Influence of Geological Structure on Micro-location of Submarine Karstic Sulphur Springs near Izola (SW Slovenia)

In the Slovenian part of the Gulf of Trieste/Trst, submarine springs occur as funnel-shaped depressions in the Holocene sandy-silt marine sediment that forms the seafloor. These springs exhibit both elevated temperatures (up to 29.6 °C) and sulphur content. Based on their location, they are divided into three groups: the Izola group (three springs), the Bele skale group (two springs), and the Ronek group (seven springs). Previous investigations linked these springs to the Izola anticline, characterized by its limestone core and flysch limbs, but no detailed explanation was provided. We propose that: A) sulphur groundwater springs from the limestone (karstic aquifer) at the stratigraphic boundary with the flysch and B) springs occur in the nearshore area, where the sedimentary cover of Quaternary deposits is thin enough to be penetrated by spring waters and washed out. According to existing data, the anticline axis is NW-SE directed, and the Izola group lies approximately on the seaward extension of the axis. Therefore, this interpretation fits perfectly for the Izola group, while the Ronek and Bele skale groups are off-axis extensions and require reinterpretation. In order to resolve the micro-locations of the Ronek and Bele skale groups, we conducted a sedimentological logging of the flysch deposits and detailed geological mapping. The investigations revealed that: A) limestone outcrops occur only in the town of Izola, B) two prominent calciturbidite megabeds that occur in the flysch enable very detailed geological mapping, and C) the axis of the Izola anticline is oriented in the WNW-ESE direction, and this moderate anti-clockwise rotation of the anticline axis explains the micro locations of all springs. The Ronek and Bele skale groups are located on the southern side, and the Izola group is on the northern side of the limestone core of the Izola anticline

Origin of the Jezero v Ledvicah lake; a depression in a gutter-shaped karstic aquifer (Julian Alps, NW Slovenia)

The Julian Alps are composed almost exclusively of Triassic to Lower Jurassic carbonates, which results in a karstified high-al­pine landscape. In such settings, large water accumulations are not expected and precipitated water drains vertically, gathers in deep, large-scale aquifers, and outflows in large karstic springs located in deeply incised valleys. Some small lakes, however, exist in high alpine areas. Most commonly, they formed above impermeable glacial sediments and are generally characterized by stagnant waters. Jezero v Ledvicah lake, which is one of the seven lakes in the Triglav Lakes Valley, is an exception, because it shows high subaqueous water inflow and outflow and occurs among highly karstified and permeable carbonates. Combining previous research with our new, detailed geological mapping of the lake surroundings and sedimentary research on the Lower Jurassic strata, we propose a hydrogeological model with the aim of explaining the extraordinary behaviour of the lake. We propose that Jezero v Ledvicah lake: A) is part of the “gutter-shaped” aquifer with perched groundwater that is situated below the floor of the Triglav Lakes Valley; B) barriers of the aquifer are structural (faults and thrust) and stratigraphic (clay interlayers in Lower Jurassic limestone); C) the lake formed in a structural, hydrogeological and morphological depression within this aquifer; D) the groundwater of the aquifer is re­charged not solely from the surface directly above the aquifer but additionally by subterraneous inflow from the overlying Slatna Nappe aquifer; and E) groundwater outflows from the aquifer at the southern end of the Triglav Lakes Valley, where the Lower Jurassic limestone pinches out.Key words: high-alpine lake, karstic aquifer, Julian Alps, Triglav Lakes Valley, Jurassic limestone, Southern Alps.Nastanek Jezera v Ledvicah – globel v žlebu podobnem kraškem vodonosniku (Julijske Alpe, SZ Slovenija)Julijske Alpe skoraj v celoti sestavljajo triasni in jurski karbonati, kar se odraža v morfologiji kraške visokogorske pokrajine. V tovrstnih razmerah ni pričakovati večjih površinskih pojavov vode, saj padavinska voda pronica vertikalno in se akumulira v obsežnih globokih vodonosnikih, iz teh pa izteka v izdatnih kraških izvirih, ki so v globoko vrezanih dolinah. Kljub temu v alpskem visokogorju obstaja nekaj manjših jezer. Večina jih je nastala nad neprepustnimi ledeniškimi sedimenti in jih lahko opredelimo kot stoječe vode. Jezero v Ledvicah, ki je eno izmed sedmih jezer v dolini Triglavskih jezer, je izjema, saj ima močno podzemno napajanje in iztok (je pretočno) ter se pojavlja med močno zakraselimi in prepustnimi karbonati. Na podlagi predhodnih raziskav, izdelave nove geološke karte okolice jezera in sedimentoloških raziskav spodnjejurskih plasti predlagamo strukturno-geološki in hidrogeološki model, da bi razložili nastanek in lokacijo jezera. Naše ugotovitve kažejo, da je A) Jezero v Ledvicah del žlebu podobnega vodonosnika z visečo podzemno vodo, ki se pojavlja v jurskih plasteh pod dnom doline Triglavskih jezer, B) da so hidrogeološke bariere vodonosnika strukturne (prelomi in nariv) in stratigrafske (plasti gline v spodnjejurskem apnencu), C) da je jezero nastalo v strukturni, hidrogeološki in morfološki depresiji znotraj vodonosnika, D) da se podzemna voda ne napaja izključno iz padavin, ki padejo neposredno na površino vodonosnika, ampak dodatno s podzemnim napajanjem iz višje ležečega vodonosnika Slatenske tektonske krpe in E) da podzemna voda izteka iz vodonosnika na južnem delu doline Triglavskih jezer, kjer se plastnati spodnjejurski apnenci (in s tem vodonosnik) izklinjajo.Ključne besede: visokogorsko jezero, kraški vodonosnik, Julijske Alpe, dolina Triglavskih jezer, jurski apnenec, Južne Alpe

O mikrolokaciji podmorskih kraških žveplenih izvirov pri Izoli: ko majhen popravek pomeni ključno spremembo: Vpliv geološke strukture na mikrolokacijo podmorskih kraških žveplenih izvirov pri Izoli (JZ Slovenija)

In the Slovenian part of the Gulf of Trieste/Trst, submarine springs occur as funnel-shaped depressions in the Holocene sandy-silt marine sediment that forms the seafloor. These springs exhibit both elevated temperatures (up to 29.6 °C) and sulphur content. Based on their location, they are divided into three groups: the Izola group (three springs), the Bele skale group (two springs), and the Ronek group (seven springs). Previous investigations linked these springs to the Izola anticline, characterized by its limestone core and flysch limbs, but no detailed explanation was provided. We propose that: A) sulphur groundwater springs from the limestone (karstic aquifer) at the stratigraphic boundary with the flysch and B) springs occur in the nearshore area, where the sedimentary cover of Quaternary deposits is thin enough to be penetrated by spring waters and washed out. According to existing data, the anticline axis is NW-SE directed, and the Izola group lies approximately on the seaward extension of the axis. Therefore, this interpretation fits perfectly for the Izola group, while the Ronek and Bele skale groups are off-axis extensions and require reinterpretation. In order to resolve the micro-locations of the Ronek and Bele skale groups, we conducted a sedimentological logging of the flysch deposits and detailed geological mapping. The investigations revealed that: A) limestone outcrops occur only in the town of Izola, B) two prominent calciturbidite megabeds that occur in the flysch enable very detailed geological mapping, and C) the axis of the Izola anticline is oriented in the WNW-ESE direction, and this moderate anti-clockwise rotation of the anticline axis explains the micro locations of all springs. The Ronek and Bele skale groups are located on the southern side, and the Izola group is on the northern side of the limestone core of the Izola anticline.slovenskem delu Tržaškega zaliva se v holocenskem peščeno-meljastem sedimentu, ki tvori ravno morsko dno, pojavljajo podmorski izviri v obliki lijakastih kotanj. V teh izvirih so opazni povišane temperature (do 29,6 °C) in vsebnost žvepla. Glede na njihovo lokacijo jih lahko razdelimo v tri skupine: skupina Izola (3 izviri), skupina Bele skale (2 izvira) in skupina Ronek (7 izvirov). Že predhodno so te izvire povezali z Izolsko antiklinalo, ki jo označujejo apnenčasto jedro in flišna krila, vendar natančnejše razlage niso podali. Predvidevava, da žveplene vode izvirajo iz apnenca (kraškega vodonosnika) na stratigrafski meji s flišem, in sicer v bližini obale, kjer je pokrov kvartarnih sedimentov dovolj tanek, da ga lahko izvirske vode izperejo. Glede na podatke naj bi bila os antiklinale v smeri SZ–JV in skupina Izola bi potemtakem ležala na protimorskem podaljšku osi. Takšna interpretacija torej povsem ustreza skupini Izola, preostali dve skupini pa padeta povsem izven podaljškov antiklinalne osi, zaradi česar je potrebna ponovna interpretacija. Da bi razložili mikrolokacije skupin Ronek in Bele skale, smo posneli sedimentološke značilnosti profilov flišnega zaporedja in izvedli natančno geološko kartiranje. Raziskave so pokazale, da a) se izdanki apnencev pojavljajo le na območju mesta Izola, b) dve kalciturbiditni veleplasti, ki se pojavljata v flišu, omogočata zelo natančno geološko kartiranje in c) je os Izolske antiklinale orientirana v smeri ZSZ–VJZ. Prav ta zmerna rotacija antiklinalne osi v nasprotni smeri urnega kazalca razloži mikrolokacije vseh izvirov. Skupini Ronek in Bele skale sta na južni strani, skupina Izola pa je na severni strani apnenčastega jedra Izolske antiklinale