A latest Anisian radiolarite event in the High Karst Nappe in the Dinarides (Montenegro)

In the High Karst Nappe in southern Montenegro radiolarites of unknown age topped the Upper Anisian Bulog Limestones (Late Pelsonian to Illyrian) in the investigated sections Boljevici near Virpazar and Obzovica on the road Budva to Cetinje. Radiolarian faunas from the radiolarites as well as conodonts from the overlying red hemipelagic limestones prove an Illyrian age of the radiolarites. The time interval of the deposition of the up to 5 m thick radiolarite successions is relatively short and started and ended in the Illyrian.
   In the section Boljevici the hemipelagic succession starts with red hemipelagic Bulog Limestone on top of shallow-water limestones equivalent to the Ravni Formation (Dedovici Member) in the Outer Dinarides or the Steinalm Formation in the Eastern Alps/West Carpathians. The drowning of the platform sediments can be dated by the occurrence of Nicoraella germanicus, Nicoraella kockeli, Gondolella bulgarica, and Gondolella cf. bifurcata as Late Pelsonian; these conodonts derive from the overlying Bulog Limestones. Deposition of the Bulog Limestones in this section lasted until the Illyrian, proven by the occurrence of Gondolella excelsa, Gondolella trammeri, and Gondolella liebermanni. Following radiolarians from the reddish laminated radiolarites on top of the Bulog Limestones prove an Illyrian age (Spongosilicarmiger italicus Zone to lower part of Ladinocampe multiperforata Zone; equivalent of Reitziites reitzi Ammonoid Zone): Baumgartneria cf. retrospina, Cryptostephanidium cornigerum, Oertlispongus inaequispinosus, Paroertlispongus multispinosus, and Triassocampe scalaris. The directly overlying sequence of the radiolarite is not exposed, but upsection follow Late Ladinian to Early Carnian shallow-water limestones and dolomites.
   In the section Obzovica the drowning sequence of the carbonate platform is not exposed. Red limestones below the radiolarite succession belong to the Bulog Limestone. Upsection follows a five metre thick succession of red and partly grey well-bedded radiolarites. From the red radiolarites we isolated a well preserved Illyrian radiolarian fauna (Spongosilicarmiger italicus Zone; equivalent of Reitziites reitzi Ammonoid Zone) with: Baumgartneria bifurcata, Baumgartneria cf. yehae, Cryptostephanidium cornigerum, Eptingium manfredi, Eptingium ramovsi, Falcispongus calcaneum, Hozmadia sp., Oertlispongus inaequispinosus, Parasepsagon asymmetricus, Pseudostylosphaera japonica, Pseudostylosphaera tenuis, Spongostephanidium sp., Triassocampe deweveri, Triassocampe scalaris. In the upper part of the radiolarite sequence up to ten centimetre thick intercalated hemipelagic filament-bearing limestones are of latest Anisian to earliest Ladinian age, proven by the following conodonts: Gondolella excelsa, Gondolella trammeri, and Gladigondolella tethydis. Upsection the radiolarian cherts decrease rapidly and the following hemipelagic red limestones are of earliest Ladinian age, proven by conodonts. These red limestones pass continuously into grey hemipelagic limestones of Late Ladinian age (with Gladigondolella tethydis and Gondolella foliata), topped by shallow-water dolomites of Late Ladinian to Early Carnian age.
   This short-lasting latest Anisian radiolarite event in the succession of the High Karst Nappe is contemporaneous with the complete demise of shallow-water carbonate production in the whole western Tethyan realm and corresponds to the onset of the first radiolarites on the Neotethys Ocean floor, as proven in Albania and northern Croatia as well as in the Meliata Unit in Slovakia and Hungary. In the late Anisian the huge parts of the passive margin facing the newly formed Neotethys Ocean became flooded and volcanic ashes and radiolarites were deposited in the whole Dinarides reaching the palaeogeographic realm of the High Karst Nappe. Obviously, volcanics in our sections are preserved only as some thin intercalations of metabentonites. The latest Anisian radiolarite deposition corresponds also to the onset of intense volcanism in the Dinarides more to the north and in the southern Alps in Italy. The studied successions are nice examples of short-lived hemipelagic basins that formed on continental margin during the late Anisian rifting and were later, in the Ladinian and Early Carnian, completely infilled with sediments of prograding carbonate platforms.