Lehnjakasti kapniki v spodmolih v slovenski Istri // Tufaceous speleothems in rock shelters in Slovenian Istria
DOI:
https://doi.org/10.3986/GV87201Keywords:
lehnjak, lehnjakasti kapniki, mahovni lehnjaki, spodmoli, Veli Badin, Stena v dolini Dragonje, slovenska Istra // tufa, tufaceous speleothems, moss tufa, rock shelters, Stena in Dragonja Valley, Slovenian IstriaAbstract
Apnenčaste stene spodmolov v slovenski Istri so pogosto prekrite s karbonatnimi tvorbami. Za te tvorbe so predhodno obstajale domneve, da gre za sige, naša domneva pa je, da so lehnjaki. Opravili smo raziskave tvorb na dveh lokacijah – Veli Badin in Stena v dolini Dragonje. Tvorbe smo fotografirali, izmerili in zabeležili posebnosti. V laboratoriju smo opravili petrološke, sedimentološke, mineraloške in geokemične analize tvorb. Ugotovili smo, da gre za poseben tip lehnjakov – lehnjakaste kapnike. Njihov nastanek je vezan na mikroklimatske pogoje, drugačne od tistih v jamah, na njihovo odlaganje pa vplivajo organizmi, ki preraščajo stene spodmolov. Prisotnost lehnjakov na izbranih lokacijah kaže, da spodmoli glede na morfologijo predstavljajo polodprti prostor tudi v predhodnih fazah njihovega razvoja in da tvorbe niso nastale v nekdanjih jamskih prostorih.
The distinct feature of rock shelters in Slovenian Istria is that the host limestone rock is frequently overlain by freshwater calcareous deposits. These deposits were in the past described as speleothems, but our assumption was that these deposits are tufas. In our study we focused on two locations – Veli Badin and Stena in Dragonja Valley. Calcareous formations were photographed and measured in the field; an inventory of the specifics of formations was made. In the laboratory we made petrological, sedimentological, mineralogical and geochemical analyses of samples of the deposits. In contrast to previous assumptions the deposits represent a specific form of tufa – tufaceous speleothems. The formation of these tufas is related to microclimatic conditions, different from those in cave environment, and the presence of organisms, which have influence on tufa deposition. As the presence of speleothems would indicate that rock shelters are former cavities now exposed to surface by erosion, the presence of tufas corroborates the idea that rock shelters in their previous formation phases morphologically represented a semi-open space.
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