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1

Electronic Resource

THE GROWTH OF CAMBRIAN AND LIASSIC CONCRETIONS (1971)

RAISWELL, R.

Oxford, UK : Blackwell Publishing Ltd

Sedimentology 17 (1971), S. 0

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ISSN: 1365-3091

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Concretions from Upper Cambrian sediments in South Wales can be divided into two groups of different ages. An early group (type) are characterised by the association of septarian structures and deformed laminae; whilst later (type Ha) concretions developed both cone-in-cone structures and parallel laminae.Determinations of the cement content of individual concretions revealed centrifugal variations related to the porosity changes within the sediment during concretionary growth. Growth of type-I concretions began in sediment of approx. 70% porosity and continued until compaction had reduced the porosity to less than 40%. Later, type-IIa concretions began growth in sediment of approx. 30–40% porosity and experienced only slight compaction over their growth spans.Liassic concretions from a prolific concretionary horizon in Dorset developed parallel laminae, but grew early in the absence of compaction (type IIIb) concretions at this horizon grew within the sediment during a pause in deposition.Evidence is described for distinguishing between concretions formed in systems open or closed to seawater. It is concluded that Cambrian concretions grew in closed systems, but the early Liassic concretions may have developed in a partially open system.A model is offered to explain the closed system growth of prolific concretionary horizons. The Cambrian concretions often proliferated along 2–3 cm thick siltstone units, which it is suggested were more permeable than the surrounding mudstones and therefore became pore-water migration paths. Along these migration paths concretionary growth may have relieved the supersaturation of mobile pore waters.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-3091.1971.tb01773.x

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2

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Isotopic constraints on growth conditions of multiphase calcite–pyrite–barite concretions in Carboniferous mudstones (2002)

Raiswell, R. ; Bottrell, S. H. ; Dean, S. P. ; [et al.]

Oxford UK : Blackwell Science Ltd

Sedimentology 49 (2002), S. 0

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ISSN: 1365-3091

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Carbonate concretions in the Lower Carboniferous Caton Shale Formation contain diagenetic pyrite, calcite and barite in the concretion matrix or in different generations of septarian fissures. Pyrite was formed by sulphate reduction throughout the sediment before concretionary growth, then continued to form mainly in the concretion centres. The septarian calcites show a continuous isotopic trend from δ13C=−28·7‰ PDB and δ18O=−1·6‰ PDB through to δ13C=−6·9‰ PDB and δ18O=−14·6‰ PDB. This trend arises from (1) a carbonate source initially from sulphate reduction, to which was added increasing contributions of methanogenic carbonate; and (2) burial/temperature effects or the addition of isotopically light oxygen from meteoric water. The concretionary matrix carbonates must have at least partially predated the earliest septarian cements, and thus used the same carbonate sources. Consequently, their isotopic composition (δ13C=−12·0 to −10·1‰ PDB and δ18O=−5·7 to −5·6‰ PDB) can only result from mixing a carbonate cement derived from sulphate reduction with cements containing increasing proportions of carbonate from methanogenesis and, directly or indirectly, also from skeletal carbonate. Concretionary growth was therefore pervasive, with cements being added progressively throughout the concretion body during growth. The concretions contain barite in the concretion matrix and in septarian fissures. Barite in the earlier matrix phase has an isotopic composition (δ34S=+24·8‰ CDT and δ18O=+16·4‰ SMOW), indicating formation from near-surface, sulphate-depleted porewaters. Barites in the later septarian phase have unusual isotopic compositions (δ34S=+6 to +11‰ CDT and δ18O=+8 to +11‰ SMOW), which require the late addition of isotopically light sulphate to the porewaters, either from anoxic sulphide oxidation (using ferric iron) or from sulphate dissolved in meteoric water. Carbon isotope and biomarker data indicate that oil trapped within septarian fissures was derived from the maturation of kerogen in the enclosing sediments.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-3091.2002.00439.x

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3

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Evidence for surface reaction-controlled growth of carbonate concretions in shales (1988)

RAISWELL, R.

Oxford, UK : Blackwell Publishing Ltd

Sedimentology 35 (1988), S. 0

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ISSN: 1365-3091

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Geosciences

Notes: Estimates for the rate of concretionary growth in shales are based on models which assume that growth is diffusion-controlled. However, laboratory and field studies of CaCO3 precipitation in organic carbon-rich sediments indicate that surface reactions control growth, due to inhibition by various dissolved species. The spatial distribution of carbonate concretions in the Jet Rock (Lower Jurassic, England) is also inconsistent with diffusion-controlled precipitation of CaCO3 into concretions, and growth must have been at least partly surface reaction-controlled.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1365-3091.1988.tb01236.x

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4

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Electrophoretic Mobility Variations During Feldspar Dissolution (1986)

Tranter, M. ; Raiswell, R.

s.l. ; Stafa-Zurich, Switzerland

Materials science forum Vol. 7 (Jan. 1986), p. 275-286

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ISSN: 1662-9752

Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008

Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics

Type of Medium: Electronic Resource

URL: http://www.tib-hannover.de/fulltexts/2011/0528/02/20/transtech_doi~10.4028%252Fwww.scientific.net%252FMSF.7.275.pdf

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5

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Diagenesis of sediments beneath the Ross Ice Shelf and their sedimentary history (1985)

Raiswell, R. ; Md. Tan, M.

[s.l.] : Nature Publishing Group

Nature 315 (1985), S. 483-485

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ISSN: 1476-4687

Source: Nature Archives 1869 - 2009

Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics

Notes: [Auszug] The 47 Ross Ice Shelf Project (RISP) cores collected at site J9 (8222' S, 16828' W) in the 1977-78 field season have lengths ranging from 15 to 122 cm and contain an upper light olive-grey unit (9-30 cm thick) at the base of which is a thin (〈1 cm) brown-orange, iron-rich layer, providing a ...

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1038/315483a0

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6

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The disposal of flue gas desulphurisation waste: sulphur gas emissions and their control (1991)

Raiswell, R. ; Bottrell, S. H.

Springer

Environmental geochemistry and health 13 (1991), S. 119-126

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ISSN: 1573-2983

Source: Springer Online Journal Archives 1860-2000

Topics: Geosciences , Medicine

Notes: Abstract Flue gas desulphurisation (FGD) equipment to be fitted to UK coal-fired power stations will produce more than 0.8 Mtonnes of calcium sulphate, as gypsum. Most gypsum should be of commercial quality, but any low grade material disposed as waste has the potential to generate a range of sulphur gases, including H2S, COS, CS2, DMS and DMDS. Literature data from the USA indicates that well-oxidised waste with a high proportion of calcium sulphate (the main UK product of FGD) has relatively low emissions of sulphur gases, which are comparable to background levels from inland soils. However, sulphur gas fluxes are greatly enhanced where reducing conditions become established within the waste, hence disposal strategies should be formulated to prevent the sub-surface consumption of oxygen.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01734303

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7

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Reactive iron enrichment in sediments deposited beneath euxinic bottom waters: constraints on supply by shelf recycling (2007)

Raiswell, R. ; Anderson, T. F.

In: Geological Society Special Publication 248: 179-194.

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Publication Date: 2007-10-08

Description: Modern and ancient euxinic sediments are often enriched in iron that is highly reactive towards dissolved sulphide, compared to continental margin and deep-sea sediments. It is proposed that iron enrichment results from the mobilization of dissolved iron from anoxic porewaters into overlying seawater, followed by transport into deep-basin environments, precipitation as iron sulphides, and deposition into sediments. A diagenetic model shows that diffusive iron fluxes are controlled mainly by porewater dissolved iron concentrations, the thickness of the surface oxygenated layer of sediment and to a lesser extent by pH and temperature. Under typical diagenetic conditions (pH < 8, porewater Fe2+ = 10-6 g cm-3) iron can diffuse from the porewaters in continental margin sediments to the oxygenated overlying seawater at fluxes of 100-1000 {micro}g cm-2 a-1. The addition of reactive iron to deep-basin sediments is determined by the magnitude of this diffusive flux, the export efficiency ({varepsilon}) of recycled iron from the shelf, the ratio of source area (S) to basin sink area (B) and the trapping of reactive iron in the deep basin. Values of {varepsilon} are poorly constrained but modern enclosed or semi-enclosed sedimentary basins show a wide variation in S/B ratios (0.25-13) where the shelf source area is defined as sediments at less than 200 m water depth. Diffusive fluxes in the range 100-1000 {micro}g cm-2 a-1 are able to produce the observed reactive iron enrichments in the Black Sea, the Cariaco Basin and the Gotland Deep for values of {varepsilon} x S/B from 0.1-5. Transported reactive iron can be trapped physically and/or chemically in deep basins. Physical trapping is controlled by basin geometry and chemical capture by the presence of euxinic bottom water. The S/B ratios in modern basins may not be representative of those in ancient euxinic/semi-euxinic sediments but preliminary data suggest that {varepsilon} x S/B in ancient euxinic sediments has a similar range as in modern euxinic sediments.

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