Origin of Authigenic Carbonates in Eocene to Quaternary Sediments from the Arctic Ocean and Norwegian-Greenland Sea

Abstract

Authigenic carbonates occur in thin layers, nodules, and burrows in fine-grained siliciclastic sediments of middle Eocene to Quaternary age that were recovered from the Arctic Ocean and Norwegian-Greenland Sea during Leg 151. At Site 913 (East Greenland Margin), concentrically zoned microspherules and rhombohedrons of ferroan rhodochrosite and manganoan siderite, 20-600 µm in diameter, are the main authigenic carbonates in the sedimentary succession. They grew displacively within the host clays and silts, and have locally coalesced to form aggregates. At Sites 909 (Fram Strait) and 911 (Yermak Plateau), very fine to fine-crystalline siderite, enriched in Ca and/or Mg, is the predominant carbonate in the sedimentary succession. It occurs as interparticle cement, disseminated crystals, and rounded intraclasts in host clays, silts, and muds. Minor micritic or radialfibrous calcite and dolomite were also found at these three sites. Most of these carbonates are interpreted to have precipitated at shallow-burial depths during early diagenesis.All authigenic carbonates (rhodochrosite, siderite, and calcite) from Site 913 are strongly enriched in 12 C (δ 13 C = -22.9 to -13.8%c) and show decreasing δ 13 C values with depth below the seafloor. This evidence, along with authigenic pyrite found in microspherule cores, suggests that dissolved carbon was derived from the oxidation of marine organic matter in the bacterial sulfate-reduction zone and during the early stages of methanogenesis. However, low organic matter content and headspace methane concentrations suggest additional derivation of dissolved carbon from thermogenic methane. The very low δ 18 θ values (-11.8%c) for rhodochrosite and the close association with barite in voids and fractures suggest rhodochrosite precipitation from Mn-charged, hydrothermal fluids, possibly related to volcanic activity associated with seafloor spreading. The δ 13 C values of most siderites from Site 909 are close to -6%c, which suggests an origin in the Fe-reduction, suboxic zone, possibly only centimeters or decimeters below the seafloor. However, minor occurrences of siderite with very low δ 13 C values (-21.8%c), along with their close association with authigenic pyrite, indicate additional derivation of dissolved carbon from bacterial sulfate-reduction and the early stages of methanogenesis. The importance of anaerobic microbial processes is further corroborated by the moderate to high organic matter content and headspace methane concentration at Site 909. The range of δ 18 θ values for siderite from Sites 909 and 911 (-10.3 to +5.0%o) appears to be related to both increasing burial temperatures and interaction between labile volcaniclastic sediment and marine pore waters.

Quaternary glaciations of northern Europe

“…This IRD influx has been timed at 2.74 Ma (Jansen et al, 2000). It is synchronous with a marked IRD pulse from ice sheets in Greenland and North America (Shackleton et al, 1984;Chow et al, 1996;Jansen et al, 2000;Knies et al, 2002) and the first glaciation of the Barents Sea shelf (Knies et al, 2009). The inception of the BIIS is also considered to be coeval with this second up-scaling phase in Northern Hemisphere Glaciation Lee et al, 2012;Thierens et al, 2012).…”

Pliocene palaeoceanography of the Arctic Ocean and subarctic seas

“…The interpretation of the records is further complicated by diagenetic processes leading, for example, to the formation of authigenic carbonates, manganese and iron oxides, and iron sulphides in the sediments (e.g. Thiede et al 1996;Chow et al 1996;Henrich et al 2002 Bennike et al 2002) and therefore sites drilled during ODP Legs 104, 105, 145, 151 and 162 in the subarctic seas still provide the majority of palaeoenvironmental information. Palaeoceanographic reconstructions in the high northern latitudes are furthermore biased to the period since the intensification of NHG in the Mid-Pliocene (e.g.…”

Ethological analysis of the trace fossil Zoophycos : hints from the Arctic Ocean

“…The trace fossil Zoophycos described in this study from cores taken on the Lomonosov Ridge therefore could be the first concrete evidence supporting the idea of a specialized behaviour as a response to seasonal fluctuations in food flux in the Arctic Ocean. Although Zoophycos has been reported from the Greenland Sea and the Yermak Plateau (Chow et al. 1996) and has been noted in Quaternary Arctic deep‐sea core material (Clark et al.…”