The last two decades of research have highlighted that volcanism occurring in sedimentary basins can have substantial effects on sedimentary formations. In particular, igneous intrusions can trigger the generation of large amounts of greenhouse gases in organic-rich host rocks, leading to dramatic climate change and mass extinctions. Volcanism can also have significant impacts on hydrocarbon-bearing sedimentary basins. The Neuquen Basin, Argentina, is a well-studied example of a hydrocarbon-producing sedimentary basin hosting massive volcanism. The combination of substantial industry subsurface data and high-quality outcrops makes the Neuquen Basin an exceptional geological object to study magma-sedimentary rock interactions and their implications to hydrocarbon systems. This contribution reviews well-studied examples from the Neuquen Basin that illustrate: (1) thermal effects of sills on maturation of the organic matter of the source rock, (2) fracturing processes in igneous intrusions and the host rock, (3) sills as producing fractured reservoirs, (4) intrusion-induced doming as structural trap or as potential fractured reservoir, (5) fluid migration along igneous intrusions, (6) reservoir compartmentalization induced by dykes, (7) generation of bitumen dykes in vicinity of intrusions, and (8) improvement of geophysical imaging using large-scale outcrops. All in all, our review documents various effects of magma-rock interactions in hydrocarbon-bearing sedimentary basins, and highlights the significant scientific value of the Neuquen Basin as a world-class case study for unravelling processes of magma-rock interactions in hydrocarbon-bearing sedimentary basins.

Borehole 6307/1-1S was drilled in the Froan Basin offshore mid-Norway in 2018. The bottom of the well penetrated the upper c. 650 m of a seismically imaged mound revealing a previously unknown volcano-sedimentary sequence, here termed the Silfari Volcano. Borehole analyses reveal four volcanic packages (V1-V4), dominated by deeply altered extrusive lava flows and subsidiary pyroclastic units interlayered with (S1-S3) and then capped by (S4) four prominent terrestrial volcaniclastic sedimentary intervals. Petrological analyses of core and sidewall core samples reveal a strongly alkaline series of basic-intermediate to evolved igneous rocks ranging from foidites, through tephri-phonolites to phonolites. Sheet intrusions and cored hydrothermal baryte-calcite-fluorite veins with very low delta 34SVCDT (9.9 parts per thousand-11.8 parts per thousand) subsequently cut the sequence. The vein formation is provisionally attributed to mixing of shallow Ba-enriched waters with saline and sulphate-rich brines ultimately derived from sub-volcanic magma-evaporite interactions with an interpreted potential Permian Zechstein sequence below the well penetration. Calcite delta 13C and delta 18O (mean -2.10 parts per thousand delta 13CVPDB and -14.79 parts per thousand delta 18OVPDB, respectively) support a modified seawater component in the vein-forming fluids. High precision U-Pb TIMS age dating on zircons extracted from the lowermost V1 (238.02 +/- 0.13 Ma) and uppermost V4 (234.96 +/- 0.47 Ma) volcanic packages bracket the activity of the Silfari Volcano across c. 3 Myr spanning the Ladinian-Carnian boundary of the Middle-Upper Triassic conformable with biostratigraphic results from overlying sediments. Magmatic zircons from within the V3 package reveal a date of 183.11 +/- 0.12 Ma, indicating that a previously undocumented Early Jurassic intrusive magmatic event influenced the area. The Silfari Volcano shares some chemical affinities with the Skagerrak Centred Large Igneous Province (SCLIP) and the Oslo Rift; however, it is located several 100 km north of the nearest SCLIP deposits and post-dates the youngest robustly dated volcanism by several million years. The identification of Triassic volcanism has significant implications for understanding the tectono-magmatic history of the NE Atlantic margins.

Abstract Supported by the mush model, the origin of crystal-poor, high-silica rhyolitic magmas (≥ 75 SiO₂ wt.%) is commonly linked to melt extraction in shallow, crystalline mushes, yet their complementary cumulates remain elusive in the upper crust. Here we present the “dynamic mush model” for the Campo Alegre-Corupá system (Brazil), combining textural analysis and thermodynamic modeling to show that high-silica melts formed through upper-crustal fractionation, leaving a granitic residue and feeding a caldera-forming eruption. Syenites and melasyenites represent their silicic-mafic cumulates, the syenites being formed at relatively low crystallinities (~16-33 of bulk vol.%) after extraction of large amounts of interstitial melts (~47-80 of liquid vol.%). In contrast to static models (extraction window ~50-70 vol.%), our results indicate early melt segregation in a dynamic reservoir. Alkali-feldspar crystals were size-selectively and hydraulically sorted by upward melt flow; aggregates were then formed at low crystallinities, supposedly via synneusis, enabling rapid sinking, and were repacked by recharge. This process, enhanced by relatively high magma fluxes, efficiently separated crystals from melt, explaining the origin of large-volume eruptible magmas in the upper crust. Our findings redefine mush evolution while underscoring the role of flow-driven crystal sorting (elutriation) in caldera-forming systems.

The Lundy Island (Bristol Channel, UK) granite is a felsic expression of the southernmost igneous centre of the North Atlantic Igneous Province that emplaced millions of cubic kilometres of magma during the Paleogene. The granite's distinctive S-type, peraluminous, two-mica +/- garnet +/- tourmaline composition has led to the hypothesis that eruptions from the Lundy volcanic centre may be the source of thick felsic ash layers within the early Eocene Fur Formation (Denmark) that act as key marker horizons for the onset and duration of the Paleocene-Eocene Thermal Maximum. This paper presents high-precision zircon U-Pb emplacement ages of 57.24 +/- 0.11/0.12/0.13 Ma for the granite and 55.970 +/- 0.021/0.030/0.070 Ma for a felsic 'lundyite' dyke. Trace and rare earth element patterns indicate close similarities between late-stage Lundy activity and ash layer -33 in Denmark. This ash layer was deposited during the Paleocene-Eocene Thermal Maximum carbon isotope excursion, suggesting that the Lundy volcanic centre is likely to be the source of this key ash horizon and that magmatism at Lundy likely continued into the early Eocene.

Dike-fed fissure vent complexes are commonly linked to basaltic eruptions but are also proposed for some intermediate to silicic eruptions in Large Igneous Provinces (LIPs) and continental rifts. Direct evidence of these complexes is scarce however, and our understanding of the associated eruptive processes remains limited. Basaltic and trachy-andesite (i.e., rhomb-or rectangle-porphyry: RP) eruptions across the Oslo Rift (part of the Skagerrak-Centered LIP) are assumed to have erupted from similar dike-fed fissures, although no direct evidence of eruptive vents has been identified. We present observations illustrating the presence of a shallow (<80 m paleo-depth) RP fissure conduit in the central Oslo Rift recording explosive eruptive activity. Previous workers interpreted these outcrops as a partially preserved lava, suggesting the basaltic unit was cross-cutting due to deposition in an erosional depression. Our studies of outcrops, hand-samples, and thin-sections illustrate three primary textural zones: 1) a core zone with ductile deformation and moderate fragmentation; 2) a heavily-fragmented ash-rich margin zone with inclusions of both rhomb-porphyry and host rock (basalt); and 3) an edge zone variably characterised by un-brecciated rock or brecciated rockwith ash-filled fractures. Lateral textural gradations (over 1-3 m width) from core to brecciated host-rock and substantial overall width (similar to 40 to << 100 m), are consistent with a near-surface (<80 m) paleo-depth, whilst heavily fragmented margins suggest mild to moderate explosive activity towards the end of the associated eruptive episode. An exposure of a slabby-to rubbly-pahoehoe RP8 flow top with mingled and overlying pyroclastic (i.e., ash and lapilli) components additionally highlights explosive processes operating in the late stages of older RP eruptions. Our observations provide the first direct evidence of elongate eruptive-conduits (i.e., fissure-conduits) in the Oslo Rift, but textural characteristics illustrate that at least some rhomb-porphyry eruptions were punctuated by episodes of moderately explosive activity during waning eruptive activity.

The Early Cretaceous opening of the South Atlantic Ocean was accompanied by extensive intrusive and extrusive magmatism collectively grouped in the South Atlantic Igneous Province (SAIP). The SAIP includes the onshore Paran & aacute;-Etendeka large igneous province (PELIP), offshore seaward-dipping reflectors sequences, the Rio Grande Rise and Walvis Ridge, and voluminous intrusive magmatism. Nonetheless, the nature of the processes that lead to continental breakup remain controversial, and the environmental impact of these events is not yet fully understood. In order to investigate the tectonomagmatic evolution of the South Atlantic, we present a new compilation of the various geochemical compositions and radiometric ages associated with the SAIP as well as an estimation of magma volumes constrained by extensive seismic, gravity, and magnetic datasets. The SAIP was formed during the Early Cretaceous, from the Valanginian to Albian (135-110 Ma), with the majority of the magmatic activity lasting c. 3.5 Myr interval between 135.5 and 132 Ma. Onshore magmatism is characterized by massive outpourings of tholeiitic basaltic flows formed by melting of hotter than normal mantle along with significant lithospheric thinning. Magma source compositions varied during magmatism with enriched "plume-like" components transitioning to more depleted "MORB-like" (Mid-Ocean-Ridge-Basalt) signatures. The total magma volume of the SAIP ranges between 10 x 10(6) km(3) and 16 x 10(6) km(3) with a striking asymmetry in volumes of the onshore and offshore volcanism along the conjugate margins. Offshore, similar to 67 to 70 % of the total magma volume is located on the African side whereas 30 to 33 % of the total magma volume is located on the South American side. Onshore, similar to 10 % of the total magma volume is located on the African side whereas 90 % of the total magma volume is located on the South American side. This asymmetry in volume distribution is attributed to different factors including variations in rifting mode, differences in initial lithospheric thickness, and structural inheritance. The geochemical data were analyzed and integrated to provide insights on magma generation and source compositions along with an updated geological model for the South Atlantic magmatism. The onset of the activity of the SAIP at the start of the Weissert Event suggests that the SAIP may have played a major role on the climatic and oceanographic changes during the mid-Valanginian.

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.

Abstract Volcanic plumbing systems emplaced in sedimentary basins may exert significant mechanical and thermal effects on petroleum systems. The last decade of research has evidenced that igneous intrusions may enhance thermal maturation of organic matter in source rocks and lead to both small- and large-scale structures that can deeply impact fluid migration or trapping. This contribution describes how the emplacement of a whole intrusive complex generated a dome structure of the overburden, which is the main trapping structure of a large producing oilfield. Our case study is the lower Miocene Cerro Bayo de la Sierra Negra (CBSN) intrusive complex, Neuquén Basin, Argentina, associated with the El Trapial oilfield where the main trapping structure is a large domal antiform centred on the CBSN complex. This study integrates the large subsurface dataset produced during the development of the El Trapial oilfield. More than 1200 vertical wells (producers and injectors) have been drilled in the flanks of CBSN complex. In addition, five 3D seismic cubes have been acquired over the years that have been merged and reprocessed into a single volume. Such a dataset allows a detailed characterization of both the structure affecting the Mesozoic strata and the geometry of the intrusive complex. Igneous rocks have been recognized along the entire stratigraphic section. Sill intrusions appear to concentrate in the shale units and the stacking of them has a direct impact on the doming structure generation. Our study allowed us to establish a direct correlation between the distribution of the intrusions and the extent, amplitude and style of doming, showing that the dome structure results from the emplacement of the intrusive complex. We also show that part of the doming is related to intrusions emplaced in the Mesozoic formations of the Neuquén Basin, whereas the other part of the doming is related to deeper structures not imaged on the geophysical data. We estimate that the amplitude of the doming reaches up to c. 500 m. The voluminous subsurface data, combined with exposed outcrops, makes the CBSN complex a world-class case study for showing how the shallow plumbing system of a volcanic complex may control the growth of large-scale trapping structures for various fluids, such as drinkable water, geothermal fluids and hydrocarbons.

Abstract Lava flows form important fluid reservoirs and have been extensively exploited for water aquifers, geothermal energy, hydrocarbon production and, more recently, for carbon storage. Effusive subaerial mafic to intermediate lava flows account for vast rock volumes globally, and form reservoirs with properties dictated by well-known lava flow facies ranging from pāhoehoe through several transitional forms to ‘a’ā lava. These variations in flow type lead to critical differences in the pore structure, distribution, connectivity, strength and fracturing of individual lava flows, which, alongside lava flow package architectures, determine primary reservoir potential. Lava flow margins with vesicular, fracture and often autobreccia-hosted pore structures can have porosities commonly exceeding 40% and matrix permeabilities over 10 −11 m 2 (>10 D) separated by much lower porosity and permeability flow interiors. Secondary post-emplacement physicochemical changes related to fracturing, meteoric, diagenetic and hydrothermal alteration can significantly modify reservoir potential through a complex interplay of mineral transformation, pore-clogging secondary minerals and dissolution, which must be carefully characterized and assessed during exploration and appraisal. Within this contribution, a review of selected global lava flow-hosted reservoir occurrences is presented, followed by a discussion of the factors that influence lava flow reservoir potential.

The Twyfelfountein Formation in Namibia and the Botucatu Formation in East South America represent a single dune-field separated through rifting of Gondwana during the Cretaceous. The Early Cretaceous Botucatu desert was the last depositional system operating in the Gondwanan heartland prior to continental drift initiated by the Paraná-Etendeka large igneous province. The dry-aeolian dunes, draas and sandsheet deposits of the Botucatu Formation are also present in the Twyfelfountein Formation. We aim to test whether the two formations had a similar provenance. The provenance of the Twyfelfountein is established using a multiproxy dataset including petrography, grain-size, heavy mineral composition and geochemistry, and detrital zircon U-Pb dating (16 samples from 5 sites in the Huab Basin, Namibia). Results indicate dominantly fine-to-medium feldspatho-quartose sands, rich in resistate minerals such as tourmaline, garnet and Fe-Ti oxides. Detrital zircon ages yielded mostly Cambrian-Neoproterozoic (450 to 650 Ma) ages. The geochemistry of garnet and tourmalines shows that these grains are originally sourced from amphibolite-facies metasedimentary rocks and acidic granitoids. The Botucatu Formation typically comprises sands that are quartzose, fine-medium sized, ZTR-rich with a predominance of Neoproterozoic detrital zircon ages. Based in this work and previously published data, the Twyfelfountein Formation sands are considered very similar to those of the Botucatu Formation, demonstrating a similar provenance for, and supporting the correlation of both units. The sands of the palaeodesert were derived from reworking of underlying strata from the Paraná and Huab basins. Furthermore, comparison of the datasets for both the Twyfelfountein and Botucatu formations shows a trend from SW to SE in sand composition due to the changes in the composition of the underlying pre-desert strata.

Abstract Cooling subvolcanic igneous intrusions are known to have a tremendous impact on fluid flow in the shallow Earth's crust. However, the long-term post-cooling legacy of subvolcanic intrusions on fluid flow has received much less attention. Here we describe geological examples in the Andean foothills, Argentina, showing that igneous intrusions have long-term effects on fluid flow after their emplacement and cooling. The case study consists of ∼11 Myr-old eroded andesitic intrusions of Cerro Alquitrán and Cerro La Paloma, northern Neuquén Basin, Argentina, at the rims of which large volumes of bitumen are naturally seeping out at the Earth's surface. The intrusions exhibit laccolithic shapes with steep-sided contacts with the host rock. Near the intrusive contacts, the andesite is intensely broken along concentric breccia bands and fracture bands, interpreted as resulting from syn-emplacement brittle magma deformation, which represent high-permeability pathways for the migrating bitumen. Organic geochemical analyses of the bitumen show that the seeping oils were generated from incipiently mature Vaca Muerta sections located in a regional kitchen to the west, implying a lateral migration of ∼10–20 km. The Cerro Alquitrán and Cerro La Paloma intrusions are demonstrative examples highlighting how extinct subvolcanic intrusions have long-term consequences for subsurface fluid circulations in sedimentary basins.

Abstract Soft sediment deformation structures may form when denser sediments or fluids are deposited on or flow over unlithified and less dense sediments. This study presents a seismic geomorphological study of the basal contact between an extrusive volcanic sequence and underlying sediments, defining the ‘Base Basalt’ surface, on the Mid-Norwegian Margin. This contribution focuses in particular on the development of geomorphological features related to the rapid loading of a several 100 m-thick lava delta package of hyaloclastite onto poorly consolidated sediments of the pre-volcanic sedimentary basin fill. Seismic horizons, sequence boundaries, volcanic facies units and attribute maps are used to characterize the seismic geomorphological features imaged within a high-quality 3D seismic cube. The ‘Base Basalt’ horizon and attribute maps reveal incised channels and a network of polygonal to irregular depressions and ridges described here as an ‘egg-box network’. More than 150 depressions, with a typical diameter of 1 km and a depth of 100 m, have been mapped. The deformation features, which are restricted to the base of the Lava Delta seismic facies unit, are interpreted to be the result of rapid loading of the Lava Delta onto poorly consolidated unlithified pre-volcanic sediments. This study presents new evidence for the dynamic nature of the transition between sedimentary basins and large-scale volcanism found along volcanic margins and basins associated with rapid volcanic deposition.

The Chachahuén Volcanic Complex is an eroded Upper Miocene arc to back-arc volcanic system that was emplaced in the north-eastern edge of the Neuquén Basin, southern Mendoza province, Argentina. It was formed as the result of shallowing followed by steepening of the Nazca plate during Miocene-Pliocene, and is characterized by a volcanism which ranges from trachydacites to basalts. Thanks to erosion, the stratigraphy and the shallow plumbing systems of the volcano are well-exposed. A new evolution for the volcano stratigraphy is proposed, based on new field observations, satellite imagery, and incorporating the radiometric and petrological data of previous works. The stratigraphy is constrained around one main explosive event, recorded by a thick dacitic pyroclastic density current (PDC) deposit (the Corrales Ignimbrite) (>150m). The main units forming the Chachahuén Volcanic Complex are (1) the pre-dacite PDC deposits (trachydacitic to rhyolitic) Vizcachas Formation, (2) the thick Corrales Ignimbrite, (3) a post-dacite trachyandesitic PDC deposits (dominated by block and ash (BAF) deposits) and thick lava flows, and (4) thin mafic basaltic lava flows. The collapse of a large elliptical caldera occurred during the Trachyandesite phase. The main magma transport channels and feeders are sub-vertical dykes, which exhibit a radial distribution centred on the main caldera depression. Moreover, cryptodomes mainly preserved outside the rim of the caldera accommodated the transport and emplacement of the more silicic magma during the Trachyandesite phase.

&lt;p&gt;The Tunguska Basin in East Siberia (Russia) hosts an extensive network of thick sills, part of the Siberian Traps Large Igneous Province. High-precision geochronology links the initial phase of sill emplacement to the end-Permian cascade of environmental catastrophes that almost expunged life on Earth (Dal Corso et al., 2022). The end-Permian atmosphere was impacted by a voluminous cocktail of gases, from CO&lt;sub&gt;2&lt;/sub&gt; and SO&lt;sub&gt;2&lt;/sub&gt; to halocarbons. Multiple lines of evidence suggest that sills emplaced within the evaporitic and coal-rich series of the Tunguska Basin acted as major contributors to this outgassing. Basin-scale observations and thermal modelling provide evidence of thermogenic gas production and release (Svensen et al., 2018). For the Tunguska sills, whole-rock geochemistry (Callegaro et al., 2021) and micro-analyses track multiple processes of magma host-rock interaction occurring at different levels across the plumbing system and the volcanic basin. Whole-rock trace elements and radiogenic isotopes reveal assimilation of variable crustal lithologies, from the crystalline basement to evaporites and carbonates in the Tunguska Basin. Assimilation of anhydrite-dominated evaporites is confirmed by whole-rocks sulfur isotopes. Assimilation of halogen-dominated evaporites is tracked by detailed mineral analyses of dolerite sills. We found widespread evolved late-stage pockets among the larger plagioclase and clinopyroxene crystals in the Tunguska dolerites. These pockets filled with an evolved, volatile-rich minerals, dominated by biotite and quartz, with minor K-feldspar, chloro-apatite, Cl-rich amphibole, sulfides and occasional baddeleyite and zircon. Biotite in the pockets is extremely enriched in Cl, especially at the rims. Plagioclase surrounding the pockets shows highly albitic rims. These compositions are widespread across the Tunguska Basin, where sills intruded halite- and anhydrite-rich evaporites, and&amp;#160;suggest extensive mobilization of crustal halogens and sulfur associated with the emplacement of the sills, along with previously demonstrated thermogenic carbon production. Notably, most investigated sills are geochemically correlated with the phase of Siberian Traps&amp;#160;magmatism coeval with the main extinction horizon (Callegaro et al., 2021).&lt;/p&gt; &lt;p&gt;&amp;#160;&lt;/p&gt; &lt;p&gt;Callegaro S., Svensen H.H., Neumann E.R., Polozov A.G., Jerram D.A., Deegan F.M. Planke S., Shiganova O.V., Ivanova N.A. &amp; Melnikov N.V., 2021. Geochemistry of deep Tunguska Basin sills, Siberian Traps: correlations and potential implications for the end-Permian environmental crisis. Contrib. Mineral. Petrol., 176, 49.&lt;/p&gt; &lt;p&gt;Dal Corso J., Song H., Callegaro S., Chu D., Sun Y., Hilton J., Grasby S.E., Joachimski M.M. &amp; Wignall P.B. 2022. Environmental crises at the Permian&amp;#8211;Triassic mass extinction. Nat. Rev. Earth Environ., 3(3), 197&amp;#8211;214.&lt;/p&gt; &lt;p&gt;Svensen H.H., Frolov S., Akhmanov G.G., Polozov A.G., Jerram D.A., Shiganova O.V., Melnikov N.V., Iyer K. &amp; Planke S. 2018. Sills and gas generation in the Siberian Traps. Phil. Trans. R. Soc. A., 376:20170080.&lt;/p&gt;

Cooling subvolcanic igneous intrusions are known to have a substantial impact on fluid flow in the shallow Earth's crust, for example activation of geothermal systems, circulation of mineralized fluids in ore deposits, fast maturation of organic matter in sedimentary rocks and the potential release of large volumes of greenhouse gases, which have triggered mass extinctions during the Earth's history. However, the long‐term post‐cooling legacy of subvolcanic intrusions on fluid flow received much less attention. Here we describe a demonstrative geological example in the Andean foothills, Argentina, showing that igneous intrusions have long‐term effects on fluid flow after their emplacement and cooling. The case study is a ca. 11‐million‐year‐old, eroded subvolcanic conduit, at the rims of which large volumes of bitumen are naturally seeping out on the Earth's surface. This contribution highlights that intense syn‐emplacement fracturing of the magma has created high‐permeability pathways that affect the regional fluid circulations, even millions of years after cooling. Our observations reveal how extinct subvolcanic intrusions have long‐term consequences on subsurface fluid circulations, which need to be accounted for in the exploration of geothermal energy, drinkable groundwater, hydrocarbons and CO 2 sequestration in volcanic basins and regions hosting ancient shallow magma intrusions.

Igneous sheet-complexes transport magma through the crust, but most studies have focused on single segments of the magma-transport-system or have low resolution. In the Jameson Land Basin in East Greenland, reflection-seismic data and extensive outcrops give unparalleled constraints on mafic intrusions down to 15 km. This dataset shows how sill-complexes develop and how magma is transported from the mantle through sedimentary basins. The feeder zone of the sill-complex is a narrow zone below basin, where a magmatic underplate body impinges on thinned crust. Magma was transported through the crystalline crust through dykes. Seismic data and published geochemistry indicate magma was supplied from a magmatic underplate, without perceptible storage in crustal magma-chambers and crustal assimilation. As magma entered the sedimentary basin, it formed distributed, bowl-shaped sill-complexes throughout the basin. Large magma volumes in sills (4-20 times larger than the Skaergaard Intrusion), and few dykes highlight the importance of sills in crustal magma-transport. On scales smaller than 0.2 km, host-rock lithology, and particularly mudstone tensile strength-anisotropy, controls sill-architecture in the upper 10km of the basin, whereas sills are bowl-shaped below the brittle-ductile transition zone. On scales of kilometres and towards basin margins, tectonic stresses and lateral lithological changes dominate architecture of sills.