Insights into cyanobacterial fossilization in Ediacaran siliciclastic environments

Newman, Sharon; Mariotti, G.; Pruss, Sara B.; Bosak, Tanja

doi:10.1130/g37791.1

Cited by 34 publications

(27 citation statements)

References 29 publications

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“…Clay minerals have been suggested to play a key role in preservation of organic matter, with several studies showing a close association between siliciclastic minerals and microbial organisms (McMahon, Anderson, Saupe, & Briggs, ; Newman, Mariotti, Pruss, & Bosak, ; Wacey et al., ). Newman et al.…”

Section: Discussionmentioning

confidence: 99%

“…Newman et al. () demonstrated through experimental preservation of cyanobacterial mats the potential for clay minerals in suspension to coat bacterial filaments and promote preservation. It has been additionally suggested that the inhibition of growth due to clay mineral coating promotes preservation of soft tissue in bacteria (McMahon et al., ).…”

Section: Discussionmentioning

confidence: 99%

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Biologically agglutinated eukaryotic microfossil from Cryogenian cap carbonates

et al. 2017

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Cryogenian cap carbonates that overlie Sturtian glacial deposits were formed during a post-glacial transgression. Here, we describe microfossils from the Kakontwe Formation of Zambia and the Taishir Formation of Mongolia-both Cryogenian age, post-Sturtian cap carbonates-and investigate processes involved in their formation and preservation. We compare microfossils from these two localities to an assemblage of well-documented microfossils previously described in the post-Sturtian Rasthof Formation of Namibia. Microfossils from both new localities have 10 ± 1 μm-thick walls composed of carbonaceous matter and aluminosilicate minerals. Those found in the Kakontwe Formation are spherical or ovoid and 90 ± 5 μm to 200 ± 5 μm wide. Structures found in the Taishir Formation are mostly spherical, 50 ± 5 μm to 140 ± 5 μm wide, with distinct features such as blunt or concave edges. Chemical and mineralogical analyses show that the walled structures and the clay fraction extracted from the surrounding sediments are composed of clay minerals, especially muscovite and illite, as well as quartz, iron and titanium oxides, and some dolomite and feldspar. At each locality, the mineralogy of the microfossil walls matched that of the clay fractions of the surrounding sediment. The abundance of these minerals in the walled microfossils relative to the surrounding carbonate matrix and microbial laminae, and the presence of minerals that cannot precipitate from solution (titanium oxide and feldspar), suggests that the composition represents the original mineralogy of the structures. Furthermore, the consistency in mineralogy of both microfossils and sediments across the three basins, and the uniformity of size and shape among mineral grains in the fossil walls indicate that these organisms incorporated these minerals by primary biological agglutination. The discovery of new, mineral-rich microfossil assemblages in microbially laminated and other fine-grained facies of Cryogenian cap carbonates from multiple localities on different palaeocontinents demonstrates that agglutinating eukaryotes were widespread in carbonate-dominated marine environments in the aftermath of the Sturtian glaciation.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Biologically agglutinated eukaryotic microfossil from Cryogenian cap carbonates

et al. 2017

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“…Two different cyanobacteria filaments were found in the morphotypes M2 and M5, both herbivorous coprolites, and probably produced inside water. According to Newman et al (2016), elevated concentrations of seawater silica and the delivery of suspended clays promote microbial preservation in a few days. Even though the chemical composition of the Urumaco coprolites and microbial material preserved therein are phosphatic, the same composition indicates the microbial remains were rapidly coated by calcium phosphate.…”

Section: Coprolite Fossilizationmentioning

confidence: 99%

Paleoecological and taphonomical aspects of the Late Miocene vertebrate coprolites (Urumaco Formation) of Venezuela

Dentzien‐Dias

Carrillo-Briceño

Francischini

et al. 2018

Palaeogeography, Palaeoclimatology, Palaeoecology

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Coprolites (fossil feces) provide important paleoecological information, such as diet of the producer, parasite infestation and gut microbiota, which cannot be accessed through body remains. The Late Miocene Urumaco Formation, in western Venezuela, has a diverse vertebrate fauna composed of ground sloths, rodents, reptiles, fishes and amphibians, as well as coprolites. Here we describe 106 coprolites produced by a range of carnivorous and herbivorous vertebrates, classified into five different morphotypes based on their size and shape, suggesting different producers. Herbivorous morphotypes (M1, M2 and M5) are the most abundant (59%). The most common inclusions in these coprolites are Poacea remains, although Eudicotyledoneae fragments, bacteria and cyanobacteria filaments were also found. The M1 morphotype is a bullet shape with longitudinal grooves; the M2 morphotype is round to oval, with at least one distinctive tapered end; and the M5 morphotype is a short cylinder with a rough surface, and rounded ends. In contrast, the morphotypes M3 and M4 are attributed by us to carnivores and have different inclusions. While M3 is a large cylinder with rounded ends and contains bacteria, nematode eggs and phytoliths, M4 is sausage-shaped and has muscle cells preserved inside. Based on the co-occurring fauna and the morphology of the coprolites, the probable producers were inferred as the following: M1, a rodent; M2, a notoungulate; M3, a crocodilian; M4, an indeterminate carnivore; and M5, a sirenian. The preservation of herbivorous and carnivorous coprolites with bacterial, parasitological and muscle remains in the same formation and even the same outcrop is rare in the geological record. This unique association and preservation suggests early lithification promoted by rapid burial, although the presence of the boring trace Gastrochaenolites in a single specimen indicates some degree of time-averaging.

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“…Interestingly, recent studies on the source of clay particles coatings on cyanobacterial filaments embedded in ancient (Ediacaran) siliciclastic deposits (Newman et al, 2016) suggest a combined, external and authigenic provenance of the fine phyllosilicate encrustations. Control experiments with living filamentous cyanobacteria in siliciclastic sediment and externally supplied by clay suspension confirmed these observations (Newman et al, 2017).…”

Section: Discussionmentioning

confidence: 99%

Authigenic replacement of cyanobacterially precipitated calcium carbonate by aluminium‐silicates in giant microbialites of Lake Van (Turkey)

2018

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Studies of modern cyanobacterial mats and biofilms show that they can precipitate minerals as a consequence of metabolic and degradational activities paired with ambient hydrochemical conditions. This study looked at modern microbial mats forming giant, tower‐like, groundwater‐fed, calcareous microbialites in the world's largest, highly alkaline lake; Van Gölü (Lake Van), East Turkey. Results show that microbial systems play a role not only in carbonate precipitation but also in the formation of siliceous mineral phases. Transmitted light microscopy, scanning electron microscopy and spectral observations revealed that, within the extracellular polymeric substances excreted by the mats abundant minute aragonite grains precipitated first in vivo. These minute grains were quickly succeeded and/or supplemented in the dead biomass of the cyanobacterial mat by authigenic Al–Mg–Fe siliceous phases. Silicon dioxide is available in large concentrations in the highly alkaline water of Lake Van. Divalent cations (Ca and Mg) are delivered to the microbialites mostly by groundwater springs. The precipitation of the fine‐grained siliceous phases is probably mediated by bacteria degrading the cyanobacterial biomass and complexing the excessive cations with their extracellular polymeric envelopes. The bacteria serve as nucleation centres for the subsequent precipitation of siliceous mineral phases. Generally, the biphasic (calcareous and siliceous) mineralization – characterizing Lake Van microbialites – is controlled by their interior highly dynamic hydrogeochemical situation. There, the dramatically different alkaline lake water and the Ca–Mg‐charged groundwater mix at various rates. The early diagenetic replacement of the in vivo aragonite by authigenic siliceous phases significantly increases the fossilization potential of the mat‐forming cyanobacteria. Lake Van and its giant microbialite tufa towers act as a model explaining the transformation of early diagenetic mineral phases observed in many modern and ancient carbonate marine deposits, particularly those influenced by diffusion of silica‐enriched and metal‐enriched pore waters from below the water–sediment interface.

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Insights into cyanobacterial fossilization in Ediacaran siliciclastic environments

Cited by 34 publications

References 29 publications

Biologically agglutinated eukaryotic microfossil from Cryogenian cap carbonates

Biologically agglutinated eukaryotic microfossil from Cryogenian cap carbonates

Paleoecological and taphonomical aspects of the Late Miocene vertebrate coprolites (Urumaco Formation) of Venezuela

Authigenic replacement of cyanobacterially precipitated calcium carbonate by aluminium‐silicates in giant microbialites of Lake Van (Turkey)

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