Ice-Rafting in Lakes in the early Neoproterozoic: dropstones in the Diabaig Formation, Torridon Group, NW Scotland

Adrian Hartley*, Bartosz Kurjanski, Jessica Helen Pugsley, Joseph Graham Armstrong

*Corresponding author for this work

Research output: Contribution to journalArticle

Abstract

A dropstone horizon is described from lake deposits in a paleo-valley from the 1000 Ma Diabaig Formation, Torridon Group, NW Scotland. Dropstones occur in wave-rippled, fine grained sandstones and siltstones that contain desiccation and syneresis cracks indicative of fluctuating lake levels. Five locally-derived dropstones occur at the same horizon over lateral distance of 250 m and display clear evidence of deflection and penetration of laminae at the base, with thinning, onlap and draping of laminae onto clast margins and tops. Mechanisms of dropstone formation are discussed with ice-rafting considered the most likely explanation. It is suggested that rafting was promoted by cold winters at 35˚S in the early Neoproterozoic, possibly in an upland setting. Interpretation of the dropstones as ice-rafted debris provides the first physical record of evidence for ice at the Earth’s surface during the late Mesoproterozoic to early Neoproterozoic.
Original languageEnglish
Pages (from-to)47-53
Number of pages7
JournalScottish Journal of Geology
Volume56
Issue number1
Early online date10 Jan 2020
DOIs
Publication statusPublished - May 2020

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