Orals: Wed, 6 May, 10:45–12:30 | Room -2.93
The end-Permian mass extinction (~252 Ma) represents the most profound biotic turnover in Earth’s history. While marine successions are well dated and chemically characterised, the terrestrial record has only recently begun to achieve comparable chronological resolution. The Karoo Basin in South Africa preserves one of the most continuous continental records spanning the extinction and early Triassic recovery, yet few sequences have direct radiometric ages. Recent progress has come from U–Pb dating of detrital zircons, although differences in maximum depositional ages, uneven stratigraphic sampling (particularly across the Triassic), and the potential for the youngest grains to be undersampled in detrital populations limit the development of a fully resolved continental timescale.
Pedogenic carbonate concretions are widespread within Karoo successions and offer an alternative chronometer. Their ubiquity and potential to preserve primary geochemical signatures make them promising but still underutilised targets for both U–Pb dating and palaeoenvironmental reconstruction. Here we evaluate their suitability through an integrated petrographic, geochemical, and geochronological approach. More than 100 carbonate concretions were collected from known end-Permian localities, representing diverse concretion morphologies, facies settings, and stratigraphic positions. This dataset enables assessment of which concretion types and growth histories best retain datable U–Pb systematics and palaeoenvironmental signals.
LA–ICP–MS U–Pb dating was carried out using a Nu Instruments Attom coupled to a Resolution SE 193 nm laser ablation system. Trace-element mapping via Q–ICP–MS (e.g. Mg, Sr, Ba, U, Th, Pb) was used as a screening tool to identify zones with favourable chemistries (e.g. U > 1 ppm and U > Pb). Initial results show that several concretion types preserve coherent U–Pb systematics and yield resolvable ages, while trace element and calcite fabrics reveal a spectrum from primary preservation through early diagenesis to complete recrystallisation. These relationships allow us to establish criteria for selecting the most reliable microdomains and concretion types for dating and to inform future field work.
This study adds to a rapidly growing body of research using LA-ICP-MS-U-Pb geochronology on pedogenic carbonates globally, and provides the first systematic attempt to geochemically characterise and directly date carbonate concretions in the Karoo Basin. It demonstrates the potential for pedogenic carbonates to refine terrestrial timescales across the end-Permian transition and contributes a framework that can be applied to continental settings globally where conventional chronometers remain limited.
How to cite: Edwards, T., Browning, C., Pickering, R., Wilton, A., and Viglietti, P.: Recording crisis and recovery: carbonate concretions as potential archives of Permo–Triassic change in the Karoo Basin, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-324, https://doi.org/10.5194/egusphere-egu26-324, 2026.
Tropical carbonate platforms accompanied the latitudinal shifts of the tropical belt throughout the Cenozoic. Their flat-topped geometries were influenced by a variety of processes, including climate and sea level changes, biofacies composition, tectonics and fluctuations in continental runoff. Within this scenario, tropical carbonate platforms grew across the global oceans between the Oligocene-Pliocene interval. Global evidence indicates that tropical platforms expanded toward higher latitudes in the early Miocene but underwent a collapse during the late Miocene and Pliocene. However, the occurrence of carbonate platforms in the South Atlantic during the Neogene is still poorly studied, creating a gap in the understanding of how warm periods influence the development of carbonate environments. Our study aims to characterize the sedimentological composition and depositional architecture of Neogene carbonates in the Santos Basin, to reconstruct the paleoenvironmental evolution and depositional history of South Atlantic tropical platforms across that interval. We use an extensive dataset of seismic data (2D and 3D) and wells to characterize the lithostratigraphy, the geometries (e.g. Isolated Carbonate Platform, rimmed shelf, homoclinal ramps and channels), and the build-up patterns (aggradation, progradation and backstepping) of carbonate platforms presented in the region. Lithostratigraphic results reveal the accumulation of a ~500 m thick calcarenite succession. Seismic interpretation shows that the shelf break was delineated by flat-topped platforms in the southern part of the Santos Basin (~28°S). Seismic analyses then indicate that middle Miocene smaller carbonate build-ups of up to 30 km in length coalesced via progradation into a 90 km long Quaternary carbonate platform. Within this interval, the transition from an aggradational to a progradational buildup is accompanied by a geometric transformation from isolated carbonate platforms to an extensive rimmed shelf. This change is supported by an isopach map which shows an intense sedimentary infilling of the inter-platform seaway and of the upper slope. In summary, the occurrence of Cenozoic carbonate platforms in the Santos Basin is divided into four stages: 1) onset of carbonate deposition occurred during the late Oligocene, driven by the late Oligocene Warming and the Oligocene-Miocene Transition which led to the establishment of a mixed siliciclastic-carbonate sedimentary environment; 2) carbonate buildups reached their aggradational peak during the middle Miocene Climate Optimum; 3) in the late Miocene, carbonate platforms evolved to a progradational stage in response to the long-term sea-level fall of the Miocene Climate Transition; 4) in the Quaternary, the development of mixed siliciclastic-carbonate homoclinal ramps buried the tropical carbonate platforms. This study reveals that the development and demise of tropical carbonate platforms in the Santos Basin were linked to global paleoclimate events, which also governed sea-level changes, the intensification of ocean currents, and sea-surface temperatures. Finally, the findings in this study demonstrate a 10° southward migration of tropical carbonate zones across the Santos Basin during the Neogene when compared to the modern, extending to 28°S latitudes whereas nowadays that environmental boundary is placed along the Abrolhos Shelf at 18°S.
How to cite: Gama, M., Tagliaro, G., Britzke, A., Bauli, P., Neto, O., and Jovane, L.: How far south did Cenozoic tropical carbonate platforms develop in the South Atlantic Ocean?, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-1313, https://doi.org/10.5194/egusphere-egu26-1313, 2026.
Modern mixed siliciclastic-carbonate benthic environments in the Egyptian northern Red Sea are shaped by continuous carbonate production and episodic siliciclastic delivery, yet their spatial patterns remain difficult to resolve where high-resolution bathymetry is lacking. To address these challenges and improve habitat classification, this study used a Satellite-Derived Bathymetry (SDB) model and explored its implications for understanding sedimentary processes in North Safaga Bay.
We compiled legacy ground truth datasets from previous studies and supplemented them with new in situ sampling, granulometric, and petrographic analyses. While SDB is limited by turbidity and substrate reflectance ambiguity, we mitigated these uncertainties using a physics-based workflow to isolate ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2) signal photons to extract depth points and a Random Forest regressor (RFR) trained on Sentinel-2 imagery. The RFR model achieved high predictive accuracy (coefficient of determination; R^2 = 0.95) at a 10 m spatial resolution, with internal cross-validation and an 80:20 training-to-test ratio. The reliability of this model was further validated against a fully independent set of in situ samples (R^2 = 0.85).
Our results reveal that high-energy bathymetric highs are dominated by compound-grain and coralgal facies, while the more sheltered back reef lagoons favor widespread foraminiferal sands, including soritid-bearing assemblages. In contrast, bathymetric depressions at the outlets of major wadi systems act as sediment traps for terrigenous siliciclastic facies. The delivery of these clastics is driven by a spectrum of episodic gravity-driven flows, including hyperpycnal events during flash floods, aeolian input, and wave-induced reworking.
The integration of remote sensing and sedimentological analyses provides a significant advancement over existing datasets by allowing quantifiable spatial correlation between geomorphology and facies distribution across the bay, rather than relying on interpolated point data. By resolving these fine-scale bathymetric controls, our results revealed a mosaic setting in which seafloor bathymetry and energy, directly dictated by the underlying inherited rift topography, act as the primary control on sediment partitioning, providing a localized model for mixed deposits in active settings.
How to cite: Altyeb, W., Rendall, B., and Mutti, M.: High-resolution mapping of a mixed siliciclastic-carbonate benthic environment using a hybrid Satellite-Derived Bathymetry (SDB) approach integrated with sedimentological data: North Safaga Bay, Egyptian Red Sea, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19266, https://doi.org/10.5194/egusphere-egu26-19266, 2026.
Late Miocene carbonate systems represent key archives of paleoenvironmental evolution related to the processes leading to the Messinian Salinity Crisis (MSC), culminating in Earth’s most recent saline giant. During the pre-MSC stage (7.1-5.97 Ma), the Mediterranean was affected by the superimposition of major global climatic and regional geodynamic forcing mechanisms, promoting overall restriction that disrupted marine circulation, amplified the effect of astronomically driven climatic oscillations on sedimentation, and impacted marine biodiversity. Within this framework, major structural and ecological changes occurred across the circum-Mediterranean region, including pronounced tectonic activity at gateway areas, shifts in terrestrial vegetation, and modifications in runoff regimes from African rivers. The spatial variability and interplay of these processes left a sedimentological expression in marine environments of different sectors of the Mediterranean. Carbonates and associated deposits represent excellent records of key parameters such as water column stratification, marine ecosystem evolution under rapid environmental change, the interaction between biotic and abiotic processes and tectonic activity.
We present two continuous bio- and magnetostratigraphically calibrated onshore pre-evaporitic successions, more than 100 m thick, from opposite Mediterranean margins (Tabernas Basin in Spain and Mesaoria Basin in northern Cyprus), focusing on exceptionally well-preserved carbonate deposits. Their integrated study through sedimentological, stratigraphic, petrological, quantitative micropaleontological, and geochemical analyses reveals the dynamic responses of these margins to progressive restriction, tectonic activity, climate forcing, and freshwater input. In the Tabernas Basin, pronounced tectonic activity in the Betic Cordillera, combined with increasing restriction, controlled the evolution of a mixed carbonate–siliciclastic platform and associated planktonic and benthic communities. Dysoxia-tolerant benthic foraminifera, deformed tests, and paragenetic relationships between pyrite and calcareous tests indicate stressed conditions and highlight the role of early diagenesis in preserving or biasing the micropaleontological record. Microbial mats developed in an inner-shelf setting, marking the climax of restriction before evaporite deposition.
In the Mesaoria Basin, early isolation and enhanced continental runoff promoted eutrophication in the upper water column, favoring algal blooms and water-column stratification, which in turn catalyzed microbial sulfate reduction at an anoxic seafloor of a bathyal setting. Ecological competition between bloom diatoms (Thalassionema nitzschioides) and opportunistic coccolithophore taxa (Reticulofenestra spp.) reveals the complex interaction between primary producers across different photic zones of a stratified basin. Precession-related cyclicity exerted a major control on pelagic sedimentation, driving the alternating deposition of carbonates and laminated marls with remarkably well-preserved calcareous nannofossils. These conditions favored the formation of “marine snow,” which is preserved in peloidal microbialites. In addition, the occurrence of Trichichnus, a trace fossil formed by giant sulfide-oxidizing bacteria, further reveals complex biotic–abiotic interactions in deep-water carbonate settings.
Our results improve the understanding of spatial and depositional variability of carbonate systems under rapidly changing paleoenvironmental conditions during a key interval of the Late Miocene. This study provides new insights for an integrated paleoceanographic reconstruction of the Mediterranean, emphasizing carbonate deposits as archives of forcing mechanisms and sedimentary processes prior to the onset of MSC.
How to cite: Lacerda Orita, G. K., Pérez-Valera, F., Natalicchio, M., Pellegrino, L., Dela Pierre, F., M. Sória, J., Corbí, H., Schito, A., Atalar, C., Gomez-Rivas, E., and Gibert, L.: Carbonates as keys to the Messinian Salinity Crisis’s Puzzle: Insights into spatial variability and sedimentary processes on opposite Mediterranean margins, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6550, https://doi.org/10.5194/egusphere-egu26-6550, 2026.
Modern sediments from reef facies at Discovery Bay, Jamaica, were analyzed to document changes in biotic sediment composition over the past four decades and to evaluate their relationship to the impacts of hurricanes, rising temperatures, and sea-level rise. Discovery Bay is a classical Caribbean reef research site, where reef community structure has been quantitatively and systematically documented since 1977, providing a robust long-term framework for interpreting sedimentary responses to environmental and climatic stressors. New data reveal that sediments from the backreef/lagoonal zone are dominated by plates of the green alga Halimeda (35.7–54.0%) and coral fragments (29.7–48.7%). Compared to the 1982–1999 period, Halimeda has nearly doubled in relative abundance, while coralline algae, echinoid fragments, and the encrusting foraminifer Homotrema rubrum have decreased by more than 50%. Despite the present scarcity of living corals in the backreef, coral fragments remain abundant in the sediments. They are derived mainly from the adjacent reef crest, where only old, dead coral skeletons are present today. Intensified wave action associated with sea-level rise promotes erosion of the old reef framework and transport of sand-sized material into the backreef. Additional coral skeletal material is supplied by storm-induced reworking of older backreef sediments. In the fore-reef zone (<30 m water depth), samples were collected along transects across a sand channel and a reef terrace. In the sand channel, sediments are dominated by coral grains (40.7–62.0%) and Halimeda fragments (21.7–41.7%), showing little change compared to 1999, except for a slight decline in coralline algae and Homotrema. On the fore-reef terrace, coral grains and Halimeda fragments contribute similar proportions (approximately 43% and 40%, respectively). With increasing depth, coral grains generally decrease, whereas Halimeda reaches its highest abundance at depths of 10–15 m. Compared to 1999, Halimeda fragments have increased by more than 10%, while coralline algae have decreased by approximately 10%.
Although living coral cover in the fore-reef zone has declined to less than 5% over the past three decades, the contribution of coral grains to sediments has remained nearly constant. This indicates that dead coral skeletons and older reef material present in the fore-reef zone have long residence times and continue to contribute to sand-sized sediment production. Consequently, fore-reef sandy sediments represent time-averaged assemblages and have limited capacity to record short-term changes in reef biotic composition.
This study was supported by the Polish National Science Centre, grant No. 2022/45/B/ST10/00599.
How to cite: Belka, Z., Dopieralska, J., Jakubowicz, M., Królikowska, S., Orzechowska, W., Thomas, S.-L., and Walczak, A.: Response of sediment composition in Jamaican reef facies to changes in environmental factors, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-3892, https://doi.org/10.5194/egusphere-egu26-3892, 2026.
Modern carbonate coastal barrier systems are rare compared to their siliciclastic counterparts. Furthermore, most existing modern carbonate barrier systems are R-type (shoals and emergent barriers that occur at the margins of rimmed platforms; eg., the Great Bahama Bank and the Great Pearl Bank), while C-type systems (barrier systems that form in shallow near-coast settings) remain poorly represented. As a result, C-type carbonate barrier facies models are still poorly defined. This study presents a high-resolution sedimentological and sequence-stratigraphic analysis of the Lagoa do Jacaré Formation (Bambuí Group, Brazil). A detailed facies analysis, conducted at a 1:20 scale across four vertical sections, identified twelve lithofacies grouped into six depositional associations: beach-barrier, back-barrier, lagoon, tidal channel, flood-tidal delta, and ebb-tidal delta. These associations illustrate the influence of wave, tidal, and storm surge processes on a barrier system. Sandy carbonates dominate the barrier and proximal deposits, while heterolithic facies are prevalent within the lagoon. Additionally, paleocurrent analysis enabled the identification of barrier orientation, as well as the directions of longshore currents (165°) and tidal channels that cross the barrier system (bidirectional at 70° and 240°). To reconstruct the spatial and temporal evolution of the depositional system, sequence-stratigraphic analysis at different hierarchical orders was essential. Regressive and transgressive cycles controlled changes in barrier morphology, with progradational patterns linked to barrier thickening and retrogradational patterns associated with barrier thinning. Two maximum regression surfaces were correlated with the GMD quarry, which increased the robustness of the depositional model and supported lateral facies migration of up to 10 km. Such migration is considered robust under the extreme greenhouse conditions of the period, when polar ice caps were absent and epicontinental seas, such as the subtropical Bambuí Sea, exhibited characteristics comparable to tropical marine systems. Barrier-island coastal configurations were more prevalent during greenhouse intervals. In the Early Cambrian, this setting was particularly important because persistent sediment reworking enhanced oxygenation at the sediment–water interface, creating localized pockets of favorable conditions for fauna to establish. Periods of increased oxygenation (the oceanic oxygenation events - OOEs) expanded available habitats, while returns to more anoxic conditions, when habitats became restricted again, likely promoted speciation processes. Consequently, the Lagoa do Jacaré Formation represents an exceptionally well-preserved example of a C-type carbonate barrier island system. It closely resembles siliciclastic barrier systems regardless of the sedimentary process and facies mobility. Its high preservation level makes it a valuable analog for improving carbonate shoreline facies models and for understanding how coastal configurations may have influenced the Cambrian radiation.
How to cite: Amaral Moura Silva, S., Jubé Uhlein, G., Uhlein, A., Veitenheimer, G., and Zhou, Y.: A Spatial-Temporal Reconstruction of a Huge Early Cambrian Carbonate Barrier Island System of Lagoa do Jacaré Formation, Bambuí Group, Brazil, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11043, https://doi.org/10.5194/egusphere-egu26-11043, 2026.
Miocene carbonate build-ups in southern Central Luconia exhibit strong lateral variability in geometry, internal facies organisation, and diagenetic overprint, despite forming within a broadly similar climatic and tectonic setting. Establishing reliable stratigraphic correlations among neighbouring build-ups therefore requires approaches that integrate internal facies successions with regional-scale stratigraphic markers, rather than relying solely on external morphology.
This contribution examines the correlation of Miocene carbonate build-ups across the southern Central Luconia province by integrating core-based facies analysis with seismic stratigraphy and geomorphology. Emphasis is placed on the identification and lateral tracing of flooding surfaces and sequence boundaries associated with Miocene depositional cycles, and on evaluating how diagenetic modification influences stratigraphic expression. Cycles II to V are shown to provide regionally consistent stratigraphic frameworks that can be recognised across multiple build-ups, despite differences in platform thickness and margin geometry.
Results indicate that flooding-related tight carbonate intervals form laterally persistent markers that enable correlation between build-ups developed on different structural highs. Facies stacking patterns reveal systematic transitions from aggradational platform growth to backstepping and pinnacle development during relative sea-level rise. Superimposed on these depositional trends, dolomitization has a significant control on facies preservation and log response, locally enhancing or masking original depositional textures. Dolomitized intervals commonly coincide with exposure-related surfaces and restricted lagoonal facies, suggesting a strong link between relative sea-level change, fluid circulation, and diagenetic alteration during the Miocene.
The integration of stratigraphic architecture and diagenetic patterns provides a more robust basis for correlating Miocene carbonate build-ups in southern Central Luconia.
How to cite: Jimenez Soto, G., Abdul Latiff, H., and Poppelreiter, M.: Controls of Facies Architecture and Dolomitization on the Stratigraphic Correlation of Miocene Carbonate Build-Ups in Southern Central Luconia, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11186, https://doi.org/10.5194/egusphere-egu26-11186, 2026.
The Lefika la Noka (LLN) tufa is the only documented tufa deposit from the hominin fossil-rich Cradle of Humankind (Cradle) in South Africa. It is situated north of the Malapa and Gladysvale fossil sites, within the Grootvlei catchment area of the Cradle. LLN tufa presents an excellent opportunity for paleoclimate reconstruction in the Cradle, particularly for the late Pleistocene – Holocene period, when Homo naledi and archaic Homo sapiens emerge in the Southern African fossil record. To reconstruct the paleoclimate of the Cradle using the tufa deposit, it is necessary to first understand the sedimentological characteristics of the tufa. Therefore, this study aims to describe the LLN tufa facies, depositional environments, and stratigraphy by using field and petrographic techniques. The tufa has a maximum thickness of about 12.5 m. Seven distinct tufa facies were identified from five drilled cores and seven outcrops. These are phytoherm framestones of calcified vertical stems and bryophytes, phytoherm boundstones of stromatolites and thrombolite-like tufa, oncoidal tufa, micritic tufa, and lithoclastic tufa. These tufa facies were deposited in a fluvial environment, with phytoherm framestones and boundstones precipitated in situ in high-energy environments, such as barrages, cascades, and waterfalls. The oncoids formed within turbulent pools. The micritic tufa precipitated slowly in the calm water pools, whereas the lithoclast tufa accumulated along the river channel during periods of flooding. The lateral and vertical facies distribution indicates the role of hydrodynamics and CO2 degassing during deposition.
How to cite: Onyeogu, T., Makhubela, T., Jinnah, Z., and Berger, L.: Facies characteristics of the Lefika la Noka tufa, Cradle of Humankind, South Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-20383, https://doi.org/10.5194/egusphere-egu26-20383, 2026.
The carbon isotope signature of carbonates across the Lower-Middle Triassic transition was investigated to reconstruct environmental change and carbon cycle dynamics in the Holy Cross Mountains (HCM, Poland). This area was located in the southeastern part of the semi-enclosed Germanic Basin, intermittently connected to the western Tethys Ocean through tectonically controlled marine gateways.
The dataset is derived from the uppermost Olenekian to upper Anisian interval of the Piekoszów IG-1 borehole. This approximately 240 m thick succession comprises mudstones, marly limestones, dolostones and limestones, locally nodular, classified as wackestones to packstones and subordinate grainstones. These deposits document the carbonate ramp setting ranging from restricted marginal to open-marine conditions. A distinctive red mudstone horizon in the lower Anisian records short-lived emersion within the ramp. The biostratigraphic framework of this succession is constrained by conodonts, bivalves, echinoderms, brachiopods and miospores.
The δ¹³C curve across the Olenekian-Anisian transition ranges from -3.16‰ to +0.70‰ VPDB. A positive shift recorded close to the Olenekian-Anisian boundary broadly corresponds to the Spathian-Anisian carbon isotope event and represents a potential regional chemostratigraphic marker. A pronounced negative excursion (down to -3.82‰) is observed within a lower Anisian dolostone interval. Miospores identified above this interval indicate the Perotrilites minor palynozone of the Lower Muschelkalk, allowing precise stratigraphic calibration of the isotope record. A second significant positive shift (+3.06‰) occurs near the Bithynian-Pelsonian boundary and correlates with coeval carbon isotope excursions documented elsewhere in the Germanic Basin and the western Tethys. This is followed by a gradual decline culminating in a negative excursion in the upper Anisian.
The δ¹³C fluctuations observed in the late Olenekian and early Anisian are interpreted to reflect local palaeoenvironmental conditions within a shallow, partly restricted epicontinental sea. Restricted circulation and episodic freshwater input likely modified the dissolved inorganic carbon pool through mixing with isotopically light terrestrial carbon and reduced exchange with open-marine reservoirs. In contrast, more positive δ¹³C values during the middle and late Anisian coincide with the development of open-marine carbonate ramp conditions, enhanced carbonate production and improved basin connectivity.
The δ¹⁸O values display a wide scatter consistent with variable early diagenetic conditions and facies-controlled overprint in a restricted to shallow-marine setting. The absence of systematic δ¹³C-δ¹⁸O covariance suggests that the main carbon isotope trends are not dominated by late-stage diagenetic alteration.
Overall, the isotope record from the HCM reflects regional palaeoenvironmental dynamics in the Polish segment of the Germanic Basin related to tectonically driven changes in basin connectivity, water circulation and third-order transgressive-regressive cycles, supporting the use of δ¹³C trends as tools for regional chemostratigraphic correlation across the Lower-Middle Triassic transition.
How to cite: Idzikowska, K., Trela, W., and Fijałkowska-Mader, A.: Carbon isotope record across the Lower-Middle Triassic transition in the Holy Cross Mountains (Poland): chemostratigraphic and palaeoenvironmental significance, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19481, https://doi.org/10.5194/egusphere-egu26-19481, 2026.
The late Wenlock (Silurian) period is characterised by biogeochemical perturbations expressed through two global regressive-transgressive eustatic cycles. These cycles are associated with a double-peaked positive carbon isotope excursion linked to the Mulde Event, also known as the “Big Crisis” (Radzevičius et al., 2014). While these features are widely recognised, the processes that explain the heterogeneity of geochemical and sedimentary responses on a basin scale remain poorly understood. Here, we present an integrated geochemical and sedimentary facies study of Homerian successions from the shelf zone of the Baltic Silurian Basin in Gotland, Sweden. For this study, we collected a total of 64 rock samples from outcrops on Gotland Island. The studied interval included the Slite, Fröjel, and Halla formations. We performed stable carbon isotope, trace element, and X-ray diffraction (XRD) analyses. Preliminary data revealed positive shifts in δ¹³C at the onset of the Mulde Event, demonstrating that these variations are systematically linked to changes in depositional facies, mineralogical composition and redox conditions. Ratios of trace elements such as U, Th, V, Cr, and Ce were used to determine the bottom-water oxygenation status. X-ray diffraction analysis was used to detect the presence of the dolomite mineral, which may indicate secondary alteration of the sediments. Results suggest that depositional environment might reflect the interaction of eustatic sea-level change, basin restriction, and water-column redox stratification rather than representing a simple, synchronous global signal. The newly obtained results can be used to gain a more detailed understanding of the mechanisms that explain Silurian climate-ocean coupling and highlight the importance of local depositional controls in modulating global biogeochemical signals.
Radzevičius, S., Spiridonov, A. & Brazauskas, A. 2014: Application of Wavelets to the Cyclostratigraphy of the Upper Homerian (Silurian) Gėluva Regional Stage in the Viduklė-61 Deep Well (Western Lithuania). In: Rocha, R., Pais, J., Kullberg, J., Finney, S. (eds): STRATI 2013. Springer Geology. https://doi.org/10.1007/978-3-319-04364-7_84
How to cite: Lukoševičiūtė, G., Rinkevičiūtė, S., and Kaminskas, D.: The depositional environment during Homerian in the Baltic Silurian Basin , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-9906, https://doi.org/10.5194/egusphere-egu26-9906, 2026.
Low-lying coral reef islands are increasingly threatened by sea-level rise and intensifying monsoon events, leading to heightened risks of coastal inundation, erosion, and consequent impacts on island habitability and human migration. Despite these challenges, such islands exhibit dynamic and non-uniform responses governed by local hydrodynamics and environmental conditions. The Western Indian Ocean is especially vulnerable, with models projecting anomalously higher rates of sea level rise and storm frequency compared to the global average. Within this context, the low-lying islands of the Lakshadweep Archipelago provide an essential case study for understanding island vulnerability and resilience.
This study presents a decadal-scale analysis (2003–2022) of ten islands in the Lakshadweep Archipelago, focusing on spatial variations in island area and their relationship with global and regional environmental factors. High-resolution satellite imagery (CNES Airbus, 0.3–0.7 m) was used to examine shoreline morphological changes on both inhabited (Bitra, Androth, Minicoy, Agatti, Kavaratti, Kalpeni) and uninhabited (Bangaram, Thinnakara, Suheli, Kalpetti) islands. Islands were categorized by size, distinguishing large (>1 km², Minicoy and Androth, Kavaratti, Agatti, Kalpeni) from small (<1 km²) islands, and by habitability to assess anthropogenic impacts. Results reveal that all islands, regardless of habitation, experienced specific changes in area: small islands showed up to 30% sediment migration, however, without losing area—especially pronounced from 2007 to 2017, coinciding with severe El Niño and low-amplitude Indian Ocean Dipole events. While the large islands lost up to 5% of their area, attributed to both natural and human influences.
These findings indicate that small islands face moderate risk due to sediment migration, while large islands are moderately to highly vulnerable, influenced by persistent erosion and anthropogenic factors. Spatial patterns of vulnerability, particularly in the southern zones, underline the need for targeted mitigation and adaptation strategies. Importantly, regional drivers such as monsoon intensity play a decisive role in shoreline resilience, differentiating these islands from their global counterparts. By identifying areas of risk and proposing conceptual models for adaptation, this study offers insights for assessing the habitability of coral reef islands in the context of ongoing climate change.
How to cite: Menon, S., Misra, S. K., and Khanna, P.: Coastal resilience and island habitability in coral reef islands: A case study of Lakshadweep Islands, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-742, https://doi.org/10.5194/egusphere-egu26-742, 2026.
Continental carbonates in semi-arid regions represent valuable archives of past hydrological and climatic variability. In northern Botswana, the Chobe Enclave hosts widespread carbonates occurring in two major facies: (1) “islands” carbonates and (2) surface calcretes. The exact origin, formation mechanisms, and paleoenvironmental significance of these carbonates remain debated.
This study investigates the genesis of these two facies using an integrated sedimentological, mineralogical, and geochemical approach. Field observations, petrography, cathodoluminescence, and X-ray diffraction are combined with stable and clumped isotope geochemistry (Δ47) and radiocarbon dating. These data are further contextualized using modern surface and groundwater isotopic compositions.
Carbonate island facies samples that generally occur at similar altitudes throughout the area, give Late Pleistocene ages (~50–10 ka) and recorded precipitation from persistent, moderately evaporated waters at relatively low temperatures (17.1 ± 3.6 °C), consistent with palustrine to lacustrine environments linked to highstands of paleo-Lake Makgadikgadi. In contrast, the younger surface calcretes (<15 ka) have greater isotopic and textural heterogeneity and higher formation temperatures (24.1 ± 3.6 °C), reflecting surface precipitation driven by seasonal precipitation and evaporation under more arid conditions at temperatures broadly comparable to modern mean annual temperatures of this region. In addition, intermediate samples with mixed isotope compositions and fabrics are interpreted as having formed during hydrological/climatic shifts and/or by partial diagenetic reworking of older carbonate islands into calcrete-like deposits.
The results of this study highlight persistent hydrological controls on carbonate formation in the Chobe Enclave throughout the Late Quaternary and demonstrate the potential of multi-proxy carbonate archives for reconstructing paleoenvironmental changes in semi-arid continental settings.
How to cite: König, S., Vennemann, T., Ramudzuli, E., and Kocsis, L.: Late Quaternary Continental Carbonates of the Chobe Enclave (Botswana): A Multi‑Proxy Study Using Stable, Clumped, and Radiocarbon Isotopes, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11268, https://doi.org/10.5194/egusphere-egu26-11268, 2026.
Anthropogenically-driven climate change is an established fact. While significant efforts are being made to understand the effects of greenhouse gasses on the climate, the effects of the related process of Ocean Acidification, through the dissolution of CO2 in seawater, receives less attention. The vast majority of ocean acidification studies have focused on the ability of marine calcifiers to precipitate skeletal material under a scenario of falling pH. The lowering of marine pH is accompanied by a decrease in calcium carbonate (CaCO3) saturation, thus increasing the dissolution of carbonate skeletal material – particularly aragonite.
Predicted future ocean surface pH values, on the basis of IPCC SSP climate scenarios, range between 8.0 and 7.7 by the year 2100. While the potential effects on marine calcifiers are worrying, such extreme reductions in pH will also have significant consequences for future carbonate sediment budgets. This is particularly a concern for low-lying tropical island nations.
This study experimentally assesses the effects of ocean acidification, at a range of predicted future pH scenarios, on carbonate bioclasts in a simulated tropical shallow marine environment. During each experimental run, targeted carbonate materials were subjected to an extended period of exposure under predicted future pH conditions. Experiments were run in duplicate, under both passive and dynamic conditions, so as to assess the effects of dissolution on the mechanical competence of sediment grains in natural transport scenarios. Project outcomes enable the construction of a predictive matrix for the potential effects of future ocean acidification pathways on carbonate sediment budgets. Outcomes will directly support informed planning and decision making, particularly in resilience and vulnerability assessments.
How to cite: Lokier, S. and Mineyko, E.: Carbonate sediment budgets under predicted future Ocean Acidification pathways, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-2029, https://doi.org/10.5194/egusphere-egu26-2029, 2026.
Fluvial stromatolites are widespread in upper Paleocene–Eocene successions of the South Pyrenean Foreland Basin (SPFB, Spain) yet their geochronological and paleoenvironmental potential remains largely unexplored. Recently documented stromatolites from the Escanilla Formation provide a unique opportunity to investigate continental environmental change across the Middle Eocene Climatic Optimum (MECO), a prolonged global warming event that is well constrained in marine archives but remains poorly dated and resolved in terrestrial records.
Although existing magnetostratigraphic frameworks provide broad temporal control, in-situ U–Pb dating of fluvial stromatolites using LA-MC-ICPMS yields absolute age constraints that refine the stratigraphic placement of the MECO within the Escanilla Formation and improve chronologic resolution across the SPFB. These age anchors allow direct integration of continental sedimentary records with global climate archives.
High-resolution stable-isotope analyses (δ¹³C and δ¹⁸O) performed using SIMS across individual stromatolite growth bands capture seasonal variability in hydrological and thermal conditions. Variations in δ¹⁸O are interpreted to reflect changes in water temperature and/or evaporative conditions, while δ¹³C variability records shift in dissolved inorganic carbon sources and microbial activity within fluvial systems. Together, these data provide insight into seasonality, hydrology, and climate sensitivity of continental environments during a major Eocene warming event.
This study demonstrates that fluvial stromatolites represent robust, datable continental archives capable of resolving both absolute timing and high-frequency environmental variability during past greenhouse climate perturbations.
How to cite: Sharma, N. and Mark, C.: In-situ carbonate U-Pb dating and high-resolution stable-isotope analysis of fluvial stromatolites, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8783, https://doi.org/10.5194/egusphere-egu26-8783, 2026.
Zechstein platforms in the Southern North Sea were thought to be fringed by kilometre-scale high-energy progradational carbonates with lowstand wedge geometries. Instead, a new well encountered a halite-rich evaporitic wedge that replicates the coveted progradational carbonates. This study integrates sedimentological observations with geochemistry, petrophysics and 3D seismic data to characterise the evaporitic replicas and then distinguish them from the genuine carbonate platform geometries. The evaporitic wedges generate laterally symmetrical rims around the platforms which are approximately 150m thick and 2000m wide. Wedge precipitation predated the well-characterised basin-wide Z2 drawdown event, and therefore the localised evaporitic progradational system was onlapped by basin-fill halite. The evaporitic wedges often feature domino slumping along weak progradational bedding planes, resulting in blocks that collapsed into the basin. The earliest progradational beds contained the highest concentration of microbialites which assisted stabilisation of the evaporitic wedges on the rims of carbonate platforms, whilst also indicating that the wedges were part of an environmental transition from marine highstand into basin desiccation. Microbial fragments were reworked downslope into brecciated debris flow deposits, demonstrating the relationship between wedge construction and syndepositional collapse on the outer slopes. Petrophysical and geochemical data show that the evaporitic wedges were closely associated with the early stages of drawdown, and a lack of post-anhydrite marine recharge resulted in the depletion of Ca2+ from the brine and accordingly limited anhydrite (CaSO4) precipitation within the wedges. This depletion in brine Ca2+ led to dolomitic microbialites (CaMg(CO3)2) in the lower wedge; however, the upper wedge features Kutnohorite (Ca(Mn,Mg)(CO3)2) showing that Mg2+ also eventually became depleted and was replaced by Mn2+. This analysis characterises a rare evaporitic phenomenon which can hide in plain sight in seismic data and act as a depositional intermediary between platform construction and basin-fill halite precipitation.
How to cite: Houghton, T., Neilson, J., Manzo, E., Brackenridge, R., de Keijzer, M., de Leeuw, K., Strauss, C., and Underhill, J.: Can halite form progradational lowstand wedges? New insights into basin margin evaporites from the Permian Zechstein, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18657, https://doi.org/10.5194/egusphere-egu26-18657, 2026.
Carbonate systems represent a major component of the Paleogene–Neogene sedimentary record along the southern Mediterranean margin; however, their three-dimensional geometry, spatial distribution, and seismic expression offshore western Libya remain insufficiently constrained. This study uses 3D seismic-reflection data calibrated with borehole-geophysical information to identify, characterize, and map buried carbonate systems in the Gabes–Tripoli Basin.
The analysis is based on approximately 1200 km² of post-stack migrated 3D seismic-reflection data tied to five industrial wells from Block NC41. Integrated seismic interpretation and seismic-geomorphological analysis reveal two principal phases of carbonate development. The Eocene interval is characterized by laterally discontinuous ramp-type carbonate bodies expressed by low- to moderate-amplitude internal reflections bounded by strong top and base reflectors. Seven recurring seismic-reflection associations (EC1–EC7) are identified and interpreted to represent nummulitic ramp limestones and associated dolomitized facies.
A second phase of carbonate development occurred during the Oligocene–Miocene and is distinguished by more localized platform growth and isolated build-up geometries. These carbonates display higher seismic relief, mound-shaped external morphologies, and pronounced reflection terminations, allowing the identification of several distinct carbonate build-ups (MC1–MC3). Compared to the Eocene ramp systems, the Oligocene–Miocene carbonates reflect a shift toward platform-dominated carbonate production influenced by changes in accommodation, relative sea level, and tectonic framework.
Seismic-attribute analysis demonstrates that amplitude-, phase-, and continuity-based attributes are effective for detecting and delineating buried carbonate geobodies and for discriminating between different carbonate system types. The results provide new insights into (i) the evolution of Tertiary carbonate systems offshore Libya, (ii) the seismic expression and reservoir-scale architecture of Eocene ramp carbonates, and (iii) the transition to localized carbonate platform development during the Neogene. More broadly, this study highlights the value of 3D seismic geomorphology and attribute-based workflows for reconstructing carbonate-system evolution along tectonically influenced continental margins.
How to cite: Khalifa, N., Back, S., and Drews, M.: Seismic geomorphology and stratigraphic evolution of Eocene and Oligocene–Miocene carbonate systems, offshore western Libya, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10409, https://doi.org/10.5194/egusphere-egu26-10409, 2026.
The study area is situated in the central part of the Carpathian Foreland in Poland. The interpreted interval includes the uppermost part of the Upper Jurassic – Lower Cretaceous carbonate complex, as well as the mixed carbonate-clastic Upper Cretaceous series. The sedimentation of the studied formations during the Late Jurassic and Cretaceous took place in the shelf zone of the northern, passive margin of the Tethys Ocean, and the paleoenvironment of sedimentation was heterogeneous and evolving over time.
For the study, 3D seismic data and geophysical (well logs) and geological information obtained from wells were used. High resolution seismic data were great input for seismic sequence stratigraphy and analysis in the Wheeler domain and enabled us to obtain insightful attribute volumes (such as spectral decomposition, sweetness and relative acoustic impedance).
The seismostratigraphy interpretation of the Upper Cretaceous mixed carbonate-clastic formations was based on the sequence stratigraphy methodology, which enabled detailed identification of depositional systems tracts and depositional sequences within these formations. Based on the analysis of the chronostratigraphic image and the Wheeler diagram, the main directions of sedimentary material transport into the Upper Cretaceous sedimentary basin in the central part of the Carpathian Foreland in Poland were determined. Numerous discontinuities and hiatuses related to erosional events or periods of non-deposition were identified in the Wheeler diagram. Small local dislocations, in some cases not visible in the seismic image, were also interpreted based on the chronostratigraphic seismic image. The interpretation has greatly contributed to the reconstruction of the basin's depositional architecture.
Seismic attribute maps, calculated directly on the surface of the interpreted intra-Cretaceous chronostratigraphic seismic horizon, allowed for a detailed analysis of paleoenvironmental elements within Upper Cretaceous formations. This seismic horizon corresponds to the maximum flooding surface (mfs) and connects the sedimentary packages deposited in a transgressive systems tract within one of the identified depositional sequences, as interpreted from the chronostratigraphic image in the structural domain and the Wheeler diagram. Based on the interpretation of the maps obtained, several elements of depositional architecture were identified, i.e., barrier Island with washover, elongated tidal banks, crevasse splays, and bay-head deltas, which generally allow for the definition of two adjacent types of transgressive coast type, i.e. the barrier island coast dominated by waves and the open estuarine coast dominated by tides.
The work was funded by the National Science Center Poland (NCN); SONATA 17: Recognition of the depositional architecture of the Upper Cretaceous sedimentary basin in the central part of the Carpathian Foreland (2021/43/D/ST10/02728)
How to cite: Kwietniak, A., Łaba-Biel, A., and Urbaniec, A.: Recognition of the depositional architecture of the Upper Cretaceous sedimentary basin in the central part of the Carpathian Foreland, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-10597, https://doi.org/10.5194/egusphere-egu26-10597, 2026.
