A structural study of the occurrence of Ikaite pseudomorphs in Neoproterozoic metalimestones on Islay, Scotland

• Main Author: Ohrazda, Christina
• Format: Others
• Language: English
• Published: Stockholms universitet, Institutionen för geologiska vetenskaper 2017
• Subjects: ikaite; Neoproterozoic; metalimestone; Islay; Scotland; Natural Sciences; Naturvetenskap; Earth and Related Environmental Sciences; Geovetenskap och miljövetenskap; Geology; Geologi
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-145322

Aligned ikaite porphyroblasts have been replaced by calcite with a maximum volume decrease of ~88% in Neoproterozoic Dalradian metalimestone exposed near Ballygrant on Islay, Scotland. Microscopic and structural analyses reveal that the ikaite minerals formed before deformation, at a time when Scotland was located at the lower latitudes, thus indicating a cold climate at the time of formation. The Ballygrant metalimestone underlies a ~900 meter thick glacial deposit that has previously been linked to the ‘Snowball Earth’ hypothesis. The discovery of these ikaite pseudomorphs below the glacial deposit points toward a relatively slow cooling of the climate near the equator reflecting a transition toward a ‘normal’ glacial period and thus refutes a suggested ‘Snowball Earth’ event, which is reported to reflect a more abrupt switch over from warm to cold climate in the sediment record.