Electron microscopy of Precambrian Vallenia  from Greenland

Hansen, Helle Ploug

doi:10.37570/bgsd-1978-si-07

bgsd

1978

DOI: 10.37570/bgsd-1978-si-07

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Electron microscopy of Precambrian Vallenia from Greenland

Helle Ploug Hansen¹

Abstract: Previously described structures within the Precambrian supposed plant fossil Vallenia erlingi Pedersen, 1967 from southwest Greenland were re-studied using STEM, high voltage TEM and x-ray microanalysis. It is concluded that the inner cell structure most likely is caused by twinning in the mineral phlogopite and is unrelated to the original cell structure.

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2019

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Geochemistry of a confirmed Precambrian impact ejecta deposit: The Grænsesø spherule layer, South Greenland

Huber

Koeberl

Smith

et al. 2019

Meteorit & Planetary Scien

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Samples from a single outcrop of the Graenseso spherule layer, Midternaes, South Greenland, consist of a spherule‐bearing dolomixtite with matrix‐supported intraclasts up to 1 m in size. In addition to field observations, we performed mineralogical and whole rock geochemical analysis, including electron microprobe, neutron activation analysis, X‐ray fluorescence, and mass spectrometry of the horizon and the overlying and underlying strata. We show that the spherules are petrographically similar to those in the Zaonega spherule layer, Karelia, Russia. Our petrographic and chemical results are consistent with the previous suggestion that the Grænsesø layer correlates with the Zaonega layer, and it is possible that both layers are related to the Vredefort impact event. The samples containing spherules, as well as the overlying rocks, have elevated REEs compared to the underlying pre‐impact layer, suggestive of a new continental source of sediment that may be coincident with the impact event. Zircons separated from the lower part of the Grænsesø spherule layer display complex age patterns suggesting that they have genetically different origins based on distinctly different Th/U ratios. Crystallization ages of all groups are ≥ 2.8 Ga, with ~2.8 Ga representing a time of major crustal growth globally. Therefore, we cannot conclusively determine in this study if the zircons are locally derived or if they are transported with the ejecta. The spherule layer was deposited by a high‐energy, subaqueous debris flow, an origin that is consistent with the hypothesis that the layer was deposited by impact‐induced waves and/or currents.

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Geochemistry of a confirmed Precambrian impact ejecta deposit: The Grænsesø spherule layer, South Greenland

Huber

Koeberl

Smith

et al. 2019

Meteorit & Planetary Scien

View full text Add to dashboard Cite

show abstract

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Electron microscopy of Precambrian Vallenia from Greenland

Cited by 1 publication

References 3 publications

Geochemistry of a confirmed Precambrian impact ejecta deposit: The Grænsesø spherule layer, South Greenland

Geochemistry of a confirmed Precambrian impact ejecta deposit: The Grænsesø spherule layer, South Greenland

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