TY - JOUR
T1 - Boron concentrations and isotopic compositions in methane-derived authigenic carbonates
T2 - constraints and limitations in reconstructing formation conditions
AU - Hong, Wei Li
AU - Lepland, Aivo
AU - Kirsimäe, Kalle
AU - Crémière, Antoine
AU - Rae, James W.B.
N1 - 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.
PY - 2022/2/1
Y1 - 2022/2/1
N2 - 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 constraints may be placed on fluid composition, the multiple competing controls on boron in these diagenetic settings limit the ability to place unique solutions on fluid CO2 chemistry using boron in these authigenic carbonates.
AB - 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 constraints may be placed on fluid composition, the multiple competing controls on boron in these diagenetic settings limit the ability to place unique solutions on fluid CO2 chemistry using boron in these authigenic carbonates.
KW - Boron
KW - Early diagenesis
KW - Methane-derived authigenic carbonate
KW - Transport-reaction modelling
U2 - 10.1016/j.epsl.2021.117337
DO - 10.1016/j.epsl.2021.117337
M3 - Article
AN - SCOPUS:85122475767
SN - 0012-821X
VL - 579
JO - Earth and Planetary Science Letters
JF - Earth and Planetary Science Letters
M1 - 117337
ER -