--> Sediment Routing of Deep-Water Syn-Rift Depositional Systems Across Faulted Terraces: Late Jurassic Lomre-Uer Terraces, North Sea Rift
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AAPG ACE 2018

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Sediment Routing of Deep-Water Syn-Rift Depositional Systems Across Faulted Terraces: Late Jurassic Lomre-Uer Terraces, North Sea Rift

Abstract

Growing normal faults can control deep-marine sediment routing and deposition in rift basins. Existing models on their tectono-stratigraphic evolution do not fully capture the complex spatio-temporal evolution of these deep-marine systems. This study is based on the eastern flank of the northern North Sea rift where major basin margin-bound delta sequences supplied sediment to turbidite fairways into the deep-water environment throughout the Late Jurassic rift phase. Using an extensive well database and regional 3D broadband seismic reflection data, we integrate seismic geomorphology and advanced seismic attributes to investigate how evolving rift structures influence the distribution and sedimentary architecture of deep-marine depositional systems in rift basins.

We grouped the Lomre- and Uer terraces into four distinct structural domains: 1) strongly rotated syn- and antithetic half graben; 2) mostly symmetric internal terrace graben; 3) transition zones at platform margin fault-segment boundaries; and 4) the mostly unfaulted Uer terrace with localized strain on the terrace-bounding normal fault. The Lomre terrace consists of an approximately 25 km wide and 50 km long complex array of rotated fault blocks arranged in a conjugate architecture that thins towards its axis. The southern part of the Lomre terrace exhibits a less well-defined conjugate geometry with fault block downstepping to the northwest.

Throughout the syn-rift package, turbidite architecture is highly heterogeneous, nonetheless there appears to be a first order control of paleo bathymetry defined by normal faults on the turbidite distribution and architecture. Based on this observation, three main tectono-stratigraphic styles were identified within the study area: 1) initial surface folding to faulting stage with ponded turbidites caused by mass wasting of updip slope instability; 2) rift climax underfilled basins dominated by axial turbidite channels; 3) forced regressive basin floor fans with minor structural control on depositional architecture. Controlling factors on turbidite distribution in all tectono-stratigraphic styles however are relative sub-basin elevation, relay ramps or segment boundaries acting as sediment pathways, or high supply settings causing updip basin overfill-and-spill scenarios. These results highlight the importance of individual sub-basin integration into regional drainage to maintain supply from shallow marine source areas and avoid sediment starvation.