Soil gas measurements of radon (²²²Rn), CO₂, and hydrocarbon concentrations, as well as gamma-ray spectrometry, were conducted at two separate locations to estimate the measurement results for known locations of hydrocarbon accumulations in the subsurface and oil seepage on the surface. The aim of the study was to confirm the applicability of the method for identifying migration pathways (e.g., faults) and to detect possible seepages of hydrocarbons to the surface as well as to investigate possible health issue potential about the soil gas analysis results. Site A investigations were performed with a large number of sampling points to provide sufficient spatial coverage to capture the influence of subsurface lithologic variability as well as the influence of the migration pathway on the measured parameters. For the investigation of site B, sampling points were positioned to reflect the situation between the area above producing hydrocarbon fields and areas with no confirmed accumulation. The results presented show that it is possible to distinguish the near-surface lithology (gamma-ray spectrometry), characterize the migration pathway, and indicate the area of oil seepage at the surface. Areas above the known hydrocarbon accumulations generally have elevated radon concentrations and detectable heavier hydrocarbons with sporadic methane in soil gas, which contrasts with the lower radon levels and lack of detectable heavier hydrocarbons in soil gas in the area with no confirmed hydrocarbon accumulation in the subsurface.

Croatia has both significant CO₂ emissions from the point sources and a history of oil and gas exploration, and this is why the CCS technology surfaced as a viable solution for curbing CO₂ emissions on a national level. Since approximately half of emissions from the stationary industrial sources occur along the Adriatic coastline, the entire offshore area became an exploration target. Regional studies revealed the potential storage plays, one of which is in the aquifer of the Mesozoic carbonate complex with dual porosity extending all along the Croatian offshore area. Three structures were chosen in its central part–Klara, Kate and Perina. For the first two, the models were constructed based on the data from old exploration wells and a regional structural map, while for the Perina structure, a new seismic interpretation was added to better characterise its properties. It came out that the Kate structure appears to be the most prospective in general (45 Mt), with neighbouring Klara as the second (39 Mt), while the initially promising Perina (7 Mt) turned out to be of far lesser importance. The Perina structure case is an example that new seismic interpretation can reduce the capacity estimate if it reveals certain limiting factors, in this case, the limitation of structural closure.

Extensional core complexes commonly develop in regions undergoing post-orogenic extension and lithospheric thinning, where extension exhumes rocks from deeper crustal levels. One such region is the southwestern margin of the Pannonian Basin System, where extension started shortly after the peak orogenic stage of the Dinarides. We present new stratigraphic and thermochronological evidence for the Early Miocene extensional exhumation of the Hrastovička Gora core complex, located at the southwestern margin of the Pannonian Basin System.The study area exposes a complete geological record related to the Early to Middle Miocene rifting and opening of the Pannonian Basin System, comprising pre-rift, syn-rift and post-rift rock units. Hrastovička Gora Mt. lies in the center of the study area, currently separating the Sava Basin to the NE from the Glina Basin to the SW.The oldest, Upper Cretaceous to Eocene pre-rift basement units are typically assigned to the so-called Sava Suture Zone of the Dinarides. They comprise Upper Cretaceous granitic and metamorphic rocks, as well as a volcano-sedimentary complex of intercalated spilites and pelagic Scaglia-type limestone, continuously overlain by Paleocene to Eocene, mostly siliciclastic, syn-orogenic flysch-type deposits.The subsequent Ottnangian to upper Badenian syn-rift deposits consist of siliciclastic conglomerates, sands, marls and limestones recording a gradual transition from alluvial to marine environments. While the surrounding Sava and Glina basins preserve this complete syn-rift succession deposited on top of the basement, the syn-rift units are entirely absent on Hrastovička Gora Mt. itself. There, the post-rift stage begins with a major Late Badenian overstepping transgression, depositing Upper Badenian to upper Pannonian post-rift successions directly above the pre-rift basement. This post-rift thermal subsidence stage forms a complete transgressive–regressive cycle, beginning with basal conglomerates and passing upward into sandstones, limestones, and marls, followed by a gradual shallowing from deep-water marls back to alluvial conglomerates, sands, and clays.Fission-track and (U–Th)/He dating of zircon and apatite from pre-rift and syn-rift rocks indicates the development of two distinct thermal paths following Late Eocene to Early Oligocene times. Thermochronological data indicate the exhumation of pre-rift basement units of Hrastovička Gora Mt. during Early to Middle Miocene times, whereas basement units of the surrounding Sava and Glina basins had already reached similar crustal levels during the Eocene. The integration of thermochronological and stratigraphic data indicate the existence of an extensional detachment, with Hrastovička Gora representing its exhumed footwall, and the Glina and Sava basins representing a supradetachment basins developed on top of hanging wall units. This detachment probably correlates with detachments previously discovered further southeast along the southwestern margin of the Pannonian Basin System in Prosara, Kozara, Motajica, Cer and Bukulja mountains.Presented research was conducted in the scope of the internal research project GeoSAVAGE at the Croatian Geological Survey, funded by the National Recovery and Resilience Plan 2021–2026 of the European Union – NextGenerationEU, and monitored by the Ministry of Science and Education of the Republic of Croatia.

The architecture of sedimentary basins is shaped by the interplay between relative sea-level changes and sediment supply combined with sediment transport processes. Relative sea-level changes are controlled by both eustatic sea-level variations and tectonics. While the effects of these factors on stratal stacking patterns have been a focus of extensive research, their distinct contributions remain incompletely understood.In this study, we interpreted high-resolution seismic profiles together with deep well data from the South Adriatic Foredeep (SAF), focusing on tectonic and sedimentary processes and sea-level fluctuations over the last 5.3 Ma. The SAF is an active basin, bounded by the Dinaric/Albanian thrust front and Apennine thrust/Apulian platform. Furthermore, the sedimentary system was further analysed by the means of 3D stratigraphic numerical modelling with DionisosFlow that accounts for the variability of the sediment and water flux combined with climatic and sea level variations, and sediment compaction. A series of models were conducted testing different subsidence, sediment supply and water discharge values, eustatic curves and sediment compaction parameters on the overall basin morphology.Based on the joint interpretation of the observational and model data, we propose a new stratigraphic model for the Miocene to Recent sedimentary evolution of the South Adriatic Foredeep. The basin is characterized by the variable length of the shelf around the basin margin with deposits of the deep-water gravity flow and bottom-currents on the slopes. The progradation of the shelf in NW reached up to 55 km, on top of the Apulian platform around 50 km, while at the footwall of the Dinaric thrust belt varies from 15 km to 30 km, with different thicknesses. The rate of the progradation at some places increased three times during Pleistocene, e.g. from 5,5 to 16 m/kry. Calculated subsidence also varies around the basin affecting the lateral change in accommodation space. Finally, the sedimentary architecture on the shelf is overprinted by compaction effects, which are most pronounced over basin confinements, sometimes causing significant deformation and subsequent aggradation.A key characteristic is the pronounced variability in sediment deposition along basin margins, driven by local tectonic and climatic forcing, as well as variation in autogenic processes. We conclude that the overall progradation was shaped by variable long-term (> 100 kyr) versus short-term (

Deep saline aquifers in the eastern part of Drava Basin were screened for potential storage sites. The input dataset included three seismic volumes, a rather extensive set of old seismic sections and 71 wells. Out of all identified potential storage objects, only two sites were found to be situated in the favorable geological settings, meaning that the inspected wells drilled through structural traps had a seal at least 20 m thick which was intersected by only a few faults with rather limited displacement. Many more closed structures in the area were tested by exploration wells, but in all other wells, various problems were encountered, including inadequate reservoir properties, inadequate seal or inadequate depth of the identified trap. Analysis was highly affected by the insufficient quality and spatial distribution of the seismic input data, as well as in places with insufficient quality of input well datasets. An initial characterization of identified storage sites was performed, and their attributes were compared, with potential storage object B recognized as the one that should be further developed. However, given the depth and increased geothermal gradient of the potential storage object B, it is possible that it will be developed as a geothermal reservoir, and this brings forward the problem of concurrent subsurface use.

The interpretation of deep 2D seismic profiles from the central Adriatic foreland of the External Dinarides in the area of the islands of Vis and Jabuka (Croatia), reveals a complex Mesozoic platform-to-basin architecture, and Cenozoic structural and sedimentary system developed on top of the central part of the Adriatic microplate (Adria). Tectonic subsidence and thick Paleogene to Neogene sedimentary loading in the latest Dinaric foredeep probably initially mobilized buried Middle Triassic evaporites from the proximal to distal foreland. Miocene tectonic is characterized by basement-rooted positive flower structures, pop-up blocks, and upward-diverging fault splays, diagnostic of a transpressional tectonic regime.The crustal-scale Quaternary subvertical faults without apparent vertical throw are associated with positive and negative structures along the strike. In the overlying sedimentary cover, localized normal faulting and extensional arrays overprint transpressional structures, interpreted as gravitational collapse above pop-up blocks, roof collapse above ascending diapirs, and lateral collapse within a mechanically decoupled cover. The positive structures are associated with the Quaternary salt diapirs, some of which are still active. However, it is not clear which faults are inducing regional seismicity.Instrumental seismicity is moderate to strong (up to M>5), shallow (≈5–15 km) and spatially clustered around the diapiric structures. Focal‑mechanism solutions predominantly indicate reverse to reverse–oblique faulting, yet the nodal planes do not clearly coincide with any single reverse fault imaged on 2D profiles, and many hypocenters project within or immediately above active salt diapirs. These observations suggest that salt diapirs act as mechanical and geometric controllers that focus stress and localize brittle failure on surrounding basement‑rooted faults, rather than being the primary source of seismic energy, which is difficult to reconcile with the seismic moment of M>5 events if salt flow alone were responsible.Active salt structures are characterized by long stems and relatively small surface expressions that are aligned along Quaternary faults. Their geometry, disconnection with original depth of the Triassic evaporites, and limited lateral extent, indicate tectonic extrusion of deep evaporites. Variations and segmentation along strike, suggest localized strain and strong structural control on diapir rise. Overall, these observations indicate that diapir growth and surface expression are controlled by the interaction between deep shear zones, active faulting, and a mechanically decoupled overburden. Within this framework, seismicity reflects the interaction between deep shear zones, evaporite mobilization and upper‑crustal faulting, highlighting the need to re‑evaluate focal mechanisms with improved 3D velocity models and to explicitly incorporate salt‑controlled structures into seismic‑hazard assessments for the region.“This work was supported by Croatian Science Foundation project SALTECTA (HRZZ-IP-2024-05-2957).”Keywords: Central Adriatic Sea, 2D seismic profiles, Transpressional deformation, Salt diapirs, Active tectonics, Seismicity.