The origin of upper Precambrian diamictites, northern Norway: a case study applicable to diamictites in general
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Date
2017-12
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Instytut Geologii UAM
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Abstract
Upper Precambrian diamictites in Varangerfjorden (northern Norway) have been examined for evidence of origin, whether
glaciogenic, gravity flow or polygenetic. Studies of geomorphology, sedimentology and surface microtextures on quartz
sand grains are integrated to provide multiple pieces of evidence for the geological agents responsible for the origin of
the diamictites. The documented sedimentary and erosional structures, formerly interpreted in a glaciogenic context (e.g.,
diamict structure, pavements and striations) have been reanalysed. Field and laboratory data demonstrate that, contrary
to conclusions reached in many earlier studies, the diamictites and adjacent deposits did not originate from glaciogenic
processes. Evidence from macrostructures may occasionally be equivocal or can be interpreted as representing reworked,
glacially derived material. Evidence from surface microtextures, from outcrops which are believed to exhibit the most unequivocal
signs for glaciation, display no imprint at all of glaciogenic processes, and a multicyclical origin of the deposits
can be demonstrated. The geological context implies (and no geological data contradict this) an origin by gravity flows,
possibly in a submarine fan environment. This reinterpretation of the diamictites in northern Norway may imply that the
palaeoclimatological hypothesis of a deep frozen earth during parts of the Neoproterozoic has to be revised.
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Keywords
Surface microtexture, debris flow, diamictite, tillite, Bigganjargga, snowball Earth
Citation
Geologos, 2017, 23, 3, pp. 163-181
ISBN
978-83-232187-4-6