SSP3.3

Sea level reconstruction based on vertical distribution of grain-size parameters and carbonate content 
in beach ridge plains
Ionel-Bogdan STAN1*
, Alfred VESPREMEANU-STROE1,2, Luminita PREOTEASA1,2, Laurentiu TUTUIANU1
1 GEODAR Research Center for Geomorphology, Geoarchaeology and Paleo-Environments, Bucharest University, 1 N. Bălcescu, 
01004 Bucharest, Romania; 
2 Sfântu Gheorghe Marine & Fluvial Research Station, Faculty of Geography, Bucharest University, Sf. Gheorghe, Tulcea, 
Romania;
*Correspondence to: Stan Ionel Bogdan. E-mail: ionel.bogdan.stan@gmail.com
KEY WORDS: SLIP, SEA-LEVEL in Late Holocene, Western Black Sea
Accurate sea-level reconstruction is important in modelling and anticipating the effects of currently
accelerated eustatic changes and the associated landscape changes.
The methodologies that determine the paleo-sea level currently involve various level indicators - Sea 
Level Index Points (SLIP) -, such as: (a) basal peat (formed in lagoons and swamps whose substrate is 
very close to contemporaneous mean sea level), (b) biological indicators: those species that support 
very shallow depths or that live at known depths, (c) speleothems (which cannot directly quantify sea-
level, but may indicate a maximum level below which the sea surface was during their formation), (d) 
archaeological material of past sea level significance (e.g., harbour structures), (e) marine terraces. Yet, 
the uncertainty range of these SLIPs is large and new and more accurate indicatora are necessary. 
Our previous studies on the morphology and sedimentology of beach ridge plains from Danube Delta 
(Preoteasa and Vespremeanu-Stroe, 2010; Vespremeanu-Stroe et al., 2016) suggest the imprint of the
mean sea level on the vertical distribution of textural parameters of sediments in the (former) foreshore 
system, especially on the beach face and berms. In the present study, we examined the vertical 
distribution of the sedimentary parameters and inorganic carbonate content along cross-shore profiles 
on several beach ridge plains from the Danube delta to capture those changes attributed to mean sea-
level changes on a larger time scale. OSL dating of the berm sediments on successive beach ridges was 
undertaken to constrain the chronological framework of the BRP formation and sea-level variation.
Our analysis shows the content of inorganic carbonates usually increases within ca. 15-30 cm envelope 
near the mean sea level and that the sediment sorting becomes poorer in the mid and lower beach face 
zone comparative to the upper beach face and berm sediments. These results supports a new method to 
track sea-level in beach ridge plains at a comparatively better resolution. A preliminary sea-level curve 
for the last 3500 years was obtained based on new data from Danube delta strandplains which shows
clear fluctuations in sea level during different climatic periods.

How to cite: Stan, I. B.: Sea level reconstruction based on vertical distribution of grain-size parametri and carbonate content in beach ridge plains, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-600, https://doi.org/10.5194/egusphere-egu22-600, 2022.

Quaternary carbonate islands have contributed significantly to the fundamental understanding of the interplay between climate and early diagenetic processes in carbonates. However, most of the studied islands, such as the carbonate islands on the Great Bahamas Bank, are situated in humid climate zones. Contrary to this, the Al-Wajh carbonate platform, situated within the arid African-Arabian desert belt on the NE Red Sea shelf (Saudi-Arabia), hosts a plethora of poorly studied carbonate islands. These islands were likely formed during the Last Interglacial (LIG) sea level highstand, commonly defined by Marine Isotope Stage 5e (MIS 5e: 124 – 119 ka). As such, these islands provide an excellent opportunity to give new insights into the paragenesis of carbonate islands within an arid climatic setting and an overall regressive/transgressive sequence.

This study investigates Shurayrah Island, located in the southern part of the Al-Wajh platform lagoon. Shaped by the prevailing NW wind direction, Shurayrah Island has an elongated shape, while a reef belt is established on the upwind NW side and carbonate sand spits accumulate on the leeward SE side. The main data base consisted of five drill cores with a total recovered length of 61 m and 150 thin sections. Eight lithofacies (LFT) and 17 microfacies types (MFT) were differentiated, including, amongst others, coral framestones, coral float- & rudstones and ooid-bioclast grainstones. Diagenetic analysis was based on a detailed petrographic investigation, while porosities (Φ) were measured from thin sections with digital image analysis (n = 150) and core plugs using a helium porosimeter (n = 102). 

Results reveal generally high porosities (mean Φ from thin sections = 29 %; mean Φ from core plugs = 45 %). Pore types are dominated by primary pores in the growth framework of coral framestones and secondary moldic & vuggy pores. Dissolution features are most pronounced in coral framestones, which show almost complete dissolution of original aragonite microstructures. Cement types include dog tooth, pore-filling and bladed cements, with a dominance of dog tooth cements in terms of frequency. Aragonite fibrous cements only occur scarcely and can be overgrown by dog tooth cements. Additionally, dog tooth and bladed cements are frequently observed to grow inside moldic pores.

The diagenetic analysis clearly reveals a dominance of porosity creating processes (dissolution) vs. porosity reducing processes (cementation) during paragenesis. In addition, results emphasize the importance of facies-controlled diagenesis: high primary porosities combined with metastable mineral composition of aragonite in coral framestones, result in a high meteoric diagenetic potential. Cement stratigraphy indicates a shift in the diagenetic realm, transitioning from marine (MIS 5e) to meteoric (MIS 5d – MIS 2) conditions, followed by a return to a marine setting with the Holocene Transgression (MIS 1). The overall strong meteoric diagenetic overprint suggests the influence of temporary humid phases (MIS 5c & a), during the overall >100 ka long subaerial exposure period. The observations highlight the significance of short-term climate fluctuations introducing meteoric waters for the diagenesis of carbonate islands in arid climate belts.

How to cite: Chirakal, T., Petrovic, A., Oyinloye, M., and Vahrenkamp, V.: Paragenesis of a Pleistocene Carbonate Island in the African-Arabian Desert Belt (Al-Wajh Carbonate Platform Lagoon, NE Red Sea, Saudi-Arabia), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8522, https://doi.org/10.5194/egusphere-egu22-8522, 2022.

Carbonate tepee structures are believed to initiate through cement growth in shallow marine hardgrounds causing lateral expansion and leading to upward buckling of cemented layers commonly along polygonal boundaries.  They reportedly form in subtidal to supratidal marine settings and are stratigraphically important markers for exposure and cycle boundaries in ancient rock sequences.  Yet in modern carbonate settings only minor occurrences have been reported from the Arabian Gulf in Abu Dhabi and Qatar as well as in Australia.  We have discovered two spectacular fields of giant polygonal tepee structures on Sheybara Island, a part of the Al Wajh carbonate platform in the NE Red Sea, KSA. Satellite and drone data were used to measure the dimensions of polygons. Samples have been collected from three transects and two boreholes for age dating, petrographic and geochemical analysis. The tepee fields cover an area of 420,000 m² and 130,000 m², respectively, in the supratidal to intertidal environment on the ocean facing side of the island.  Individual tepees are composed of chaotically superimposed rugged slabs reaching 3-10 cm in thickness.  Tepee ridges range in height from 10-50 cm.  Tepees are aligned along larger structures of well-defined polygonal shapes.  Their diameters range from 5m to 55m (n =100) with the majority having a diameter of 10-25 m (n=69).  Peculiar to many polygons is a central domal buckle with extensional fracture patterns. The tepees have formed in a well-cemented layer of shallow marine bioclastic sand to gravel-sized sediments composed predominantly of coral, red algae, benthic foraminfera, bivalve and gastropod debris that overlie a paleo-reef flat.  Grains are heavily micritized, cemented by clotted micrite and fibrous to acicular rim cements and occasionally covered by lace-like meshes of organic matter, likely indicating microbial activity.  SEM images from tepee samples show evidence for the presence of microbial activity - biofilms, morphologies that strongly resembles filamentous and coccoidal cyanobacteria, and mineralized cyanobacterial mats. Environmentally corrected C¹⁴ age data indicate that polygons formed between 3000 to 1000 years before present (b.p.) correlating with a sealevel regression from a mid-Holocene sealevel highstand some 4000 to 5000 years b.p.  Dead and blackened finger corals commonly encrust tepees indicating that the elevated tepee crusts provide preferential seeding for coral colonialization upon re-submergence.

How to cite: Vahrenkamp, S., Panagiotou, M., Petrovic, A., Khanna, P., Chandra, V., and Vahrenkamp, V.: Giant polygonal Tepee structures discovered in the NE Red Sea - AL Wajh carbonate platform, KSA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4156, https://doi.org/10.5194/egusphere-egu22-4156, 2022.

Stromatolites are the vestige of first life on earth and were the dominating carbonate forming marine biota in the Archean and Proterozoic.  During the course of the Phanerozoic their importance in producing carbonates has been reduced to niche occurrences usually found in challenging environments, such as hypersaline marine settings and alkaline lakes.  Most recently, the discovery in 2010 of a new chlorophyll type - chlorophyll f - from stromatolites in Hamelin Pool in Shark Bay, Western Australia has sparked much additional interest in the genesis and composition of modern stromatolites.  

We report the discovery of stromatolites in the NE Red Sea on Sheybara Island, Al Wajh carbonate platform, KSA.  Based on satellite and drone surveys calibrated by site surveys, the Red Sea stromatolites are distributed over an area of about 50,000 m² in an intertidal to very shallow subtidal setting on a paleo-reef flat facing the open sea.  Two principal growth shapes are recognized: (i) elongated rhomboidal structures 10-100 cm in length, up to 5-50 cm in width and up to 10 cm in height and (ii) low relief (height <3 cm) irregular shaped tabular sheets in the shallow subtidal environment.  The rhomboidal intertidal stromatolites are pustular on the outside and laminated internally. X-ray CT scanning of the stromatolite samples showed moderately well laminated, millimeter scale, lithified layers potentially representing alternating modes of sedimentation and growth. Scanning Electron Microscopy (SEM) revealed that laminae consist of heavily bored carbonate grains, calcified tubes of filamentous cyanobacteria, mucoid sheets and spider-web like organic matter of likely dehydrated extracellular polymeric substance (EPS).  Carbonate precipitates of sub-micron size equant crystals and elongated aragonite needles, either occurring as single rods or in mashes, were also apparent from SEM. Molecular analysis of bacteria diversity show that cyanobacteria dominate the stromatolite surface, while heterotrophic bacteria are the main component in deeper layers.

During a sampling campaign in March 2021 salinity, pH and dissolved oxygen have been measured with average values at 42ppt, 7.8±0.1 and 5.9±0.5mg/L, respectively, typical for coastal Red Sea surface marine waters.  Water temperatures range from 18°C in the winter to 29°C in the summer.  During exposure at low tides surface temperatures over the tidal flats may fall as low as 12°C in the winter exceeding 43°C in the summer.  Large numbers of cerithid gastropods were found grazing on the stromatolite surfaces apparently not affecting their growth.

Hence, the setting and conditions are overall similar to some of the stromatolites found on the Exuma Islands in the Bahamas, the only other known occurrence of stromatolites in normal marine waters.  Research is continuing on the environmental conditions, the aerial distribution, the microbial diversity and chemical composition of these modern stromatolites to determine why they form in this particular location and if they are similar or not to other reported occurrences of stromatolites.

How to cite: Vahrenkamp, V., Garuglieri, E., Petrovic, A., Khanna, P., Chandra, V., Marasco, R., Van Goethem, M., and Daffonchio, D.: Modern Marine Stromatolites discovered in the NE Red Sea - Al Wajh carbonate platform, KSA, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3899, https://doi.org/10.5194/egusphere-egu22-3899, 2022.

The interplay between carbonate production and siliciclastic input in marine mixed depositional systems results in spatially complex distribution of facies. In this study, we investigate this interplay in a lacustrine setting to explore hypotheses for the facies distribution and stratigraphic architecture in such settings. The Yacoraite Formation (Maastrichtian-Danian) is a mixed lacustrine carbonate-siliciclastic succession within the Salta Group in the Salta rift Basin (Argentina). The Yacoraite Fm has been thoroughly characterized in the southern part of the basin (Metán-Alemania sub-basins), whereas the northern sub-basin of Tres Cruces, focus of this study, remains largely understudied. In this project we applied high-resolution stratigraphic and sedimentological analyses to characterize in detail the depositional environment and the stratigraphic architecture of the Yacoraite Fm. Facies are mainly represented by lacustrine marginal and littoral associations. The facies associations, their distribution and stacking pattern are interpreted to reflect deposition in a predominantly shallow water balanced-fill lake basin type. Littoral and sub-littoral facies associations are dominated by oolitic, skeletal and microbial carbonates, frequently intercalated with fine-grained siliciclastic facies, ranging from mudstones and siltstones deposited in mudflats, shoreline sandstone deposits and distal profundal shales. The Yacoraite Fm is tentatively subdivided in two intervals. The lower part (lower 100 m) is characterized by carbonate-dominated facies, showing a marked and regular cyclicity, with metric-scale sequences of carbonate-dominated facies overlying fine-grained siliciclastics and mudstone-wackestone. These cycles are interpreted as shallowing-upwards cycles, composing the regressive hemicycles of metric-scale Transgressive-Regressive (T-R) cycles. These cycles are often asymmetric and result from lacustrine expansion-contraction cycles, controlled by climatically influenced lake-level fluctuations. The middle-upper part (m 100 to 220 circa) is dominated by siliciclastic facies and is characterized by a decrease in regularity of cyclicity, with high frequency T-R cycles being asymmetric and often lacking the transgressive hemicycles. Frequent desiccation cracks and tepees mark the top of the regressive hemicycles in the middle to upper part, indicating repeated sub-aerial exposures. Our observations are in line with the hypothesis that alternating phases of deposition between clastic-dominated facies and carbonate-dominated facies are the result of climatically driven lake-level fluctuations. Carbonate production is enhanced during arid climatic phases (lake contraction), whereas siliciclastic-dominated facies are mainly deposited during humid phases, coeval with an increase of water inflow and sediment input into the lake, corresponding to expansion phases. Based on our sedimentological and stratigraphical analysis the evolution of the lake system has been inferred, with the identification of two lake stages in the evolution of the Yacoraite paleo-lake. A first lake stage is characterized by a perennial lake system that progressively changes into a more rapidly fluctuating ephemeral setting; this shift appears to be gradual as there is no clear stratigraphic expression corresponding to the transition itself. Climate appears to be the primary control on the stratigraphic architecture, with rapid lake-level variations resulting in sharp facies transitions from carbonate to siliciclastic facies and prevalently stratigraphic mixing. Compositional mixing is limited to the littoral facies, due to the local presence of siliciclastic input sources by riverine inflows into the Yacoraite paleo-lake system.

How to cite: Vallati, M., Tomás, S., Winterleitner, G., Galli, C., and Mutti, M.: Exploring hypotheses about mixed carbonate-siliciclastic successions in lacustrine settings: a case study from the Yacoraite Formation (Salta Basin, Argentina), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11724, https://doi.org/10.5194/egusphere-egu22-11724, 2022.

Carbonates often experience a heterogeneous distribution of pore system properties caused by overprinting of the primary pore fabric by multiple phases of diagenetic modifications, leading to high uncertainties in predicting porosity and permeability. This has been also observed in the Middle Miocene marginal lacustrine carbonates of the Nördlinger Ries crater lake in Southern Germany, where primary pore types are overprinted by subsequent phases of diagenetic processes and their products, such as the formation of secondary pores by dissolution and the occlusion of pores by calcite cement. These modifications in the pore system occur patchily, vary at sub-centimeter scale and show no facies-dependence. The goal of this study was to precisely capture diagenetic features on thin section images by using Digital Image Analysis (DIA) and then quantify the impact of secondary pore formation and cementation on porosity and permeability generation. This further allows for reconstructing the pore system throughout each stage of its evolution, both numerically and visually. At first, thin section images have been acquired from rock cylinders which have been used to determine total porosity and permeability with routine gas-injection method, revealing a non-relationship between both petrophysical parameters in the studied lacustrine carbonate succession. The images were then processed with DIA in order to segment the pore space, classify primary and secondary pore types, and detect the calcite cement. Various pore geometry parameters have then been measured to infer porosity and permeability. By processing each thin section image with a graphic software, pore system representations for each diagenetic stage have been produced and then repeatedly analysed with DIA. The resulting quantitative data have then been compared with the previously obtained values of the original pore system, resulting in distinct values of porosity-permeability change for diagenetic stage. Due to the formation of secondary pores, porosity has increased to 14.42 % in average and permeability has increased towards 227.07 mD. Cementation of pore space instead caused a decrease in porosity towards 8.44 %, whereas permeability has decreased to 154.53 mD. The percentage of change in porosity (- 41.47 %) and permeability (- 31.94 %) by cementation can then be used as quantitative measures characterizing the impact of cementation on porosity and permeability. Since cementation occurs patchily, varies at a sub-centimeter scale and can therefore not be precisely located in the studied outcrop, these distinct values serve as lower threshold values for porosity and permeability estimations. This allows for assessing the origin of the previously observed heterogeneous porosity-permeability distribution which cannot be realized by using routine petrophysical measurements, solely. With the hereby presented approach it is demonstrated how quantitative information obtained from DIA applied on thin section images highly improve the prediction of porosity and permeability as well as the distribution of diagenetic features both in the outcrop and the subsurface.

How to cite: Maerz, S. and Mutti, M.: Reconstructing Pore System Evolution with Digital Image Analysis (DIA): A case study from Miocene Lacustrine Carbonates (Southern Germany), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12140, https://doi.org/10.5194/egusphere-egu22-12140, 2022.

Understanding the roles played by biota in the evolution of carbonate architecture requires integrating interdisciplinary datasets due to the complex interplay of biological, oceanographic, mineralogical and ecological factors that create stratigraphic and sedimentological changes in carbonate systems through geologic time. Stratigraphic forward modelling enables this approach by using mathematical equations, algorithms and empirical assumptions to numerically reproduce the processes and factors that acted over geologic time. One of the many factors that strongly influence stratigraphic heterogeneity and architectural evolution of carbonate systems is biogenic carbonate production, whose impact still requires detailed investigation. Hence, in this study we attempted to investigate, using stratigraphic forward modelling, the role of different biogenic sediments in the evolution of carbonate systems geometries using the Llucmajor platform as a reference case study.

We developed several forward models of the coral-dominated Llucmajor platform based on parameters from published outcrop and well data, as well as modern analogues. These models were validated through comparison with published outcrop and well data, leading to the reference model on which several sensitivity analyses were carried out. Carbonate production was modelled by creating five model sediment classes (massive corals, dish corals, reworked grains, and muds, and rhodalgal sediments) to reflect the biotic associations that have been interpreted from outcrops of the platform. These model sediments classes interacted with environmental parameters such as wave agitation, sea level fluctuation and bathymetric modification to produce four lithofacies comparable with the Llucmajor lithofacies: backreef lagoon, reef core, forereef slope and open shelf lithofacies.

By studying, through numerous sensitivity tests, the complex interplay between carbonate production and environmental changes, our results show that: 1) progradation of carbonate systems is strongly influenced by the interaction between the bathymetric profile of the basin and variation of carbonate production alongside accommodation; 2) increased production rate of rhodalgal sediments results in increased progradation of the platform, whereas reduced rhodalgal production rate results in the opposite response; and 3) platform geometry and internal architecture varies significantly according to the interaction of the predominant carbonate producing biotas, such as the production of rhodalgal sediments versus coral sediments.

How to cite: Tella, T., Winterleitner, G., and Mutti, M.: How differential biogenic sediment production impact the stratigraphic architecture of carbonate systems: a stratigraphic forward modelling study of Miocene Llucmajor platform., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-12088, https://doi.org/10.5194/egusphere-egu22-12088, 2022.

Over the past decades, neodymium isotopes have received considerable attention in palaeoceanography as a tool for reconstructing past seawater circulation, local weathering inputs, and sea-level changes. In this study, we have investigated the Nd isotope composition of Serpukhovian (Carboniferous) carbonates of a shallow-water succession to test icehouse cyclicity and seawater dynamics on the Karatau carbonate platform in southern Kazakhstan. The cyclic succession formed in response to glacio-eustasy and composed of subtidal and intertidal limestones displays a large variation in the ε_Nd(326 Ma) values from –1.6 to +4.3, corresponding to differences in the isotopic composition of two seawater masses present in the adjacent Uralian–Turkestan Ocean during the Serpukhovian, highly radiogenic deep water and less radiogenic surface water. The Nd isotope excursions within the icehouse cycles are more complex than simple transgressive-regressive cycles. They probably reflect a temporal pattern of the sub-Milankovitch climatic perturbations during the interglacial periods in the Carboniferous. The episodic appearance of rich brachiopod communities was forced by the inflow of highly radiogenic, nutrient-rich waters, presumably driven by upwelling. Nd isotope analyses of cyclic intertidal and subtidal carbonates have great potential to produce high-resolution records of seawater dynamics on shallow-water carbonate platforms.

This study was supported by the Polish National Science Centre, grant No. 2013/11/B/ST10/04751.

How to cite: Belka, Z., Skompski, S., Jakubowicz, M., Dopieralska, J., Walczak, A., and Mustapayeva, S.: Testing icehouse cyclicity and seawater dynamics on an ancient carbonate platform with Nd isotopes (Carboniferous, southern Kazakhstan), EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5916, https://doi.org/10.5194/egusphere-egu22-5916, 2022.

Reef islands in monsoonal regions undergo constant erosion and accumulation, making seasonally shifting morphologies part of their nature. Additionally, sea-level rise alongside climate change is thought to be incisive and challenge coastal communities. With multiple pressures acting on sediment-generating coral reef ecosystems, changes in sediment supply may force further response of these dynamic landforms. Here we present new sedimentological data from a larger reef island in the Spermonde Archipelago, Indonesia. By evaluating the subsurface data in the context of the island’s morphological behavior, we reconstruct its agile past and present. Based on remote sensing data complemented by reports of local citizens, we find the inhabited island to have tripled its surface area in the past century, however also losing more than 10% of surface area in the recent decades. The deeper sediments of the island are dominated by coral fragments, the youngest and uppermost sediments indicate the green algae Halimeda as dominating material contributor. Our study thereby (1) underlines the highly and far-reaching dynamics of reef islands and (2) suggests their adaptive potential to altering material budgets.

How to cite: Kappelmann, Y., Westphal, H., Kneer, D., and Mann, T.: From rapid growth to intense area loss within one century: The moving past and present of an inhabited reef island in Indonesia, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9107, https://doi.org/10.5194/egusphere-egu22-9107, 2022.

The loss of coral reefs in the past is not well understood with a number of theories proposed for their loss and expansion. The Queensland Plateau has one of the best-established coral histories. It is known that coral reefs were first established in the Early Miocene. These reefs then disappeared between 11-6 Ma during the Late Miocene but reestablished around 3.6 Ma. The loss of the reefs has often been tied to cool nutrient rich water during the Late Miocene where as the reestablishment of the reefs have been tied to increases in warmer nutrient poor waters. This model has been used to explain the loss of corals in other parts of the globe. However, there have been questions about the d18O records this has been based on and how accurately they reflect SSTs. In this presentation, we show new TEX₈₆ SST data from the Queensland Plateau. Our data shows, instead of cooler SSTs during the Late Miocene, warmer SSTs than the modern Coral Sea and similar temperatures than the West Pacific Warm Pool. In fact, our temperatures fall comfortably in the modern coral growth window. Furthermore, we found little evidence of increases in local nutrients during this time. All this makes it unlikely that cooler SSTs during the Late Miocene caused the loss of corals on the Queensland Plateau. Instead, the changes seem to be linked to more Pacific wide changes during this period of time. Given the modern debate about the future of coral reefs in a warmer world it is critical to understand what changes drive the loss of coral reefs in the past. Our records show that new ideas about coral loss are needed and that better paleoclimate records are needed from these critical environments.

How to cite: Petrick, B., Reuning, L., Auer, G., Auderset, A., Zhang, Y., Wang, X., Schwark, L., Pfeiffer, M., and Martínez-Garcia, A.: Reassessing the influence of Sea Surface Temperature change on coral reef development on the Queensland Plateau during the Late Miocene., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11479, https://doi.org/10.5194/egusphere-egu22-11479, 2022.

Coralline red algae (CRA) are important ecosystem engineers in oceans. They play key roles as a primary food source and carbonate producers in marine habitats. CRA are also vital for modern reef systems, where they act as a substrate for coral growth and stabilizers of reef frameworks. Calcification in CRA occurs as the precipitation of high-magnesium calcite along the polysaccharide microfibrils within the organic walls of individual cells. Through this process, total CRA biomass consists of 80-90% high-magnesian calcite.

However, morphotaxonomic identification of these important marine organisms is hampered because morphological concepts used for their classification do not correspond to molecular data. We present the first analysis of nanoscale features in calcified cell walls of CRA in a globally distributed sample set. Using a simple fracture-based preparation method, nanoscale ultrastructures were gathered using a field-emission scanning electron microscope (SEM). We used the gathered morphological traits based on these cell wall ultrastructures to construct an independent morphological phyletic tree with good congruency with existing CRA molecular phylogenies.

The results of our SEM analyses highlight cellular ultrastructures as a tool to define the phenotypic expression of genotypic information. We illustrate the potential of ultrastructure-based studies to unify morphology with molecular phylogeny. Furthermore, we show a strong biological control of calcification along the fixed organic templates in CRA cell walls, confirming that it is biomineralization in a strict sense. The morphological difference between the primary (PW) and secondary (SW) cell wall crystallites highlights the radically different organization of the organic matrix present in the PW and SW of CRA. Further evidence that PW and SW calcification are controlled by distinct metabolic processes/pathways is offered by the fact that the magnesium-to-calcium ratio of PW and SW calcite is also radically different.

The described skeletal ultrastructures in the secondary cell wall of CRA subfamilies provide an independent morphotaxonomic concept that appears widely consistent with molecular phylogenic clades/subfamilies. This level of distinction was previously only accomplished by the application rarely present soft tissue features in CRA reproductive organs. Secondary wall ultrastructures are in accordance with molecular phylogenies and provide evidence that crystal shapes formed by the secondary calcification step of CRA cells reflect larger phylogenetic CRA groups.

On a higher (sub)- familial taxonomic level, our independent morphological analysis of nanoscale PW ultrastructures corresponds with the phylogenetic clades/subfamilies. This study ultimately highlights the need and potential for detailed and integrative analyses of skeletal ultrastructure-based approaches to complement molecular phylogeny. Only integrating both recent and fossil morphological with molecular data will provide accurate information on the evolutionary relationships of taxa, not only in CRA but also in many other organism groups.

Citation: Auer, G., & Piller, W. E. (2020). Nanocrystals as phenotypic expression of genotypes—An example in coralline red algae. Science Advances, 6, eaay2126. https://doi.org/10.1126/sciadv.aay2126

How to cite: Auer, G. and Piller, W. E.: Nanocrystals as phenotypic expression of genotypes—An example in coralline red algae, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2405, https://doi.org/10.5194/egusphere-egu22-2405, 2022.