Vpliv geološke zgradbe na genezo jame Pečina v Zjatih na Matarskem podolju

Preradović Hlede, Špela (author), Verbovšek, Timotej (mentor), Rožič, Boštjan (co-mentor)

V sklopu magistrskega dela sem preučila litološke in strukturne lastnosti apnenca, ki so vplivale na genezo jame Pečina v Zjatih, ki leži na JZ delu Matarskega podolja, nekaj km S od vasi Skadanščina. Jama je nastala v močno razpokanem apnencu albijsko-cenomanijske starosti s povečano vsebnostjo organske snovi. Trenutno je v fazi razpada, voda se zaradi freatičnega skoka pretaka globlje v kamnini. Vhod v jamo predstavlja udorna vrtača, katere nastanek je povzročil vdor zunanjih klimatskih pogojev, ki so uničili večino primarnih jamskih oblik. Zaradi udiranja stropa v vhodnem delu jame je nastalo krioklastično pobočje, ki sega vse do osrednjega dela jame. V notranjem delu jame je glavni jamski rov v obliki ključavnice, ki je nastal v freatičnih in epifreatičnih pogojih. V ospredju raziskav so začetni horizonti, ki se pojavljajo v vhodnem delu jame. To so lezike, ki prve prožijo raztapljanje po končani diagenezi zaradi ugodnih litoloških, fizikalnih in geokemičnih lastnosti plasti, ki ležijo pod in nad njimi. Začetne horizonte v vhodnem delu jame sem prepoznala po freatičnih kanalih, ki se pojavljajo tik ob lezikah ter po večji količini sige, ki prekriva plasti pod lezikami. V laboratoriju sem plastem nad in pod začetnimi horizonti določila mikrofaciese ter jih analizirala s pomočjo fluorescenčne spektrometrije in žaroizgube. Za bolj reprezentativne rezultate sem preučila tudi plasti nad in pod lezikami, ki niso začetni horizonti. S pomočjo strukturnega kartiranja vrtač na površju sem uspela določiti tri prelome, ki so vplivali na usmerjenost jame ter na nastanek površinskih kraških oblik. Začetni horizonti se pojavljajo predvsem tam, kjer sta prisotna mikrofaciesa bioklastični wackestone ter mudstone do wackestone z bioklasti. Ob začetnih horizontih imata mikrofaciesa večje količine organske snovi kot pa drugod v vhodnem delu jame, kjer se prav tako pojavljata, zato domnevam, da je imela organska snov velik vpliv na nastanek začetnih horizontov. Najverjetneje so se pri oksidaciji sprostile agresivne kisline, ki so bile bolj topne od ogljikove in so uspele hitreje raztapljati apnenec.

• Language: Slovenian
• Keywords: Začetni horizont, speleogeneza, apnenec, Matarsko podolje, Pečina v Zjatih.
• Work type: Master's thesis/paper
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Year: 2021
• PID: 20.500.12556/RUL-125702
• COBISS.SI-ID: 62070531
• Publication date in RUL: 03.04.2021

Secondary language

• Language: English
• Title: Influence of geological setting on the genesis of the cave Pečina v Zjatih (Matarsko podolje, SW Slovenia)

Abstract

Out of more than 200 caves, which are found on Matarsko podolje, Pečina v Zjatih was chosen for a detailed research of its genesis. This cave is found on the SW of Matarsko podolje, several km north of the village Skadanščina. The cave was formed in phreatic, epiphreatic, and vadose conditions in slightly bituminous Albian-Cenomanian limestone and is currently in decay phase. Water no longer flows through it. The cave entrance is a collapse doline, which has caused an intrusion of outside climatic conditions, which have destroyed most of the cave’s original features. At the entrance, ceiling breakdown has caused the formation of a cryoclastic slope, which extends to the middle part of the cave. The interior of the cave is represented by a main passage, which was first formed in phreatic conditions along an inception horizon. Later on, the water with abrasive flysch material from Brkini hills carved a canyon into the bottom of the phreatic passage. The focus of this thesis are inception horizons, which are located at the entrance of Pečina v Zjatih. Inception horizons are bedding planes, where dissolution of limestone first takes place, due to favourable lithological, physical and geochemical properties of beds above and below them. Inception horizons were identified by phreatic channels, which have formed along them, and flowstone, which has covered the beds below them. In a laboratory, I have identified microfacies of beds above and below inception horizons and I have performed both the XRF and LOI analysis of those beds. For more representative results I have also analysed beds above and below those bedding planes, which show no signs of dissultion. With structural mapping of dolines I have identified three faults, which had an impact on the cave's orientation and the formation of surface karst features. Results show that inception horizons at the cave’s entrance are mostly associated with bioclastic wackestone and mudstone to wackestone with bioclasts. Both microfacies have organic matter and they appear in other parts of the cave’s entrance. However, organic matter in both microfacies is much higher along the inception horizons than anywhere else. Therefore, I assume that organic matter had a big influence on the formation of inception horizons. During oxidation it probably caused the formation of aggressive acids, which were able to dissolve the rock much faster than the carbonic acid, which is usually present in the water.

• Keywords: Inception horizon, speleogenesis, limestone, Matarsko podolje, Pečina v Zjatih.