The First Discovery of Authigenic Carbonates on the Laptev Sea Flank of Gakkel Ridge (Arctic Ocean)

Abstract

This paper describes the first finding of authigenic carbonates on the southern flank of Gakkel Ridge in its junction with the continental margin of the Laptev Sea of the Russian Federation. The samples are represented by compact magnesian calcites and aragonites, including rounded and angular fragments of terrigenous material, as well as microphytoplankton and spores and pollen of terrestrial and aquatic plants of various ages. The elemental and organochemical characteristics are indicative of the predominant oxidation conditions or those intermediate between oxidation and reduction conditions of carbonate crystallization likely due to the fact that carbonates were formed near the bottom surface. The O, C, and Sr isotopic compositions make it possible to conclude that diagenetic carbonates of Gakkel Ridge were deposited mainly in isotopic equilibrium with bottom water at a temperature of about 0°C, corresponding to measurements from the research vessel. A wide range of δ13С (from –23.5 to –37.3) is indicative of the fact that methane was an important, but not the sole source of carbon in carbonates. Based on wide variations in 87Sr/86Sr (0.70906–0.70933) correlated with δ13С values, the carbonate-forming fluid was not only modern seawater, but also diagenetic solutions coming from the sedimentary cover together with methane and methane and organic matter oxidation products. The active discharge of heterogeneous methane-bearing fluids can be related to the high modern tectonic activity of the study region.