Sedimentološka in mineraloška analiza holocenskih rečnih sedimentov Planinskega polja : magistrsko delo

Braniselj, Anej (author), Šmuc, Andrej (mentor)

Planinsko polje je kraško poplavno polje po katerem teče reka Unica. Namen pričujoče raziskave je bilo določiti strukturo in sestavo holocenskih rečnih sedimentov Planinskega polja ter prepoznati njihov izvor in ugotoviti ali se struktura sedimenta in njegova mineraloška sestava spreminjata znotraj Planinskega polja – od izvira reke Unice v vhodnem delu Planinske jame pa vse do ponornega območja na severu polja. Vzorce sedimenta sem pobral na 23 vzorčnih mestih iz dveh različnih sedimentacijskih okolij, in sicer rečnega korita ter poplavnih ravnic, na treh različnih globinah; 25, 50 in 75 cm. Za določitev razredov drobnozrnate frakcije je bila narejena granulometrična analiza. Vzorce sem nadalje pripravil za analizo rentgenske praškovne difrakcije (XRD), kjer sem pridobil podatke o mineraloški sestavi sedimenta. Ugotovil sem, da večina vzorcev sedimenta poplavnih ravnic pripada skupinama rahlo glinen peščeni melj in rahlo peščen rahlo glinen melj. Vzorci vzeti ob ali iz rečnega korita pa pripadajo skupinama rahlo glinen meljasti pesek in zelo malo glinen (rahlo) meljasti pesek. Rezultati analiz kažejo, da se struktura sedimenta spremeni od izvornega proti ponornemu delu v smeri katerega rahlo vpada delež peščene frakcije, hkrati pa se povečuje delež melja in gline. Ugotovil sem, da se vzorci glede na strukturo ločijo na tiste s poplavnih ravnic, in na tiste, ki so pobrani iz ali ob rečnem koritu Unice. Rezultati mineraloške sestave sedimenta so v obravnavanih vzorcih pokazali prisotnost kremena, dolomita, albita, kalcita ter v sledovih še goethit in hematit. V izbranih vzorcih so bile opravljene še dodatne analize, kjer sem potrdil glinene minerale illit, klinoklor in kaolinit. V vzorcih se dolomit, kremen in ilit pojavljajo z najvišjimi odstotnimi deleži. Ugotovil sem, da vzorci z večjo vsebnostjo dolomita pripadajo lokacijam v ali ob rečnem koritu Unice, medtem ko vzorci z večjo vsebnostjo kremena in ilita pripadajo lokacijam poplavnih ravnic. Slednji imajo tudi večjo vsebnost ostalih glinenih mineralov. Delež dolomita proti ponornemu območju rahlo upada, hkrati pa se povečuje vsebnost kremena in ilita. Na podlagi opravljenih analiz strukture in mineralne sestave sedimentov lahko zaključim, da se izvor siliciklastičnega sedimenta poplavnih ravnic lahko pripiše predvsem Postojnskemu flišnemu zaledju. Izvor karbonatnega materiala pa pripisujem transportu iz bližnje okolice, saj večina polja leži na triasnem dolomitu. Poleg tega je izvor karbonatnega materiala možno povezati s pretransportacijo s Cerkniškega polja.

• Language: Slovenian
• Keywords: Planinsko polje, Unica, sedimentologija, geologija krasa, mineralogija
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: NTF - Faculty of Natural Sciences and Engineering
• Place of publishing: LJubljana
• Publisher: A. Braniselj
• Year: 2023
• Number of pages: XIV, 76 str.
• PID: 20.500.12556/RUL-152950
• UDC: 55
• COBISS.SI-ID: 177395715
• Publication date in RUL: 13.12.2023

Secondary language

• Language: English
• Title: Sedimentological and mineralogical analysis of Holocene fluvial sediments of Planinsko polje : master's thesis

Abstract

Planina polje is a karstic floodplain on which the river Unica flows. The purpose of this study was to determine whether the texture of sediments and its mineral composition change within the Planina polje – from the source at the entrance to the Planina cave and all the way to the ponor area on the Northern parts. I took the sediment samples from 23 sampling points that belong to two different sedimentary environments, namely from the river bed and the flood plain, at three different depths; 25, 50 and 70 cm. Granulometric analysis was conducted to classify the fine-grained fraction. Furthermore, I have also prepared the samples for X-Ray diffraction analysis (XRD), from which I acquired the data about the mineralogical composition of the sediment. I have determined that the majority of samples taken from the flood plains belong to the classes of slightly clayey sandy silt and slightly sandy slightly clayey silt. Samples taken along or from the river bed belong to the classes of slightly clayey silty sand and very slightly clayey (slightly) silty sand. Results of the analysis show that the sediment texture varies from the source to the ponor area, in such a way that the sand fraction percentage decreases and the percentage of silt and clay increases. I have determined that based on their texture, the sediment samples belong to those of the flood plain and to those that were collected along or from the Unica river bed. The results of the mineralogical composition of the sediment showed the presence of quartz, dolomite, albite, calcite and traces of goethite and hematite. Additional analysis were carried out on selected samples to confirm the presence of clay minerals illite, clinochlore and kaolinite. Dolomite, quartz and illite have the highest percentage share in the samples. I determined that the samples with a higher quantity of dolomite belong to the locations inside or along the Unica river bed, whereas samples with a higher quantity of quartz and illite belong to the locations on the flood plain. The latter have also a higher quantity of other clay minerals. The content of dolomite decreases towards the ponor area, and concurrently the content of quartz and illite increases. Based on the conducted analysis of sediment texture and mineral composition, I can conclude that the source of siliciclastic flood plain sediment can be attributed to the Postojna flysch hinterland. The source of carbonate material can be attributed to transportation from the surrounding area due to the fact that the majority of the field lies on Triassic dolomite. In addition, the source of carbonate material can be attributed to retransportation from Cerknica polje.

• Keywords: Planina polje, Unica, sedimentology, karst geology, mineralogy