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| Titel |
Magnetic Mineral diagenesis in changing water environments in the Black Sea since ∼41.6 ka |
| VerfasserIn |
Jiabo Liu, Norbert Nowaczyk, Ute Frank, Helge Arz |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250140394
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| Publikation (Nr.) |
 EGU/EGU2017-3775.pdf |
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| Zusammenfassung |
| Magnetic mineral diagenesis plays a key role in the global iron cycle. To understand
the authigenic magnetic mineral formation by diagenesis is also fundamentally
important for the interpretation of environmental magnetic as well as paleomagnetic
signals. Core MSM33-55-1, recovered from the SW Black Sea, was subjected to
rock-magnetic and SEM studies. The results demonstrate that four different magnetic
mineral assemblages associated to specific water conditions can be observed. Between
∼41.6 ka and ∼19 ka, magnetite and greigite are alternatively in dominance in the
sediment. Due to low organic matter input during the late MIS 3 and the last glacial
maximum (LGM), oxygenated bottom water in the Black Sea was favourable for
preserving detrital magnetite. Greigite in this interval have irregular shapes and
assemble in spots, which were formed in a micro environment with limited sulfate
availability. Between ∼19 ka and ∼16.5 ka, black layers were deposited as a result of
organic matter accumulation induced by productivity blooming and riverine discharge
soaring after the LGM. Hence less oxygenated bottom water conditions developed,
and more fine grained greigite was formed. After melt-water pulse (MWP) events
(∼16.5 ka), both primary productivity and the sea level were continuously rising
until ∼8.3 ka, leading to the depletion of oxygen in bottom water. In addition to
greigite, pyrite was also formed and gradually in dominance as approaching the
Holocene. The influx of salt water masses from the Mediterranean Sea after ∼8.3 ka
contributed to the establishment of the anoxic Black Sea, which resulted in the formation
of ubiquitous frambiods of pyrite. Additionally, bacterial magnetic minerals are
likely present in the sediment younger than ∼8.3 ka as indicated by rock magnetic
results. In this paper, four different magnetic mineral assemblages, reflecting gradual
changes from an oxic to an anoix Black Sea, were identified, yielding insights into
the relation between magnetic minerals diagenesis and bottom water conditions. |
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