Abstract
Middle Triassic deposits in the Karst Dinarides (south Lika area, near Gracac) were investigated for petrological, sedimentological and biostratigraphic determinations. Within two continuously recorded sections of sedimentary carbonates and interlayered pyroclastic rocks (Mali Kunovac and Kunovac sections) reflecting variable sedimentary-magmatic environments, valuable cephalopod fauna ranging from the middle Illyrian to the upper Illyrian age was found. The most significant was the recovery of the ammonoids Asseretoceras sp., indicating the upper part of the Illyrian Paraceratites trinodosus Zone, and Reitziites reitzi species which marks the upper part of the Illyrian Reitziites reitzi Zone. The discovery of the Reitziites reitzi species was not known from the Karst Dinarides until this finding.
Highlights
IntroductionBiostratigraphic zonation according to ammonoids has a very high resolution and is still considered one of the best correlative principles for the Middle Triassic
Since no tectonic breaks are recorded and the layer orientation of both sections is the same, they are considered as a continuous depositional sequence, with the Mali Kunovac section representing the older, and the Kunovac section representing the younger strata
A severe and abrupt change of lithology occurs, from shallow marine limestones with abundant green algae interlayered with pyroclastics, to the pelagic limestones with thin-shell bivalves and radiolarians, accompanied with tuffs
Summary
Biostratigraphic zonation according to ammonoids has a very high resolution and is still considered one of the best correlative principles for the Middle Triassic. The Anisian-Ladinian boundary was defined by Brack et al (2005) by means of ammonoids/conodonts. Our investigation was focused on ammonoid bearing Middle Triassic strata in the Karst Dinarides. The already known cephalopod bearing strata was recorded by Koch (1911) and Salopek (1914). According to the specimens collected from the green clastic rocks, Salopek (1914) determined the investigated area is of transitional Anisian-Ladinian age. No continuous sampling of ammonoids was conducted and this study presents a new and precise biostratigraphic definition of the Middle Triassic. The two sections were investigated by means of petrography, sedimentology and ammonoid biostratigraphy
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