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Carbonate Cobbles And Blocks From The Upper Cretaceous (Campanian) Debris Flow, Ozalj Area, NW Croatia

The Dinaridic orogenetic belt comprise some of the thickest and most continuous Mesozoic sedimentary successions of the Perimediterranean region. Its deposits include a major part of the Cretaceous successions of Croatia, which are predominantly characterized by carbonates (Outer Dinarides) or mixed carbonates/siliciclastics (Inner Dinarides). While the area of the Outer Dinarides was characterized predominantly by shallow-marine deposition on the Adriatic Carbonate Platform, the area of the Inner Dinarides was characterized by basinal Gosau-type sedimentation consisting of deep-water carbonates (Scaglia), marls and gravity flow deposits which followed after relatively short periods of shallow-marine sedimentation. The Vivodina area in the Žumberak Mts. of NW Croatia comprises such deposits. Within the upper flysch type succession several types of gravity flow beds can be clearly differentiated based on their composition, grain-size and thickness. The most common are relatively thin (up to aprox. 10–20 cm) turbidite beds of carbonate or commonly mixed carbonate– siliciclastic composition. Interlayered with the thin sandstone turbidites are thick (often >1 m) carbonate turbidite beds consisting of coarse rudite carbonate lithoclasts at their bottom which upward grade into finer-grained, mostly skeletal detritus. Also within the succession occasional thick debris flow deposits occur characterized by chaotic structure composed of large carbonate clasts up to 1 m in size. Near Ozalj, an outcrop of a thick carbonate bed composed of fossiliferous carbonate pebbles, cobbles and blocks was investigated in order to determine the origin and fossil content of the redeposited material. Textural characteristics of the analyzed cobbles and blocks ranges from wackestones– packstones to grainstones. Macrofossils are represented by numerous small requieniids and some caprinids. Microfossil communities determined in thin sections are composed of Dicyclina schlumbergeri (MUNIER CHALMAS), Palorbitolina lenticularis (BLUMENBACH) and Praeorbitolina cormyi SCHROEDER as well as numerous miliolids. According to the macro- and microfossil communities the age of the carbonate clasts from this locality range from Aptian to Middle Turonian. In the wider area ZUPANIČ (1974) reported the presence of clasts ranging from Paleozoic to Upper Cretaceous in similar carbonate beds. The depositional paleoenvironment in which the above mentioned fossils thrived ranges from low-energy to relatively high-energy shallow subtidal. Biostratigraphically, requieniids are present throughout the Cretaceous, while caprinids range from the Aptian to the Cenomanian. Both clingers (requieniids) or mostly recumbents and rarely elevators (caprinids), thrive in more open paleoenvironments with relatively higher water energy, such as low-angle open shelf margin complexes, isolated build-ups, and steep margin complexes (for recumbent caprinids) (ROSS & SKELTON, 1993). These debris flows consist of clasts which range from pebbles to blocks with fine-grained matrix between them. They were probably deposited on steep and short slopes along the southwestern margins of the Late Cretaceous foreland basin which flanked the emerged Adriatic Carbonate Platform.

debrite flows, Ozalj, carbonates, Upper Cretaceous

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