Contrasting microfossil preservation and lake chemistries within the 1200–1000 Ma Torridonian Supergroup of NW Scotland

Wacey, David; Brasier, Martin D.; Parnell, John; Culwick, Timothy; Bowden, Stephen; Spinks, Sam; Boyce, Adrian J.; Davidheiser‐Kroll, Brett; Jeon, Hee Jin; Saunders, Martin; Kilburn, Matt R.

doi:10.1144/sp448.6

Cited by 5 publications

(5 citation statements)

References 38 publications

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“…These data add to recent studies that report concentrations of elements indicative of clays (e.g. aluminium and iron) adjacent to other Proterozoic fossils [21][22][23]. The organisms studied here probably represent a variety of evolutionary clades, including eukaryotic chlorophyte algae and cyanobacteria [24][25][26][27]29].…”

Section: Kaolinite and Proterozoic Fossilizationsupporting

confidence: 68%

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Aluminosilicate haloes preserve complex life approximately 800 million years ago

et al. 2020

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Mudstone-hosted microfossils are a major component of the Proterozoic fossil record, particularly dominating the record of early eukaryotic life. Early organisms possessed no biomineralized parts to resist decay and controls on their fossilization in mudstones are poorly understood. Consequently, the Proterozoic fossil record is compromised—we do not know whether changing temporal/spatial patterns of microfossil occurrences reflect evolution or the distribution of favourable fossilization conditions. We investigated fossilization within the approximately 1000 Ma Lakhanda Group (Russia) and the approximately 800 Ma Svanbergfjellet and Wynniatt formations (Svalbard and Arctic Canada). Vertical sections of microfossils and surrounding matrices were extracted from thin sections by focused ion beam milling. Elemental mapping and synchrotron-based infrared microspectroscopy revealed that microfossils are surrounded by haloes rich in aluminium, probably hosted in kaolinite. Kaolinite has been implicated in Cambrian Burgess Shale-type (BST) fossilization and is known to slow the growth of degraders. The Neoproterozoic mudstone microfossil record may be biased to tropical settings conducive to kaolinite formation. These deposits lack metazoan fossils even though they share fossilization conditions with younger BST deposits that are capable of preserving non-mineralizing metazoans. Thus metazoans, at least those typically preserved in BST deposits, were probably absent from sedimentary environments before approximately 800 Ma.

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Section: Kaolinite and Proterozoic Fossilizationsupporting

confidence: 68%

“…Intriguingly, elements indicative of these clays (e.g. aluminium and iron) have also been reported adjacent to some Proterozoic fossils, but their host phases are difficult to constrain [21][22][23]. Do aluminium-and/or iron-rich clay minerals promote fossilization in Proterozoic strata?…”

Section: Introductionmentioning

confidence: 99%

Aluminosilicate haloes preserve complex life approximately 800 million years ago

et al. 2020

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“…5g, h). These data indicated that different suites of lakes within the Torridonian had different chemistries, with those of the Stoer Group being sulphate-rich and phosphate-poor compared with those of the Cailleach Head and Diabaig formations (for further details on contrasting fossil preservation in these lakes, see Wacey et al 2016).…”

Section: Colour Online/ Colour Hardcopymentioning

confidence: 98%

Advanced analytical techniques for studying the morphology and chemistry of Proterozoic microfossils

Wacey

Battison

Garwood

et al. 2016

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This paper outlines the suite of advanced multi-scalar techniques currently available in the toolkit of the modern Proterozoic palaeobiologist. These include non-intrusive and nondestructive optical, laser and X-ray techniques, plus more destructive ion beam and electron beam methods. Together, these provide morphological, mineralogical and biochemical data at flexible spatial scales from that of an individual atom to the largest Proterozoic microfossils. An overview is given of each technique and a case study from the exceptionally well-preserved Torridonian biota of NW Scotland is presented. This microfossil assemblage was first recognized over a century ago, but its great diversity and evolutionary importance has only recently come to light, due in no small part to the research efforts of Martin Brasier.

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“…STEM‐EDS maps plus extracted spectra reveal it is made of Ti and O (Figure 3b,e), and electron diffraction in the TEM shows it is the TiO 2 phase anatase (Figure 3d). Other surrounding mineral phases such as francolite, and iron–magnesium‐rich and potassium‐rich clay minerals are identified via EDS spectra and mapping, and with comparison to previously published work (Wacey, Battison, Garwood, Hickman‐Lewis, & Brasier, 2016; Wacey, Brasier, et al, 2016; Wacey et al, 2014, 2019).…”

Section: Resultsmentioning

confidence: 82%

Authigenic anatase within 1 billion‐year‐old cells

et al. 2020

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The siliciclastic ~1 Ga‐old strata of the Torridon Group, Scotland, contain some of the most exquisitely preserved three‐dimensional organic‐walled microfossils (OWMs) of the Precambrian. A very diverse microfossil assemblage is hosted in a dominantly phosphatic and clay mineral matrix, within the Diabaig and the Cailleach Head (CH) Formations. In this study, we report on several microfossil taxa within the CH Formation (Leiosphaeridia minutissima, Leiosphaeridia crassa, Synsphaeridium spp. and Myxococcoides spp.) that include populations of cells containing an optically transparent and highly refringent mineral, here identified using electron microscopy as anatase (TiO2). Most anatase crystals occur entirely within individual cells, surrounded by unbroken carbonaceous walls. Rarely, an anatase crystal may protrude outside a cell, interpreted to correspond to zones where the cell wall had broken down prior to anatase precipitation. Where an anatase crystal entombs an organic intracellular inclusion (ICI), the ICI is large and well preserved. These combined observations indicate that the intracellular anatase is an authigenic sedimentary phase, making this the first report of in situ precipitated anatase intimately associated with microfossils. The ability of anatase to preserve relatively large volumes of intracellular and cell wall organic material in these cells suggests that the crystallisation of anatase entombed cellular contents particularly quickly, soon after the death of the cell. This is consistent with the strong affinity of Ti for organic material, the low solubility of TiO2, and reports of Ti occurring in living organisms. With the data currently available, we propose a mineralisation pathway for anatase involving Ti complexation with organic ligands within specific cells, leading to localised post‐mortem anatase nucleation inside these cells as the complexes broke down. Further overgrowth of the anatase crystals was likely fuelled by very early diagenetic mobilisation of Ti that had been bound to more labile organic material nearby in the sediments.

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Contrasting microfossil preservation and lake chemistries within the 1200–1000 Ma Torridonian Supergroup of NW Scotland

Cited by 5 publications

References 38 publications

Aluminosilicate haloes preserve complex life approximately 800 million years ago

Aluminosilicate haloes preserve complex life approximately 800 million years ago

Advanced analytical techniques for studying the morphology and chemistry of Proterozoic microfossils

Authigenic anatase within 1 billion‐year‐old cells

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