Towards a morphology diagram for terrestrial carbonates: evaluating the impact of carbonate supersaturation and alginic acid in calcite precipitate morphology

Mercedes‐Martín, Ramon; Rogerson, Mike; Prior, Timothy J.; Brasier, Alexander T.; Reijmer, John J.G.; Billing, Ian; Matthews, Anna; Love, Tracy; Lepley, Scott; Pedley, Martyn

doi:10.31223/x51k6v

Cited by 3 publications

(3 citation statements)

References 57 publications

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“…A large body of literature confirms the effects of thermodynamic variables such as supersaturation, ionic strength and the concentration of foreign ions or organic compounds on calcite morphologies and fabrics (e.g. Frisia et al, 2000;Sunagawa, 2005;Sand et al, 2012;Frisia, 2015;Hong et al, 2016;Mercedes-Martín et al, 2021). The morphological variety of CCCs observed in this study can be viewed as an expression of changing crystallisation driving forces in response to progressive freezing.…”

Section: Sample Characterisationsupporting

confidence: 68%

²³⁰Th ∕ U isochron dating of cryogenic cave carbonates

et al. 2022

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Cryogenic cave carbonates (CCCs) are a type of speleothem, typically dated with 230 Th/U disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre-to centimetre-sized loose crystals and crystal aggregates on the floors of cave chambers, so they lack a framework that would allow ages to be validated by stratigraphic order. Correction factors for the initial 230 Th ( 230 Th 0 ) are often based on the bulk-earth-derived initial 230 Th/ 232 Th activity ratio (( 230 Th/ 232 Th) 0 ), which is a well-established approach when 230 Th 0 is moderately low. For samples with elevated levels of 230 Th 0 , however, accuracy can be improved by constraining ( 230 Th/ 232 Th) 0 independently. Here, we combine detailed morphological observations from three CCC patches found in Water Icicle Close Cavern in the Peak District (UK) with 230 Th/U analyses. We find that individual CCC crystals show a range of morphologies that arise from non-crystallographic branching in response to the chemical evolution of the freezing solution. Results of 230 Th/U dating indicate that samples with a large surface area relative to the sample volume are systematically more affected by contamination with 230 Th 0 . By fitting isochrons to these results, we test whether the CCCs in a patch formed during the same freezing event, and demonstrate that ( 230 Th/ 232 Th) 0 can deviate substantially from the bulk-earth-derived value and can also vary between the different CCC patches. Where CCCs display elevated 230 Th 0 , isochrons are a useful tool to constrain ( 230 Th/ 232 Th) 0 and obtain ages with improved accuracy. Detritus absorbed to the crystal surface is shown to be the most likely source of 230 Th 0 . Our results suggest that some previously published CCC ages may merit re-assessment, and we provide suggestions on how to approach future dating efforts.

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Section: Sample Characterisationsupporting

confidence: 68%

²³⁰Th ∕ U isochron dating of cryogenic cave carbonates

et al. 2022

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Section: Sample Characterisationsupporting

confidence: 68%

²³⁰Th/U Isochron Dating of Cryogenic Cave Carbonates

Töchterle

Steidle

Edwards

et al. 2022

Preprint

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Abstract. Cryogenic Cave Carbonates (CCCs) are a type of speleothem, typically dated with 230Th/U disequilibrium methods, that provide evidence of palaeo-permafrost conditions. In the field, CCCs occur as distinct patches of millimetre- to centimetre-sized loose crystals and crystal aggregates on the floor of cave chambers, lacking a framework to validate ages by stratigraphic order. Correction factors for initial 230Th (230Th0) are often based on the bulk-earth derived ratio of initial 230Th/232Th activity ((230Th/232Th)0), which is a well-established approach when 230Th0 is moderately low. For samples with elevated levels of 230Th0, however, accuracy can be improved by constraining (230Th/232Th)0 independently. Here, we combine detailed morphological observations from three CCC patches found in Water Icicle Close Cavern in the Peak District (UK) with 230Th/U analyses. We find that individual CCC crystals show a range of morphologies that arise from non-crystallographic branching in response to the chemical evolution of the freezing solution. Results of 230Th/U dating indicate that samples with a large surface area relative to the sample volume are systematically more affected by contamination with 230Th0. By fitting isochrons to these results, we test whether the CCCs in an individual patch formed during the same freezing event, and demonstrate that (230Th/232Th)0 can deviate substantially from the bulk-earth derived value and also vary between the different CCC patches. Where CCCs display elevated 230Th0, isochrons are a useful tool to constrain (230Th/232Th)0 and obtain ages with improved accuracy. Detritus absorbed to the crystal surface is shown to be the most likely source of 230Th0. Our results suggest that some previously published CCC ages may merit re-assessment and we provide suggestions on how to approach future dating efforts.

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“…Although all of the abiotic and biotic processes described here are considered to play a role in travertine deposition, evaluation of their contributions is difficult (e.g. Mercedes‐Martín et al ., 2021). With regard to the abiotic process, precipitation rate is usually described as a function of bulk water chemistry (e.g.…”

Section: Introductionmentioning

confidence: 99%

Abiotic and biotic processes controlling travertine deposition: Insights from eight hot springs in Japan

et al. 2021

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Contributions of abiotic and biotic processes on travertine deposition are still not well‐understood due to technical difficulties, despite that the travertines draw attention as analogues for ancient microbial carbonates and oil reservoirs. To evaluate their contributions, this study examined eight hot springs in Japan. Water chemistry analyses showed common downstream trends: a decrease in CO2 concentration and increases in CO32− concentration and pH. Mineralogical analysis showed that the constituent minerals of travertines at six hot springs were both calcite and aragonite, while one was just calcite and another only aragonite. Microscopic observations of travertine surfaces indicated the dominance of cyanobacteria secreting extracellular polymeric substances without a detectable amount of carboxyl groups. Small particles were sometimes entangled/covered by these cyanobacteria. Microelectrode measurements showed the occurrence of abiotic CaCO3 precipitation and photosynthetic induction/inhibition of CaCO3 precipitation, the extent of which was different at each site. By integrating these results, the contributions of abiotic and biotic processes were evaluated. Cyanobacteria inhabiting travertine surfaces were generally not calcified regardless of an ambient high CaCO3 saturation state; instead, they contributed to creating pore spaces and trap/bind suspended particles. Downstream CO2 degassing increased the CaCO3 saturation state by shifting carbonate chemical equilibrium and caused abiotic CaCO3 precipitation. Suspended particles trapped by cyanobacteria increased the surface area for crystal growth to further accelerate precipitation. The contribution of photosynthesis‐induced CaCO3 precipitation was low because of several factors, including variable cyanobacteria populations and photosynthetic inhibition of CaCO3 precipitation. The average contributions of photosynthesis‐induced CaCO3 precipitation, Ca2+ adsorption and abiotic precipitation in the eight hot springs were 16%, 3% and 81%, respectively, indicating predominance of the abiotic process for travertine deposition. Mineralogical composition of travertines significantly correlated with concentrations of SO42− and Mg2+, much more than with Mg/Ca ratio and water temperature, suggesting their importance for controlling CaCO3 polymorphs in travertines.

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Towards a morphology diagram for terrestrial carbonates: evaluating the impact of carbonate supersaturation and alginic acid in calcite precipitate morphology

Cited by 3 publications

References 57 publications

²³⁰Th ∕ U isochron dating of cryogenic cave carbonates

²³⁰Th ∕ U isochron dating of cryogenic cave carbonates

²³⁰Th/U Isochron Dating of Cryogenic Cave Carbonates

Abiotic and biotic processes controlling travertine deposition: Insights from eight hot springs in Japan

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Towards a morphology diagram for terrestrial carbonates: evaluating the impact of carbonate supersaturation and alginic acid in calcite precipitate morphology

Cited by 3 publications

References 57 publications

230Th ∕ U isochron dating of cryogenic cave carbonates

230Th ∕ U isochron dating of cryogenic cave carbonates

230Th/U Isochron Dating of Cryogenic Cave Carbonates

Abiotic and biotic processes controlling travertine deposition: Insights from eight hot springs in Japan

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²³⁰Th ∕ U isochron dating of cryogenic cave carbonates

²³⁰Th ∕ U isochron dating of cryogenic cave carbonates

²³⁰Th/U Isochron Dating of Cryogenic Cave Carbonates