magistrsko delo
Lucija Slapnik (Author), Boštjan Rožič (Mentor)

Abstract

Že v sklopu predhodnih raziskav smo v dolini pod Peski v Julijskih Alpah preučevali rdeče sedimentne zapolnitve zgornje triasnih megalodontidnih školjk. Na podlagi optične in katodoluminiscentne mikroskopije ter rentgenske fluorescenčne analize smo potrdili štiri generacije zapolnjevanja školjk. Ker je eno izmed temeljnih vprašanj predhodnih raziskav, vezano predvsem na izvor sedimenta v megalodontidah, ostalo delno neodgovorjeno, smo se odločili še natančneje raziskati tamkajšnjo okolico. Detajlno smo popisali in vzorčili kamninsko zaporedje nekaj metrov pod in nad »glavno« plastnico z zgoraj omenjenimi megalodontidami. Že med prvotnim vzorčenjem smo namreč opazili, da se v obdajajočih kamninah pojavljajo paleokraške votlinice, ki so zapolnjene s podobno obarvanim rdečkastim sedimentom, oziroma kamnino, kot v megalodontidah. Z namenom dodatnega preučevanja neptunskih dajkov in njihovega vpliva na zapolnitve v zadnji generaciji smo podrobneje raziskali še dodatnih pet dajkov v bližnji okolici. Na podlagi izbranih vzorcev smo izdelali detajlne mikrofacielne analize sedimentacijskega zaporedja in neptunskih dajkov. Preučevani profil dachsteinskega apnenca večinoma predstavljajo plasti intraklastičnih peloidnih apnencev tip packestone do wackestone z večjimi bioklasti (megalodontide, polži) in korozijskimi votlinicami. V nekaj vzorcih smo na večjih bioklastih opazili prevleke mikroproblematike Thaumatoporella. V zgornjem delu profila se pojavijo plasti s stromatolitnimi laminami in plasti emerzijskih breč s črnimi intraklasti (»black pebbles«). Slednji se ponekod pojavljajo tudi v rdečih paleokraških sedimentnih zapolnitvah. V korozijskih votlinicah smo opazili večgeneracijsko zapolnjevanje z menjavanjem kalcitnega cementa in rdečih sedimentnih zapolnitev. Preiskovane neptunske dajke smo pri opisih generalno razdelili na podlagi dimenzij in lokacije pojavljanja. Dva izmed njih, ki se nahajata neposredno na »glavni« plastnici z rdeče zapolnjenimi megalodontidami in vsebujeta planktonske foraminifere, kar kaže na srednjejursko oz. mlajšo starost. Naslednja dva preučevana dajka se nahajata tik nad »glavno« plastnico. Eden izmed njiju vsebuje klaste s kalpionelami, značilne za obdobje pozne jure do začetka krede. Zadnji dajk, katerega smo raziskovali, se nahaja nekaj deset metrov stran od »glavne« plastnice in je mnogo večjih dimenzij kot vsi prejšnji. Gre za več sto metrov dolg neptunski dajk z raznolikimi sedimentnimi zapolnitvami, ki kažejo na več ločenih faz zapolnjevanja. V nekaj vzorcih smo v tem dajku določili spodnjekredne planktonske foraminifere. Na podlagi mikroskopske analize se je izkazalo, da so rdečkaste paleokraške sedimentne zapolnitve v korozijskih votlinicah izredno podobne sedimentnim zapolnitvam prve in druge faze v megalodontidnih školjkah. Zapolnitve so torej del kompleksnejšega paleokraškega sistema, ki ga opazujemo v dachsteinskemu apnencu. Pomembnejše ugotovitve v povezavi z zadnjo fazo zapolnitev školjk smo dognali s pomočjo sedimentarne analize neptunskih dajkov, kjer se je pokazala mikrofacielna podobnost med zadnjo sedimentno zapolnitvijo v megalodontidah in nekaterimi neptunskimi dajki na »glavni« plastnici. Za zaključek in odprt konec raziskave pa smo v zgornjem delu profila v eni izmed korozijskih votlinic odkrili santonijsko – maastrichtijsko sedimentno zapolnitev z globotrunkanami.

Keywords

Južne Alpe;Krnski pokrov;zgornji trias;jura;megalodontidne školjke;paleokraške zapolnitve;neptunski dajki.;

Data

Language: Slovenian
Year of publishing:
Typology: 2.09 - Master's Thesis
Organization: UL NTF - Faculty of Natural Sciences and Engineering
Publisher: [L. Slapnik]
UDC: 55
COBISS: 85672451 Link will open in a new window
Views: 239
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Other data

Secondary language: English
Secondary title: sedimentary succession with paleokarst infills and neptunian dikes in Pod Peski Valley in Krn Mountain Range
Secondary abstract: As part of the previous research, we have examined red fillings of the Upper Triassic megalodontid bivalves at a selected location in the Julian Alps, in the Pod Peski Valley. Based on optical and cathodoluminescent microscopy and X-ray fluorescence analysis (XRF), we confirmed four generations of shell infillings. Since one of the basic questions of previous research, mainly related to the origin of the last generation of the sediment infill in megalodontids remained unanswered, we decided to further examine this area. We described and in detail sampled the rock sequence a few meters below and above the »main« layer with the above-mentioned megalodontids. Already during the previous sampling campaign, we noticed that solution voids appear in the surrounding rocks. These voids are filled with reddish sediment infill, similar to that in the megalodontids. In order to further study neptunian dykes and their impact on fillings in the last generation, we investigated in more detail five additional dykes in the surrounding area. Based on selected samples, we performed a detailed microfacies analysis of sediment sequence and neptunian dykes. The studied section of Dachstein limestone mainly consists of intraclastic peloidal packestone to wackestone with larger bioclasts (megalodontides, gastropods) and solution voids. In a few samples, we observed a presence of Thaumatoporella. Stromatolites and emersion breccias with black intraclasts (»black pebbles«) appear in the upper part of the section. These intraclasts also appear in some places in red paleokarst solution voids. In thesolution voids, we observed a multi-generational filling with alternation of calcite cement and red sedimentary fillings. The investigated neptunian dykes were generally divided on the basis of dimensions and location of occurrence. Two of them, located directly on the »main« layer with red-filled megalodontids, contain planktonic foraminifera, which indicates the Middle Jurassic or younger age. The next two studied dykes are located just above the »main« layer, one of which contains clasts with calpionellis, characteristic of the Late Jurassic / Early Cretaceous . The last dyke we explored is located a few tens of meters away from the »main« bedding plane and is much larger than all the previous ones. It is a hundreds of meters long, with diverse sedimentary fillings indicating several separate generations of filling. In a few sample from this dyke we identified Early Cretaceous planktonic foraminifera. Based on microscopic analysis, the reddish paleokarst sedimentary fillings in the solution voids were found to be remarkably similar to the sedimentary fillings of the first and second phases in the megalodontid bivalves. The fillings are part of the more complex paleokarst system observed in the Dachstein limestone. More important findings, related to the last generation, were also found in the neptunian dykes, where optical microscopy also showed similarity between the last sediment filling in megalodontids and some neptunian dykes on the »main« bedding plane. For ending of our research, we discovered a Santonian - Maastrichtian sedimentary filling with globotruncanid foraminifers in the upper part of the succession in one of the solution voids.
Secondary keywords: Southern Alps;Krn Nappe;Upper Triassic;Jurassic;megalodontid bivalves;paleokarst infills;neptunian dykes.;
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: 13525427