SSP3.3 | Carbonates - archives of time, space and change
EDI

Carbonate sediments have formed in a wide range of marine and non-marine settings through the complex interplay of biological, chemical and physical processes. Precisely-constrained high-resolution stratigraphic records are important for determining past global change and understanding the complex interactions between climatic processes, oceanographic and environmental changes, the biosphere, stratigraphic architecture and subsequent diagenesis. The complementary study of Recent carbonate depositional systems is crucial to the interpretation of these systems. This session invites contributions from general and interdisciplinary topics within the diverse fields of Carbonate Sedimentology, Stratigraphy and Diagenesis, the session will explore a broad range of geochemical, biological and stratigraphic proxies and their applications to understanding Earth history.

Co-sponsored by IAS
Convener: Stephen Lokier | Co-conveners: Péter Németh, Chelsea PedersonECSECS, Gabriella KoltaiECSECS, Katja GoetschlECSECS, James Hendry
Orals
| Tue, 25 Apr, 08:30–10:15 (CEST)
 
Room -2.21
Posters on site
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
Hall X3
Posters virtual
| Attendance Tue, 25 Apr, 14:00–15:45 (CEST)
 
vHall SSP/GM
Orals |
Tue, 08:30
Tue, 14:00
Tue, 14:00

Orals: Tue, 25 Apr | Room -2.21

Chairpersons: Stephen Lokier, Chelsea Pederson, Péter Németh
08:30–08:35
08:35–08:45
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EGU23-3270
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SSP3.3
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On-site presentation
Anne-Christine Da Silva, antoine triantafyllou, and Nicolas Delmelle

Portable X-Ray fluorescence (PXRF) instruments have become more and more common tools in the last few years for chemical analysis (major, minor and some traces elements) in carbonates and sedimentary rocks. PXRF is a relatively cheap and fast technique, non-destructive and prevents tedious sample preparation. Manufacturers calibrations are usually made for a very large range of rock types or materials but specific empirical calibrations are essential to improve the quantification of multi-elemental concentrations.

We present a general workflow for building an empirical calibration model for a PXRF spectrometer from choosing reference materials to validating calibration’s efficiency and quantifying its limit of quantification. We also compare the quantified results on a sedimentary rock suite obtained from sixteen calibrations that were built using several software available on the market, including a simple homemade spreadsheet, the Bruker calibration software named EasyCal, a free and open-source calibration app named CloudCal, and the built-in GeoMining and GeoExplorer calibrations provided by Bruker manufacturer on the Tracer 5 PXRF. This decoupled approach allows (i) to explore the pros and cons for each calibration software solutions, (ii) to investigate and weight the effect of each correction parameters (i.e. regression line geometry, peaks interferences, spectra normalization, influence coefficients, multi-phases excitation conditions) on the quantified results and (iii) to propose an original and empirical approach to estimate the lower limit of quantification (LOQ) of a PXRF instrument and its calibration.

For quality check, each of these newly built calibrations was then validated on carbonate samples of known composition, corresponding to a series of Devonian limestones (Belgium) showing a large CaCO3 content ranging between 20 and 99 wt% and for which powder press pellets were formerly measured on a laboratory WD-XRF. These matrix-match empirical calibrations are systematically bringing improvement of the quantification efficiency, compared to the manufacturer calibrations.

 

How to cite: Da Silva, A.-C., triantafyllou, A., and Delmelle, N.: Portable X-Ray Fluorescence calibration – Workflow to Optimize the Analysis of Carbonates., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3270, https://doi.org/10.5194/egusphere-egu23-3270, 2023.

08:45–08:55
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EGU23-15052
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SSP3.3
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ECS
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On-site presentation
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Shradha Menon and Pankaj Khanna

Isolated carbonate platforms in tropical regions exhibit varying geomorphic characteristics as a consequence of differences in carbonate factories, hydrodynamic and global climatic controls. The stability of islands is dependent on the interplay between local and global factors and thus, ascertaining these factors is significant. Determining the facies and their correlation with lagoon filling is significant in determining the future of the islands to sea level rise. In the Indian context, the Lakshadweep Archipelago forms the best repository to understand the variability in sediment production to local hydrodynamics and global sea level change.

The Lakshadweep Archipelago is in the Arabian Sea off the western coast of the Indian Peninsula with an average elevation of 0.5m to 6m. This study investigates two islands, viz Agatti and Kavaratti and the adjacent lagoons utilizing sedimentological data; supplemented with satellite geomorphological studies. Geomorphic units have been identified by satellite and field studies. 42 samples have been collected from Agatti lagoon and 24 samples from the Kavaratti lagoon along E-W transects. The samples have been characterized texturally based on Dunham classification. Furthermore, petrographic analysis has been carried out for the soft sediments, representing different grain size classes to characterize the major sediment producers and grain types. These datasets are utilized to develop the depth and the first facies maps of these lagoons.

Both, the islands are approximately 4 sq km in size and are present on the eastern part of the atoll. The lagoon is about 17 sq.km for the Agatti that is more than thrice of Kavaratti that is 5 sq km. The average depth is 2m and maximum observed depth is 4m for both the lagoons. Satellite studies indicate well developed patch reefs (Acropora and Porites) and lobate sand features. The sediments are mostly coarse to medium-grained carbonate sand. No correlation between sediment size and lagoon depths has been identified. Petrographic analyses illustrate corals and foraminifera as predominant sediment producers for the coarse-grained fraction along with algae (Halimeda) and some gastropods. Based on the annual hydrodynamic patterns it is observed that the SW monsoon plays a dominant role in sediment distribution. With significant warming, the sediment production could be lowered/reduced thereby affecting the lagoon infilling and the future of the islands. The study, thus, emphasizes the necessity of acknowledging local factors and quantifying the different carbonate factories and how they will be influenced by warming seas will be critical in determining the stability of an island.

How to cite: Menon, S. and Khanna, P.: Carbonate sediment production, redistribution and accumulation in ongoing climate warming – The case of Lakshadweep Archipelago, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15052, https://doi.org/10.5194/egusphere-egu23-15052, 2023.

08:55–09:05
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EGU23-14502
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SSP3.3
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On-site presentation
Yannis Kappelmann, Hildegard Westphal, Dominik Kneer, and Thomas Mann

Reef islands accumulate as shallow landforms on or adjacent to reef complexes and are mainly composed of reef-derived carbonate sediment. Due to their unconsolidated and low-lying nature, reef islands are exposed to hydrodynamic processes, whereby they naturally experience erosion and accumulation. In order to compensate deficits of sediments lost during erosion, a sufficient supply of suitable carbonate sediment is required for accumulation. Under changing environmental conditions, the reefs are exposed to multiple stress factors that, among other things, can alter carbonate production and thus also threaten the stability of the reef islands. Hence, it is of importance to understand how past changes in the production of carbonate sediment have affected the evolution of reef islands systems, in order to assess potential future scenarios. Here we reconstruct the Holocene and recent sedimentological dynamics from one inhabited Indonesian reef island on the outer shelf of the Spermonde Archipelago, directly bordering the Strait of Makassar. We investigate the carbonate facies from sediment obtained from deep push cores up to 8 meters below surface and from shallow, hand-drilled boreholes. Targeted radiocarbon dating helps to reveal the temporal understanding of facies evolution and formation dynamics. Our data show that the island complex started to form in the mid-Holocene, around 6,400 years cal BP. The carbonate sediment from this time is almost exclusively composed of sand-sized coral fragments. Over time, the sediment composition becomes more diverse, with increased abundances of mollusks and algae, likely reflecting the ecological evolution of the reef. The shallow samples close to mean relative sea-level show radiocarbon ages of 4,000 to 3,000 years cal BP, suggesting that the initial island formed around this time and accreted in the following millennia. Of note, the proportions of the green algae Halimeda is even further increased in the youngest sediments. Overall, this suggests that the island has been able to continue growing despite changes in the ecosystems that provide the sediment, and that the increased production of green algae may have even promoted island accretion in general. Our study provides valuable insights into the dynamics of reef island development in the context of evolving reef systems and extends the understanding of Holocene island formation in the study area.

How to cite: Kappelmann, Y., Westphal, H., Kneer, D., and Mann, T.: From coral to Halimeda: Green algae as an important factor for Holocene reef island formation in Southeast Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14502, https://doi.org/10.5194/egusphere-egu23-14502, 2023.

09:05–09:15
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EGU23-1149
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SSP3.3
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On-site presentation
Adrian Immenhauser, Yisi Zhong, Stephen W. Lokier, Dominik Hennhoefer, Chelsea L. Pederson, and Mathias Mueller

Marine calcite cement's crystal habit is often considered a function of the fluid Mg/Ca ratio. In contrast, marine aragonite fabrics are commonly described as acicular (needle) cement with pointed terminations and width-to-length ratios in the order of 1:10. Similarly, botryoidal or spherulitic aragonite cements are well-known from Mesozoic (and older) reefal and slope depositional environments but are less common in Recent depositional environments. Here, we explore a wide range of abiogenic aragonite cement habits (morphologies) in caves and coastal marine depositional environments. We propose that the cement habit represents a novel (and underexplored) archive of diagenetic environment, fluid chemistry and precipitation kinetics. Based on SEM imaging, we find the often-described acicular and fibrous fabrics but also a plethora of less well-known morphotypes such as columnar (often pseudo-hexagonal prisms) and lath, tabular and sheet-like (prismatic single crystals) forms. Twinning of (flat) needle aragonite is observed and might point to precursor phases. Based on the data available, the common needle-type aragonite cement typifies normal marine diagenetic (porewater) environments. Increasingly complex habits (polysynthetic twins, flat needles, pseudo-prismatic and prismatic sheet-like) aragonite crystals) are present under increasing levels of restriction and precipitate from high-salinity porewaters. Intriguingly, pseudo-prismatic aragonite crystals are also present in meteoric, gravity-defying cave carbonates, specifically helictites. Aragonite cement habits are documented and placed into context with their depositional and diagenetic environment, and preliminary interpretations are presented.

How to cite: Immenhauser, A., Zhong, Y., Lokier, S. W., Hennhoefer, D., Pederson, C. L., and Mueller, M.: Abiogenic aragonite crystal habit – Novel archive of precipitation environment?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1149, https://doi.org/10.5194/egusphere-egu23-1149, 2023.

09:15–09:25
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EGU23-12673
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SSP3.3
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ECS
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Virtual presentation
Xutong Guan and Chaodong Wu

Oncoids and thrombolites are microbial carbonates and important indicators for paleogeography. We firstly found lacustrine oncoids and thrombolitic clots mixed with terrigenous clasts in the Lower Cretaceous in the Junggar Basin in Central Asia and aimed at their mixing process and the paleogeographic significance. We conducted a comprehensive petrological study including optical, cathodoluminescence, fluorescence, quantitative evaluation of minerals by scanning electron microscopy, Raman spectroscopy, carbon and oxygen isotopes. Intraclasts, calcite spherulites, botryoidal grains, cortoids, and ooids also mixed with the terrigenous clasts. The cortices of oncoids and ooids are composed of layers of organic carbon-rich micrites, sparry calcites, and apatites. Some oncoids exhibit alternating dark and light laminae with unequal thicknesses and binding structures of microbiota. Thrombolitic clots grew with silt-sized terrigenous clasts and ooids. Grains were cemented by fibrous, dog-tooth, and interstitial granular calcite cement, and some grains are enveloped by micrites. Compared to published data in the Tianshan Region and the Junggar Basin, positive δ13C of the mixed siliciclastic-carbonate sediments may indicate the 12CO2 absorption of microbiota. Based on the geomorphology and sedimentary distribution, we concluded that mixed siliciclastic-carbonate sediments were developed on a gentle slope with a relatively inadequate sediment supply during highstand periods. The sparry calcite-cemented mixed siliciclastic-carbonate sediments experienced rapid in-situ mixing process in an agitated lakeshore environment. Sparry carbonate cortices peeled off from the oncoids were densely packed in a shallow lake environment. These mixed siliciclastic-carbonate sediments were sedimentary response to extensive lake transgression and humidification in the Early Cretaceous following coarse-grained alluvial sediments and aridification in the Late Jurassic. 

How to cite: Guan, X. and Wu, C.: Lacustrine oncoids and thrombolitic clots mixed with terrigenous clasts in the Lower Cretaceous Junggar Basin, Central Asia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12673, https://doi.org/10.5194/egusphere-egu23-12673, 2023.

09:25–09:35
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EGU23-5993
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SSP3.3
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Virtual presentation
Timothy Tella, Gerd Winterleitner, Michele Morsilli, and Maria Mutti

Despite the numerous studies dedicated to understanding distally steepened carbonate ramps, the origin of these carbonate systems and controls over their development remain an ongoing discussion. Previous studies have shown the possible impact of climate, tectonics, inherited slope, and differential sedimentation on distally steepened ramp development. However, how these processes create steep slopes in carbonate ramps has yet to be fully understood. To test the role of different processes such as sea-level fluctuation, paleosurface inclination, differential sedimentation, and wave propagation on the geometry of carbonate ramps, we developed a highly constrained stratigraphic forward model referenced to the well-studied Upper Miocene Menorca ramp (Spain). Based on this forward model, several sensitivity analyses were performed and revealed that a complex interaction of changes in accommodation, carbonate production and sediment transport controls steep slope development in carbonate ramps. The results also show that protracted sea level low stand followed by high-frequency sea-level fluctuations with amplitude between 30 m and 40 m favour the initiation of steepened slopes in carbonate ramps. In contrast, models developed with low-frequency and higher amplitude sea-level fluctuations of about 115 m showed no significant slope development. Testing with different inclinations of paleosurfaces shows that flat-to-subhorizontal paleosurfaces result in ramps that mirror the antecedent slope. In contrast, steeper paleosurfaces tend to result in ramps with well-defined slopes. Steeper paleosurfaces also enhance facies differentiation and steep slope development than flat paleosurfaces. Our models, thus, show that the ramp profile becomes more influenced by the depth constraints on the carbonate sediment producers than by the geometry of the underlying topography as the inclination of the paleosurface increases. The models also show that shallow carbonate production tends towards steep slopes due to the low-transport characteristic due to seagrass trapping. This steepness could, however, be altered by the introduction of high-transport sediment grains from deeper carbonate producers, which fill the slopes and more distal sections of the ramp profile.

How to cite: Tella, T., Winterleitner, G., Morsilli, M., and Mutti, M.: Investigating the controls on the development of distally steepened carbonate ramps: A stratigraphic forward modelling of the Upper Miocene distally steepened Menorca ramp, Spain., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5993, https://doi.org/10.5194/egusphere-egu23-5993, 2023.

09:35–09:45
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EGU23-4075
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SSP3.3
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On-site presentation
Nadine Hallmann, Gilbert Camoin, Anton Eisenhauer, Elias Samankassou, Claude Vella, Albéric Botella, Glenn Milne, Marc Humblet, Juan Carlos Braga, Jan Fietzke, and Tyler Goepfert

The detailed reconstruction of reef geometry, composition and evolution during the mid-late Holocene brings valuable information regarding coral reef dynamics and coastal processes during periods of higher sea level and wave energy regimes.

This study provides a high-resolution reconstruction of the reef growth history in French Polynesia and their response to low-amplitude, high-frequency relative sea-level (RSL) changes and associated environmental changes over the past 6,000 years. After the stabilisation of sea level at its present position, the newdevelopment of reef systems was initiated by the creation of accommodation space due to a glacio-eustatic sea-level rise from 6.0 to 4.1 kyr BP, and controlled by the antecedent topography of the islands. A single,short-lived sea-level highstand of less than one metre between 4.1 and 3.4 kyr BP is documented preceding a fall in sea level between 3.6 and 1.2 kyr BP. The reported RSL changes are characterized by slow rates ranging from a few tens of millimetres per year up to 2.5 mm/yr and by significant sea-level stability (stillstands) lasting more than a century and up to 250 years, defining a step-like pattern.

Regionally, the persistence of stable and optimal depositional environments over the last 6,000 years is demonstrated by the constant overall composition and diversity of reef communities and the almost continuouswidespread development of microatoll fields and reef flat units. The facies distribution as well as the lateral extension and shift of facies belts have been governed by variations in accommodation space, which are controlled by RSL changes and antecedent topography. The recurrent sea-level stillstands that punctuated the mid-late Holocene sea-level history have played a significant role in the development of dense reef frameworks.

The widespread development of mid-late Holocene reef deposits in coastal areas, especially reef flat units and storm conglomerate deposits, suggests that they have played a prominent role in the formation and shaping of modern islands and islets, creating significant topographic features that formed the foundations of these islands.

How to cite: Hallmann, N., Camoin, G., Eisenhauer, A., Samankassou, E., Vella, C., Botella, A., Milne, G., Humblet, M., Braga, J. C., Fietzke, J., and Goepfert, T.: Dynamics and facies analysis of Mid-Late Holocene reef systems in French Polynesia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4075, https://doi.org/10.5194/egusphere-egu23-4075, 2023.

09:45–09:55
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EGU23-5711
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SSP3.3
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ECS
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On-site presentation
Yifan Zhang, Mathias Mueller, René Hoffmann, Sylvia Riechelmann, Sumit Chakraborty, Christopher Beyer, and Adrian Immenhauser

Dolomite, CaMg(CO3)2 and related Mg/Ca carbonates (disordered calcian dolomite, high Mg calcite, and similar) are common rock-forming minerals that occur widely in numerous diagenetic settings. They represent pore-filling precipitates (cements), diagenetic replacement phases of precursor carbonates or hydrothermal/metamorphic phases. Dolomites crystallize in the space group R-3 with trigonal symmetry and quite typical rhombohedral growth habit. A unique subtype of dolomites are saddle-dolomites which are characterized by curved (warped) surfaces. These show sweeping extinction under cross-polarized light which points to internal lattice strain. Saddle dolomites are of significance because, based on empirical evidence, they are considered to be one of the key indicators of warm-to-hot hydrothermal fluids in the burial diagenetic realm. However, saddle dolomites are not present in all natural hydrothermal deposits, and where they occur, they may coexist with Mg/Ca carbonates that often (but not always) lack warped crystal surfaces. Thus, the physicochemical conditions that lead to their formation remain unclear. We have undertaken an experimental study to explore the growth of saddle dolomites systematically as a function of various parameters (temperature, crystal size of reactants, fluid salinity, and Mg/Ca ratio of solutions). It was found that newly formed dolomites that grow epitaxially on rhombohedral or saddle dolomites exhibit warped surfaces whereas Mg-rich calcite crystals that grow on calcite seeds form flat surfaces. High Mg-calcite that forms at high temperatures (~ 220 °C) from calcium-rich fluids (Mg/Ca = 0.43) also have curved surfaces. In all cases, crystals with curved surfaces are characterized by excess calcium (Mg/Ca ~ 0.31 – 0.35). These results suggest that curvature of high Mg calcites and dolomites are related to excess Ca in the structure that causes lattice strain. Availability of dolomite precursors on which the crystals can grow, environments that provide excess Ca (e.g. highly saline ones) and rapid growth kinetics at high temperatures seem to facilitate the formation of crystals with curved surfaces. Thus this study identifies some factors that control the formation of high Mg-carbonates with curved surfaces and will aid to anticipate settings where they may be expected to occur in nature and understand why dolomites with curved as well as flat surfaces may coexist.

How to cite: Zhang, Y., Mueller, M., Hoffmann, R., Riechelmann, S., Chakraborty, S., Beyer, C., and Immenhauser, A.: Mg/Ca carbonates with curved crystal surfaces: an experimental study, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5711, https://doi.org/10.5194/egusphere-egu23-5711, 2023.

Cryogenic carbonates
09:55–10:05
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EGU23-9506
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SSP3.3
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On-site presentation
Christoph Spötl, Gabriella Koltai, Yuri Dublyansky, and Peter Németh

So-called coarse-grained cryogenic cave carbonates (CCC) have gained increasing attention in recent years as indicators of past glaciation episodes in caves. Unlike the fine-grained variety, which forms seasonally by freezing water films, the coarse-grained type has never been observed in statu nascendi. This limits the significance of geochronological and geochemical data obtained from these speleothems.

The patchy distribution of coarse-grained CCC in currently ice-free caves and recent observations of CCC associated with ice in a few modern ice caves suggest that coarse-grained CCC form by very slow freezing of pools in ice created by drip water. It is assumed that an ice cap is formed on such pools by freezing and that CCC precipitation occurs subaqueously in a semi-closed system, limiting degassing of carbon dioxide, and producing a characteristic depletion in O and an enrichment in C isotopic values. This hypothesis has never been tested.

During winter 2021/22 we conducted freezing experiments in the inner and microclimatically fairly stable part of a large Alpine ice cave (Eisriesenwelt). We filled artificial holes in floor ice with water and monitored the freezing process. Freezing was completed within a few weeks and resulted in an updoming of the ice cap, formation of radial cracks, and episodic pulses of small amounts of residual water escaping through these cracks. The newly formed ice contained abundant pressurised gas inclusions which led this ice to break easily, sometimes associated with a distinct bursting noise.

The H and O isotope data of the newly formed ice define a slope lower than the meteoric water line, consistent with theoretical and experimental freezing studies. The H and O isotope values increase from top down and from the margin to the centre of the frozen pool, consistent with a progressive centripetal advance of the freezing front.

A few tenths of gram of CCC per litre of melted ice were obtained from the inner part of the former pools. The CCC range in size from a few hundredths to several tenths of a millimetre and would thus classify as the fine-grained type. Only calcite was identified by X-ray diffraction. A variety of morphologies were found including thin plates, branched aggregates, dumbbell- and rice-shaped forms. Despite their small particle size the CCC show depleted O and enriched C isotopic compositions, similar to coarse-grained CCC of Pleistocene age from this cave, and consistent with precipitation due to progressive freezing in a semi-closed system.

Our experiments provide a first field-based validation of the conceptual model of coarse-grained CCC formation in freezing water pools. The small crystal size suggests that the freezing rate at our experimental site was likely significantly faster than in settings where mm- to even cm-size aggregates formed during climatically cold periods.

Our data also show that grain size is not a reliable indicator of the mode of CCC formation, which calls for a revision of the currently used CCC terminology (coarse vs. fine grained).

How to cite: Spötl, C., Koltai, G., Dublyansky, Y., and Németh, P.: Formation of cryogenic carbonates: experimental validation in a modern ice cave setting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9506, https://doi.org/10.5194/egusphere-egu23-9506, 2023.

10:05–10:15
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EGU23-14557
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SSP3.3
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On-site presentation
Yuri Dublyansky, Christoph Spötl, and Gabriella Koltai

Cryogenic cave carbonates (CCCs) and, more generally, cryogenic cave minerals, form by solute rejection mechanisms when water enters and freezes in caves, or parts of caves, at temperatures below the freezing point. Negative temperatures may occur in caves in conjunction with climatic factors ranging from seasonal (e.g., sag-type cave entrances or ventilated parts of caves) to millennial (development of permafrost in karst massifs) timescales. When using CCCs for paleoclimate reconstructions, it is important to understand the environment in which they were formed.

Conventionally, two ‘end-members’ of cave microclimate settings are distinguished, in which water freezes either rapidly or slowly. These settings are responsible for the formation of fine-grained (typical sizes < 1 mm) vs. coarse-grained CCC (> 1 mm; the largest individual CCC encountered so far weighs 123 g). Besides difference in size, these two types of CCC show distinct stable isotope (O and C) patterns, currently considered as the most reliable (if not the only) feature that allows discriminating between the two types. The slowly formed CCCs that are coarse grained and show characteristic trends of 18O depletion and 13C enrichment (relative to non-cryogenic carbonates from the same cave) are thought to represent markers of past permafrost.   

Although both defining features, size and stable isotopic properties of CCCs, are controlled by the rate of freezing, the control may have different characteristic times. The rate of freezing is controlled by: (1) the overcooling of the site; (2) the amount of water entering the cave; and (3) the regime of water inflow (semi-continuous or pulse-like). Large amounts of water (even of low temperature) entering a cave entrain large amounts of heat that need to be dissipated before freezing commences. Further, the release of latent heat maintains the temperature of the freezing water body at 0 °C for the duration of the freezing process. Slow freezing leads to progressive depletion of the residual water in 18O and, as a result, CCCs are also increasingly depleted in 18O. We observed depletions of several permil in the time span of a few days in laboratory experiments.  

In caves located in relatively cold environments (e.g., Alpine or high-latitude caves) seasonal freezing conditions can be created by low-intensity influx of outside cold air into sections of caves located in already relatively cold rock. In such zones a small overcooling may be maintained for a sufficiently long time, producing CCCs with isotope properties mimicking (partly or entirely) those of CCCs forming in static settings of “true” permafrost.

How to cite: Dublyansky, Y., Spötl, C., and Koltai, G.: Settings of cryogenic cave carbonate formation, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14557, https://doi.org/10.5194/egusphere-egu23-14557, 2023.

Posters on site: Tue, 25 Apr, 14:00–15:45 | Hall X3

Chairpersons: Katja Goetschl, Gabriella Koltai, James Hendry
X3.68
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EGU23-16743
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SSP3.3
Chelsea Pederson, Tobias Kluge, Vasileios Mavromatis, and Adrian Immenhasuer

The clumped isotope (Δ47) proxy provides specific information on formation conditions of carbonate minerals, for example the related fluid temperature. Although the clumped isotope paleothermometer often allows the direct temperature reconstruction due to the measurements being relatively free of vital effects or mineral-specific fractionation, clumped isotope geochemistry during the diagenesis and recrystallization of sedimentary rocks is understudied. This work evaluates clumped isotope data during the alteration of bivalve shells to better understand how the proxy develops under varying diagenetic conditions. Aragonitic bivalves were experimentally altered in closed vessels with variations in durations (0-16 weeks), fluid chemistry (burial and meteoric fluids) and temperature (130 to 200°C).

Results generally show increasing calculated temperatures (lower measured Δ47 values) with increasing experimental temperature and duration. Different fluid chemistries (burial versus meteoric fluids) also resulted in a constant offset of values for modern samples following alteration. Fossil carbonates seem to be more resistant to alteration of Δ47 values, indicating a reduced alteration potential compared to modern samples. Lastly, fast re-equilibration during the alteration experiments seem to follow a relatively simple model, similar to the proposed solid-state isotope re-ordering model of Passey and Henkes (2012) and others, but at much higher rate constants and starting at lower temperatures.

How to cite: Pederson, C., Kluge, T., Mavromatis, V., and Immenhasuer, A.: Clumped isotope evolution during aragonite diagenesis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16743, https://doi.org/10.5194/egusphere-egu23-16743, 2023.

X3.69
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EGU23-2818
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SSP3.3
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ECS
Ancilla Maria Almeida de Carvalho, Youri Hamon, Olinto Gomes de Souza Junior, Nivea Goulart Carramal, and Nathalie Collard

The Aptian carbonate rocks of Santos Basin, in the Brazilian southeastern continental margin, show reservoir quality strongly controlled by the characteristics of the depositional environment and associated diagenetic alterations. This study presents a quantitative approach based on petrography, mineralogy, and geochemical data of the Barra Velha Formation to integrate spatial and stratigraphic distribution of sedimentological and diagenetic aspects and provide insights into the parameters controlling the genesis and distribution of the diagenetic phases of Pre-Salt carbonate reservoirs of Santos Basin.

The Barra Velha Formation consists of a heterogeneous mix of in-situ and reworked grains. The in-situ facies are composed of fascicular calcite (shrubs), spherulites, microcrystalline calcite, and clay minerals, whereas the reworked facies present different proportions of shrubs and spherulite fragments, siliciclastic/volcanoclastic grains, and variable clay content. The facies with higher Mg-clay content predominate in lower structural positions and regions with low relative relief. Higher proportions of spherulites occur in the transitional zones, and fascicular calcite occurs preferentially in the transitional and higher structural areas. Grainstone facies are observed in all depositional environments but with variations in their composition (intraclasts, siliciclastic/volcanoclastic grain, and clay content). Stratigraphically, facies with higher Mg-clay content predominate in Units 3 (base) and 2 (intermediate), whereas Unit 1 (top) is marked by a higher proportion of grainstones and fascicular calcites. In Unit 1, fascicular calcite crusts tend to expand from the structural high toward lower areas.

The main diagenetic products and their association with different facies highlight the roles of depositional settings and primary constituents in the diagenetic processes. The tectonic and climatic context of the BVF favored Mg-clay precipitation that accumulated preferentially in lower structural portions of the basin. Mg-clays also show a preservation pattern strongly linked to the structural setting, with higher structural portions and fault zones more susceptible to their major diagenetic alterations. Dolomite is a major diagenetic phase in the studied samples, followed by silica. These diagenetic phases are largely associated with Mg-clay alteration and predominate in Unit 1. The dissolution of Mg-clays and high alteration of the carbonate phases are concentrated in higher structural positions. Given the higher occurrence of faults in these areas and the presence of saddle dolomite, barite, celestine, and fluorite, which can be associated with hydrothermal alterations, part of the dissolution processes may be related to hydrothermal processes. The depositional and diagenetic aspects indicate a close connection between the hydrochemical evolution of the lake waters with the origin and diagenesis of these deposits.

 

How to cite: Almeida de Carvalho, A. M., Hamon, Y., Gomes de Souza Junior, O., Goulart Carramal, N., and Collard, N.: Spatial and stratigraphic distribution of sedimentological and diagenetic features of an Aptian carbonate reservoir of the Santos Basin, Brazil., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2818, https://doi.org/10.5194/egusphere-egu23-2818, 2023.

Cryogenic carbonates
X3.70
|
EGU23-8350
|
SSP3.3
Gabriella Koltai, James U.L. Baldini, Christopher J. Ottley, Alexander A. Iveson, and Christoph Spötl

Coarsely crystalline cryogenic cave carbonates (CCC for short) are unique speleothems that precipitated in small water pools in cave ice via slow freezing. Their formation requires cave air temperatures very close to the 0°C isotherm. CCC have become increasingly important over the last decade and are one of the best terrestrial archives providing highly precise chronological constraints on paleo-permafrost degradation. Although a growing number of studies use CCCs as a time-marker of permafrost thawing, the details of their formation mechanism remain unanswered.

CCC found at over a dozen sites in the ice-free parts of Eisriesenwelt (Tennengebirge, Eastern Alps) cover a wide spectrum of morphologies from skeletal crystals to more complex beak-like and hemispheric structures. At some sites one or two morphologies are dominant, while at other sites several different types occur together. The mechanisms of formation of many of the morphologies remain enigmatic.

Here we present first results of high-resolution trace element (Mg, Sr, Ba, and U) and stable isotope (C and O) analyses of a white pea-like spherulite (~8 mm) and two beak-like aggregates (~12 and 15 mm in diameter) from Eisriesenwelt. The latter type shows an amber-coloured inner core, overgrown by more porous light brown to almost whitish calcite.

Oxygen isotope ratios of one of the beak-like aggregates reduce progressively by 4.8‰ from the core towards the rim, while carbon isotope values increase by 2.1‰, reflecting the progressive freezing of the water. The dark brown calcite is characterized by low Mg, Sr, and Ba but high U values compared to the light brown calcite. Trace element analyses also indicate an increase in Mg and Sr towards the rim, whereas U shows the opposite trend. In the white hemispheric spherulite sample, oxygen isotope ratios show a larger (up to 2‰) intracrystalline variability, and a 5.8‰ decrease over the last 2 mm of the sample. In contrast, carbon isotope values vary only by 0.5‰. Mg values show an increasing trend through time, from core to rim. Sr, U, and Ba concentrations do not exhibit a clear pattern, except for a sharp change before the cessation of CCC growth. This is likely related to the presence of a thin (hundreds of 100µm), translucent calcite rim, expressed as an increase (decrease) in Mg, Sr, U (and Ba) concentrations. In both morphologies Ba follows a similar pattern as Sr, however Ba values decrease progressively before the cessation of CCC growth.

Formation of CCC of the coarse crystalline variety has not been observed in-situ, limiting their significance as robust indicators of thawing conditions in ice caves. Studying individual CCC samples using a combination of high-resolution stable isotope and trace-element analyses is an important, but currently underdeveloped, approach to improving our understanding of CCC formation.

How to cite: Koltai, G., Baldini, J. U. L., Ottley, C. J., Iveson, A. A., and Spötl, C.: High-resolution stable isotopic and trace element data of cryogenic cave carbonates from an alpine cave: preliminary results, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8350, https://doi.org/10.5194/egusphere-egu23-8350, 2023.

X3.71
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EGU23-1133
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SSP3.3
|
ECS
|
Anett Lázár, Máté Karlik, Zsombor Molnár, Attila Demény, and Péter Németh

Ikaite (CaCO3*6H2O) is a cryogenic calcium carbonate phase, which forms below about 5°C. If the temperature increases above 5-7 °C ikaite transforms to calcite. Understanding the transformation process is important to interpret paleoclimatological data from glendonites, i.e., calcite pseudomorphs after ikaite in sediments. Tollefsen et al. (2020) suggested that the transformation occurs via a coupled dissolution–reprecipitation mechanism at the ikaite–calcite interface (1). In contrast, Vickers et al. (2022) proposed a quasi-solid state ikaite to calcite transformation mechanismand suggested that stable isotope data of glendonite can be used for reconstructing paleotemperatures(2). However, in sediments the majority of the ikaite to calcite transformation occurs in diagenetic environments, where ambient solutions interact with the transforming mineral.

We synthesized ikaite at 2 °C in alkaline environment in order to study its transformation using organic solvents, vacuum pumping and rapid (1 min) heating from 5 to 30 °C. These experiments indicated the formation of amorphous calcium carbonate (ACC) during the ikaite to calcite transition. We also monitored the ikaite transformation by letting the 2 °C parent solution to reach room temperature (25 °C) within ~5 hours. We observed ACC and calcite formations depending on the alkalinity of the parent solution. Our experiments suggest that the ikaite to calcite transition is a two-step process consisting of the solid-state ikaite → ACC transformation and the ACC → calcite dissolution–reprecipitation mechanisms. During these transitions ikaite lost all its water but preserved its original morphology. We hypothesize that the occurrence of a transient amorphous phase during the ikaite to calcite transition implies the alteration of the isotopic data, similar to what was reported for the ACC to calcite transition (3).

We acknowledge the financial support of NKFIH ANN141894 grant.

 

References:

(1) E. Tollefsen, T. Balic-Zunic, C. M. Mörth, V. Brüchert, C. C. Lee and A. Skelton, Scientific Reports, 2020, 10, 8141.

(2) M. L.Vickers, M. Vickers, R. E. M. Rickaby, H. Wu, S. M. Bernasconi, C. V. Ullmann, G. Bohrmann, R. F. Spielhagen, H. Kassens, B. P. Schultz, C. Alwmark, N. Thibault and C. Korte, Geochimica et Cosmochimica Acta, 2022, 334, 201-216.

(3) A. Demény, Gy. Czuppon, Z. Kern, Sz. Leél-Őssy, A. Németh, M. Z. Szabó M. Tóth, C.-C. Wu, C.-C. Shen, M. Molnár, T. Németh, P. Németh and M. Óvári, Quaternary International, 2016, 415, 25-32.

How to cite: Lázár, A., Karlik, M., Molnár, Z., Demény, A., and Németh, P.: Ikaite (CaCO3*6H2O) -> ACC (amorphous calcium carbonate) -> calcite transformation and its paleoclimatological implication, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1133, https://doi.org/10.5194/egusphere-egu23-1133, 2023.

X3.72
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EGU23-9098
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SSP3.3
|
ECS
Michael Wedenig and Martin Dietzel

The formation of CaCO3 under ambient and low temperature environmental conditions has been extensively studied during the last decades. However, available data on the formation kinetics and mechanisms of CaCO3 at temperatures far below 0 °C are sparse. Here, we present CaCO3 formation pathways at -15 °C using a hypersaline sodium chloride solution at distinct molar Mg:Ca ratios of 0, 0.5, and 1. The (trans)formation process is monitored by pH and in-situ Raman spectroscopy. The freeze-dried precipitates are characterized by X-ray diffraction and the morphology is studied by scanning electron microscopy. These preliminary results help to understand the formation mechanisms of CaCO3 at temperatures below zero degree centigrade from homogeneous media and to refine experimental setups for mimicking extreme environmental carbonate formation conditions, e.g., in Antarctica or extraterrestrial environments.

How to cite: Wedenig, M. and Dietzel, M.: CaCO3 formation at -15 °C and non-freezing conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9098, https://doi.org/10.5194/egusphere-egu23-9098, 2023.

Posters virtual: Tue, 25 Apr, 14:00–15:45 | vHall SSP/GM

Chairpersons: James Hendry, Gabriella Koltai, Katja Goetschl
vSG.11
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EGU23-7994
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SSP3.3
Marie Diane Tonye, Salomon Bertrant Bisse, Gaspard William Manga Owona, Cédric Belinga Belinga, Boris Secke Bekonga Gouott, and Emile Ekomane

The Babouri-Figuil Basin is located in the northern part of Cameroon and is part of the Bénoué trough. One of the most remarkable features of this basin is the presence of carbonate concretions commonly called septaria. However, the understanding of nature of these concretions remains limited. In the first phase of this study a detailed field work was carried in the basin. The Babouri-Figuil Basin has four lithofacies encompassing limestones, marlstones, sandstones and conglomerates. Its depositional environment is fluvial to fluviolacustrine. These facies are organized in asymmetrical synclines and crossed by basaltic intrusions. The concretions identified occurs in the marly facies. Numerous descriptive criteria noted in the field made it possible to give their size, their context of establishment, as well as the factors which control the forms of these septarias. These septarias are greyish or dark brown and massive in structure. Their size varies from 15-57.5 cm with circumferences ranging from 23-87cm. They also have intersection cracks due to their maturity or aging. These intersection of septarian cracks are filled and indicate different generations. Ovoid, rounded, disc, elongated and chocolate bar morphologies have been observed in the study area. These shapes are controlled by the thickness and shape of the marls. Thus, where the thickness is important, the septarias are well developed and generally take ovoid, rounded or spherical shapes because the marl has weak planes. On the other hand, when the thickness of the marl is thin or in lens, the septarias tends to follow only the space and the shape that the marl occupies and, tending to make it disappear, thus creating elongated, flattened and even rounded shapes. Consequently, the septarias of the Babouri-Figuil Basin is post-sedimentary to the marl deposits.

How to cite: Tonye, M. D., Bisse, S. B., Manga Owona, G. W., Belinga Belinga, C., Secke Bekonga Gouott, B., and Ekomane, E.: Septarias in the Babouri-Figuil Basin (Northern Cameroon): Morphology and controls on emplacement., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7994, https://doi.org/10.5194/egusphere-egu23-7994, 2023.

vSG.12
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EGU23-6209
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SSP3.3
Weijing Liu

The Lower Cambrian carbonate platform sequences in the central Tarim Basin play an important role in controlling the development of hydrocarbon source rocks and reservoirs, as well as the formation and distribution of oil and gas. A large number of studies have been conducted on its formation and evolution, but most of them are based on qualitative analysis and paid little attention to the influence of differential deposition of the carbonate platform sequences.

Based on previous research findings and supplementary analysis of key seismic sections, outcrops, well logs, core, and cuttings, we have investigated the Early Cambrian paleoenvironment in the central Tarim Basin. By using the Earth System Science approach, we studied the Lower Cambrian carbonate platform sequences through stratigraphic forward modeling (SFM) by taking into consideration of key geological factors such as the initial paleo-topography, tectonic movement, high-frequency sea-level changes, carbonate growth/denudation, and clastic sediment input. The 3D stratigraphic forward model was calibrated and validated using a variety of geological data.

Through uncertainty analysis of different geological factors and variables, and combined with previous research findings, we have systematically analyzed the tectono-sedimentary evolution process responsible for the development of the carbonate platform margin facies in both time and depth domains and evaluated the contribution of key factors on the evolution of platform margin facies quantitatively, and finally clarified the formation mechanisms and evolution model of the platform margin facies in central Tarim Basin.

The study showed that the initial paleogeomorphology and tectonic subsidence jointly controlled the fluctuation of relative sea level, which determined the migration direction and internal structure of the carbonate platform margin. The differential stratigraphic architecture and stacking patterns of the carbonate sequences were primarily caused by the exposure duration and the slope angles of the platform margin collectively.

How to cite: Liu, W.: Tectono-sedimentary evolution in central Tarim Basin during the early Cambrian: New insights from stratigraphic forward modeling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6209, https://doi.org/10.5194/egusphere-egu23-6209, 2023.

Cryogenic carbonates
vSG.13
|
EGU23-1178
|
SSP3.3
|
ECS
|
Ozioma Carol Uwakwe, Sylvia Riechelmann, René Hoffmann, Christoph Spötl, Anne Jantschke, and Adrian Immenhauser

Cryogenic cave carbonates (CCCs) are speleothems precipitated from freezing water bodies in caves. A series of scholarly papers have explored natural CCC precipitation kinetics, crystal habit, mineralogy, crystallography and geochemistry. However, cave depositional environments are complex multi-parameter systems, and the inherent difficulty of unravelling the physicochemical parameters of ancient speleothem formation also applies to CCCs. In order to test previous models and concepts, experiments were conducted by cooling calcium-rich bicarbonate water under controlled laboratory conditions. The experiments involved calcite precipitation at different durations (6 to 91 days) and temperatures (1, +0, -0.5, -0.7, -1 and -2 °C). The results show that subtle changes in temperature and calcite saturation index (SIcc) remarkably affect the CCC morphological variability and mineralogy. Rhombohedral calcite crystals precipitated both in experiments with and without ice. In contrast, spherulitic crystals (vaterite) precipitated from near-completely frozen waters with high calcite saturation indices. Experimental water monitoring revealed increased calcite precipitation followed by decreased water conductivity values. The formation of CCCs is accompanied by non-equilibrium reaction kinetics, which tends to enrich the isotopic composition of the parental water. Longer experimental durations lead to increasing CO2 degassing and 13C enrichment of the water. Data from the first experimental work dealing with cryogenic carbonate precipitation and isotope geochemistry, as documented here, shed light on the origin of these peculiar speleothems and provides constraints to interpret morphologies and isotopic compositions of ancient CCCs.

 

How to cite: Uwakwe, O. C., Riechelmann, S., Hoffmann, R., Spötl, C., Jantschke, A., and Immenhauser, A.: Experimental precipitation of cryogenic calcite and vaterite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1178, https://doi.org/10.5194/egusphere-egu23-1178, 2023.