In 2011, we were called to survey several shallow water ponds (wp) in the Kog (KOG) area, which geologically belongs to an antiform termed the Ormož-Selnica Antiform (OSA) (Fig.1). It is built of Neogene marls, sands to sandstones, shales, limestones, conglomerates, and thin lignite interbeds. The OSA was formed between two deep regional SW-NE reverse faults (Lj – Ljutomer f.; D – Donat f.). In the hilly Kog area, the Neogene OSA crops out, while it plunges slowly toward NE under Quaternary fluvial sediments. It is intersected by numerous normal faults running either along or perpendicular to the main regional reverse faults.
In the wider Kog region, surface seepages of oil were historically known at several sites. In the fields of Petišovci (Pt), Lovászy (L), Selnica (S), Peklenica (P) (Fig.1) and some others, hydrocarbons (HCs) were exploited at several time periods since the second half of the 19th century. A small production still exists in the Petišovci (Pt) field. In the last ten years, the Pt field, connected with the Lovászy (L) field in Hungary, was also an area of new exploration by deep reflection seismic survey and drilling of two wells, 3500 m deep.
Today, the knowledge about geomanifestations in the form of small seepages of oil in the Kog area is very scarce. There is no contemporary overview of them nor referring to their sites nor to their scientific explanation. Therefore, an initiative that came from Ivan Kerš (today living in Maribor), to look at four “oily” ponds that he remembered from his child-times in the 1940s, was very welcome. To his information, water from these ponds was not potable due to “oily matter”, while water from some other sites and from a close brook was good to drink. As seen from the photos (Figs.2 and 3), the water ponds occur in a swampy land. They are up to 4 m wide, and 30 m long. On the surface, there was visible a very thin “screen” of decayed organic matter and an “oily” appearance (Fig 3). Visible was also bubbling of gas due to decay of deposited organic matter at the bottom of the ponds. There was no smell of water eventually indicating the presence of HCs.
Despite that we did not try to drink this water 😊 but took three samples. Analysis of polycyclic aromatic HCs (PAH) (Fig.4; first column) showed concentration of 0.005 µg/l of water and below (limit for potable water is 0.1 µg/l). Concentration of mineral oils (MOs) was below 0.1 mg/l (Fig.4, second column), while the limit for the surface waters by Slovenian legislation is 0.05 mg/l. It is interpreted that MOs origin from the local “man-caused” pollution due to not-responsible management with motor, heating, chain-sawing and similar oils, and therefore are not a true geomanifestation.
Markič, M., Toman, M., 2011: GeoZS Report Arch.No: C-II-30d/b1-1/44, 6p.
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