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| Titel |
Characterization of diagenetic siderites formed in recent and ancient ferruginous sediments of Lake Towuti, Indonesia. |
| VerfasserIn |
Aurele Vuillemin, Jens Kallmeyer, Dirk Wagner, Helga Kemnitz, Richard Wirth, Andreas Luecke, Christoph Mayr |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250123360
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| Publikation (Nr.) |
 EGU/EGU2016-2594.pdf |
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| Zusammenfassung |
| Authigenic minerals in lacustrine settings can be formed in the water column and within the
sediment, abiotically and/or triggered by biological activity. Such minerals have been used as
paleosalinity and paleoproductivity proxies, reflecting trophic state, and/or early diagenetic
conditions. They have also been considered as potential biosignatures of past and present
microbial activity.
Here we present a study from Lake Towuti, a deep tectonic basin in Sulawesi, Indonesia.
Its geographic position makes it a prime location to record paleoclimatic changes in the
tropical Western Pacific warm pool in its sedimentary sequence. The ultramafic rocks and
surrounding lateritic soils in the catchment area supply considerable amounts of iron and
other metals to the lake. These elements further restrain primary productivity along with the
development of specific microbial metabolic pathways involved in early diagenesis. Lake
Towuti is stratified with anoxic conditions below 130 m, allowing metal reduction processes
to take place in the hypolimnion. The extreme scarcity of sulphate and nitrate/nitrite make
Lake Towuti’s bottom waters a modern analogue for the Archaean Ocean. It was
therefore chosen as a drilling target by the International Continental Drilling Program
(ICDP).
In May to July 2015, the Towuti Drilling Project recovered a total >1000 m of sediment
core from three drilling sites, including a 114 m long core drilled with a contamination tracer
dedicated to geomicrobiological studies. Heavy mineral fractions were extracted from core
catcher samples and siderite crystals (FeCO3) were selected from different depths.
Characterization of their habitus was achieved via SEM and TEM imaging. Preliminary
results show that siderites grow from amorphous into nanocrystalline phases and
form twinned aggregates developing into mosaic monocrystals with depth. Gradual
filling of vugs and microporosity were observed along with inclusions of magnetite
nanocrystals.
Work in progress includes parallel δ13C measurements on bulk organic matter (OM)
surrounding the minerals and on the siderites themselves to trace organic to inorganic carbon
transfer associated with microbial respiration of OM and infer possible relationships to
methane oxidation processes. Analysis of δ56Fe compositions will complement this dataset
to highlight the role of dissimilatory Fe (III) reduction in siderite formation. We
hypothesize that sedimentary siderite is formed by precipitation from pore water due to
saturation resulting from microbial OM and iron respiration processes. A similar
approach will be applied to vivianite crystals (Fe3(PO4)3⋅8H2O) that were found
concomitantly with siderite in sedimentary horizons intercalated with tephra layers. |
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