Sedimentological analysis of Neoproterozoic glacigenic successions in Norway and Scotland

Abstract

<p>There is much debate regarding the severity of glaciation during the Neoproterozoic, particularly in response to the snowball Earth hypothesis that suggests ice repeatedly covered the Earth from equator to poles during this time. A detailed sedimentological analysis of the Neoproterozoic Smalfjord Formation of northern Norway and the Port Askaig Formation of Scotland was conducted in order to reconstruct the nature of paleoenvironmental change and assess the evidence for such severe glacial conditions. This study focuses on identifying the depositional origin of Neoproterozoic diamictites and the assessment of the relative importance of tectonics and climate in controlling sedimentation. Analysis of the Smalfjord Formation in two different areas of northern Norway shows that diamictites and associated facies were primarily deposited by sediment gravity flow processes, making determination of past ice mass form or distribution impossible. Sedimentological and allostratigraphic analysis of the Port Askaig Formation, showed that the thick succession of diamictites interbedded with sandstones, conglomerates and mudstones was deposited in a glacially-influenced marine setting affected at different stages of its development by both tectonic and climatic forces. Detailed analysis of the Great Breccia, a distinctive diamictite unit within the Port Askaig Formation, showed that it was the product of catastrophic subaqueous mass failure indicating substantial tectonic activity during the early stages of Port Askaig deposition. Elsewhere in the succession, diamictites show a greater degree of glacial influence on sedimentation and record fluctuating climatic conditions. This study shows that diamictites in Neoproterozoic successions cannot be presumed to represent glacial conditions. Sedimentation at both study sites appears to have been influenced by tectonic activity related to basin development. The Smalfjord and Port Askaig formations contain only limited evidence for glacial influence on sedimentation and do not appear to record the severe glacial conditions required by the snowball Earth hypothesis.</p>