The Late Jurassic Evolution of the Lemeš Basin and Source Rock Evaluation of the Lemeš Formation: Part of the Mesozoic Adriatic Carbonate Platform, Poštak Mountain, SW Croatia.

Michael Vitzthum

Research output: ThesisMaster's Thesis


The carbonatic deep-water and partly organic-rich deposits (black shales) of the Late Jurassic Lemeš Basin in southern Croatia were investigated in respect to (1) biostratigraphy, (2) depositional environment, and (3) source rock potential. An Oxfordian onset of deeper-water sedimentary rocks (siliceous limestones, bituminous limestones and organic-rich marls and claystones) is recognized after the long-lasting shallow-water evolution of the Adriatic Carbonate Platform. The layer of organic-rich strata in the Lemeš succession could be dated as Early Kimmeridgian or imperceptibly older by Ataxioceras sp. from overlaying siliceous limestones. This level is characterised by the highest concentration of organic matter in the succession and thereby utilized to reconstruct the depositional environment on basis of his biomarker characteristics, Rock-Eval and Leco analysis, microfacies and stable carbon and oxygen isotopes. The results point to a periodically restricted to semi-restricted basin, and to a marine organic system (dominance of liptinites, average n-alkane: ∑-nC15-20/∑n-C15-35=0.41, ∑n-C21-25/∑n-C15-35=0.37, ∑n-C26-32/∑n-C15-35=0.22; average sterane: ΣC27/ΣC27-29=0.31, ΣC28/ΣC27-29=0.27, ΣC29/ΣC27-29=0.42;) of marine zoo- and phytoplankton and bacteria, without significant influence of land plants. The thermal maturity (average: T-max 429 °C) for hydrocarbon expulsion was not reached in this surface outcrop. A low Source Potential Index (in total 1.32 t Hydrocarbon/m2) related to the 31.68 m thickness coupled with the overall low petroleum potential of the black shales is not sufficing, however the organic potential is proven with an oil-prone type-II kerogen (average Hydrogen Index of reactive organic carbon ~550 mg Hydrocarbon/g Total Organic Carbon) and a good to very good Total Organic Carbon content (average 3.57wt%). In an overthrust position the Lemeš black shales should be therefore a very good source rock. The depositional conditions of the siliceous deeper-water limestones overlaying these black shales are more oxygenated, documented by the microfacies with ammonites, radiolaria and thin-shelled bivalves besides others. The upsection continuing organic-rich levels in the alternating succession, still deposited under semi-reducing conditions, have less Total Organic Carbon content than the older black shale level. In the uppermost, Tithonian part of the succession shallow-water debris reached the Lemeš Basin and filled it up throughout the Late Jurassic showing a shallowing upward trend. The Late Jurassic Lemeš Basin evolution is overall attributed to an extensional tectonic regime. This interpretation is questioned based on the distinct sedimentary features of the succession and the evolution of the basin fill. Therefore, an alternative model is discussed descending from the general geologic history of the Dinarides. This model proposes the Outer Dinarides as dependent and affected by the geodynamics of the Inner Dinarides, characterized by ophiolite obduction and contemporaneous thrusting and folding of the wider Adriatic plate in lower plate position. West-ward propagating ophiolite obduction resulted in formation of a nappe stack in the Inner Dinarides and affected the Outer Dinarides by relatively mild tectonic movements, forming anti- and synclines. During certain times, the relatively small but deep synclines were isolated from the water-exchange with the open-marine realm, during these periods organic-rich layers have been deposited.
Translated title of the contributionKohlenwasserstoffpotential der oberjurassischen Lemeš Formation im Bereich der Adria Karbonatplattform (Mt. Poštak, sw Kroatien)
Original languageEnglish
Awarding Institution
  • Montanuniversität
  • Gawlick, Hans-Jürgen, Supervisor (internal)
Award date18 Dec 2020
Publication statusPublished - 2020

Bibliographical note

embargoed until null


  • Outer Dinarides
  • Kimmeridgian
  • organic-rich deposits
  • anoxia
  • depositional environment
  • biostratigraphy

Cite this