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Seismic Geomorphology of Deep-Water Rift Basins—Depositional Architectures in a Late Jurassic Syn-Rift Turbidite Province Offshore Norway


Syn-rift intervals host important accumulations of hydrocarbons throughout many petroleum provinces worldwide. One key reason for failure of wells targeting syn-rift prospects is reservoir absence. Predicting stratigraphic trapping, the location and architecture of syn-rift reservoirs is highly challenging due to the complex interplay of evolving rift-topography and sedimentary processes. Past studies have mostly focused on major crustal scale rotated half graben basins and shallow marine to continental settings. In contrast, deep-water rift basins in areas with complex normal fault networks have received relatively little attention. This study uses state-of-the-art seismic attribute techniques applied to well-calibrated regional 3D seismic reflection data to investigate Late Jurassic syn-rift turbidites from the eastern flank of the Viking Graben in the northern North Sea rift.

The study area lies northwest of the Horda Platform and consists of down-stepping fault terraces with syn- and antithetic normal faults, intrabasinal highs and footwall islands. Each of these geomorphic features has first order control on: 1) where syn-rift turbidite fairways are prone to be characterized by deposition, bypass, or erosion, and 2) what kind of stratigraphic architecture the resultant deposits exhibit. Early rift stratigraphy was deposited on a basin-floor with numerous active folds and surface-breaking normal faults, creating 1-3 km wide terraces. These terraces formed a down-stepping array that ponded turbidites whose stratigraphy evolved in a fill-and-spill manner. When normal faulting localized on few major structures during the rift climax, depositional architectures are mostly channelized, either in small axial systems or in major channel complexes. Exposed footwall islands are fringed by perched fan architectures on their hangingwall, suggesting short sedimentary fairways derived from immediate footwall crest degradation.

Our results emphasize on the importance of timing for deep-water sedimentary systems relative to the different stages of rifting. Early rift turbidites are distributed ubiquitously along the deltaic margin and encounter a bathymetry modified by strain distribution on many small-scale structures. The rift climax to rift waning stages are characterized by strain localization on few large-scale normal faults and thus seem to focus sedimentary systems into rift-axial direction or through normal fault segment boundaries.