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  • 1
    Electronic Resource
    Electronic Resource
    Botryoidal aragonite and its diagenesis (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Sedimentology 33 (1986), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.1986.tb00549.x
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  • 2
    Electronic Resource
    Electronic Resource
    Late diagenetic calcitization of anhydrite from the Mississippian of Saskatchewan, western Canada (2001)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 48 (2001), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Mississippian nodular anhydrites beneath an unconformity in the subsurface of southern Saskatchewan are locally replaced by calcite, pyrite and celestite. Triassic clastics above the unconformity are green, rather than red, and a usually developed subunconformity alteration zone (where carbonates are dolomitized, and porosity is filled with anhydrite) is absent. The unconformity lacks karstic features (unlike in the USA), and probably formed in a hyperarid climate. Mississippian anhydrites near the unconformity are not preferentially dissolved, nor were they extensively hydrated. Anhydrite calcitization occurred only after the unconformity was shallowly buried by redbeds, and it probably involved sulphate-reducing bacteria. Hydrogen sulphide, generated by bacteria, reduced redbed pigments. The replacement calcite contains pseudomorphs and relicts of anhydrite, and pseudomorphs of secondary gypsum. These indicate calcitization occurred only after original Mississippian gypsum was altered to anhydrite and this, in turn, was partially converted back to secondary gypsum beneath the unconformity. Replacement occurred concurrently with the formation elsewhere of the dolomitized zone beneath the unconformity. Sulphur isotopic ratios of replacement pyrite are depleted relative to Mississippian sulphate values, consistent with the activities of sulphate-reducing bacteria. Carbon isotopic ratios of replacive calcites, however, do not support this interpretation, and are identical to those of Mississippian limestones. Simple replacement of sulphate by pore-water bicarbonate (in equilibrium with host limestones) is unlikely because protons generated during the reaction should have created acidic conditions in which calcite would have dissolved. A full explanation of the calcitization remains elusive, but may involve replacement occurring in an active groundwater system and/or bacterial sulphate reduction occurring upstream of the site of calcitization.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-3091.2001.00350.x
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  • 3
    Electronic Resource
    Electronic Resource
    Compaction in halite-cemented carbonates – the Dawson Bay Formation (Middle Devonian) of Saskatchewan, Canada (2000)
    Oxford UK : Blackwell Publishing Ltd
    Sedimentology 47 (2000), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Halite-impregnated carbonates in the Dawson Bay Formation of Saskatchewan lie between beds of halite and are buried to a depth of 1 km. They exhibit two different diagenetic styles – some resisted compaction and had high pre-salt porosities; others contain compaction-broken fossils and pressure-solution seams. The uncompacted rocks, together with the difficulty of explaining how halite cement could enter the Dawson Bay after overlying bedded halites were deposited, suggest that halite cementation occurred early with only a few tens of metres of overburden. Early diagenetic compaction is suggested by the presence of unbroken, displacive skeletal halite crystals, which cross-cut compaction structures, and by the difficulty of explaining how (1) later compaction could occur in halite-cemented rocks and (2) how pore-fluids could be expelled after surrounding rocks lost their permeability. The organic-rich nature of many carbonates may explain why compaction was both early and extensive, but this explanation fails to explain how similar compaction developed in horizons with lower organic contents. Chemical compaction may also have been enhanced by aragonite dissolution during seawater evaporation or brine dilution. Early chemical compaction in Dawson Bay carbonates indicates that compaction in other carbonates need not signify deep burial diagenesis; neither can compaction be used indiscriminately to identify other diagenetic events as being of deep burial origin. Early halite cementation, as in the Dawson Bay Formation, preserves carbonates at early diagenetic stages and may thus preserve geochemical information unmodified by later diagenesis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2000.00285.x
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  • 4
    Electronic Resource
    Electronic Resource
    ‘Sediment’–cement relationships in a Pleistocene speleothem from Italy: a possible analogue for ‘replacement’ cements and Archaeolithoporella in ancient reefs (2001)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 48 (2001), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Ancient carbonate buildups may contain extraordinarily large amounts of early diagenetic precipitates. In some, host rock lamination may be traced into inclusion bands within the ‘cement’ crystals, suggesting that the crystals are replacive. By analogy with a Pleistocene speleothem from the Sorrento Peninsula, however, these relationships can be explained differently. In the speleothem, large, repeatedly split and dendritic calcite crystals occur within a laminated carbonate. Lamination consists of sub-mm alternations of micrite and microspar. Micritic laminae pass laterally into inclusion-rich growth bands in the dendritic calcite crystals, and have replaced an aragonitic cement, whereas the microspar laminae were primary calcite cements. Three types of inclusion-rich bands occur in the dendrite crystals: (1) with aragonite relicts, (2) ‘ribbon calcite’ and (3) with oriented micropores. When aragonite precipitated, the calcite dendrite branches were unable to keep growing as single crystals and split into crystallites (separated by micropores, some forming ribbon calcite), whereas during episodes of calcite lamina precipitation, the larger crystals were regenerated by crystallite coalescence. Calcite crystals are primary: they did not replace a micritic precursor. By analogy with the Italian speleothem, some ancient reefal sparry carbonates may not be replacements of earlier laminated sediments, but may have grown concurrently with them. It is also probable that some ancient laminated sediments were instead sea-floor precipitates, and that stromatolites containing cross-cutting crystal fabrics, and the alternating micrite-microspar laminae typical of Archaeolithoporella, could be largely abiotic crystal growths.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2001.00391.x
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  • 5
    Electronic Resource
    Electronic Resource
    Reef margin collapse, gully formation and filling within the Permian Capitan Reef: Carlsbad Caverns, New Mexico, USA (1999)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 46 (1999), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: An area of reef margin collapse, gully formation and gully fill sedimentation has been identified and mapped within Left Hand Tunnel, Carlsbad Caverns. It demonstrates that the Capitan Reef did not, at all times, form an unbroken border to the Delaware Basin. Geopetally arranged sediments within cavities from sponge–algal framestones of the reef show that the in situ reef today has a 10° basinwards structural dip. Similar dips in adjacent back-reef sediments, previously considered depositional, probably also have a structural origin. Reoriented geopetal structures have also allowed the identification of a 200-m-wide, 25-m-deep gully within the reef, which has been filled by large (some  〉15 m), randomly orientated and, in places, overturned blocks and boulders, surrounded by finer reef rubble, breccias and grainstones. Block supply continued throughout gully filling, implying that spalling of reef blocks was a longer term process and was not a by-product of the formation of the gully. Gully initiation was probably the result of a reef front collapse, with a continued instability of the gully bordering reef facies demonstrated by their incipient brecciation and by faults containing synsedimentary fills. Gully filling probably occurred during reef growth, and younger reef has prograded over the gully fill. Blocks contain truncated former aragonite botryoidal cements, indicating early aragonite growth within the in situ reef. In contrast, former high-magnesian calcite rind cements post-date sedimentation within the gully. The morphology of cavern passages is controlled by reef facies variation, with narrower passages cut into the in situ reef and wider passages within the gully fill. Gully fills may also constitute more permeable zones in the subsurface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.1999.00222.x
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  • 6
    Electronic Resource
    Electronic Resource
    Pleistocene decalcification of Late Pliocene Red Crag shelly sands from Walton-on-the-Naze, England (2000)
    Oxford UK : Blackwell Science Ltd
    Sedimentology 47 (2000), S. 0 
    Details
    ISSN: 1365-3091
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Geosciences
    Notes: Uppermost sands of the Red Crag at Walton-on-the-Naze (Essex) and elsewhere in East Anglia have been decalcified to iron-stained quartz sands. In contrast, lower sands are only minimally altered and contain aragonitic and calcitic shells. Aragonitic shells are slightly dissolved (chalkified), but calcitic shells are unaffected. Cementation is limited to an addition of iron oxides, now mainly haematite, which also coat carbonate grains. Abundant iron-oxide fines in the upper decalcified sands were liberated from the coatings of shells; shells that have since dissolved. The diagenetic nature of the contact between decalcified upper and unaffected lower sands is evident where it transects cross-bedding. The contact is knife-sharp, even smoothly truncating large shells, and is usually planar and subhorizontal. Shelly sands immediately beneath the boundary contain similar amounts of aragonitic material, as do sands further below. Locally the decalcification boundary has been contorted by cryoturbation, implying that carbonate dissolution was a Pleistocene event. Decalcification probably occurred when the area was affected by permafrost. Lower sands were cemented by ice and protected from dissolution. Upper sands were above the ice table and subject to chemically aggressive waters during summer thaws. Decalcification is believed to have taken place during an episode of climate amelioration when downward retreat of the ice table accompanied replacement of tundra by boreal forest. Highly acidic and podzolic soils developed, beneath which shell-carbonate dissolved. Sharp based decalcified zones in Lowestoft Till and Devensian deposits in other parts of England can also be attributed to dissolution associated with permafrost.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3091.2000.00349.x
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  • 7
    Electronic Resource
    Electronic Resource
    The isolation and characterisation of a catalase-deficient mutant of barley (Hordeum vulgare L.) (1983)
    Springer
    Planta 159 (1983), S. 505-511 
    Details
    ISSN: 1432-2048
    Keywords: Catalase deficiency ; Hordeum (mutant) ; Mutant (barley) ; Photorespiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A mutant line of barley, R(othamsted)-Pr 79/4, has been isolated which grows poorly in natural air, but normally in air enriched to 0.2% CO2. Analysis of the products of 14CO2 fixation showed that there was no major block in photosynthetic or photorespiratory carbon metabolism in the mutant and that rates of CO2 fixation were only slightly lower than those measured in the wild type (c.v. Maris Mink). Leaves of the mutant line contained only 10% of the catalase (EC 1.11.1.6) activity found in the wild type; and the two major bands of catalase activity detected after starch-gel electrophoresis of extracts of normal leaves were missing from similar extracts of RPr 79/4. Peroxisomes isolated from mutant leaves contained negligible catalase activity, but normal levels of other enzymes involved in photorespiration. Genetic analysis has shown that the mutation is recessive and that both air-sensitivity and catalase-deficiency segregate together in F2 plants derived from a cross between the mutant and the cultivar Golden Promise. [1-14C]Glycollate was not converted to 14CO2 faster in the mutant leaves than in the normal leaves. Thus there was no evidence that photorespiratory CO2 may be obtained by the chemical action of H2O2 on glyoxylate or hydroxypyruvate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00409139
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  • 8
    Electronic Resource
    Electronic Resource
    The value of mutants unable to carry out photorespiration (1988)
    Springer
    Photosynthesis research 16 (1988), S. 155-176 
    Details
    ISSN: 1573-5079
    Keywords: Hordeum ; mutants ; nitrogen metabolism ; photosynthesis ; photorespiration ; Pisum
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Manipulation of the CO2 concentration of the atmosphere allows the selection of photorespiratory mutants from populations of seeds treated with powerful mutagens such as sodium azide. So far, barley lines deficient in activity of phosphoglycolate phosphatase, catalase, the glycine to serine conversion, glutamine synthetase, glutamate synthase, 2-oxoglutarate uptake and serine: glyoxylate aminotransferase have been isolated. In addition one line of pea lacking glutamate synthase activity and one barley line containing reduced levels of Rubisco are available. The characteristics of these mutations are described and compared with similar mutants isolated from populations of Arabidopsis. As yet, no mutant lacking glutamine synthetase activity has been isolated from Arabidopsis and possible reasons for this difference between barley and Arabidopsis are discussed. The value of these mutant plants in the elucidation of the mechanism of photorespiration and its relationships with CO2 fixation and amino acid metabolism are highlighted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00039491
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  • 9
    Electronic Resource
    Electronic Resource
    Characteristics of a photorespiratory mutant of barley (Hordeum vulgare L.) deficient in phosphogly collate phosphatase (1987)
    Springer
    Photosynthesis research 11 (1987), S. 89-96 
    Details
    ISSN: 1573-5079
    Keywords: photosynthesis ; photorespiration ; barley ; mutants ; phosphoglycollate ; phosphatase
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract A barley mutant RPr84/90 has been isolated by selecting for plants which grow poorly in natural air, but normally in air enriched to 0.8% CO2. After 5 minutes of photosynthesis in air containing14CO2 this mutant incorporated 26% of the14C carbon into phosphoglycollate, a compound not normally labelled in wild type (cv. Maris Mink) leaves. The activity of phosphoglycollate phosphatase (EC 3.1.1.18) was 1.2 nkat mg−1 protein at 30°C in RPr 84/90 compared to 19.2 nkat mg−1 protein in the wild-type leaves. Phosphoglycollate phosphatase activity was not detected after protein separation by electrophoresis of leaf extracts from the mutant on polyacrylamide gels; on linear 5% acrylamide gels three bands with enzyme activity were separated from extracts of wild type plants. Gradient gel electrophoresis followed by activity staining showed two bands in Maris Mink tracks of MW 86,000 and 96,000, but no bands in 84/90. This is the first report of isozymes of phosphoglycollate phosphatase in barley which were absent in the mutant extracts. Our results confirm an earlier report of isozymes of this phosphatase in Phaseolus vulgaris [18]. The photosynthetic rate of RPr 84/90 in 1% O2, 350 μl CO2 l−1 was 9–12 mg CO2 dm−2 h−1 at 20°C, whereas the wild-type rate was 27–29 mg CO2 dm−2 h−1 at 20°C. In 21% O2, 350 μl CO2 l−1 the rate was 2–3 mg CO2 dm−2 h−1 in the mutant and 20 mg CO2 dm−2 h−1 in the wild type. Genetic analysis has shown that the mutation segregates as a single recessive nuclear gene.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00117676
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