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Wyszukujesz frazę "Jeans, C." wg kryterium: Autor


Wyświetlanie 1-3 z 3
Tytuł:
Geochemical and stable isotope patterns of calcite cementation in the Upper Cretaceous Chalk, UK: Direct evidence from calcite-filled vugs in brachiopods
Autorzy:
Hu, X.
Jeans, C.
Dickson, T.
Powiązania:
https://bibliotekanauki.pl/articles/139259.pdf
Data publikacji:
2012
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
cement kalcytowy
diageneza
historia
izotopy stabilne
kreda
pierwiastki śladowe
wpływ drobnoustrojów
anoxia
calcite cement
chalk
diagenesis
history
Microbial influence
oxia
stable isotopes
suboxia
trace elements
Opis:
The history of research into the cementation of the Upper Cretaceous Chalk of the UK is reviewed. Calcite-filled vugs within the shell cavities of terebratulid brachiopods from the Cenomanian Chalk of eastern england have been investigated by cathodoluminesence imaging, staining, electron microprobe and stable isotope analysis. This has provided the first detailed analysis of the geochemistry of the Chalk.s cement. two cement series, suboxic and anoxic, are recognized. Both start with a Mg-rich calcite with positive [delta^13]C values considered to have been precipitated under oxic conditions influenced by aerobic ammonification. The suboxic series is characterized by positive [delta^13]C values that became increasingly so as cementation progressed, reaching values of 3.5[per mil]. Manganese is the dominant trace element in the earlier cement, iron in the later cement. Mn-and Fe-reducing microbes influenced cement precipitation and the trace element and [delta^13]C patterns. The anoxic series is characterized by [delta^13]C values that became increasingly negative as cementation progressed, reaching values of .6.5[per mil]. Trace elements are dominated by iron and manganese. Sulphate-reducing microbes influenced cement precipitation and the trace element and [delta^13]C patterns. Both cement series are related closely to lithofacies and early lithification pre-dating the regional hardening of the Chalk. The suboxic series occurs in chalk which was continuously deposited and contained hematite pigment and limited organic matter. The anoxic series was associated with slow to nil deposition and hardground development inc halks that originally contained hematite pigment but no longer do so, and an enhanced supply of organic matter.
Źródło:
Acta Geologica Polonica; 2012, 62, 2; 143-172
0001-5709
Pojawia się w:
Acta Geologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Sulfur isotope patterns of iron sulfide and barite nodules in the Upper Cretaceous Chalk of England and their regional significance in the origin of coloured chalks
Autorzy:
Jeans, C. V.
Turchyn, A. V.
Hu, X.-F.
Powiązania:
https://bibliotekanauki.pl/articles/139390.pdf
Data publikacji:
2016
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
Cretaceous
diagenesis
iron sulfide nodules
δ34S values
bacterial control
coloured chalks
volcanogenic events
NW Europe
kreda
diageneza
siarczan żelaza
wartości δ34S
kontrola bakteryjna
Europa
Opis:
The relationship between the development of iron sulfide and barite nodules in the Cenomanian Chalk of England and the presence of a red hematitic pigment has been investigated using sulfur isotopes. In southern England where red and pink chalks are absent, iron sulfide nodules are widespread. Two typical large iron sulfide nodules exhibit δ34S ranging from -48.6‰ at their core to -32.6‰ at their outer margins. In eastern England, where red and pink chalks occur in three main bands, there is an antipathetic relationship between the coloured chalks and the occurrence of iron sulfide or barite nodules. Here iron sulfide, or its oxidised remnants, are restricted to two situations: (1) in association with hard grounds that developed originally in chalks that contained the hematite pigment or its postulated precursor FeOH3, or (2) in regional sulfidization zones that cut across the stratigraphy. In the Cenomanian Chalk exposed in the cliffs at Speeton, Yorkshire, pyrite and marcasite (both iron sulfide) nodules range in δ34S from -34.7‰ to +40.0‰. In the lower part of the section δ34S vary from -34.8‰ to +7.8‰, a single barite nodule has δ34S between +26.9‰ and +29.9‰. In the middle part of the section δ34S ranges from +23.8‰ to +40.0‰. In the sulfidization zones that cut across the Cenomanian Chalk of Lincolnshire the iron sulfide nodules are typically heavily weathered but these may contain patches of unoxidised pyrite. In these zones, δ34S ranges from -32.9‰ to +7.9‰. The cross-cutting zones of sulfidization in eastern England are linked to three basement faults – the Flamborough Head Fault Zone, the Caistor Fault and the postulated Wash Line of Jeans (1980) – that have affected the deposition of the Chalk. It is argued that these faults have been both the conduits by which allochthonous fluids – rich in hydrogen sulfide/sulfate, hydrocarbons and possibly charged with sulfate-reducing bacteria – have penetrated the Cenomanian Chalk as the result of movement during the Late Cretaceous or Cenozoic. These invasive fluids are associated with (1) the reduction of the red hematite pigment or its praecursor, (2) the subsequent development of both iron sulfides and barite, and (3) the loss of overpressure in the Cenomanian Chalk and its late diagenetic hardening by anoxic cementation. Evidence is reviewed for the origin of the red hematite pigment of the coloured chalks and for the iron involved in the development of iron sulfides, a hydrothermal or volcanogenic origin is favoured.
Źródło:
Acta Geologica Polonica; 2016, 66, 2; 227-256
0001-5709
Pojawia się w:
Acta Geologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Redox conditions in the Late Cretaceous Chalk Sea: the possible use of cerium anomalies as palaeoredox indicators in the Cenomanian and Turonian Chalk of England
Autorzy:
Jeans, C. V.
Wray, D. S.
Williams, C. T.
Powiązania:
https://bibliotekanauki.pl/articles/139095.pdf
Data publikacji:
2015
Wydawca:
Polska Akademia Nauk. Czytelnia Czasopism PAN
Tematy:
chalk environments
rare earth element (REE) anomalies
methods
palaeoredox indicators
diagenesis
history
pierwiastki ziem rzadkich
REE
anomalie
metody
diageneza
historia
Opis:
The cerium anomalies preserved in the Chalk have been investigated as possible palaeoredox indicators of the Late Cretaceous Sea and its sediment. This has been based upon over a hundred new rare earth element analyses of selected samples and grain size fractions from the Chalk. Particular attention has been given to the methodology of differentiating between the cerium anomalies preserved in the bioclastic calcite and those in carbonate-fluorapatite preserved in the acetic acid insoluble residues of chalks. Variations in the cerium anomaly of different particle size fractions of uncemented chalks suggest that fractionation of rare earth elements between the Chalk’s seawater and the various organisms that contributed skeletal material to the bioclastic calcite of the Chalk may have occurred. Post-depositional processes of calcite cementation and late diagenetic sulphidisation have had no apparent effect on the cerium anomaly of the acetic acid insoluble residues. The cerium anomalies associated with the acetic acid insoluble residues from (1) an alternating sequence of chalks and marls from Ballard Cliff (Dorset, UK) typical of Milankovitch cyclicity show a marked diagenetic pattern, whereas those from (2) non-volcanic and volcanic marls display a pattern that is best explained by the variations in the availability of phosphorus and the timing of argillisation of volcanic glass during diagenesis. The general conclusion is drawn that the cerium anomalies preserved in the Chalk can provide an insight into the changing palaeoredox conditions in the Late Cretaceous Sea as well as in the pore fluids of its sediments.
Źródło:
Acta Geologica Polonica; 2015, 65, 3; 345-366
0001-5709
Pojawia się w:
Acta Geologica Polonica
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-3 z 3

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