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- Högström, Anette, et al.
(author)
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Palaeopascichnus from the Ediacaran of the Digermulen Peninsula, Arctic Norway and the age of the Varanger Ice Age
- 2018
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In: 5th International Palaeontological Conference. ; , s. 292-
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Conference paper (peer-reviewed)abstract
- Palaeopascichnids are possibly the longest-ranging macroscopic Ediacaran fossils (ca. 565-542 Ma).They are bedding plane-parallel modular fossils composed of series of closely spaced millimeter sizedcircular, sausage- or kidney- shaped units. Earlier regarded as trace fossils, they are now seen as bodyfossils: possible xenophyophoran protists or protists of uncertain affinities. The Cryogenian to lower Cambrian succession (Vestertana group) exposed on the Digermulen Peninsula starts with the glacial Smalfjorden, interglacial Nyborg and glacial Mortensnes fms, collectively known as the Varanger Ice Age.Together with the succeeding Stáhpogieddi Fm. they reflect changes from global icehouse to greenhouse conditions. The Stáhpogieddi Fm. starts with the Lillevannet Mbr. followed by the Indreelva Mbr., yielding Ediacara-type fossils. The highest member in the Stáhpogieddi Fm, the Manndrapselva Mbr, contains the Ediacaran- Cambrian boundary. Palaeopascichnus is found at three horizons within the Stáhpogieddi Fm. The youngest, within the Manndrapselva Mbr., is latest Ediacaran, based on associated trace fossils, as well as occurring below trace fossils from the Treptichnus pedum ichnozone. Palaeopascichnus is also present near the base of the Manndrapselva Mbr. The oldest occurrence is from a horizon transitional between the Lillevannet and Indreelva Mbrs. Age constraints on the Varangerian glacial deposits are poor and their relationship to Neoproterozoic glacial events is equivocal. Studies over the last several decades have placed the Smalfjorden Fm. within the globally developed Marinoan glaciation (ca. 645–635 Ma) based on the presence of cap dolostones. The Mortensnes Fm. has been aligned within the Ediacaran Gaskiers glaciation(ca. 580 Ma) on the basis of carbon isotope stratigraphy. However, alternative interpretations exist,including that of a Marinoan affinity for all of the Varanger ice age. Palaeopascichnus at the Lillevannet Mbr. to Indreelva Mbr. transition indicates that this part of the succession is younger than 565 Ma. Because the transition between the Mortensnes Fm. and the succeeding Stáhpogieddi Fm. is seemingly without major breaks in sedimentation, this is consistent with a Gaskiers, or younger age for the Mortensnes Fm. An older age (Marinoan) requires the discovery of major breaks in the sedimentary record.
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