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3. Structural diagenesis using clumped isotope paleothermometry : applications and potential caveats

Author

Herlambang, Adhipa, John, Cédric Michael, and Cosgrove, John

Subjects
551.8
Abstract

Fluid flow commonly results in mineral precipitation in fractures which can yield a chemical archive of the physico-chemical conditions during tectonic deformation. However, interpreting subsurface conditions from traditional geochemical proxies can be ambiguous. Here we test clumped isotope thermometry as a tool to provide better understanding of the relationship between deformational structures and diagenetic processes. Three main questions are addressed by this PhD thesis. The first question regards the reliability of clumped isotope compared to fluid inclusions in fractures within granites. We selected calcite veins resulting from deep-biosphere activity in oligotrophic fractures environment in Sweden. The clumped isotope results demonstrate that the optimal habitat to support microbial activity was below the detection limit of fluid inclusion. Hence, carbonate clumped isotope in this case is a valuable tool complementary to fluid inclusions that offers tighter constraints on the temperature and origin of diagenetic fluid. The second objective was to investigate potential kinetic fractionation effects due to precipitation rates in fractures filled with meteoric cements. To address this objective, we apply clumped isotopes and trace element analysis along a detailed transect of single minerals of calcite in faults. The strong correlation between the ratio of Mn/Fe with clumped isotope temperature lead us to argue that this is indicative of variable crystal precipitation rates and in some cases kinetic fractionation. Thus for the first time we can independently show potential kinetic fractionation within ancient natural calcite samples that resulted in clumped isotopes temperature higher than ambient. The third and final objective of the thesis was to apply clumped isotopes within an integrated study aiming at understanding the relationship between paleo-temperature, fluid flow and salt-doming in Jebel Madar, Oman. The results lead us to re-interpret the structural diagenesis of Jebel Madar, and demonstrate the value of clumped isotopes in structural diagenesis studies in general.

Published
2021
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12. Physicochemical Conditions of the Devonian-Jurassic Continental Deep Biosphere Tracked by Carbonate Clumped Isotope Temperatures of Granite-Hosted Carbonate Veins

Author

Herlambang, Adhipa, John, Cedric M., Drake, Henrik, Herlambang, Adhipa, John, Cedric M., and Drake, Henrik

Abstract

Previous studies have shown that microorganisms thrive in oligotrophic fracture systems, and metabolisms include consumption and production of methane. In the Laxemar, Gotemar, and Forsmark areas of Sweden, ancient microbial activity has previously been demonstrated by large delta C-13(VPDB) variability of carbonate vein infillings within granitic host rocks. Here, we apply carbonate clumped isotope thermometry to reconstruct the temperature of precipitation of the carbonate within these veins. The carbonate clumped isotope temperatures indicate that mineralization took place between 46 degrees C and 108 degrees C, in line with previously published fluid inclusion data (<50 degrees C to 113 degrees C). The new carbonate clumped isotope data more accurately narrows temperatures at the lower end of this range as fluid inclusions are not easily applicable below 80 degrees C, a temperature regime of high importance for paleobiological reconstructions. Our results demonstrate that large volumes of biogenic carbonate cement were formed from low-temperature microbial processes in low-salinity water, succeeding calcite of deep brine origin. The known burial and thermal history of the region combined with our carbonate clumped isotope data place the microbial activity at the end of the Variscan orogeny and later events (e.g., Jurassic). Thus, carbonate clumped isotope thermometry reduces uncertainties in deep biosphere studies by providing more accurate temperature constraints in the low-temperature regime, the biogenic processes, and the origin of the diagenetic fluids.

Published
2023
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17. Structural diagenesis using clumped isotope paleothermometry: applications and potential caveats

Author

Herlambang, Adhipa, John, Cédric Michael, and Cosgrove, John

Abstract

Fluid flow commonly results in mineral precipitation in fractures which can yield a chemical archive of the physico-chemical conditions during tectonic deformation. However, interpreting subsurface conditions from traditional geochemical proxies can be ambiguous. Here we test clumped isotope thermometry as a tool to provide better understanding of the relationship between deformational structures and diagenetic processes. Three main questions are addressed by this PhD thesis. The first question regards the reliability of clumped isotope compared to fluid inclusions in fractures within granites. We selected calcite veins resulting from deep-biosphere activity in oligotrophic fractures environment in Sweden. The clumped isotope results demonstrate that the optimal habitat to support microbial activity was below the detection limit of fluid inclusion. Hence, carbonate clumped isotope in this case is a valuable tool complementary to fluid inclusions that offers tighter constraints on the temperature and origin of diagenetic fluid. The second objective was to investigate potential kinetic fractionation effects due to precipitation rates in fractures filled with meteoric cements. To address this objective, we apply clumped isotopes and trace element analysis along a detailed transect of single minerals of calcite in faults. The strong correlation between the ratio of Mn/Fe with clumped isotope temperature lead us to argue that this is indicative of variable crystal precipitation rates and in some cases kinetic fractionation. Thus for the first time we can independently show potential kinetic fractionation within ancient natural calcite samples that resulted in clumped isotopes temperature higher than ambient. The third and final objective of the thesis was to apply clumped isotopes within an integrated study aiming at understanding the relationship between paleo-temperature, fluid flow and salt-doming in Jebel Madar, Oman. The results lead us to re-interpret the structural diagenesis of Jebel Madar, and demonstrate the value of clumped isotopes in structural diagenesis studies in general. Open Access

Published
2020
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