Slovenia is positioned in an area with ongoing convergence between the Adriatic microplate and the Eurasian plate. This results in a noticeable number of active faults – exhibiting deformation during the Quaternary, which are mostly dextral strike-slip faults. Their direction is evident from geomorphology with elevations from 0 to 2864 m a.s.l. In eastern Slovenia, several groundwater and gas phenomena occur along the regional fault zones, which can be determined only by subsurface investigation, e.g. geophysical measurements.

Slovenia is a country rich in groundwaters. They are predominately used as a drinking water resource, but there are many special waters and other features, which can be named geomanifestations. It is interesting that the majority of these geomanifestations are to be found in NE Slovenia.

Phenomena of natural seepage of geogenic CO₂ gas are called mofette. They are mostly observed between the towns Lenart in Slovenske gorice and Radenci in NE Slovenia, and can occur either as a dry seepage, recognizable only due to special vegetation or bare soil near the CO₂ vents, or as a wet mofette, where a different intensity of gas bubbles is visible in streams or holes filled with rainwater. The gases are proved to be emitted from the Earth‘s mantle. The noble gas composition of two sites, one near Radenci and the other at Rogaška Slatina, seems to be surprisingly similar, which we attribute to two regional and obviously very deeply permeable fault zones, the Raba and the Donat fault zones.

Subthermal springs, these are the relatively cold ones with a temperature not exceeded the medium annual air temperature by 20°C, are known at 10 sites in Slovenia, but not in the North East. Moreover, 35 sites all over the country can produce thermal waters with outflow temperatures of 20°C or more. Most of them are situated and exploited in NE Slovenia, where the elevated heat flow is attributed to thinner crust below the Pannonian basin. Thermomineral waters with characteristics of thermal and mineral water groups occur at 18 sites. These waters reach up to 75°C in NE Slovenia and are intensively used for balneology, spa and various types of space heating.

Mostly in the eastern part of the country, along the River Ščavnica and at the towns Radenci and Rogaška Slatina, we recognized 17 sites with mineral waters, having at least 1000 mg/l of total dissolved solids or 250 mg/l of free CO₂ or a significant amount of a chemical substance (e.g. iron, sulfur). Due to locally high occurrence of such hydraulically connected springs, we even have three officially delineated mineral water spring areas.

The Mura-Zala sedimentary basin on the outskirts of the Pannonian basin also hosts several organic deposits. Paralic brown coal occurs in Pontian beds which are best ascertained between Lendava (SLO) and Mursko Središće (CRO). Similarly, oil and natural gas seeps were known between Slovenske gorice (SLO) and Međimurje (CRO) but many have ceased due to oil and gas production in the middle of the 20th Century. Nowadays, tight gas is produced near Lendava while other hydrocarbons only in symbolic quantities.

Nina Rman
Geological Survey of Slovenia (GeoZS)

References

Gabor, L., Rman, N. 2016: Mofettes in Slovenske gorice, Slovenia. Geologija 59/2, 155-177.
Markič, M., Turk, V., Kruk, B., Šolar, S. V. 2011: Coal in the Mura Formation (Pontian) between Lendava (Slovenia) and Mursko Središće (Croatia), and in the wider area of NE Slovenia (in Slovene). Geologija 54/1, 97-120.
Pleničar, M. 1954: Oil fields in the Obmurje. Geologija 2, 36-93.
Rman, N., Lapanje, A. 2016: Map of mineral and thermal waters and mofettes. In: The Geological Atlas of Slovenia, GeoZS.

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