Global C cycle perturbations recorded in marbles: a record of Neoproterozoic Earth history within the Dalradian succession of the Shetland Islands, Scotland

A. R. Prave, R. A. Strachan, A. E. Fallick

Research output: Contribution to journalArticlepeer-review

29 Citations (Scopus)

Abstract

The Shetland Islands in Scotland contain a c. 12 kill thick, mostly siliciclastic Neoproterozoic succession that experienced deformation and greenschist- to amphibolite-facies metamorphism during the Ordovician-Silurian Caledonian Orogeny. Correlating these rocks with Neoproterozoic successions elsewhere has remained problematic. However, four marble units punctuate the succession: these are, in stratigraphic order, the Weisdale. Whiteness, Girlsta and Laxfirth Limestones, two of which record hallmark C-isotopic excursions diagnostic of Neoproterozoic time. The Whiteness Limestone is lithologically similar to the 635 Ma Marinoan post-glacial cap carbonate sequence and displays a delta C-13(carbonate) profile in which values decline front a range of 0 to +2 parts per thousand to a nadir of -5 parts per thousand and then rise towards and oscillate around 0 parts per thousand. The Girlsta Limestone is a 700-900 in thick marble unit With values of -9 parts per thousand to -11 parts per thousand and is interpreted as recording the late Neoproterozoic Shuram-Wonoka event. These correlations permit linking the Shetland succession to Neoproterozoic sections elsewhere and also show that rift-related rocks in Shetland post-date the Shuram-Wonoka event (post c. 600 Ma-pre c. 550 Ma) thereby supporting the concept of a diachronous phase of extensional tectonism, from e. 700 Ma in east-central Laurentia to near the close of the Proterozoic in northeastern Laurentia, prior to the opening of the lapetus Ocean.

Original languageEnglish
Pages (from-to)129-135
Number of pages7
JournalJournal of the Geological Society
Volume166
DOIs
Publication statusPublished - Jan 2009

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