Chapter 2 Phases of Diagenesis and Authigenesis

Fairbridge, Rhodes W.

doi:10.1016/s0070-4571(08)70841-0

Cited by 65 publications

(47 citation statements)

References 90 publications

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“…A periodically agitated low energy environment appears to be necessary (Van Andel and Postma, 1954;McRae, 1972;Odin, 1975), but in many occurrences, current generated structures probably reflect reworking after the glauconite was formed (e.g., Ward and Lewis, 1975;McConchie, 1978;McConchie and Lewis, 1978). A pH of 7 to 8 (Fairbridge, 1967) and slightly reducing conditions (Eh < 0) are generally considered to be the most favorable (Cloud, 1955;Burst, 1958a;Fairbridge, 1967), although the reducing conditions may be confined to the immediate vicinity of the proto-glauconite (Burst, 1958a;Norris, 1964), while the overall conditions remain slightly oxidizing (Van Andel and Postma, 1954).…”

Section: Glauconite Genesismentioning

confidence: 99%

A Mössbauer Investigation of Glauconite and its Geological Significance

McConchie

1979

Clays and clay miner.

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Ahstraet--M6ssbauer spectra of 9 glauconite samples from Upper Cretaceous and Lower Tertiary strata in the South Island of New Zealand contain a broad shoulder due to low intensity absorption continuous between 1.0 and 2.5 mm/sec when the absorber is at room temperature; the shoulder is absent, and sharp peaks are apparent in spectra taken with the absorber at 80~ The data suggest that electron transfer occurs between adjacent Fe 3+ and Fe z+ ions at room temperature. The low temperature spectra indicate that all Fe in the glauconites is in octahedral coordination. Fe z+ and Fe z+ ions occur in both cis and trans sites; Fe z+ shows a strong preference for cis sites whereas Fe 2+ shows an even stronger preference for trans sites.The partially variable oxidation state of Fe in glauconite is interpreted in terms of a geochemical model for glauconitization of a degraded or incomplete progenitor phyllosilicate. The model involves exchange of Fe ~+ for other cations which temporarily stabilize the progenitor, followed by FeZ § 3+ charge transfer reactions. Each reaction results from the system's tendency towards equilibrium. The model is supported by the observation that artificially leached glauconite increases both its Fe z+ and its Fe z+ content when placed in a solution containing Fe 2+ as the only Fe ion present.

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Section: Glauconite Genesismentioning

confidence: 99%

A Mössbauer Investigation of Glauconite and its Geological Significance

McConchie

1979

Clays and clay miner.

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“…Pyrite also occurs within the chalk section, outlining or filling burrow traces surrounded by typical liesegang rings (see Figure 2). These rings document a diffusion phenomenon of periodic alterations between solution mobility (diffusion) and supersaturation (nucleation and precipitation) (Fairbridge, 1967). Because this process is dependent primarily on a diffusion gradient away from a burrow locus, it might be expected to form concentric circles in a homogeneous medium such as the chalks.…”

Section: Geologymentioning

confidence: 99%

“…The physicochemical conditions in the microenvironment of many organic processes remains largely unknown. But, if pH is lowered and held to about 6.0 some calcite may dissolve and, in addition, conditions favor the direct formation of marcasite rather than pyrite (Fairbridge, 1967;Tröger, 1967;Rickard, 1969). Once initiated, marcasite proceeds to precipitate as the stable form.…”

Section: Marcasitementioning

confidence: 99%

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Marcasite in Miocene Calcareous Sediments from Hole 315A

Kelts¹

1976

Initial Reports of the Deep Sea Drilling Project

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This chapter notes the occurrence of the pyrite dimorph, marcasite, as a minor diagenetic cement in light purple to bluish-white Miocene calcareous oozes. It occurs as the only mineral phase cementing small, elongate, gray aggregates with the morphology of worm burrows and may represent a worm's last stand. Scanning electron micrographs reveal clumps of typically fluted or curved orthorhombic dipyramids of marcasite supporting a framework of broken and corroded siliceous fossil fragments. Pyrite co-occurs in the same stratigraphic horizons. Marcasite has apparently formed in association with animal decay that creates a microenvironment where pW is near or below 6.0. It may later invert to pyrite, possibly in association with the initial cementation and compaction processes leading to a chalk marked by pyritic liesegang rings. Iron sulfide occurrences in Hole 315 are consistent with the very high sedimentation rates reported in the variegated Miocene oozes and chalks.

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“…Existia uma forte tendência de o termo ser restrito a gênese de minerais exóticos, ou seja, distintos dos arcabouços onde se originaram, tendo como exemplos os argilominerais neoformados (Fairbridge 1967). Essa tendência é ainda forte no Brasil (Suguio 2003) e empregada em publicações internacionais recentes (Flügel 2004), onde os minerais autigênicos são entendidos como os formados após a deposição e durante a diagênese, incluindo tanto aqueles precipitados em poros, na forma de cimento, como os originados por substituição de minerais preexistentes.…”

Section: Sobre O Uso Do Termo Autigêneseunclassified

Sedimentação autigênica neoproterozóica e mineralizações associadas: um registro não uniformitarista

Boggiani¹

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Chapter 2 Phases of Diagenesis and Authigenesis

Cited by 65 publications

References 90 publications

A Mössbauer Investigation of Glauconite and its Geological Significance

A Mössbauer Investigation of Glauconite and its Geological Significance

Marcasite in Miocene Calcareous Sediments from Hole 315A

Sedimentação autigênica neoproterozóica e mineralizações associadas: um registro não uniformitarista

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