News from FROMAGE Members

Tribovillard N., Lyons, T.W., Riboulleau,A., Bout-Roumazeilles, B., 2008.
Bull. Soc. Geol. Fr., 179, 1, 3-12.

(find here the high res image)

Molybdenum is a trace metal commonly used as a marker of paleoredox conditions of ancient depositional settings. Pyrite is an important Mo host for enriched sedimentary rocks. In this paper we study the relationship between Mo and pyrite in the Bancs Jumeaux Formation, a Jurassic succession in northern France consisting of limestone and pyrite-rich marls. This formation is relatively enriched in Mo compared to other redox-sensitive trace metals. Our approach is grounded on bulk rock chemical analysis and delineation of two contrasting types of pyrite that can be extracted from the rocks: polyframboids and nonframboidal concretionary masses. The morphological characteristics of both morphotypes were studied using scanning electronic microscopy. The polyframboids are richer in Mo than the concretions but are not markedly enriched in other trace metals. This discrepancy in geochemical composition could result from pyrite precipitation at different times during early diagenesis. Our results tend to indicate that the polyframboids would have formed very early in reducing "microniches", within dominantly dysoxic sediment. This early pyrite precipitation occurred at shallow depth below the sediment-water interface close to the abundant Mo source in overlying oxic seawater (molybdate ions), and would have fostered Mo-capture by the polyframboids in relatively large amounts. The concretions would have formed later during early diagenesis (within the sulfidic zone) under conditions of more limited Mo availability.

Phosphogenesis in recent upwelling areas: The importance of microbial communities indicated by lipid biomarkers

E.T.ARNING, D.BIRGEL, H.N.SCHULZ-VOGT, B.B. JØRGENSEN and J.PECKMANN

Original abstract - poster

The burial of phosphorus and the formation of phosphorites (phosphogenesis) in marine sediments represent an important sink in the global phosphorus cycle. Numerous basin-scale phosphorite deposits were formed in the geological past (e.g., Trappe 1998). Phosphogenesis is not only found in ancient settings, it is reported in recent sediments of upwelling regions as for example off Namibia, Peru, and Chile (Föllmi 1996).
These sediments contain dense populations of large nitrate-storing sulfide-oxidizing bacteria Thiomargarita, Beggiatoa, and Thioploca, respectively. Due to metabolic activities of the thiotrophs generating sulfate, a close spatial connection to sulfate-reducing bacteria is established. Differences in the motility of the thiotrophs at the three study sites lead to different distributions of sulfate reducers in sediments off Namibia, Peru, and Chile. Profiles of lipid biomarkers attributed to sulfate reducers (10MeC16:0 fatty acid, ai-C15:0 fatty acid, and mono-O-alkyl glycerol ethers) document the close association to thiotrophs. Depth profiles of mono-O-alkyl glycerol ethers have been found to correlate best with the occurrence of large sulfur bacteria. This suggests a particularly close link between mono-O-alkyl glycerol ether- synthesizing sulfate reducers and thiotrophs. Lipid biomarker profiles indicate that the interaction between thiotrophs and sulfate-reducing bacteria favors phosphate enrichment, triggering phosphorite formation in upwelling areas. Studying recent phosphogenic environments provides a basis to better understand micobial influence on phosphogenesis and to better constrain the role of microorganisms in the formation of ancient phosphorites.
References
Föllmi K.B. (1996), Earth Sci Rev40:55-124. Trappe J. (1998), Lecture Notes in Earth Sciences 76. Springer, pp. 316.

Gareth Law

If metal proxies are to be confidently used in palaeo–environmental research, then as a prerequisite, metal behaviour within the modern ocean must be fully understood.

In view of this ethos, my PhD research aims to address the influences of (1) bio-mineralisation, (2) Fe/Mn cycling and (3) bioturbation; on trace metal behaviour within the sedimentary environment.

My investigations have focused on metal dynamics throughout the Arabian Sea Oxygen Minimum Zone and within a stratified Scottish Sea Loch (Loch Etive). Here a diverse range of well documented biogeochemical regimes provide a natural laboratory for the study of metal behaviour. Through the completion of a detailed experimental program involving in situ and ex situ measurements of metals in both the dissolved and particulate phase within the sediments and overlying water, together with the measurement of state variables, nutrients and organic matter; novel incites are being generated regarding trace metal diagenesis/authigenesis.

My PhD forms part of a larger Natural Environment Research Council (UK) funded research program entitled: ‘Benthic processes in the Arabian Sea: Interrelationships between the benthos, sediment biogeochemistry, and organic matter cycling’.

More information regarding this multidisciplinary project can be found at:

http://www.sams.ac.uk/research/marine%20geochemistry/arabian.htm

Steve Walsh

My investigation of trace elements in sedimentary phosphorites is well under way and I am just commencing laser ablation ICP-MS analyses of my sample collection from Chatham Rise NZ, South Island NZ, Eastern Australian continental rise, Fiji, Nauru Is, Phosphoria Formation.. and recently samples from Russia courtesy of Dr. Andrei Ilyin. He has also invited me to join a phosphate/cadmium group which has 60 samples needing investigation...which I will do. I also have samples coming from South Africa and Central Australia.

At David McConchie's suggestion I am asking you to place an advertisement like:

WANTED: Sedimentary phosphorite samples for trace metal analyses.
Whole rock samples preferred. Data suppled to contributors.
Send to:
Stephen Walsh
Centre for Coastal Management
Southern Cross University
PO box 5125 East Lismore
NSW, Australia
email: swalsh@scu.edu.au

Iyer Sridhar D.

Alteration of basaltic glasses from the Central Indian Ocean
In: J. Geological Society of India, 1999, v.54: 609-620

Abstract: Textural, mineralogical and compositional characteristics of basaltic glasses from the Central Indian Ocean show them to be altered to varying extents through their interaction with the seawater, resulting in the formation of palagonite. The major chemical changes are the loss of Si, Mg and Ca and a gain of Na and K whilst, Fe and Ti remained immobile.
It reflects that the basaltic glasses have undergone initial to intermediate stages of palagonitisation under low temperature oxidative alteration. Subsequent accretion of ferromanganese oxides over the glasses have halted the progress of alteration.

e-mail: iyer@darya.nio.org
iyer@csnio.ren.nic.in

Links to concrections photos on the Web. Peter Mozley's photo page: http://www.ees.nmt.edu/Geol/GeoPhotos.html Imatra Stones: http://www.koulut.imatra.fi/vnlukio/polut/0/imatrankiveteng.html A possible capture of molybdenum during early diagenesis of dysoxic sediments Tribovillard N., Lyons, T.W., Riboulleau,A., Bout-Roumazeilles, B., 2008. Bull. Soc. Geol. Fr., 179, 1, 3-12. (find here the high res image) Molybdenum is a trace metal commonly used as a marker of paleoredox conditions of ancient depositional settings. Pyrite is an important Mo host for enriched sedimentary rocks. In this paper we study the relationship between Mo and pyrite in the Bancs Jumeaux Formation, a Jurassic succession in northern France consisting of limestone and pyrite-rich marls. This formation is relatively enriched in Mo compared to other redox-sensitive trace metals. Our approach is grounded on bulk rock chemical analysis and delineation of two contrasting types of pyrite that can be extracted from the rocks: polyframboids and nonframboidal concretionary masses. The morphological characteristics of both morphotypes were studied using scanning electronic microscopy. The polyframboids are richer in Mo than the concretions but are not markedly enriched in other trace metals. This discrepancy in geochemical composition could result from pyrite precipitation at different times during early diagenesis. Our results tend to indicate that the polyframboids would have formed very early in reducing "microniches", within dominantly dysoxic sediment. This early pyrite precipitation occurred at shallow depth below the sediment-water interface close to the abundant Mo source in overlying oxic seawater (molybdate ions), and would have fostered Mo-capture by the polyframboids in relatively large amounts. The concretions would have formed later during early diagenesis (within the sulfidic zone) under conditions of more limited Mo availability. Phosphogenesis in recent upwelling areas: The importance of microbial communities indicated by lipid biomarkers E.T.ARNING, D.BIRGEL, H.N.SCHULZ-VOGT, B.B. JØRGENSEN and J.PECKMANN Original abstract - poster The burial of phosphorus and the formation of phosphorites (phosphogenesis) in marine sediments represent an important sink in the global phosphorus cycle. Numerous basin-scale phosphorite deposits were formed in the geological past (e.g., Trappe 1998). Phosphogenesis is not only found in ancient settings, it is reported in recent sediments of upwelling regions as for example off Namibia, Peru, and Chile (Föllmi 1996). These sediments contain dense populations of large nitrate-storing sulfide-oxidizing bacteria Thiomargarita, Beggiatoa, and Thioploca, respectively. Due to metabolic activities of the thiotrophs generating sulfate, a close spatial connection to sulfate-reducing bacteria is established. Differences in the motility of the thiotrophs at the three study sites lead to different distributions of sulfate reducers in sediments off Namibia, Peru, and Chile. Profiles of lipid biomarkers attributed to sulfate reducers (10MeC16:0 fatty acid, ai-C15:0 fatty acid, and mono-O-alkyl glycerol ethers) document the close association to thiotrophs. Depth profiles of mono-O-alkyl glycerol ethers have been found to correlate best with the occurrence of large sulfur bacteria. This suggests a particularly close link between mono-O-alkyl glycerol ether- synthesizing sulfate reducers and thiotrophs. Lipid biomarker profiles indicate that the interaction between thiotrophs and sulfate-reducing bacteria favors phosphate enrichment, triggering phosphorite formation in upwelling areas. Studying recent phosphogenic environments provides a basis to better understand micobial influence on phosphogenesis and to better constrain the role of microorganisms in the formation of ancient phosphorites. References Föllmi K.B. (1996), Earth Sci Rev40:55-124. Trappe J. (1998), Lecture Notes in Earth Sciences 76. Springer, pp. 316. Gareth Law If metal proxies are to be confidently used in palaeo–environmental research, then as a prerequisite, metal behaviour within the modern ocean must be fully understood. In view of this ethos, my PhD research aims to address the influences of (1) bio-mineralisation, (2) Fe/Mn cycling and (3) bioturbation; on trace metal behaviour within the sedimentary environment. My investigations have focused on metal dynamics throughout the Arabian Sea Oxygen Minimum Zone and within a stratified Scottish Sea Loch (Loch Etive). Here a diverse range of well documented biogeochemical regimes provide a natural laboratory for the study of metal behaviour. Through the completion of a detailed experimental program involving in situ and ex situ measurements of metals in both the dissolved and particulate phase within the sediments and overlying water, together with the measurement of state variables, nutrients and organic matter; novel incites are being generated regarding trace metal diagenesis/authigenesis. My PhD forms part of a larger Natural Environment Research Council (UK) funded research program entitled: ‘Benthic processes in the Arabian Sea: Interrelationships between the benthos, sediment biogeochemistry, and organic matter cycling’. More information regarding this multidisciplinary project can be found at: http://www.sams.ac.uk/research/marine%20geochemistry/arabian.htm Steve Walsh My investigation of trace elements in sedimentary phosphorites is well under way and I am just commencing laser ablation ICP-MS analyses of my sample collection from Chatham Rise NZ, South Island NZ, Eastern Australian continental rise, Fiji, Nauru Is, Phosphoria Formation.. and recently samples from Russia courtesy of Dr. Andrei Ilyin. He has also invited me to join a phosphate/cadmium group which has 60 samples needing investigation...which I will do. I also have samples coming from South Africa and Central Australia. At David McConchie's suggestion I am asking you to place an advertisement like: WANTED: Sedimentary phosphorite samples for trace metal analyses. Whole rock samples preferred. Data suppled to contributors. Send to: Stephen Walsh Centre for Coastal Management Southern Cross University PO box 5125 East Lismore NSW, Australia email: swalsh@scu.edu.au Iyer Sridhar D. Alteration of basaltic glasses from the Central Indian Ocean In: J. Geological Society of India, 1999, v.54: 609-620 Abstract: Textural, mineralogical and compositional characteristics of basaltic glasses from the Central Indian Ocean show them to be altered to varying extents through their interaction with the seawater, resulting in the formation of palagonite. The major chemical changes are the loss of Si, Mg and Ca and a gain of Na and K whilst, Fe and Ti remained immobile. It reflects that the basaltic glasses have undergone initial to intermediate stages of palagonitisation under low temperature oxidative alteration. Subsequent accretion of ferromanganese oxides over the glasses have halted the progress of alteration. e-mail: iyer@darya.nio.org iyer@csnio.ren.nic.in
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