Evaluating Microbial Influence on Marine Carbonate Concretions using Clumped Isotope Paleothermometry
Abstract
Carbonate concretions forming within organic rich, mixed-system sedimentary sequences, have been shown to exhibit strong evidence for microbial induced cementation based on extremely negative carbon isotope values. However, several new carbonate concretions from the Dominican Republic (Early Pliocene, Gurabo Fm. and Late Miocene, Cercado Fm.) and Colombia (Late Pleistocene, La Popa Fm.) indicate variable carbon isotope values between concretions within the same formations. Many of the carbonate concretions show δ13C values ranging from -35‰ to -5‰, generally with more negative values towards the initial growth centers and less negative values towards the edges of the concretions, which have been interpreted as evidence of bacterial sulfate reduction (BSR). Other concretions, however, exhibit a much less negative overall δ13C signal with little variability from center to edge, indicating that several of these concretions may have undergone a slightly modified mechanism of precipitation, either via inorganic processes or through buffering of the system through varied rates of chemical diffusion within the surrounding carbonate. Paleotemperatures calculated from Δ47 clumped isotope values indicate temperatures up to 45°C, although the geologic history of these concretions do not indicate exposure to such elevated burial temperatures. Clumped isotope derived temperaturesshow a correlation with δ13C values among concretions showing a central carbon excursion, with higher temperatures corresponding to more negative carbon values. This suggests that BSR may be influencing the disequilibrium in clumped isotope Δ47 values, resulting in the elevated temperatures recorded within several of the concretions. Overall, the stable and clumped isotopic profiles throughout carbonate concretions may serve as a reliable indicators for diagenesis within sedimentary sequences.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPP41E1883S
- Keywords:
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- 0473 Paleoclimatology and paleoceanography;
- BIOGEOSCIENCESDE: 1051 Sedimentary geochemistry;
- GEOCHEMISTRYDE: 3675 Sedimentary petrology;
- MINERALOGY AND PETROLOGYDE: 4863 Sedimentation;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL