Sedimentološka in mikropaleontološka analiza spodnjekarnijskega masivnega apnenca pri Lesnem Brdu

Hočevar, Manca (avtor), Gale, Luka (mentor)

V okviru magistrskega dela sem raziskala litološko sestavo masivnega apnenca v kamnolomu Lesno Brdo. Pobrala sem vzorce za izdelavo zbruskov, na podlagi katerih sem določila mikrofaciese. Vzdolž štirih etaž kamnoloma sem posnela profil v skupni dolžini 15,5 m. Makroskopsko sem profil razdelila na tri faciese. Prvi je drobnozrnat mikritni apnenec, ki predstavlja 59% celotnega profila. V nekaj decimetrov do nekaj metrov velikih oglatih blokih ali zaobljenih kroglastih telesih najdemo mikrobialitni boundstone. Ta se nahaja v prvih 1,7 m profila in predstavlja 15,5% celotnega profila. Poleg mikrobialita (stromatolitov) najdemo v manjšem deležu tudi spužve in korale. Tretji facies je terebelidni apnenec, ki se pojavlja v obliki nepravilnih lečastih teles predvsem v spodnjem in srednjem delu profila. Predstavlja 13% celotnega profila. V spodnjem delu kamnoloma je vidna tudi breča, ki pa ni zajeta v profil. Faciesi so na mikroskopskem nivoju tako heterogeni, da jih lahko razdelim na več mikrofaciesov. Apnenec, ki makroskopsko deluje mikritno, sem tako razdelila na: peloidni bioklastični grainstone, bioklastični peloidni wackestone, peloidni wackestone, drobnozrnti grainstone s fragmentiranimi bioklasti, peloidi in intraklasti, peletni wackestone, spran bioklastični packstone in bioklastični in onkoidni floatstone. Terebelidni apnenec delimo na terebelidni floatstone in terebelidni rudstone. Mikrobialitni boundstone je preveč raznolik in s preveč hitrimi prehodi med teksturami, da bi ga lahko natančneje razdelili. Na podlagi že prej določenih fosilov masivni apnenec v kamnolomu Lesno Brdo uvrščamo v obdobje karnija. Masivni apnenec iz kamnoloma Lesno Brdo predstavlja samo majhen del celotne karbonatne platforme in je bil odložen na zgornjem delu pobočja ali na robu karbonatne platforme. Glede na prisotnost rudstone in grainstone tekstur sklepam na zmerno energijsko okolje.

• Jezik: Slovenski jezik
• Ključne besede: Zunanji Dinaridi, Lesno Brdo, apnenec, trias, karnij, greben, sedimentologija, mikrofacies, mikrobialit, mikrofosili.
• Vrsta gradiva: Magistrsko delo/naloga
• Organizacija: NTF - Naravoslovnotehniška fakulteta
• Leto izida: 2019
• PID: 20.500.12556/RUL-106840
• COBISS.SI-ID: 1464414
• Datum objave v RUL: 19.03.2019

Sekundarni jezik

• Jezik: Angleški jezik
• Naslov: Sedimentological and micropaleontological analysis of Lower Carnian massive limestone at Lesno Brdo

Izvleček

The subject of research was the massive limestone exposed in the quarry at Lesno Brdo. Samples for microfacies analysis were taken. From a section logged across four floors of a quarry in the total lenght of 15,5 m. Macroscopically the section was divided into three facies: Fine-grained micritic limestone, represents 59% of the section. Microbialite boundstone can be found as a few decimeters to a few meters large square blocks or rounded globular bodies. It is located in the first 1.7 m of the section and represents 15.5% of the total lenght of the section. In addition to microbialite (stromatolite), sponges and coral are also found in a smaller proportion. The third facies is terebellidal limestone, which occurs in the form of irregular lenses, especially in the lower and middle part of the section. It represents 13% of the section. The fourth facies, breccia, is exposed only in the lower part of the quarry and was not included in the logged part of the quarry. The facies types due to their heterogenous nature were further divided into several microfacies. I divided the limestone macroscopicaly assigne as micritic into: peloid bioclastic grainstone, bioclastic peloid wackestone, peloid wackestone, grainstone with fragmented bioclasts, peloids and intraclasts, pelet wackestone, washed bioclastic packstone and bioclastic and oncoid floatstone. Terebellid limestone is divided into a terebellidal floatstone and a terebellidal rudstone. Boundstone is too diverse to be further divided. On the basis of the previously defined fossils, massive limestone in the Lesno Brdo quarry is believed to be Carnian in age. The exposed part in the Lesno Brdo quarry is only a minor part of the carbonate platform. This section was probably deposited on the upper part of the slope or at the edge of the carbonate platform. Depending on the presence of rudstone and grainstone textures the water had moderate energy.

• Ključne besede: External Dinarides, limestone, Triassic, reef, sedimentology, microfacies, microbialites, microfossils.