Thrombolites, spherulites and fibrous crusts (Holkerian, Purbeckian, Aptian): Context, fabrics and origins

Kirkham, Anthony; Tucker, Maurice E.

doi:10.1016/j.sedgeo.2018.07.002

Cited by 42 publications

(28 citation statements)

References 47 publications

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“…It can be speculated that the spherulites were originally composed of vaterite or aragonite during initial crystallization. Because of the unstable nature of these calcium carbonate polymorphs, the initial mineralogy was replaced by calcite during early diagenesis, although, calcite may also be original (Tucker, 2001;Kirkham and Tucker, 2018). Whether original or replaced, the radial fibrous crystals of spherulites in calcareous concretions from the 2 nd cycle of the Manndrapselva Member are currently calcite.…”

Section: Discussionmentioning

confidence: 99%

“…With the exception of the Lower Cretaceous lacustrine carbonate reservoirs in the South of extracellular polymeric substances), which generated a favourable microenvironment for calcium carbonate precipitation, at the sediment-water interface or a few cm to m below the interface (e.g., Buczynski and Chafetz, 1991;Verrecchia et al, 1995;Mercedes-Martín et al, 2016;Kirkham and Tucker, 2018); however, an abiotic origin has also been suggested (e.g., Wright and Barnett, 2015). Calcite forming spherulites is suggested to be either replaced aragonite, vaterite, or original (e.g., Tucker, 2001;Wright and Barrett, 2015).…”

Section: Introductionmentioning

confidence: 99%

“…The results of this study may be of interest for sedimentologists working on palaeoenvironmental reconstructions at the Ediacaran-Cambrian transition. They may also be of interest for geobiologists, as carbonate formation, especially in the case of calcite spherulites, is commonly thought to be closely associated with microbial activity (e.g., Buczynski and Chafetz, 1991;Verrecchia et al, 1995;Mercedes-Martín et al, 2016;Kirkham and Tucker, 2018), although non-microbial processes cannot be ruled out (Wright and Barnett, 2015).…”

Section: Introductionmentioning

confidence: 99%

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First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance

Meinhold

Jensen

Høyberget³

et al. 2019

Precambrian Research

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We report for the first time carbonates from the upper Ediacaran sedimentary succession of Finnmark, Arctic Norway. Carbonates occur as calcareous siliciclastic beds, lenses, and concretions, some with calcite spherulites and cone-in-cone (CIC) calcite, in a mudrock to fine-grained sandstone succession from approximately 3 m to 26 m above the base of the 2 nd cycle of the Manndrapselva Member of the Stáhpogieddi Formation (Vestertana Group). They occur c. 40 m below the Ediacaran-Cambrian boundary, which is well defined by trace fossils. Thin-section petrography and scanning micro X-ray fluorescence elemental mapping reveal a layered composition of the calcareous sedimentary rocks. In some of those, welldeveloped nested cones of CIC calcite form the outer layer. Thin clay coatings outline individual cones. The inner layers are composed of (1) carbonate with calcite spherulites (grainstone) and (2) thinly laminated fine-grained calcareous siliciclastics (mudstone and wackestone) indicated by elevated concentrations of Al, Si, Fe, and Ti. The inner siliciclastic layers contain framboidal pyrite and probably organic matter. Formation of calcite spherulites took place probably at the sediment-water interface either in a coastal littoral environment or in situ in the sublittoral zone under high alkaline conditions whereas CIC calcite formed during burial diagenesis and clearly in pre-Caledonian time before metamorphism and cleavage formation. This new record of carbonates with calcite spherulites and CIC structures from the Ediacaran of Arctic Norway adds to their rare occurrences in the geological record.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance

Meinhold

Jensen

Høyberget³

et al. 2019

Precambrian Research

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“…In the geological record, carbonate spherulites associated with Mg‐silicate minerals and poorly crystalline Mg‐Si substances or “gels” have been reported in the economically important Lower Cretaceous (Aptian) “Pre‐Salt” South Atlantic lacustrine carbonate rocks (Muniz & Bosence, 2015; Saller et al., 2016; Terra et al., 2010) and have also been reported in lake deposits of Carboniferous age (Rogerson et al., 2017). The contribution of biological processes to lacustrine spherulite formation remains a topic of significant debate, due to unclear preservation of any microbial component in geological examples and a paucity of suitable modern analogues (Awramik & Buchheim, 2012; Kirkham & Tucker, 2018), making their designation as microbialites uncertain.…”

Section: Introductionmentioning

confidence: 99%

Spherulitic microbialites from modern hypersaline lakes, Rottnest Island, Western Australia

et al. 2020

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Microbialites are organosedimentary deposits formed by the interaction of benthic microbial communities with their environment (Burne & Moore, 1987) and provide the only continuous macroscopic record for life spanning its appearance in the Archean through to the present day (Riding, 2000). Biological, physical, and chemical processes combine to produce an internal structure characteristic of microbialites, which include laminated fabrics and clotted to unlayered fabrics (Kennard & James, 1986).

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“…Calcite and aragonite spherulites have been observed in various travertine and lacustrine case studies and attributed to microbial mediation or EPS influence and presence of organic acids (Guo and Riding, 1992; Folk, 1993; Dupraz et al, 2009; Arp et al, 2012; Mercedes Martin et al, 2016; Kirkham and Tucker, 2018), or abiotic precipitation within silica gels (Wright and Barnett, 2015; Tosca and Wright, 2018). Spherulites are polycrystals commonly linked to high supersaturation levels and far from equilibrium precipitation (Jones and Renaut, 1995; Jones, 2017a).…”

Section: Interpretation and Discussionmentioning

confidence: 99%

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

Porta

Reitner²

2020

Preprint

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The study of hydrothermal travertines contributes to the understanding of the interaction between physico-chemical processes and the role played by microbial mats and biofilms in influencing carbonate precipitation. Three active travertine sites were investigated in Central Italy to identify the types of carbonate precipitates and the associated microbial mats at varying physico-chemical parameters. Carbonate precipitated fabrics at the decimetre- to millimetre-scale and microbial mats vary with decreasing water temperature: a) at high temperature (55-44°C) calcite or aragonite crystals precipitate on microbial mats of sulphide oxidizing, sulphate reducing and anoxygenic phototrophic bacteria forming filamentous streamer fabrics, b) at intermediate temperature (44-40°C), rafts, coated gas bubbles and dendrites are associated with Spirulina cyanobacteria and other filamentous and rod-shaped cyanobacteria, c) low temperature (34-33°C) laminated crusts and oncoids in a terraced slope system are associated with diverse Oscillatoriales and Nostocales filamentous cyanobacteria, sparse Spirulina and diatoms. At the microscale, carbonate precipitates are similar in the three sites consisting of prismatic calcite (40-100 μm long, 20-40 μm wide) or acicular aragonite crystals organized in radial spherulites, overlying or embedded within biofilm EPS (Extracellular Polymeric Substances). Microsparite and sparite crystal size decreases with decreasing temperature and clotted peloidal micrite dominates at temperatures < 40°C, also encrusting filamentous microbes. Carbonates are associated with gypsum and Ca-phosphate crystals; EPS elemental composition is enriched in Si, Al, Mg, Ca, P, S and authigenic aluminium-silicates form aggregates on EPS.This study confirms that microbial communities in hydrothermal travertine settings vary as a function of temperature. Carbonate precipitate types at the microscale do not vary considerably, despite different microbial communities suggesting that travertine precipitation, driven by CO2 degassing, is influenced by biofilm EPS acting as template for crystal nucleation (EPS-mediated mineralization) and affecting the fabric types, independently from specific microbial metabolism.

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Thrombolites, spherulites and fibrous crusts (Holkerian, Purbeckian, Aptian): Context, fabrics and origins

Cited by 42 publications

References 47 publications

First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance

First record of carbonates with spherulites and cone-in-cone structures from the Precambrian of Arctic Norway, and their palaeoenvironmental significance

Spherulitic microbialites from modern hypersaline lakes, Rottnest Island, Western Australia

The influence of microbial mats on travertine precipitation in active hydrothermal systems (Central Italy)

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