Boron concentrations and isotopic compositions in methane-derived authigenic carbonates : constraints and limitations in reconstructing formation conditions

• Published in: Earth and Planetary Science Letters
• Main Authors: Hong, Wei Li, Lepland, Aivo, Kirsimäe, Kalle, Crémière, Antoine, Rae, James W.B.
• Other Authors: University of St Andrews. School of Earth & Environmental Sciences, University of St Andrews. Centre for Energy Ethics, University of St Andrews. St Andrews Isotope Geochemistry
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2022
• Subjects: Boron; Early diagenesis; Methane-derived authigenic carbonate; Transport-reaction modelling; QE Geology; QD Chemistry; Geophysics; Geochemistry and Petrology; Earth and Planetary Sciences (miscellaneous); Space and Planetary Science; NDAS; SDG 14 - Life Below Water; QE; QD; Arctic; Norway; Arctic Gas Hydrate, Environment and Climate
• Online Access: http://hdl.handle.net/10023/24759; https://doi.org/10.1016/j.epsl.2021.117337

The work is supported by Norwegian Research Council through the schemes PETROMAKS2-NORCRUST (grant number 255150 ) and Centre for Arctic Gas Hydrate, Environment and Climate (CAGE grant number 223259 ) as well as Lundin Norway AS. Cruise MSM57-1/-2 was funded by the German Research Foundation (DFG), the Research Center/Excellence Cluster “The Ocean in the Earth System” at MARUM–Center for Marine and Environmental Sciences, University of Bremen and funds from CAGE. The boron content and isotopic composition (δ11B), of marine carbonates have the potential to constrain CO2 chemistry during carbonate growth conditions. However, obtaining and interpreting boron compositions from authigenic carbonates in geological archives present several challenges that may substantially limit their application. In particular, contamination from non-carbonate phases during sample preparation must be carefully avoided, and a variety of controls on boron composition during authigenic growth conditions must be evaluated. To advance understanding of the use and limitations of boron in authigenic carbonates, we present data and modelling results on methane-derived authigenic carbonate (MDAC), a by-product of microbially mediated anaerobic oxidation of methane, taken from three cold seep sites along the Norwegian margin. We present a novel sequential leaching method to isolate the boron signals from the micritic (Mg-calcite) and cavity-filling (aragonitic) MDAC cements in these complex multi-phase samples. This method successfully minimizes contamination from non-carbonate phases. To investigate the factors that could potentially contribute to the observed boron signals, we construct a numerical model to simulate the evolution of MDAC δ11B and B/Ca ratios over its growth history. We show that diagenetic fluid composition, depths of precipitation, the physical properties of sediments (such as porosity), and mineral surface kinetics all contribute to the observed boron compositions in the different carbonate cements. While broad ...