Igneous sills are common components in rifted sedimentary basins globally. Much work has focused on intrusions emplaced at relatively shallow palaeodepths (0 – 1.5 km). However, owing to constraints of seismic reflection imaging and limited field exposures, intrusions emplaced at deeper palaeodepths (>1.5 km) within sedimentary basins are not as well understood in regard to their emplacement mechanisms and host-rock interactions. Results from a world-class, seismic-scale outcrop of intruded Jurassic sedimentary rocks in East Greenland are presented here. Igneous intrusions and their host rocks have been studied in the field and utilizing a 22 km long ‘virtual outcrop’ acquired using helicopter-mounted lidar. The results suggest that the geometries of the deeply emplaced sills ( c. 3 km) are dominantly controlled by host-rock lithology, sedimentology and cementation state. Sills favour mudstones and even exploit centimetre-scale mudstone-draped dune-foresets in otherwise homogeneous sandstones. Sills in poorly cemented intervals show clear ductile structures, in contrast to sills in cemented units, which show only brittle emplacement structures. The studied host rock is remarkably undeformed despite intrusion. Volumetric expansion caused by the intrusions is almost exclusively accommodated by vertical jack-up of the overburden, on a 1:1 ratio, implying that intrusions may play a significant role in uplift of a basin if emplaced at deep basinal levels. Supplementary materials: Uninterpreted versions of Figures 7, 8 and 11 are available at http://doi.org/10.6084/m9.figshare.c.3281882
In several basins across the world, dynamic topography, which is created by internal mantle dynamics distinct from plate-boundary tectonics, has been shown to exert significant control on source-to-sink sediment distribution. In the Paleocene North Sea, peaks in sediment flux and transient uplift have  been previously associated with perturbations in dynamic topography created by a precursor to the modern-day Icelandic Plume. However, previous studies have had a limited understanding of the regional paleogeographic context of the area, due in part to data constraints. Here, we will investigate the Paleocene - Early Eocene paleogeographic and stratigraphic evolution of the East Shetland Platform in terms of the extent and timing of erosion versus deposition and how these can be used to reconstruct the behavior of an associated dynamic topography anomaly.The stratigraphic record of the East Shetland Platform and the adjacent Viking Graben were interpreted using >60 000 km² of 3D seismic data, revised biostratigraphic picks and c. 300 previously interpreted well-logs. This allowed the construction of multiple chronostratigraphic “Wheeler” diagrams, relative sea-level (RSL) curves and high temporal resolution paleogeographic maps. Using the resultant seismic surfaces and well data, sediment volumes and masses were calculated for multiple Cenozoic units, which were then used to constrain sediment fluxes deriving from Shetland.Multiple episodes of RSL fall and basinward offlap advance are recorded throughout the Paleocene, and from Late Thanetian to Ypresian, at least five well-preserved unconformity-bounded sequences are marked by prograding, alternating normal and forced regressive clinoforms of the Dornoch Formation. Temporal and spatial variations in the distribution of depocenters and individual subaerial unconformities indicate significant variability in patterns of shelf accommodation/erosion and fan deposition in the basinal Viking Graben. All of these are interpreted as a result of the complex interplay between laterally-uneven RSL fall, time-varied sediment entry point distribution, along-shore sediment transport/supply (evidenced by linear clinoform morphologies) and control by inherited topography/bathymetry. Most importantly, we infer a first-order control on erosion and sediment distribution promoted by the transiently and differentially uplifted topography of the ESP, as showcased by unconformities and paleogeographic maps.Preliminary results indicate that peak sediment fluxes may predate the Dornoch progradation and correspond to the deeper water Lista formation of Selandian to Early Thanetian age. This peak matches published well-based sedimentation rates for the Cenozoic North Sea and predates uplift curves reconstructed from drainage networks in Shetland and Faroe, but fits the peak modelled dynamic topography of the Icelandic Plume. However, sediment fluxes and knickpoint-derived uplift rates are both extremely sensitive to the ages assigned to individual units/surfaces and the temporal resolution of analysis, and the uncertainty related to these is sufficient to drastically change the ages or even presence of individual peaks.Ultimately, the area must have been influenced by shorter-wavelength spatial variations in uplift than what is assumed in typical models of dynamic topography, perhaps as a result of additional modulation of dynamic uplift by lithospheric structures of the North Sea or by some other mechanism that has not been resolved in current mantle imaging and modelling attempts.
Supplementary files to the paper Seismic interpretation of sill complexes in sedimentary basins: implications for the sub-sill imaging problem by CH Eide et al https://doi.org/10.1144/jgs2017-096
Rift-related magmatism resulting in widespread igneous intrusions has been documented in various basins, including the Faroe Shetland Basin (UK), the Voring and Møre basins (Norway), and along the NW Shelf of Australia. Seismic mapping, combined with fieldwork, has resulted in greater understanding of subsurface intrusive plumbing systems but knowledge of emplacement style and the mechanisms by which intrusions propagate is limited. The interpretation of a 3D seismic dataset from the Exmouth Sub-basin, NW Shelf of Australia, has identified numerous igneous intrusions where a close relationship between intrusions and normal faults is observed. These faults influence intrusion morphology but also form pathways by which intrusions have propagated up through the basin stratigraphy. The steep nature of the faults has resulted in the intrusions exploiting them and thus manifesting as fault-concordant, inclined dykes; whereas in the deeper parts of the basin, intrusions that have not propagated up faults typically have saucer-shaped sill morphologies. This transition in the morphology of intrusions related to fault interaction also highlights how dykes observed in outcrop may link with sills in the subsurface. Our interpretation of the seismic data also reveals subsurface examples of bifurcating intrusions with numerous splays, which have previously only been studied in outcrop. Supplementary material: Figures showing uninterpreted seismic lines are available at https://doi.org/10.6084/m9.figshare.c.4395974
The sub-basalt domain of the Norwegian continental shelf (NCS) is one of the last remaining hydrocarbon exploration frontiers in Europe. While there is an established geological and tectonic framework, little has been published that addresses the remaining hydrocarbon exploration risks/uncertainties. Unlike the Faroe Shetland Basin and Rockall Trough, at the time of writing, there are currently no industry-drilled sub-basalt well penetrations on the Norwegian continental shelf. Numerous potential Mesozoic sub-basalt hydrocarbon plays exist on the NCS but, due to the lack of industry-drilled sub-basalt penetrations, there is a perceived large exploration risk. By using cross-border analogues, basin modelling workflows and integration of available seismic data the main uncertainties across the NCS are outlined including charge timing, structural definition, and details of reservoir presence. Generically the Late Cretaceous and Middle Jurassic intervals are potential plays which may be present on the Norwegian Margin. However, there is considerable uncertainty on their depth and preservation. Although significant challenges and uncertainties remain, the authors believe that the integration of well results, consideration of basin modelling driven heat flow estimates and new 3D seismic data may open sub-basalt opportunities for a new exploration frontier on the NCS. Thematic collection: This article is part of the New learning from exploration and development in the UKCS Atlantic Margin collection available at https://www.lyellcollection.org/topic/collections/new-learning-from-exploration-and-development-in-the-ukcs-atlantic-margin
Abstract Clinoform surfaces are routinely used to mark transitions from shallow waters to deep basins. This concept represents a valuable tool for screening potential reservoir intervals in frontier basins where limited data are available. Variations in the character of clinoform geometries and shoreline and shelf‐edge trajectories are indicators of a range of different factors, such as palaeobathymetry, changes in relative sea‐level and sediment supply. Applications of conceptual and generalized models might, however, lead to erroneous assumptions about the supply of coarse‐grained material to the delta front and basin when superficial similarities between clinoform geometries are not treated holistically. The present study examines the mudstone‐dominated Middle Triassic Kobbe Formation – a potential hydrocarbon reservoir interval in the Barents Sea, where prodeltaic to deltaic deposits can be examined in cores, well logs and two‐dimensional and three‐dimensional seismic data. Despite pronounced acoustic impedance contrast to the surrounding shale, channel belt networks are not observed close to the platform edge in seismic datasets, even at maximum regressive stages. However, sub‐seismic prodeltaic deposits observed on the shallow platform indicate that prodeltaic deposits were sourced directly from the delta plain. Clinoform surfaces with different geometries and scale are observed basinward of the palaeoplatform edge of underlying progradational sequences, correlative to mudstone‐dominated prodeltaic core sections. Results indicate that platform‐edge deltas developed at discrete sites in the basin due to normal regression, but the positions of these deltas are not directly relatable to variations in clinoform geometries. Transitions from third‐order to fourth‐order clinoform geometries record discrete transgressive–regressive cycles but are not necessarily good indicators of sandstone deposition. Because of prolonged periods with high accommodation, channel avulsions were frequent and only very fine‐grained sandstone was deposited in heterolithic units at the delta front. Sandstones with good reservoir properties are predominantly found along basin margins.
Sills are important components of magmatic plumbing systems because of their role in magma storage. Previous studies have indirectly investigated sill propagation and architecture by using laboratory experiments, remote sensing, modelling and theory. However, these studies often struggle to include the complexity of natural systems, which commonly involves strong interplay between hosts and intrusions. To highlight the importance of host rock and magma interaction, we present the results from a study of combined unmanned aerial vehicle and outcrop datasets from a world-class 1.3 km long, 30 m high 3D exposure of a 12 m thick alkaline trachybasalt sill in Mussentuchit Wash, San Rafael Swell, Utah. The sill intruded into Jurassic, dominantly sandy, sedimentary rocks. Results of this study show that the propagation of the Mussentuchit Wash Sill features both fracture-driven and complex non-brittle fluid interaction emplacement, which are strongly influenced by local sedimentology and presence of porewater. Segregated melt emplaced progressively within the sill during emplacement is used to document the evolution of sill inflation. The fracture-driven propagation is initiated along sedimentary discontinuities through hydrofracturing, whereas the non-brittle fluid interaction is caused by the presence of local porewater within the sedimentary host rocks. This suggests that local lithology may exert strong control on the architecture and morphology of sills in sedimentary basins. Supplementary material: Uninterpreted images of the sill are available at https://doi.org/10.6084/m9.figshare.21269265.v1 and are included as DR1.
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)
'/%3e%3c/defs%3e%3cpath fill='%23012169' d='M0 0h10080v5040H0z'/%3e%3cpath stroke='%23fff' stroke-width='.6' d='m0 0 6 3m0-3L0 3' clip-path='url(%23b)' transform='scale(840)'/%3e%3cpath stroke='%23e4002b' stroke-width='.4' d='m0 0 6 3m0-3L0 3' clip-path='url(%23c)' transform='scale(840)'/%3e%3cpath stroke='%23fff' stroke-width='840' d='M2520 0v2520M0 1260h5040'/%3e%3cpath stroke='%23e4002b' stroke-width='504' d='M2520 0v2520M0 1260h5040'/%3e%3cg fill='%23fff'%3e%3cuse xlink:href='%23d' x='2520' y='3780'/%3e%3cuse xlink:href='%23a' x='7560' y='4200'/%3e%3cuse xlink:href='%23a' x='6300' y='2205'/%3e%3cuse xlink:href='%23a' x='7560' y='840'/%3e%3cuse xlink:href='%23a' x='8680' y='1869'/%3e%3cuse xlink:href='%23e' x='8064' y='2730'/%3e%3c/g%3e%3c/svg%3e)