SPATIAL AND TEMPORAL CHANGES IN GEOMETRIES OF FLUVIAL CHANNEL BODIES FROM THE TRIASSIC SNADD FORMATION OF OFFSHORE NORWAY

摘要

During the Triassic, the Barents Sea Basin was gradually filled by a low-gradient prograding alluvial to deltaic plain, sourced from the Ural and Caledonian mountain belts in the southeast and stretching over 1000 km to Spitsbergen in the north. Progradation was made possible by high sediment yield and large trunk river systems on the scale of modern continental drainage systems. Analysis of six 3D seismic volumes from the southwest Barents Sea samples the Middle to Late Triassic Snadd Formation at various locations along an oblique depositional dip profile. By investigating spatial variability and stratigraphic evolution, this study reveals a variety of fluvial seismic geomorphological features, including point-bar systems and ribbon channel sandstone bodies. The fluvial part of the Snadd Formation is dominated by channel bodies up to 20 km wide that decrease in size to hundreds of meters over a distance of 300 km in a proximal-distal direction. There is a significant change in channel body geometries towards the top of the formation, with a decrease in maximum width from 20 to 5 km and maximum thickness from 58 to 40 m. In addition, there is an upward decrease in the channel-to-overbank ratio, and more elongated sandstone bodies have been identified in the upper part of the formation. Temporal changes are interpreted to reflect an allogenic response to changes in the hinterland, whereas spatial changes were governed by autogenic processes. This new regional understanding of the fluvial succession of the Snadd Formation provides insight into the architecture of ancient large-scale fluvial systems.