A framework for the extraction and interpretation of organic molecules in speleothem carbonate

Wynn, P.; Brocks, Jochen J.

doi:10.1002/rcm.6843

Cited by 19 publications

(20 citation statements)

References 40 publications

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“…In this study, we identified, quantified, and eliminated such contaminants using so‐called exterior/interior ( E / I ) experiments. Generally, in these experiments, hydrocarbon contaminants are identified by removing exterior rock surfaces using a diamond wafering saw (Brocks et al ., ), a micro‐ablation apparatus (Jarrett et al ., ) or an acid bath (Wynn & Brocks, ), followed by separate quantification of molecular concentrations in both the exterior (‘ E ’) and interior (‘ I ’) portions. Surficial contamination is then recognized by elevated E/I ratios for individual molecules, while indigenous hydrocarbons will commonly yield ratios of ca.…”

Section: Resultsmentioning

confidence: 99%

Early sponges and toxic protists: possible sources of cryostane, an age diagnostic biomarker antedating Sturtian Snowball Earth

et al. 2015

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The period 800-717 million years (Ma) ago, in the lead-up to the Sturtian Snowball glaciation, saw an increase in the diversity of eukaryotic microfossils. To afford an independent and complementary view of this evolutionary period, this study presents the distribution of eukaryotic biomarkers from three pre-Sturtian successions across the supercontinent Rodinia: the ca. 780 Ma Kanpa Formation of the Western Australian Officer Basin, the ca. 800-740 Ma Visingsö Group of Sweden, and the 740 Ma Chuar Group in Arizona, USA. The distribution of eukaryotic steranes is remarkably similar in the three successions but distinct from all other known younger and older sterane assemblages. Cholestane was the only conventional structure, while indigenous steranes alkylated in position C-24, such as ergostane, stigmastane, dinosterane and isopropylcholestane, and n-propylcholestane, were not observed. This sterane distribution appears to be age diagnostic for the pre-Sturtian Neoproterozoic. It attests to the distinct evolutionary state of pre-Snowball eukaryotes, pointing to a taxonomic disparity that was still lower than in the Ediacaran (635-541 Ma). All three basins also show the presence of a new C28 sterane that was tentatively identified as 26-methylcholestane, here named cryostane. The only known extant organisms that can methylate sterols in the 26-position are demosponges. This assignment is plausible as molecular clocks place the appearance of the earliest animals into the pre-Sturtian Neoproterozoic. The unusual 26-methylsterol may have protected sponges, but also other eukaryotes, against their own membranolytic toxins. Some protists release lytic toxins to deter predators and kill eukaryotic prey. As conventional membrane sterols can be the site of attack for these toxins, sterols with unusual side-chain modification protect the cell. This interpretation of cryostane supports fossil evidence of predation in the Chuar Group and promotes hypotheses about the proliferation of eukaryophagy in the lead-up to the Cryogenian.

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Section: Resultsmentioning

confidence: 99%

Early sponges and toxic protists: possible sources of cryostane, an age diagnostic biomarker antedating Sturtian Snowball Earth

et al. 2015

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“…We cleaned the stalagmite surfaces using 1N HCl (Wynn & Brocks, 2014) and then extracted powdered samples using a 1-mm-diameter diamond-tipped hand drill. We carried out acid digestion of the OM entrapped in the calcite using a cleaned HCl solution, prepared by repeatedly shaking HCl with dichloromethane until the fluorescence emission of the HCl was negligible (generally six times, Blyth et al, 2006).…”

Section: Stalagmite Samplesmentioning

confidence: 99%

Geochemical mapping of organic carbon in stalagmites using liquid-phase and solid-phase fluorescence

et al. 2015

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“…Earlier finds of Archaean biomarkers are now discredited and shown to result from contamination, and it is now thought that all Archaean rocks are too thermally mature to preserve biomarkers (French et al ., ); this applies also to the vast majority of Neoproterozoic sections. It has also been established that even in thermally immature rocks, contamination is a major issue, even in young material (Wynn & Brocks, ). An example of the problem is the biomarker assemblage, indicative of a diverse microbial ecosystem including phototrophic and heterotrophic bacteria and eukaryotes, found in industrial core of presumed Sturtian‐age rocks from Brazil by Olcott et al .…”

Section: Biotic Responses and Innovationsmentioning

confidence: 99%

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

2016

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Sedimentological insights underpin many of the important recent advances in understanding of Earth system behaviour in the Neoproterozoic Era. This article reviews three main areas: (i) chemical proxies and their preservation, with emphasis on carbonate facies; (ii) glacial and post-glacial facies, including their age constraints; (iii) sedimentary evidence for biotic innovations and responses. Chemostratigraphy plays an important role in ordering Neoproterozoic events and defining disturbances to the carbon cycle. There is increasing attention being paid to assessing the role of diagenetic origination or modification of chemostratigraphic signals. Alongside this, new criteria for identifying primary dolomite and precursor metastable phases such as ikaite have been developed. In respect of oxygenation, geochemical proxies substantiate the concept of a Neoproterozoic Oxygenation Event as a very gradual transition, the ocean being at any one time a heterogeneous assemblage of ferruginous, sulphidic and oxic conditions, with some evidence of increasing deep-sea oxidation through the Ediacaran Period. Techniques such as Fe-speciation need to be supplemented with proxies sensitive to suboxic conditions. More generally, it is predicted that petrographically constrained microanalytical studies will also become more important in reconstructing palaeoenvironmental conditions. The global distribution of Neoproterozoic glacial deposits combined with palaeomagnetic evidence supports the concept of panglaciations in which ice sheets reached sea-level in the tropics. Advances in radiometric dating have demonstrated the synchronous onset of global (Sturtian) glaciation at 717 Ma and the demise of a second (Marinoan) glaciation at 635 Ma, and plausibly indicate long durations for each (55 Myr for Sturtian and 5 to 15 Myr for Marinoan). However, a compilation of radiometric dates indicates ambiguities indicating the need for further improvements to the radiometric and Sr-isotope database to understand events within the Sturtian time frame, the timing of onset of Marinoan glaciations, and the age and synchroneity of individual negative d 13 C anomalies. Sturtian deposits are typically thick, rift-related successions containing a range of environments influenced or dominated by dynamic glaciers, as well as ice-free marine intervals. Marinoan glacial deposits, by contrast, tend to be thin and continental. During the latter interval, oxygen isotope systematics of sulphate demonstrate that atmospheric CO 2 was high, as predicted by Snowball Earth theory, and that sedimentation was influenced by orbital forcing. The Sturtian record, by comparison, needs to be searched for evidence of cold-climate hiatuses on the one hand and orbital forcing on the other. Cap carbonate formation appears to have coincided with rising sea-levels following panglaciations. Snowball theory considers that they formed rapidly in the postglacial greenhouse, but an alternative (2016) 63, 253-306 doi: 10.1111/sed.12261 STATE OF THE SCIENCE model o...

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A framework for the extraction and interpretation of organic molecules in speleothem carbonate

Cited by 19 publications

References 40 publications

Early sponges and toxic protists: possible sources of cryostane, an age diagnostic biomarker antedating Sturtian Snowball Earth

Early sponges and toxic protists: possible sources of cryostane, an age diagnostic biomarker antedating Sturtian Snowball Earth

Geochemical mapping of organic carbon in stalagmites using liquid-phase and solid-phase fluorescence

Sedimentological perspectives on climatic, atmospheric and environmental change in the Neoproterozoic Era

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