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Biostratigraphy of Turonian to Coniacian shallow-water carbonate succession on the island of Cres, northern Adriatic, Croatia

An assemblage of rudists, benthic foraminifera, and associated microfossils characterizes Upper Cretaceous peritidal carbonates on the island of Cres (northern Adriatic, Croatia), overlying the hemipelagic Cenomanian/Turonian limestones. The strata investigated are characterized by predominantly mud-rich well-bedded limestones with numerous Aeolisaccus and Thaumatoporella. Oligotypic character of the fossil association suggests deposition in shallow areas of the carbonate platform, with low-energy and restricted circulation. Contrary to the older mid-Cretaceous shallow-water limestones rich in rudists and benthic foraminifera, the Upper Cretaceous strata contain a low-diversity association. However, the association implies that following the hemipelagic conditions, which prevailed during sedimentation of the underlying deposits during the latest Cenomanian-Early Turonian within a wider area environment later again became favourable for population of larger foraminifera, and sporadically, rudists. Rudists (Mollusca, Hippuritacea) are the most frequent macrofossils within the strata investigated. Radiolitids (Radiolitidae) have been sporadically found both in autochthonous (in situ bouquets, clusters and small lens-like thickets) or para-autochthonous position (displaced locally in vicinity of their habitats). Besides poorly preserved radiolitids of minor biostratigraphical value, there are rare hippuritids (Hippuritidae), that have been commonly found in bouquets characterized by three to four conjoined specimens. Due to poor preservation of diagnostic shell features, only several forms that confer to four hippuritid species have been determined: Hippurites cf. incisus DOUVILLÉ, Hippurites cf. socialis DOUVILLÉ, Hippurites cf. toucasi D’ ORBIGNY (=Hippurites cf. praetoucasi TOUCAS) and Vaccinites cf. rousseli (DOUVILLÉ). The aforementioned Hippuri tes species have been frequently reported from Turonian to Santonian deposits of the (peri)Adriatic area. However, within the Croatian part of the area the genus Vaccinites has been reported exclusively from Santonian and stratigraphically younger deposits. This range is also incorporated into an important, recently published biochronostratigraphical review. Thus, this is the first report on the genus from Croatia, which in association with the afforementioned hippuritids imply Turonian to Coniacian age of the strata investigated. Furthermore, a few “ primitive” species of the genus have been previously reported from Turonian to Coniacian deposits of the wider area. Therefore, the defined biostratigraphic range of previously mentioned “ primitive” Vaccinites species from western Europe, is confirmed also within Periadriatic domain, and should be added to the chart. Microfossil association does not contain many stratigraphically relevant taxa as well. Moreover, the stratigraphic ranges of the only three “ index” species, which are very common in the Late Cretaceous of Croatia are still disputable. The least debate is on the first appearance of Moncharmontia apenninica DE CASTRO, which is Late Turonian. On the other hand, various authors gave very different data on the stratigraphic range of Scandonea samnitica DE CASTRO: Turonian to Early Campanian. Similar is the case with Pseudocyclammina sphaeroidea GENDROT, that is Turonian to Santonian. However, there is one additional clue to narrow the stratigraphic range of the examined sequence. Namely, the foraminifera (Dicyclina schlumbergeri MUNIER-CHALMAS, Accordiella conica FARINACCI, Keramospherina tergestina (STACHE), Scandonea mediterranea DE CASTRO, and Nummofalotia apula (LUPERTO SINNI)), that on the Adriatic Carbonate Platform appear in the Santonian, were not found in the study area. Therefore, based on the microfossil and macrofossil association, and knowing that underlying hemipelagic deposits are accurately attributed to the Cenomanian-Turonian boundary, the age of the investigated sequence is Turonian to (?)Coniacian.

Adriatic Carbonate Platform; Biostratigraphy; Rudists; Cres

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