Changing depositional environments in the semi-restricted Late Jurassic Lemeš Basin (Outer Dinarides; Croatia)

Michael A.J. Vitzthum, Hans Jürgen Gawlick, Reinhard F. Sachsenhofer, Stefan Neumeister

Publikation: Beitrag in FachzeitschriftArtikelForschungBegutachtung


The up to 450 m-thick Upper Jurassic Lemeš Formation includes organic-rich deep-water (max. ~ 300 m) sedimentary rocks deposited in the Lemeš Basin within the Adriatic Carbonate Platform (AdCP). The Lemeš Formation was investigated regarding (1) bio- and chemostratigraphy, (2) depositional environment, and (3) source rock potential. A multi-proxy approach—microfacies, Rock–Eval pyrolysis, maceral analysis, biomarkers, and stable isotope ratios—was used. Based on the results, the Lemeš Formation is subdivided from base to top into Lemeš Units 1–3. Deposition of deep-water sediments was related to a late Oxfordian deepening event causing open-marine conditions and accumulation of radiolarian-rich wackestones (Unit 1). Unit 2, which is about 50 m thick and Lower early Kimmeridgian (E. bimammatum to S. platynota, ammonite zones) in age, was deposited in a restricted, strongly oxygen-depleted basin. It consists of radiolarian pack- and grainstones with high amounts of kerogen type II-S organic matter (avg. TOC 3.57 wt.%). Although the biomass is predominantly marine algal and bacterial in origin, minor terrestrial organic matter that was transported from nearby land areas is also present. The overlying Unit 3 records a shallowing of the basin and a return to oxygenated conditions. The evolution of the Lemeš Basin is explained by buckling of the AdCP due to ophiolite obduction and compressional tectonics in the Inner Dinarides. Lemeš Unit 2 contains prolific oil-prone source rocks. Though thermally immature at the study location, these rocks could generate about 1.3 t of hydrocarbon per m2 surface area when mature.
Frühes Online-Datum18 Dez. 2021
PublikationsstatusVeröffentlicht - Jan. 2022

Bibliographische Notiz

Funding Information:
We specially thank Stephen Ajuba, Doris Gross, Reinhard Gratzer, and Achim Bechtel (Montanuniversitaet Leoben) for their support, guidance, and consultation during analysis and laboratory work. Additionally, we thank Laszlo B ujtor (P?cs) for the preparation, photographs, and identification the ammonite Ataxioceras sp. Careful reviews of Herbert Volk (Hampton Hill) and Anonymous as well as linguistic improvements by Joel Bensing are grateful acknowledged.

Publisher Copyright:
© 2021, The Author(s).

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