Biogenic magnetite: Authigenesis and diagenesis with changing redox conditions in Lake Greifen, Switzerland

Conference · Fri Mar 01 00:00:00 EST 1991 · AAPG Bulletin (American Association of Petroleum Geologists); (United States)

OSTI ID:5617727

Hawthorne, T B; McKenzie, J A ^[1]

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1. Geology Inst., Zurich (Switzerland)

A mineralogic, chemical, and rock-magnetic investigation was conducted in Lake Greifen, a moderate-sulfate containing eutrophic lake, in order to assess iron mineral diagenesis in a sedimentary sequence deposited during different tropic states and varying redox conditions. The sedimentary sequence is composed of 0.25 m of eutrophic anoxic varved sediments underlain by transitional laminated marls, deposited as the lake changed from oxic to dysaerobic conditions, and then a basal unit of pre-eutrophic bioturbated marls. Grain size, morphology, and composition of magnetite observed by TEM suggest that single-domain biogenic magnetite is currently produced within the upper anoxic varved sediments. Similarly characterized fine-grained magnetites observed in the pre-eutrophic sediments indicate magnetite authigenesis prior to eutrophication. Low values of NRM, susceptibility, SIRM, and ARM in the anoxic varved sediments below the zone of magnetite production indicate the rapid destruction of magnetite. Iron speciation analyses, interstitial water results, and the ARM:SIRM ratio indicate that reductive dissolution is progressive. These results suggest that (1) rapid destruction of fine-grained magnetite occurs in high productivity, low-sulfate containing anoxic sediments following dissolution of ferric phases; and (2) magnetite preservation reflects redox conditions that, in Lake Greifen, are determined by productivity. These findings differ from marine reductive diagenetic models in which magnetite dissolution is considered insignificant, or slow, in the absence of high sulfide concentrations.

• OSTI ID: 5617727
• Report Number(s): CONF-910403-; CODEN: AABUD
• Journal Information: AAPG Bulletin (American Association of Petroleum Geologists); (United States), Vol. 75:3; Conference: Annual meeting of the American Association of Petroleum Geologists (AAPG), Dallas, TX (United States), 7-10 Apr 1991; ISSN 0149-1423
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
LAKES
ROCK-FLUID INTERACTIONS
MAGNETITE
BIOCONVERSION
DIAGENESIS
MINERALIZATION
SWITZERLAND
CRYSTALLIZATION
DISSOLUTION
GEOCHEMISTRY
GRAIN SIZE
INTERSTITIAL WATER
MINERALOGY
MORPHOLOGY
PRECIPITATION
REDOX REACTIONS
SEDIMENT-WATER INTERFACES
SEDIMENTS
CHEMICAL REACTIONS
CHEMISTRY
CRYSTAL STRUCTURE
DEVELOPED COUNTRIES
EUROPE
GROUND WATER
HYDROGEN COMPOUNDS
INTERFACES
IRON ORES
MICROSTRUCTURE
MINERALS
ORES
OXIDE MINERALS
OXYGEN COMPOUNDS
PHASE TRANSFORMATIONS
SEPARATION PROCESSES
SIZE
SURFACE WATERS
WATER
580000* - Geosciences