Perspectives on geochemical proxies; the impact of model and parameter selection on the quantification of carbonate recrystallization rates

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doi: 10.1016/j.gca.2017.08.023
Author(s): Huber, Christian; Druhan, Jennifer L.; Fantle, Matthew S.
Author Affiliation(s): Primary:
Brown University, Department of Earth, Environmental and Planetary Sciences, Providence, RI, United States
University Illinois at Urbana-Champaign, United States
Pennsylvania State University, United States
Volume Title: Geochimica et Cosmochimica Acta
Source: Geochimica et Cosmochimica Acta, Vol.217, p.171-192. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037 CODEN: GCACAK
Note: In English. Includes appendices. 45 refs.; illus., incl. 3 tables
Summary: Diagenetic reactions in marine sediments, such as the recrystallization of carbonates, can impact the accuracy of paleo-environmental and paleo-climatic reconstructions by geochemical proxies. The extent to which the recrystallization of carbonates affects the chemistry of sedimentary archives depends on the reaction rate, extent of isotopic disequilibrium, and duration of reaction. The reaction rate, which is obviously critical, can be constrained by the elemental and isotopic compositions of pore fluids. Such constraints are affected by assumptions regarding the temperature in the sedimentary column relative to the temperature of formation, the burial rate, pore fluid advection, the composition of the sediments (carbonate-rich versus siliciclastic), and the porosity of the sediment column. In this study, we use a steady-state analytical solution to the diagenetic equations to constrain depth-dependent reaction rates (and extents of recrystallization) based on the Ca isotopic compositions of pore fluids in sedimentary columns at multiple ocean drilling sites (Sites 807, 984, 1170, and 1171), which encompass a diverse range of sedimentary compositions and conditions. We find that carbonates in siliciclastic sediments are generally less altered by diagenesis than their carbonate-rich counterparts. The discrepancy in recrystallization rates between siliciclastic and carbonate-rich sedimentary sections is, however, significantly smaller than previously estimated, suggesting that siliciclastic archives are not immune to diagenetic effects. While we find that diagenesis can decouple contemporaneous proxies of sea surface temperature (Mg/Ca and δ18O), our calculations also reveal that δ18O-based temperature estimates are more robust in siliciclastic sections relative to carbonate-rich sections. Sensitivity tests of the calculated extent of recrystallization suggest that uncertainties in porosity and burial rate are generally the greatest sources of error to proxy reconstruction from diagenetically altered sediments. The conclusions drawn using the analytical solution are benchmarked against a depth-dependent, forward numerical model using the CrunchFlow software (Steefel et al., 2015); ultimately, this comparison demonstrates that the assumptions necessary in deriving the analytical solutions have a relatively minor impact on the resulting conclusions.
Year of Publication: 2017
Research Program: IODP Integrated Ocean Drilling Program
ODP Ocean Drilling Program
Key Words: 02 Geochemistry; 06 Petrology, Sedimentary; Alkaline earth metals; Atlantic Ocean; Burial; Ca-44/Ca-40; Calcium; Carbonate sediments; Carbonates; Clastic sediments; Crystal chemistry; Diagenesis; Equatorial Pacific; Indian Ocean; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Leg 130; Leg 162; Leg 189; Lithofacies; Magnesium; Marine sediments; Mathematical methods; Metals; Mg/Ca; Models; North Atlantic; North Pacific; Northwest Pacific; O-18/O-16; ODP Site 1170; ODP Site 1171; ODP Site 807; ODP Site 984; Ocean Drilling Program; Ontong Java Plateau; Oxygen; Pacific Ocean; Pore water; Recrystallization; Reykjanes Ridge; Sediments; South Pacific; Southwest Pacific; Stable isotopes; Tasman Sea; Water-rock interaction; West Pacific
Coordinates: N033622 N033626 E1563730 E1563728
Record ID: 2018013775
Copyright Information: GeoRef, Copyright 2018 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands