Mixed axial and transverse deep-water systems: The Cretaceous post-rift Lysing Formation, offshore Norway

Deep-water stratigraphic successions from syn- to post-rift stages are an archive of evolving physiographic configurations, and can record axial and transverse sedimentary sources. The healing of topography decreases the influence of syn-rift structures on sedimentation patterns and transport processes over time, which leads to a long-term transition from dominantly axial to transverse dispersal patterns. The Halten and Dønna terraces, offshore mid-Norway, comprise a series of rift-related sub-basins established during the Jurassic, which were infilled with sediments during the Cretaceous. The Cretaceous Lysing Formation developed as slope- and basin-floor fans within a series of weakly confined post-rift sub-basins with some shallow marine deposits interpreted on the basin margins. A deep-water setting is supported by seismic interpretation, and bed type and architectural element analysis in all cored and uncored wells in the area. We document that an axial submarine fan system was active throughout the post-rift stage due to subtle inherited topography from syn-rift structures, which interacted with locally sourced transverse sediment sources. This led to a complicated stratigraphic architecture, with lobe fringe deposits of the axial fan system juxtaposed with channel-fills and channel-lobe transition zone deposits of transverse systems. The refined palaeogeographic reconstruction of the Lysing Formation illustrates how subtle topography can impact sediment routing patterns many millions of years after the end of rifting and can be used for palaeoenvironmental interpretations in other post-rift settings.