Sverre Planke

The emplacement of igneous sill intrusions induces rapid heating of host rocks, generating fluids that migrate through structures known as hydrothermal vent complexes (HTVCs). While sill geometry and permeability are considered important factors controlling fluid migration around igneous sill intrusions, the precise mechanisms controlling vent distribution remain unclear. To improve the understanding of the primary controls on the final distribution of HTVCs, we are using a 3D seismic data set from the Mid‐Norwegian margin to analyze HTVCs associated with the ∼56 Ma Infinity Sill. The sill covers 237 km ² and is associated with 79 HTVCs, 25 of which are classified as mini‐vents. The HTVCs have outer diameters ranging between ∼0.1–2.7 km, are separated by spacings between ∼1.2–4.8 km, have conduit heights ranging between ∼0.6–1.1 km, and variable upper terminations. Our analysis reveals a large‐scale fluid migration pattern dominated by venting along the sill margins and above the sill interior, controlled by factors such as the fluid generation potential around the sill, the density of local highs in the sill interior as well as the mode and heights of sill transgression. Sill geometry is thus found to affect the formation, size and spacing of HTVCs, and is interpreted to constitute a primary control on the final distribution and morphological characteristics of HTVCs. Our findings contribute to a better understanding of subsurface fluid dynamics associated with sill intrusions emplaced in organic‐rich strata and have broader implications for understanding the climatic effects of hydrothermal venting at the Paleocene‐Eocene transition.

Boulder fields can preserve valuable information on the processes that shape and modify landscapes, but their interpretation is commonly based on limited clast samples that do not capture population-scale spatial variability. Here we investigate Stone Garden, a large and previously underexplored boulder field in the Altai Mountains, within a complex paraglacial valley shaped by repeated Quaternary glaciations, deglaciations, and outburst floods. Using a high-resolution digital surface model, we quantify the distribution, size, orientation, clustering, and erosional context of the entire boulder population. Situated on a terrace ~70 m above the Katun River, Stone Garden is a strongly heterogeneous boulder field, comprising two major boulder concentrations that together encompass three morphometrically distinct domains. The central and southern domains form an elongated marginal boulder accumulation downstream of a major valley constriction, with spatial organization and boulder fabrics consistent with deposition as a flow-separation berm during a high-magnitude flood. The northern domain occupies a lower terrace level, contains smaller boulders and a contrasting fabric, and is associated with a separate step-confined valley expansion, indicating formation as a distinct marginal berm under different flow conditions. Published chronological constraints place boulder emplacement and terrace stabilization broadly within late MIS2–early MIS1 (~19–7 ka) but do not resolve individual stages. Together, these geomorphic relationships define a testable three-stage evolutionary framework involving primary berm emplacement, localized erosional reworking, and later formation of the northern domain. Similar integrated analyses may help determine whether boulder fields formed in different geomorphic settings preserve diagnostic spatial and morphometric signatures.

Understanding ancient climate dynamics is crucial to accurately forecast future changes to Earth’s climate system. The Norwegian High-Arctic archipelago of Svalbard experiences higher-magnitude warming than the lower latitudes. Its sedimentary succession provides an important climate archive spanning much of the Phanerozoic, including several hyperthermal events and mass extinctions of global importance. These include the End-Permian Mass Extinction (EPME) and the Paleocene–Eocene Thermal Maximum (PETM). In addition, the High Arctic Large Igneous Province (HALIP) provides an opportunity to study how igneous sills interact with organic-rich shales to generate greenhouse gases during contact metamorphism. The ongoing multidisciplinary international project SvalCLIME aims to systematically study these hyperthermal events and their relationships to Phanerozoic climate evolution. SvalCLIME seeks to drill multiple shallow boreholes at four sites in Spitsbergen that will provide a semi-continuous record of Phanerozoic stratigraphy from an underexplored region. The drill cores, in conjunction with outcrops, will provide a Permian–Eocene climate record of unprecedented continuity. Here, we synthesise existing pre-Quaternary Phanerozoic (540–2.58 Ma) paleoclimate and paleoenvironmental data from Svalbard in curated data packages to complement a recently published comprehensive review article. The data packages are organised by proxy, facilitating the addition of future data sets. We present composite data coverage plots of key proxies (stable carbon isotopes [δ13C], oxygen isotopes [δ18O], pyrolysis, mercury) that illustrate data availability and current data gaps. Further, we give an overview of available geochronological constraints for Svalbard’s pre-Quaternary Phanerozoic rock record, likewise curated into two data collections of 1) various methods that provide age constraints and 2) biostratigraphy. We also discuss the integration of various data sets in four case studies to illustrate the benefit of compiling such data for both drill cores (Longyearbyen CO2 lab and Deltadalen) and outcrops (Festningen, Lusitaniadalen, Munindalen and Billefjorden).

The Woodfjorden area in northwestern Svalbard hosts the world's northernmost onshore thermal springs, extinct Quaternary volcanoes (the Bockfjorden Volcanic Complex), late Miocene lava flows (the Seidfjellet Formation) that overlie a Devonian sedimentary basin, and a long‐lived regional fault zone. To contribute to a better understanding of subsurface fluid flow in this volcanic region, we conducted a 3D magnetotelluric (MT) survey at 12 sites, combined with water and gas sampling at the thermal spring clusters (Trollkjeldene and Jotunkjeldene). While the MT survey has a limited aperture due to the remoteness of the region and complex logistics, the identified structural features put several constraints on the evolution of this poorly studied hydrothermal system. The electrically conductive zones (1–10 m), under Trollkjeldene and the Halvdanpiggen volcanic center, are interpreted as signatures of deep hydrothermal fluids or mineralized zones; the resistive anomalies (1–10 km) at 1–4 km depth under the Sverrefjllet volcano indicate buried magmatic or basement rocks. Stable isotope data indicate both meteoric and crustal components for thermal waters. Carbon and noble gas isotope ratios support a mixed gas source involving crustal, atmospheric, and mantle components. Helium isotope ratios suggest a mantle‐derived fraction of 6%–8%. These findings suggest extinct magmatic activity and ongoing hydrothermal circulation, likely prolonged due to fluid compartmentalization at depth by low‐permeability magmatic or metamorphic rocks.

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 δ ³⁴ S _VCDT (9.9‰–11.8‰) 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 δ ¹³ C and δ ¹⁸ O (mean −2.10‰ δ ¹³ C _VPDB and −14.79‰ δ ¹⁸ O _VPDB , 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.

Large parts of the Arctic, including Svalbard, have experienced significant uplift and erosion over the last 15–20 million years, coinciding with localized magmatism and seafloor spreading in the Arctic and northernmost Atlantic Oceans. This recurrent uplift has left sparse onshore stratigraphic records, limiting our understanding of Miocene tectono-sedimentary processes across this vast region. The volcanic Seidfjellet Formation of northwestern Spitsbergen, Svalbard, provides a rare and valuable onshore record of the Miocene. To understand its emplacement mechanism, volcanic processes, and pre-volcanic paleoenvironment, we conducted detailed field investigations, including facies analysis, complemented by digital outcrop model analysis and palynological studies. We documented 10–20 basaltic lavas with cumulative thickness of ~400 m, exposed at elevations of 600–1350 m. At the contact with the underlying Devonian strata, we observed an undulating pre-volcanic surface that defines several hundred meters wide depressions locally draped by volcaniclastic deposits and filled by hyaloclastites, organized into steeply dipping foresets ~150 m thick. At the base of the formation, we identified previously unreported sedimentary pockets, marking the first evidence of the pre-volcanic phase in this unit. Our palynological analysis suggests a conifer-dominated wetland environment prior to lava emplacement of Late Oligocene–Early Miocene or Late Miocene age. Here, we present the first systematic description of the volcanic facies and architecture of the unit, as well as constraints on its spatial extent. Additionally, through the pre-volcanic sedimentary record, we provide novel paleoenvironmental reconstructions predating lava emplacement, thus evaluating the interplay between magmatism, uplift, and Miocene evolution in Svalbard.

Hydrothermal vent complexes are degassing structures that form in response to rapid volatile generation and release associated with igneous sill intrusions in sedimentary basins. They are discovered in numerous basins worldwide, originating from sills and contact aureoles and terminating at the paleosurface where they form up to 10 km wide craters. Field studies and numerical models have suggested that the venting processes were explosive, releasing aureole-derived gases, sedimentary pore fluids, and fragmented sedimentary rocks to the seafloor or land surface. However, ejecta deposits originating from hydrothermal vent complexes are poorly studied and hard to identify, hampering detailed reconstructions of vent formation and evolution. Here we report the characteristics of a possible ejecta deposit from Vøring Basin Hole U1570D drilled as part of IODP Expedition 396 in 2021. During core logging, an unusual layer was identified immediately overlaying the top Paleocene strata. This layer is about 2m thick, contains Apectodinium augustum dinocysts restricted to the Paleocene Eocene Thermal Maximum (PETM), and also yields abundant reworked Paleocene and Cretaceous microfossils. Moreover, the layer is characterized by rounded fragments of claystone, angular chert and quartz fragments, dolerite fragments, fresh and devitrified volcanic tephra, and a mixed groundmass of smectite-illite with diatoms and early diagenetic pyrite. Electron microprobe analyses document a bimodal tephra geochemistry, with both basaltic and rhyolitic compositions and morphologies indicating no or minor reworking. In the presentation we will discuss two possible formation scenarios for the layer, including 1) erosion from nearby marginal highs, and 2) ejecta deposit sourced from an explosive submarine eruption from a hydrothermal vent complex, mobilizing Cretaceous and Paleocene strata from the conduit zone. In any case, the bimodal tephra composition stresses the presence of an evolved igneous system in the Vøring Basin during the PETM, with a potential genetic link to a recently discovered Paleocene granite.

The magma plumbing system of large igneous provinces may include emplacement of voluminous sill complexes in sedimentary basins. Key examples include the North Atlantic Igneous Province (NAIP; c. 56 Ma), the Karoo-Ferrar province (c. 183 Ma), and the Siberian Traps province (c. 251 Ma). In these basins, thousands of kilometer-sized hydrothermal vent complexes are associated with the sill complexes. We have interpreted new and legacy 2D and 3D seismic data in the Vøring and Møre basins offshore Norway to characterize the sill and hydrothermal vent complexes in a 100,000 km2 large region. The upper part of one of the hydrothermal vent complexes, the Modgunn Vent, was cored by five boreholes during IODP Expedition 396 in 2021. Saucer-shaped sills and overlying domes at the Top Paleocene level characterize the Jolnir, Tulipan and Infinity sill complexes in the Møre Basin. In contrast, sill complexes in the Vøring Basin display more variable morphologies, including ponding thick sheets and transgressive sheets reflecting the variations in deep basin structure and type of host rocks. The extensive Vivel Sill in the Vigrid Syncline is locally more than 200 m thick in the deeper parts of the basin, with some domal-shaped geometries that crosscut the deep basin stratigraphy and layer-parallel planar geometries at shallow stratigraphic levels. The hydrothermal vent complexes are mainly present as pipe-like disruptive seismic anomalies above transgressive sill segments connecting the contact aureoles with crater- or eye-shaped upper parts of the vent complexes near the Top Paleocene reflection. Scientific and industry drilling samples document that the vent craters were infilled during earliest Eocene times, most likely related to sill emplacement during the Paleocene-Eocene Thermal Maximum (PETM). In conclusion, the current geometries of voluminous igneous sheet intrusions both reflect the pre-emplacement deep basin structure and post-emplacement structural deformation, whereas the contact metamorphic processes triggers pipe-like deformation and focused fluid flow during formation of hydrothermal vent complexes.

Basaltic rocks host abundant pore space and reactive mineral phases that make them attractive targets for CO₂ storage via mineral trapping, yet their seismic response presents significant challenges for monitoring due to strong scattering and wavefield complexity. Within the framework of the PERBAS project (Permanent sequestration of gigatons of CO2 in continental margin basalt deposits), we assess the potential for high-resolution time-lapse (4D) seismic methods to detect subsurface changes in a basalt-dominated offshore setting and to inform efficient monitoring strategies applicable to future CO₂ storage operations.We analyze two P-Cable high-resolution 3D seismic volumes acquired over Skoll High in the Vøring Basin (mid-Norwegian margin), a 2022 baseline and a 2024 repeat survey that reoccupied 17 of 26 original sail lines. Both datasets used consistent acquisition parameters and were processed with a uniform workflow incorporating geometry assignment, noise attenuation, amplitude correction, and high-resolution binning (6.25 × 6.25 m). A key objective was to maximize seismic repeatability as a prerequisite for robust 4D analysis in basaltic terrain.Time-lapse calibration included cross-correlation for phase and time shifts, shaping filters, cross-correlation statics, and amplitude cross-normalization. Different calibration windows were defined above the top basalt and including the top basalt sequence in order to analyze the impact of non-repeatable signal variability within the volcanic complex. The normalized root-mean-square (NRMS) metric was used to quantify repeatability across the repeat survey area.Our initial results indicate that high spatial repeatability is attainable with P-Cable 3D seismic data in a basalt setting when acquisition and processing are carefully controlled, though areas of complex basalt morphology and structural heterogeneity exhibit higher NRMS values. Difference volumes highlight regions of anomalous repeatability that correlate with geological features. These findings underscore both the promise and limitations of time-lapse seismic monitoring in basaltic reservoirs and contribute to establishing realistic detection thresholds and optimized survey designs for CO₂ storage monitoring.This study expands the understanding of seismic repeatability in volcanic margin environments and provides groundwork for advancing cost-effective monitoring strategies in basalt-hosted storage projects.

Hydrothermal vent complexes (HTVCs) form when water, carbon dioxide (CO₂), methane (CH₄), and other fluids, along with sediment, are rapidly ejected into the ocean and atmosphere, driven by the expansion and boiling of pore fluids surrounding intrusive magma in sedimentary basins. HTVCs are a common feature of Large Igneous Provinces (LIPs), which host the largest known magmatic intrusions on Earth. Given their nature and chronology, LIPs have historically been linked to major mass extinctions and global climate change, owing to their role in carbon degassing. The North Atlantic Igneous Province (NAIP, 61–58Ma and 56–53Ma) is the youngest large LIP emplacement and hosts hundreds of hydrothermal vents within the Vøring and Møre basins. Due to their timing and potential to emit a large volume of greenhouse gases, the HTVCs within the NAIP have been proposed to play a role in the onset and long duration of the Paleocene-Eocene Thermal Maximum (PETM, ca. 56 Ma). However, several aspects of the formation, timing, and impact of these particular HTVCs formation on the carbon cycle remain poorly understood. Here, we present a detailed stratigraphic and morphological reconstruction of the Modgunn Vent in the Vøring Basin, offshore Norway. High-resolution 3D P-Cable seismic data and borehole observations from the International Ocean Discovery Program (IODP) Expedition 396 reveal a multi-crater architecture, with four sub-craters formed through individual eruptive events, each associated with discrete sill intrusions and sediment infill phases. The four mapped craters present distinct subsidence, infill stratigraphy, and uplift signatures, indicating that, although currently clustered in a single HTVC, they formed independently and later amalgamated. Crater-specific uplift patterns and internal vent deformation features suggest a late-stage reactivation of vent conduits driven by renewed sill emplacement or fluid and mud migration. Biostratigraphic data tie the formation of the youngest crater in the Modgunn vent to the period immediately preceding the PETM. However, our seismic interpretation shows that the other three craters formed earlier. Our findings emphasise isochronous vent activity across the North Atlantic Igneous Province and reinforce a prolonged, dynamic scenario of greenhouse gas release. Further detailed subsurface imaging and stratigraphic analysis are crucial for refining models of vent evolution and, consequently, carbon degassing and its role in rapid climate perturbations.