This study refers to some problems regarding the lithological succession, facies and carbonate microfacies, and to biostratigraphic markers of the Upper Jurassic-Lower Cretaceous carbonates from Bihor Mountains. Three types of facies (external marginal facies, subtidal and peritidal facies) were separated for the Upper Jurassic, and two (coastal-peritidal and open shelf facies) for the Lower Cretaceous carbonates. The micropaleontological assemblages identified contain species that allow the separation of the two formations of different age: Labyrinthina mirabilis, Kurnubia palastiniensis, Neokilianina rahonensis, Clypeina sulcata (Kimmeridgian-Lower Tithonian) and Parakoskinolina? jourdanensis, Montseciella arabica, Palorbitolina lenticularis, Falsolikanella danilovae (Barremian – Lower Aptian). Field observations and data obtained from studies on thin sections and polished slabs indicate that a large part of the Triassic (Ladinian-Lower Carnian) and Lower Cretaceous limestones from Gârda Seacă-Hodobana region, delimited on the geological maps 1:50 000 scale, sheets 56b (Poiana Horea) and 56d (Avram Iancu) (Bleahu et al., 1980; Dimitrescu et al., 1977), belong in fact to the Upper Jurassic carbonate succession.

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