Footwall geomorphology during necking domain evolution: A new model for the Frøya High, mid‐Norwegian rifted margin

Observations and modelling results from highly extended regions indicate that detachment fault systems recording displacements of 10 km or more become associated with footwall uplift and back‐rotation. This is commonly explained by the rolling hinge model, which predicts detachment fault back‐rotation and severe dip reduction (<20°) controlled by the amount of extension. Although detachment faults within necking domains at rifted margins often record displacements in orders consistent with those for the rolling hinge model, it is rarely invoked to explain the associated footwall configurations. Our study area encircles the necking domain of the mid‐Norwegian rifted margin, where the Middle Jurassic–Early Cretaceous Klakk Fault Complex (KFC) directly separates the Frøya High from the Rås Basin. The Frøya High represents the eroded footwall of the KFC detachment fault system which records displacements of 20–40 km. Seismic mapping and well correlation across the Frøya High reveal how three erosional unconformities correspond to three laterally extensive top basement segments which follow the strike of the sinuous KFC. The segments differ in terms of dip, basement geomorphology and the composition and age of the sediments that rest unconformably on the top of basement. We attribute the associated cross‐cutting basement unconformities across the Frøya High to footwall uplift and back‐rotation during fluctuating relative sea‐level and repeated subaerial exposure during Middle Jurassic–Early Cretaceous times. We herein introduce a revised tectono‐sedimentary model for the evolution of the Frøya High, with significant implications for sediment (re‐)routing across the high during rifting. The model indicates that spatio‐temporal sediment distribution was ultimately controlled by the process of necking and evolution of the KFC. Our findings indicate a rolling hinge‐type evolution for the KFC and further suggest that the associated mechanisms may be more common in the necking domains of rifted margins than previously assumed.

Displacements on large normal faults have long been recognized to induce significant footwall rebound due to tectonic unloading (Axen & Bartley, 1997;King & Ellis, 1990). Footwall uplifts range from amplitudes of a few to hundreds of meters in rift-flank uplifts (e.g. Gawthorpe & Leeder, 2000) to exhumation of tens of kilometres of mid-crustal rocks in metamorphic core complexes bound by detachment faults (e.g. Axen & Bartley, 1997;Mizera et al., 2019;Spencer, 1984;Wernicke & Axen, 1988). The latter case is often ascribed to the process of a 'rolling hinge model', where the locus of incremental uplift migrates through the footwall as displacement increases, causing uplift and back-rotation of the detachment and its footwall (Axen & Bartley, 1997;Brun et al., 2018;Buck, 1988;Escartín et al., 2017;Lavier et al., 1999;Little et al., 2019;Mizera et al., 2019;Olive et al., 2019;Spencer, 1984;Wernicke & Axen, 1988). Virtually all published numerical and analogue models of rolling hinges are produced and presented in 2D (Axen & Bartley, 1997;Brun et al., 2018;Lavier et al., 1999). These models show how the amount of footwall back-rotation is incremental with increasing displacement (e.g. Lavier et al., 1999) and it follows that along strike, going from two to three dimensions, the effect of the rolling hinge will decrease away from the area of maximum displacement (Gresseth et al., 2023;Kapp et al., 2008;Osmundsen & Péron-Pinvidic, 2018). This implicitly motivates increased sinuosity of detachment faults, as they become affected by varying isostatic response along strike and eventually by deformation of the detachment across an antiformal dome (Gresseth et al., 2023;Kapp et al., 2008). Sinusoidal detachment faults enveloping hyperbolic metamorphic core complexes in their footwalls are recognized world-wide in extensional settings, both in the continental realm, for example, Basin & Range, western US (Wernicke & Axen, 1988) and along oceanic spreading ridges, for example, North Atlantic (Escartín et al., 2017). Metamorphic core complexes are typically exhumed in the footwall of large-scale detachments recording tens of kilometres of displacement (Whitney et al., 2013). Such large-scale detachment systems are also a defining feature of necking breakaway complexes within rifted margins (Osmundsen & Péron-Pinvidic, 2018; Figure 1).
Necking breakaway complexes are associated with relatively large amounts of footwall uplift (Osmundsen & Péron-Pinvidic, 2018). With fluctuating relative sea-level, the footwall may be prone to alterations between subaerial and submarine exposure and, potentially, the formation of incising erosional surfaces such as wave-cut platforms. Implicitly, the preservation potential for footwalls in necking domains may be significantly lower compared to the footwalls of oceanic detachments and may in some cases also be lower than for intercontinental detachment fault systems, depending on the variability in the strength of exposed lithologies, tectonic deformation rates and climatic conditions (Olive et al., 2022). The establishment of the mid-Norwegian rifted margin is associated with the opening of the Atlantic Ocean Fossen, 2010;Péron-Pinvidic et al., 2013). The Atlantic rift and associated seaway reached the mid-Norwegian margin during Early Jurassic , and both local and regional domes and uplifts developed during Early to Middle Jurassic (Brekke et al., 2001). Consequently, the mid-Norwegian margin's necking domain was influenced by fluctuating relative sea-levels during its establishment, ultimately affecting, and modifying established hinterlands and depocentres locally (Bell et al., 2014;Brekke et al., 2001).
The KFC along the Frøya High exhibits a combined inner and outer necking breakaway complex, representing both the first fault on the margin showing significant thinning and associated footwall uplift (inner), and the first coupling fault cutting both upper and lower crust, likely reaching the upper mantle (outer; Osmundsen & Péron-Pinvidic, 2018). West of the Frøya High, the KFC accommodated nearly all necking domain strain during the stress associated with Middle Jurassic-Early Cretaceous rifting (Gresseth et al., 2023), in contrast to other large faults to the north, for example, Vingleia, Bremstein and Ytreholmen Fault Complexes, as well as along the northern continuation of KFC bounding the Sklinna Ridge ( Figure 1). The Frøya High has previously been suggested to represent a pivot structure imperative for local geodynamic evolution (Péron-Pinvidic, Åkermoen, et al., 2022). The Frøya High has been interpreted to represent a metamorphic core complex (Muñoz-Barrera et al., 2020), where the central parts of the high represent an eroded turtleback structure (Figure 1; Gresseth et al., 2023). For this study, we investigate the temporal evolution of footwall uplift, subsequent erosion and associated sedimentary response in a necking domain, represented by the Frøya High and the KFC. We suggest that the footwall geometry was severely modified by erosion due to relative sea-level fluctuations, and that its present configuration reflects discrete periods of syn-rift rotation and erosion followed by post-tectonic rotation and burial. We propose that our model is of relevance for local geodynamic modelling as we identify candidates for extension discrepancies along the KFC. Also, our model suggests new scenarios for sediment age and distribution across the high during the Middle Jurassic-Early Cretaceous. As the most prolific reservoir rocks within the Norwegian Sea shallow water domain are Jurassic sandstones , this study is likely of significant relevance for future hydrocarbon exploration within the area. On a more general level, our revised evolutionary model for the Frøya High may prove significantly relevant for tectono-stratigraphic schemes for detachment fault systems world-wide.
The stretching phase involved mild rifting in the mid-Carboniferous and more extensive rifting during the Permian-Lower Triassic (Blystad et al., 1995;Bunkholt et al., 2021;Faleide et al., 2008). This phase largely established the margin's proximal domain, creating NNE and NE striking extensional basins, for example, the Froan Basin Osmundsen et al., 2021). The following thinning phase involved a seaward focusing of deformation to the areas west of the present Trøndelag Platform including the Halten Terrace, Slørebotn Subbasin and the Rås and Traena basins (Figure 1). Mild rifting during the Early Jurassic was followed by major rifting during Middle to Late Jurassic times. Large-magnitude (detachment) fault systems were established during this phase, for example, the Bremstein and Vingleia, Klakk and Ytreholmen fault complexes (Bell et al., 2014;Blystad et al., 1995;Bunkholt et al., 2021;Osmundsen & Péron-Pinvidic, 2018;Péron-Pinvidic, Åkermoen, et al., 2022). Out of these, the former two represent the inner whilst the latter two represent the outer necking breakaway complexes according to the definition of Osmundsen and Péron-Pinvidic (2018). Notably, the KFC represents a combined inner and outer necking breakaway complex south of the Halten Terrace along the corridor where it directly separates the Frøya High from the Rås Basin (Gresseth et al., 2023;Osmundsen & Péron-Pinvidic, 2018;Péron-Pinvidic, Åkermoen, et al., 2022; Figure 1). The thinning phase is also associated with the establishment of the taper break (Osmundsen & Redfield, 2011), where the outer necking breakaway complex cuts middle to lower crust, effectively thinning it to a thickness of 10 km or less. The faults in the outer necking breakaway complex thus effectively separate the necking and distal domains of the margin (Osmundsen & Péron-Pinvidic, 2018;Osmundsen & Redfield, 2011). A major rift event during the earliest Cretaceous marks the onset of the third rifting phase; the hyperextension-exhumation phase in which deformation largely focused in the margin's distal domain (Osmundsen & Péron-Pinvidic, 2018). Mild rifting also occurred during the mid-Cretaceous (Bell et al., 2014;Blystad et al., 1995;Zastrozhnov et al., 2020). Rifting created hyperextended crust and sag basins, likely associated with mantle serpentinization and, possibly, mantle exhumation under parts of the Rås Basin (Osmundsen & Péron-Pinvidic, 2018;Péron-Pinvidic et al., 2013;Zastrozhnov et al., 2020). Postrift thermal subsidence also affected the region during the mid-Cretaceous, subjecting it to incipient down-to-the-west tilting Lien, 2005). Oceanization and break-up occurred during early Cenozoic time producing the Møre and Vøring marginal highs prior to continental break-up in earliest Eocene and subsequent continental drift (Faleide et al., 2008;Zastrozhnov et al., 2020).

| Main structural features
Our study area on the mid-Norwegian rifted margin is located where the west dipping KFC separates the Frøya High in its footwall from the Rås Basin in its hangingwall ( Figure 1). Within the study area, displacements in the order of 20-40 km have been mapped out along the ca. 120-km-long KFC, which is defined as late Middle Jurassic-Early Cretaceous in age (Blystad et al., 1995;Muñoz-Barrera et al., 2020).
The Frøya High constitutes the footwall of the KFC where it directly separates the high from the Rås Basin. Further north, the KFC separates the Sklinna Ridge from the Rås Basin ( Figure 1). The northern spur of the Frøya High is separated from the Halten Terrace by the late Middle Jurassic-Early Cretaceous Vingleia Fault Complex. The eastern extent of the northern spur of the Frøya High is defined by the Permo-Triassic Frøya fault (following the nomenclature of Bunkholt et al. (2021)), which separates it from the Froan Basin. Displacement along the Frøya fault decreases southward, before it dies out and the Frøya High to Froan Basin transition is associated with the presence of highly rotated, truncated strata of the Froan Basin stratigraphy.
The NNE-trending Froan Basin was established during the structuring of the margin's proximal domain (Blystad et al., 1995;Bunkholt et al., 2021;Osmundsen et al., 2021). In its northern part, the Froan Basin represents a downto-the west supradetachment basin. The eastern boundary of the basin and the associated detachment fault likely represent the offshore continuation of a Devonian strikeslip fault and detachment zone, reactivated during Permo-Triassic rifting (Osmundsen et al., 2021). Southwards, the basin shifts polarity as the down-to-the east Frøya fault delimits the basin from the Frøya High. In this area, the Frøya fault shows signs of activity from the Permian until the Middle Jurassic ).

| Stratigraphic framework
The stratigraphic framework for our study area is outlined in Figure 2. Several hundred meters thick sedimentary successions were deposited across the Halten Terrace, Frøya High, Froan Basin and Slørebotn Subbasin during the Triassic (Dalland et al., 1988;Jongepier et al., 1996;Osmundsen et al., 2021;Richardson et al., 2005). Whilst the Triassic sediment record in the Slørebotn Subbasin consists mainly of clastic deposits (Jongepier et al., 1996), marine flooding from the north in the Ladinian caused evaporite deposition in local depocentres across the Halten and Dønna terraces . The associated Ladinian unconformity (LaU) can be observed across the northern spur of the Frøya High where significant volumes of uplifted and rotated strata are eroded as interpreted on seismic data  Figure 2).
Late Triassic-Middle Jurassic stratigraphy is dominated by alternating fluvio-lacustrine to paralic-to-shallow marine sandstones and mudstone deposits of the Båt and Fangst groups Dalland et al., 1988). The Atlantic rift reached the area in the Late Pliensbachian-Early Toarcian, causing significant fault-block rotation and intrabasin Toarcian erosion (ToU; Bunkholt et al., 2021; Figure 2). Sea-level rise and, consequently, drowning of the Halten Terrace during the Late Jurassic was associated with deposition of the deep-marine, mudstone-dominated Melke and Spekk formations. During the Callovian-Oxfordian, deep erosion was initiated along uplifted escarpments of large fault complexes and the Frøya High, Sklinna Ridge and partly the Nordland Ridge experienced peneplanation (Bell et al., 2014;Bunkholt et al., 2021). As such, the most prominent basement highs (e.g. the Frøya High) likely remained subaerial during the Middle and Late Jurassic and represented sources of clastic material as evidenced by, for example, the Intra Melke and Rogn sandstone formations (NPD, 2022e). These sand-rich, shallow marine systems are associated with several phases of erosion during Middle-Late Jurassic times, the most prominent being the Intra Melke unconformity (IMU; Figure 2). They are constrained in several wells across the Frøya High, both in the immediate footwall of the VFC (Rogn Formation; 6406/12-4S), further south in the immediate footwall of the KFC (Intra Melke Formation sandstones; 6306/5-2) and in the central part of the Frøya High (Rogn Formation; 6306/9-1; NPD, 2022e; Figure 3).
The regional and seismically prominent Tithonian-Berriasian Base Cretaceous Unconformity (BCU) marks the transition from Jurassic to Cretaceous sedimentation. The overlying Cromer Knoll and Shetland groups, primarily composed of claystones interbedded with thin carbonate and sandstone stringers, were deposited in a deep marine environment (Dalland et al., 1988; Figure 2). The Base Cenomanian Unconformity (BCenU) separates the Cromer Knoll and Shetland groups, as a result of regional tilting during Early Cretaceous times . Whilst the Lyr Formation onlaps the KFC footwall scarp, the Lange Formation onlaps the BCU on the Frøya High. The transition between the Shetland and the overlying Rogaland Group is marked by the regional Base Palaeocene Unconformity (BPalU; Bunkholt et al., 2021). Claystones with thin siltstone beds largely make up the Rogaland Group, which also includes tuffs within the Tare Formation (Dalland et al., 1988). Both the overlying Hordaland and Nordland groups are largely composed of claystones with interbedded silt and sandstone, where the latter is more dominant in the Nordland Group (Dalland et al., 1988; Figure 2).
In the southernmost part of the Rås Basin, where the KFC separates the basin from the Frøya High in its footwall, Muñoz-Barrera et al. (2022) performed a qualitative study on the undrilled hangingwall sedimentary deposits. The study revealed three mega-sequences of inferred pre-Middle Jurassic (pre-tectonic), Middle Jurassic to earliest Cretaceous (syn-tectonic) and Early Cretaceous (post-tectonic) ages. More recently, the basin has been correlated northwards, effectively connecting the basin segments flanking the Frøya High into a major supradetachment basin roughly following the outline of where the KFC constrains the Frøya High (Gresseth et al., 2023).

| Seismic data
For this study, seismic interpretation was performed using the Schlumberger Petrel 2020® software on a suite of regional and local 2D and three 3D seismic surveys ( Figure 1). All seismic data are in the public domain, and accessible via the Norwegian Petroleum Directorate in their DISKOS database. The different seismic surveys record depths varying from 5 to 12 s TWT (seconds twoway time). Further information about subsurface datasets can be found in Supporting Information. We display the seismic reflection data, processed to zero-phase, according to the Society of Exploration Geophysicists (SEG) reverse polarity convention: increases (peaks) and decreases (troughs) in acoustic impedance are displayed in blue and brown respectively. Additionally, we display the timestructure map for the top basement horizon as a frequencyprocessed RGB-blend map. The frequency spectral decomposition volume used for this work was produced by Dr. Israel Polonio at AkerBP ASA using the Geoteric® software. Frequency spectral decomposition volumes are generated by transforming seismic data from the time domain to the frequency domain and then creating a volume of the amplitude at each frequency. Extracting frequency information within this volume at levels corresponding to the interpreted top basement surface facilitated investigation of frequency variations in the seismic data, which in turn can reflect variations in impedance, thickness and tuning effects. Specific frequency channels correspond to red, green and blue colour schemes honoured and displayed in the filtered RGB-blend maps (McArdle, 2013). The resultant maps are courtesy of AkerBP ASA. F I G U R E 2 Stratigraphic column for the mid-Norwegian margin, modified after Dalland et al. (1988), Bell et al. (2014) and Bunkholt et al. (2021). Notice how the Middle to Late Jurassic IMU is associated with several local also smaller unconformities producing sandstone stringers at different intervals; Callovian-Oxfordian, Oxfordian-Kimmeridgian and Tithonian prior to the regionally extensive BCU . 'Global sea-level estimate' represents a smoothed version of the Haq et al. (1987) eustatic sea level, retrieved from Bell et al. (2014). Local sea-level basins provide an estimate of relative sea-level in the Halten Terrace and Rås basins determined from sedimentary facies information, and an estimate for sea level in the vicinity of the Frøya High. Numbered circles indicate the following constraints from Bell et al. (2014); (1) the Froan Basin must be in shallow water depths in the Kimmeridgian, and (2) the Sklinna Ridge must be submarine by the Turonian-Coniacian. BCenU: Base Cenomanian unconformity; BCU, Base Cretaceous unconformity; BPalU, Base Palaeocene unconformity; IMU, Intra Melke unconformity; LaU, Ladinian unconformity; ToU, Toarcian unconformity.

| Well data
Various data from a total of eight exploration wells within and adjacent to the study area are incorporated in this study. The admissible well data vary both in amount of information and detail, as some of the wells are recently drilled and not all data nor analyses have yet been made public (Table 1). Available and relevant data from six key wells across the study area are correlated and summarized in Figure 3. Where not specified otherwise, petrophysical data and formation tops are retrieved via the NPD (2022e).

| Footwall constraints
This study covers the northern structural recess and central footwall segment of the KFC and Frøya High detachment fault system as outlined in Gresseth et al. (2023; see also Gresseth et al., 2022;Muñoz-Barrera et al., 2020Figures 1 and 4). Within the study area, the Frøya High forms the partly degraded footwall of the KFC, which separates it from the Rås Basin to the west (Figures 4 and 5). To the east, the Frøya High is bordered by the southernmost part of the

| Footwall geomorphology
The geomorphology of the top basement surface across the Frøya High exhibits two main transverse ridges that are semi-parallel to the KFC and traceable throughout the study area ( Figure 4). The transverse ridges are observed as knick-points on seismic cross sections ( Figure 5), and effectively outline three top basement segments, A, B and C respectively ( Figure 4). The difference in dip angle between the surfaces is notably observed on seismic data in the time domain, and their detailed geometries might be slightly affected by depth conversion. Osmundsen and Ebbing (2008) provided average velocities strata for the mid-Norwegian rifted margin terrace domain; Cenozoic: 1.8-2.4 km/s, Upper Cretaceous: 2.4-3.2 km/s and Lower Cretaceous: 2.8-3.2 km/s. The top basement surface of the Frøya High is located at relatively shallow depths, that is, ~1.5-2.5 s TWT. It is therefore reasonable to presume that depth-conversion would not yield drastic changes to the contrasting dip-angles of the Frøya High top basement. More importantly, there are no observable variations in sedimentary facies and associated overburden velocities which correspond to and can account for the laterally traceable knick-points across the high ( Figures 5 and 7). Also, the knick-points are clearly preserved on published depth-converted seismic sections across the high (Muñoz-Barrera et al., 2020). We, therefore, presume that depth conversion would yield other dip angle values for each basement segment, but that the relative changes in dip would be preserved. The different basement segments also correspond to different frequency responses across the top basement surface ( Figure 6). Whilst Figure 4 presents the geometrical variations, the RGB-blend maps displayed in Figure 6 further exhibit variations in the frequency signature of the seismic signal corresponding to locations mapped out using conventional seismic interpretation workflows.
Several wells across the study area reveal significant variations in descriptions of the pre-Cretaceous sandy units that variably rest on the top basement surface. More importantly, these variations correlate to specific basement segments, suggesting that each segment can be associated with a specific chrono-and lithostratigraphy that differs from the neighbouring basement segment.

| Basement segment A
Basement segment A (BsA) on average dips ENE, with a gradually increasing TWT dip angle from south to north (Figure 4). The BsA corresponds to the base of the Froan T A B L E 1 Summary of incorporated well data within and adjacent to the study area.

| Basement segment B
Basement segment B exhibits a lower average dip angle relative to both BsA and Basement segment C (BsC; Figure 4d), whilst the dip azimuth changes polarity from ENE across BsA to WNW on BsB (Figure 4c). Timestructure maps based on interpretations of tightly spaced 2D seismic reflection lines display how BsB consists of less tightly spaced, wider channels relative to BsC ( Figure 6). Further, interpreted sediment transport directions across BsB vary (Figures 6 and 7).

| Overburden stratigraphy
All wells drilled within Basement segment B encountered the Late Jurassic Rogn Formation; 6306/9-1, 6306/3-2 and 6306/3-1S. 6306/9-1 encountered 152 m of sandstone of which 73 m are inferred to represent the Rogn Formation. Below the Rogn Formation, sandstones of unknown age were encountered (NPD, 2022b). 6306/3-2 and 6306/3-1S also reportedly encountered 40 and 27 m of the Rogn Formation sandstones respectively (NPD, 2022c(NPD, , 2022d. Although 6306/6-1 is located just east of the transition between BsB and BsA (Figure 3), the well offers stratigraphic control for the strata directly above top basement within BsB. East of the central footwall salient, an eastward prograding delta-deposit of late Middle-Late Jurassic age can be observed on seismic sections (Figure 7). This represents a strong contrast in terms of depositional environment to the BsC, which is dominated by a westward directed canyon and channel sedimentary distribution system observed on the top basement surface, and reported from well 6306/6-2 (Rogn Fm; NPD, 2022a; Figures 6 and 7).
Well 6306/3-2 drilled the distal part of a channel system with sediment transport direction towards the east, targeting an Upper Jurassic sandstone reservoir (NPD, 2022d; Figure 6). Well 6306/3-1S, on the other hand, drilled a canyon system with a similar target, but notably with a sediment transport direction towards the NNW (NPD, 2022c; Figure 6). Conversely, Formation Micro-Imager (FMI) logs from well data across the lower Rogn section in 6306/9-1 suggest eastward dipping bedsets supporting interpretation of eastward sediment transport for a suite of sandstones associated with the Viking Gp (S. Thomas, personal communication, October 26, 2022). This aligns with the interpretations of Henstra et al. (2023), defining three eastward prograding Upper Jurassic deltas within BsB, east of the central salient. All three mentioned wells encountered the Rogn Fm above top basement, indicating varying sediment transport directions for the Upper Jurassic channel system across the BsB. These observations can either indicate local elevation differences during deposition of Upper Jurassic strata, or a change in landscape tilt during late Middle-Late Jurassic times.

| Basement segment C
The westernmost BsC is located closest to the KFC and dips WNW, with an overall relatively higher dip angle than the neighbouring BsB (Figure 4). The areal extent of BsC follows the trend of the KFC and is identifiable on both the central footwall salient and in the footwall of the northern structural recess (Figure 4). The basement terrain is eroded, and distinct canyons define the top basement landscape ( Figure 6). Most canyons are V-shaped and westward sediment transport is indicated as canyon-widths increase eastward. Some of the canyons also consist of two or more canyons linking up in their distal parts ( Figure 6).

| Overburden stratigraphy
6306/6-2 is drilled within BsC (e.g. Figure 4). According to NPD (2022a), the well encountered a unit expected to be the Rogn Formation above top basement. The Rogn Formation is described in its type-well 6407/9-1 as a coarsening upwards sandstone unit, with smaller amounts of siltstones and shales at its base (NPD, 2022e). In well 6306/6-2 however, the encountered Rogn Formation is described as atypical, as it consists of "extremely calcite cemented, arkosic sandstone grading to limestone, quite different from the normal Rogn Formation" (NPD, 2022a). Instead, calcilithic hybrid arenites interbedded with thin stringers of arkosic sandstone, rest unconformably on top basement (Chawshin, 2011).
Basement segment C is onlapped by late Early Cretaceous strata, of which the well-tied (wells 6306/5-2 and 6306/6-2) seismic reflector associated with the Lysing Formation onlaps the BsC east of 6306/6-2 ( Figure 5). In terms of known regional unconformities, the reported presence of the Viking Gp infers the presence of both the IMU and the BCU within BsC ( Figure 5). However, on seismic reflection data, top channel infill within BsC is not associated with a prominent seismic reflector presenting a candidate for BCU-associated shales (Figure 7e). This makes it difficult to distinguish BsC channel infill, which is Late Jurassic in age according to 6306/6-2 (NPD, 2022a), from the overlying miscellaneous Early Cretaceous sediments (Figure 7).

| Basement segment A
Based on the well-constrained ages for the basement segments A-C, it is evident that the BsA preserves the oldest sedimentary strata within the study area (e.g. Figure 3). The transverse ridge separating the BsA from the BsB follows the strike of the Frøya fault but continues several kilometres south of where the Frøya fault dies out (Figure 4). We interpret the transverse ridge between BsA and BsB to represent a combined response to the continued increasing displacement and reactivation of the Frøya fault further north from Permo-Triassic to Middle Jurassic times, and continued basin subsidence in the Froan Basin area . The eldest sedimentary strata rest tabular to the top basement within the Froan Basin in the non-fault-controlled transition between the basin and the Frøya High ( Figure 5).
As the eldest stratigraphy above top basement within BsA is represented by the Triassic Red Beds (well 6703/1-1S), we suggest a Late Permian-Early Triassic age for the top basement landscape, possibly partly eroded by the Ladinian unconformity (LaU in Figures 2 and 5). This is consistent with the onset of fault activity during the Permian and continued reactivation and growth of the Frøya fault during Middle Triassic (Ladinian) times Figure 5). Semi-regional deposition of Upper Red Bed conglomerates and evaporites in the deeper basins occurred during this phase (Blystad et al., 1995;Bunkholt et al., 2021;Jongepier et al., 1996;Osmundsen et al., 2021). Also, according to Bell et al. (2014), basins to the west on the Halten Terrace remained shallow marine during this period, and local structural highs such as the Frøya High experienced subaerial exposure (Figure 2).

| Basement segment B
The BsB preserves younger stratigraphy of Middle-Late Jurassic ages directly above top basement, indicating a younger age for the erosional surface, relative to BsA. It follows that this involves either non-deposition or deposition and later erosion of Triassic strata on the BsB. The well-tied Intra Melke Formation sandstones (IMU) indicate that renewed erosion of the Frøya High basement terrain across BsB occurred during Callovian-Oxfordian times ( Figure 5). This period also coincides with a period of large-scale rifting and displacement along the KFC (Blystad et al., 1995;Bunkholt et al., 2021;Muñoz-Barrera et al., 2022), and a relative sealevel rise starting in the Early Jurassic (Figure 2). According to Bell et al. (2014), parts of the Frøya High likely remained subaerially exposed throughout this period, indicating that continental channel erosion took place in a semi-arid to humid environment, as the Norwegian Sea was located at approximately 55° N by Middle Jurassic times (Johannessen & Nøttvedt, 2008a). Middle Jurassic sediments (i.e. Intra Melke Fm sandstones) are also deposited in the hangingwall basin in the northern structural recess of the Frøya High (well 6306/5-2; Figure 5). Biostratigraphic data indicate that erosion involved reworking of older deposits as Devonian, Carboniferous and Permian spores were present in well 6306/5-2 (PL 936 Relinquishment Report, 2022; Figures 4 and 5). Within the BsB, both 6306/9-1 and 6306/3-2 wells report sandstones of unknown ages below the Upper Jurassic Rogn Formation (NPD, 2022d, 2022b). We find this indicative of an erosional landscape development during Callovian-Oxfordian times, corresponding to the IMU (Figure 2). The IMU landscape possibly cannibalized and locally eroded a precursing erosional landscape established during Toarcian-Pliensbachian times. Both suggested erosional periods coincided with known extensional events affecting the region (Figure 2), whilst only the Callovian-Oxfordian rift phase with a rift initiation stage during Bajocian-Bathonian has previously been suggested to affect the KFC (Muñoz- Barrera et al., 2022).
Despite several wells drilled in recent years, the age of the BsB erosional landscape remains ambiguous. The angular unconformity separating Lower from Upper Jurassic strata in the Mandel basin (informal name) has been suggested to be of Kimmeridgian age (PL 998 Relinquishment Report, 2020), which post-dates the onset of the IMU in the Callovian-Oxfordian (e.g. Bunkholt et al., 2021). Also, lowrelief structures west of the Mandel basin have previously been suggested to represent local palaeo-islands along the KFC fault scarp as a result of footwall uplift during Early Cretaceous, yielding shoreface sandstone deposits simultaneously with deposition of Lower Cretaceous shales as reported in 6306/6-1 (PL 998 Relinquishment Report, 2020). In summary, recent observations and reports cannot exclude the possibility that the onset of the IMU formation in the Callovian-Oxfordian might have overprinted a precursing erosional landscape developing during the Pliensbachian-Toarcian, nor that the IMU also locally reflects younger (Kimmeridgian) erosion.

| Basement segment C
The 'untraditional' sandstones of the Rogn Formation encountered in well 6306/6-2 were reportedly arkosic, extremely calcite cemented and graded into limestone (NPD, 2022a). Limestone sequences are not described from the pre-Cretaceous sediments overlying top basement within BsB. In terms of depositional environment, deposition of carbonates and marls is more typical for the Lower Cretaceous sediments in the region, deposited during a relative sea-level rise (Bell et al., 2014;Bunkholt et al., 2021). Recently published reports compositionally link the encountered 'Rogn Fm' in 6306/6-2 to underlying granitic basement (PL 936 Relinquishment Report, 2022). Chawshin (2011) suggested, based on qualitative petrographic and well log data analyses that the calcilithic hybrid arenites directly above top basement in the same well represented reworked sediments deposited in a highenergy shallow marine shelf environment. We find this to indicate that the rocks previously correlated with the Rogn Formation encountered on the BsC were (re-)deposited during Early Cretaceous times rather than in the Late Jurassic. This is consistent with the reported 'Jurassic-Cretaceous age' for marine cementation of the Rogn Fm in well 6306/6-2 (PL 936 Relinquishment Report, 2022).
The interpreted differential ages for BsA-BsC as outlined above introduce an alternative interpretation of the seismic stratigraphy across the Frøya High, strongly challenging previous consensus. The most significant finding is an Early Cretaceous age for the BsC, effectively discarding that the top basement landscape within BsC represents the Late Jurassic IMU as presented in previous publications (Muñoz-Barrera et al., 2020; NPD, 2022a; Trice et al., 2019), but rather suggesting that it might represent younger basement erosion. Implicitly, this allows for an interpretation that the channel systems within BsC (Figure 7) are filled by erosional products and reworked sediments of possibly Lower Cretaceous strata (i.e. possible equivalents to the Lyr and/or Lange Formation sandstones).

| DISCUSSION
Uplift of footwall culminations involving exhumation of middle to lower crust in detachment systems along rifted margins has been interpreted on seismic data and reported elsewhere, for example, the Iberian margin (Péron-Pinvidic et al., 2013;Sutra & Manatschal, 2012), on the west coast of Angola (Unternehr et al., 2010), on the Alpine Thetys margin (Masini et al., 2013;Mohn et al., 2010Mohn et al., , 2012Ribes et al., 2020) and in Papua New Guinea Mizera et al., 2019). These studies underline how the processes controlling significant footwall uplift in detachment fault systems, as vigorously reported from and studied in large-scale continental rifts (e.g. Basin & Range, US, e.g. Axen & Bartley, 1997;King & Ellis, 1990;Spencer, 1984;Wernicke & Axen, 1988), are applicable to detachment fault systems along rifted margins (Chenin et al., 2015;Manatschal, 2004;Mohn et al., 2012;Osmundsen & Péron-Pinvidic, 2018;Péron-Pinvidic et al., 2013Ribes et al., 2020). Ideally, detachment fault systems will experience the greatest magnitudes of fault displacement, and consequently footwall exhumation, in the central segment of the fault system, resulting in a sinusoidal fault trace (Gresseth et al., 2023;Kapp et al., 2008;Osmundsen & Péron-Pinvidic, 2018). Consequently, this area of maximum displacement corresponds to the highest elevation of local footwall topography, which experiences increased sensitivity to base-level drops and erosion. This will also correspond to the area most inclined to record the highest extension discrepancy along-strike (Reston, 2009). The term is a typical trait of highly extended regions and relates to how the amount of extension estimated from fault geometries using seismic reflection data tends to be insufficient to explain the observed crustal thinning and subsidence (McDermott & Reston, 2015;Reston, 2009). Footwall erosion or detachment fault rotation to lower angles will effectively mask the crustal cut-off level typically used to estimate amounts of displacement along the fault-plane between footwall and hangingwall. Along rifted margins specifically, the interplay between detachment system footwall exhumation and erosion has been proven to control the tectono-sedimentary evolution in both the distal (Masini et al., 2013 andnecking (Ribes et al., 2020) domains, both in offshore seismic and onshore field work studies.
Rifting within the necking domain of the mid-Norwegian rifted margin occurred episodically during Middle Jurassic-Early Cretaceous times (Figure 2; e.g. Bell et al., 2014;Bunkholt et al., 2021;Dalland et al., 1988;Gresseth et al., 2023;Muñoz-Barrera et al., 2020). Within our study area, this involved partly reactivating older (e.g. Muñoz-Barrera et al., 2020), and partly generating new fault splays along the KFC (Gresseth et al., 2023). It stands to reason that documented repeated activity along the KFC likely caused continued footwall uplift during the lifespan of the fault complex. In the following, we discuss footwall configuration and associated tectono-sedimentary distribution on and adjacent to the Frøya High, considering the differential top basement segments as outlined in this study.

| Necking domain erosion
The necking domain along rifted margins is established during the thinning phase, which follows the establishment of the proximal domain during the stretching phase (e.g. Péron-Pinvidic et al., 2013). The transition between the two thus involves the focusing of initially widely distributed extension on fewer faults (i.e. necking breakaway complexes; Osmundsen & Péron-Pinvidic, 2018;Péron-Pinvidic, Åkermoen, et al., 2022;Péron-Pinvidic et al., 2013). This transition has previously been recorded by the so-called necking unconformity (Chenin et al., 2015;Masini et al., 2013) in the proximal domain, marking the transition between syn-tectonic deposits and passive infill on seismic reflection data (Chenin et al., 2015). For the Frøya High, this unconformity is represented by the Callovian-Oxfordian IMU (Figures 2 and  5). We note that the age of the IMU does not necessarily represent the age of refocusing of extensional deformation from the proximal to the necking domain (e.g. KFC). The IMU indeed records subaerial exposure and erosion of the uplifted footwall topography on the Frøya High and rotated strata in the Froan Basin, but this erosion was also largely controlled by relative sea-level fluctuations (Bell et al., 2014; Figure 2). As such, necking unconformities and their age merely provide evidence and age constraints for necking domain footwall subaerial exposure, not necessarily age constraints for tectonic deformation migration. Furthermore, the IMU is locally associated with up to three erosional events/subset unconformities (Figure 2), revealing how local tectonic adjustments (e.g. local subsidence, uplift and rotation of structural elements) may cause 'regional' unconformities to form and develop as diachronous features. The tectono-sedimentary history of the Frøya High thus forms another example of how the classical subdivision into pre-, syn-and post-rift sequences is not applicable for rifted margins that have typically experienced spatio-temporal migration of tectonic activity whilst simultaneously being affected by variations in relative sea-level (Masini et al., 2013;Péron-Pinvidic et al., 2013).
Nevertheless, the IMU can be correlated to the transverse ridge separating BsA from BsB where it transitions from eroding Middle Jurassic and older strata in the Froan Basin at a high angle, to forming the BsB landscape of eroded basement lithologies on the Frøya High (Figures 5  and 7). We, therefore, attribute the formation of BsB to the onset of IMU erosion during Callovian-Oxfordian times, following rifting and footwall uplift during the late Middle Jurassic. Ribes et al. (2020) provided evidence based on quantitative field work analysis that basement exhumation during lithospheric thinning produced a new source area for siliciclastic sedimentary deposits for the necking domain of the Alpine Tethys margin (i.e. the Mont Blanc detachment system and the siliciclastic Grès Singuliers unit). We argue for a similar scenario for the erosion associated with the IMU and associated younger unconformities (e.g. Oxfordian-Kimmeridgian and Tithonian; Figure 2) within BsB. This ultimately led to the deposition of the Middle Jurassic Intra Melke Formation sandstones and the Late Jurassic Rogn Fm on the Frøya High (NPD, 2022b(NPD, , 2022c(NPD, , 2022d, in adjacent areas, for example, the Froan Basin (Nakken et al., 2022;NPD, 2022e), and in the hangingwall basin in the northern structural recess (Figures 3 and 5; NPD, 2022e; PL 936 Relinquishment Report, 2022).

Frøya High
Multidirectional sedimentary distribution channels on and around the Frøya High ( Figure 6) align with commonly used tectono-sedimentary models for rift basins in coastal/marine settings (e.g. Gawthorpe & Leeder, 2000). Current models predict that with increasing fault displacement, associated footwall uplift eventually causes additional footwall drainage opposite the hangingwall direction (i.e. dip-slope setting). This effectively forms a drainage divide between the transverse and reverse drainage systems across the footwall, semi-parallel to the associated fault (Gawthorpe & Leeder, 2000). The BsB-BsC transition (e.g. Figure 4) has previously been suggested to represent such a drainage divide ('water divisor line') across the Frøya High (Muñoz-Barrera et al., 2020). Basement lithology erosion (PL 936 Relinquishment Report, 2022) and reworking of Upper Jurassic sedimentary deposits in a likely shallow marine, high-energy setting in a humid climate (e.g. Chawshin, 2011), indicate an Early Cretaceous age for the BsC. Similar reworking of both basement lithologies, and Upper Jurassic sandstone deposits remains undocumented for the Early Cretaceous within BsB, as the constrained Upper Jurassic successions are reportedly draped by the Early Cretaceous Lyr and Lange formations following sea-level rise and drowning of the high during the late Early Cretaceous (Lyr Fm: Valanginian-Early Aptian in age; NPD, 2022e; Figures 2, 5 and 7). The differential geomorphological configuration and varying age constraints as outlined in this study for BsB and BsC rather indicate that their establishment relates to different depositional environments, and more importantly, occurred at various points in time. Consequently, despite opposite depositional directions for BsB and BsC (e.g. Figure 6), we find it unlikely that their transition represents a drainage divide following the model outlined above.
An alternative interpretation for the BsC is that it represents (post-tectonic) fault scarp erosion and partial footwall crest collapse (Muñoz-Barrera et al., 2020). However, footwall scarp erosion is usually associated with catchments eroding into the footwall from tens of meters to 3 km at most, for example, 1.8 km scarp retreat in the central Exmouth Plateau, North West Australia (Barrett et al., 2021;Bilal et al., 2020) and overall 2 km scarp retreat on the northern Frøya High on the footwall of the BFC in the Halten Terrace area (one dendritic catchment involves 3 km scarp retreat; Elliott et al., 2012). The BsC on the other hand has an E-W extent ranging from 7 to 13 km, perpendicular to the KFC (Figure 4). Fault scarp erosion extending into the footwall with such lengths would require a significant relative sea-level sensitivity across the BsC, and thus a low relief pre-erosional landscape. Conversely, such a landscape would yield low-energy deposits mixed in a shallow marine setting, not the formation of incising valleys and sedimentary strata indicating deposition in a high-energy environment. Only the latter is observed within BsC ( Figure 6) and is indicated from petrographical analyses of well data (Chawshin, 2011). Moreover, this would presume an unlikely close-to-no footwall uplift associated with the latest Late Jurassic-earliest Early Cretaceous (Tithonian-Berriasian) rift phase (Figure 2) affecting the KFC . Activity for the KFC during this rift phase is documented from the formation of a younger fault splay linking in depth with the sinuous original detachment of the KFC established during late Middle Jurassic rifting (i.e. northern structural recess; Figure 4; Gresseth et al., 2022Gresseth et al., , 2023, and inferred from seismo-stratigraphic analysis of deposits within the Rås Basin (Muñoz- Barrera et al., 2022). Implicitly, this rift phase cannot be discarded for the tectono-stratigraphic evolution of the Frøya High. Based on the arguments as outlined above, we remain reluctant to attribute BsC configuration to fault scarp erosion.

| Frøya High exhumation and backrotation
Continental core complexes in the footwalls of detachment fault systems are commonly elliptical and elevated to create a dome-shaped relief, up to 1-2 km above the surrounding hangingwall (Whitney et al., 2013;references therein). Exhumation is typically attributed to isostatic/flexural uplift in the footwall as a response to the substantial crustal thinning accommodated by the associated detachment fault system (Spencer, 1984;Wernicke & Axen, 1988;Whitney et al., 2013;references therein). For the Frøya High, the radial dispersal pattern of incising valleys and pathways for sediment transport from the Frøya High central salient in the footwall to the Rås Basin in its hangingwall is indicative of a hyperbolic footwall exhumation pattern (Figure 4), in line with previous interpretations of the Frøya High as a metamorphic core complex exhumed to form a turtleback structure (Gresseth et al., 2023; Muñoz-Barrera et al., 2020; Figure 1). The central salient also corresponds to high gravity anomalies within the study area, substantiating the interpretation of the Frøya High representing a metamorphic core complex in which the largest magnitude of basement fabric exhumation occurred within the central salient area (Gresseth et al., 2023;Muñoz-Barrera et al., 2020). A Callovian-Oxfordian age has been interpreted for the radially dispersed incising valleys outlining the western flank of the Frøya High (Figure 4; Bunkholt et al., 2021). Stratal thickness of the Upper Jurassic Rogn Fm deposits decreases away from the central footwall salient/ 'turtleback' (i.e. 93 m in 6306/6-1; 73 m in 6306/9-1; 40 m in 6306/3-2 and 27 m in 6306/3-1S (NPD, 2022b(NPD, , 2022c(NPD, , 2022d, see Figure 4 for location). The erosional pattern and sedimentary distribution thus indicate a late Middle Jurassic onset of hyperbolic footwall exhumation, aligning with rift initiation along the KFC during the Middle Jurassic (Bajocian-Bathonian; Blystad et al., 1995;Bunkholt et al., 2021;Muñoz-Barrera et al., 2020). Hyperbolic footwall exhumation is, according to published models, typically associated with the development of synclinal depocentres flanking the footwall area experiencing the greatest amount of exhumation (i.e. footwall 'turtleback'; Figure 1; Gresseth et al., 2023;Osmundsen et al., 2022). Corresponding synclinal depocentres are recognized in the northern and southern structural recesses of the KFC within the Rås Basin (Figure 1). Inferred ages of the lowermost strata within these basins are Lower to Middle Jurassic (Muñoz- Barrera et al., 2022), lending further support to the interpretation of an hyperbolic footwall configuration being established by Middle Jurassic times.
Exhumation of domal geometries in footwall core complexes has been explained by the rolling hinge model (Buck, 1988;Whitney et al., 2013;references therein). Common observations for rolling hinge type systems include how the locus of incremental uplift migrates through the footwall and causes footwall and fault plane back-rotation during extension (Axen & Bartley, 1997;Brun et al., 2018;Buck, 1988;Escartín et al., 2017;Lavier et al., 1999;Mizera et al., 2019;Olive et al., 2019;Spencer, 1984;Wernicke & Axen, 1988). Historically, the model is abundantly described from the Basin and Range, western US (e.g. Spencer, 1984;Wernicke, 1995;Wernicke & Axen, 1988) and from oceanic core complexes along spreading ridges (e.g. Escartín et al., 2017;Olive et al., 2019). A current, active example can be found in SE Papua New Guinea, where the Suckling-Dayman core complex is exhumed and back-rotated in the footwall of the Mai'iu detachment fault Mizera et al., 2019). The rolling hinge model has also been linked to the Alpine Tethys margin (Lavier & Manatschal, 2006;Ribes et al., 2020), where the associated principles are invoked to explain footwall configuration and tectono-sedimentary evolution within the margin's necking domain (i.e. Mont Black Core Complex and the Grès Singuliers sedimentary unit; i.e. Ribes et al., 2020). The severe footwall and detachment fault plane backrotation reported from rolling hinge systems presents a possible explanation for the angular unconformity observed for the BsB and BsA in the Froan Basin ( Figure 5). As such, we interpret the Frøya High to have been exhumed following the principles of the rolling hinge model during late Middle Jurassic rifting. This, possibly enhanced by slip-parallel footwall contraction ; references therein) produced an elevated turtleback structure in the area of the central salient, and an eastward rotation of tabular strata within BsA. The following IMU-associated erosion thus caused; (i) footwall peneplanation and established the radial pattern of incising valleys on the western flank of the high, (ii) an angular unconformity between back-rotated Triassic to Middle Jurassic strata in the BsA (Froan Basin) and the BsB (Frøya High) and (iii) stratal thickness distribution of erosional products decreasing away from the central salient.
The radial pattern of incising valleys indicating the hyperbolic exhumation of the Frøya High follows the BsC (Figure 4), indicating that the valleys remained conduits of sediment distribution also during BsC formation in the Early Cretaceous. This effectively links BsC formation and footwall uplift of the Frøya High during Tithonian-Berriasian rifting. Continued uplift during the earliest Cretaceous aligns with previous suggestions of the Frøya High remaining subaerially exposed during Early Cretaceous times (Bell et al., 2014). Preservation of Upper Jurassic strata across the BsB simultaneously with subaerial exposure of BsC implies that this earliest Cretaceous rifting phase, similar to Callovian-Oxfordian rifting, involved a renewed backrotation of the Frøya High during footwall uplift, focused on the western flank of the high. The amount of footwall backrotation is incremental with increasing displacement (e.g. Lavier et al., 1999), aligning with the observations of how the BsC distribution is longest in E-W direction in the central salient area, corresponding to the area of maximum displacement along the KFC. This topography would consist of an uplifted segment of basement landscape previously affected by IMU erosion. Continued erosion would thus cause reworking and cannibalization of the precursing Late Jurassic landscape during Early Cretaceous times. This aligns with the Early Cretaceous age suggested for the formation of BsC.
Currently, the BsB can be observed as a semi-horizontal surface, whilst the BsC is tilted towards the west (Figure 4). The Frøya High experienced significant down to the westtilting both during mid-Cretaceous times and again from mid-Miocene to present due to post-rift thermal subsidence and Cenozoic uplift of the hinterland in the east (Bell et al., 2014;Lien, 2005;Muñoz-Barrera et al., 2020;Trice et al., 2019). This indicates that pre-mid Cretaceous, BsB likely dipped towards the east, BsC either dipped westward at a lower angle than currently observed or even possibly had semi-horizontal configuration. The westward tilting of the Frøya High would also affect the KFC dip angles, which in depth converted sections generally decrease from ca. 54° ± 9°, to 12° ± 4° at ca. 14 km depth (table 4 in Muñoz-Barrera et al., 2020. A more easterly tilt of the Frøya High and the KFC pre-mid Cretaceous would lower the current dip angles for the KFC, and thus also be consistent with low dip angles (<20°) at higher crustal levels as typically predicted for detachment fault systems developing rolling hinges (e.g. Lavier et al., 1999;Whitney et al., 2013;references therein).
Geomorphological, stratigraphic and structural evidence for exhumation, backrotation and erosion of the Frøya High are presented in this study. An important note is the consequential extension discrepancy (sensu McDermott & Reston 2015) that this tectono-stratigraphic evolutionary history involves for the Frøya High. As exhumed footwall topography is subsequently eroded after uplift, the erosion will effectively remove and thus mask former footwall cut-offs. Previously published displacement estimates (e.g. 25-35 km;Muñoz-Barrera et al., 2020) for the KFC within the study area are therefore likely underestimated. Mass-balance restoration has not been performed for this study, but we suggest our findings encourage such a study to be conducted within the area to help constrain and quantify values (amount, angles) for uplift, and back-rotation of the Frøya High during Middle Jurassic-Early Cretaceous times.

| Tectono-stratigraphic evolution of the central Frøya High: A new model
We find that the differential basement segment distribution and configuration across the Frøya High indicate that footwall uplift followed the principles of the rolling hinge model and involved back-rotation during Middle Jurassic-Early Cretaceous rifting. Contemporaneously, unconformities involving basement erosion continuously modified the Frøya High landscape during relative sea-level rise and fall. In the following, we present a new tectono-stratigraphic scheme for the Frøya High and discuss its possible implications for local spatio-temporal sedimentary distribution (Figure 8).
The configuration of the Frøya High during the Early Jurassic rifting is enigmatic. The rift initiation stage for the KFC system has until now been defined as associated with the Middle Jurassic Bajocian-Bathonian rift event (e.g. Blystad et al., 1995;Bunkholt et al., 2021;Doré et al., 1999;Elliott et al., 2012), but we argue that there is no evidence that the Hettangian-Sinemurian rift phase did not also affect the Frøya High region. Syn-tectonic deposition of Early Jurassic sediments (Pliensbachian-Toarcian) is found in down-faulted halfgrabens in the Froan Basin, at the Halten and Dønna terraces, and in the Rås Basin in the hangingwall of the YFC . The associated faults, such as the KFC, strike NNE (Figure 1). Whilst the Froan Basin and its controlling faults are considered features of the proximal domain, the YFC is defined as the necking breakaway complex in the northern part of the mid-Norwegian margin. We, therefore, find it likely that the successive basinward deformation associated with the transition from stretching to thinning phase for the margin might have been initiated during Early Jurassic times. Following this argument, the KFC could have initiated during this Early Jurassic rift event, and later been reactivated during the thinning phase in Middle Jurassic times (Figure 8a). Associated deposits of the Båt Gp would be expected to be removed during the IMU erosion event on the Frøya High itself but may be present in the deeper parts of the Rås Basin to the west. Corresponding deposits are reported from the Froan Basin (e.g. Ror and Tofte formations in well 6307/1-1S). This line of argument establishes the Frøya High as a possibly subaerially exposed horst structure in Early Jurassic times, in line with published palaeo depositional environment maps for this period (Johannessen & Nøttvedt, 2008a). It further lengthens the lifespan of the KFC with initiation during Early rather than Middle Jurassic times. This further suggests Early to Middle Jurassic ages for the undated, tabular strata below the IMU within the NNE trending Mandel basin on the Frøya High (e.g. Figures 4 and 7). Earlier erosion associated with the ToU (Figure 2) in the region is only reported locally in the Norwegian Sea region (e.g. Halten and Dønna terraces, Trøndelag Platform; Bunkholt et al., 2021), but may be masked on the Frøya High due to IMU overprint. Erosional products from the ToU are present in the Froan Basin north of the Frøya High in well 6407/11-1, where the Rogn Fm unconformably overlies the Tofte Fm (NPD, 2022e). We do, however, note that this source-to-sink system remains unconstrained for the southern part of the Froan Basin and central Frøya High.
Despite an overall eustatic sea-level rise, the Frøya High remained subaerially exposed throughout the Jurassic, flanked by a marine environment in the Rås and Froan basins to the west and east respectively (Figure 2; Bell et al., 2014;Bunkholt et al., 2021;Johannessen & Nøttvedt, 2008a, 2008b Figure 8a).
The late Middle-early Late Jurassic (Callovian-Oxfordian) marks the period of the rift climax for the KFC (Blystad et al., 1995;Bunkholt et al., 2021), coinciding with the proposed onset of the BsB development. During Callovian times, westward prograding river plain and delta depositional environments caused erosion of the western flank of the high (Johannessen & Nøttvedt, 2008a). This led to the formation of incising valleys and shedding erosional products (Intra Melke Fm sandstones as documented in well 6306/5-2; NPD, 2022e) across the KFC into the Rås Basin . The radial dispersal pattern of these incising valleys from the central salient segment of the Frøya High indicates that hyperbolic footwall exhumation was associated with this rift period.
In Late Jurassic ((late Oxfordian) Kimmeridgian-Tithonian), the KFC continued to be active (Bell et al., 2014;Bunkholt et al., 2021;Muñoz-Barrera et al., 2020, likely motivating continued footwall uplift of the Frøya High. Upper Jurassic (erosional) sediments, that is, Rogn Fm, were deposited locally and around the high, with sedimentation occurring both towards the west and east (Johannessen & Nøttvedt, 2008b). Footwall uplift and continued back-rotation of the Frøya High, in coincident with F I G U R E 8 Schematic sketch illustrating the tectonosedimentary evolution of the Frøya High during Early-Middle Jurassic to Late Cretaceous times with a perspective from central salient and the area of maximum displacement, looking approximately north. Not to scale. (a) Early-Middle Jurassic setting with the onset of footwall uplift and backrotation of the Frøya High. Shallow water setting is indicated in the Froan Basin area, relative to the Rås Basin. Onset of backrotation of BsA indicated. (b) Late Jurassic setting with submarine fans dominating in the Rås Basin, whilst a shallower water setting prevails in the Froan Basin. The Frøya High western flank is heavily eroded by incising valleys associated with the Intra Melke Unconformity, which, based on sandstone distribution as constrained in wells seems to be associated with a subset of closely related unconformities (i.e. the different ages for the Callovian-Oxfordian Intra Melke Unconformity sandstones and the Kimmeridgian-Tithonian Rogn Fm thermal subsidence, enhanced the basin topography with a deepening of the Rås Basin and steep fault scarps along the western flank of the Frøya High . Our model indicates that footwall back-rotation caused an easterly rotation of the Frøya High, in line with reported deep marine sandstones along its western flank (e.g. Johannessen & Nøttvedt, 2008b), and a shallow marine setting in the Froan Basin during the Kimmeridgian (i.e. Draugen-field, Bell et al., 2014;Figure 8b). The Upper Jurassic Rogn Formation sandstones reported from well 6306/6-1 are Kimmeridgian to Late Tithonian-Early Berriasian in age (NPD, 2022e), indicating a westward migration of shallow marine bar deposits associated with the Rogn Fm during Tithonian-Berriasian on the eastern flank of the Frøya High. According to Brekke et al. (2001), an initial sea-level rise during the Late Jurassic was followed by a relative sea-level fall in the Early-Mid Tithonian, with lowstand setting possibly lasting locally (i.e. BsC) into the Berriasian (Brekke et al., 2001).
By earliest Early Cretaceous (Late Tithonian-Berriasian-Valanginian), the KFC experienced renewed rifting (e.g. Muñoz-Barrera et al., 2020), and according to our model, a late-stage doming of the Frøya High western flank (Figure 8c). Rift shoulder uplift, combined with continued back-rotation, caused footwall erosion and formation of the BsC simultaneously with easterly tilt of the BsB landscape. This aligns with the Upper Berriasian (i.e. Ryazanian in former official nomenclature (Dalland et al., 1988)) shales of the Spekk Fm draping the Rogn Fm within the BsB according to well 6306/6-1 (NPD, 2022e). Early Cretaceous deposition within the Rås Basin was likely heavily influenced by basin floor fans sourced within the BsC, and possibly axial turbidites common for deep marine settings within hangingwall configurations (Gawthorpe & Leeder, 2000). This is in line with the lack of confirmed Jurassic sediments, with Lower Cretaceous sediments unconformably resting on the top basement surface within the BsC reported from well 6306/6-2 (PL 936 Relinquishment Report, 2022). Within the northern structural recess of the Frøya High, the earliest Cretaceous reactivation of the KFC caused the development of a new fault segment, laterally linking up with the KFC (Figures 4  and 8c). This was likely a response to the increased sinuosity acquired by the KFC during Middle and Late Jurassic rifting (Gresseth et al., 2023), and adds to the evidence (e.g. up to 9.5 s TWT displacement of the 'BCU' reflector from the Frøya High to the Rås Basin; Bunkholt et al., 2021) for reactivation of the KFC during earliest Early Cretaceous times.
By mid-Cretaceous, and through Cenozoic times, thermal subsidence and hinterland uplift caused a westward tilting of the system (Figure 8d High was eventually drowned due to relative sea-level rise during Early and Late Cretaceous times (Figure 8d), evidenced by how the Lyr and Lange formations onlap and drape the Frøya High respectively ( Figure 5).

REMARKS
We herein present a new Middle Jurassic-Early Cretaceous tectono-stratigraphic scheme for the Frøya High region within the necking domain of the mid-Norwegian rifted margin. 3D and tightly spaced 2D seismic reflection data have allowed us to investigate and correlate the observable geometrical features (e.g. Figures 4 and 5), geophysical properties (e.g. Figure 6), overlying seismic facies signatures ( Figure 7) and available well data (Figure 3) across the top basement surface of the Frøya High. In combination, the datasets provide evidence for three, laterally extensive erosive surfaces across the high. The associated cross-cutting unconformities are progressively younger westward and can be tied to known periods of rifting along the KFC, associated footwall uplift and relative sea-level fluctuations. This indicates a strong tectonic influence on their development. The previously identified metamorphic core complex (in e.g. seismic and gravity anomaly data; Gresseth et al., 2023;Muñoz-Barrera et al., 2020) within the Frøya High central salient is outlined by the KFC and a radial pattern of incising valleys. We find that the erosional channels developed and were reworked simultaneously with eastward tilting of former datums and sediment distribution systems, effectively showing that the localized footwall exhumation also involved backrotation. These observations align with known principles for rolling-hinge style deformation during rifting. As such, the associated mechanisms served as controlling factors for the tectono-stratigraphic evolution of the Frøya High and KFC system during Middle Jurassic-Early Cretaceous rifting. Based on our observations, we make the following concluding remarks: • Three distinct top basement segments can be identified across the Frøya High. The difference in dip between the different top basement segments is a likely result of multiple erosional events during exhumation and uplift of the footwall of the KFC. Most likely, exhumation followed principles consistent with the rolling hinge model. • The different top basement segments correspond to their own specific chrono-and lithostratigraphy above top basement, becoming progressively younger from the east towards the KFC. We suggest Late Permian-Middle Triassic (Ladinian), late Middle Jurassic (Callovian-Oxfordian) and Early Cretaceous (late Tithonian-Berriasian/early Valanginian) ages for the respective basement segments. This effectively prolongs the control of the KFC on Frøya High erosional history relative to previously published models. • Necking domains in rifted margins pose viable candidates for the rolling hinge models in effect during rifting. The Frøya High on the mid-Norwegian margin shows how the effects of a rolling hinge model are likely to be masked in the footwalls of breakaway complexes, as they typically, in contrast to deep marine spreading ridge-or intracontinental settings, will develop in shelf-edge settings and be sensitive to base-level drops/ sea-level fluctuations as the controlling mechanisms of erosion. • Repeated base-level drop during footwall uplift and backrotation will create cross-cutting unconformities. It follows that the youngest erosional surfaces may hold the potential to partly or fully obliterate remnants of older drainage systems associated with older erosional landscapes depending on the magnitude of the baselevel drop in relation to the degree of footwall tilting. • Detachment fault geometry evolution and footwall back-rotation during lithospheric necking may have multiple immense effects on the sedimentary systems: (i) sediment rerouting will be expected in the necking hangingwall during detachment evolution, (ii) footwall drainage systems will be uplifted and therefore partly/ completely eroded and/or cannibalized during subsequent erosional events and (iii) backrotation will lead to reverse drainage from necking footwall into the proximal domain.