Diagenetic Environments of Authigenic Carbonates and Opal-CT Crystallization in Lower Miocene to Upper Oligocene Deposits of the Norwegian Sea (ODP Site 643, Leg 104)

Henrich, Rüdiger (1989) Diagenetic Environments of Authigenic Carbonates and Opal-CT Crystallization in Lower Miocene to Upper Oligocene Deposits of the Norwegian Sea (ODP Site 643, Leg 104) Proceedings of the Ocean Drilling Program: Scientific Results, 104 . pp. 233-247. DOI 10.2973/odp.proc.sr.104.119.1989.

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Abstract

Different generations of complex authigenic carbonates formed in siliceous muds (lithologic Unit IV) and hemipelagic clays (lithologic Unit V) of ODP Site 643, Leg 104 Norwegian Sea. The dominant phase in Unit IV is an early diagenetic Mn, Fe-calcite with a strong negative 5 13C (- 14 to - 16 %o) signature, and slightly negative 8 180 values. The strong negative 8 13C results from extensive incorporation of 12C-enriched C02 derived from bacterial degradation of marine organic matter into early Mn, Fe—calcite cements. Concomitant framboidal pyrite precipitation and abundant SEM microtextures showing excellent preservation of delicate structures of fragile diatom valves by outpourings with early Mn-calcites strongly support their shallow burial formation before the onset of compaction. Later generations of authigenic mineralizations in lithologic Unit IV include minor amounts of a second generation of calcite with platy crystals, possibly precipitated along with opal-A dissolution, and finally opal-CT crystallization in deeper seated environments overgrowing earlier precipitates with films and lepispheres. The last mineralization is collophane (fluor apatite) forming amorphous aggregates and tiny hexagonal crystals. Authigenic mineral assemblages in lithologic Unit V consist of rhodochrosites, transitional rhodochrosite/manganosiderites, and apatite. A negative 8 13C (- 7.1 to - 15.6 %o) and a fluctuating 8 180 signal indicates that the micritic to sparitic rhodochrosites, transitional rhodochrosites/manganosiderites were formed at various burial depths. C02 resulted from organic matter degradation in the lowermost sulfate reduction zone and from biogenic methane generation in the lowermost sediments, resulting in variable and negative 8 13C signals. The change in carbonate mineralogy reflects major compositional differences compared to sediments in Unit IV. Most prominent is an increase in altered ash as a primary sediment component and a sudden decrease of siliceous microfossils. Upward diffusion of cations, lowered salinities in pore waters, and elevated temperatures provide diagenetic environments favoring increased remobilization processes.

Document Type: Article
Keywords: ODP Leg 104, Norwegian Sea
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
Refereed: No
DOI etc.: 10.2973/odp.proc.sr.104.119.1989
ISSN: 1096-7451
Projects: ODP
Date Deposited: 13 May 2019 13:35
Last Modified: 14 May 2019 12:12
URI: http://eprints.uni-kiel.de/id/eprint/46702

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