SSP1.3 | Amalgamating chemistry, microbiology and sedimentology within a non-restrictive model. A tribute to Judith McKenzie’s career
Amalgamating chemistry, microbiology and sedimentology within a non-restrictive model. A tribute to Judith McKenzie’s career
Co-sponsored by IAS
Convener: Daniel Ariztegui | Co-conveners: Anelize Bahhniuk, Michael E. Böttcher, Patrick Meister, Patricia RoeserECSECS, Mónica Sánchez-Román, Crisogono Vasconcelos
Orals
| Tue, 16 Apr, 14:00–15:40 (CEST), 16:15–18:00 (CEST)
 
Room G2
Posters on site
| Attendance Wed, 17 Apr, 16:15–18:00 (CEST) | Display Wed, 17 Apr, 14:00–18:00
 
Hall X3
Orals |
Tue, 14:00
Wed, 16:15
Back in 1982, Judith McKenzie published a scientific article entitled Carbon-13 Cycle in Lake Greifen: A Model for Restricted Ocean Basins (*). Two systems in which she worked and made noteworthy contributions are mentioned in the title: Lakes and oceans. Her career, on the other hand, was completely unrestrictive. She used isotope geochemistry, a significant new method, to study the development of dolomite in the Abu Dhabi sabkha for her PhD thesis. When it came to establishing isotope geochemistry in sedimentology, paleoceanography, and limnology, Judy was a pioneer. She had a key role in the establishment of the stable-isotope laboratory at the ETH Zürich, one of the first isotope labs in European Earth Science departments at the time. The Mediterranean salinity crisis was one of her early exciting research themes where she made a number of significant scientific contributions. She played a pivotal role in fostering the participation of numerous scientists in international ocean drilling programs, catalyzing the careers of countless early-career researchers. Since the early 90’s her research refocused on exploring the interface between geology and biology and in particular the influence of microbes on the formation of dolomite and other minerals. Judy's groundbreaking achievements have significantly advanced sedimentary geology within the realms of limnogeology, paleoceanography, chemical sedimentology and geomicrobiology. To honor her career and celebrate her scientific achievements we invite contributions from both established and early-career scientists dealing with the various aspects of Judith McKenzie’s research that show the incredible legacy she leaves behind.

(*) Judith A. McKenzie, 1982, Carbon-13 Cycle in Lake Greifen: A Model for Restricted Ocean Basins. In: Nature and origin of Cretaceous Carbon-rich Facies (S.O. Schlanger and M. B. Cita, eds.). Academic Press, 197-207.

Orals: Tue, 16 Apr | Room G2

Chairpersons: Daniel Ariztegui, Anelize Bahhniuk, Mónica Sánchez-Román
Lakes, oceans and isotopes
14:00–14:10
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EGU24-3855
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On-site presentation
Helmut Weissert

 

Fundamentals of C-isotope geochemistry were established in the mid-1950s. Its use as a proxy in paleoceanography and paleoclimatology was long underestimated. While oxygen isotope geochemistry was identified early as a powerful tool in Ice Age history, carbon isotope geochemistry evolved only in the 1970s into a valuable instrument in paleoceanography and paleolimnology.  In 1976, Judy McKenzie was offered the chance to build the first stable isotope lab at ETH Zürich. Judy was, together with her team, among the first geoscientists searching for applications of C-isotope geochemistry in paleoceanography and limnogeology. Seasonal fluctuations in lake productivity were monitored in C-isotope composition of lake sediments and C-isotope records measured in pelagic carbonates served as a tracer of circulation and productivity in Cenozoic and Mesozoic oceans. In the eighties C-isotope geochemistry was recognized as a proxy of the global carbon cycle and its history was traced in C-isotope records measured in pelagic carbonates. The ETH Lab contributed with the several publications on C-isotopes and the carbon cycle to the seminal Chapman conference on “The Carbon Cycle and Atmospheric CO₂: Natural Variations Archean to Present” (Florida, 1984). An improved understanding of marine carbon fractionation processes allowed to use paired carbonate and organic carbon isotope analyses as a proxy for past atmospheric carbon dioxide concentrations. Today C-isotope geochemistry is established as a most valuable tool in paleoclimatology and paleoceanography, in sedimentology and geomicrobiology.

How to cite: Weissert, H.: Early days of carbon isotope geochemistry in paleoceanography and limnogeology - tales from Judy’s ETH Lab , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3855, https://doi.org/10.5194/egusphere-egu24-3855, 2024.

14:10–14:30
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EGU24-12046
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solicited
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On-site presentation
Peter Swart and Chaojin Lu

The pioneering work of Judith McKenzie and her colleague Kerry Kelts identified the presence of dolomites associated with the oxidation of organic material in sediments obtained from the Deep Sea Drilling Project.  This discovery led to the wide spread recognition that dolomites form in association with microbial sulfate reduction.   Later Judy’s work proposed that the microbes were more than agents of creating a suitable geochemical environments, but actually were instrumental in precipitating dolomite.  This work stimulated the research of many, but the questions have always arisen as to what degree microbial processes are responsible for dolomite formation and other carbonate minerals in the ancient record.  Some have proposed different geochemical indices such as carbon or magnesium isotopes or the concentration of certain elements, maybe diagnostic of microbial processes.  However, these tools frequently provide equivocal evidence and therefore are not definitive. In this presentation we provide several examples of the use of a new geochemical tool, the dual clumped isotope proxy (Δ47 and Δ48).  Deviations from equilibrium, particular of Δ48 values, provide strong evidence of the influence of different mechanisms of the precipitation of dolomite and calcite.  In this presentation we present several examples in which the dual clumped isotope proxy has been employed.  These include not only dolomites, but also meteoric LMC calcite cements, previously believed to have form without the influence of microbial processes.  While the dual clumped proxy may also yield equivocal results, it will be a welcome addition to the tools used to understand the roles of microbes during carbonate precipitation.

 

How to cite: Swart, P. and Lu, C.: Identification of microbial influences on carbonate precipitation using dual clumped isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12046, https://doi.org/10.5194/egusphere-egu24-12046, 2024.

14:30–14:40
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EGU24-11488
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On-site presentation
Flavio Anselmetti, Dominic Perler, Simone Benguerel, Hansjörg Brem, Florence Gilliard, Jens Hornung, Thomas Keiser, Urs Leuzinger, Sebastian Schaller, Sönke Szidat, Hendrik Vogel, and Martin Wessels

Judith McKenzie contributed pivotal studies in using lacustrine sedimentary systems as natural analogues for the much larger marine environment. In this context, she introduced marine depositional processes and concepts to lakes, and in turn, used their smaller dimensions and more controllable boundary conditions to gain more insights into the controls of lithological and geochemical signals in any sedimentary system. One example of using this approach is the study of the prograding mixed carbonate-siliciclastic shallow-water shelf of Lake Constance, that is characterized by endogenic carbonate production ('lacustrine chalk'), water currents, progradation and related drift deposits, as they also have been investigated in the marine domain. A recent bathymetric survey of Lake Constance revealed ~170 mysterious mounds composed of loosely deposited rocks aligned in a ~10-km-long chain along the southern Swiss shoreline of Lake Constance in a water depth of 3–5 m. The mounds are 10–30 m in diameter and up to 1.5 m high. Over their entire length of occurrence, the mounds are estimated to be composed of ~60 million individual boulders, with a total weight of ~78,000 t. A ground penetrating radar (GPR) survey showed that the mounds are not linked to the glacial substrate but were rather deposited artificially on the edge of a prograding shelf composed of mixed carbonate-siliciclastic Late Glacial to Holocene lake sediments. Here, we present the results of a coring campaign with four piston cores along a GPR transect across one of the mounds. The cores recovered the full postglacial sedimentary succession all the way into the basal till that is overlain by lacustrine sediments dating back to ~14,400 cal. BP. The four cores are merged into a ~12.4-m-long composite section reflecting continuous sedimentation from the siliciclastic-dominated Late Glacial to the carbonate-rich Late Holocene. The stratigraphic horizon representing the mound's construction was radiocarbon-dated to ~5,600–5,300 cal. BP, placing them in the Neolithic period. This age was confirmed by radiocarbon dating of wood samples collected during underwater excavation of the mounds. Geochemical analysis of the Holocene sedimentary succession shows generally high carbonate contents (average of 69%). The interval from 5,750 to 4,950 cal. BP, a part of the mound period, is characterized by a Holocene minimum in carbonate content (average of 57%) and by larger mean grain sizes. Comparing these values to those from a recent surface-sediment depth transect indicates that this was a period of rather low lake levels, which might have favored mound construction. Correlations to nearby archaeological sites and to the general West-Central European lake-level record indicates that the mounds likely were built during a short phase of low lake levels during a general trend of climatic cooling followed by a lake-level transgression.

How to cite: Anselmetti, F., Perler, D., Benguerel, S., Brem, H., Gilliard, F., Hornung, J., Keiser, T., Leuzinger, U., Schaller, S., Szidat, S., Vogel, H., and Wessels, M.: Swiss lakes as model oceans: A mixed carbonate-siliciclastic shelf drift hosting a 10-km-long chain of 170 submerged Neolithic mounds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11488, https://doi.org/10.5194/egusphere-egu24-11488, 2024.

14:40–14:50
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EGU24-9689
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On-site presentation
Angelo Camerlenghi, Christian Huebscher, Aaron Micallef, Claudia Bertoni, Giovanni Aloisi, and Johanna Lofi

From 2016 to 2020, Judy McKenzie joined the community of COST Action CA15103 - Uncovering the Mediterranean salt giant (MEDSALT) to verify her hypothesis that an ongoing dolomitization front exists in the pelagic sediments overlying Messinian evaporites below the Messina Abyssal Plain, in ~4000 water depth in the Ionian Sea, central Mediterranean. Legacy scientific ocean drilling data from DSDP Leg 42A, Site 374 reveal a 25 m-thick latest Miocene dolomitic mudstone capped by 8.5 m of earliest Pliocene dolomite above gypsum/dolomitic mudstone cycles and anhydrite and salts. The Pliocene dolomite is made of dolomicrite with an unusual crystal morphology, suggesting diagenetic replacement of the original pelagic calcite ooze. The underlying latest Messinian dolomitic mudstone with minor gypsum layers contains Ca-rich dolomite with white spherules of lüneburgite. DSDP Site 374 shipboard interstitial water geochemical profiles further indicate that saline brine is diffusing upwards into the early Pliocene dolomicrite. A significant decrease in sulfate concentration suggests ongoing bacterial sulfate reduction, whereas the chloride profile remains constant.

Following discussion and brainstorming with Judy, a geophysical site investigation cruise on the RV Meteor was organized by the University of Hamburg. Cruise M-144 was conducted in 2018 with a multi-channel reflection seismic survey centered at DSDP Leg 42A, Site 374 using a 6 kjoule sparker source and a digital 144-channel streamer with an active length of 600 m. The objectives of the cruise were to:

  • Obtain a detailed seismic stratigraphy in the surrounding of DSDP Leg 42A, Site 374, which was targeted as re-occupation Site within IODP Proposal 857C - The demise of a salt giant: climatic-environmental transition during the terminal Messinian Salinity Crisis (Claudia Bertoni and co-workers);
  • Estimate the lateral dimensions of the combined dolomite/evaporite lithologic units in the lonian Sea.

Objective 1 was achieved, and the drilling proposal supported by the R/V Meteor Site Survey was forwarded by the Science Evaluation Panel to the JR Facility Board for scheduling. Unfortunately scheduling could not happen before the end of IODP.

Objective 2 was based on the assumption that the acoustic impedance contrasts induced by the dolomitization front could be detected in relatively high-resolution seismic reflection data. In the M-144 data, the uppermost Messinian dolomite- and gypsum-bearing sediments are characterized by a package of strong and positive reflection amplitudes (High Amplitude Reflection Package, HARP). The lateral continuity of the reflections is very low and the upper boundary is quite irregular. Based on the seismic data, the areal extent of the dolomite deposit beneath the lonian abyssal plain can be estimated in a few tens of thousands km2. This would be the Rosengarten of the Ionian Sea that Judy was looking for.

This abstract will present previous and new seismic data, collected with Meteor Cruise M-199 in February-March 2024 with similar acquisition parameters to those of M-144, to further address objective 2. However, crucial sedimentological and geochemical data to validate Judy’s fascinating hypothesis can only be derived from new scientific drilling.

How to cite: Camerlenghi, A., Huebscher, C., Micallef, A., Bertoni, C., Aloisi, G., and Lofi, J.: The intriguing hypothesis of a modern “Rosengarten” in the subsurface of the deep Ionian Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9689, https://doi.org/10.5194/egusphere-egu24-9689, 2024.

14:50–15:00
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EGU24-2826
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On-site presentation
Elisabetta Erba and Mariano Parente

During the Cretaceous, the Berriasian-Aptian interval witnessed a transition from a relatively cool climate with intermittent polar ice to a greenhouse state that persisted throughout the Late Cretaceous. These palaeoclimatic changes were associated with the construction of Large Igneous Provinces (LIPs), which significantly perturbed the ocean-atmosphere system by introducing large amounts of CO2, trace metals, and micronutrients, thereby impacting the biosphere. Our study focused on the Tethyan Ocean during the Early Cretaceous, examining the resilience of planktonic and shallow-water benthic calcifying algae to environmental changes. We observed their adaptation, recovery dynamics, and the influence of palaeoCO2 levels on their resilience. Calcification patterns of calcareous nannoplankton served as a proxy for ecological and engineering resilience. While calcareous nannoplankton as a whole showed high resistance, individual taxa exhibited varying levels of resilience. Nannoconids, particularly narrow-canal ones, were highly sensitive and had low resistance. In contrast, Watznaueria barnesiae showed the least sensitivity and highest resistance, likely due to its adaptive strategies and long lifespan. Nannoplankton calcification recovery (engineering resilience) from the Weissert Event took approximately 3 million years. After OAE1a, instead, nannoplankton did not return to pre-perturbation conditions. In shallow-water platforms, Dasycladales, aragonitic benthic calcifiers, exhibited lower resilience compared to nannofossils. They experienced a decline in species diversity across both the Weissert Event and the OAE 1a, which could indicate higher sensitivity to reduced carbonate saturation under high pCO2 conditions. After the Valanginian Weissert Event, Dasycladales were able to recover, albeit they show a much lower engineering resilience compared to nannoconids, as it took nearly 10 million years to revert to pre-disturbance diversity. The OAE 1a represented a more intense perturbation: their decrease of species diversity was much more drastic and permanent, and Dasycladales were unable to recover, losing their dominant role as carbonate platform biocalcifiers for the remainder of the Cretaceous. Our study provides an assessment of the resilience of Tethyan phytoplanktonic and shallow-water benthic calcifying algae to disturbances during the Early Cretaceous, with implications for tipping points associated with palaeo-CO2 levels. The differential responses in terms of timing and magnitude and the recovery dynamics contribute to the understanding of the potential impacts of current and future global changes on the resilience of marine ecosystems and the thresholds that may lead to ecological crises.

How to cite: Erba, E. and Parente, M.: The resilience of Tethyan planktonic and benthic calcifying algae to Early Cretaceous perturbations: comparison between the Valanginian Weissert Event and the early Aptian Oceanic Anoxic Event 1a, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2826, https://doi.org/10.5194/egusphere-egu24-2826, 2024.

(Bio)minerals
15:00–15:10
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EGU24-18784
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ECS
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On-site presentation
Sarah Bonilla-Correa, Encarnación Ruiz-Agudo, María Pilar Asta Andrés, Lisa Huber, Concepción Jiménez de Cisneros, and Cristina Liñán-Baena

The Nerja Cave is located in an alpine folding chain, specifically in the Inner Zone of the Betic Range (SE, Spain), and it is developed within middle Triassic dolomite marbles (Carrasco et al., 1998). Its mean annual temperature is 18.1 ± 0.1 °C (Jiménez de Cisneros et al., 2021). Moon-milk deposits, a white substance present inside caves. Samples were collected in the touristic part of the cave and were characterized using synchrotron high-resolution XRD (HR-XRD), X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FTIR), and transmission electron microscopy (TEM). We detected the presence of amorphous magnesium carbonate (AMC), huntite, and dolomite. Additionally, the AMC formation and the subsequent crystallization process were studied in laboratory conditions to gain a more comprehensive understanding of the processes occurring in the cave. We performed titration experiments using magnesium and calcium chloride solutions and potassium carbonate buffers to investigate nucleation and transformation processes at elapsed times (1, 2, 7, and 14 days). The filtered solids were characterized by XRD, SEM, FTIR, Raman, and TEM. The results of these analyses highlighted the critical role of AMC in the formation of Ca-Mg crystalline carbonates.

Acknowledgment to financial support is given by the Spanish Ministry of Science and Innovation through the research project PID2021-125305NB-I00 and the project from the Junta de Andalucía through the EMERGIA research program under the grant agreement EMERGIA20_38594.

Carrasco F, Durán JJ, Andreo B, Liñán C, Vadillo I (1998) Consideraciones sobre el karst de Nerja. Karst en Andalucía 173–181

Jiménez de Cisneros, C., Peña, A., Caballero, E., & Liñán, C. (2021). A multiparametric approach for evaluating the current carbonate precipitation and external soil of Nerja Cave (Málaga, Spain). International Journal of Environmental Research, 15, 231-243.

How to cite: Bonilla-Correa, S., Ruiz-Agudo, E., Asta Andrés, M. P., Huber, L., Jiménez de Cisneros, C., and Liñán-Baena, C.: Non-Classical Crystallization in Moon-Milk Deposits in the Nerja Cave, Spain , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18784, https://doi.org/10.5194/egusphere-egu24-18784, 2024.

15:10–15:20
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EGU24-22168
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On-site presentation
Jean Rene Marius Tuyishime, Edith Hammer, Martí Pla i Ferriol, Karina Thånell, Carl Alwmark, and Hanbang Zou

Routine methods of concrete production contribute 9% to anthropogenic CO2 emissions and demands 2-3% energy, along with 9% water consumption. Despite these environmental costs, concrete structures frequently undergo deterioration due to unavoidable physical, chemical, and biochemical stressors, resulting in cracks that permit gas diffusion, water, and pollutants penetration, ultimately compromising its integrity and internal steel reinforcement. Microbially induced CaCO3 precipitation has emerged as a sustainable way of concrete protection and self-healing. However, the detailed mechanisms and formation of various CaCO3 polymorphs remain inadequately explored.

In this ongoing study, samples were prepared by inoculating a growth medium, containing urea and nutrients, with different fungi under diverse growth conditions. High-resolution Scanning Transmission X-ray Microscopy (STXM) in the Ca 2p energy range (340−360 eV) were employed to investigate the fungal-induced formation and chemical speciation of CaCO3 at the cellular base or interface between hypha and the surrounding ions. To discriminate potential absorption saturation effects, only spectra (NEXAFS) extracted from thin regions (≈ 30 nm) of the entire sample thickness were considered for spectral analysis. Furthermore, SEM with EDS was used to reveal morphology and elemental distribution, and composition in studied sample thin sections.

The preliminary results suggest that the samples spectra resembled those of pure calcite and aragonite, according to reference spectra. These are the most stable CaCO3 biomaterials. Notably, the intensity of weak peaks preceding each main resonance peak of the Ca L3 and Ca L2 edges were relatively smaller for aragonite-dominated spots than in calcite-dominated spots. As revealed by the spectral analysis, some fungi showed the ability to form CaCO3, predominantly in the form of either calcite or aragonite. Other fungal strains demonstrated a more heterogeneous precipitation behavior by forming both phases, albeit in distinct nano spots within the same sample. Furthermore, a few fungal species exhibited the ability to precipitate other crystalline Ca minerals, most likely CaPO4, as shown by SEM/EDS analyses.

In conclusion, the results of this ongoing investigation provided not only valuable insight on distinctive fungal behaviors in the biomineralization process, but also revealed spatial nanoscale heterogeneity in CaCO3 speciation under the same fungal conditions.

How to cite: Tuyishime, J. R. M., Hammer, E., Pla i Ferriol, M., Thånell, K., Alwmark, C., and Zou, H.: Nanoscale insights: unraveling fungal-induced precipitation of CaCO3 polymorphs for self-healing concrete, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22168, https://doi.org/10.5194/egusphere-egu24-22168, 2024.

15:20–15:30
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EGU24-14998
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ECS
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On-site presentation
Brianne Palmer, Sabina Karacic, Gabriel Bierbaum, and Carole Gee

The formation of leaf compressions is dependent on the type of sediment in which the leaves are buried and on burial depth because greater burial depth leads to a more anoxic environment conducive to fossilization. Recent research has hypothesized that the presence of a microbial biofilm on leaf surfaces in the early stages of decay also enhances preservation. In decaying leaves, the biofilm community is likely influenced by the same factors: sediment type and burial depth. Here we investigate experimentally the microbial community composition of microbial biofilms formed on floating and buried leaves of living Ginkgo in four sediment types—montmorillonite clay, kaolin clay, quartz sand, and pond mud. Leaves were placed in aquariums with pond water under identical light conditions and room temperatures for three months. The leaves, sediments, and pond water were then evaluated with 16S and ITS sequencing to identify the bacterial and fungal communities. We found that the biofilms on the floating and buried leaves differed in their basic microbial community composition. The leaves buried in the kaolin clay showed the most distinctive microbial communities, while the montmorillonite clay buried leaves contained several genera noted for biomineralization. In general, the buried leaves had microbial communities that were more diverse than those on the floating leaves and richer in anaerobic microbes and biomineralizers. These results suggest that biofilms form best in very fine-grained sediments with low organic content, such as kaolin and montmorillonite clays, and under burial conditions fostering anaerobic environments and the incorporation of minerals that enhance biomineralization on leaf surfaces. Our results provide new insights into the role of microbial biofilms and microbe–sediment interactions in the early stages of leaf fossilization.

How to cite: Palmer, B., Karacic, S., Bierbaum, G., and Gee, C.: Deciphering Fossilization Pathways: Sediment Composition Impacts Biofilm-Forming and Biomineralizing Microbial Communities in Early Stages of Leaf Taphonomy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14998, https://doi.org/10.5194/egusphere-egu24-14998, 2024.

15:30–15:40
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EGU24-11076
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On-site presentation
Jens Kallmeyer, Fátima Ruiz-Blas, Cynthia Henny, James Russell, Hendrik Vogel, and Aurèle Vuillemin

Ferruginous conditions prevailed in the oceans through much of Earth’s history. However, past biogeochemical cycling inferred from mineral components in ancient iron formations remain poorly constrained in terms of microbial processes prior to lithification. In Lake Towuti, Indonesia, ferruginous sediments are deposited under stratified conditions that mimic the Earth’s early oceans. Over geologic time, Lake Towuti experienced dynamic redox conditions, resulting in variable ferric and organic matter fluxes feeding microbial life at the lake floor. Although environmental conditions exert control over microbial assemblages at the time of deposition, geochemical evolution of these substrates select for specific groups of microorganisms capable of maintaining metabolic activity during entombment.

The 100 m long core retrieved by the ICDP Towuti Drilling Project allowed for investigations of the subsurface biosphere, pore water geochemistry and diagenesis of iron minerals. We established the abundance and phylogenetic distribution of microorganisms along the 1 Ma stratigraphic record, and created integrated environmental and geochemical datasets in order to identify the main taxa and metabolic features involved in sediment mineralization. Ferruginous conditions predominantly selected for Bathyarchaeia. Relevant metabolisms identified from metagenome-assembled genomes indicated sulfur transformation and (homo)acetogenesis, suggesting that heterotrophic dark carbon fixation and cryptic sulfur cycling linked to iron minerals may be prominent features of microbial life in this ferruginous system.

Changes in environmental processes and conditions lead to variability in metal and organic substrate concentrations with depth, while sustaining different microbial processes in various depth intervals. Geochemical profiles reflect microbial activity after deposition and demonstrated mineral precipitation induced by microbial mineralization. Precipitation of magnetite (Fe3O4), millerite (NiS), siderite (FeCO3), and vivianite (Fe3[PO4]2 · 8H2O) from pore water constitute biosignatures of microbial iron and sulfate reduction, fermentation and methanogenesis. For example, oxygen, iron, and carbon isotopes measured on siderites enabled us to differentiate between depositional and diagenetic signals. Siderite δ18O signatures reflected in-lake hydrological fluctuations. Low negative δ56Fe values recorded periods of water column stratification and oxygenation events, with minor diagenetic redistribution. Negative δ13C signatures reflected incorporation of biogenic HCO3- during organic matter fermentation, whereas positive δ13C excursions indicated mass balance due to increased production of biogenic methane.

How to cite: Kallmeyer, J., Ruiz-Blas, F., Henny, C., Russell, J., Vogel, H., and Vuillemin, A.: Subsurface biosphere, pore water geochemistry and mineral biosignatures along the 1 Ma sediment archive of ferruginous Lake Towuti, Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11076, https://doi.org/10.5194/egusphere-egu24-11076, 2024.

Coffee break
Chairpersons: Patrick Meister, Patricia Roeser, Michael E. Böttcher
Dolomite
16:15–16:35
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EGU24-1334
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solicited
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On-site presentation
Angelika Kühnle

The hydration structure at the mineral-water interface is decisive for understanding fundamental reactions taking place at mineral surfaces, including mineral dissolution, growth and weathering. Recent advancements in three-dimensional atomic force microscopy (3D AFM) have opened the potential to directly image the hydration structure above a surface, providing unparalleled structural insights into mineral−water interfaces [1].

Here, the hydration structures at the calcite-water [2] and dolomite-water [3] interface will be presented with an emphasis on discussing the differences that arise from the presence of magnesium in dolomite as compared to calcium in calcite. Analysing site-specific vertical positions of hydration layers and comparing them with molecular dynamics simulations unambiguously unravels the minute but decisive difference in ion hydration and provides a clear means for telling calcium and magnesium ions apart.

 

[1]         T. Fukuma, Y. Ueda, S. Yoshioka, H. Asakawa, Phys. Rev. Lett. 2010, 104, 016101

[2]         H. Söngen, M. Nalbach, H. Adam, A. Kühnle, Rev. Sci. Instrum. 2016, 87, 063704

[3]         H. Söngen, C. Marutschke, P. Spijker, E. Holmgren, I. Hermes, R. Bechstein, S. Klassen, J. Tracey, A. S. Foster, A. Kühnle, Langmuir 2017, 33, 125

How to cite: Kühnle, A.: Hydration structure on dolomite: Telling calcium and magnesium apart, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1334, https://doi.org/10.5194/egusphere-egu24-1334, 2024.

16:35–16:45
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EGU24-8190
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On-site presentation
Stefano Bernasconi, Ricarda Rosskopf, Nathan Looser, and Jordon Hemingway

The formation of dolomite in the sediments of the Sabkha of Abu Dhabi was the subject of Judy’s PhD thesis and the question of the origin of dolomite remained at the center of her scientific interests throughout her career. The main focus was on the influence of microbial activity on dolomite formation, both in the field and through laboratory experiments. Over the years, Judy’s contributions particularly advanced our understanding of the role of microbes in the formation of dolomite.

With the development of clumped isotope geochemistry, a new tool is now available to better characterize the conditions leading to the formation of dolomite in the geological record. This tool exploits the preference of13C-18O bonds in carbonate molecules to form with decreasing temperature and provides a thermometer that can be used to constrain the formation temperature and the oxygen isotope composition of the fluids involved in the precipitation of dolomite. The interpretation of dolomite clumped isotopes in the geological record, however, is complicated by the fact that early-diagenetic dolomite is generally poorly ordered and non-stoichiometric, and it converts to a more stable form during diagenesis. In this contribution we will present case studies from the Alps to show how the original clumped isotope compositions of dolomite are modified during diagenesis under different thermal regimes, and we will discuss the preservation of clumped isotope signatures in dolomite.

How to cite: Bernasconi, S., Rosskopf, R., Looser, N., and Hemingway, J.: Understanding the origin of dolomite in the sedimentary record: the contribution of clumped isotope thermometry., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8190, https://doi.org/10.5194/egusphere-egu24-8190, 2024.

16:45–16:55
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EGU24-3489
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On-site presentation
Meng Ning, Judith A. McKenzie, Crisogono Vasconcelos, and Bing Shen

Early lithification of carbonate mud during the subaerial exposure stage, under semiarid conditions, has been proposed to facilitate dolomite formation. However, how the biogeochemical processes during subaerial diagenesis promote dolomite formation remains unclear. Here, we employ a multiproxy approach to investigate the process of dolomite formation by analyzing modern dolomite crusts forming in lagoon Brejo do Espinho (LBE). Petrological analysis reveals that the crusts comprise coexisting high-Mg calcite (HMC) and dolomite. Low Fe and Mn concentrations indicate the formation of dolomite under oxic conditions, while a higher Sr concentration in well-lithified crust suggests primary bacterial-induced dolomite precipitation. The Mg isotopic composition of the crusts exhibits a lighter value compared to that of modern sabkha dolomite, suggesting different dolomitization processes and Mg sources. More negative δ13C values of the crusts than unlithified carbonate mud in LBE, indicating the incorporation of 13C depleted organic carbon. The biogeochemical processes related to decaying organic matter during subaerial diagenesis generate partially oxidized organic matter that promotes Mg2+ dehydration and enhances the dissolution of primary HMC, ultimately triggering the transition of HMC to dolomite or/and direct dolomite precipitation. The ancient "dolomite factory" operated through cyclic deposition of carbonate sediments and penecontemporaneous subaerial diagenesis.

How to cite: Ning, M., McKenzie, J. A., Vasconcelos, C., and Shen, B.: Dolomite formation during penecontemporaneous subaerial diagenesis: Evidence from modern dolomite crusts forming in lagoon Brejo do Espinho, Brazil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3489, https://doi.org/10.5194/egusphere-egu24-3489, 2024.

16:55–17:05
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EGU24-17981
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ECS
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On-site presentation
Peter Methley, Clancy Jiang, Justin Strauss, and Nicholas Tosca

As a metastable precursor to crystalline carbonate minerals, amorphous calcium-magnesium carbonate (ACMC) has been implicated in the formation of enigmatic fabrics and minerals, such as calcite microspar, fibrous cements and fabric-retentive dolomite, that characterise both modern and ancient carbonate systems (e.g. Wang et al., 2012). The detection of nanocrystals within ancient dolomicrite, using high-resolution transmission electron microscopy, strengthens this hypothesis (Meister & Frisia, 2019).

However, it has remained unclear whether natural, abiotic processes could produce ACMC, because of a requirement for extreme carbonate supersaturation. This study tests the hypothesis that – in the presence of micromolar concentrations of aqueous phosphate, which can inhibit aragonite precipitation (Roest-Ellis et al., 2021) – the evaporation of Neoproterozoic seawater may have increased alkalinity, pH, and carbonate saturation enough to precipitate ACMC in shallow-water settings.

We conducted evaporation experiments using phosphate-free and phosphate-bearing ([PO4]Total = 50 μmol/kg) synthetic seawater with Tonian composition. Solution samples, pH and alkalinity measurements were collected at regular intervals over 9-14 days. Final solids were collected and analysed using X-ray diffraction, Raman spectroscopy, and scanning electron microscopy.

Experimental data show that phosphate-bearing seawater undergoing evaporative concentration reaches increasingly high alkalinity, pH and carbonate saturation until the first solid phase forms. Analytical data indicate that ACMC precipitated during evaporation of phosphate-bearing seawater, whereas aragonite dominated in phosphate-free systems. When evaporating the water more slowly, the ACMC is observed to recrystallise into other metastable carbonate minerals – either fibrous monohydrocalcite or needles of hydromagnesite, depending on the solution’s initial Mg/Ca ratio.

These results suggest that low concentrations of species which inhibit crystalline carbonate precipitation allow extreme carbonate supersaturation to be reached upon evaporation. We speculate that this pathway may have facilitated platform-scale production of metastable precursors to syndepositional and early diagenetic dolomite in shallow-water late Proterozoic carbonate sediments, consistent with sedimentological and stratigraphic evidence for evaporation.

How to cite: Methley, P., Jiang, C., Strauss, J., and Tosca, N.: Evaporation of seawater produces amorphous calcium-magnesium carbonate when aragonite precipitation is inhibited, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17981, https://doi.org/10.5194/egusphere-egu24-17981, 2024.

Microbialites
17:05–17:15
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EGU24-3371
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On-site presentation
Nicola McLoughlin and Karabo Mahlapha

At Schoenmakerskop on the coast near Gqeberha (Port Elizabeth), modern microbialite deposits are forming where CaCO₃-supersaturated groundwater emerges at the contact between Pleistocene aeolianites and the underlying Cape Supergroup bedrock (Edwards et al. 2017). Two different systems were investigated: well-laminated spring line tufa deposits above intertidal beachrocks, and a series of barrage pools with active and remnant rimstone deposits showing thrombolitic and laminated mesofabrics. Petrographic light-microscopy and scanning electron microscopy (SEM) were used to investigate the relative contributions of biotic and abiotic processes in the formation of these microbialites.

Light-microscopy identified isopachous light-brown sparry crusts consisting of tabular or platy carbonate, interpreted to have formed predominantly by chemical precipitation. Hybrid crusts were also found comprising alternating organic-rich layers and sparry crusts, along with colloform and micritic microtextures. Fossilised algal filaments were identified and SEM observations revealed both densely and loosely packed layers of hollow, unbranched filaments encrusted by microcrystalline carbonate. Exceptionally well-preserved draping biofilms were also found in some samples. Evidence for trapping and binding of clastic material was very limited, with only occasional diatom fragments. Taken together our observations point to a system dominated by chemical precipitation of carbonate with rapid precipitation leading to exceptional preservation of biofilms in submerged samples, and entombment of algal and sometimes microbial filaments. Evidence for biologically induced extracellular mineralisation of the algal filaments and microbial biofilms is recorded in these microbialites. The potential of these deposits to serve as analogues for chemical stromatolites in the fossil record is explored.

Edwards et al. (2017). Macro- and Meso-fabric structures of peritidal tufa stromatolites along the Eastern Cape coast of South Africa. Sedimentary Geology 359: 62-75.

How to cite: McLoughlin, N. and Mahlapha, K.: Microtextures of modern tufa stromatolites from the peritidal zone near Schoenmakerskop, Eastern Cape, South Africa: investigating the relative contributions of microbes, algae and chemical precipitation to microbialite growth   , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3371, https://doi.org/10.5194/egusphere-egu24-3371, 2024.

17:15–17:25
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EGU24-4713
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On-site presentation
Simon V. Hohl, Yibo Lin, Sebastian Viehmann, and Ashley Martin

Hamelin Pool in Shark Bay, Western Australia, is a natural laboratory to study in situ stromatolitic carbonate formation in a hypersaline lagoon. Stromatolitic carbonates sampled at three different tidal environments (supratidal, intertidal and subtidal; cf. Martin et al., 2023) show a gradual increase in Ba isotopic compositions (d138Ba) from -0.12 ‰ to modern open ocean values (up to 0.6 ‰) with decreasing Ba concentrations following classic Rayleigh pattern. Declining Ba/Ca ratios (0.93 to 0.32) follow conservative mixing trends with increasing Co, Li, Sr and Ni concentrations from the shore to subtidal environments. Due to the lack of riverine influx into Shark Bay, groundwater discharge is the likeliest source for two end-members mixing with seawater. We observe fingerprints of the groundwater end-member in a supratidal sample showing particular low, stable Ba isotope values (-0.12 ‰), which further corresponds with elevated Mn/Sr ratios and the lowest O isotope compositions (2.9 ‰) as an indicator for a meteoric origin. This end-member likely reflects carbonate precipitation near shore under the influence of groundwater discharge and reaction with high alkalinity fluids derived from the local Tamala Limestone aquifer (d138Ba = 0.09 to 0.24 ‰ at 0.3 to 19 PSU; cf., Mayfield et al., 2021). In contrast, the stromatolitic carbonates that form in equilibrium with a saline end-member show heavy Ba isotope compositions (0.57‰).

Injection of alkaline groundwaters into the hypersaline waters of Hamelin Pool likely contributed to an enhanced rate of carbonate precipitation, possibly catalysed by nucleation within or onto extra-polymeric substances of diverse microbial mats. Interaction of benthic microbes, especially cyanobacteria, in alkaline waters may offer promising carbon sequestration pathways in the modern high pCO2 atmosphere and small-scale mitigation to the harmful impacts of the current climate crisis.

References: Martin et al., 2023, GCA; Mayfield et al., 2021, Nature Communications

How to cite: Hohl, S. V., Lin, Y., Viehmann, S., and Martin, A.: Conservative mixing of highly alkaline groundwater with hypersaline seawater at Shark Bay recorded by Ba isotopic compositions in stromatolitic carbonates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4713, https://doi.org/10.5194/egusphere-egu24-4713, 2024.

Ferromanganese concretions
17:25–17:35
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EGU24-16540
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ECS
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On-site presentation
Joonas Wasiljeff, Johanna Salminen, Andrew Roberts, Pengxiang Hu, Maxwell Brown, Jukka Kuva, Sari Lukkari, Ester Jolis, Atko Heinsalu, Wei-Li Hong, Aivo Lepland, Sten Suuroja, Joni Parkkonen, and Joonas Virtasalo

Ferromanganese concretions, ubiquitous both in deep ocean environments and shallow-water coastal regions worldwide, are the subject of renewed scientific interest due to their multifaceted importance as underwater habitats, critical raw material sources, and invaluable repositories of paleoceanographic information. The magnetic properties of ferrimagnetic minerals within concretions, as well as the origins of their natural remanent magnetization, represent areas of study that are still in their early stages of exploration. Recent findings have unveiled the role of biogenic magnetite in the development of biogeochemical remanent magnetization within deep ocean crusts and nodules, pointing to the influence of microbial catalysis in their precipitation. While extensive research on magnetic properties of deep ocean Fe-Mn deposits has been conducted, similar investigations in fast-growing shallow-water concretions have remained notably absent. Furthermore, the specific mechanisms governing the formation and (bio)mineralization of diverse concretion morphotypes (crust-like, discoidal and spheroidal) in shallow-water setting remain enigmatic.

Our work focuses on ferromanganese concretions in shelf areas and seas, with samples from the the Baltic Sea. We report here the magnetic characteristics, microstructure, and origin of Baltic Sea concretions, which sheds light on their formation processes and environmental implications. To achieve this, we combined nano- and micro-computed tomography imaging, electron microscopy, micro-X-ray fluorescence spectroscopy, and a suite of detailed magnetic property investigations. Spheroidal concretions are prevalent in many parts of the coastal Baltic Sea and contain a higher proportion of fine-grained magnetite with evidence of bullet-shaped magnetofossils produced by magnetotactic bacteria. Bullet-shaped magnetofossils are usually produced in eutrophic and less oxic environments, as supported by the possible presence of rhodochrosite, which indicates diagenetic Mn release from surrounding sediments, especially in deeper water settings. In contrast, crust and discoidal concretions in shallower waters contain higher proportions of detrital (including magnetically hard) minerals, which reflects an increased continental influence. Microstructural analysis of the concretions reveals multiple growth stages, with laminated, columnar, and dendritic structures indicating varying hydrodynamic and depositional conditions. In general, spheroidal concretions seem to form in more tranquil settings compared to discoidal and crust concretions.

Our results provide insights into the complex interplay of environmental conditions, biogenic processes, and mineralogical composition that influence ferromanganese concretion growth and magnetic properties in the Baltic Sea. We further argue that biogenic magnetite contributes globally to the remanent magnetization of shallow and deep-sea ferromanganese concretions.  

This work was supported by the Research Council of Finland (Fermaid project, grant 332249).

How to cite: Wasiljeff, J., Salminen, J., Roberts, A., Hu, P., Brown, M., Kuva, J., Lukkari, S., Jolis, E., Heinsalu, A., Hong, W.-L., Lepland, A., Suuroja, S., Parkkonen, J., and Virtasalo, J.: Morphology-Driven Magnetic Characteristics of Shallow-Water Ferromanganese Concretions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16540, https://doi.org/10.5194/egusphere-egu24-16540, 2024.

17:35–17:45
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EGU24-9000
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ECS
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On-site presentation
Renata Majamäki, Lotta Purkamo, Jenni Hultman, Joonas Wasiljeff, Eero Asmala, Pirjo Yli-Hemminki, Kirsten Jorgensen, Karoliina Koho, Jukka Kuva, and Joonas Virtasalo

The transition to renewable energy and the acceleration of technology demand vast amounts of hi-tech metals that are critical in green energy technology. Due to increasing demand for hi-tech metals, rising interest in mining from more unconventional sources, such as the seafloor, is inevitable. Ferromanganese concretions, which are centimeter-scale accumulations of iron and manganese oxides, are common in the Baltic Sea. In addition to iron and manganese, concretions contain hi-tech metals, such as cobalt. The Fe-Mn concretions are important reaction surfaces for diverse microbial communities, and they regulate metal and nutrient cycling in the concretions. Extraction of Fe-Mn concretions from the Baltic Sea could impact the seafloor ecosystem, biogeochemical cycling of elements, concretion growth, and recovery. This study provides information on Baltic Sea Fe-Mn concretion growth rates and conditions in laboratory experiments.

The ferromanganese concretions were collected from the Baltic Sea during May and June 2022 for a 12-week laboratory incubation and metal tracer experiments. Triplicate concretion samples and one abiotic control sample were collected into bottles containing artificial brackish seawater and incubated in the dark at +5 °C in an orbital shaker at 100 rpm to imitate seafloor conditions. Bottles were sampled at the beginning and the end of the 12-week incubation experiment. We assessed the concretion growth with X-ray computed tomography and freshly formed concretion material with a scanning electron microscope. We analyzed the headspace methane concentrations and pH of the incubation solution. We measured phosphorus and metal (Mn, Fe, Co, V, Ni, Zn, Mo) concentrations of the incubation solution with triple quadrupole ICP-MS.

The results provide new information on the growth rates and conditions of Fe-Mn concretions. It was confirmed that concretions grew in laboratory conditions, and new growth was as much as 10 µm in 12 weeks. Headspace methane concentrations decreased in all samples during incubation, but least in abiotic controls, where the microbial activity was eliminated. The microbes living on the surface of concretions utilized methane, indicating that concretions have methanotrophic communities. Incubation solutions’ metal analysis showed that metal concentrations increased more in the abiotic controls than in biotic triplicates after a 12-week incubation, thus metals dissolved from concretions into the incubation solution faster without the activity of microbial communities. We suggest that microbes occupying the concretions have an important role in the concretions’ growth and the factors affecting the accumulation and release processes of metals.

This work was supported by the Finnish Natural Resources Research Foundation and the Research Council of Finland (Fermaid project, grant 332249).

How to cite: Majamäki, R., Purkamo, L., Hultman, J., Wasiljeff, J., Asmala, E., Yli-Hemminki, P., Jorgensen, K., Koho, K., Kuva, J., and Virtasalo, J.: Baltic Sea ferromanganese concretion growth rates and conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9000, https://doi.org/10.5194/egusphere-egu24-9000, 2024.

17:45–17:55
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EGU24-2796
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On-site presentation
Sebastian Viehmann, Viona Klamt, Dennis Kraemer, Ingo Horn, Claus Rüscher, Simon V. Hohl, Oscar Fernandez, and Stefan Weyer

Modern to Cenozoic hydrogenetic FeMn nodules and crusts are reliable geochemical archives of past seawater chemistry. In this study, we report the first petrographic and geochemical data of Jurassic FeMn nodules and crusts from the Calcaereous Alps of the Pyhrntal area (Austria) that were formed ca. 170 million years ago and, thus, ~ 10 million years after the Toarcian extinction event. The combined approach of petrographic data, including XRD and SEM+BSE, with major and trace element signatures and stable U-Mo isotopes of individual FeMn nodule and crust layers obtained by tandem ICP-MS and MC-ICP-MS, respectively, is used to extend the geochemical record of marine FeMn deposits roughly 100 million years back in time and evaluate their reliability as archives for Jurassic seawater. Trace elements and redox-sensitive U-Mo isotopes aid in reconstructing the origin of the FeMn nodules and redox conditions of Tethian seawater in the aftermath of the Toarcian extinction event.

The FeMn deposits of the Pyhrntal area can be subdivided into four types: Type I nodules rich in carbonates (< 90wt %; calcite, rhodochrosite) with minor Fe-oxides (10 wt%; hematite, goethite) and clays (< 20 wt %). Manganese-rich type II nodules (< 75 %; todorokite, ranceite) contain fewer carbonates (< 47 wt %), Fe oxides (<40 wt %), and clays (< 10 wt %). Type III nodules and crusts rich in Fe oxides (< 60 wt %) and carbonates (< 60 wt %) with minor Mn oxides and type IV nodules with Fe- (< 50 wt %) and Mn- oxides (10 wt %), carbonates (< 30 wt %) and < 12 wt % of clay. Despite their different mineralogy, all four FeMn deposit types show sub-parallel shale-normalized rare earth elements and yttrium (REYSN) patterns that are typical of (modern) hydrogenetic FeMn deep-sea nodules and crusts, suggesting a seawater-derived origin. Typical REYSN features include strong positive CeSN anomalies due to the oxidation of Ce3+ to Ce4+ on (hydr)oxide surfaces and a negative YSN anomaly related to higher complex stability of Y in seawater relative to neighboring REY. Furthermore, stable U and Mo isotope compositions of all four types show a narrow range in δ98/95Mo (-0.97 to -0.56 ‰) and δ238/235U (-0.75 to -0.47 ‰), consistent with isotopic values observed in modern and Cenozoic FeMn deposits, suggesting an overall oxic water column at latest 18 Ma after the Toarcian extinction event.

The approach using petrography with major and trace element systematics in combination with stable U-Mo isotope signatures highlights the Tethian FeMn deposits as unique geochemical archives of Jurassic seawater that enable a reliable reconstruction of the origin of the Alpine FeMn deposits and the ambient redox conditions in Tethian paleo-environments. 

How to cite: Viehmann, S., Klamt, V., Kraemer, D., Horn, I., Rüscher, C., Hohl, S. V., Fernandez, O., and Weyer, S.: The origin of Jurassic FeMn deposits and their reliability as geochemical archives for Tethian seawater, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2796, https://doi.org/10.5194/egusphere-egu24-2796, 2024.

17:55–18:00

Posters on site: Wed, 17 Apr, 16:15–18:00 | Hall X3

Display time: Wed, 17 Apr, 14:00–Wed, 17 Apr, 18:00
Chairpersons: Michael E. Böttcher, Mónica Sánchez-Román, Anelize Bahhniuk
Lakes, oceans and isotopes
X3.82
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EGU24-18286
Leonardo Cury, Kei Sato, Joicy Micheletto, Larissa Santos, Joachim Amthor, and Anelize Bahniuk

The 87Sr/86Sr ratio stands as a crucial isotopic marker for the paleogeographic and paleoenvironmental reconstruction of Aptian carbonate sequences in the offshore Campos and Santos basins in Brazil, as well as the Namibe basin in Angola. It facilitates the identification of distinct stratigraphic successions and alterations in the basin's source areas, allowing for valuable geological correlations and interpretations on both margins. Furthermore, it can indicate diagenetic processes, hydrothermal events involving chemical mobility, and textural modifications associated with regional tectonic events linked to the evolution of the South Atlantic rift.

In isotopic dilution analyses, the quality of the results is ensured by eliminating interferences and ensuring a stable signal during spectrometric reading, where the 87Sr/86Sr ratios have analytical precision between the 5th and 6th decimal place. However, samples with a significant compositional variation, such as laminations, microstructures, microveins, or even with clastic minerals, may yield scrambled distinct signals during the grinding and homogenization processes, making it difficult to recognize subtle variations. Strontium isotope analyses by laser ablation coupled to multi-collector ICP-MS Neptune Plus, obtained through the in situ 87Sr/86Sr method have great potential and broad applicability in cases where the search for gentle isotopic signal variations is relevant, such as in the study of drilling cores. By using integrated petrographic information, it has become possible to perform high-resolution analyses, addressing different components of the crystalline system, with strontium intensities ranging from 200 mg/L to ~ 6000 mg/L. The speed of the analyses, from sampling rock fragments to performing laser-based analyses, provides a large volume of results in a relatively short period of time, facilitating correlations between stratigraphic intervals.

The in situ 87Sr/86Sr method has analytical precision between the 4th and 5th decimal place, with sufficient sensitivity to characterize different groups defined by ratios in the ranges of 0.712 - 0.714 (predominantly continental), 0.710 - 0.711 (mixed), and 0.709 - 0.710 (marine influence). Its application in the study of pre-salt carbonates brings a significant advancement in recognizing the environment, and its genetic and diagenetic processes, with great potential to advance our understanding of chemostratigraphy and unravel the transition between continental and marine environments in the early stages of the South Atlantic Ocean's history.

How to cite: Cury, L., Sato, K., Micheletto, J., Santos, L., Amthor, J., and Bahniuk, A.: Unraveling the early South Atlantic records: in situ 87Sr/86Sr isotopic analysis in Aptian carbonates from the conjugated margins of Brazil and Angola., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18286, https://doi.org/10.5194/egusphere-egu24-18286, 2024.

X3.83
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EGU24-6853
Michael E. Böttcher, Patricia Roeser, Jens Kallmeyer, Vera Winde, Albrecht Leis, Tillman Harum, Anna Noffke, Iris Schmiedinger, Antje Schwalb, Martin Wessels, and Thomas Wolf

Benthic sulfur cycling in fresh-water lakes is typically characterized by low concentrations of dissolved sulfate in the overlying water column. This electron acceptor is the major driver for the anaerobic mineralization of organic matter in brackish-marine systems. Post-glacial development in marginal seas like the Baltic or Black Sea are often characterized by a transition from fresh to brackish water conditions, and initial sulfur isotope signatures of lacustrine sediments are often found to be superimposed by later diagenesis. To better understand the link between sulfate sources and the developing sedimentary sulfur isotope signatures in lake systems, Lake Constance’s main inflows, vertical water column profiles and sediment samples were geochemically and isotopically (S-34, O-18) characterized.

We found that dissolved sulfate concentrations and stable isotope signatures for the two major riverine contributors, Alpenrhein and Bregenzer Aach, differed substantially in their isotopic composition. The Alpenrhein dominates sulfate contribution into the lake system and its contribution could be traced throughout the lake with some indication for potential minor sulfur cycling within the water column. Wells demonstrated that the Bregenzer Aach lost water to an underground passage towards Lake Constance. Water-rock interactions also provided minor amounts of sulfate to the migrating groundwater.

The top 10 cm of surface sediments, representing the Anthropocene, indicated fast gross and net dissimilatory sulfate reduction and the formation of iron sulfides that are isotopically close to water column sulfate, but they were found to be depleted in the heavier isotope at greater depth, indicating lower ratios of net sulfate reduction versus sulfate replenishing rates in the past.

How to cite: Böttcher, M. E., Roeser, P., Kallmeyer, J., Winde, V., Leis, A., Harum, T., Noffke, A., Schmiedinger, I., Schwalb, A., Wessels, M., and Wolf, T.: Controls of sulfur authigenesis in lacustrine sediments of the (pre-)Anthropocene: Sulfur and oxygen isotopes can tell, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6853, https://doi.org/10.5194/egusphere-egu24-6853, 2024.

(Bio)minerals
X3.84
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EGU24-19036
Francisca Martinez-Ruiz, Adina Paytan, Crisogono Vasconcelos, Fadwa Jroundi, Maria del Mar Abad, Victor Villasante, and Maria Teresa Gonzalez-Muñoz

The investigation of mechanisms involved in barite formation in the mesopelagic zone has served to demonstrate the importance of extracellular polymeric substances (EPS) in promoting microenvironments in which Ba can precipitate. Barite formation in the ocean was not fully understood until experimental work and observations from microenvironments of intense organic matter mineralization in the ocean water column demonstrated the role of bacteria and EPS in concentrating Ba. The organomineralization processes leading to barite formation are expected to be similar to those involved in the formation of other biominerals in which bacterial cells and EPS provide charged surfaces that bind metals inducing mineralization. Thus, EPS production plays a major role in promoting locally high concentrations of Ba leading to barite precipitation. Regarding the crystallization pathway, scanning and high-resolution transmission electron microscopy analyses have shown the occurrence of P-rich amorphous precursor phases, which supports that phosphate groups in EPS and bacterial cells are the main sites for binding Ba. These P-rich amorphous particles evolve into poorly crystallized barite and eventually into micrometer-sized barite crystals. The ubiquitous presence of bacteria and EPS in aquatic systems, and in the mesopelagic zone at depths of intense organic matter mineralization, and their inherent ability to biomineralize, make them extremely important agents in driving the Ba biogeochemical cycle. Thus, further investigating microbial processes in the open ocean is essential to better understand metal cycling. The strong link between organo-mineralization and microbial processes further supports the microbial role in biogeochemical cycles. Other than Ba, EPS may also play an important role in concentrating other metals in seawater, which still needs further investigation.

How to cite: Martinez-Ruiz, F., Paytan, A., Vasconcelos, C., Jroundi, F., Abad, M. M., Villasante, V., and Gonzalez-Muñoz, M. T.: Role of extracellular polymeric substances (EPS) in mineral precipitation in the ocean water column, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19036, https://doi.org/10.5194/egusphere-egu24-19036, 2024.

Dolomite
X3.85
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EGU24-17887
Mónica Sánchez-Román

Carbonates are prevalent in the geologic record throughout Earth's history and are also found on Mars and within meteorites. The chemical and isotopic compositions of carbonates have been used to elucidate the composition of ancient oceans and the prevailing conditions during the development of life and its subsequent rapid evolution1-5. Carbonate mineral compositions reflect the environmental conditions under which they were formed4,5 .

 

Dolomite is particularly abundant in ancient rock formations but is scarce in modern sedimentary environments. Many ancient dolomites are suspected of being alteration products of preexisting dolomite phases rather than being originally formed, unaltered dolomites6. The geochemical and neomorphic alteration of dolomite have been studied extensively, with the principal driving forces for neomorphism being the inherent thermodynamic instability of non-stoichiometric dolomites and the surface free energy-driven recrystallization of fine crystalline mosaics to coarser crystalline6.  Recent studies have demonstrated that microorganisms can produce dolomite with a geochemical signature distinct from those formed abiotically1-4. Our research integrates field studies, state-of-the-art laboratory experiments, mineralogical, and geochemical analyses to investigate the processes and environmental conditions that control the chemical composition of low-temperature carbonates. The role of inorganic-organic interactions is evaluated in natural field laboratories and carefully controlled laboratory experiments performed under abiotic and biotic conditions.

 

In summary, the research focuses on understanding the processes and environmental conditions that control the chemical composition of low-temperature dolomite. A multidisciplinary approach, integrating field studies, laboratory experiments, microscopic, mineralogical, and geochemical analyses, is employed to investigate the role of inorganic-organic interactions in the formation of these carbonates. This work has the potential to provide insights into the development of life on Earth and the evolution of terrestrial and Martian carbonates.

 

References:

[1] Sánchez-Román M., et al. (2011) Chemical Geology 281, 143 - 150.

[2] Sánchez-Román M., et al. (2014) Scientific Reports 4, 4767.

[3] Sanchez-Roman M., et al (2023) Geochimica et Cosmochimica Acta 356, 66-82.

[4] Sánchez-Román M., et al. (2011) Geochimica et Cosmochimica Acta 75, 887-904.

[5] Li M., et al. (2021) Geology 49, 698–702.

[6] Mazzullo, S.J., et al. (1991) Carbonates Evaporites 7, 21–37.

 

 

How to cite: Sánchez-Román, M.: Exploring Low-Temperature Dolomite as a Biosignature, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17887, https://doi.org/10.5194/egusphere-egu24-17887, 2024.

X3.86
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EGU24-12162
Inigo A. Müller, Marion Peral, Perach Nuriel, and Philippe Claeys

During the Jurassic, southern Germany was covered by a shallow sea environment with active formation of carbonate platforms. As these platforms never experienced extreme pressure and temperature conditions due to deep burial or metamorphic overprint from nearby orogeny, we expect them to preserve relatively pristine formation fabrics. Still the top of these mainly limestone buildups are dolomitized and it is not well understood how this dolomitization proceeded.

We study the origin of the dolomitization process of these Jurassic platforms with microscopic cathodoluminescence imaging to visualize different formation events, clumped isotope thermometry to derive the formation temperature and with the analysis of the elemental concentration distribution by µ-XRF we aim to obtain new insights on the formation process and the origin of the precipitation fluid.

How to cite: Müller, I. A., Peral, M., Nuriel, P., and Claeys, P.: Dolomite formation in Jurassic carbonate platforms of Southern Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12162, https://doi.org/10.5194/egusphere-egu24-12162, 2024.

X3.87
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EGU24-225
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ECS
Daniel A. Petrash, Philip T. Staudigel, Miguel Bernecker, Patricia Roeser, and Giovanna Della Porta

This study aims to enhance the understanding of geomicrobiological processes and low-temperature dolomite formation, a field significantly developed by Judith A. McKenzie1. It focuses on shallow burial diagenetic dolomite from the onset of the Miocene Climatic Optimum (MCO, 16.9-14.7 Ma)2. Our investigation entailed examining interstitial ferroan and calcian dolomite in claystone (dolomitic mudstone), and integrates bulk-rock stable isotopes (C, N, Δ47 and Δ48) and elemental concentration analyses. The mineral is partially ordered (mean I(015)/I(110)=0.42), microcrystalline (2 to 12 μm) and predominantly subhedral (planar-s). Isotopic data revealed it formed under substantial benthic microbial activity, as evidenced by δ15N values suggestive of sustained N2 losses (+8.59 ± 2.51 ‰, median 9.50 ‰, N=19)—as typically observed in sedimentary settings featuring high rates of denitrification and anammox. Dolomite δ¹³C values (+1.41 to +11.44 ‰, median 7.58‰, N=19) record a mixture of dissolved inorganic carbon sources, dominated by methanogenic CO2. In the ca. 70 m-thick, partially eroded lacustrine succession, conspicuous correlation between dolomite abundances and bulk-rock potassium and barium levels provides evidence of episodic increases in chemical weathering during the warm and humid MCO climate2. The results reveal complex causal interactions linked to fluctuating pore-water dolomite precipitation potentials. Accordingly, Miocene oscillations in pCO2 levels accelerated silicate weathering in catchment areas dominated by alkaline igneous bedrocks, including  trachybasalt3, K-rich peridotite and granitoids, thus enriching nearby prevalently anoxic rift paleolake with dolomite-ankerite reactants (i.e., reducible Fe3+, Mg2+ and Ca2+)3 and macronutrients (e.g., iron(III) oxide-bound PO43-). Overall, these sedimentary dynamics, coupled with the influx of soil-derived oxidized nutrients, enhanced benthic ferric iron-based respiration and the sediment redox buffering capacity, which was conducive to punctuated, interstitial dolomite cementation. The dolomite-bearing claystone levels, characterized by Post-Archean Shale-normalized positive europium anomalies, challenge traditional hydrothermal interpretations of dolomitization in rift lakes. Their coupled isotope values (∆47 and ∆48, Bernecker et al., 2024: EGU24-11056) point to formation at temperatures below 40°C, and in a shallow-burial diagenetic realm where the pore fluids and dolomite interacted within a closed system4.  Climate variability during the onset of the MCO, along with changes in precipitation and weathering regimes, likely played a fundamental role in establishing the internal boundary conditions necessary for lacustrine dolomite formation.

References

1. Vasconcelos, C., McKenzie, J., Bernasconi, S. et al. Nature 377, 220–222 (1995).
2. Kříbek, B., et al. J. Paleolimnol. 58, 169–190 (2017).
3. Rapprich, V. et al. Depos. Rec. 9, 871–894 (2023).
4. Staudigel, P., et al. Geochemistry, Geophysics, Geosystems 24, e2023GC011117 (2023).

How to cite: Petrash, D. A., Staudigel, P. T., Bernecker, M., Roeser, P., and Della Porta, G.: An examination of episodic dolomite cementation in an Early-Miocene Eger Rift lake deposits (Czech Republic), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-225, https://doi.org/10.5194/egusphere-egu24-225, 2024.

X3.88
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EGU24-17897
Patricia Roeser, Michael Böttcher, Alina Liebezeit, Ulrich Harms, Laura Epp, Ulli Raschke, David Schleheck, Iris Schmiedinger, Flavio Anselmetti, Martin Wessels, and Antje Schwalb

Placed in a carbonate-rich catchment at the northern foot of the Alps, Lake Constance is one of the largest lakes in Central Europe, and the hard water lake chemistry makes it a natural laboratory to investigate in detail the carbonate formation, preservation, and the interactions with the detrital carbonate fraction, the latter with a major dolomite component. The highly reactive lacustrine carbonates are great paleoenvironment archives - due to the climate sensitivity in their formation either as erosional sources of suspended matter or through lake internal processes; still, they are prone to diagenetic overprints that shall be considered in a major context. For that, the (post-)glacial sediment deposits were investigated up to 24 m long cores recovered from the northernmost deep portions of Lake Constance, at approximately 200 mwd. The benthic carbon cycle and mineral sources and (trans)formations, were investigated through porewaters and sedimentary solid phases analyses for stable isotope signatures (CHOS), and major- and trace element compositions.

The water isotope signatures display a trend towards lighter data with depth, indicating the development in the lake water composition with time, superimposed by diffusion processes in the sediments. The dissolved inorganic carbon (DIC) concentrations increase below the sediment-water interface and are generally higher in the postglacial sediments, indicating that mineralization rates followed the enhancement of lake productivity under milder climate conditions. The δ13C-DIC shows the lightest values in the glacial sediments and displays an enrichment in Holocene sediments, together with pore water hydrochemistry, indicative of organic matter (OM) oxidation, carbonate dissolution, and potential involvement of methane. The sulfur isotope record indicates that minor dissimilatory sulfate reduction is involved in OM degradation. Bulk carbonate C and O isotope signatures show strong variations partly induced by non-authigenic dolomite. Vertical variations in the composition of porewaters, bulk, and acid-soluble phases, in combination with SEM investigations, allow insights about the (trans)formation of authigenic mineral phases and the destruction of allochthonous carbonates, as possible modifiers of the sedimentary record.

How to cite: Roeser, P., Böttcher, M., Liebezeit, A., Harms, U., Epp, L., Raschke, U., Schleheck, D., Schmiedinger, I., Anselmetti, F., Wessels, M., and Schwalb, A.: Carbon diagenesis in dolomite- and calcite-bearing limnic sediments: A multi-phase stable isotope geochemical perspective on Lake Constance, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17897, https://doi.org/10.5194/egusphere-egu24-17897, 2024.

X3.89
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EGU24-8073
Patrick Meister, Susanne Gier, Erich Draganits, Peter Steier, Monika Bolka, Franz Ottner, Christoph Spötl, Dorothee Hippler, and Stephanie Neuhuber

Authigenic Mg-calcite and dolomite are currently forming in Lake Neusiedl (Neuhuber et al. 2024), an episodically evaporative shallow lake in eastern Austria (Draganits et al., 2022). Radiocarbon dating by Neuhuber et al. (2024) revealed average ages of 200 to 3700 cal yr BP, reflecting extremely slow precipitation rates. The relatively high ages of fine-grained crystals agree with high radiocarbon ages of dolomite from Deep Springs Lake (California; Peterson et al., 1963). Such comparably high ages are commonly explained by the slow formation of dolomite due to its high kinetic barrier. Close examination by transmission electron microscopy (Meister et al., 2023) revealed concentric zones of Mg-rich carbonate replacing less Mg-rich precursors. However, no considerable progress in ripening has been noticed in older layers buried below 30 cm depth, which are no longer affected by sediment reworking (Fussmann et al., 2023). It appears that ripening of the metastable phase to the stable phase does not occur as long as the porewater remains supersaturated with respect to a metastable Mg-calcite phase. Ripening of Mg-calcite to protodolomite and ordered dolomite may however occur at the sediment-water interface, where the bottom water becomes episodically undersaturated with respect to Mg-calcite. Fussmann et al. (2023) observed a drop in pH in the benthic boundary layer, which can be caused by the release of acidic fermentation products and aerobic respiration.

Ripening due to episodic undersaturation of water with respect to a metastable Mg-calcite phase is consistent with a model of dolomite formation under conditions fluctuating between supersaturation and undersaturation with respect to the metastable phase, conforming to Ostwald’s step rule. This effect has recently been reproduced using density function theory (Kim et al., 2023). This model could also explain the formation of nano-domains of ordered dolomite in coherent crystallographic orientation within the protodolomite due to oscillating conditions at the recrystallization front (Meister et al., 2023). The case of authigenic carbonate formation in Lake Neusiedl exemplifies that the model of dolomite formation under fluctuating hydrochemical conditions is well applicable to natural conditions in modern, as well as ancient, environments.

 

Draganits, E. et al. (2022) Lake Neusiedl Area: A Particular Lakescape at the Boundary Between Alps and Pannonian Basin. In: Embleton-Hamann, C. (ed.), Landscapes and Landforms of Austria. World Geomorphological Landscapes. Springer, Cham, pp. 207-222.

Fussmann, D. et al. (2020) Authigenic formation of Mg-Ca-carbonates in shallow alkaline water in Lake Neusiedl, Austria. Biogeosciences 17, 2085–2106.

Kim, J. et al. (2023) Dissolution enables dolomite crystal growth near ambient conditions. Science 382, 915–920.

Meister, P. et al. (2023) Nanoscale pathway of modern dolomite formation in a shallow, alkaline lake. Cryst. Growth Des. 23, 3202–3212.

Neuhuber, S. et al. (2024) Radiocarbon ages of microcrystalline authigenic carbonate in Lake Neusiedl (Austria) suggest millennial-scale growth of Mg-calcite and protodolomite. Sedimentology in press.

Peterson, M.N.A. et al. (1963) Radiocarbon studies of recent dolomite from Deep Spring Lake, California. J. Geophys. Res. 68, 6493–6505.

How to cite: Meister, P., Gier, S., Draganits, E., Steier, P., Bolka, M., Ottner, F., Spötl, C., Hippler, D., and Neuhuber, S.: Millennial-scale growth of (proto)dolomite in Lake Neusiedl (Austria) is consistent with Ostwald's step rule, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8073, https://doi.org/10.5194/egusphere-egu24-8073, 2024.

Microbialites
X3.90
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EGU24-17528
Anelize Bahhniuk, Paulo Quezada Pozo, Carolina Henriquez Valenzuela, Mauricio Calderón, Guido Alonso, and Leonardo Cury

The sedimentation in the alkaline lakes could be understood as a product of intrinsic and extrinsic factors’ interaction, where both can exert influence with alternating or progressive predominance due to the large-scale geochemical scenario, promoted by the tectonic and geomorphological settings, the climate and hydrology, the sedimentation, and the environments of deposition. Sedimentological studies of modern carbonate deposits in extreme environments provide access to a better understanding of physical-chemical reactions under the intense influence of natural conditions of desert climate, such as UV radiation, temperature variation, altitude, and heavy winds. Modern carbonate environments, where alkaline lakes are forming under comparable geomorphological, biological, climatic, volcanic, and tectonics characteristics as those during the formation of the Aptian Pre-Salt lakes on the Brazilian continental shelf, are possible analogues to improve our understanding of the physical-chemical processes involved the formation of ancient carbonate deposits. Nevertheless, it is difficult to study a single modern example, which fulfils all the criteria required to define a realistic evolutionary model for the Aptian equivalent. Thus, we have selected for our evaluation several modern alkaline lake locations, which form under variable environmental conditions, e.g., the Pantanal, Central Brazil, and Patagonia, Chile. These environments present vastly different conditions, which can furnish important insights, and taken together provide fundamental information to decipher relationships between the inorganic and organic processes involved in carbonate reservoir formation. In the Pantanal region, thousands of lakes are distributed throughout one of the largest fan river systems. Microbial activity in many of these water bodies mediates the production of carbonates associated with authigenic clay mineral precipitation, e.g., smectite. In Chile’s Patagonia Torres Del Paine region, the Sarmiento and Amarga lakes are located in an area of glacial regression, which represents an environment with recent microbialite formation in a cold and arid climate. Additionally, in this cold, arid region, Lake Pali Aike, situated in the crater of a dormant volcano, is potentially an interesting case study. Each of these three different regions is characterized by extreme environmental conditions, such as a desert climate with high temperatures during the day and very low temperatures at night, strong winds, and a high incidence of solar radiation. The primary goal of integrating studies of these three distinctly diverse environments located in varying geological settings is to develop an actualistic facies model representing the ancient conditions of the various Pre-Salt lacustrine depositional environments, ranging from deep subaqueous, intermediate subaqueous, shallow subaqueous, and subaerial systems.

How to cite: Bahhniuk, A., Quezada Pozo, P., Valenzuela, C. H., Calderón, M., Alonso, G., and Cury, L.: Modern Microbial Carbonates Deposits in South America: New insights of sedimentation and diagenesis in alkaline lakes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17528, https://doi.org/10.5194/egusphere-egu24-17528, 2024.

X3.91
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EGU24-14614
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ECS
Tatiana Stepanenko, Guido Alonso, Anelize Bahniuk, and Leonardo Cury

      Botijuela travertine system is located at the western edge of the Salar de Antofalla at 3433 meters above sea level, the area shows several hot springs still active and several fossilized carbonate deposits. One of the main outcrops of this area is Vega Verde, which develops in a north-south direction where the carbonate deposits start from a vent and reach the Salar de Antofalla basin. In this place, it was possible to observe the development of several microbial ecosystems: non-lithified and lithified microbial mats in the closest area to the vent, as well as cyanobacterial biofilms and lithified stromatolites in the mixing zone between freshwater and thalassic water. In this work, we present the geochemical and mineralogical characterization of these microbial ecosystems. Mineralogically, the lithified ecosystems were composed mainly of calcite, and a less extended Mg-bearing calcite, aragonite, gypsum, and halite. Stable Isotopes C & O analyses showed that the samples from the vent presented an isotopic signature related to hydrothermal origin with δ13C (2,05 – 7,82) and δ18O (-6,59- -9,77) values. While the stromatolite from the Salar de Antofalla (in the mixing zone) showed high δ18O (0,8-1,12) and δ13C (7,63-13,26) values, which suggests that the evaporation process is the main fractionation force.   Although is considered that the main processes driving the travertine mineral precipitation are degassing and evaporation, petrological and SEM analyses showed that microbial activity appears to be contributing to the sedimentological textures of Vega Verde samples rocks. Moreover, the mineral morphologies and carbonate growth structures found in the SEM rock samples were also found in the in vitro carbonate precipitation experiments, but exclusively when microbial mats were present, and not in the negative control. These results suggest a strong influence of hydrothermal flows, evaporation process, and microbiological mediation during the Vega Verde carbonate systems formation.

How to cite: Stepanenko, T., Alonso, G., Bahniuk, A., and Cury, L.: Geochemical and microbiological signatures in the Vega Verde carbonate system, Botijuela, Puna Argentina., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14614, https://doi.org/10.5194/egusphere-egu24-14614, 2024.

X3.92
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EGU24-13960
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ECS
Guido Ezequiel Alonso, Leonardo Fadel Cury, and Tatiana Mariel Stepanenko

Carbonate accumulation processes in modern non-marine systems producing tufa and travertine deposits have gained relevance in recent years due to their importance as possible analogues to the hydrocarbon reservoirs of the Brazilian and African Pre-Salt. The biotic/abiotic genesis of these carbonates is related to the fact that these rocks create favorable situations for the proliferation of benthic microbial communities, which can influence the genesis of travertine and/or its final form. The aim of this study is to characterize the carbonate deposits and the biotic influence in the Botijuela travertine systems, located on the western margin of the Salar de Antofalla in the Puna region of Argentina. Descriptions of morphological features and sedimentary facies in the outcrops, thin-slice petrography, mineralogical analysis by X-ray diffraction (XRD), chemical analysis by X-ray fluorescence (XRF), and stable isotopes of C and O (V-DPB) were done. The Botijuela was divided into two active systems: Vega Verde and Vega Blanca. The vent of the first one is a conical mound (~15m) with a length of 530 m, and the second one is a fissure ridge with fractures with a length of 325m, also with two fossilized travertine systems, named I and II. At the proximal depositional zone of Vega Verde, the system presents carbonate facies of mudstones with bubbles, shrub-boundstones, and oncoidal (~0.5cm diameter) rudstones. The fractures of Vega Blanca in the proximal zone present halite and subsequent development of carbonate pools (transversal 2–7 cm) and big oncoids (~2 cm in diameter). Dams and barrages in the pools present botryoids in areas that show subaerial exposure. Oncoids and dendriform shrubs are well developed in the proximal-intermediate depositional zones in low-slope areas. Intermediate zones of both systems are characterized by higher-energy carbonate facies: crenulated mudstones, oncoidal grainstones, and rudstones. The distal area of Vega Verde presents rudstones with detrital fragments, diatoms, and ostracods that interbed with siliciclastic sediments of the Antofalla Salar basin. Vega Blanca presents bigger (~15cm) transversal carbonate pools with oncoids and botryoids at the dams. Mineralogically, the systems are mainly calcite, and calcite low in Mg. Geochemically, Vega Verde shows a content of CaO of ~51.05% and Vega Blanca ~46.63%, with average loss of ignition values of ~40% for both. Vega Verde proximal zone is characterized by a high Fe-As-Pb content (Fe2O3 ~4.3%, Pb-As 0.5 to 1.7%) with an isotopic signature of δ13C (1.97-10.84) and δ18O (-0.67-8.91). In comparation, Vega Blanca systems show averagely higher values of SiO2 (I~10.79% -, II~5.17%) and Na2O (I~ 0.32; II~1.47%), with isotopical signatures for system I of δ13C (5.31~14.78) and δ18O (-4.86~ -0.24), for system II of δ13C (6.34~15.36) and δ18O (-3.20~ -0.71). Signatures indicate a water hypogene origin with δ13C fractionation enrichment towards the Antofalla basin. Geochemical data allows us to infer that the systems have a different water origin. Overall, high-resolution facies analysis of travertine systems and their integration with their geochemical framework and tectonic setting constitute a step forward regarding the environmental distribution of microbially related deposits and the comprehension of their main constraints.

How to cite: Alonso, G. E., Fadel Cury, L., and Stepanenko, T. M.: Sedimentological and geochemical aspects of the Botijuela travertine systems , Antofalla Salar- Central Andes, Argentina., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13960, https://doi.org/10.5194/egusphere-egu24-13960, 2024.

X3.93
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EGU24-14127
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ECS
Paulo Quezada, Leonardo Fadel Cury, Mauricio Calderón, Carolina Henríquez, Joicy Micheletto, Nicolás Bruna, José Manuel Pérez-Donoso, Gustavo Barbosa Athayde, and Anelize Bahniuk Rumbelsperger

The study focuses on the deposition of freshwater lacustrine tufa in recently deglaciated areas, specifically in Lago Sarmiento. Lago Sarmiento is a large (water volume of ca. 9 km3 and a maximum depth of ca. 310 m), alkaline and oligotrophic lake situated on folded, mudstone-rich turbiditic deposits from the Upper Cretaceous. The lake margin features a semicontinuous tufa section, reaching up to approximately 10 meters in thickness. This section comprises variably amalgamated tufa mounds that can merge into terraces or be arranged as isolated mounds, domes, and V-shaped build-ups of metric sizes. The deposits are irregular, displaying a clotted to slightly dendritic fabric, and high porosity. Vugs within them are filled with authigenic materials (peloids and gastropods) and terrigenous grains (quartz + plagioclase ± Fe-Mg silicates). Microbialites records are discernible at the microscale within the tufa framework. These records consist of variably micritized and/or eroded shrubs composed of fascicular Mg-calcite (mostly 6 - 8.5 mol% MgCO3) encrusting filamentous structures interpreted as formed after the calcification of EPS around radially organized cyanobacteria of the genus Rivularia, as deduced from 16S rRNA analysis in a microbial mat sample. Scant framboidal pyrite is observed in SEM images, suggesting minimal contributions of sulfate-reducing bacteria to carbonate precipitation. Stable isotope analysis of the tufa (δ13C and δ18O) and lake waters (δ2H, δ18O, and δ13C-DIC) indicates that the positive δ13C tufa composition results from variable amounts of CO2 degassing and microbial photosynthesis over a lake DIC pool that remained near isotopic equilibrium with atmospheric CO2. The slightly negative δ18O tufa composition is interpreted as precipitation during warm/dry periods in the Holocene. Lake water chemistry is characterized by relatively low Mg/Ca molar ratios (0.51 – 1.8), intermediate alkalinity (6 – 11.6 meq/L), and low Ca/Alk ratios (0.1 – 0.59 meq/L). In lakes with similar water chemistry, the supply of Ca+2 and Mg+2 is required to achieve carbonate saturation, e.g., through groundwater discharge. A distinctive record of tufa filling fractures in the mudstones that compose the bedrock is identified in the uppermost portions of the lacustrine tufa section, resembling a seepage system that fed the lake. The putative "seepage carbonates" include thicker infills (up to 20 cm) with microfabrics similar to lacustrine tufa, as well as thin (> 2 cm) and laminated cements with syntaxial crystal growth, arranged as interconnected vein-like structures. The "seepage carbonates" exhibit higher aragonite content, Sr/Ca ratio, and lower content of Mg in calcite than the lacustrine tufa. However, the similar δ13C and δ18O composition among both groups suggest the precipitation of the former in sub-lacustrine conditions. In-situ 87Sr/86Sr analysis of lacustrine tufa formed in opposed margins of the lake reveals strong heterogeneity in the source of Sr, with 87Sr/86Sr compositions spanning between those of the bedrock (~0.7075) and Holocene volcanism in southern Patagonia (~0.7050). These findings indicate complex interactions between intrabasinal and extrabasinal sources, climate, and microbial mediation that influenced the multi-episodic growth of the tufa deposits after the local retreat of the glaciers approximately 12.5 ka BP.

How to cite: Quezada, P., Fadel Cury, L., Calderón, M., Henríquez, C., Micheletto, J., Bruna, N., Pérez-Donoso, J. M., Barbosa Athayde, G., and Bahniuk Rumbelsperger, A.: A multi-method approach to understand the origin of lacustrine tufa deposition in Lago Sarmiento (Chilean Patagonia) , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14127, https://doi.org/10.5194/egusphere-egu24-14127, 2024.

X3.94
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EGU24-15945
Daniel Ariztegui

Judith McKenzie's scientific pursuit focused on comprehending the processes that lead to observable phenomena in the geological record. She consistently emphasized to students and colleagues the fundamental importance of this understanding before delving into any attempt to use proxies. In the late nineties, Judy joined us for a field trip in Patagonia, where we conducted fieldwork in the Maquinchao Basin, Argentina. This location hosts both living and fossil microbialites, presenting a unique opportunity to investigate their formation processes—a goal aligned with Judy's scientific philosophy.

Fossil microbialites, distinguished by their globular and cauliflower shapes, populate a continuous palaeoshoreline of a former lake at an altitude of 830 m. Meanwhile, their living counterparts thrive exclusively in the tranquil waters of sheltered or meandering sections of the Maquinchao River. To unravel the intricate interplay between environmental and biological factors governing their development, we sampled and studied living microbialites and their host waters. Contemporary microbialites appear exclusively in freshwater environments with elevated Ca2+ levels. Microscopic inspection reveals heightened photosynthetic organisms in the upper green layer, associated with crypto/microcrystalline calcite (nanoglobules), compared to the lower beige-white biofilm. The latter contains more low-Mg calcite (rhombohedra) precipitates, forming millimeter-sized aggregates in the underlying anoxic layer. While sulphate-reducing bacteria are present throughout the mat, their abundance is more notable in the lower beige-white layer, always associated with Mg calcite.

Distinct conditions, such as low salinity and low-turbidity water, coupled with microbial (photosynthetic and heterotrophic) activity, emerge as pivotal factors promoting low-Mg calcite precipitation in the Maquinchao Basin. Notably, these conditions sharply contrast with those proposed for recently described lacustrine microbialites at high altitudes in the subtropical and tropical Andes, as well as in Chilean Patagonia. These observations underscore the significance of geomicrobiological studies in discerning proxies for the hydrological conditions prevailing during the formation of freshwater microbialites.

How to cite: Ariztegui, D.: Unlocking the Formation Dynamics of Modern Microbialites: A Geomicrobiological Study in the Maquinchao Basin, Argentina, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15945, https://doi.org/10.5194/egusphere-egu24-15945, 2024.

X3.95
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EGU24-13688
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ECS
Carolina Henriquez, Mauricio Calderon Nettle, Leonardo Cury, Paulo Quezada, and Anelize Bahniuk

On geological timescales, the volume of CO2 in the atmosphere is influenced by processes such as silicate weathering. In particular, the weathering of basaltic rocks increase the availability of divalent cations such as Mg2+ and Ca2+ in natural waters enabling carbonate formation under atmospheric conditions. Therefore, the existence of carbonate deposits in basaltic provinces provides an excellent opportunity to contribute for the regional environmental record. The Pali Aike Volcanic Field consist of basaltic rocks that covers an area of ca. 4500 km2 in southernmost South America, which were sourced from a deep Mantle source since ca. 4 Ma until the Holocene. The Laguna Timone is a maar filled by a brine developed after explosive volcanic eruptions and constitutes an endorheic hydrological system where carbonate precipitation (calcite and magnesium calcite) is controlled by enrichment of Ca2+ and Mg2+ ions released during the weathering of alkaline basalts. X- ray fluorescence analyses in basaltic rocks reveal high concentration of elements such as CaO (9.73 - 10.57 wt.%) and MgO (9.49-12.76 wt.%).  X-ray diffraction results verify that basalts contain pyroxene (Na, Ca) (Mg, Fe, Al) (Al, Si)2O6, olivine (Fe, Mg)2SiO4 and plagioclase NaAlSi3O8-CaAl2Si2O8 which are suitable phases for the mineral carbonation process. The δ13C DIC values of lake range between −12‰ and −16‰ while for the water of the river values of -7‰. These isotopic ratios are associated to three possible sources/processes: weathering of silicates by carbonic acid, atmospheric CO2 and degradation of organic matter. Furthermore, Sr isotope ratios of carbonates (tufa fragments and thin crust in pebbles) define a range between 0.70408 and 0.70475 which is discussed on basis of the data of basaltic rocks (0.70316 to 0.70351) and top soils (0.705382) in the PAVF. Although the Sr isotope ratios of carbonates are indicative of their derivation from the weathering of basalts an exogenous input from relatively enriched 87Sr material is required, this could be associated to 87Sr leached from the top soils and transported by strong wind. Contrastingly a carbonate vein preserved in the tuff ring deposit of the maar has Sr isotope ratios ranging from 0.70265 to 0.70314, similar to the compositional range of the Mantle xenoliths (0.70264 to 0.70431) and basalts. These data indicate that primary sources of carbonates in the lake are related to in-situ weathering of mafic and ultramafic rocks.

How to cite: Henriquez, C., Calderon Nettle, M., Cury, L., Quezada, P., and Bahniuk, A.: Carbonate Mineralization Related to Weathering of Mafic and Ultramafic Rocks in the Pali Aike Volcanic Field, Extra-Andean Patagonia, Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13688, https://doi.org/10.5194/egusphere-egu24-13688, 2024.

X3.96
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EGU24-19412
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ECS
Franziska R. Blattmann, Tomaso R.R. Bontognali, Negar Haghipour, Simon E. Rouwendaal, and Timothy Eglinton

Microbial mats are considered among the earliest forms of life to have inhabited our planet and occur in early Archean sedimentary sequences. Living mats consist of a coherent network of metabolically diverse microorganisms that produce extracellular polymeric substances, which allows them to thrive in harsh environments. Despite their importance for the study of early life on Earth and their relevance in the search for life on Mars, growth rates as well as carbon cycling of microbial mats remain unclear. Past radiocarbon (14C) studies of microbial mats show the presence of allochthonous organic particles trapped within the autochthonous biomass which complicate reconstruction of the mat growth rates (Bahniuk Rumbelsperger, 2013). In this study, millimeter-scale sampling and radiocarbon analysis was conducted on vertical profiles of microbial mats and lagoon water samples from two modern coastal sabkhas located on the Northwest and South coast of Qatar, respectively. The 14C measurements of mats from both studied sabkhas show increasing Δ14C values from the surface downwards, from an average of -25 ‰ up to a maximum 180 ‰. At the base of the mat there is an abrupt ~150 ‰ decrease in Δ14C values. This clear and shared trend between different sites and profiles shows that in both sites organic matter is predominantly being produced in situ via photosynthesis. Moreover, this 14C trend correlates with the global bomb spike carbon signal (Graven, 2015) and implies that these 45-55 mm thick mats are relatively modern structures and cannot be more than 60 - 70 years old. Therefore, the microbial mat growth rate is higher than previously estimated, suggesting that stromatolites, possibly those from earlier in Earth history, may have formed in a relatively short time. The trend also shows that most organic bound carbon is not extensively recycled within the mat. Instead, the primary source of in-situ produced organic carbon is the dissolved inorganic carbon of the lagoon water. These findings shed new light on the development of one of the earliest life forms on our planet.

REFERENCES
Bahniuk Rumbelsperger A.M., 2013. Coupling organic and inorganic methods to study growth and diagenesis of modern microbial carbonates, Rio de Janeiro State, Brazil: Implications for interpreting ancient microbialite facies development, PhD Thesis ETH Zurich, ETH No. 20984.
Graven, H.D., 2015. Impact of fossil fuel emissions on atmospheric radiocarbon and various applications of radiocarbon over this century. Proceedings of the National Academy of Sciences, 112(31): 9542-9545.

How to cite: Blattmann, F. R., Bontognali, T. R. R., Haghipour, N., Rouwendaal, S. E., and Eglinton, T.: 14C Bomb Spike Signal Constrains Microbial Mat Growth Rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19412, https://doi.org/10.5194/egusphere-egu24-19412, 2024.

Ferromanganese concretions
X3.97
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EGU24-7279
Martin Liira, Johanna Maria Ojap, Aivo Lepland, Sten Suuroja, Markus Ausmeel, Beata Szymczycha, Wei-Li Hong, Michael E. Böttcher, Joonas Virtasalo, Hannah Mikenberg, Atko Heinsalu, and Krete Roopõld

This study investigates the distribution and geological implications of iron-manganese (Fe-Mn) oxyhydroxide precipitates on the seafloor of the Gulf of Finland, with a particular focus on associated pockmarks and Fe-Mn concretions. The formations occur in regions devoid of modern sediment deposition, revealing exposure of late glacial glacio-lacustrine varved clays, glacial tills, or bedrock. Pockmarks, up to 3 m deep and 30-60 m wide, coexist with Fe-Mn concretions, exhibiting sub-vertical walls and microbial colonies, suggesting active seepage of chemically reduced fluids from underlying strata.

Globally occurring Fe-Mn concretions, sedimentary bodies primarily composed of iron and manganese compounds, exhibiting round or crust-like shapes formed through redox-driven processes in seabed environments. Microbial activity accelerates necessary redox reactions, influencing the growth of these concretions. The study delves into the morphological, chemical, and mineralogical characteristics of Fe-Mn concretions in the Gulf of Finland, identifying two distinct types—concentric and crust-like—with varied compositions, hinting at diverse formation mechanisms.

Elevated concentrations of precious and rare earth metals in these concretions raise interest for potential industrial applications. Fe-Mn concretions also serve as valuable indicators of sedimentary processes' geological history, exposing environmental changes over time, including anthropogenic pollution. Despite advancements, the genetic types of Fe-Mn concretions in Estonian sea areas remain elusive, emphasizing the need for further research.

The study integrates findings from three recent international expeditions to the central Gulf of Finland, aiming to comprehensively understand the relationships between fluid seepage, Fe-Mn concretions, and seafloor features. These expeditions collect representative materials, focusing on the timing and controls of groundwater discharge, mineral precipitation, and associated seafloor microbial processes. The preliminary results provide insights into the intricate geological processes underlying the observed seafloor features.

In conclusion, this collaborative effort contributes valuable information about the distribution and genetic characteristics of Fe-Mn precipitates and associated features in the Gulf of Finland. The simultaneous investigation of pockmarks and Fe-Mn concretions, along with their geological implications, enhances our understanding of these complex marine environments. Further research is essential to unravel the exact genetic types of Fe-Mn concretions in Estonian sea areas and to refine our knowledge of the dynamic interactions between fluid seepage, mineral precipitation, and microbial processes on the seafloor.

How to cite: Liira, M., Ojap, J. M., Lepland, A., Suuroja, S., Ausmeel, M., Szymczycha, B., Hong, W.-L., Böttcher, M. E., Virtasalo, J., Mikenberg, H., Heinsalu, A., and Roopõld, K.: Insights into the genesis and geological significance of iron-manganese precipitates in the Baltic Sea, Gulf of Finland seafloor, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7279, https://doi.org/10.5194/egusphere-egu24-7279, 2024.