Raine, Robert James
(2010).
The Durness Group of NW Scotland: a stratigraphical and sedimentological study of a Cambro-Ordovician passive margin succession.
University of Birmingham.
Ph.D.
Abstract
The Cambrian to Ordovician Durness Group was deposited on the Scottish sector of the passively-subsiding, continental margin of the Laurentian craton, and now forms part of the Hebridean terrane, lying to the west of the Moine Thrust zone. It represents c. 920 m of shallow marine, peritidal carbonates with minor siliciclastic and evaporitic strata. Facies analysis shows that the carbonates represent deposition within coastal sabkha, intertidal and shallow subtidal to shelfal environments and sedimentary logging of all available sections has revised the thicknesses of the lithostratigraphic formations within the Durness Group. A diverse array of microbialites is documented, and their application for interpreting the sea-level and palaeoenvironmental history is discussed. The enigmatic ‘leopard rock’ texture is here concluded to represent a thrombolite, thus significantly increasing the abundance of microbial facies within the section. A revised conodont biostratigraphy for the Ordovician upper five formations of the Durness Group allows more precise correlation with the once contiguous sections in western Newfoundland and Greenland and dating of the lithostratigraphical and sequence stratigraphical subdivisions for the first time. Based upon the new conodont biostratigraphy, a sequence stratigraphical model for the Cambro-Ordovician strata in Scotland is proposed, comprising four depositional megasequences, which correlate well with the Sauk sea level sequence recognised across Laurentia. This study allows for further correlation with Laurentian margin sections and the global sea-level record.
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