Contributions presenting an applied as well as a theoretical approach are invited, including papers related to reconstructions (at various time and space scales), fractionation factors, measurement methods, proxy calibration, and verification.
Environmental changes and the geodynamic evolution of continents have facilitated both the emergence of life on Earth and the diversification of mineral species from the early Archean until today. However, the physico-chemical conditions of ancient environments remain poorly understood, particularly regarding the processes and consequences of major oxygenation events (e.g., the Great Oxidation Event, Neoproterozoic Oxygenation Event, and Phanerozoic Oceanic Anoxic Events) and associated mass extinctions, as well as the influence of continents and mantle processes in modulating ocean chemistry at different times in Earth’s history.
Understanding key processes shaping modern and ancient environments; such as weathering, hydrothermal alteration of the oceanic crust, bacterial activity, sedimentation, and diagenesis; is crucial for reconstructing paleo-environments. Redox processes and Earth’s oxygenation during critical transitions and biotic crises are central to unraveling the links between environmental change and biological evolution.
With this session, we encourage contributions from the interdisciplinary fields of geochemistry, oceanography, sedimentology, mineralogy, and geo(micro)biology with a particular emphasis on geochemical and isotope-based approaches to redox reconstructions, element cycling, and paleoenvironmental modeling. We welcome studies addressing the evolution of early life habitats, biomineralization, and paleobiological responses during intervals of profound environmental and climatic change, highlighting the links between Earth's chemical evolution and life.
Orals: Wed, 6 May, 08:30–12:25 | Room 0.49/50
Reconstructing past climate dynamics on terrestrial environment remains a major challenge in paleoclimate research. Improving our understanding of how continental ecosystems responded to abrupt climate oscillations is essential for assessing future climate impacts on terrestrial environments and human societies. While ice-core and marine archives document large-scale and rapid climate variability, the links between climate and continental surface processes remain poorly constrained. Identifying robust climate proxies in continental sedimentary records is therefore crucial.
Fossil earthworm calcite granules preserved in loess–paleosol sequences have recently emerged as promising archives of past climate conditions, providing insights into temperature and precipitation during the last glacial period in Western Europe. However, the climatic interpretation of these proxies requires a robust calibration based on modern earthworm calcite granules to better constrain the environmental and biological parameters controlling granule formation, such as temperature, soil moisture, and litter composition.
Here, we present an experimental calibration approach using modern earthworms (Lumbricus terrestris) reared under controlled environmental conditions. Soil temperature and food sources were systematically varied to assess their influence on granule production and isotopic signatures. Calcite granules were analysed for δ¹⁸O and δ¹³C, while δ¹³C was also measured in soil organic matter and litter. For the first time, clumped isotope (Δ₄₇) measurements were performed on earthworm calcite granules, allowing direct temperature estimates independent of past soil-water δ¹⁸O.
This experimental approach provides new constraints on vital effects and isotopic fractionation in earthworm calcite granules and improves their use as quantitative paleoclimate proxies. Our results complement previously established empirical relationships between (i) the oxygen isotopic composition of meteoric water, granules, and temperature, and (ii) the δ¹³C of litter and the δ¹³C of granules, strengthening the potential of earthworm calcite granules for reconstructing past terrestrial climate dynamics.
How to cite: Prud homme, C., Rigaudier, T., Auclerc, A., and Daëron, M.: Reconstructing climate dynamics on terrestrial environment using the stable isotope composition of earthworm calcite granule: An experimental approach, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7400, https://doi.org/10.5194/egusphere-egu26-7400, 2026.
In many carbonate archives, Δ47 signatures appear to be primarily driven by crystallization temperatures, with little evidence for other influencing factors, implying that 13C and 18O isotopes are effectively (re)distributed among carbonate isotoplogues in accordance with thermodynamic stability during or just before mineralization. This is not the case for all types of carbonates, but appears to hold true for biocarbonates such as bivalves, gastropods, or planktic foraminifera. For historical reasons, things are not as clear-cut when it comes to benthic foraminifera, a particularly important source of information on past marine environments at the scale of the Cenozoic and beyond. In hope of fostering productive discussions, we revisit this issue with a focus on the following questions:
- What is the current body of evidence from modern/recent observations?
- How much do the various Δ47 calibrations currently applied to foraminifera differ?
- Is there any practical difference between Δ47 calibrations based exclusively on modern/recent foraminifera and "composite" calibrations based on many different types of carbonates?
- What should be the foraminifer Δ47 community's next steps to try and resolve these issues?
How to cite: Daëron, M. and Gray, W.: Does it matter whether benthic foraminifera achieve clumped-isotope thermodynamic equilibrium?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19790, https://doi.org/10.5194/egusphere-egu26-19790, 2026.
The Mundrabilla meteorite can be classified as a medium octahedrite nickel-iron type, the kamacite being the dominant mineral. The meteorite was discovered in 1911 in Mundrabilla (Australia), the most important fragments weighing between 3.5 kg and 24 tons.
To get more information concerning the structure and composition of a 1.5 kg fragment of the Mundrabilla meteorite existing in the collection of the National Geological Museum, Bucharest, a small fragment was extracted using a water jet cutter. More analytic techniques, such as XRD, SEM-EDX, and ultra-low background gamma ray spectrometry, were used to analyse it.
A detailed investigation performed by XRD evidenced the presence of the α-FeNi phase, identified as kamacite. Its crystal chemical formula, calculated based on SEM-EDX analysis, was Fe0.937Ni0.063. The cell parameters of kamacite, as determined by least squares refinement of the X-ray powder data, are: a = 2.8717(7) Å and V = 23.68 Å3. On the diffraction pattern, minor peaks were observed, which could be attributed to γ-FeNi taenite.
The geochemical composition determined by SEM-EDX investigation is typical of iron-bearing meteorites. XRD indicates as main phase kamacite, but traces of other elements reflect the presence of other minor mineral phases. The presence of quite abundant C and minor Si fits with the presence as minor phases of moissanite (SiC) and cohenite (Fe,Ni)3C. The S content could be related to traces of troilite (FeS) or pyrrhotite (Fe1-xS), while the presence of minor P could be attributed to rhabdite (Fe, Ni)P.
The gamma-ray spectroscopy performed in the ultra-low background laboratory at the Slanic (Prahova) salt mine evidenced the presence of 26Al and 60Co, two cosmogenic radionuclides produced by cosmic neutrons through the spallation of 28Si or resulting from the β-decay of 60Fe, which is also generated by the neutron activation of the stable 28Fe. Both 26Al and 60Fe are long-lived isotopes with half-life times of 0.747 and 2.62 My, respectively, which explain their presence in meteorites.
How to cite: Dumitras, D.-G., Radulescu, C., Margineanu, R. M., Ricman, C., Blebea-Apostu, A.-M., Gomoiu, C., Dulama, I.-D., Stihi, C., Bucurica, I.-A., Duliu, O. G., Marincea, S., and Sirbu-Radaseanu, D. S.: Ultra-low background gamma-ray spectrometry, SEM-EDX and XRD investigation of a fragment of the Mundrabilla (Australia) iron meteorite. Rare cosmogenic 26Al and 60Co radioisotopes evidenced, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10242, https://doi.org/10.5194/egusphere-egu26-10242, 2026.
The Azores Front marks the boundary between subtropical and
subpolar water in the North Atlantic. Its position during glacial periods
is debated, tracing it would improve our understanding of glacial ocean
circulation. Neodymium (Nd) isotopes are an important tracer for past and
current water mass mixing. They are however subject to overprinting on
local scales by processes including erosion and volcanic activity.
Cold-water corals incorporate Nd into their skeletons without
fractionation, making them valuable archives. In this work, the epsilon-Nd
of corals from several locations close to the Azores Islands was measured.
The corals were previously dated by U/Th measurements, which revealed ages
between 0.458 and 22.14 ka. The epsilon-Nd measurements found a range of
values between -12.07 and -1.26. The results reveal clear
evidence of radiogenic overprinting, which occurs on decadal timescales
and can most likely be attributed to volcanic activity. The extent and
frequency at which this overprinting occurs does not depend on climate
phases. A part of the samples may represent unaltered seawater values,
these show no evidence of a change in water mass mixing over the last 20
ka.'
How to cite: Schöfer, C. and Frank, N.: Epsilon-Nd-Signatures and Radiogenic Overprinting in Cold-Water Corals near the Azores, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-22506, https://doi.org/10.5194/egusphere-egu26-22506, 2026.
The analysis of isotopic composition (δ18O and δ2H) in precipitation is a powerful approach for investigating (paleo)climatic processes within the hydrological cycle. Variations in δ18O and δ2H in precipitation result from successive isotopic fractionation processes during atmospheric transport and are observed across both spatial and temporal scales. While modern isotopic records are extensively documented, e.g., through the IAEA/WMO network, European datasets are largely limited to monthly resolution and remain sparse at the regional scale. This is particularly the case for the Swabian Alb (or Swabian Jura) in southwestern Germany, a karst plateau south of Stuttgart, approximately 220 km long and 40 km wide, with mean elevations around 500 m and peaks reaching 1110 m. The Swabian Alb holds international significance as a UNESCO Global Geopark and includes six caves designated as UNESCO World Heritage sites. The region constitutes a natural divide between two significant European basins: the Rhine and the Danube. The oxygen isotopic composition of meteoric water from the Swabian Alb provides key insights into modern moisture sources and, when preserved in paleoclimate archives such as speleothems, offers valuable information on past atmospheric circulation and hydroclimate.
Here, we compare measured δ18O and δ2H in meteoric water with simulations of isotope-enabled climate model (ECHAM6-wiso) to investigate spatial and temporal variabilities, and identify climatic factors influencing regional isotopic patterns. We present δ18O and δ2H records of weekly to monthly sampled rainwater across the Swabian Alb from October 2023 to present-day. We examine simulated and observed interannual changes in precipitation, teleconnections, and seasonality patterns. In addition, we fill a gap by providing daily δ18O and δ2H values of meteoric water collected at a weather station located in Tübingen.
Investigating variations in modern water isotope records across the Swabian Alb is essential for regional paleoclimate research and allows the validation of isotope-enabled climate models on the local scale. Our results show the first model–data comparison for the Swabian Alb and pave the way towards regional climatic reconstructions e.g., paleoclimate of the last glacial period, when modern humans occupied caves of the Swabian Alb.
How to cite: Ballian, A., Racky, M., Maisch, M., Novello, V., Lo Triglia, D., and Rehfeld, K.: A regional scale data–model comparison of modern oxygen stable isotopes in precipitation (Swabian Alb, southwest Germany) , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7765, https://doi.org/10.5194/egusphere-egu26-7765, 2026.
Lead (Pb) and its isotopes are known to be released incongruently during early chemical weathering in continental settings. Incongruent weathering implies that a chemical weathering induced continental runoff trace metal isotope signature is not identical to bulk rock isotopic compositions. The incongruent release of Pb can mostly be ascribed to preferential chemical weathering of less weathering resistant accessory uranium and thorium-rich mineral phases present that are most abundant in differentiated continental crust. If this continental crust is ancient, these accessory mineral phases contain present-day Pb isotopic signatures that are in places extremely radiogenic, as well as substantially different from bulk rock Pb isotopic compositions. Several studies that investigated the Pb isotopic runoff evolution in the Labrador Sea, NW Atlantic and Arctic Beaufort Sea already reported very radiogenic Pb isotopic runoff signatures in these marine basins bordering the Laurentide Ice Sheet (LIS) during key time intervals of the last deglaciation. These earlier results require the existence of very radiogenic Pb isotopic freshwater signatures inland North America that were generated during incipient post-glacial chemical weathering reactions in response to the retreat of the LIS during the last deglaciation.
We targeted subarctic Lake Melville in central Labrador aiming to resolve how the Pb specific chemical weathering signature changed in response to deglacial warming, in an initially subglacial setting that transitioned to completely ice-free conditions in the early Holocene. Lake Melville is a fjord‑like subarctic estuary in central Labrador that receives most of its freshwater and sediment from the Churchill River and other major tributaries draining a large early to mid-Proterozoic shield. We analysed two sediment cores from central Lake Melville that together archived the ambient dissolved Pb isotope signature over the past 13 ka. Our authigenic Pb isotope records are complemented by associated bulk detrital Pb isotope compositions, enabling us to compare the dissolved Pb isotope signature in the lake with corresponding sedimentary signatures. The lake was covered by the LIS until about 10.3 ka BP, yet still located in an ice-proximal setting until 8.5 ka BP. The region Labrador-Québec was ice free after ca. 5.7 ka BP.
The most striking result of our record is the observation of (i) very radiogenic authigenic Pb isotope compositions throughout that are (ii) much elevated relative to the associated detrital compositions, which are rather unradiogenic. Very invariant Pb isotopic signatures observed until 10.5 ka BP confirm the suggested subglacial lacustrine sedimentary setting in the oldest section. The subsequent deglaciation witnessed most variable compositions, with most radiogenic compositions seen at ~8.2 ka BP. The record becomes substantially smoother after ~6 ka BP when the catchment area was no longer influenced by direct glacial runoff. While the detrital compositions suggest some geographic variability in sediment sourcing, the authigenic Pb isotopic compositions are not following these detrital signatures. Our results highlight the unique geological setting that make authigenic Pb isotopes in proximal North American sediment cores a sensitive proxy for for the detection of elevated deglacial runoff fluxes in circum-North American marine basins.
How to cite: Gutjahr, M., Thomsen, S., Hallmaier, M., Gebhardt, C., and Ohlendorf, C.: Continental runoff lead isotopic signatures released during incongruent chemical weathering in subarctic Lake Melville associated with the retreat of the Laurentide Ice Sheet over the past 14 ka, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10274, https://doi.org/10.5194/egusphere-egu26-10274, 2026.
This presentation examines recent developments in the application of oxygen stable isotope analyses to lacustrine invertebrate remains (e.g. chironomids) within palaeoenvironmental science. We explore improvements to instrumentation and measurement, and the opportunities that this presents for a more nuanced palaeoenvironmental approach. The improvements to the existing methodology of δ18Ochitin measurements now allow the possibility of taxon specific δ18Ochitin reconstructions and thus the potential to enhance our understanding of paleoclimate dynamics. Opportunities to reduce the sample size required have come from improvements to instrumentation, through more sensitive Thermal Conversion Elemental Analyser isotope ratio mass spectrometry (TC/EA-IRMS). We discuss the considerations needed to assess the sample size measured and avoid systematic bias. Is smallest always best or does this lead to a biased environmental reconstruction? Further, it is also unclear what between-taxa offsets exist for different chironomid morphotypes and whether δ18Ochitin offsets between taxa are stationary across large climate transitions, and the extent to which changing vital effects play a role. We present new data on taxon-specific trends from the robustly dated late-glacial sediment record from Lake Llangorse, UK. This will allow us to determine whether temperature is the main driver of the δ18Ochitin signal of each taxon, or if vital effects play a role.
How to cite: Lamb, A. and Engels, S.: Stable isotope analyses of lacustrine chitinous invertebrate remains: analytical advances, challenges and potential., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10452, https://doi.org/10.5194/egusphere-egu26-10452, 2026.
Cryogenic cave calcite is a relatively rare type of cave deposit formed in periglacial environments by drip water freezing and discharging its soluble components in form of mostly calcium carbonates. While cryogenic calcite formation as a phenomenon was recognized early on by researchers (see [1,2] for references), most studies to date have focused on the morphological characteristics of these deposits or their stable isotope composition.
In this contribution we investigate the elemental and stable isotopic composition of cryogenic cave carbonate deposits (pearls) from the Scărișoara Ice Cave, Romania. The pearls were collected from within the cave at locations where active drip water was present. Samples (millimeters to centimeters in diameter) were embedded in epoxy resin, cut in half and the exposed surface was analyzed. Laser ablation inductively coupled mass spectrometry (LA ICP TOF MS) was used to identify the qualitative distribution of trace elements that can we expected to reach the cave from atmospheric deposition above the cave, rather that from the bedrock. A Teledyne Photon Machine 193 nm wavelength excimer laser Iridia was used in conjunction with Nu Instruments Vitesse time-of-flight ICP MS for elemental mapping. Stable isotopic (δ13C and δ 18O) composition was explored using laser ablation isotope ratio mass spectrometry (Photon Machines Fusions CO2 laser coupled to a Sercon HS2022 IRMS).
Elemental data shows highly zoned structures in the studied deposits. Layers of clear detrital input (characterized by high 89Y and low 48Ca+/28Si+) alternate with layers with monotonous chemical composition. Furthermore, the layers of detrital input are often characterized by the presence of 3–5 micron Au-containing particles. We believe those particles to be anthropogenic pollutants windblown from areas with historically intense Au mining located in relative proximity of the cave.
[1] I.D. Clark, B. Lauriol, Kinetic enrichment of stable isotopes in cryogenic calcites, Chem. Geol. 102 (1992) 217–228.
[2] K. Žák, B.P. Onac, A. Perşoiu, Cryogenic carbonates in cave environments: A review, Quat. Int. 187 (2008) 84–96.
How to cite: Pușcaș, C. M., Stremțan, C. C., Perșoiu, A., and Schlatt, L.: Elemental mapping and stable isotope analyses of cryogenic cave carbonates from Scărișoara Ice Cave, Romania, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21375, https://doi.org/10.5194/egusphere-egu26-21375, 2026.
Evaporites are rarely recorded in the Precambrian. In the oldest rocks they are known mostly from pseudomorphs of salt minerals, or can be inferred from other sedimentary and geochemical features. Only in some younger rocks are they present as salt minerals.
About 50 inferred or definitive occurrences of evaporites in Archean through Mesoproterozoic rocks were compiled. These data allow characterisation of the mineralogy and sedimentary environments of the earliest evaporite sediments and insight into their evolution over time.
The earliest documented evaporites are from the Archean eon, with about 15 occurring mostly in the Paleoarchean (3.6–3.2 Ga) and Neoarchean era (2.8–2.5 Ga).
The earliest Paleoarchean deposits considered as „evaporitic” in origin are bottom-grown barite crystals, formerly interpreted as pseudomorphs after gypsum, and silica pseudomorphs after radiating splays of aragonite in North Pool Chert of the Dresser Formation (3.48 Ga old), Australia. Barite and aragonite presumably crystallized in a volcanic caldera evaporitic basin from brine of both hydrothermal and seawater derivation. However barite, unlike aragonite, cannot be classified as an evaporite mineral due its very low solubility. The other Palaeoarchean evaporites are represented mostly by enigmatic pseudomorphs (after possible gypsum, aragonite, nahcolite, halite, and others). The Archean evaporite crystals are interpreted as precipitated in both marine and non-marine environments, including soils or weathering zones where they could represent terrestrial or pedogenic evaporites.
In the Proterozoic eon the most frequent occurrences are from the Paleoproterozoic (Rhyacyan, Orosirian and Statherian; 2.3–1.6 Ga). Their appearance directly follows the beginning of the Great Oxidation Event in Siderian at about 2.4 Ga. The first abundant evaporites, with mineralogy similar to the present-day marine evaporites (carbonates, Ca-sulphates, halite, and KMg sulphates), appear in the Mesoproterozoic and include several saline giants (evaporites with volume ≥ 1000 km3). The oldest ones are: a) 2.31 Ga old Gordon Lake Formation, Canada, and Kona Dolomite, USA, b) ca 2.0 Ga old Tulomozero Formation, Onega Basin, Karelian craton, Russia (with preserved KMg salts), c) 2.1 Ga old Juderina Formation, Yilgarn craton, Australia. They strongly suggest appearance of marine water very similar to the modern ocean water.
Information about evaporite minerals from the Archean era is uncertain and ambiguous, coming from enigmatic pseudomorphs and geochemical signals. This evidence originates from sedimentary environments that are not widely recognised, including marine, terrestrial, hydrothermal and/or lacustrine environments. Such evidence does not provide a basis for unambiguously characterising the composition of Archean seawater.
How to cite: Kremer, B. and Bąbel, M.: Evidence and significance of the oldest Paleoarchean to Mesoproterozoic evaporites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14831, https://doi.org/10.5194/egusphere-egu26-14831, 2026.
On the modern Earth, oxidative weathering of continental crust constitutes the dominant source of most nutrient elements to the ocean that ultimately sustains the biosphere over geological timescales. However, continental crust exposed above sealevel may have been scarce on the early Earth, and oxidation was limited prior to the rise of atmospheric O2 at ca. 2.4-2.3 billion years ago (Ga). Several experimental and modelling studies have therefore suggested that anoxic seafloor weathering and hydrothermal alteration provided the major sources of bioessential elements such as phosphate and transition metals. Here, these datasets are reviewed, and new supportive evidence is presented from the Paleoarchean North Star and Mount Ada basalts (3.5-3.47 Ga) in the Pilbara craton, Western Australia. Alteration gradients reveal depletion in key nutrients, supporting the idea that this process contributed to sustaining microbial ecosystems at that time. Direct evidence of a Paleoarchean seafloor biosphere is preserved in the form of microbialites found in an offshore marine setting with no evidence of felsic material influx. Collectively, these findings show that life could be maintained on an ocean-dominated planet; however, continental emergence was perhaps important for biological diversification and innovation over the later course of Earth’s history.
How to cite: Stüeken, E.: Exploring seafloor alteration as a viable mechanism to sustain Earth’s earliest biosphere, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2631, https://doi.org/10.5194/egusphere-egu26-2631, 2026.
Oceanic anoxic events represent major perturbations of marine redox conditions with varying spatial extents of ocean deoxygenation through Earth’s history. The isotopic composition of redox-sensitive elements, preserved in sedimentary archives, particularly molybdenum (Mo) and uranium (U) isotopes, are powerful proxies for reconstructing past ocean oxygenation. However, Mo and U isotope compositions can be influenced by both global ocean anoxia and local depositional conditions. Both isotope systems show opposite isotope fractionation behavior under variable local redox conditions but are expected to be shifted in the same direction (towards lower values) at a global expansion of seafloor anoxia, allowing combined U-Mo isotope analyses to discriminate between local and global redox signals. The Toarcian Oceanic Anoxic Event (T-OAE; ~183 Ma) represents an Early Jurassic interval of marine deoxygenation and environmental perturbation, but it remains incompletely understood whether ocean anoxia was globally extensive or locally restricted.
Here, we present combined U-Mo isotope data from black shales deposited during and after the T-OAE at two locations within the European Epicontinental Sea (Schandelah, North German Basin, and Metzingen, South German Basin). During the T-OAE, all sections are characterized by light Mo and U isotope compositions, reaching values as low as 0.61-0.73 ‰ for δ⁹⁸Mo and -0.19 to -0.13 ‰ for δ²³⁸U. Following the T-OAE, both isotope systems show an increase towards heavier δ⁹⁸Mo values between 1.66 and 1.73 ‰ and δ²³⁸U values between 0.12 and 0.19 ‰ across both sites. This observed positive correlation between Mo and U isotope compositions is consistent with a global expansion of seafloor anoxia. To further exclude potential local effects, we used redox- and salinity-sensitive proxies, such as Fe/Al, Sr/Ba, B/Ga, and TS/TOC ratios. These proxies show no significant variations across the T-OAE interval and beyond, indicating stable depositional conditions at both localities. Therefore, the U-Mo isotope shifts in the black shales likely reflect a global expansion of seafloor anoxia during the T-OAE.
How to cite: Klamt, V., Krencker, F.-N., Mann, T., Kaufmann, A., Arp, G., van de Schootbrugge, B., Viehmann, S., and Weyer, S.: Reconstructing marine redox conditions during the Toarcian Oceanic Anoxic Event constrained by combined U-Mo isotopes in black shales, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7126, https://doi.org/10.5194/egusphere-egu26-7126, 2026.
The rare earth elements (REE) are transported and transformed coherently in the environment, yet subtle differences in their chemical properties cause variable fractionation patterns. In the ocean, their relatively long residence times (centuries to millennia) allow REE to be advected across basins while recording fractionation processes en route. Scavenging onto sinking particles – especially metal oxides and organic matter – leads to their burial on the seafloor, where their abundances can be further modified by early diagenetic processes. The fraction of REE preserved in sediments enters the geological record where it can be used to reconstruct past ocean chemistry provided their marine geochemical cycling is understood well enough.
Here we present REE concentration data from authigenic phases of a global suite of marine sediments. We assess which environmental parameters they predominantly relate with, how early diagenesis affects the archived REE, and whether authigenic REE can be used to reconstruct past ocean chemistry and particle fluxes.
How to cite: Blaser, P., Monedero-Contreras, R., Scholz, F., Jaccard, S. L., and Frank, M.: Rare Earth Elements as tracers for past ocean chemistry, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20576, https://doi.org/10.5194/egusphere-egu26-20576, 2026.
Banded Iron Formations (BIFs) are important archives of early Earth's history, offering critical geochemical insights on Archaean oceanic and atmospheric chemistry. BIFs provide critical constraints on ancient seawater conditions, temperature, pH, nutrient cycles, redox processes and the evolution of microbial metabolisms, which are fundamental to understanding early planetary habitability. In the Singhbhum Craton of India, their immense economic importance has made BIFs a primary research target for decades.
But so far, the different BIF units exposed within the Singhbhum Craton remain yet to be dated and characterized. Numerous BIF units are distributed within the Singhbhum Craton, which holds immense potential to unravel deep insights into not only seawater chemistry but also conditions related to the emergence of the craton and/or presence of terrestrial landmass. Recent studies have placed BIFs exposed in the southern part of the Singhbhum Craton amongst some of the oldest BIFs with evidence for terrestrial inputs around ca. 3.37 Ga. Here, we report ancient BIFs of the Gorumahisani Greenstone Belt that are well exposed near the mining town of Gorumahisani, with alternate banding of Si- and Fe-rich bands and intercalated with cherts. To date, the age of this critical iron formation within the Gorumahisani greenstone sequence remains poorly known. We dated an intrusive granitoid within the BIF sequence. U-Pb dating of zircon crystals recovered from the intrusive granitoid provided a 207Pb/206Pb age of 3286 ± 10 Ma. The emplacement age of this granitoid brackets the minimum age for the Gorumahisani greenstones, and on the other hand, it is identified as part of the Singhbhum Granitoid Complex (i.e., the Singhbhum Suite). Field and geochronological evidence confirms the presence of Palaeoarchaean BIFs in the Gorumahisani belt, establishing a critical foundation for future studies to determine precise depositional constraints and unravel details of early Earth surface processes.
How to cite: Jodder, J. and Elburg, M.: Banded Iron Formation of the Gorumahisani Greenstone Belt, Singhbhum Craton, India: Insights into Archaean surface processes., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21888, https://doi.org/10.5194/egusphere-egu26-21888, 2026.
As a consequence of the evolution of the water-bearing basal magma ocean (MO), water-induced mantle overturn can well account for many puzzling observations in the early Earth, such as the formation of the Archean continents, the Archean–Proterozoic boundary, and high Archean paleomagnetic field (Wu et al., 2023; Wang and Wu 2026). The early Earth may have experienced a deep-water cycle totally different from the current. High pressure studies suggest that the whole-mantle MO evolved into an outer MO and a basal MO. With the solidification, water in the basal MO moved toward the core-mantle boundary and the basal MO eventually became gravitationally unstable because of the enrichment of water (Fig.1). The instability triggered the massive mantle overturns and resulted in the major pulses of the thick SCLM and continental crust generations in the Neoarchean. The mantle overturns eventually got rid of the whole basal MO and the mechanism which generated the Archean-type SCLM and continents likely no more worked after the overturns. Thus, water-induced mantle overturns can account for why Archean-type SCLM and continents basically occurred in the Archean (Wu et al., 2023). The mantle overturn can substantially accelerate the cooling of the core and strengthen the geomagnetic field, which explains well the high paleointensity records from ~3.5–2.5 Ga (Wang and Wu 2026).
Besides the enrichment of water, the basal MO was enriched with ferric iron. This study shows that the ascent of ferric-rich basal MO and its mixing with the upper mantle could account for the observed shift in the redox state of the upper mantle during the Archean. Both the redox state shift and the generation of Archean continents result from these mantle overturns. Therefore, it is expected that the shift in mantle fO2 aligns with the timing of continental generation, which is supported by the observations. The mantle overturns are rare with age > ~ 3.6 Ga, but their frequency increases with age < ~3.6 Ga and reaches the maximum in the Neoarchean. The combined effects of the ascent of the deep oxidized material, the emergence of continents, and oxygenic photosynthesis generated the broader First Redox Revolution of the Earth system, ultimately initiating the GOE shortly after the end of the Archean.
Wu, Z., Song, J., Zhao, G., and Pan, Z. (2023). Water-induced mantle overturns leading to the origins of Archean continents and subcontinental lithospheric mantle. Geophysical Research Letters, 50, e2023GL105178. https://doi.org/10.1029/2023GL105178
Wu, Z., and Wang, D. (2026) Water-Induced Mantle Overturn Explains High Archean Paleointensities. National Science Review. https://doi.org/10.1093/nsr/nwaf578
Figure 1. Schematic illustration of the water-induced mantle overturns (superplumes). The waterdrop is used to describe the hydrous silicate melts although hydrogen mainly exists as hydroxyls in silicate melts. (a) The solidification of a whole mantle magma ocean (MO) at the mid mantle forms an outer MO and a basal MO. (b) The basal MO eventually becomes gravity unstable and generates mantle overturns because of the enrichment of water
How to cite: Wu, Z., Deng, X., and Song, J.: Water-Induced Mantle Overturns Leading to the Oxidation of Archean Upper Mantle, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3482, https://doi.org/10.5194/egusphere-egu26-3482, 2026.
The mechanisms that allowed the oxygenation of the Earth’s atmosphere to occur at the end of the Archean, an event known as the Great Oxidation Event (GOE), remain unclear. For the GOE to occur, two conditions must be met: first, oxygenic photosynthesis must evolve; second, the net production of dioxygen by photosynthesizers (i.e. the imbalance between carbon fixation and respiration corresponding to burial of organic matter), must exceed oxygen sinks such as reduced volcanic gases. Evidence points toward oxygenic photosynthesis evolving long before the traces of the GOE appear in the geological record. Thus, the oxygenation of Earth’s atmosphere may have been triggered by a combination of an increase in the burial flux of organic carbon (net O2 source) or a decreased O2 sink (e.g. via a decrease in the volcanic emissions of reduced gases). However, the drivers and dynamics of each of these processes are complex, and leveraging the geological record (e.g. stable carbon isotope record) to draw mechanistic conclusions about geochemical cycling at the time of the GOE remains challenging.
Recent modeling studies have highlighted the role of ecological competition for nutrient between anoxygenic and oxygenic photosyntheses as a potential driver for a delayed oxygenation of the atmosphere following the emergence of oxygenic photosynthesis (Ozaki et al 2019; Olejarz et al 2021). Here, I use adaptive dynamics theory (Metz et al., 1992) to rigorously and efficiently model the outcome of ecological competition in the upper layer of the Archean ocean as a function of boundary conditions set by the compositions of the deep ocean and of the atmosphere. Using a separation of timescales assumption, I then use the steady-state outcome of this ecological model as a boundary condition in a simplified geochemical model of phosphorous and iron cycling, and atmospheric oxygen.
The model shows how small perturbations in the delivery rate of iron or phosphorous to the deep ocean can trigger reversible or irreversible global oxygenation events. I examine a scenario where the upper ocean is initially phosphorous-limited and photoferrotrophs (anoxygenic photosynthesis where the electron donor is soluble iron) competitively exclude oxygenic photosynthesis. Then I assume that delivery rates of iron and phosphorus evolve or are perturbed such that the upper ocean transitions to conditions where photoferrotrophs would be iron-limited, giving oxygenic photosynthesis a fitness advantage (owing to its use of abundant water as an electron donor). In this scenario, an initially rare variant performing oxygenic photosynthesis may take come to dominate phototrophic primary production while the total remains constant, if local oxidation of soluble iron by dioxygen is fast enough (i.e. if the pH is high enough). The model demonstrates that coexistence between anoxygenic and oxygenic photosyntheses may not prevent oxygenation of the atmosphere, if the total productivity is high enough, and determines conditions where small perturbation in the geochemical system can trigger reversible or irreversible atmospheric oxygenations.
How to cite: Affholder, A.: Eco-Evolutionary dynamics of oxygenic and anoxygenic photosyntheses in the late Archean., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21473, https://doi.org/10.5194/egusphere-egu26-21473, 2026.
The Cambrian Sauk transgression marks one of the most extensive episodes of marine inundation in Earth’s geological record. Despite its importance, accurately constraining its timing remains problematic in many regions because of limited biostratigraphic indicators and the scarcity of robust chronometric tools. In this study, we introduce an integrated petrographic, geochemical, and geochronological framework to constrain the age of the Sauk transgression on the southeastern Arabian Plate. This is achieved through analysis of trace-fossil burrows developed along the Cambrian maximum flooding surface (Cm20 MFS) within the middle Miqrat Formation of central Oman. Microscopic examination shows that calcite cement infilling the burrows is characterized by a drusy crystal fabric and occupies loosely arranged framework grains, indicating early cementation under near-surface conditions soon after sediment deposition. This interpretation is corroborated by clumped isotope (Δ47) data, which indicate calcite precipitation temperatures between 33.8°C and 36.4°C, with a mean value of approximately 34.8°C. These temperatures align well with independently estimated middle Cambrian sea-surface conditions. Measured Sr87/86 ratios of the burrow-filling calcite range from 0.7088456 to 0.7090134 (mean 0.7089270), yielding an inferred age of approximately 508.20–509.86 Ma, with an average age of 509.26 Ma. This age assignment falls within the middle Cambrian and is marginally younger than the maximum depositional age of ~511 Ma obtained from detrital zircon analyses. The ages reported here represent the first direct numerical constraints on the Sauk transgression from the southeastern Arabian Plate and demonstrate consistency with equivalent ages documented from the northern and northwestern parts of the plate. Overall, the results highlight the effectiveness of Sr87/86 isotope analysis of early diagenetic calcite as a chronostratigraphic tool. Because such calcite precipitates from marine-derived fluids shortly after deposition, it faithfully records the seawater isotopic composition at the time of cementation, allowing reliable dating of sedimentary successions.
How to cite: El-Ghali, M., Moustafa, M., Ahmed Abbasi, I., Shelukhina, O., Salad Hersi, O., and Ali, A.: Timing the Cambrian Sauk Transgression in the Southeastern Arabian Plate: Evidence from Radiogenic Strontium of Early Calcite Cement, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16562, https://doi.org/10.5194/egusphere-egu26-16562, 2026.
The end-Guadalupian (Middle Permian) mass extinction represents a pivotal yet enigmatic event in Earth's history. Its drivers, often attributed to the emplacement of the Emeishan Large Igneous Province, are intensely debated, with proposed mechanisms ranging from volcanic outgassing to sea-level fluctuations and widespread marine anoxia. However, a critical lack of high-resolution, multi-proxy records from key paleo-tropical regions has hindered a unified model. This study presents a fully integrated dataset combining field sedimentology, microfacies analysis, and a comprehensive suite of major, trace, and rare earth element geochemistry from the Wordian carbonates of the Salt Range, Pakistan, a classic Neotethyan margin. Our data reveal a pronounced transgressive systems tract, marked by a shift from peritidal cycles to deeper-water carbonates. Crucially, geochemical proxies (e.g., Sr/Ca, Mn/Sr) confirm this sea-level rise was accompanied by a shift in oceanic chemical budgets. More significantly, we identify a pre-extinction perturbation in redox-sensitive trace elements (e.g., V/Cr, U/Th, Mo enrichment) and nutrient tracers (P, Ba), indicating a trend towards deoxygenation and increased nutrient loading in the Tethyan ocean during the Wordian. We interpret this coupled sedimentological-geochemical signal as a direct record of eustatic rise-driven oceanographic stagnation. The transgression likely flooded vast continental shelves, enhancing organic matter burial and fostering the development of stratified, anoxic water masses on a near-global scale. The synchronicity of this event with the onset of Emeishan volcanism suggests a powerful feedback mechanism: sea-level rise created the environmental context in which the effects of volcanism (e.g., nutrient runoff, greenhouse warming) were dramatically amplified. By providing a high-resolution record from the Tethyan gateway, this research places the Wordian of the Salt Range as a vital recorder of pre-extinction environmental deterioration. Our findings demonstrate that the stage for the end-Guadalupian catastrophe was set several million years earlier by oceanographic upheaval, forcing a re-evaluation of the extinction's triggers and providing a critical ancient analogue for modern sea-level rise and ocean deoxygenation.
How to cite: Wadood, B.: Pre-Extinction Stress in the Salt Range: Wordian Eustasy and its Role in the End-Guadalupian Crisis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-546, https://doi.org/10.5194/egusphere-egu26-546, 2026.
Posters on site: Thu, 7 May, 16:15–18:00 | Hall X5
Around the Late Priabonian-Early Rupelian, the Paris Basin is characterized by an incomplete succession of sediments deposited at the marine-continent interface. In the overall marine record, this interval is marked by the Eocene-Oligocene Transition (EOT), characterized by a climate deterioration and a significant sea level drop, associated with the permanent establishment of the Antarctic ice cap. Nevertheless, the EOT is poorly documented and understood in terrestrial areas.
Located between the active tectonic regions of the Pyrenean and Alpine orogens and the West-European Cenozoic Rift Systems, the lagoon to lacustrine deposits of the Paris Basin therefore enable to acutely record both global and local processes (glacio-eustasy, climate, tectonic). A detailed stratigraphic framework is consequently necessary to estimate the contribution of each of these controls. This study is based on: 1) a large-scale correlation of boreholes in order to study the 3D organization of deposits and their lateral and vertical variations, and 2) an elementary and isotopic geochemical, mineralogical, and paleontological study to clarify the depositional environments and the causes of the observed variations (sea level, tectonic and hydrological changes). The analyzed sites are located around tectonic structures (the Bray, Beynes-Meudon, and Remarde anticlines and the Saint-Denis syncline) and in various areas, ranging from the edges to the center of the Paris Basin.
We established a correlation between lagoon-marine deposits of the center of the basin and lacustrine deposits of its southern and eastern edges. Detailed sedimentological studies of the sites reveal a two-steps evolution. The first step is marked by marls deposited during the latest Priabonian. Their mineralogical and chemical composition indicates a deposition evolving from a clastic to a chemical-dominated system in a wetter to drier climate. The second step, during Early Rupelian times, shows the return to detrital deposition in a wetter climate. More specifically, the sections show a mineralogical, chemical and environmental separations. The Priabonian cycle is influenced by sea level variations (marine incursion, then confinement of the basin) and a climate changing from wetter to drier. The Rupelian cycle shows a global transgression in a wetter climate, briefly interrupted by a confinement of the basin, but above all the reactivation of tectonic structures linked to the Pyrenean compression, which caused palustrine deposits on the anticlines and marine deposits in the synclines.
The Paris Basin shows to a lesser extent the same record of the EOT as several marine sites. The major regression is only illustrated by the confinement and partial emersion of the basin in the latest Priabonian; the cooling seems to be recorded by the progressive increase in oxygen isotope values, and the aridification by mineralogical proxies and the known floral evolution. The basin also reflects the west-European regional geodynamics with the recurrence of tectonic structures in the Early Rupelian associated with the African-Eurasian convergence, illustrated for instance as well by the inversion of the Cotentin and Hampshire basins, further north of the Paris Basin.
How to cite: Beernaert, M., Le Callonnec, L., Minoletti, F., Bauer, H., and Quesnel, F.: A not so tranquil basin: recording of the west-European geodynamics amidst marine incursions and retreats in the Paris Basin., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7870, https://doi.org/10.5194/egusphere-egu26-7870, 2026.
Isotope distribution in precipitation along with climate monitoring data such as amount of precipitation, temperature and relative humidity were collected from a region characterized by a high continentality index, region situated in the external sector of the Southern Carpathians. Stable isotope composition of hydrogen and oxygen in precipitation were collected monthly from 2012 to 2025, with climate monitoring measured automatically each 30 minutes. The isotope and temperature signals were split in two groups including October to April and May to September, variations over an interval of 14 years being statistical presented. For the intervals considered, the LMWL show the effect of secondary evaporation of falling raindrops with lower slope for the warm season. The data support significant relationships between d18O and d D values and average air temperatures with r2 = 0.7, n = 150. Deuterium excess values over the year are compatible with seasonal variations for the origin of moisture, with high values during wintertime, possible resulting from the input of seasonal related Mediterranean moisture during November to February. The strong seasonal distribution of precipitation amount combined with elevated temperature peaks during July have a strong impact on the clastic multi-layered aquifers situated in the Lower Quaternary deposits, driving during the last years to complete evaporation of the highest aquifer.
How to cite: Bojar, A.-V., Chmiel, S., Bojar, H.-P., Pelc, A., and Vaida, F.: Stable isotope composition of precipitation and temperature seasonal distribution from the South Carpathians: insights for climate variations in the interval 2012 to 2025, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5244, https://doi.org/10.5194/egusphere-egu26-5244, 2026.
Constraining the weathering history of the British Isles in the Cenozoic is limited by the sparse distribution of terrestrial rock units of appropriate age. This has prompted many workers to rely on examination of the regional marine record to make inferences about terrestrial weathering and climate in this era. We have begun a project to date supergene mineral deposits across the region to provide direct temporal information about the timing and extent of weathering processes. We show first results of dating with the 40Ar/39Ar technique on cryptomelane (KMn8O16) from Scotland, suggesting a late Miocene age. A full sample suite from across Great Britain and Ireland is currently being analysed.
In addition to dating of cryptomelane and other Hollandite group minerals, the NEIF argon isotope laboratory at SUERC has developed the capability of dating difficult hydrous sulphate minerals alunite and jarosite that occur across the region and will be the subject of future weathering studies. Sample preparation remains a challenging aspect of dating supergene minerals. This is because of the fine-grained nature of the material coupled with the intergrowth of potentially complicating phases such as clay, feldspar or quartz. HF leaching of materials to remove silicate impurities have shown promise, suggesting a reduction in the budget of trapped atmospheric argon, and reproducible ages have been obtained for samples as young as Pleistocene. Attempts at micro-sampling, for example, growth layers in cryptomelane using microdrill techniques, have met with limited success. Future work will look at laser micro-sampling coupled with high precision and high sensitivity 40Ar/39Ar analysis on the next-generation THERMO ARGUS VI mass spectrometer.
How to cite: Barfod, D. and Pickersgill, A.: Progress on supergene mineral dating utilising the 40Ar/39Ar technique and terrestrial weathering in Great Britain & Ireland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12719, https://doi.org/10.5194/egusphere-egu26-12719, 2026.
Loess–paleosol sequences (LPS) constitute continuous terrestrial archives of Quaternary climate change, recording both local environmental conditions and large-scale atmospheric dynamics. While LPS have been extensively studied worldwide, those of the Lower Danube–Black Sea (LDBS) region of Romania and Bulgaria remain comparatively underexplored. Situated at the nexus of Mediterranean, central European, and continental western Asian air masses, the LDBS region offers a unique opportunity to investigate large-scale climate shifts and their associated environmental responses.
The LOEs-CLIMBE project, funded by the Swiss National Science Foundation (SNSF) through the Multilateral Academic Projects (MAPS) scheme with support from the Romanian (UEFSCDI) and Bulgarian funding agencies, addresses this gap through a high-resolution, multi-proxy investigation of two key LPS sites: Urluia (Romania) and Kolobar (Bulgaria). Spanning the last ~800 ka, with particular focus on the Mid-Brunhes Event onwards (MBE), the project integrates elemental composition, stable isotope records, and molecular biomarkers within a newly established chronological framework. These proxies support reconstructions of vegetation dynamics, climate variability, and pedogenic processes across multiple glacial–interglacial cycles.
Here, we present preliminary results from both LPS. The site at Urluia, located in southeastern Romania, is a former quarry exposing a >20 m thick, continuous LPS. The sequence comprises multiple complex palaeosols (S1–S5), interpreted as interglacial soils, interbedded with massive loess units deposited during glacial periods.
Near the village of Kolobar, situated in northeastern Bulgaria and distal from both the Danube and the Black Sea, is an active quarry. Here, a ~25 m thick LPS is exposed with ~1.1 m of modern soil on top. Approximately seven major palaeosols (S1–S7) extend back to ~800 ka. Field observations identify a marked stratigraphic shift at S4, from thick loess units with thin palaeosols above to massive palaeosols with thinner loess below. This transition coincides with an increase in bulk density from ~1.41 to 1.61 g cm⁻³ and is interpreted as the onset of the MBE, a transition not represented at Urluia. Carbonate precipitation is observed in all palaeosols above the S7, while loess dolls occur in the L1 and L2. Bioturbation, including crotovinas from mammals and earthworm burrows as well as root traces, is widespread throughout the whole sequence. However, this is present at different depths in different assemblages. Altogether, these field observations argue for an apparent grass steppe vegetation with fluctuating populations of burrowing organisms throughout the last 800 ka, while hydrological and sedimentary conditions have changed considerably between periods with predominant loess sedimentation and stronger soil formation. We will present these first findings and support them with elemental and stable isotope composition alongside organic matter composition gained from infrared spectroscopy measurements.
How to cite: Trott, A., Veres, D., Jordanova, D., and Wiesenberg, G.: A reconstruction of Lower Danube-Black Sea climate history. First insights from novel loess-paleosol sequences., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2744, https://doi.org/10.5194/egusphere-egu26-2744, 2026.
There is a growing need within the paleoclimate community for robust soil paleoproxies capable of reconstructing past terrestrial environments with high precision. Existing proxies for past mean annual air temperature (MAT), such as branched GDGTs (1) and chironomids (2), suffer from large uncertainties (i.e., ≥ 4°C error on these land temperature reconstructions), which limit their applicability.
Bacteriohopanepolyols (BHPs) are pentacyclic triterpenoid membrane lipids produced by bacteria that are ubiquitous in terrestrial and aquatic environments (3). Functionalized BHPs have a large structural diversity both in the rings and head groups. They have been detected in sedimentary archives extending back 1.2 Myr (4), underscoring their considerable potential as tools for reconstructing past climatic conditions.
BHPs with nucleoside (adenosyl and inosyl) head groups (Nu-BHPs) have been widely used as indicators of terrestrial organic matter input into marine systems (Rsoil) (5). Recently, a large range of previously unknown Nu-BHPs were identified thanks to a newly developed method using Ultra High Performance Liquid Chromatography – high resolution Orbitrap Mass Spectrometry (6). The relative abundances of several Nu-BHPs found in Alaskan soils were shown to correlate with pH and temperature and thus are potential paleotemperature proxies (7). To validate these correlations on a global scale, we present Nu-BHP abundances analyzed across 89 globally distributed surface soil samples. These include soils previously used to calibrate branched GDGTs (1), as well as soils from Northern Norway and Finland and Brazil, to complete coverage from the Arctic to the tropics. Complementary analyses included six soil environmental variables (pH, latitude, total organic carbon (TOC), C/N, δ¹³C, δ¹⁵N) and four climate parameters (mean annual and warmest quarter air temperature, obtained from CHELSA climatological data (8), annual and wettest quarter precipitation, retrieved from the Copernicus Climate Change Service (9)).
Forty-eight Nu-BHPs were identified in soils with a pH range of 3.3-8.1 and total organic carbon (TOC) range of 0.2 and 48.4%. The most dominant compound in the dataset is adenosylhopane with 0 methylations. Of the forty-eight Nu-BHPs, thirty compounds were present in trace amounts (less than 1% of total relative abundances). The remaining eighteen Nu-BHPs were further used to investigate climatic controls on Nu-BHP abundances.
This showed that only a few Nu-BHPs showed a good correlation with pH (R2 ~0.65), while temperature did not appear to influence Nu-BHP distributions. Non-metric multidimensional scaling analysis was conducted on relative abundance of these eighteen Nu-BHPs, along with the soil environmental variables and climate parameters (Fig. 1). This revealed that none of the measured parameters measured fully explains the variability in Nu-BHP distributions. We hypothesize that the main control factors instead are related to nutrient availability and/or bacterial community diversity. Future work includes investigating these variables using samples with strong nutrient and pH gradients; and known bacterial community abundances.
References
- Weijers et al., 2007.
- Brooks et al., 2001.
- Cooke et al., 2009.
- Zhu et al., 2011.
- Talbot et al., 2014.
- Hopmans et al., 2021.
- O’Connor, 2025.
- Krager et al., 2017.
- Dorigo et al., Copernicus Climate Change Service (C3S) Climate Data Store (CDS).
How to cite: Novik, O., Schouten, S., Chen, Y., Berke, M., Gleixner, G., Mackay, H., van der Meer, M., Hopmans, E., and Rush, D.: Investigating the controlling factors of nucleoside bacteriohopanepolyol abundances in soils, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11598, https://doi.org/10.5194/egusphere-egu26-11598, 2026.
Carbonates are widely used as paleoenvironmental archives because they record past environmental conditions through their chemical and isotopic signatures. However, primary crystallization processes and subsequent diagenetic alterations can modify these signatures, potentially affecting their reliability as paleoenvironmental proxies.
This study investigates isotopic changes during the precipitation of amorphous calcium carbonate (ACC) into crystalline CaCO₃ under variable pH and temperature (T) conditions, in order to better constrain the role of ACC in calcification processes and its influence on the final isotopic composition of the crystalline carbonate polymorphs. ACC was synthesized by automated titration of an equimolar CaCl₂ solution into NaHCO₃ (+NaOH) solutions. A first set of experiments was conducted over a pH range of 8–11 and at temperatures of 10, 20, and 30 °C. A second set was performed at pH 8 and T of 10, 20, and 30 °C in the presence of polyaspartic acid (pASP) to simulate biomineralization effects on ACC metastability and its transformation to crystalline CaCO3 polymorphs. Precipitates were characterized using scanning electron microscopy, Fourier-transform infrared spectroscopy, X-ray diffraction and in-situ Raman; oxygen and carbon isotope ratios were measured by isotope-ratio mass spectrometry.
The onset of vaterite precipitation from ACC occurs rapidly at all investigated pH and T conditions, with transformation times less than 1 min. In the presence of pASP, ACC is stabilized and crystalline phase precipitation is delayed to 5 min. The transformation of ACC into calcite is strongly T dependent, with shorter transformation time periods at higher T for all pH conditions. Spherulitic ACC size is strongly controlled by pH and T, decreasing from ~0.25 µm at pH 8 and 10 °C to ~0.10 µm at pH 11 and 30 °C.
For all investigated temperatures and pH conditions, oxygen isotope values of the initial ACC (e.g. at 10 °C and pH 8: δ¹8OVPDB = –4.94 ‰) decrease during CaCO₃ precipitation, reaching lower values in the resulting calcite (e.g. δ¹8OVPDB = –6.10 ‰), with values systematically decreasing with increasing T and pH. In contrast, carbon isotope values are comparatively more constant, showing only limited differences between ACC and crystalline phases (e.g. at 10 °C and pH 8, δ¹³CVPDB= –3.99 ‰ for ACC and –4.95 ‰ for calcite). This relative stability reflects the weaker temperature dependence of carbon isotope fractionation and the dominant control exerted by pH on dissolved inorganic carbon (DIC) speciation, sensitive to pH variations.
Oxygen and carbon isotope equilibrium between carbonate phases and the initial reactive water is variably approached depending on pH, T, and mineral phase. At high pH (≥10) and elevated T, isotopic equilibrium is not reached for ACC and the resulting crystalline phases due to rapid precipitation and transformation kinetics that limit isotope exchange with the aqueous phase. Lower pH and moderate T favor closer approach to equilibrium, whereas low water/solid ratios and the presence of pASP promote isotopic disequilibrium by limiting recrystallization-driven exchange.
These results highlight the potential for kinetically controlled isotopic signatures in carbonates formed via amorphous precursors, with implications for paleoenvironmental interpretations.
How to cite: Pace, A., Pettauer, M., Dietzel, M., Auer, G., and Asta, M. P.: Effect of pH and temperature on oxygen and carbon isotope fractionation during ACC transformation to crystalline carbonates., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-12194, https://doi.org/10.5194/egusphere-egu26-12194, 2026.
Understanding the dynamics between past global climate events and their impact on marine ecosystems and paleoclimate is essential for the estimation of potential future changes. Accordingly, sedimentary archives accumulating on the seafloor provide crucial information on climate-driven environmental variability during the late Quaternary. Sediment cores were taken from the Gulf of Edremit, which is located in the northern Aegean Sea. We aimed to provide a preliminary, multi-proxy parameters, including sedimentological and geochemical records during the Holocene. During the marine survey with the R/V TÜBİTAK MARMARA Research Vessel, three sediment cores (E-01, E-02, and E-03A) obtained from different water depths across the gulf were investigated. Lithological observations from all cores indicate a sedimentation pattern dominated by fine-grained clay- and silt-sized deposits. However, locally occurring black laminae and FeS bands reflect depositional conditions sensitive to variations in bottom-water oxygenation. Fluctuations in the density and magnetic susceptibility measured by MSCL further support variability in sediment input and depositional processes at the sea floor. TOC data from core E-02 (at a water depth of 86 m) show low values (0.8–1.0 wt%) in the lower part, indicating low productivity and/or poor preservation of organic matter. TOC then rises to ~1.0–1.5 wt% further up the core, suggesting improved productivity or preservation. The highest values (1.5–2.0 wt%) in the uppermost 0–10 cm may reflect the presence of sapropelic material. XRF data from core E-03A reveal a Sr/Ca peak at 40–50 cm, which indicates increased salinity during drier periods. At 140–150 cm, the Sr/Ca ratio decreases while the Ca/Ti ratio increases, suggesting enhanced carbonate deposition relative to detrital input. In core E-01, a Mn/Fe peak at 10–15 cm reflects changes in redox and oxygen conditions. There is strong variability in Ca/Ti and Sr/Ca at 45–50 cm: higher Sr/Ca above this depth indicates greater carbonate production, while lower Ca/Ti implies reduced clastic input. Below 65 cm, falling Sr/Ca and rising Ca/Ti suggest diminished carbonate production and a return to lithogenic dominance. As a conclusion, sedimentation in the Gulf of Edremit appears to be highly sensitive to climate and carbon cycle changes.
This study was granted and supported by the TÜBİTAK (The Scientific and Technological Research Council of Türkiye) with Project number 123Y108.
Keywords: Gulf of Edremit, Holocene, multi-proxy analysis, TOC, XRF.
How to cite: Vurmuş, Z. D., Erol, İ., Biltekin, D., Eriş, K. K., Atabay, H., Özsu, E., Çiftbudak, Ö. F., Tolun, L. G., Akyol, O., Kanbur, S., Ustaoğlu, B., Koç, D. E., Uçarkuş, G., and Schwamborn, G. J.: Paleoenvironmental and Paleoclimate Changes in the Gulf of Edremit (Northern Aegean Sea) during the Holocene based on Sedimentological and Geochemical Multi-Proxy Records, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5038, https://doi.org/10.5194/egusphere-egu26-5038, 2026.
The geochemical signatures of clastic sedimentary sequences are determined by the parent rocks, weathering intensity, and the complex processes of transport and deposition. These variables define the mineralogical and chemical attributes of the basin fill, offering significant insights into the prevailing geodynamic settings and paleoclimatic conditions. The Upper Cretaceous deposits in the Lesser Caucasus are widely distributed and represent a vital geological archive for studying the region’s history. To reconstruct the paleogeographic and depositional conditions of the northeastern slope of the Lesser Caucasus, Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was employed for high-precision elemental analysis, while X-ray diffraction (XRD) was utilized to determine the mineralogical composition of the sequences. The terrigenous sequences of the region comprise the diverse lithological assemblages, primarily categorized as shales, iron-rich shales (Fe-shales), and greywackes. These rocks exhibit low compositional and mineralogical maturity, indicating accumulation in high-energy environments with a significant influx of fresh volcaniclastic material. Geochemical proxies for chemical weathering reveal a transition from intensive to moderate alteration. This low maturity is further substantiated by the preservation of primary silicates, which is characteristic of rapid sediment burial. Elemental analysis indicates that the detrital material was predominantly derived from first-cycle mafic and ultramafic magmatic sources, reflecting the significant erosion of ophiolitic and associated sequences. Geochemical indicators confirm a first-cycle sedimentary regime with minimal recycling and limited hydraulic sorting. Tectonic discrimination functions identify an oceanic island arc setting, where volcaniclastic and terrigenous debris accumulated in basins governed by active subduction and convergence processes. These findings are consistent with semi-humid and semi-arid paleoclimatic conditions that prevailed during the Late Cretaceous. Collectively, these indicators elucidate the geodynamic setting of the region and emphasize the interplay between arc volcanism and the regional tectonic framework in shaping the Mesozoic sedimentary record.
How to cite: Guliyev, E. and Aliyeva, E.: Geodynamic and paleogeographic settings of the Upper Cretaceous terrigenous successions, northeastern slope of the Lesser Caucasus: Geochemical and mineralogical constraints , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16974, https://doi.org/10.5194/egusphere-egu26-16974, 2026.
Benthic foraminifera are widely considered as marker proxy for past changes in surface and deep water productivity, organic matter flux, bottom water oxygenation, and deep water circulation. This study presents benthic foraminiferal relative abundance records from ODP Site 1087 (31°27.9137’S, 15°18.6541’E, water depth 1374m), located in the southeast Atlantic Ocean beneath the productive Benguela Upwelling System (BUS). The main objective is to assess long-term productivity and oceanographic variability in the region from the Late Miocene to Pleistocene. Our results indicate a major shift in regional oceanographic conditions at ~10 Ma. A distinct increase in the relative abundance of Bulimina striata, a dysoxic, infaunal species associated with elevated flux of organic matter, suggests enhanced surface productivity and marks the emergence of the BUS. This timing closely matches with the onset of the BUS as inferred from multiple independent proxy records. The late Miocene–early Pliocene biogenic bloom (~ 8–5 Ma), characterised by sustained and widespread high productivity across the Indian, Pacific and Atlantic Oceans, is often indicated by higher relative abundance of Uvigerina proboscidea, a suboxic, infaunal species associated with high delivery rates of organic matter to the seafloor. A similarly higher relative abundance of U. proboscidea is clearly recorded in our benthic assemblages, pointing to intensified export productivity during this interval. Additionally, an increased relative abundances of the opportunistic species Epistominella exigua during ~8 to 6 Ma and ~3.7 to 3.0 Ma indicate seasonal input of phytodetritus from the surface waters due to extensive phytoplankton blooms associated with the strengthening of the upwelling. The early Pliocene interval between ~5 and 3.7 Ma is marked by the co-occurrence of Globocassidulina subglobosa, U. proboscidea, and B. striata. This assemblage reflects alternating oxic and suboxic–dysoxic benthic environments, which might be linked to oligotrophic and eutrophic surface conditions, respectively. Decreased surface productivity related to reduced upwelling and enhanced oxygenation of bottom waters favoured oxic species, but the continued presence of dysoxic-suboxic species indicate a continuous nutrient supply, perhaps related to Agulhas Leakage. A rapid increase in U. proboscidea and Uvigerina peregrina during the Plio–Pleistocene cooling reflects re-intensification of BUS-related productivity. Overall, benthic foraminiferal assemblages at ODP Site 1087 provide a robust record of productivity and associated oceanographic changes in the Southeast Atlantic Ocean between the Late Miocene and Pleistocene.
How to cite: Mohanty, R. N., Gupta, A. K., and Majumder, J.: Late Miocene to Pleistocene deep water Productivity in the Southeast Atlantic: Evidence from Benthic Foraminiferal Assemblages, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18474, https://doi.org/10.5194/egusphere-egu26-18474, 2026.
Phosphorous availability is required for biological productivity, nutrient cycling and oxygenation. Over recent years, reduced phosphorous (phosphite) has moved into focus as a potentially new proxy that can provide information about environmental conditions and biogeochemical cycles in deep time. Phosphite can be generated by a range of biological and abiotic processes, but its distribution and implications are so far poorly understood.
To address this knowledge gap, we investigated phosphate and phosphite concentrations in stromatolites spanning from the Archean to the modern. Stromatolites are among the oldest life forms found on Earth, preserved in the fossil record, dating back to 3500 million years ago. They are formed in shallow water, mostly by the metabolic activity of a diverse microbial ecosystem. They are composed of carbonate minerals, which can trap both phosphate and phosphite in their crystal lattice.
We measured phosphorus speciation with Ion Chromatography and Inductively coupled plasma mass spectrometry. The data reveal that carbonate-associated phosphate and phosphite date back to the early Precambrian, presenting the first record of phosphite in carbonate rocks of low metamorphic grade. The phosphite may be of biogenic origin, but also non-biological sources such as meteorite impacts, hydrothermal activity or weathering of high-grade metamorphic rocks are plausible. These abiotic sources could potentially be more important on Mars, whose mantle has a lower oxygen fugacity, and where impact debris is well-preserved near the surface. Our study reveals that carbonate records can be used to reconstruct the history of phosphorus redox speciation on Earth and perhaps early Mars.
How to cite: Tsinidis, M. and Stueeken, E.: Tracking phosphorus redox speciation in microbial carbonates through Earth’s history and beyond, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5153, https://doi.org/10.5194/egusphere-egu26-5153, 2026.
The Oxfordian interval is characterized by a long-term (~6 Myr) increase in carbon isotope values, punctuated by several short-lived (<1 Myr) positive carbon isotope excursions (CIEs) occurring in the lower Oxfordian, and in the middle Oxfordian. These excursions have only been recognized in a limited number of sections and their spatial extent, stratigraphic reproducibility, and paleoenvironmental significance remain poorly constrained, and their potential relationship to oceanic anoxic events (OAEs) remains uncertain.
Here, we present a high-resolution, multi-proxy chemostratigraphic dataset from shallow-marine Oxfordian successions of northwestern Europe, integrating inorganic and organic carbon isotopes (δ13Cinorg and δ13Corg), palynofacies analysis, and Rock-Eval pyrolysis. The dataset combines subsurface data from the Konrad #101 borehole (southeastern Lower Saxony Basin, northern Germany) with new outcrop data from the northern Paris Basin (Normandy, France). Both successions are constrained by robust biostratigraphic frameworks, enabling detailed intra- and interbasinal correlations.
Our results reveal pronounced and reproducible carbon isotope trends, including a ~3.0‰ positive CIE recorded in both δ13Cinorg and δ13Corg within the lower to middle Oxfordian interval. Comparison with available records from Europe, western Asia, and the Gulf of Mexico suggests that these excursions may reflect regionally synchronous perturbations of the exogenic carbon cycle, although the degree of global synchronicity remains equivocal. The integration of geochemical and palynofacies data provides new insights into the paleoenvironmental context of these events by demonstrating that the observed carbon isotope fluctuations are not driven by changes in organic matter preservation or mixing of organic matter sources (e.g., marine versus terrestrial inputs). This multi-proxy approach allows a critical assessment of whether Oxfordian CIEs constitute robust chemostratigraphic markers and whether they can be plausibly linked to episodes of widespread marine oxygen depletion.
How to cite: Krencker, F.-N., Hansen, J., Rudolph, M., Andrieu, S., Blumenberg, M., Mann, T., and Heimhofer, U.: Carbon isotope excursions during the Oxfordian: multi-proxy constraints on carbon cycle dynamics, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10177, https://doi.org/10.5194/egusphere-egu26-10177, 2026.
The Zr/Hf ratio of modern seawater (150-3001) is significantly fractionated relative to the chondritic value (32.7-34.22) and magmatic systems. This deviation is driven by the higher particle reactivity of Hf relative to Zr in low-temperature, aqueous systems, resulting in preferential sorption of Hf onto (particle) surfaces. The Zr/Hf ratio of aqueous systems increases from the continents towards the open oceans, varies with water depth and water mass age, making it a powerful tool for tracing water masses. While reasonably well constrained in modern aquatic systems, the Zr/Hf composition of ancient seawater remains poorly understood, but may provide unique insights into the circulation of water masses.
To investigate the Zr/Hf evolution of the seawater throughout Earth’s history, banded iron formations (BIFs) represent a viable archive for the Precambrian seawater chemistry because they are chemical sedimentary rocks and reflect the chemistry of the seawater from which they precipitated. Here, we present new high-precision Zr–Hf data from Precambrian BIFs, complemented by available literature data, to evaluate the Zr/Hf ratio as a paleoceanographic tracer of ancient water masses.
Archean BIFs predominantly display near-chondritic Zr/Hf ratios, with ratios not exceeding 75. The first super-chondritic Zr/Hf ratios occur in individual BIF-layers at ~2.51 Ga, and the formation showing overall super-chondritic Zr/Hf ratios is the ca. 2.4 Ga Hotazel Formation, indicating widespread Zr/Hf fractionation in marine environments. Formation-scale averages largely remain near-chondritic until ~2.0 Ga, while younger BIFs show predominantly super-chondritic ratios. This secular trend from chondritic towards super-chondritic Zr/Hf ratios in the early to mid Proterozoic likely reflects changing seawater conditions that enabled widespread Zr–Hf fractionation. The increasing availability of Fe–Mn(oxide) particles, based on increasing atmospheric oxygenation but also the progressive development of modern-style estuarine and shelf environments, may have led to global Zr-Hf fractionation in marine systems by that time. Within individual formations, Zr/Hf ratios correlate with Mn/Fe ratios, indicating a link between Zr-Hf fractionation and the redox-evolution of the Earth. Moreover, regional differences among coeval BIFs suggest variable depositional settings and distinct water-mass circulation patterns already in the Neo-archean. Thus, our results highlight the potential of Zr/Hf ratios in BIFs and other chemical sedimentary rocks to trace the redox-evolution of the Earth with the appearance and spatial heterogeneity of oxygenated water masses in Early Earth oceans.
1Godfrey et al., 1996, GCA 60
2Münker et al., 2025, GPL 36
How to cite: Krayer, J., Ravindran, A., Pakulla, J. J., Münker, C., Weyer, S., and Viehmann, S.: Zr/Hf ratios in Banded Iron Formations as tracers of Early Ocean evolution , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18713, https://doi.org/10.5194/egusphere-egu26-18713, 2026.
Banded iron formations (BIFs) are authigenic marine sedimentary rocks that formed in Precambrian oceans. They may record the chemical composition of the ambient seawater and are thus important archives for reconstructing ancient marine environments. The ca. 3.25 Ga Algoma-type BIF of the Fig Tree Group in the Barberton Greenstone Belt, South Africa, provides insights into the Palaeoarchaean marine environments and seawater chemistry during the early development of the Kaapvaal Craton [1,2]. However, it remains incompletely understood, which mineral phases within this BIF most reliably preserve primary seawater-derived signatures and therefore represent the most suitable archives for palaeo-environmental reconstructions.
We present trace and major element concentrations of 28 individual layers of Fig Tree Group BIF. These layers are dominated by either magnetite, chert, or siderite. In addition, mudstones intercalated with BIF were also analysed. All samples originate from the BARB 4 drill core and were digested using HF–HNO₃–HCl digestion combined with ICP-MS and OES analyses to investigate the geochemical composition of the different mineral phases and their reliability as archive for ancient seawater chemistry.
Immobile element (Zr, Th) concentrations are in the ppb to ppm level range and vary over four orders of magnitude between the BIF samples. Samples with the highest immobile element concentrations show non-seawater-like shale-normalised (subscript SN) rare earth element and yttrium (REY) patterns and a positive correlation of REY and immobile element concentrations (e.g. Zr), in indicating detrital contamination. However, cherts and five of the magnetite samples with the lowest immobile element concentrations show typical Archaean seawater-like signatures with positive LaSN GdSN, and YSN anomalies as well as a depletion of light REY relative to heavy REYSN, indicating a seawater-derived origin. Positive EuSN anomalies indicate contributions of high-temperature hydrothermal fluids. The lack of negative CeSN anomalies indicates anoxic depositional conditions with respect to the Ce3+-Ce4+ redox couple. The chert layers, however, show Th/U fractionation compared to the value of the continental crust, suggesting redox-dependent uranium mobilization, indicative of slightly oxic conditions.
We identified chert and magnetite, if devoid of detrital contamination, to be the most suitable phases in Fig Tree Group BIF for obtaining information to reconstruct their depositional environment. The remaining layers, on the contrary, do not reflect pure seawater precipitates and have to be excluded for interpretations regarding ancient seawater chemistry.
[1] Hofmann, 2005, Precambrian Res. 143, 23-49
[2] Satkoski et al., 2015, EPSL 430, 43-53
How to cite: Winkler, V., Krayer, J., Hofmann, A., Weyer, S., and Viehmann, S.: An evaluation of phases in banded iron formation of the 3.25 Ga Fig Tree Group (Barberton Greenstone Belt) suitable as a seawater archive , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11051, https://doi.org/10.5194/egusphere-egu26-11051, 2026.
Banded Iron Formations (BIFs) are authigenic marine sedimentary rocks that record the composition of Precambrian seawater and provide key insights into early marine environments. The Paleoarchean Algoma-type Tomka BIF from the Daitari Greenstone Belt (India) is considered to be ~3.37–3.50 Ga old and to have experienced only greenschist-facies metamorphism, in contrast to many Eo- to Paleoarchean BIFs that were metamorphosed under much higher amphibolite-facies conditions. Despite this relatively low metamorphic overprint, the potential of the Tomka BIF as a reliable archive of ancient seawater chemistry has not yet been evaluated. Still, this location may be crucial to better understand the evolution of Palaeoarchean marine habitats and their interactions with early landmasses and the atmosphere.
To better constrain both the depositional age and the paleoenvironmental conditions of the Tomka BIF, we analysed major and trace element abundances together with radiogenic Hf–Nd isotope compositions of individual Fe- and Si-rich BIF layers, as well as an associated shale. Tomka BIF samples lacking detrital contamination and post-depositional alteration display typical Archean, shale-normalised seawater-like rare earth and yttrium (REYSN) patterns. These include positive LaSN, EuSN, and GdSN anomalies, superchondritic Y/Ho ratios, the absence of negative CeSN anomalies, and enrichment of heavy relative to light REYSN. Collectively, these signatures indicate deposition in an anoxic marine environment influenced by high-temperature submarine hydrothermal activity.
BIF samples preserving pristine Hf–Nd isotope compositions define coherent trends along the 176Lu–176Hf and 147Sm–143Nd reference isochrons corresponding to the inferred depositional age of 3.37–3.50 Ga. Initial εNd values (+0.1 to +5.3) indicate a juvenile source contribution to Tomka seawater, while the associated shale (εNd = -0.3 to +1.1) reflects a similarly juvenile provenance for the detrital component. In contrast, initial εHf values of the BIFs (-4.8 to +145) are strongly decoupled from the Nd isotope system and from the so-called terrestrial array, which reflects the coupled behaviour of Hf-Nd in magmatic systems. A Hf-Nd isotope decoupling in low-temperature systems, however, is related to incongruent Hf weathering, as described by the so-called zircon effect. Applied to the Daitari BIFs, this decoupling likely reflects the emergence and weathering of a zircon-bearing crust in the proto-Singhbhum Craton, which influenced Archean seawater chemistry by at least 3.37 Ga.
How to cite: Viehmann, S., Krayer, J., Jodder, J., Pakulla, J., Münker, C., Hofmann, A., Schulz, T., Koeberl, C., and Weyer, S.: Banded Iron Formations as archives for ca. 3.5 Ga old marine environments: Insights from REE and Hf-Nd isotope signatures, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2702, https://doi.org/10.5194/egusphere-egu26-2702, 2026.
Posters virtual: Fri, 8 May, 14:00–18:00 | vPoster spot 4
EGU26-279 | ECS | Posters virtual | VPS7
Sedimentary Environment Evolution and Response to Mesozoic Toarcian Oceanic Anoxic Event (T-OAE) in the Eastern TethysFri, 08 May, 14:00–14:03 (CEST) vPoster spot 4
Mesozoic Oceanic Anoxic Events (OAEs) are critical geological episodes linked to global carbon cycle perturbations, climate warming, and ecosystem restructuring. However, the regional expression of OAEs in the eastern Tethys remains insufficiently constrained. This study focuses on the Early Jurassic Toarcian OAE (T-OAE)—integrating petrological, mineralogical, and geochemical analyses of two key sections to reconstruct Early Jurassic sedimentary evolution, paleoclimate-paleoenvironment dynamics, and their responses to the T-OAE. Pronounced negative carbon isotope excursions (CIEs) are recorded in both marine strata, correlatable with global T-OAE records. Intensified continental chemical weathering and enhanced terrigenous detrital input are common responses of the eastern Tethys to T-OAE, driven by global warming. Redox proxies reveal oxic-suboxic conditions in open marine settings of the eastern Tethys during OAEs, regulated by regional factors (water depth, basin restriction, freshwater input), contrasting with the anoxic-euxinic environments in the western Tethys. Bioproductivity showed spatial heterogeneity: organic matter accumulation was controlled by redox conditions and productivity, with high accumulation in restricted lagoons versus low-moderate in open shelves.
This study reveals the regional response patterns of the eastern Tethys to Mesozoic OAEs, highlighting the spatial heterogeneity of redox and productivity dynamics, and provides new insights into the Mesozoic climate-ocean-biosphere system.
How to cite: Yi, J. and Fu, X.: Sedimentary Environment Evolution and Response to Mesozoic Toarcian Oceanic Anoxic Event (T-OAE) in the Eastern Tethys, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-279, https://doi.org/10.5194/egusphere-egu26-279, 2026.
EGU26-633 | ECS | Posters virtual | VPS7
Microbially Induced Sedimentary Structures in a Mesoproterozoic Erg System: A Case Study from the Mangabeira Formation, BrazilFri, 08 May, 14:03–14:06 (CEST) vPoster spot 4
Microbially Induced Sedimentary Structures (MISS) are syndepositional primary structures that occur both in some of the earliest forms of life and in modern environments. Throughout geological time, microorganisms developed metabolic strategies that enabled their establishment and proliferation in a wide range of settings, including arid environments such as deserts. However, MISS are widely recognized in tidal flats and other shallow-marine environments, whereas examples preserved in continental deposits remain comparatively scarce. A comprehensive review of Precambrian MISS occurrences indicates a notable expansion of documented records during the Mesoproterozoic, coincident with the assembly of the Columbia supercontinent and a concurrent rise in atmospheric oxygenation. These global transitions may have promoted the ecological diversification of microbial communities and facilitated their dispersal into progressively drier continental interiors. Under favorable conditions, microorganisms proliferate and form microbial mats that interact with external factors such as sedimentation, currents, erosional processes, and other physical drivers. Their presence in arid terrestrial deposits is thus of considerable importance, as it underscores how microbial communities evolved and developed adaptive capabilities that enabled them to colonize and persist within intermittently wet landscapes subjected to elevated environmental stress. This study documents the occurrence of MISS within continental desert depositional systems of the Mangabeira Formation, São Francisco Craton, Brazil (1.6 Ga), preserved in wet sandsheet deposits. These occurrences broaden the sparse record of MISS in Proterozoic desert environments and offer new constraints on the capacity of early microbial communities to endure highly stressful and intermittently wet conditions. To investigate the conditions that enabled microbial establishment in this ancient desert, this study applies a multi-method approach integrating sedimentological, stratigraphic, petrographic, and microtextural datasets. The vertical succession reveals six distinct drying-upward cycles, each associated with fluctuations in groundwater level that periodically generated stable, moisture-rich surfaces suitable for microbial mat development. Within these intervals, MISS occur in millimetric heterolithic laminites displaying wavy–crinkly lamination, wrinkle marks, roll-up structures, deformational features, authigenic minerals with convolute morphologies, trapped grains, and organic carbon remnants. Complementary Raman analyses reveal characteristic carbonaceous peaks (at ~1370, 1590, and 1610 cm⁻¹), confirming the presence of organic carbon and kerogen. Collectively, the integrated dataset indicates that microbial colonization in the Mangabeira Formation was episodically favored by groundwater-controlled moisture stability, which enhanced substrate cohesion and enabled the formation of distinctive biosedimentary fabrics. These findings, contextualized within the broader Mesoproterozoic expansion of MISS, highlight the capacity of early microbial communities to establish themselves in hydrologically stressed desert landscapes and refine the sedimentological and geochemical criteria necessary for recognizing MISS in deep-time continental systems.
How to cite: Feitosa, A., Bállico, M., Souza, E., Scherer, C., Callefo, F., Balbinot, V., Tatsch, G., Yokoyama, E., Leite, A., Reis, A., Silva, S., and Santos, A.: Microbially Induced Sedimentary Structures in a Mesoproterozoic Erg System: A Case Study from the Mangabeira Formation, Brazil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-633, https://doi.org/10.5194/egusphere-egu26-633, 2026.
EGU26-14428 | Posters virtual | VPS7
Controls on Ash-Fall Deposit Preservation in Low-Energy Depositional Systems of the Rio Bonito Formation, Paraná Basin, BrazilFri, 08 May, 15:00–15:03 (CEST) vPoster spot 4
The Paraná basin is composed of stratigraphic units that record distinct paleoenvironmental settings, organized into six supersequences. The Gondwana I Supersequence (Permian) records a transgressive-regressive cycle associated with tectonic and climatic changes, in which periglacial successions (Itararé Group), coastal and marine (Guatá Group), and continental deposits (Passa Dois Group) are preserved. These sedimentary units crop out along the eastern margin of the Paraná Basin in a complex structural configuration that reveals significant tectonic displacements attributed to normal faults, resulting in the lateral juxtaposition of stratigraphically distinct units. Due to this arrangement, volcanogenic deposits play a fundamental role as stratigraphic markers, as they allow the establishment of precise geochronological correlations. This study presents geochronological data obtained from a volcanogenic deposit at Morro dos Conventos outcrop, and compares it with a compilation of the ages of volcaniclastic sediments interbedded with sedimentary deposits from the Rio Bonito Formation, aiming to constrain the evolution of depositional systems that enabled the preservation of such volcanogenic deposits within this interval. The detailed stratigraphic section of the outcrop was conducted and samples were collected for geochronological analysis. U-Pb zircon ages were determined by LA-MC-ICP-MS from a volcanogenic layer. The results reveal a unimodal zircon population with a concordia age of 286 ± 1.4 Ma (N = 9; MSWD = 1.2), allowing correlation of the deposit with the Artinskian Stage. Sedimentological and stratigraphic analysis of the section indicates a paleoenvironment of storm wave-dominated shelf, with interbedded subsystems recording high-frequency cycles associated with changes in sea level or sedimentation rates within the second-order Permian transgressive sequence. Sedimentological and geochronological data suggest that the studied succession correlates with the upper portion of the Rio Bonito Formation, in a context of progressive drowning by the Palermo Sea. At the top of the section, a progradation of subsystems is observed, characterized by the arrangement of subaerial sequences under humid backshore conditions. A similar configuration has been documented in other areas of the basin during the Cisuralian, where pelitic successions associated with coal deposits preserve centimeter-thick intercalated volcanic ash layers. The preservation of these features is attributed to paleoenvironmental conditions of subsystems developed along the margins of subaqueous bodies, dominated by low-energy settings with limited reworking, favoring the deposition of fine-grained sediments. In the studied outcrop, the preservation of the volcanogenic deposit is interpreted as a result of deposition within fine-grained sediments characterized by redoximorphic structures, indicative of fluctuating conditions between dry and wet periods typical of subaerial environments influenced by aqueous systems. A similar preservation context is observed in volcanogenic deposits recorded both in CPRM wells (Brazilian Geological Survey) and in nearby outcrops of this stratigraphic interval. The coexistence of low-energy depositional systems and episodes of high-magnitude explosive volcanism along the western margin of Gondwana enabled the preservation of ash-fall deposits in the Paraná Basin stratigraphic record, commonly associated with the Choiyoi Magmatism during the proposed Rio Bonito Formation sedimentation interval.
How to cite: Ribeiro Franqueira, A. V., Bettarel Bállico, M., Moreira Florisbal, L., Oliveira Manna, M., and Marlon dos Santos Scherer, C.: Controls on Ash-Fall Deposit Preservation in Low-Energy Depositional Systems of the Rio Bonito Formation, Paraná Basin, Brazil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14428, https://doi.org/10.5194/egusphere-egu26-14428, 2026.
