EVIDENCE FOR GLACIAL AND TECTONIC ACTIVITY IN THE NEOPROTEROZOIC SMALFJORD AND VEINESBOTN FORMATIONS, VARANGERFJORDEN, NORWAY

The Smalfjord Formation of northern Norway is one of two Neoproterozoic glacigenic successions, which accumulated in the extensional Gaissa basin. Excellent exposures are found around Varangerfjorden where diamictite, conglomerate and sandstone overlie a regional unconformity and the Veinesbotn Formation. Controversy over the Smalfjord Formation lies in its interpretation and paleoclimatic significance. Some workers have argued for a glacial terrestrial setting, while others have proposed a marine setting with limited glacial influence and possible tectonic activity related to extensional basin development. Identifying the relative importance of glacial and tectonic controls on sedimentation is important for regional paleoclimate reconstructions and recent debates over the severity of Neoproterozoic glaciations.

Detailed sedimentological analysis of the Smalfjord Formation and descriptions of the underlying unconformity are presented from several sites around Varangerfjorden in order to reconstruct paleoenvironmental conditions and assess the relative influence of glacial and tectonic controls on sedimentation. Coarse-grained facies such as conglomerate, sandstone and pebbly sandstone at these sites exhibit rapid lateral facies changes, various amounts of deformation and progradational geometry. They are interpreted to record deltaic/fluvial conditions. Complex ductile deformation of sandstone and conglomerate results predominantly from shearing and may record glacial advance over proglacial outwash and deltaic sediment. Other sites previously described are dominated by sediment gravity flow facies with no evidence of direct deposition by ice. The Smalfjord Formation in Varangerfjorden thus records different depositional conditions with varying glacial influence on sedimentation. The underlying unconformity is low-angle and striated at the classic site of Bigganjargga. In other places, it exhibits significant relief with scarps or offsets. While some show smooth truncation of underlying beds and may reflect paleotopography, others appear to record localized faulting. Preliminary analysis thus suggests that tectonic activity along with glacial conditions have played a significant role in determining the nature of this succession.