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 Fe_0.937Ni_0.063. 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 ų. 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 (Fe_1-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 δ¹⁸O_chitin measurements now allow the possibility of taxon specific δ¹⁸O_chitin 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 δ¹⁸O_chitin 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 δ¹⁸O_chitin 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.