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Abstract Details

Carbonate Clumped Isotope Thermometry in Deep Time: Insights from Early Triassic Brachiopods and Bulk Carbonates

Edward O, Luz ZAS, Bucher H & Vennemann T

Edward O, Luz ZAS, Bucher H & Vennemann T (2020) Goldschmidt Abstracts, 2020 646

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14b: Plenary Hall, View in program

Listed below are questions that have been submitted by the community that the author will try and cover in their presentation. To submit a question, ensure you are signed in to the website. Authors or session conveners approve questions before they are displayed here.

Submitted by Kimberly Lau on
Are there any processes or factors that could drive the D47 results to lower values from what was "primary"? Thank you!
Thank you for your question. Yes, there indeed are factors which could result in non-primary D47 results. These include biologically mediated disequilibrium precipitation (vital effects), diagenesis (notably in the absence of seawater), solid state reordering and variations in fluid-rock ratios. With respect to the current dataset, although the brachiopods measured belong to different genera, we cannot unequivocally attribute the differences/range in the D47 composition of individual specimens to vital effects as the range quite large (> 20 degrees). Instead, we believe that what this D47 range represents is the variation in the preservation state (degree of calcite recrystallization) in different sites within the same shells. Solid state reordering is assumed to be of no importance for our results as there are no indications that it occurs at temperatures less than 100 degrees.

Submitted by Georgina Lukoczki on
Dear Oluwaseun, what an impressive dataset! Were these all collected for this specific study? The wide temperature range and the fairly strong correlation between the D47 and d18O suggest rock buffered recrystallization as you also point out. I wonder how you determine what is the “real” seawater composition if even the lowest temperature data gives a calculated fluid d18O composition that appears too low for “normal” seawater and may be the result of meteoric diagenesis. What do you mean by “transient variation in seawater d18O?” Can this be potentially caused by riverine input of fresh water into this shallow marine environment?
Dear Georgina, thank you for your question. Yes, all data presented here were collected for this specific study. In essence, our judgement of real seawater composition is the co-occurrence of seawater temperatures within the range modern tropical seawater (25 - 32 degrees) with calculated water d18O which approximates that of modern seawater range. Indeed transient variations in seawater could be caused by freshwater input, however, this is actually unlikely to be the case as the depositional environment of the studied carbonates is quite distal (offshore seamounts). Therefore, the likelier possibility may be that these samples with low temperatures and very low fluid d18O reflect meteoric diagenesis after subaerial exposure of the shells.

Submitted by Josué Jautzy on
Thanks for the presentation. That is a nice set of data. I would have a couple questions: (1) Is their any constraints on the burial history of these samples? can we imagine temperature high enough for solid-state reordering? (2) It seems that you have some chronological measurement on some of your bivalves (i.e. early vs late shell growth). Could variable "vital effect" depending on the life stage of the bivalve (i.e. early vs late life stage) explain some of the trend seen within a bivalve shell? Thanks.
Hi Josué, Thanks for your question. With regards to burial history, the indications we have are that these carbonates have not been thermally altered (conodont CAI values of 1). There are no indications of temperatures high enough for solid state reordering (the highest calculated temperature is 95degrees C). The biogenic carbonates investigated are brachiopods and the sampling was conducted along growth lines where possible. In these instances, variability in the D47 compositions is apparent. This could indeed imply some vital effect, however, in some other samples, the range is quite high and we believe this is instead indicative of differential recrystallization of individual shells, also given the correlation between D47 and d18O.

Submitted by Josué Jautzy on
Thanks for the presentation. That is a nice set of data. I would have a couple questions: (1) Is their any constraints on the burial history of these samples? can we imagine temperature high enough for solid-state reordering? (2) It seems that you have some chronological measurement on some of your bivalves (i.e. early vs late shell growth). Could variable "vital effect" depending on the life stage of the bivalve (i.e. early vs late life stage) explain some of the trend seen within a bivalve shell? Thanks.


Submitted by Josué Jautzy on
Thanks for the presentation. That is a nice set of data. I would have a couple questions: (1) Is their any constraints on the burial history of these samples? can we imagine temperature high enough for solid-state reordering? (2) It seems that you have some chronological measurement on some of your bivalves (i.e. early vs late shell growth). Could variable "vital effect" depending on the life stage of the bivalve (i.e. early vs late life stage) explain some of the trend seen within a bivalve shell? Thanks.


Submitted by Josué Jautzy on
Thanks for the presentation. That is a nice set of data. I would have a couple questions: (1) Is their any constraints on the burial history of these samples? can we imagine temperature high enough for solid-state reordering? (2) It seems that you have some chronological measurement on some of your brachiopods (i.e. early vs late shell growth). Could variable "vital effect" depending on the life stage of the bivalve (i.e. early vs late life stage) explain some of the trend seen within a brachiopod shell? Thanks.


Submitted by Josué Jautzy on
Thanks for the presentation. Nice set of data. I have a couple questions: (1) Is there any constraints on the burial history of these samples? Would solid-state reordering be possible? (2) It seems that you have some interesting trends within brachiopod shell growth (i.e. early vs late shell growth). Could variable "vital effects" explain these?


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