a stratified redox water column characterized by weakly oxic surface waters, localized sulfidation, and anoxic bottom conditions. This research highlights the role of marine oxidation processes and their controlling factors during the Tonian period, as recorded in the Wangshan Formation, and provides new insights into oceanic redox evolution prior to the NOE.
The Cambrian Explosion represents one of the most important evolutionary events in Earth history. Trace fossils play a crucial role in documenting the trend of increasing morphological complexity and taxonomic diversity during the Ediacaran–Cambrian transition. New ichnological data from the terminal Ediacaran Dongpo Formation and Cambrian Series 2 Xinji Formation in southwest Henan Province, North China, record evolutionary innovations in shallow-marine communities during the Cambrian Explosion. One ichnogenus and one ichnospecies have been recognized from the Dongpo Formation, and 8 ichnogenera and 16 ichnospecies from the Xinji Formation. Multidimensional cubes of ecospace utilization and ecosystem engineering show a positive correlation between these proxies and ichnodiversity and ichnodisparity, with increased values through the Ediacaran–Cambrian. The occurrence of Didymaulichnus, Treptichnus, and Psammichnites in this interval indicates enhanced ability for sediment modification during biogenic reworking. The ichnofauna in the Cambrian Series 2 Xinji Formation records the second phase of ichnodiversity increase during the Cambrian Explosion.
The Mesoproterozoic was once regarded as the "Boring Billion", yet studies of an increasing number of geological records have revealed that this may not be the case. This study presents the lithium (Li) isotopes and sophisticated geochemical data of the transitional sedimentary strata of the Xiamaling and Longshan formations from Tianjin and Hebei in the North China Craton and discusses their climatic implications in detail. The abundance of Li shows a decreasing trend, while the δ7Li value increases correspondingly, and the Chemical Index of Alteration (CIA), Chemical Index of Weathering (CIW) and Plagioclase Index of Alteration (PIA) decrease from the upper part of the Xiamaling Formation to the lower part of the Longshan Formation. Additionally, the indices of chemical weathering intensity, such as K2O/Al2O3 and Na2O/Al2O3, show an increase trend in their ratios, whereas the Rb/Sr value decreases. These results indicate that chemical weathering weakened across the sedimentary succession. These can be attributed to large-scale basic volcanic activities, warm and humid climatic conditions, and intermittent oxygenation during the deposition of the Xiamaling Formation, which enhanced chemical weathering to varying degrees. This led to excessive consumption of atmospheric CO2, ultimately resulting in a gradual cooling of the climate and a weakening of chemical weathering during the early phase of sedimentation s of the Longshan Formation. Although further evidence is needed to study the cause, scale, and impact of this cooling event in the late Mesoproterozoic, this research provides a new direction for exploring the evolution of the ocean and Earth’s environment during that time.
Early metazoan reefs provide important insights into the early development of complex marine ecosystems and life–environment co-evolution. Here we present a sedimentological investigation of the upper Xiannüdong Formation (Cambrian Stage 3) at the Xiaoshenshan section in the Hannan–Micangshan area of South China. A total of eight lithofacies and two archaeocyath-built reef types have been recognized, the latter of which were previously undocumented from South China. The first type comprises small lenticular buildups (typically 20–30 cm thick and 20–40 cm long) formed at or slightly below the fair-weather wave base (mid-ramp setting). These buildups nucleated on stacked, platelike archaeocyath skeletons and developed a dense composite framework of archaeocyaths and calcimicrobes, with shelter cavities hosting cryptic communities and associated dwellers (e.g., trilobites, echinoderms, and small shelly fossils). The second type is a shallow-water, low-relief buildup (∼60 cm high and >3 m wide) formed in a moderate-energy distal inner ramp setting. Nucleated on stabilized ooid sand substrates and hosting a dweller assemblage compositionally comparable to but less abundant than that of the lenticular reefs, this reef exhibits morphological and architectural variability that likely reflects contrasting paleoenvironmental conditions and divergent ecological strategies. Together with known calcimicrobe-dominated buildups, these findings reveal greater-than-previously-recognized diversity in early Cambrian reef architecture in South China, and constrain the ecological differentiation and environmental controls that governed early metazoan reef development.
The impact of large volcanic eruptions on marine phytoplankton productivity remains poorly constrained in the geological record, particularly in semi-restricted basins such as the Tethyan and Paratethyan realms during the Early Oligocene. This study addresses this gap by quantitatively analyzing calcareous nannoplankton assemblages associated with two Early Oligocene Rhodope eruptions, exposed on Limnos Island, northeastern Aegean Sea, Greece. The three studied sections comprise a continuous, >1500-m-thick siliciclastic sedimentary succession across the Eocene-Oligocene boundary, including three tuff beds. The tuff beds, dated at 33.3 +/- 0.1 and 32.7 +/- 0.1 Ma, are consistent with the ages of the corresponding eastern Rhodope eruptions in Bulgaria. Nannofossil analyses reveal significant fluctuations in abundance and species richness across the transition. We speculate that the changes may represent the nannoplankton response to these Early Oligocene supereruptions. In the open, deeper Thrace Basin (Limnos), post-eruption assemblages show increases in high-nutrient-preferring and temperate-water taxa, consistent with volcanically driven nutrient fertilization and enhanced productivity. In contrast, smaller, shallower, and more isolated Paratethyan basins (Hungary, Romania and Bulgaria) exhibit declines in abundance and diversity, alongside an increase of cold-water-preferring taxa in the nannofossil assemblages. These contrasting responses highlight the importance of basin size and connectivity in modulating ecological response to volcanic forcing. Overall, the results provide new evidence for volcanically driven climatic and productivity changes in Early Oligocene open to semi-restricted Tethyan and Paratethyan marine systems.
This comprehensive macromorphological and cuticular anatomical study investigates Bennettitalean foliage specimens collected from the Yaojie Formation (Middle Jurassic) of the Baojishan Basin, Gansu Province, northwestern China. These fossils were assigned to the genus Nilssoniopteris Natorst, and two new species are formally described: Nilssoniopteris baojishanensis Xin et Zhang sp. nov. and Nilssoniopteris specialis Xin et Zhang sp. nov. N. baojishanensis sp. nov. is characterized by strap-shaped leaves with entire margins, typically straight anticlinal cell walls and subsidiary cells bearing 3-6 papillae. N. specialis sp. nov. exhibits oblong to lanceolate leaves with entire margins, strongly sinuous anticlinal cell walls and is featured by a hollow papilla on the periclinal walls of the abaxial epidermal cells. This is the first macromorphological and cuticular anatomical description of Nilssoniopteris in the Middle Jurassic flora of the Baojishan Basin. Based on cuticular analyses of the two new species, floral composition, and sedimentological data, we infer that the Middle Jurassic Nilssoniopteris from the Baojishan Basin inhabited predominantly warm and humid habitats, albeit with seasonal or intermittent droughts. The two present Nilssoniopteris species may have been adapted to relatively open, high-light, and windy habitats within the basin, potentially including settings such as river terraces and forest margins. The papillate surfaces and trichome bases may have promoted leaf-surface self-cleaning, maintained photosynthetic efficiency, and enhanced defense against herbivorous insects. (c) 2026 The Author(s). Published by Elsevier B.V. on behalf of China University of Petroleum (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Glacial features in basement rocks were first interpreted in 1871, located on the Scottish island of Islay. It was a century later that a detailed memoir of the glacial geology of Islay and the Garvellachs was published, which remains an essential source to this day. The Garvellachs are islands to the north–east of Islay, and they provide a showcase for what became known as the Port Askaig Formation. These particular rocks are of Neoproterozoic age and have been used to correlate diamictite-like sediments from localities ranging from Connemara in Ireland to the north–east of Scotland. Different views, however, have emerged about the interpretation of depositional environments.This work has three aims: to review geological evidences and disputed interpretations; to highlight issues deserving greater attention; and to re-appraise the significance of the geology of the Garvellachs.There are three main models of diamictite formation, each reflecting different depositional processes: (1) movement of grounded ice, which physically transports and deposits unsorted material; (2) glacial rainout, where debris is released from melting ice into water; and (3) mass-flow deposits, resulting from gravity-driven sediment flows that may occur independently of glacial influence. Published discussions of these models are summarised to show that the evidence has ambiguities.This paper contributes to the discussion by focusing on four broader contextual issues. First, the global tectonic framework indicates that tectonics not only accounts for basinal subsidence exceeding 1000 m, but also actively drives processes of erosion and sediment deposition. Second, this dynamic tectonic regime can generate a wide range of sedimentary features, including those characteristic of diamictites. Third, the quartz-rich sandstones deserve a status greater than interbeds signalling interglacial phases, and they point to an active depositional system driven by tectonics. Fourth, the presence of dolostones poses a challenge for proponents of glaciation. Evidence suggests that freshly precipitated dolomite formed substantial layers of relatively pure sediment. Traditionally, dolomite is associated with warm, tropical waters, yet the Garvellachs’ dolostones represent a prominent component of the succession. The reappraisal presented here is that the Garvellachs are a witness to active tectonism in Neoproterozoic times, not glaciation.
Girvanella, a cyanobacterial fossil commonly found in Cambrian carbonates, plays a crucial role in the formation of many microbialites. Despite considerable advancements in elucidating calcifying Girvanella and its biomineralization mechanisms, the understanding of iron-mineralized Girvanella and its iron-mineralization mechanism is still relatively vague. This paper investigates the ferruginous stromatolites from the Mantou Formation Member II (Cambrian Miaolingian Series) of southern North China Block. Through an integrated analysis of sedimentology, mineralogy and geochemistry, we explore the sources of iron minerals, the genesis of chamosite, and the role of Girvanella in iron mineralization. The results indicate that the ferruginous stromatolites consist of dark laminae with densely distributed Girvanella and light laminae with sparsely distributed Girvanella. The tube core of Girvanella is primarily composed of calcite, whereas the tube wall of Girvanella contains hematite and chamosite. The iron minerals within the stromatolites were mainly originated from continental weathering of the Ordos Land and transported into the relatively enclosed study area in a colloidal suspension. This process supplied essential Fe-Al-Si material for the formation of chamosite. The low-energy hydrodynamic condition, coupled with suboxic to weakly reducing settings as reflected by the presence of residual organic kerogen, can provide favorable hydrochemical conditions for the formation of chamosite in ferruginous stromatolites. The authigenic chamosite formed by natural crystallization exhibits a widespread and random distribution within the stromatolitic laminae. In contrast, cryptocrystalline chamosite and hematite are restricted to the Girvanella sheaths and their surroundings. This strongly indicates a close relationship between the formation of cryptocrystalline iron minerals and the iron mineralization of Girvanella. Through CO2-concentrating mechanism, Girvanella generates a large number of anions in its surroundings. During respiration and organic matter decomposition, Fe3+ is partially reduced to Fe2+, and these anions adsorb Fe2+, Mg2+ along with dissolved SiO42-and Al3+, facilitating nucleation on Girvanella cell wall and/or EPS (extracellular polymeric substances), leading to the formation of cryptocrystalline chamosite. A subset of chamosite is subsequently oxidized into hematite under the influence of Girvanella photosynthesis. The coupling of oxidation and reduction processes induced by microbial respiration and Girvanella photosynthesis result in the coexistence of iron and ferrous minerals on the Girvanella sheaths.
In the mid-1950s, Alfred Wegener's long-discarded drift hypothesis was revived by paleomagnetic studies, primarily by comparing results from Europe and North America, with interpretations that a decade later - with emphasis on the North Atlantic evolution, led to the plate tectonic (PT) revolution. But in their later years, the two iconic figures behind this upheaval - Keith Runcorn and John Tuzo Wilson - acknowledged that the sudden change around 1968 had been a complete mistake. Due to a combination of neglected facts and misinterpretation of crucial observations, an entirely new paradigm was needed, Tuzo Wilson (1992) argued. Therefore, it is of paramount importance to look at some of the central scientific problems of the North Atlantic that already existed when PT took root - and none of the critical problems have later been resolved. Based on published data and conclusions from numerous independent and diverse geophysical and geological studies, this paper summarizes the unsustainable situation and points towards a new coherent understanding. It is beyond doubt that the shallow transoceanic ridge - from Shetland to Greenland via Iceland - has variably thick continental crust making it senseless to talk about North Atlantic seafloor spreading. Moreover, along the Mid-Atlantic Ridge there is an abundance of ultramafic mantle rocks and Precambrian metamorphics, while fresh basalts are very rare. Thus, a paleomagnetic source rock for the linear marine magnetic anomalies - a crucial prerequisite for the seafloor spreading model - does seemingly not exist. Deep-sea drilling in the North Atlantic and elsewhere has shown that the main sequence of deep-marine sediments is of Upper Mesozoic age. This means that the ocean basins must also be correspondingly young. Also, the large volume of the world's oceans implies that the main volume of water emitted from the Earth's interior have occurred in tandem with delamination of the crust - with associated isostatic subsidence of deep-sea basins. Progressive gravitative loss of the lower crust (thinning upwards) depends on it having become eclogitized, for which sufficient hydrous pressure apparently is required. The fact that the ocean basins, the bulk of seawater, and the varyingly thin deep-sea crust have late Mesozoic origins imply that surface conditions, crustal constitution and crustal thickness must have been completely different in pre-Mesozoic times. In this respect, modern geophysics and rock evidence suggest that the original pan-global crust must have been continental, and with the Cambro-Silurian higher life forms described as cosmopolitan, it follows that the early surface was relatively featureless and capped by a shallow continental sea of relatively warm water discharged from the mantle. Thus, the early Cambrian expulsion of virgin water flooded a Precambrian surface of weathered and loose blocks, giving rise to the Great Unconformity. Furthermore, the advancing pulse-like water supply with frontal accumulation of eroded rock debris is the likely explanation for the terminal Precambrian and Paleozoic diamictites on the North Atlantic continents and elsewhere in the world. With the assumed late Precambrian and Palaeozoic surface conditions, glaciation seems unlikely, even at palaeopolar latitudes. Therefore, the concept of a "Snowball Earth" is dismissed. The slow outgassing of the Earth and its associated episodic rotational changes can further be seen as providing the main dynamo-tectonic driving forces for Earth history. In that context, brief considerations of two unresolved phenomena -hydrocarbons and Upper Mesozoic metal-bearing black shales are discussed.
Changhsingian (Late Permian) represents a prosperous stage in the development of hyper-calcified sponges. Quantifying reef-building sponge assemblages is essential for understanding niche partitioning among communities, internal (lithological and biotic) heterogeneity within reef complexes, and the growth architecture of sponge bioherms. Here we analyze Changhsingian sponge reefs exposed in the Jiantianba quarry by integrating point-intercept transects with a high-resolution three-dimensional digital outcrop model (DOM). Eight common species of hypercalcified sponges were identified. Cluster analysis of resampled quadrats differentiates four lithofacies and eight biocommunities that show pronounced lateral and vertical variability across the reef core. This research provides insights into the understanding of the lithological and biological heterogeneity within the Late Permian hypercalcified sponges reef in South China, demonstrating that multi-trace line analysis can identify lateral heterogeneity and rapid changes in reefs, providing a more comprehensive research perspective for understanding the growth and development process of the reef, and the correlation between environmental and biological factors. (c) 2026 The Author(s). Published by Elsevier B.V. on behalf of China University of Petroleum (Beijing). This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).
Previous studies have interpreted the Paleoproterozoic Reany Creek Formation as a glacial deposit based largely on the presence of lonestones that were regarded as dropstones. In the first paper of this three-part series (Larue, 2026b), a new classification system was introduced to more precisely describe and interpret lonestones. That framework is applied here to the Reany Creek Formation, in which five distinct lonestone types are recognized. Type 1 lonestones are outsized clasts resting in and disrupting layering within laminated mudstone. Type 2 lonestones occur within homogeneous mudstone beds. Type 3 lonestones form chains of outsized clasts in mudstone intervals, sometimes showing a basal erosional contact. Type 4 lone-stones are isolated clasts immediately above pebbly mudstone units in laminated muddy sediments. Type 5 lonestones are outsized clasts residing in tectonically foliated mudstone. The findings of this study indicate that none of these lonestone types can be uniquely attributed to glacial dropstone origins. Lonestone types 2 through 5, and possibly type 1, have also been documented within non-glacial, deep-water deposits of the Cretaceous Pigeon Point Formation and the Miocene San Onofre Breccia in California. The Reany Creek Formation consists predominantly of mudstone interbedded with abundant conglomeratic intervals and subordinate sandstone beds. All conglomerate and sandstone units are interpreted as products of sediment gravity flows, while the mudstone intervals record hemipelagic settling and low-density turbidity currents. Soft-sediment deformation structures are common within the muddy facies, indicating syndepositional instability. Lonestone types 2, 3, and 5 are interpreted as components of sediment gravity-flow deposits. The overall stratigraphic architecture and associated sedimentary features are consistent with deposition in a deep-water slope environment. This interpretation is supported by close sedimentological parallels with the non-glacial Pigeon Point Formation, which provides a modern analog. Importantly, no sedimentological or stratigraphic evidence was found to support glacial influence during deposition of the Reany Creek Formation.
