LicenseCalpionellid biostratigraphy and sedimentation of the Biancone limestone from the Rudnica Anticline (Sava Folds, eastern Slovenia)

Abstract

Mt Rudnica in eastern Slovenia structurally belongs to the Sava Folds. The mountain itself is an exposure of the Mesozoic core of the Rudnica Anticline. The major part of the core is composed of Triassic rocks deposited on the NE margin of the Dinaric (Adriatic) Carbonate Platform, overlain locally by deep-marine Berriasian Biancone limestone. The latter formation was logged in a newly discovered section on the northern slopes of Mt Rudnica near the village of Loka pri Žusmu. The Biancone limestone of Mt Rudnica is mostly monotonous, calpionellid-bearing limestone with only minor up-section differences in colour, chert presence, and clay content. It is characteristic pelagic facies for the entire Tethyan Realm of the time. Using calpionellid as well as dinocyst biostratigraphy, the formation was subdivided into Early Berriasian Calpionella Zone-Alpina and Ferasini Subzones, Middle Berriasian Calpionella Zone-Elliptica Subzone and upper Berriasian Calpionellopsis Zone-Oblonga Subzone. Within the Early Berriasian part of the formation a synsedimentary slump was documented, whereas the largest increase in clay content is observed in the topmost, i.e. Late Berriasian part of the formation. Izvleček Gora Rudnica v vzhodni Sloveniji strukturno pripada Posavskim gubam. V osrednjem delu gore izdanja mezozojsko jedro Rudniške antiklinale. Večji del jedra sestavljajo triasne kamnine, ki so se odlagale na severovzhodnem obrobju Dinarske (Jadranske) karbonatne platforme, nad njimi pa je mestoma odložen globokomorski, berriasijski biancone apnenec. Slednji je bil posnet v novo odkritem profilu na severnih pobočjih Rudnice pri vasi Loka pri Žusmu. Biancone apnenec iz Rudnice je povečini monoton apnenec s kalpionelami, ki vzdolž zaporedja kaže le manjše spremembe v barvi, prisotnosti roženca in vsebnosti gline. Predstavlja značilen pelagični facies celotne Tetidine province tega časa. Na podlagi kalpionelidne in tudi dinocistne biostratigrafije je bila formacija razdeljena na spodnji berriasij (Calpionella cona-Alpina in Ferasini podconi), srednji berriasij (Calpionella cona-Elliptica podcona) in zgornji berriasij (Calpionellopsis cona-Oblonga podcona). V spodnjeberriasijskem delu formacije je bil dokumentiran sinsedimentni plaz, medtem ko v vrhnjem, zgornjeberriasijskem delu formacije opazujemo povečano vsebnost glinene komponente.