Discontinuity surfaces recorded in lower jurassic carbonates of Gorski kotar, Lika and Velebit Mt.

Martinuš, Maja (2013) Discontinuity surfaces recorded in lower jurassic carbonates of Gorski kotar, Lika and Velebit Mt.. Doctoral thesis, Faculty of Science > Department of Geology.

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Abstract

Discontinuity surfaces (DS) are common in successions of carbonate platforms. They are formed by subaerial exposure of sediment or by erosion and omission of sedimentation in marine conditions. The study of DS has been carried out on Lower Jurassic carbonate deposits exposed in the areas of Gorski Kotar, Lika and Velebit Mt. Petrographic, sedimentologic and diagenetic characteristics of the rocks were analysed in detail. Microfossil content was investigated in order to obtain biostratigraphic time control. On selected samples, analyses of stable carbon and oxygen isotopic composition, powder XRD analyses of bulk samples and cathodoluminiscence microscopy were carried out. Within studied deposits, larger number of lithofacies units was determined and evolution of depositional environments was interpreted in detail. The age of units ranges from the Late Hettangian to the Early Toarcian. Foraminiferal species Socotraina serpentina was found for the first time in Early Toarcian deposits (“spotty limestones”). Fischer plots of the studied section depict changes in accommodation space and correlate well with facies changes. Therefore, they document relative sea-level changes: long-term relative sea-level rise during the Early Jurassic and maximum transgression in Early Toarcian recognized in resedimented carbonates in the area of southern Lika. Numerous DS are determined and classified into four groups (subaerial exposure surfaces, marine omission, erosion and polygenic surfaces) with several subtypes. Vertical and lateral distribution of DS was investigated. Subaerial exposure surfaces are most numerous in highstand deposits and are interpreted as result of small-scale relative sea-level falls superimposed on large-scale relative sealevel rise or fall. Subaerial exposure surfaces tend to group within thin stratigraphic intervals, which point to important events in evolution of the basement and the initial phase of Adriatic-Dinaridic Carbonate Platform related to periods of enhanced tectonic activity (especially during the Sinemurian– Pliensbachian transition and the Late Pliensbachian) also recognized in successions of the Trento and Pelagonian Carbonate Platforms. Marine omission surfaces are most common and vary the most in transgressive deposits. They do not tend to group within thin stratigraphic intervals. This is the first more detailed study of DS in Lower Jurassic carbonates in Croatia. Different types of DS point to complexity of depositional processes and gave new information about evolution of the Lower Jurassic carbonate platform nowadays exposed in the area of the Karst Dinarides. By studying only the accumulated sediment and neglecting the DS, important events in carbonate platform evolution are often omitted. It is difficult to determine the duration of nondeposition and/or erosion, and although DS, expressed as bed and intrabed surfaces mostly represent short hiatuses, altogether they can “cover” a significant proportion of time in the succession.

Item Type: Thesis (Doctoral thesis)
Keywords: discontinuity surfaces, carbonates, subaerial exposure, hardground, Lower Jurassic, Adriatic-Dinaridic Carbonate Platform, Croatia
Supervisor: Bucković, Damir
Date: 2013
Number of Pages: 274
Subjects: NATURAL SCIENCES > Geology
Divisions: Faculty of Science > Department of Geology
Depositing User: Sonja Borak
Date Deposited: 10 Feb 2014 11:18
Last Modified: 10 Feb 2014 11:18
URI: http://digre.pmf.unizg.hr/id/eprint/385

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