magistrsko delo
David Gerčar (Author), Boštjan Rožič (Mentor), Luka Gale (Co-mentor)

Abstract

V okviru magistrskega dela opisujem sestavo in stratigrafski položaj blokovne breče na območju Ponikvanske planote. Območje raziskav se nahaja približno 7 km jugovzhodno od Tolmina. Uvrščeno je v strukturno enoto Južnih Alp in je del Ponikvanske tektonske krpe, ki predstavlja erozijski ostanek Podmelškega pokrova (strukturno najnižji del Tolminskega pokrova). Podmelški pokrov sestavljajo mezozojske kamnine Slovenskega bazena, ki so bile paleogeografsko najbližje Dinarski karbonatni platformi. Južni razvoji Slovenskega bazena so bili do sedaj slabo raziskani, posebno jurska stratigrafija. Blokovne breče sem zajel v enem detajlnem, enem parcialnem in dveh shematskih profilih, ki so bili posneti na podlagi predhodno izdelane in dopolnjene geološke karte. Terenska opazovanja sem dopolnil s preiskavo zbruskov. Starost klastov in veziva sem določil s pomočjo foraminifer. Ponikvansko tektonsko krpo sestavlja zgornjetriasno do zgornjekredno zaporedje globokomorskih kamnin, ki so v inverzni legi. Jursko zaporedje se začne s 110 m tankoplastnatih mikritnih apnencev Krikovske formacije, čez katere je erozijsko diskordantno odložen do 80 m debel horizont blokovne apnenčeve breče, ki je bila predmet raziskav. Sledi 18 m debelo zaporedje močno okremenjenih mikritnih apnencev in presedimentiranih apnencev Tolminske formacije. Jursko zaporedje se zaključi z apnenci tipa biancone. Navidez masivno brečo sestavlja več plasti apnenčeve blokovne breče z erozijsko spodnjo mejo in podrejeno kalkareniti. Klasti pripadajo plitvomorskim in podrejeno globljemorskim faciesom. Fosili, predvsem foraminifere, dokazujejo, da je večji del klastov zgornjetriasne starosti in da so nastajali v perigrebenskem okolju, del klastov pa pripada spodnje- in srednjejurskim kamninam. Starost veziva je zaradi dolomitiziranosti težje določljiva, a posamezne izolirane foraminifere Protopeneroplis striata Weynchenk določajo srednjejursko starost. Masivno brečo zato uvrščam v Tolminsko formacijo. Slaba sortiranost, velika debelina posamičnih plasti in erozijska meja kažejo, da je breča nastala s sedimentacijo iz drobirskih tokov, katerih nastanek je morda povezan s tektonsko pogojenim rušenjem severnega roba Dinarske karbonatne platforme

Keywords

Ponikvanska tektonska krpa;Južne Alpe;Slovenski bazen;srednja jura;apnenčeva breča;Tolminska formacija;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL NTF - Faculty of Natural Sciences and Engineering
Publisher: [D. Gerčar]
UDC: 55
COBISS: 1369950 Link will open in a new window
Views: 1941
Downloads: 859
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Other data

Secondary language: English
Secondary title: sedimentology and stratigraphy of Jurassic limestone blocky breccia from Ponikve tectonic klippe
Secondary abstract: In the master's thesis I describe composition and stratigraphic position of a blocky limestone breccia from the Ponikvanska planota plateau. Research area is located approximately 7 km southeast of Tolmin (NW Slovenia). It structurally belongs to the Southern Alps and is a part of Ponikva tectonic klippe, which is an erosional remnant of the Podmelec Thrust sheet, the lowermost subunit of the Tolmin Nappe. Podmelec Thrust sheet includes mesosoic successions of the Slovenian Basin which were most proximal to the Dinaric Carbonate platform. The lithostratigraphic succession in this part of the Tolmin nappe is poorly researched, especially regarding the Jurassic part of the sequence. Blocky breccias were investigated in one detailed, one partial and two schematic profiles, which were recorded based on an existing and improved geological map. Field observations were complemented with petrographic microscopy. The age of lithoclasts and matrix is based on foraminiferal assemblage. The Ponikva Tectonic klippe consists of Upper Triassic to Upper Cretaceous deep marine successions of the Slovenian Basin in an inverted position. The Jurassic succession starts with 110 m of thin bedded micritic limestones of the Krikov Formation, which are unconformably overlain by an up to 80 m thick limestone breccia horizon – the main subject of the research. The breccias are overlain by 18 m of bedded cherty micritic limestones and resedimented limestones of the Tolmin Formation. The Jurassic succession ends with limestones of Biancone type. Seemingly massive breccia horizon is actually composed of numerous limestone blocky breccia and subordinate calcarenitic beds. The lower boundary is erosional. Lithoclasts predominantly consist of shallow marine and subordinate deep marine carbonates. Fossils, mostly foraminifera confirm that most of the lithoclasts are Upper Triassic in age and were originally deposited on the platform margins, with some lithoclasts also Lower and Middle Jurassic in age. Due to dolomitization of the matrix, its’ age was difficult to define. But foraminifera Protopeneroplis striata Weynschenk dates the matrix to Middle Jurassic. Therefore, I consider these breccias as a part of the Tolmin Formation. Poor sorting and large bed thickness indicate that the breccias were deposited via debris flows, which might have been a consequence of tectonically induced collapse of the northern margins of the Dinaric Carbonate Platform.
Secondary keywords: Ponikva tectonic klippe;Southern Alps;Slovenian basin;Middle Jurassic;breccia;Tolmin formation;
Type (COBISS): Bachelor thesis/paper
Study programme: 0
Thesis comment: Univ. v Ljubljani, Naravoslovnotehniška fak., Oddelek za geologijo
Pages: VIII, 60 str.
ID: 10911711