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Paleoenvironment Of Gastropod Fauna From The Campanian Deposits Of Gornje Orešje (Medvednica Mt., Croatia)

Gosau-type basins, typical for Austroalpine and Inner Dinaric regions, were characterized by vertical succession of transgressive facies, with the development of fluvial–lacustrine to shallow-marine environments which characterizes deposition of conglomerates, coal-bearing marls, siliciclastics rich in corals, acteonellid and nereneid gastropods and rudist limestones, which finally passed into deep- water Scagila-type limestones or marls. At the Gornje Orešje locality on the Medvednica Mt. (NE Croatia) (MORO et al. 2016) from allochtonous, weathered part of of the Gosau- type facies outcrop rich in corals and rudists, 78 specimens of gastropod fauna were collected. Within collection 10 species and 15 genera were determined: Trochactaeon (Neotrochactaeon) giganteus (Sowerby, 1835), Trochactaeon (Neotrochactaeon) cf. giganteus (Sowerby, 1835), Trochactaeon (Neotrochactaeon) goldfussi (d`Orbigny, 1850), Trochactaeon (Neotrochactaeon) sanctaecrucis (Futterer, 1892), Trochactaeon (Neotrochactaeon) obtusus (Zekeli, 1852), Trochactaeon (Neotrochactaeon) subglobosus (Muenster, 1844), Trochactaeon (Neotrochactaeon) sp., Trochactaeon sp., Parasimploptyxis buchi (Muenster, 1829), Parasimploptyxis cf. buchi (Muenster, 1829), Parasimploptyxis pailletteana (d`Orbigny, 1842), Parasimploptyxis indet., Pseudamaura bulbiformis (Sowerby, 1831), Pseudamaura sp., Trochus sp., Palaeocancellaria hoelleitenensis Kollmann, 1976, Echinobathra sp., Bicarinella sp., Astraea sp., Punctospira sp., Bathrotomaria sp., Cernina sp., Turritella fittoniana (Muenster), Natica sp. and Drepanocheilus sp. From the collected material 11 specimens remained taxonomically indeterminated. According to the chronostratigraphic and biostratigraphic data from the fossil assemblage, Campanian age has been determined. In comparison with other Gosau-type facies successions, the gastropod diversity is quite low concerning both genera and species. That could be due to the ecological preferences of determined genera within the investigated transgressive succession. Presumably abovementioned gastropod assemblage thrived as epifaunal vagrant benthos. They preferred mixed calcareous mud–siliciclastic substrate of shallow-marine moderately agitated subtidal platform environments. That kind of paleoenvironment was relatively narrow within the vertical succession of the typical transgressive Gosau-type facies, resulted with short period of gastropod’s fauna abundant presence. Moreover, this characteristics of substrate could be one of ecological reasons for the rareness and absence of gastropods from typical subtidal paleoenvironments of the Adriatic Carbonate Platform (AdCP).

Gosau-type facies, transgression, gastropods

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