Abstract
AbstractStructurally controlled bathymetry in rifts has a significant influence on sediment routing pathways and depositional architecture of sediment gravity flow deposits. In contrast to rift segments characterized by crustal‐scale half‐grabens, the tectono‐stratigraphic evolution of deep‐water rift domains characterised by distributed faulting on narrow fault terraces has received little attention. We use 3D broadband seismic data, calibrated by boreholes, from the Lomre and Uer terraces in the northern North Sea rift to investigate Late Jurassic syn‐rift sediment gravity flow systems on fault‐terraced slopes. The sediment gravity flow fairways were sourced from hinterland drainages via basin margin deltaic systems on the Horda Platform to the southeast. The deep‐water sedimentary systems evolve from initial, widespread submarine channelized lobe complexes, through submarine channels, to incised submarine canyons. This progressive confinement of the sediment gravity flow system was concomitant with progressive localization of strain onto the main terrace‐bounding faults. Although the normal fault network on the terraces has local impact on deep‐water sediment transport and the architecture of gravity flow deposits, it is the regional basin margin to rift axis gradient that dominantly controls deep‐water sediment routing. Furthermore, the gravity flow deposits on the Lomre and Uer terraces were predominantly sourced by rift margin deltaic systems, not from erosion of local uplifted footwall crests, emphasising the significance of hinterland catchments in the development of volumetrically significant deep‐water syn‐rift depositional systems.
Highlights
The stratigraphic evolution of rift basins is closely linked to growing normal faults that control most of the surface topography during rifting (Cowie et al, 2005; Gawthorpe & Leeder, 2000)
We have summarized our observations from the Lomre and Uer terraces into a two-stage structural evolution model for syn-rift deep-water depositional systems on narrow fault terraced slopes
The gravity flow sediment routing follows the dominant regional slope gradient towards the deep rift axis graben and sediment is mostly sourced from basin-margin deltas or shelf edge failures (A and B; Figure 19a)
Summary
The stratigraphic evolution of rift basins is closely linked to growing normal faults that control most of the surface topography during rifting 35/11-5 , together with other north-w esterly wells (35/11-6 , 35/8-2 , 34/2-1; Figure 5), is dominated by high-g amma ray mudstone, and shows that low-gamma ray deposits occur in the central Lomre Terrace and the hanging wall of Kinna Fault (e.g. 35/8-2 , 35/11-6, 35/11-5) These deposits have informally been referred to as intra-Heather Formation sandstones (Koch et al, 2017; Zhong et al, 2020). The regional seismic surface displayed in the amplitude map (Figure 11d) intersects 35/11-2 strata on top of the overall fining-upward sequence and likely images the high-amplitude reflection caused by the impedance contrast between the mud-d ominated upper canyon fill against the gravity-flow sandstone strata of the lower canyon fill. SU1 thickens towards the N/NW and generally ranges from 0.1 to 0.2 s (TWT), and locally up to 0.3 s (TWT) in some N-to NE-trending, fault-bounded hanging wall depocenters on the northern
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