Ivar Midtkandal

In microtidally influenced rivers, tides are generally assumed to leave virtually no signatures in the sedimentary record. However, this hypothesis has been surprisingly poorly tested using modern river analogues, which provide an opportunity to assess whether sedimentary signatures of microtidal regimes can develop in rivers that lack diagnostic evidence of tidal control on large‐scale channel morphology. This study investigates the capability of microtidal processes to leave signatures in deposits within the 180 km long backwater, fluvial–marine transition zone of the Po River (Italy). The Po River enters the Adriatic Sea (tidal range ca 1 m) through several deltaic distributary channels that exhibit no evidence of funnelling or cuspate meanders, indicating a clear morphodynamic dominance of fluvial over tidal processes. Hydrological data show that river water levels are modulated by tidal influence up to ~90 km and ~ 40 km from the river mouth during low‐discharge and ‐discharge stages, respectively. Approximately 30 km from the mouth, deposits formed by riverine floods exhibit clear tidal sedimentary structures, including sand–mud couplets and bidirectional ripples. Around 40 km from the mouth, cross‐stratified sand displays bundles with cyclic organisation, which are absent further upstream and are interpreted here as the effects of semi‐diurnal tidal modulation on the migration of fluvial bedforms. Additionally, these bundles are deposited above the average intertidal zone, indicating that flood‐enhanced water levels enable tide‐modulated sedimentation to extend beyond the typical intertidal range. This study shows that evidence of tidal processes can be common even in deposits of microtidally influenced rivers, highlighting that tidal sedimentary structures may develop where tides exert little to no control on large‐scale morphodynamics. Overall, these findings emphasise caution when interpreting dominant morphodynamic processes solely from sedimentary structures.

The Greater Barents Sea Basin (GBSB) is a unique area in the Arctic, as it hosts relatively well-preserved large-scale Cretaceous progradational wedges. Multiple regional studies document temporal and spatial variations in clinoform progradation directions and sedimentation styles across different parts of the GBSB and reveal a fundamental tectonically driven reorganization of drainage systems during the Early Cretaceous. This study uses an integrated source-to-sink approach combining regional seismic datasets with new detrital zircon U–Pb ages from the analysis of 11 samples spanning the Valanginian to Campanian that are combined with seismic interpretation and mass balance calculations. This work presents a unified chronostratigraphic framework for the whole GBSB and correlates internal changes to large-scale plate tectonic events, and major volcanism, in the source area and the Arctic in general. It reveals that sediment input varied throughout the Cretaceous with low sediment input from local sources in the Late Jurassic–Hauterivian, which dramatically increased in the Barremian due to High Arctic Large Igneous Province activity. Relatively high sediment input took place in the Albian–Cenomanian due to catchment reorganization, followed by relatively low sediment input in the Turonian–Coniacian with a last increase in the Campanian. A new provenance dataset, including new zircon data, confirms a catchment reorganization to a dominant northeasterly source, and constrains this change to the Aptian–Albian.

This study investigates the processes controlling the development of nested clinoforms in outcrops of the Eocene Sobrarbe Deltaic Complex of the Aínsa Basin, highlighting their significance as archives of basin-margin evolution. Small-scale clinoforms record the higher-frequency cycles of delta progradation and the coetaneous development of a carbonate factory, while large-scale clinoforms record longer-term high-energy processes on the shelf/slope, including the reworking of previous deltaic/shelf deposits. High-resolution lithological variations were characterized across three of the high-frequency cycles, revealing a downdip transition along the small-scale clinothems from subaqueous channels to distal delta front/shelf settings. The coarsest grain sizes are restricted to the proximal delta plain environments evidencing limited coarse sediment transfer to deeper waters in this part of the deltaic complex, enabling the development of a coeval carbonate factory resistant to moderate clastic input and water turbidity. The small-scale clinoforms display steeper slopes than expected for siltstone to fine sandstones, which is explained by early cementation of the carbonate-rich horizons preserving relatively steep clinoform slopes and preventing their collapse. The study emphasizes the importance of recognizing heterogeneity in such mixed siliciclastic-carbonate environments, which has implications for understanding reservoir quality and connectivity in subsurface systems.

Sills are fundamental elements of volcanic plumbing systems emplaced in sedimentary basins. Even though sills are commonly considered simple, planar concordant igneous sheets, they are actually complex 3‐dimensional objects. Detailed knowledge of the 3D structure of sills and their host rocks is of primary relevance to better constrain the emplacement mechanisms and the impacts of sills on sedimentary basins. This study describes the results of 3‐dimensional geological mapping of a large (~14 × 9 km), well‐exposed Early Cretaceous dolerite sill in Central Spitsbergen, Svalbard, Arctic Norway, using a combination of digital outcrop modelling and field mapping. The sill was emplaced within Upper Palaeozoic sedimentary formations of Svalbard. It is made of distinct segments emplaced at different stratigraphic levels of the host rock stratigraphy. The mapping shows a clear stratigraphic control on the intrusion morphology. Sill segments emplaced at the boundary between two formations, which mark a strong lithological and rheological boundary, are straight and concordant. Conversely, segments emplaced within a more homogeneous formation exhibit more irregular, locally discordant shapes. The sill segments emplaced at distinct stratigraphic levels are connected by steeply dipping steps, which formed through dilatant shearing between the tips of the sill segments. The preferred NW‐SE orientation of the steps and the thinning of the sill towards the SE suggests a propagation direction of the magma towards the SE. Our study shows how 3‐dimensional knowledge of igneous intrusions is key for revealing their emplacement mechanisms.

Submarine canyon and channel systems are the primary paths for sediment transport from platforms to deep‐sea terminal depositional fans and are present on all continental margins. The temporal morphological expression of such systems should be documented in order to fully understand the development of these important sediment pathways. We utilise a 3D seismic dataset from the northern Shetland Platform to the southern Møre Basin region and map two regionally continuous seismic horizons. The dataset includes an early Eocene northward‐oriented canyon‐channel system that allows high‐resolution mapping of erosion and sedimentation. The morphology of the system allows a subdivision of platform, upper, middle, and lower slope, and basin floor. It is further subdivided from east to west according to the degree of erosive maturity. The platform contains channel shapes and their fill stretching from the south towards the platform edge and upper slope, where dendritic canyon heads developed. Scars in the canyon sidewalls indicate slope failure as an important widening mechanism. The slope canyons progressively shallow and widen basinward. At the canyon exits, deepwater submarine channels developed and continued onto the basin floor. We document progressive filling and overspilling of channels towards the terminal fan. The filling of the channels that resulted in overbank deposition is likely due to a decrease in slope gradient leading to an increased deposition rate that exceeds the channel capacity. Post‐depositional differential compaction of the clastic channel fill and the surrounding muddy sediments causes the channel fills to form elongated ridges that lead towards the terminal fan. It is further shown that the morphological elements observed in the canyon‐channel system adjust towards an equilibrium profile with a shallower gradient. These detailed observations provide an enhanced understanding of how canyon‐channel systems develop on active margins and how sediment transport pathways are influenced by the submarine equilibrium profile and post‐depositional processes.

The nature of rifting episodes and their associated volcanism mark key stratigraphic events in the evolution of volcano-sedimentary basins. Following the final assemblage of Pangea, the European region was subject to rifting and magmatism during crustal re-equilibration throughout the Permian. The aborted, partially eroded Oslo Rift is an excellent archive of this Permian magmatism, but the late-stage volcanological evolution is poorly understood. We present the first detailed documentation of a succession covering this period, with mafic lavas and volcaniclastic (tuff breccia) deposits, trachy-andesitic tuffs, and rheomorphic to moderately welded ignimbrites. Contrary to previous ideas, we show evidence suggesting the development of Strombolian-type scoria-cones, silicic fissure-fed eruptions, and major periods of rift-wide volcanic quiescence. Our observations highlight episodic silicic volcanism characterised by rapid evolution from high-grade ignimbrites to moderately and poorly welded ignimbrites. We infer rapid emptying of large, shallow silicic reservoirs and frequent source switching is responsible for the observed characteristics.

We analyse 498 faults identified in satellite imagery and interpret the height and width of associated footwall ranges with respect to co‐seismic elastic rebound from tectonic and erosional unloading. The dynamics of footwall uplift link uplands to catchment patterns and interrelated hanging wall sedimentary fans. Height–length relations of some catchments and associated alluvial fans scale linearly whereas others, such as fault‐slope catchments and related down‐fault fans (building out from faults) show a significant scatter without an obvious trend. Perched basins abandoned in the footwalls of younger faults offer catchment‐fan height–length relations like watergap and dipslope‐related fans and, besides, hint at reduction of dip angle due to rollback of larger faults before abandonment. Analysis of the width‐to‐height ratio (W/h) of footwall ranges offer a robust linear statistical trend, h = 0.06 W and is identical between datasets. This trend is valid for both arid and tropical rifts, the latter offering smaller rebounds. Contributions of elastic rebound on fault throw in our data are simplistically considered through comparison to global trends on fault length versus throw. This allows consideration around maximum throw (T_max) linked to the maximum height of footwall ranges (h) and to their width (W) above the reference level. Basic calculations indicate that co‐seismic rebound contributes from c. 50 km) show less spread than smaller faults. Such large faults expectedly dissect the brittle crust, indicating that these large faults which root in the ductile–brittle transition approach a balanced, steady‐state kinematic pattern. We speculate that significant crustal thinning associated with these large faults triggers the onset of isostatic adjustments that drive fault rotation, instigating fault abandonment and disconnected perched basins.

Source‐to‐sink sedimentary systems associated with volcanic rifted margins serve as important archives for basin development by recording lithospheric changes affecting the depositional systems. Distinguishing between sediment transport processes and their sediment source(s) can guide the interpretation of a basin's history, and thereby inform regional paleogeographic reconstructions. In this contribution, we integrate and utilize wireline geophysical logs, detailed petrographic observations from side‐wall cores, and seismic analysis to describe and decipher a Maastrichtian to Danian‐aged basin‐floor depositional system in the deep outer Møre Basin, mid‐Norwegian margin. Well 6302/6‐1 (Tulipan) is a spatially isolated borehole drilled in 2001 that penetrates Maastrichtian and younger strata. A succession of hitherto undescribed carbonates and sandstones in the outer Møre Basin was discovered. It is investigated for sediment transport, provenance, and depositional processes on the basin floor surrounded by structural highs and ridges. The strata from the lower parts form a basin‐floor apron consisting of redeposited carbonate sourced from a westerly sub‐aerial high. The apron transitions vertically from mixed siliciclastic and carbonate into a purely siliciclastic fan with intercalated sandstone and mudstone, providing a rare high‐resolution record of how depositional environments experience a complete shift in dominant processes. The development coincides with similar latest Cretaceous‐earliest Palaeocene sequences recorded south of this region (e.g., well 219/20‐1) and may have been influenced by regional uplift associated with the onset of magmatism in the Northeast Atlantic. This study improves our understanding of a late, pre‐breakup source‐to‐sink sedimentary system developed near the breakup axis of an infant ocean, and documents what is possibly the northernmost chalk deposit in the Chalk Group.