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Wyświetlanie 1-2 z 2
Tytuł:
The origin of upper Precambrian diamictites, northern Norway: a case study applicable to diamictites in general
Autorzy:
Molén, M. O.
Powiązania:
https://bibliotekanauki.pl/articles/94363.pdf
Data publikacji:
2017
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
surface microtexture
debris flow
diamictite
tillite
Bigganjargga
snowball Earth
mikrotekstura powierzchni
spływ kohezyjny
diamiktyt
tillit
Ziemia-śnieżka
Opis:
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.
Źródło:
Geologos; 2017, 23, 3; 163-181
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
Tytuł:
Reconsidering the glaciogenic origin of Gondwana diamictites of the Dwyka Group, South Africa
Autorzy:
Molén, Mats O.
Smit, J. Johan
Powiązania:
https://bibliotekanauki.pl/articles/2204360.pdf
Data publikacji:
2022
Wydawca:
Uniwersytet im. Adama Mickiewicza w Poznaniu
Tematy:
surface microtexture
sediment gravity flows
Late Palaeozoic Ice Age
pavement
Nooitgedacht
mikrotekstura powierzchni
osad
epoka lodowcowa
nawierzchnie
Opis:
The Gondwana Late Palaeozoic Ice Age is probably best represented by the Dwyka Group in South Africa. Striated and grooved surfaces or pavements are commonly considered to have formed subglacially, as are diamictites which have been interpreted as in-situ or reworked tillites. These interpretations were tested by investigation of outcrops in formerly well-studied areas, throughout South Africa. Detailed analyses have focused on striated surfaces/pavements and surface microtextures on quartz sand grains in diamictites. The sedimentological context of four pavements, interpreter to be glaciogenic, display features commonly associated with sediment gravity flows, rather than glaciation. A total of 4,271 quartz sand grains were subsampled from outcrops that are considered mainly to be tillites formed by Continental glaciation. These grains, analysed by SEM, do not demonstrate the characteristic surface microtexture combinations of fracturing and irregular abrasion associated with Quaternary glacial deposits, but mainly a mix of surface microtextures associated with multicyclical grains. The Dwyka Group diamictites warrant reinterpretation as non-glacial sediment gravity flow deposits.
Źródło:
Geologos; 2022, 28, 2; 83--113
1426-8981
2080-6574
Pojawia się w:
Geologos
Dostawca treści:
Biblioteka Nauki
Artykuł
    Wyświetlanie 1-2 z 2

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