Reworked neritic fauna in the Lower Cretaceous ‘Lower Flyschoid Formation’ of the Tolmin Nappe (Slovenia): New data on biostratigraphy and palaeogeography

Abstract

A mixed assemblage of planktonic and benthonic foraminifera (e.g. orbitolinids) is reported from proximal calciturbidites within the ‘Lower Flyschoid Formation’ of the western part of the Slovenian Basin. The presence of reworked orbitolinids from the Slovenian territory is well known, but their treatment in open nomenclature has hitherto hindered biostratigraphic analyses. The onset of sedimentation of the Lower Flyschoid Formation was previously indicated as Albian and possibly Aptian. The records of Palorbitolina lenticularis (Blumenbach) and Mesorbitolina gr. lotzei Schroeder tibetica (Cotter) at the base of the formation, which overlies the Biancone Limestone with an erosional contact indicates the presence of uppermost lower Aptian reworking in some places. The presence of Conicorbitolina cuvillieri (Moullade) in the upper parts of the studied sections indicates a late Albian–early Cenomanian age. The ages obtained from the neritic faunal elements is generally in line with the data obtained from the associated planktonic foraminifera. C. cuvillieri characterizes platform margin and upper slope deposits, with very few records in the literature. From the wider area, it has been recorded from the northernmost part of the Dinaric-Friuli Carbonate Platform of Italy and Slovenia thus allowing for platform-to-basin as well as inter-basinal correlations. The youngest age obtained from the Lower Flyschoid Formation is middle Cenomanian. The new data indicate a diachronous base of the Lower Flyschoid Formation needing further investigations for deciphering the palaeogeographic configuration at the northwestern edge of the Friuli Carbonate Platform as well as platform events in relationship to contemporaneous basinal sequences.