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Tracing Temperature and Oxygen Isotope Compositions of Early Triassic Seawater with Clumped Isotope Thermometry
Vennemann T, Edward O, Luz Z & Bucher H
Vennemann T, Edward O, Luz Z & Bucher H (2020) Goldschmidt Abstracts, 2020 2674
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14b: Plenary Hall, View in program
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Comparing the results of this study with that of co-author Oluwaseun Edward in this session, I wonder how the samples of these two studies relate to each other both spatially and temporally. Is there temporal overlap in the Smithian samples of the two studies? Is the reason for promoting "large climatic oscillations" that the two studies suggest different d18O values for the coeval seawater (one more brackish, the other more evaporatively concentrated)? Do you have an explanation for why the RAJ samples preserved the original clumped isotope compositions but no the others?
Dear Georgina, Thanks for your question and indeed the approach for the results of co-author Oluwaseun Edward in this session and my own was the same BUT the samples are different (fossils and whole rocks for Olu's study and massive inorganic precipitates in my case here) AND the time slices covered are different too (Smithian-Spathian for Olu's study and Dienerian in my case); finally the sections occur in different parts of Oman as exotic blocks with sediments with/without underlying oceanic crust exposed too... Taking the errors into account, the differences in d18O of water are not all that different really but certainly we believe that this does suggest true differences in the seawater with time, all sections are believed to be true open ocean settings (off-shelf and/or seamount deposits for the Dienerian).
Comparing the results of this study with that of co-author Oluwaseun Edward in this session, I wonder how the samples of these two studies relate to each other both spatially and temporally. Is there temporal overlap in the Smithian samples of the two studies? Is the reason for promoting "large climatic oscillations" that the two studies suggest different d18O values for the coeval seawater (one more brackish, the other more evaporatively concentrated)? Do you have an explanation for why the RAJ samples preserved the original clumped isotope compositions but not the others?
The RAJ samples also have a very low conodont alteration index and were not directly deposited on the oceanic crust compared to the WAD samples that might have seen higher temperatures related to a "warmer" oceanic crust directly in contact with the carbonates here...
Interesting results, thanks! I wanted to ask about what lines of evidence you might have that would suggest a seawater-derived fluid was involved during fluid-rock interactions (such as for the WAD2 sample). Thanks!
This is simply the result of the calculation of a fluid in equilibrium with the carbonate (d18O of it) at the measured clumped temperature... Such a fluid comes out at close to zero or generally higher, up to +3.5 permil or in the case of the Oluwaseun Edward's study up to even +7 permil. Given the general relationship that the samples with lower d18O also give higher clumping temperatures, this thus suggests exchanged seawater that has exchanged with the overlying carbonate pile before and hence been buffered to higher values.
Thanks for your presentation. I was wondering how many replicates you are typically running (for both large and small samples) to get to the typical precision you are referencing (i.e. 15 and 7ppm)?
Dear Josué, Thanks for asking, normally three replicates for the "small" samples of about 400 to 500 micrograms, two for the large samples of 3 to 4 mg's... But in this case for the study we did six large ones...
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