Silicification of Fossils

Carson, G.A.

doi:10.1007/978-1-4899-5034-5_10

Cited by 33 publications

(24 citation statements)

References 80 publications

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“…This could explain why the fossil bones from these outcrops present a poor histological preservation but keep their original size, preventing the volumetric changes which occur in the bones coming from the other biozones (like those studied by Holz & Schultz in 1998) caused by the expansive growing of calcite crystals inside the bones. The silicification of fossils, as an eodiagenetic process, turns them relatively resistant to any other subsequent diagenetic processes (Carson, 1991), as compression or physical distortions.…”

Section: Discussionmentioning

confidence: 99%

Diagenetic pattern of vertebrate fossils from the Traversodontidae Biozone, Santa Maria Formation (Triassic), southern Brazil

Reichel

Schultz²,

Pereira

2005

RBP

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-Two outcrops of the Traversodontidae Biozone, located in the municipal districts of Santa Cruz do Sul and Venâncio Aires, were analyzed for their diagenetic patterns. Both outcrops share a very similar faunal content, with a predominance of non-mammalian cynodonts, and also a common biostratinomic pattern. Macroscopically, the bones are characterized by the presence of a thin, dark coloured layer composed by manganese oxides, attached to the external surface and for the absence of volumetric distortions caused by diagenesis, which often occur in the fossils of the Santa Maria Formation. On the microscopic level, a poor osteological preservation is found. X-ray diffractometry and scanning electron microscopy analyses revealed a high percentage of quartz in the samples, unlike the fossil bones found in other locations and stratigraphic levels within the Santa Maria Formation, where only minimal concentrations of silica are found. The amount of quartz filling the bones reflects different paleoenvironmental conditions and is here also correlated to the volumetric changes in the bones at the different biozones within the Santa Maria Formation. In addition to the diagenetic patterns shared by the Santa Cruz do Sul and Venâncio Aires outcrops, their similar biostratinomy and faunas corroborate the hypothesis that both represent a distinct biozone within the Santa Maria Formation.Key words: Bone diagenesis, cynodonts, faunal assemblage, silica, biozone.RESUMO -Dois afloramentos da Biozona de Traversodontidae, localizados nos municípios de Santa Cruz do Sul e Venâncio Aires, foram analisados em relação ao seu padrão diagenético. Os afloramentos apresentam um conteúdo faunístico muito semelhante, dominado pela presença de cinodontes não-mamalianos e, também, um padrão bioestratinômico comum a ambos, considerando suas tafocenoses. Macroscopicamente, os ossos são caracterizados pela presença de uma fina camada de coloração escura, composta de óxidos de manganês, na superfície externa, e pela quase ausência de deformações morfológicas (aumento de volume). Em nível microscó-pico, encontra-se uma pobre preservação osteológica. As difratometrias de raios-x e a microscopia eletrônica de varredura revelaram uma alta porcentagem de quartzo nas amostras, diferente dos fósseis encontrados em outras localidades da Formação Santa Maria, onde apenas concentrações mínimas são encontradas. A quantidade de quartzo preenchendo os ossos reflete diferentes condições paleoambientais e é aqui também relacionada às deformações volumétricas nos ossos de diferentes biozonas. O padrão diagenético similar dos afloramentos de Santa Cruz do Sul e Venâncio Aires, além de suas características bioestratinômicas e faunísticas semelhantes, corrobora a hipótese de que ambos representem um nível distinto na Formação Santa Maria, reforçando a presença de uma biozona distinta.

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Section: Discussionmentioning

confidence: 99%

Diagenetic pattern of vertebrate fossils from the Traversodontidae Biozone, Santa Maria Formation (Triassic), southern Brazil

Reichel

Schultz²,

Pereira

2005

RBP

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“…Silica polymerization and the subsequent formation of silica nanoparticles occur in many modern terrestrial environments (e.g., hot springs, brines, deep reservoirs) but they have also played an important role in ancient geological settings (e.g., most Archean fossils were preserved in silica cherts; Barghorn and Tyler, 1965;Knoll, 1985;Carson, 1991;Westall and Walsh, 2000). Furthermore, these processes are believed to have been crucial to the formation of silica-rich deposits recently observed on Mars (Squyres et al, 2008).…”

Section: Introductionmentioning

confidence: 97%

Quantification of initial steps of nucleation and growth of silica nanoparticles: An in-situ SAXS and DLS study

Tobler

Shaw

Benning

2009

Geochimica et Cosmochimica Acta

136

111

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“…Maliva and Siever (1988) suggested a combination of heterogenic nucleation of opal-CT and quartz, interstitial growth, and forced crystallization-controlled replacement of carbonate and recrystallization of opal-CT to quartz to form flint. Recently, biogenic opal-A from diatom frustules and sponge spicules is generally accepted as the main source for the silica (Wise and Weaver 1974;Calvert 1974;Clayton 1986;Knauth 1994;Zijlstra 1987;Carson 1991;DeMaster 2004), although Altschuler et al (1963) and Buurman et al (1973) suggested that the silica was released from alteration of volcanic rocks and clays. Nonetheless, considerable debate still continues about how exactly this important process works.…”

Section: Introductionmentioning

confidence: 97%

Diagenesis of Flint and Porcellanite in the Maastrichtian Chalk at Stevns Klint, Denmark

Madsen

Stemmerik

2010

Journal of Sedimentary Research

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Flint is common in many successions, but since the nodules can be the result of a series of replacement and void filling processes, their origin and broader paleo-oceanographic significance can remain enigmatic. This study addresses the origin of flint, in the Campanian-Maastrichtian chalk of Denmark using the 450-m-long Stevns-1 core as a natural laboratory.Four types of siliceous nodules occur in the core: porcellanite, white flint, white flint with a core of dark flint, and dark flint. All nodules consist mainly of microquartz with subordinate lutecite, spherulitic chalcedony, megaquartz, and dolomite. The lutecite replaces macrofossil fragments, mainly bryozoans and shells, microquartz replaces coccoliths, and the chalcedony and megaquartz are pore-filling. The preservation of the external shape of bryozoans, shells, and coccoliths suggest that siliceous nodules were formed early by a one-by-one volume replacement of chalk. Values of d 18 O smow of microquartz and lutecite around 33% indicate temperatures of 15-17uC at the time of precipitation; in contrast, the d 18 O smow values of megaquartz indicate precipitation at temperatures up to 48uC. The occurrence of chalcedony together with more stable and ordered megaquartz in irregular voids indicates that silica gel and/or opal-CT transformed to the a-quartz phases, microquartz, lutecite, chalcedony, and megaquartz, through the dissolution-precipitation process (Ostwald ripening).These results motivate a conceptual model in which the replacement process was initiated by microbial decomposition of organic matter and took place during periods of low rate of, or even stopped, sedimentation which fixed the redox boundary and the microbial metabolic zones at a specific depth below the sea floor. Biogenic opal-A incorporated in the sediment column below the sea floor was dissolved and precipitated at the redox boundary as silica gel and/or opal-CT, possibly aided by sulfideoxidizing bacteria. During burial, the dissolution-precipitation process transformed the silica gel and opal-CT to the a-quartz phases.The results of this study indicate that precipitation of the flint precursor can be controlled by a combination of an abundant biosiliceous source and high microbial activity in the sediments immediately below the seafloor. Flint is therefore likely to reflect deposition in a narrow interval at relatively shallow depths and therefore might be useful in studies of shallow-water carbonates.

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Silicification of Fossils

Cited by 33 publications

References 80 publications

Diagenetic pattern of vertebrate fossils from the Traversodontidae Biozone, Santa Maria Formation (Triassic), southern Brazil

Diagenetic pattern of vertebrate fossils from the Traversodontidae Biozone, Santa Maria Formation (Triassic), southern Brazil

Quantification of initial steps of nucleation and growth of silica nanoparticles: An in-situ SAXS and DLS study

Diagenesis of Flint and Porcellanite in the Maastrichtian Chalk at Stevns Klint, Denmark

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