magistrsko delo
Nina Valand (Author), Boštjan Rožič (Mentor), Luka Gale (Co-mentor)

Abstract

Begunjščica je pogorje v Južnih Karavankah. Jurske plasti na Begunjščici izdanjajo na njenem južnem pobočju in so relativno dobro razgaljene. Begunjščica tako predstavlja pomembno območje za razumevanje jurske sedimentarne evolucije Julijskega praga. Jurske plasti loči vsaj en močnejši prelom, ki jih razdeli na severni in južni blok. V svoji magistrski nalogi sem preučila in opisala jurske plasti v južnem tektonskem bloku Begunjščice. Izdelala sem sedimentološki profil in iz detajlne mikrofacielne in biostratigrafske analize interpretirala sedimentarno evolucijo jurskega zaporedja. Obravnavano zaporedje sem razdelila na štiri glavne litostratigrafske enote. Profil se začne z mikritnimi apnenci z biogenim drobirjem in vmesnimi apnenčevimi brečami, ki so se odlagali na že poglobljenem območju v zgodnji juri. Prisotni so tudi manganovi gomolji in skorje, ki kažejo na izredno počasno sedimentacijo. Sledi izrazito nepravilna meja in nato kratko zaporedje glinavcev, laporovcev, rožencev in apnencev, močno obogatenih z manganom in manganovimi skorjami, katerih spodnji del je verjetno sočasen s spodnjetoarcijskim oceanskim anoksičnim dogodkom. Zaporedje se v toarciju nadaljuje s kondenziranimi apnenci tipa ammonitico rosso, med katerimi se prav tako pojavljajo apnenčeve breče, z manganiziranimi klasti in klasti starejših kamnin. Proti vrhu profila se zaporedje vedno bolj spreminja v močno sinsedimentno deformiran apnenec s kaotično strukturo, ki je nastal s sinsedimentnimi plazovi. Starost teh plasti je vprašljiva, lahko da so še toarcijske starosti, možno pa je, da so iz sredine srednje jure in je pod njimi stratigrafska vrzel. Profil se zaključi z menjavanjem pelagičnih in turbiditnih sedimentov, ki najverjetneje predstavljajo apnenčeve razvoje pred plastnatimi roženci, ki se na severnem bloku Begunjščice začnejo odlagati neposredno preko tanke plasti kaotične apnenčeve breče, profil južnega bloka pa jih več ne zajema. Analiza jurskih plasti južnega bloka Begunjščice je potrdila podobnosti z razvoji severnega bloka, kar dokazuje, da se jursko zaporedje na južnem pobočju večkrat ponovi zaradi manjših gub in preloma. Zaporedji se sicer razlikujeta predvsem v debelini plasti, kar kaže na verjetno bolj potopljen južni blok že v juri. Današnji prelom je najverjetneje samo reaktiviran mezozojski normalni prelom. Regionalna korelacija pokaže, da na ožjem območju nekdanje Julijske karbonatne platforme primerljivih razvojev s toarcijskimi apnenci tipa ammonitico rosso ni, so pa ti značilni za ostale paleogeografske enote Južnih Alp in tudi ostala območja jurskega pasivnega roba Jadranske mikroplošče.

Keywords

Južne Alpe;Julijski prag;jura;toarcijski anoksični dogodek;mangan;apnenec ammonitico rosso;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL NTF - Faculty of Natural Sciences and Engineering
Publisher: [N. Valand]
UDC: 55
COBISS: 1535070 Link will open in a new window
Views: 621
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Other data

Secondary language: English
Secondary title: Jurassic sequence with limestone breccias on the southern slopes of Mt. Begunjščica
Secondary abstract: Mt. Begunjšcica is a mountain range in the Southern Karavanke Mountains. The Jurassic beds of Mt. Begunjšcica are relatively well exposed on its southern slope and therefore Mt. Begunjščica represent an important section for the understanding of Jurassic sedimentary evolution of Julian High. Jurassic beds are separated by at least one stronger fault, which divides them into the north and south block. In my master's thesis, I studied and described the Jurassic succession in the southern tectonic block of Mt. Begunjščica. A sedimentological section was logged and sampled for thin sections. I interpreted the sedimentary evolution of the Jurassic succession from detailed microfacial and biostratigraphic analysis. The succession is composed of four major lithostratigraphic units. The section begins with micritic limestones with biogenic debris and intermediate limestone breccias deposited in a deepened environment in the Early Jurassic. Manganese nodules and crusts are also present, indicating extremely slow sedimentation rates. After that irregular boundary follows and a short succession of shales, marls, cherts and limestones heavily enriched with manganese, with the lower part very likely deposited during the Early Toarcian oceanic anoxic event. The Toarcian sequence continues with condensed limestones of Ammonitico Rosso type, among which limestone breccias also occur, with manganese clasts and older rocks. Towards the top of the profile, the sequence changes more to the highly deformed limestone created by slumps. The age of these layers is questionable, they may still be of the Toarcian age, but it is also possible that they are Middle Jurassic in age and deposited above the stratigraphic gap. The section ends with alternating pelagic and turbiditic sediments, representing more calcareous development prior to radiolaritic deposits, which begin depositing at the northern block of the Mt. Begunjščica at the end of the Middle Jurassic but are not covered by the profile of the southern block anymore. The analysis of Jurassic beds on the south block of Mt. Begunjščica confirmed similarities with the section of the north block, which proves that the Jurassic sequence is repeated several times due to minor folds and a fault. The successions differ, in particular, in the thickness of the beds, indicating probably more submerged southern block already in the Jurassic. Today's fault is probably just a reactivated Mesozoic normal fault. The regional correlation shows that there are no comparable successions with Toarcian Ammonitico Rosso limestones in the narrower Julian Carbonate Platform, but they are typical for other paleogeographic units of the Southern Alps as well as other areas of the Jurassic passive margin of the Adriatic microplate.
Secondary keywords: Southern Alps;Julian High;Jurassic;Toarcian oceanic anoxic event;manganese;limestones Ammonitico Rosso;
Type (COBISS): Master's thesis/paper
Study programme: 0
Embargo end date (OpenAIRE): 1970-01-01
Thesis comment: Univ. v Ljubljani, Naravoslovnotehniška fak., Oddelek za geologijo
Pages: XIII, 77 f.
ID: 11351333