SSP3.6

The birth (and death) of minerals is controlled by a series of basic physical and chemical processes such as nucleation, growth, dissolution, diffusion and adsorption, which normally occur over time and length scales that are not easily accessible to common experimental investigation methods. However, reconciling these microscopic processes with macroscopic observations may represent a key to the interpretation of the geological archive as well as to optimizing the engineering of geomaterials based on the exploitation of mineral resources.
Motivated by this need, an overview of commonly used numerical techniques for the simulation of mineral forming processes, and their relevant input parameter, is provided, with the aim of assessing the potential and limitations of specific computational tools in different scenarios.
The scope and suitability of methods such as Molecular Dynamics, Kinetic Modelling, Cellular Automata, Monte Carlo and Population Balance are illustrated, with a brief introduction of the theoretical principles, followed by examples of applications to specific case studies.  
Challenges and future perspective, with emphasis on multiscale modelling, are discussed.

How to cite: Valentini, L.: How can computer models help us understand mineral forming processes?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2904, https://doi.org/10.5194/egusphere-egu21-2904, 2021.

Diagenetic reactions in sediments and sedimentary rocks are controlled by both fluid transport and surface reactivity. In this chapter, the major focus is on the effect of crystal surface reactivity and its variability. The “energetic landscape” of the solid material in contact with the fluid exerts control on reaction type, kinetics, and products. Critical surface processes include sorption, catalysis, dissolution, and precipitation. For diagenetic reactions, the sequence of processes and thus the potential inhibition of subsequent reactions due to surface modifications is of great interest. Consequently, the evolution of porosity and permeability is governed by the chronological sequence of surface reactions during the diagenetic history. This provides feedback to the fluid transport behaviour in the complex porous material. Because of this coupling, numerical approaches address the problem appropriately by the use of reactive transport codes. Pore scale treatment follows mechanisms at the scale of crystal surfaces that form the pore walls of the sedimentary rock. Such surface-chemical exercises require a parametrization that includes mechanistic understanding and connection to first-principles treatment. At larger scales, so-called continuum scale simulation treats fluid transport and fluid-solid reactions in a more generalized quantitative way. While such field-scale treatment is required and applied for multiple challenges, the small-scale mechanistic understanding is still a crucial part of geochemical research. The observed heterogeneity of surface reactivity requires specific upscaling strategies that are not yet reflected in large-scale analysis and predictions.

How to cite: Fischer, C.: Mineral surface reactivity: mechanisms and concepts, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13041, https://doi.org/10.5194/egusphere-egu21-13041, 2021.

Fans and hemispheres comprised of crystals of calcium carbonate that directly grew on the seafloor are an intriguing feature of ancient carbonate environments. Calcium carbonate fans from across Earth history are typically made up of crystals of neomorphosed calcium carbonate that maintain an acicular morphology that is pseudohexagonal in cross – section with blunt terminations, pointing to an aragonite precursor. Crystal fans may occur as isolated bodies, or may form larger aggregates that are sometimes associated with microbialites, and form larger, reef – like structures. Some of the first occurrences of these features are within Neoarchean carbonates, when the crystals fans grew to impressive sizes, with lengths of over 1 m, formed layers of marine cement that reached thicknesses of up to several meters, are laterally continuous over 10s of km or more, and formed across carbonate platform settings from high energy subtidal settings to lower intertidal environments. Crystalline carbonate fans become less common and smaller (cm – scale) in the Paleoproterozoic, and nearly disappear prior to the Neoproterozoic, when they are associated with cap carbonates, and are primarily found in deeper water or outer shelf settings with low sedimentation rates. Seafloor cements are rare during the Phanerozoic, and are typically limited to small geographic areas with unusual sedimentary conditions, or are found in void spaces, where seawater chemistry was able to undergo modifications that would allow precipitation of cement fans. The exception is during the interval of time that followed the Permian – Triassic mass extinction, when small, cm – scale fans and hemispheres are found in Lower Triassic and lowermost Middle Triassic rocks. These cement fans occur in a variety of settings, although they are typically found in deeper water environments. Calcium carbonate fans that formed following the Permian – Triassic extinction may have microbial remains preserved within the cements, and are frequently found in close lateral or stratigraphic association with microbialites. However, some examples of post – extinction carbonate fans appear to have formed abiotically, without any microbial influence. Overall, crystalline calcium carbonate fans signal high levels of calcium carbonate supersaturation in ancient oceans. The initial decline in seafloor cement growth from the Neoarchean into the Proterozoic may have been the result of accelerated micrite production, while Neoproterozoic calcium carbonate fan growth is associated with glacial decay and retreat. Lower Triassic seafloor cements are likely the result of stratification and stagnation of the deep oceans that led to enhanced alkalinity. Calcium carbonate crystal fans are an intriguing feature of ancient carbonates that signal depositional systems and ocean chemistry that is much different from modern ocean, and provide a fascinating glimpse into non – uniformitarian sedimentary environments.

How to cite: Woods, A.: Calcium carbonate crystal fans: Geologic occurrences and controls on growth, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9021, https://doi.org/10.5194/egusphere-egu21-9021, 2021.

Three principal models exist for iron (oxyhydr)oxide concretion formation in the Navajo Sandstone in southern Utah, USA and the most recent model by Yoshida et al. (2018) suggests that calcite concretions are precursors to iron (oxyhydr)oxide concretions. This model could account for the existence of a gradient of carbonate and iron concretions found in both red diagenetic facies (with primary hematite grains coatings retained) and white diagenetic facies (primary hematite grain coatings removed during diagenesis). However, evidence for calcite precursor minerals and an understanding of the fluid chemistries involved in these diagenetic reactions is lacking. This research focuses on spheroidal concretions in the Navajo Sandstone at Coyote Gulch—a site that is down gradient, but upsection from Spencer Flat (the focus of previous work) and tests the hypothesis that calcite concretions are precursors to iron (oxyhydr)oxide concretions. Bulk mineralogy, bulk geochemistry, and petrography provide elemental and mineralogical composition of the concretions and show that the concretions are calcite cemented (~40 wt.%) and the host rock is predominately iron (oxyhydr)oxide cemented (~3 wt.%). The host rock surrounding embedded concretions shows secondary iron (oxyhydr)oxide precipitation and decreases in calcite in transects away from the concretion. These relationships suggest that the calcite concretions formed prior to the precipitation of secondary iron (oxyhydr)oxides and may have provided a localized buffering environment for the precipitation of iron (oxyhydr)oxides. This study also represents an opportunity to determine a universal model for carbonate and iron (oxyhydr)oxide spheroidal concretion formation, and to understand the influence of fluid interactions in the search for subsurface redox reactions to power metabolisms on Earth and Mars.

How to cite: Baker, D. and Potter-McIntyre, S.: Working towards a universal formation model for spheroidal iron (oxyhydr)oxide concretions, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3365, https://doi.org/10.5194/egusphere-egu21-3365, 2021.

In his 1897 article on the formation and transformation of solid phases, Friedrich Wilhelm Ostwald described the phenomenon that hydrous sodium chlorate precipitates from an oversaturated solution, despite the fact that this phase is much more soluble than the non-hydrous salt. The fundamental concept, also known as Ostwald’s step rule, is best summarized on page 307 of his article (here translated to English):

“... Such phenomena also frequently occur during melting and condensation of steam and even in homogeneous chemical reactions, and I would like to summarize the previous experiences with this matter in the single phrase that during departure from any state, and the transition to a more stable one, not the under given circumstances most stable state is reached, but the nearest one.“

Despite its major importance for mineral formation under Earth’s surface conditions, this concept is still not fully understood on a mechanistic level. While Ostwald’s step rule is commonly explained with the classical nucleation theory, there are several inconsistencies, especially the conundrum that sometimes stable phases, such as dolomite or quartz, do not form as long as a metastable phase is supersaturated. I propose an alternative interpretation that would be consistent with Ostwald’s (1897) original formulation as well as with several observations from natural environments and laboratory experiments. If “nearest” (in German: “nächstliegend”) is not understood as “thermodynamically most similar”, but as the phase with the lowest kinetic barrier, Ostwald’s step rule should be always valid. The kinetic barrier is surface specific and independent of supersaturation, but it depends on the atomic scale interfacial energy landscape. This concept would better represent the power of Ostwald’s step rule to explain mineral formation processes and how they are affected by chemical and biological influences. New nano-scale analytical techniques in combination with advanced molecular dynamic modelling bear great potential to explain and appreciate the importance of Ostwald’s step rule.

How to cite: Meister, P.: Ostwald’s step rule: a consequence of growth kinetics and nano-scale energy landscape, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8176, https://doi.org/10.5194/egusphere-egu21-8176, 2021.

Recent studies have shown that surfaces rich in functional groups can facilitate nucleation of low-temperature (low-T) dolomite. However, to date few experiments have investigated the details of the nucleation mechanisms nor determined how naturally occurring substances influence crystallization pathways of low-T dolomite. In this study we isolated and characterized extracellular polymers (EPS) from a hypersaline sabkha, as well as clay standards and performed mineralization experiments with these surfaces as seed material. Mineralization experiments were carried out in batch reactors in a solution supersaturated with respect to dolomite. Our results showed that over a five-month period the rate of low-t dolomite formation in samples seeded with EPS was significantly higher compared to those seeded with clay. The observed rates were also shorter than previously published experiments using bacterial cultures (e.g., Kenward et al., 2013, Deng et al., 2019). Precipitates from samples seeded with EPS show crystallization of dolomite pre-cursors after several days and assemblages of dolomite crystals from 10-days forward [Figure 1]. Measurements from EPS seeded samples showed significant depletion of Ca and Mg in solution within one week as well as elevated alkalinity that coincided with dolomite crystallization. Samples seeded with clay and control samples without seed materials showed little and no dolomite crystallization, respectively, during the same time-frame. Overall, the results of this work shows that EPS isolated from microbial mats are preferential nucleation surfaces for carbonate precipitation when compared to clays. Additionally, the findings reveal that the properties of nucleation surfaces such as functional group type and concentration are a key factor driving low-T dolomite precipitation.

Figure 1: Dolomite like phases and representative EDS spectra from a solution seeded with EPS.

References:

Kenward PA, Fowle DA, Goldstein RH, Ueshima M, González LA, Roberts JA. Ordered low-temperature dolomite mediated by carboxyl-group density of microbial cell walls. AAPG bulletin. 2013 Nov 1;97(11):2113-25.

Liu D, Xu Y, Papineau D, Yu N, Fan Q, Qiu X, Wang H. Experimental evidence for abiotic formation of low-temperature proto-dolomite facilitated by clay minerals. Geochimica et Cosmochimica Acta. 2019 Feb 15;247:83-95.

How to cite: Diloreto, Z., Liu, H., Lu, X., Bontognali, T., and Dittrich, M.: A comparative study of low-temperature dolomite formation driven by exopolymers from hypersaline microbial mats and clays, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16415, https://doi.org/10.5194/egusphere-egu21-16415, 2021.

The composition of modern carbonate sediments in nearshore tropical marine settings typically reflects a suite of somewhat proximal processes of carbonate production and erosion. Here, we document pelagic Sargassum as an emergent vector of carbonate sediment import to tropical Atlantic and Caribbean shorelines: a process with distal (oceanic) origins that has the potential to impart a distinct record of regional to global change within nearshore sediments. This process arose as recently as 2011, when a major new Sargassum bloom region emerged in the central Atlantic Ocean and resulted in Caribbean, West African, and northern Brazilian shorelines being inundated with Sargassum at unprecedented scales. Subsequent near annual recurrences of these coastal inundations at increasingly large scales suggest they are becoming an established norm. Socio-economic and ecological implications are widespread and potentially serious, and include potential impacts on the established sources and stability of nearshore carbonate sediments. This study, however, focuses on new sediment delivered to these coastal settings in the form of calcareous epiphytic communities that colonise Sargassum (i.e., bryozoans, serpulid worms, and red algae). Our analysis of Sargassum collected from coastal waters of the Mexican Caribbean in 2018 indicates a mean carbonate content of 2.09% wet weight at shoreline arrival. Based on data from 11 sites in Quintana Roo, Mexico (spanning 11.15 km of a 60 km section of shoreline), we further estimate the average drained weight of Sargassum that arrived at the coast during 2018 to have been 7.0x10³ kg m^-1 of shoreline. Together, these findings indicate that mean import of new carbonate sediment by Sargassum was 179 kg m^-1 of shoreline in 2018, which is close to our upper estimate of annual proximal sediment production by Thalassia seagrass epiphytes (210 kg m^-1 of shoreline). Prior to the onset of these massive Sargassum inundations, grains recognisable as bryozoan skeletons and serpulid tube casings were rare in coastal sediments of the Mexican Caribbean. Consequently, if these calcareous Sargassum epiphytes that are evidently now being imported in large volumes are retained and preserved, they can be expected to impart a distinct record within these coastal sediments. Although quantitative data on Sargassum inundations from other locations are sparse, numerous reports from the scientific community and the media suggest the scale of these events is comparable for many exposed tropical Caribbean and Atlantic shorelines. This represents the first documentation of pelagic Sargassum as a major vector of coastal sediment import, the significance of which has likely only arisen since the onset of large-scale inundations in 2011.

How to cite: Salter, M., Perry, C., Rodríguez-Martínez, R., Alvarez-Filip, L., and Jordan-Dahlgren, E.: Pelagic Sargassum as an emergent high-rate importer of carbonate sediment to tropical Atlantic coastlines, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15898, https://doi.org/10.5194/egusphere-egu21-15898, 2021.

Such factors as climate, currents, morphology, riverine input, and the source rocks influence the composition of the sediments in the Arctic Ocean. Heavy minerals being quite inert in terms of transport can reflect the geology of the source rock clearly and indicate the riverine input. There is a long history of studying the heavy mineral composition of the sediments in the Arctic Ocean. The works by Vogt (1997), Kosheleva (1999), Stein (2008), and others study the distribution of the minerals both on a sea scale and oceanwide. The current study covers Russian shelf seas: Barents, Kara, Laptev, East Siberian, and Chukchi Seas. To collect the material several data sources were used: data collected by the institute VNIIOkeangeologia during numerous expeditions since 2000 for mapping the shelf, data from the old expedition reports (earlier than 2000) taken from the geological funds, and datasets from PANGAEA (www.pangaea.de). About 82 minerals and groups of minerals were included in the joint dataset. The density of the sample points varied significantly in all seas: 1394 data points in the Barents Sea, 713 in the Kara Sea, 487 in the Laptev Sea, 196 in the East Siberian Sea, and 245 in the Chukchi Sea. These data allowed comparing the areas in terms of major minerals and associations. Maps of prevailing and significant components were created in ODV (Schlitzer, 2020) to demonstrate the differences between the seas and indicate the sites of remarkable changes in the source rocks. Additionally, the standardized ratio was calculated to perform quantitative comparison: the sea average was divided by the weighted sea average and then the ratio of that number to the mineral average was found. Only the minerals present in at least four seas and amounting to at least 20 points per sea were considered. As a result, water areas with the highest content of particular minerals were detected. The ratio varied from 0 to 3,4. Combining the ratio data for various minerals allowed mapping specific groups or provinces for every sea and within the seas.

Kosheleva, V.A., & Yashin, D.S. (1999). Bottom Sediments of the Arctic Seas. St. Petersburg: VNIIOkeangeologia, 286pp. (in Russian).

PANGAEA. Data Publisher for Earth & Environmental Science https://www.pangaea.de/

Schlitzer, R. (2020). Ocean Data View, Retrieved from https://odv.awi.de.

Stein, R. (2008). Arctic Ocean Sediments: Processes, Proxies, and Paleoenvironment. Oxford: Elsevier, 602pp.

Vogt, C. (1997). Regional and temporal variations of mineral assemblages in Arctic Ocean sediments as a climatic indicator during glacial/interglacial changes. Berichte Zur Polarforschung, 251, 309pp.

How to cite: Popova, E.: Characteristics of the Russian shelf seas in the Arctic Ocean regarding the content of heavy minerals in surface sediments: new data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1166, https://doi.org/10.5194/egusphere-egu21-1166, 2021.

Mollies Nipple—a butte located in the Grand Staircase-Escalante National Monument (GSENM)—is of special interest because of the presence of unusual alunite and jarosite cements within the caprock. These minerals precipitate in hyperacidic environments (pH1-2) and are not stable over ~pH5; yet they are abundant on Mars where they are used to interpret depositional and diagenetic environments. The caprock at Mollies Nipple is historically interpreted as Navajo Sandstone via photogeologic mapping; however, it is ~200 m above the mapped upper extent of the Navajo Sandstone in this region. The units overlying the Navajo Sandstone have complex stratigraphic relations in this region and the caprock could be the Carmel or Temple Cap Formations, or the Page Sandstone. This study aims to characterize Mollies Nipple through measured sections, mineralogical analyses, palynomorph analysis, and radiometric age dates from ash lenses present in the caprock. The results will better define the stratigraphy of Mollies Nipple and determine the regional correlation of the caprock. Ultimately, this work will contribute to the understanding of how alunite and jarosite were precipitated at Mollies Nipple; why these minerals are still present at Mollies Nipple, and potentially revise the understanding of Martian depositional environments.

How to cite: Walker, J. and Potter-McIntyre, S.: Revising the stratigraphy at Mollies Nipple, Kane County, Utah, USA to better understand the origin of jarosite and alunite cements, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8032, https://doi.org/10.5194/egusphere-egu21-8032, 2021.

Indicator minerals have special physical and chemical properties that can be analyzed to glean information concerning the composition of host rocks and formational (or altering) fluids. Clay, zeolite, and tourmaline mineral groups are all ubiquitous at the Earth’s surface and shallow crust and distributed through a wide variety of sedimentary, igneous, metamorphic, and hydrothermal systems. Traditional studies of indicator mineral-bearing deposits have provided a wealth of data that could be integral to discovering new insights into the formation and evolution of naturally occurring systems. This study evaluates the relationships that exist between different environmental indicator mineral groups through the implementation of machine learning algorithms and network diagrams. Mineral occurrence data for thousands of localities hosting clay, zeolite, and tourmaline minerals were retrieved from mineral databases. Clustering techniques (e.g., agglomerative hierarchical clustering and density based spatial clustering of applications with noise) combined with network analyses were used to analyze the compiled dataset in an effort to characterize and identify geological processes operating at different localities across the United States. Ultimately, this study evaluates the ability of machine learning algorithms to act as supplementary diagnostic and interpretive tools in geoscientific studies.

How to cite: Williams, J., Potter-McIntyre, S., Filiberto, J., Morrison, S., and Hummer, D.: Analyzing the occurrence of environmental indicator minerals using clustering techniques and mineral networks, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14074, https://doi.org/10.5194/egusphere-egu21-14074, 2021.

Keywords: Ikaite; Glendonite; Palaeoclimate; Powder X-Ray Diffraction; Clumped isotope thermometry

Marine sedimentary ikaite is the parent mineral to glendonites, stellate pseudomorphs found throughout the geological record. Glendonites are a controversy in palaeoclimatic studies as there is an ongoing debate as to whether their presence in sedimentary successions may be used as cold-climate indicators. Glendonites are typically found associated with glacial sediments, and for a long time ikaite was believed to only nucleate and grow at temperatures < 7 °C. However, with the successful laboratory synthesis of ikaite at higher temperatures, the climatic significance of glendonites was brought into question. This study uses a combination of physical and inorganic chemistry techniques to demonstrate the variable stability of natural marine sedimentary ikaites over short (minutes to hours) and longer (weeks to months) timescales, both between ikaite samples, and in a given ikaite. We examine the nucleation of calcite from the destabilized ikaite, observing that this process is much more complex than previous studies suggest. We demonstrate that over much longer (e.g. months or more) timescales, natural marine sedimentary ikaites are not stable above 5 °C, and thus glendonite presence in sedimentary successions may be considered cold climate indicators.

How to cite: Vickers, M., Vickers, M., Rickaby, R., Wu, H., Bernasconi, S., Ullmann, C., Bohrmann, G., Spielhagen, R., Thibault, N., and Korte, C.: The ikaite to calcite transformation: A key to understanding the palaeoclimatic significance of glendonites?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10140, https://doi.org/10.5194/egusphere-egu21-10140, 2021.

Calcite crusts from the Elephant Hill Moraine (EHM) (76°17'35" S  157°20'05" E) collected during 1983-84  were interpreted as formed in subglacial environments influenced by hydrothermalism (Faure et al., 1988). More recently, ²³⁴U enrichment in these crusts was used to suggest that during the warm MIS 11 interglacial (ca. 400 ka), the ice sheet margin at the Wilkes Basin retreated about 700 km inland (Blackburn et al., 2020). Their ²³⁴U data from separate analyses of pure calcite and pure opal crusts suggested that “connate seawater would impart marine signatures to subglacial waters” (Blackburn et al., 2020), with the former associated with massive melting during MIS 11.  However, robust U-series dating by Blackburn et al (2020) was only possible on pure end members of opal and calcite, whilst other EHM crusts did not yield reliable ages and were discarded. The inferred MIS11 ice-loss was then based on a model of ²³⁴U accumulation and on those carbonate ages that fit their hypothesis that connate seawater influenced the subglacial environment.

Here, we investigated the nanostructure of EMH samples that yielded unreliable U-Th ages, which were too old to fit into the ²³⁴U-based model of MIS11 connate seawater influencing subglacial waters. High-resolution transmission electron microscope images showed a complex history of precipitation, dissolution, re-precipitation, including the co-precipitation of nanocrystalline calcite and opal. Co-precipitation was documented by the inclusion of micrometre-scale opal spherules within calcite crystals whose lattice orientation does not change across the spherules and can be explained by the fluid being extremely enriched in silica. The calcite immediately surrounding the opal spherules was characterized by twins and likely a response to sub-ice sheet stress during their precipitation. The calcite-opal mixture partially replaced pre-existing calcite crystals, which appear broken, corroded and pre-date a final, pure calcite void-filling cement. Clearly, these EHM samples document several stages of crystallization, which imply repeated mobilization of chemical species. Preliminary Fluid Inclusion analyses of the crusts yielded a temperature of about 85^oC, which inferred that at one stage calcite precipitation may have been influenced by hydrothermalism associated with volcanism.  Our identification of complex crystallization histories for the Elephant Moraine subglacial carbonates opens up alternative formation hypotheses to that proposed by Blackburn et al. (2020) such as the existence of multiple sources of aqueous solutions. Consequently, it is fraught to infer that all the EMH formed from connate marine waters generated 400 ka without dating of multiple phases of calcite precipitation from each sample.

References: Blackburn, T. et al. 2020, Nature, 583 (7817), pp.554-559. Faure, G.  et al, 1988, Nature, 332(6162), pp.352-354.

How to cite: Frisia, S., Németh, P., Borsato, A., Hellstrom, J. C., Demény, A., and Pécz, B.: Nano-scale investigation of co-precipitated subglacial calcite and opal, antarctica, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3547, https://doi.org/10.5194/egusphere-egu21-3547, 2021.

Primary phases in carbonate rocks archive a wealth of geochemical information about depositional conditions and environmental changes. Secondary phases may record additional—albeit more cryptic—information, potentially complicating interpretation of primary signatures. The ability to compositionally characterize and date multiple, texturally distinct generations of primary, diagenetic, and metamorphic carbonate phases enables deciphering of complex depositional and post-depositional histories carbonate successions have experienced. Combined trace-element mapping and U-Pb geochronology of calcite in situ (in thin sections) by LA-ICP-MS provides opportunities to assign absolute ages to calcite crystallization and recrystallization with petrographic and geochemical context. We have applied this approach to two samples of apparently pristine, unmetamorphosed Ordovician bioclastic limestones from the Viki drill core (western Estonia), representing the eastern part of the Baltoscandian Basin. The depositional ages of the samples are constrained by biostratigraphic correlation to ca. 460 and 445 Ma (Hints et al., 2014). Several lines of evidence—such as very low organic-matter maturation and properties of clay minerals—indicate that this sequence did not experience temperatures above 100 °C, and likely not above 50 °C, since deposition (Kirsimäe et al., 2020). Optical petrography and backscatter-electron (“BSE”) imaging reveal low-porosity “BSE-bright” calcite spar cement in pore spaces between “BSE-dark” micro-porous calcite bioclasts. Trace-element mapping of several areas (several mm² each) in each thin section by LA-quadrupole-ICP-MS reveals variably elevated Mn/Sr, U concentration, and U/Pb in the calcite spar cement. The trace-element maps were subsequently used to guide the placement of laser spots for U-Pb dating by LA-multicollector-ICP-MS. Primary bioclastic calcite in both samples has low U/Pb (²³⁸U/²⁰⁶Pb < 7) and, thus, does not yield precise Concordia-intercept dates. The primary calcite does, however, yield imprecise intercept dates within uncertainty of the depositional ages. Calcite spar cement has higher U/Pb (²³⁸U/²⁰⁶Pb up to ~15.7) and including all analyses, yields intercept dates of ca. 415 Ma in each sample. Additionally, several of the domains with the highest U/Pb from each sample yield slightly younger dates of ca. 400­-380 Ma. The timing of calcite (re)crystallization and cementation identified here overlaps with the timing of continent collision during the Caledonian orogeny in Scandinavia. We tentatively interpret this to be a result of fluid flow in response to the collision far-inboard (>500 km) from the orogenic front. Furthermore, this work demonstrates that apparently pristine carbonates may have experienced recrystallization (or at least chemical-isotopic perturbation) in open systems long after deposition.

References

Hints, O., Martma, T., Männik, P., Nõlvak, J., Põldvere, A., Shen, Y., Viira, V. 2014. New data on Ordovician stable isotope record and conodont biostratigraphy from the Viki reference drill core, Saaremaa Island, western Estonia. GFF 136, 100–104.

Kirsimäe, K., Somelar, P., Jõeleht, A. 2020. Illitization of the lower Cambrian (Terreneuvian) Blue Clay in the northern Baltic Palaeobasin. Estonian Journal of Earth Sciences 69, 200–213.

How to cite: Hagen-Peter, G., Wang, Y., Hints, O., and Lepland, A.: Cryptic secondary cementation of Ordovician limestones in the Baltoscandian Basin, northern Europe, revealed through trace-element mapping and U-Pb dating by LA-ICP-MS, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12547, https://doi.org/10.5194/egusphere-egu21-12547, 2021.

Stratigraphic units of the Colorado Plateau comprise a remarkable Mesozoic section in Utah. Thse units are ideal for studying sandstone diagenesis where there is established basinal context of depositional facies and tectonics, as well as continuity of exposure. To untangle the complex relationships and diagenetic histories, it is crucial to understand host rock properities (porosity and permeability), authigenic mineralogies (that give clues to fluid composition), diagenetic textures, and age dating. This study is a review and synthesis of previous work that has contributed to the understanding of the diagenetic history recorded in authigenic iron oxide precipitates. We discuss cement generations and mineralogies, fluid chemistries, origins and mobilization of iron, and timing of precipitation. Spheroidal cemented mineral masses (concretions) are common within many Mesozoic units of Utah – most notably the Jurassic Navajo Sandstone.  However, formation of these concretions is still not completely understood. Spheroidal concretions are currently a “hot topic”, especially since the discovery of similar “blueberry” features on Mars with their implications for habitability, and the potential for these nodules to host biosignatures. Several models for spheroidal concretion formation are evaluated. Understanding how iron is mobilized and precipitated and how spheroidal concretions form have implications for similar geometries and mineralogies in many terrestrial regions, but will require continued integrated studies across multiple scales (see Baker and Potter-McIntyre, this session). These scales include the submicroscopic levels of understanding and detecting the potential role of microbes in mineral precipitation, to the larger scale mapping of regional diagenetic coloration and mineral patterns that could represent records of basinal fluids and the response to climate, tectonics, and regional hydrology.

How to cite: Potter-McIntyre, S. and Chan, M.: Diagenetic complexities of iron oxide cements in Mesozoic sandstones of Utah, U.S.A., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10145, https://doi.org/10.5194/egusphere-egu21-10145, 2021.