DARWIN Digitale Dissertationen German Version Strich

FU Berlin
Digitale Dissertation

Andreas Hübner :
Geochemical and mineralogical investigation of sediments from the anoxic, hypersaline Urania basin (eastern Mediterranean) to characterize marine sedimentation under extreme conditions
Geochemische und mineralogische Untersuchung von Sedimenten aus dem Bereich des anoxischen, hypersalinen Urania-Beckens (östliches Mittelmeer) zur Charakterisierung von mariner Sedimentation unter extremen Bedingungen

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Abstract

This research aimed to investigate the sedimentation under hypersaline and anoxic conditions and the related geochemical processes. Two sediment cores from the anoxic-hypersaline Urania basin (eastern Mediterranean) were studied. Furthermore, sapropels from the vicinity of the basin were analysed in terms of their early diagenetic alteration and compared to the basin sediments. A major component of the Urania basin sediments is elemental S (6.5-18.9 wt.%). Dissolved sulfate, which is derived from messinian evaporites, is reduced by bacterial activity to dissolved sulfide. Organic carbon and methane are the main reducing agents. Aqueous sulfide is oxidised to elemental S at the seawater/brine interface and accumulates at the basin floor. Contrasting this, pyrite is only a minor sink for dissolved sulfide (~1 wt.% pyrite). Elemental S and pyrite show similar delta34S-values between -2 and -11 permil. These values differ significantly from values of sedimentary pyrites usually found, e.g. in eastern Mediterranean sapropels (< -35 permil). The relatively positive delta34S-values originate most probably from a special population of (halophile?) microorganisms. About 1/3 of the bulk carbonate in the sediments is made up of dolomite. A recently published dolomitisation model (Vasconcelos and McKenzie, 1997) may explain primary dolomite precipitation in the Urania basin. The form and size of the dolomite crystals as well as the chemical composition of the brine point to dolomite formation within the brine. Dolomite from nearby the Urania basin in sediments which are not covered by brine indicates brine migration to sediments outside the basin. In the deepest part of the Urania basin, fluids and particles are introduced into the basin from deeper sedimentary levels. A layer of a few cms thickness in the sedimentary succession from outside the basin proves that anoxic mud similar to Urania basin sediments extruded outside the basin. Comparison of Urania basin sediments with sapropels, which were equally deposited under anoxic conditions, showed marked differences between these two sediment types. This is due to different material sources and sedimentation processes. The different analysed sapropels showed various states of preservation. The youngest sapropel S-1 is completely preserved. Opposed to that, sapropel S-2 is completely oxidised and only identified in the core by Mn- and Ba-distribution. Sapropels S-5 and S-6 exhibit different degrees of early diagenetic alterations. Sapropel S-3 lies within the region of the core which contains dolomite rather than calcite. Migrating brines fuelled sulfate reduction in this sapropel, which led to the complete dissolution of all carbonate in S-3.

Table of Contents

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Titelblatt, Danksagung und Inhaltsverzeichnis
1. Ausgangsfragen und Zielsetzung 1
2. Geologischer Rahmen des Arbeitsgebietes 3
2.1 Paläogeographie und Geologie des Arbeitsgebietes 3
2.2 Evaporitbildung im Mittelmeer am Ende des Miozäns 5
2.3 Die Brine-Becken des Mittelmeeres 6
2.4 Sapropele im Mittelmeer: Eigenschaften, Bildung und Vorkommen 7
3. Material und Methoden 9
3.1 Sedimentkerne 9
3.2 Bearbeitung an Bord 10
3.3 Weitere Probenbearbeitung und Analysemethoden 11
4. Ergebnisse 15
4.1 Stratigraphie 15
4.1.1 Kerne 3SL, 4MC, LC17 und 8GK 15
4.1.2 Kern 6SL 15
4.2 Beschreibung der Kornfraktionen und der Mineralogie 17
4.2.1 Kern 3SL 17
4.2.2 Kern 4MC 20
4.2.3 Kern 6SL 21
4.2.4 Dolomitstöchiometrie 24
4.2.5 Semiquantifizierung der Tonminerale 24
4.3 Verteilung von Karbonat und organischem Kohlenstoff 25
4.3.1 Kerne 3SL, 4MC und LC17 25
4.3.2 Kern 6SL 26
4.4 Elementgeochemie 28
4.4.1 Kern 3SL 28
4.4.2 Kern 4MC 28
4.4.3 Kern 6SL 28
4.5 Schwefelgehalte und -spezies 37
4.6 Isotopenverteilung: C, O, S 38
4.6.1 Kohlenstoff- und Sauerstoffisotopenverteilung 38
4.6.2 S-Isotopenverteilung 39
4.7 Untersuchung der Präzipitate (Gipse) 40
4.8 Laugungsversuche 41
4.9 Wasserchemie 42
5. Diskussion 45
5.1. Urania-Becken Sedimente: Geochemie und Genese 45
5.1.1 Kern 3SL 45
5.1.2 Kern 4MC 47
5.1.3 Schwefel-Kreislauf im Urania-Becken 49
5.1.4 Brine-Geochemie 52
5.1.5 Lösung und Fällung von CaCO3 im Urania-Becken 53
5.1.6 Dolomitisierung I: Urania-Becken Sedimente 55
5.1.7 Die exotische Lage oberhalb S-1, Kern 6SL 58
5.2 Kern 6SL: Geochemie und Genese 64
5.2.1 Konzentration und vertikale Verteilung der Haupt-, Neben- und Spurenelemente 64
5.2.2 Dolomitisierung II: Dolomitbildung ausserhalb des Urania-Beckens 66
5.2.3 Sapropelgeochemie 71
6. Wichtigste Schlussfolgerungen und Ausblick 83
7. Zusammenfassung 85
8. Literaturverzeichnis 87
9. Anhang 94

More Information:

Online available: http://www.diss.fu-berlin.de/2002/150/indexe.html
Language of PhDThesis: german
Keywords: sediment anoxic hypersaline Urania basin sulfur eastern Mediterranean
DNB-Sachgruppe: 31 Geowissenschaften
Date of disputation: 19-Jul-2002
PhDThesis from: Fachbereich Geowissenschaften, Freie Universität Berlin
First Referee: Professor Dr. Peter Halbach
Second Referee: Professor Dr. Kay-Christian Emeis
Contact (Author): ahb@zedat.fu-berlin.de
Contact (Advisor): hbrumgeo@zedat.fu-berlin.de
Date created:09-Aug-2002
Date available:13-Aug-2002

 

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