Repeated occurrences of methanogenic zones, diagenetic dolomite formation and linked silicate alteration in southern Bering Sea sediments (Bowers Ridge, IODP Exp. 323 Site U1341)

Online Access: Get full text
doi: 10.1016/j.dsr2.2013.09.008
Author(s): Wehrmann, Laura M.; Ockert, C.; Mix, A. C.; Gussone, N.; Teichert, B. M. A.; Meister, P.
Author Affiliation(s): Primary:
University of California at Riverside, Department of Earth Sciences, Riverside, CA, United States
Other:
Universität Münster, Germany
Oregon State University, United States
Max Planck Institute for Marine Microbiology, Germany
Volume Title: Plio-Pleistocene paleoceanography of the Bering Sea
Volume Author(s): Takahashi, Kozo, editor; Ravelo, A. Christina; Okazaki, Yusuke
Source: Plio-Pleistocene paleoceanography of the Bering Sea, edited by Kozo Takahashi, A. Christina Ravelo and Yusuke Okazaki. Deep-Sea Research. Part II: Topical Studies in Oceanography, Vol.125-126, p.117-132. Publisher: Elsevier, Oxford, International. ISSN: 0967-0645
Note: In English. 139 refs.; illus., incl. 3 tables, sketch map
Summary: Diagenetic precipitates, such as dolomite, and the chemistry of residual deeply buried porewater often represent the only traces of past biogeochemical activity in marine sediments. A 600 m thick sedimentary section, recently drilled at Integrated Ocean Drilling Program (IODP) Site U1341 on Bowers Ridge (southern Bering Sea), provides insight into such a 4.3 Ma old paleo-diagenetic archive. Hard-lithified calcite-dolomite layers, and laminae of disseminated carbonate, were recovered in diatom-rich sediments over a depth range of 400 m. Carbon isotope values of the diagenetic carbonates between -16.6 and -14.4 ppm (VPDB) and strontium isotope ratios of dolomites close to past seawater values suggest carbonate precipitation induced by the production of dissolved inorganic carbon (DIC) during elevated rates of organic carbon mineralization, primarily via sulfate reduction, at shallow sediment depth below the paleo-seafloor. Diagenetic carbonates at 280-440 m below seafloor were likely also produced by the intermittent onset of sulfate reduction coupled to the anaerobic oxidation of methane (AOM) at sulfate-methane transition zones (SMTZ). These microbially mediated processes do not occur in the sediment at this site at present but were likely connected to the presence of a methanogenic zone at 2.58-2.51 Ma. A minimum in sulfate concentrations in modern porewaters and low sedimentary Ba/Al ratios resulting from former sulfate depletion are reminiscent of the presence of this large methanogenic zone. The minimum in sulfate concentrations is reflected in a minimum in magnesium concentrations, less radiogenic strontium and isotopically light calcium in the porewater. It is proposed that magnesium was removed from the porewater during carbonate precipitation and volcanic ash alteration which occurred in the former methanogenic zone and also released strontium with a less radiogenic isotope ratio and isotopically light calcium into the porewater. The isotopic composition of porewater calcium was also influenced by ammonium-calcium exchange on clay minerals and carbonate recrystallization. Our study elucidates the response of porewater element concentrations and isotopic profiles interlinked with the formation of diagenetic carbonates to changes in the deposition of organic carbon in sediments of deeper water sites (>2000 m water depth) over prolonged timescales. It shows that variations in biogeochemical processes in response to changes in oceanographic conditions and a dynamic subseafloor biogeochemical zonation have to also be taken into account at these deep water sites for a global assessment of organic carbon burial fluxes and remineralization. Abstract Copyright (2016) Elsevier, B.V.
Year of Publication: 2016
Research Program: IODP Integrated Ocean Drilling Program
Key Words: 02 Geochemistry; 12 Stratigraphy, Historical Geology and Paleoecology; Aliphatic hydrocarbons; Alkaline earth metals; Alkanes; Bering Sea; Bowers Ridge; C-13/C-12; Ca-44/Ca-40; Calcium; Carbon; Carbonates; Cenozoic; Chemostratigraphy; Cores; Diagenesis; Dolomite; Expedition 323; Geochemistry; Hydrocarbons; IODP Site U1341; Integrated Ocean Drilling Program; Isotope ratios; Isotopes; Lithostratigraphy; Magnesium; Marine sediments; Metals; Methane; Neogene; North Pacific; Northwest Pacific; O-18/O-16; Organic compounds; Oxygen; Pacific Ocean; Pleistocene; Pliocene; Pore water; Quaternary; Reduction; Sedimentary rocks; Sediments; Sr-87/Sr-86; Stable isotopes; Strontium; Sulfates; Tertiary; West Pacific; X-ray diffraction data
Coordinates: N540200 N540200 E1790031 E1790031
Record ID: 2017013130
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands