The evolution of catchment‐depositional system relationships on the dip slopes of intra‐rift basement highs: An example from the Frøya High, Mid‐Norwegian rifted margin

Abstract

Basement highs form one of many potential sediment source areas during the evolution of continental rifts and rifted margins and add to the topographic complexity typical of active rifts. Footwall basement highs acting as a source area to sedimentary systems in the hangingwall of major faults has been documented in many systems worldwide. However, the back-tilted footwall dip slopes of such highs have received comparatively little attention. Here we investigate a subsurface case study from the Norwegian continental shelf, where catchments and shallow marine syn-rift sedimentary systems on a dip slope are preserved due to early transgression of an intra-rift high. At the onset of Late Jurassic rifting, the Frøya High emerged as a prominent, N-S trending, 25 km wide basement high tilted towards the east in response to several kilometers of displacement along the Klakk Fault Complex, a major normal fault zone at the Frøya High's western edge. Using well-calibrated 3D seismic reflection data, we observe a series of conspicuous Upper Jurassic wedges along the eastern edge of the Frøya High along the margin of the Froan Basin. Internally, these wedges show sigmoidal geometries marking topand foresets of clinoform packages with a maximum thickness of ca. 200 meters with foresets between 30 -200 m high, dipping ca. 10 degrees towards the east, south east and north east. We interpret these wedges to represent a series of eastward prograding deltas positioned along a constructional shoreline, connected to E-W trending valleys and river catchments updip. The deltas show strong progradation, interpreted to reflect the impact of continued uplift of their catchments. prior to abrupt termination of sediment supply from drainage capture by footwall scarp drainages. The presence of a connected, largely constructional shoreline has implications for Late Jurassic sediment distribution around the Frøya High, providing primary sedimentary input for longshore driven sedimentary systems in the Draugen Ridge to the north. Comparisons with other syn-rift dip slope systems highlights a broadly similar evolution but shows a distinct lack of the protracted backstepping observed in other dip slope systems. We postulate that different structural configurations of dip slope systems, being footwall uplift, Preprint / Henstra et al. 2023 / The evolution of catchment-depositional system relationships on the dip slopes of intra-rift basement highs 2 or hangingwall subsidence driven, may drive the strongly progradational character of the deltaic systems on the Frøya High. The Frøya High example highlights the need to constrain primary sediment input points to aid interpretation of volumetrically significant, but short-lived and subtle depositional systems, especially within complex, tectonically active settings.

Late Jurassic rift physiography of the Froan Basin and Frøya High, offshore Mid‐Norway: Development of a syn‐rift shallow marine system

“…6407/9‐1), southwest of the Draugen Field area in well 6407/11‐1 and on the central Frøya High in wells 6306/6‐1 and 6306/9‐1 (Figure 1b). Early depositional models for the Rogn Formation from the Draugen Field area, and more recent studies of the Vingleia and Klakk fault complex, support the rift physiography shown herein, with sediment being eroded from the uplifted areas and transported back onto the footwall, down the gently dipping dipslope (Bell et al, 2014; Chiarella et al, 2020; Elliott et al, 2017, 2021; Goesten & Nelson, 1992; Gresseth et al, 2023; Henstra et al, 2023; Jones et al, 2020; Muñoz‐Barrera et al, 2021; Provan, 1992; Van der Zwan, 1990). In comparison, the Rogn Formation recorded on the Frøya High has received less attention but has been interpreted to be connected along the strike of the footwall island to age‐equivalent deposits in the Draugen Field area (Chiarella et al, 2020; Henstra et al, 2023).…”

“…Seemingly isolated sandbodies of the Rogn Formation are presently identified locally in wells drilled in these uplifted areas (i.e. on the Frøya High and in the immediate footwall of the Vingleia Fault Complex; e.g, wells 6306/6‐1 and 6407/9‐1; Chiarella et al, 2020; Dalland et al, 1988; Elliott et al, 2017; Henstra et al, 2023; Provan, 1992). In the study area, the sandstone‐rich Rogn Formation typically forms coarsening‐upward, heavily bioturbated units, interpreted to be deposited in a shoreface to the offshore‐bar environment (Chiarella et al, 2020; Elliott et al, 2017; Henstra et al, 2023; Provan, 1992; Van der Zwan, 1990); however, the more regional distribution of this enigmatic unit remains poorly constrained, due to limited good coverage, seismic resolution and few regional studies (e.g.…”

“…As such, only relatively small, localised drainage systems and fault‐scarp degradation complexes formed in its footwall, supplying sediment westwards to the Halten Terrace (Elliott et al, 2012, 2021). In contrast, further southwards, major uplift occurred in the footwall of the Vingleia and Klakk fault complexes, resulting in the formation of an intra‐rift footwall island (Bell et al, 2014; Elliott et al, 2017, 2021; Gresseth et al, 2023; Henstra et al, 2023; Jones et al, 2020; Muñoz‐Barrera et al, 2020, 2021). As a result, major rift‐related unconformities developed in this region (i.e.…”

“…During the rift episode, most areas on the Trøndelag Platform, and basins west of the platform (e.g. Halten Terrace), were subsiding, whereas seismic and well data indicate that large portions of the Frøya High and the western margin of the central Froan Basin experienced a phase of subaerial exposure, flanked by submerged areas characterised by relatively shallow (<100 m) water depths (Figure 1b; Bell et al, 2014; Chiarella et al, 2020; Elliott et al, 2017, 2021; Henstra et al, 2023). Seemingly isolated sandbodies of the Rogn Formation are presently identified locally in wells drilled in these uplifted areas (i.e.…”

“…The formation is an example of a footwall-sourced syn-rift depositional system that developed on the back-tilted footwall of a major normal fault system, providing a rare record of tectonically controlled sediment supply and accommodation generation. Previous studies of Upper Jurassic syn-rift deposits on the Trøndelag Platform have been based on seismicstratigraphic, sedimentological, and biostratigraphic analysis (Chiarella et al, 2020;Elliott et al, 2017Elliott et al, , 2021Henstra et al, 2023;Provan, 1992;Van der Zwan, 1990). In these studies, a shallow marine interpretation for the Rogn Formation is inferred based on seismic and borehole data.…”