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.

Ophiolite exposures in NW Croatia have been attributed to the Western Vardar Ophiolitic Unit and interpreted as derived from the Meliata–Maliac–Vardar branch of the Neotethys Ocean. Blocks within the ophiolitic mélange on Mt Ivanščica were investigated to determine the petrological and geochemical characteristics of the effusive rocks and to carry out radiolarian dating of the associated pelagic sedimentary rocks. The analysed effusive basic rocks represent chemostratigraphically uniform subalkaline high-Ti massive tholeiitic basalts characterized by an enriched composition typical of incompatible element-enriched mid-ocean ridge basalt (E-MORB). These basalts are compatible with c. 9–11% of partial melting of an enriched mantle source transitional between primitive and depleted MORB-type mantle and were formed in the non-subduction geotectonic setting of E-MORB-type rocks. This reflects an initial succession of oceanic protocrust formation and the onset of ocean spreading. Radiolarians from the chert and shale successions associated with the basalts indicate a Late Anisian–Early Ladinian age of initial ocean floor spreading, which continued into the Langobardian. The obtained data are correlative with reported blocks interpreted as remnants of the Triassic Neotethys crust from the ophiolitic mélange of the Western Vardar Ophiolitic Unit and reaffirm a common origin from a single ocean basin located east of the Adria microplate. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists