The origin of upper Precambrian diamictites, northern Norway: a case study applicable to diamictites in general

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.

Late-Holocene relative sea-level changes and palaeoenvironment of the Pre-Viking Age ship burials in Salme, Saaremaa Island, eastern Baltic Sea

“…Grain-size results show few distinct peaks of fine sand fraction at depths of 110, 150 and 200 cm, which are in contrast, for example, with the depth of 130 cm where the share of fine sand is smaller (Figure 3b). A combination of grain-size and SEM studies show that finer grains tend to be more angular (Fuller and Murray, 2002; Mahaney, 2002; Molen, 1992) and this also seems true for our results. Two samples, where a finer fraction dominates, carry more grains with a high surface relief, which is something that is likely linked with an increased number of angular grains.…”

Field evidence suggests that the Palaeoproterozoic Gowganda Formation in Canada is non-glacial in origin

“…The present study reaffirms the interpretation of a gravity flow origin, as based on the evidence in the outcrops of laminated sediments at Cobalt, and junction 129/554, which had previously been interpreted as evidence of glaciation. Furthermore, the evidence from lonestones is at odds with a simple marine/lake rain-out model, and sedimentary Molén (2017Molén ( , 2021. Not included in the column are structures that form by non-glaciogenic processes in a glacial environment, e.g., debris flows.…”

“…Many researchers refer to the hypothesis of Snowball Earth, for which the Gowganda Formation is an important area in worldwide correlations (Young, 2013(Young, , 2014. However, the evidence for Snowball Earth scenarios is equivocal, as has been confirmed by detailed dating of outcrops of Neoproterozoic (Le Heron et al, 2020) and Palaeoproterozoic strata, including the Gowganda Formation (Kump et al, 2013;Young, 2014Young, , 2019, by the geochemical record (Bahlburg & Dobrzinski, 2011;Bristow et al, 2011;Grotzinger et al, 2011;Zimmermann et al, 2011), including (mainly for Neoproterozoic and younger strata) ikaites/glendonites -the minerals that are supposed to be stable only in cold temperatures (Aspler et al, 2001;Hoffman, 2013;Fairchild et al, 2016), but are documented to have formed in temperate and even tropical waters (Popov et al, 2019) and, lastly, by numerous studies of the geology of Precambrian diamictites (e.g., Eyles, 1993;Molén, 2017;Kennedy et al, 2019;Kennedy & Eyles, 2021).…”

“…There are a number of criteria for characterising a till, but most of these may be displayed by co-hesive gravity flows (Schermerhorn, 1974;Molén, 2017Molén, , 2021, for example striations produced on clasts by gravity flows and glaciers are difficult to differentiate (Atkins, 2003(Atkins, , 2004. In short, if there are systematic sedimentary regularities or patterns in a diamictite, it may be possible to consider if outcropping rocks were produced by a gravity flow or a glacier.…”

Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa

“…Differences between glaciogenic and mass flow features often can be revealed by comparing data from different geological disciplines (compare Shanmugam et al, 1994;Major et al, 2005;Talling et al, 2007Talling et al, , 2012Dakin et al, 2013;Shanmugam, 2016;Molén, 2017Molén, , 2021Molén, , 2022aMolén, , 2022bDietrich & Hofmann, 2019;Peakall et al, 2020;Cardona et al, 2020). Geological features which are commonly interpreted as glaciogenic, for example, striated, grooved and polished bedrock, including all kinds of chevron structures/crescentic gouges/chattermarks, grooves and nailhead striations, can form as a result of different kinds of mass movements, such as avalanches, slides and different kinds of sediment gravity flows (Draganits et al, 2008;Dakin et al, 2013;Molén, 2017Molén, , 2021Molén, , 2022aMolén, , 2022bKennedy & Eyles, 2021). A lahar generated by the Mount St. Helens eruption truncated volcanic boulders and produced, in places "... a surface similar to a glacial pavement cut in conglomerate" (Scott, 1988, p. A43).…”