High-Alumina Glaucony from the Middle Cambrian of Oland and Bornholm, Southern Baltoscandia

Berg‐Madsen, Vivianne

doi:10.1306/212f82dd-2b24-11d7-8648000102c1865d

Cited by 14 publications

(20 citation statements)

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“…sus -P. atavus, and Hypagnostus parvifrons. Its lowermost bed, the Acrothele granulata conglomerate, is the equivalent of the Exsulans Limestone/Kalby marl (Berg-Madsen 1983), but no echinoderm fragments have been found here.…”

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confidence: 67%

Middle Cambrian cystoid (sensu lato) stem columnals from Bornholm, Denmark

Berg‐Madsen

1986

LET

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A rich material of echinoderm fragments from two Middle Cambrian stratigraphical levels on Bornholm are preserved due to phosphatization of the original calcitic stereom. Preservation of echinoderms in this way ‐ not previously recorded from the Middle Cambrian ‐ permits detailed analysis of the three‐dimensional stereom structure. Identifiable are fragments of stylophorans and eocrinoids. Stem columnals, most likely from eocrinoids, show a wide and advanced morphological variation indicating articulation similar to that of crinoids. The material from the Exsulans Limestone/Kalby marl (Ptychagnostus gibbus Zone) represents stem‐bearing cystoids older than Akadocrinus from Bohemia. The Andrarum Limestone (Sole‐nopleura brachymetopa Zone) contains echinoderm fragments from a higher stratigraphical level, a level correlatable with that from which the oldest North American stem–bearing cystoid, Eustypocystis, has been recorded.

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confidence: 67%

Middle Cambrian cystoid (sensu lato) stem columnals from Bornholm, Denmark

Berg‐Madsen

1986

LET

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“…Nevertheless, the observed compositional similarity between incipiently formed glauconitic minerals and well developed glauconitic peloids in our data rules out 'degree of maturity' as the main factor in dictating composition of the glauconitic minerals. More plausibly, high a K + in the porewater arising from dissolution of Kfeldspars was conducive for the mineralization to proceed ( [Dasgupta et al, 1990] and [Deb and Fukuoka, 1998] Berg-Madsen, 1983] and [Dasgupta et al, 1990]). The only reported occurrence from a deep marine environment, however, identified associated ferromagnesian minerals as the possible source of Mg (Deb and Fukuoka, 1998).…”

Section: Origin Of the 'Glauconitic Minerals' In The Semri Groupmentioning

confidence: 99%

“…These authors, however, recorded a compositional gap in terms of Fe 2 O 3 (total) between ferric illite and 'true' glauconites at higher K 2 O content, Fe 2 O 3 (total) not exceeding 10% in the immature variety and not less than 15% in the mature examples. Subsequent workers, nevertheless, found a compositional continuum between glauconite and ferric illite and included the latter in the glauconitic minerals family ( [Dasgupta et al, 1990] and [Deb and Fukuoka, 1998]; see also [Berg-Madsen, 1983] and [Ireland et al, 1983]). This paper subscribes to the later viewpoint because the green minerals in the Semri Group are similar to glauconitic minerals structurally and in terms of their K 2 O content, even though they were incipiently developed.…”

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confidence: 99%

Mg-rich ferric illite in marine transgressive and highstand systems tracts: Examples from the Paleoproterozoic Semri Group, central India

Banerjee

Jeevankumar

Eriksson

2008

Precambrian Research

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This paper focusses upon two glauconitic sandstones in the Paleoproterozoic Deoland Formation and Chorhat Sandstone, both belonging to the Semri Group, central India. In both the cases glauconitic minerals occur in sandstones deposited in the marine realm, within a transgressive systems tract (TST) for the former unit and within a highstand systems tract (HST) for the latter. The proportion of glauconitic minerals increases in the paleo-offshore direction. Petrography reveals selective early glauconitization of detrital K-feldspars along their fringes, cleavages and the fractures created by volume expansion during progressive alteration, leading to the generation of peloids with small relics of the precursors. XRD and mineral chemistry reveal a structure typical of glauconite, and more akin to Mg-rich ferric illite. The mineral chemistry of the glauconitic mineral phases remains the same whether the glauconitization process was incipient or at an advanced stage.These findings contrast with the previously held belief that ferric illite is confined to terrestrial or marginal marine sediments, and concurs with recent observations that the mineral can form in the open sea, but with high Mg. Since there are no ferro-magnesian minerals in association with these Vindhyan glauconitic sandstones, the seawater appears

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“…(Eder et al 2007). Independently of its green or brown color, which has never been systematically evaluated together with associated chemical variations, the origin of Al-rich glauconite is debated, and the physicochemical changes that have led to such Al enrichment have been interpreted as related to synsedimentary (Berg-Madsen 1983) or postsedimentary processes, the latter corresponding to weathering (Odin & Fullagar 1988), diagenesis (Longuépée & Cousineau 2006, and references therein) or anchimetamorphism (Guimaraes et al 2000). The maturation and alteration of Upper Jurassic Siberian glauconite have been studied by petrography, powder X-ray diffraction, several spectroscopic methods and analytical electron microscopy to establish the chemical and mineralogical composition and its relation to changes in optical properties such as color and index of refraction.…”

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confidence: 99%

Color, Mineralogy and Composition of Upper Jurassic West Siberian Glauconite: Useful Indicators of Paleoenvironment

Navas¹,

Martín‐Algarra²,

Eder³

et al. 2008

The Canadian Mineralogist

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Changes in color of Upper Jurassic glauconite of the Georgiev Formation, in the West Siberian Basin, in Russia, are related to changes in physicochemical conditions that caused glauconite maturation and alteration, driven by regional paleoenvironmental evolution. Maturation produces dark green (bluish) glauconite formed from Fe-rich smectite by increasing the content of Fe 2+ together with K. Alteration produces brown rims and cracks that are enriched in Al and depleted in Fe and K with respect to the glauconite cores. The change from a yellowish green to dark green color in progressively more mature glauconite is explained by light absorption induced by enrichment in octahedrally coordinated Fe 2+ relative to the total Fe, associated with the progressive decrease in the proportion of Fe 3+ -rich smectite interleaved with glauconite. The brown color in alteration rims is due essentially to light scattered by nanometric inclusions of Fe oxyhydroxides. These, together with residual Al-rich glauconite and a subordinate Fe-rich smectite, constitute reaction products formed by leaching of K and Fe 2+ , and by the oxidation of yellowish green glauconite cores. Berthierine formed later in the brown rims on Al-rich glauconite, and pyrite formed as a result of drowning of the platform during the latest Jurassic -earliest Cretaceous and sedimentation of black shales under increasingly reducing conditions. Keywords SoMMAiRELes changements en couleur de la glauconite de la Formation de Georgiev, d'âge jurassique supérieur, dans le bassin Sibérien Occidental, en Russie, sont liés aux changements des conditions physicochimiques qui ont provoqué la maturation et l'altération de la glauconite, conditions régies par l'évolution du milieu paléo-environnemental. La maturation a produit une couleur vert foncé (bleuâtre) de la glauconite formée aux dépens de la smectite ferrifère par augmentation de la teneur en Fe 2+ et en potassium. L'altération a produit une bordure brune et des craquelures qui sont enrichies en Al et appauvries en Fe et K par rapport aux noyaux de glauconite. Le changement de couleur, de vert jaunâtre à vert foncé dans la glauconite progressivement plus mature, serait dû à l'absorption de la lumière induite par enrichissement du Fe 2+ en coordinence octaédrique par rapport au fer total, ainsi que la diminution progressive de la proportion de smectite riche en Fe 3+ en intercalation avec la glauconite. La couleur brune des lisérés d'altération serait due surtout à la dispersion de la lumière par des inclusions nanométriques d'oxyhydroxides de fer. Ces particules, ainsi que la glauconite résiduelle riche en Al et une proportion subordonnée de smectite riche en fer, constituent les produits de réaction formés par lessivage de K et Fe 2+ , et par l'oxydation des noyaux de glauconite vert jaunâtre. La berthierine s'est formée plus tard sur les bordures brunes des grains de glauconite alumineuse, et la pyrite s'est formée lors d'une submersion de la platteforme à la fin du Jurassique et au début du Crétacé, e...

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High-Alumina Glaucony from the Middle Cambrian of Oland and Bornholm, Southern Baltoscandia

Cited by 14 publications

References 0 publications

Middle Cambrian cystoid (sensu lato) stem columnals from Bornholm, Denmark

Middle Cambrian cystoid (sensu lato) stem columnals from Bornholm, Denmark

Mg-rich ferric illite in marine transgressive and highstand systems tracts: Examples from the Paleoproterozoic Semri Group, central India

Color, Mineralogy and Composition of Upper Jurassic West Siberian Glauconite: Useful Indicators of Paleoenvironment

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