Tectonically-controlled biofacies distribution in the Eocene Foraminiferal Limestone (Pag, Croatia): A quantitative-based palaeontological analysis

Abstract

[eng] This paper analyses the lower tomiddle Eocene carbonate succession exposed at the Island of Pag (Croatia), in theExternal Dinarides, providing its palaeoenvironmental, palaeobathymetric, and stratigraphic reconstruction. A totalof 125 samples have been collected within the Foraminiferal Limestone and the overlying Transitional Beds unitscropping out in the sites of Vrčići and Pag for the quantitative analysis of the skeletal assemblage (point counting)and the foraminiferal association (area counting), including both large benthic and small benthic foraminifera. Furthersamples were collected from the overlying Dalmatian Flysch, to constrain the age of the top of the successionusing calcareous nannofossil biostratigraphy. On these bases, the Foraminiferal Limestone has been dated from theYpresian to themiddle Eocene (late Lutetian/early Bartonian). Thanks to the analysis of the skeletal and foraminiferalassemblages, and the use ofmultivariate statistics, sevenmain biofacies were identified within the ForaminiferalLimestone and one biofacies within the Transitional Beds. The porcelaneous and agglutinated benthicforaminifera biofacies (BF1) indicates a well-illuminated, oligotrophic to mesotrophic, shallow water, lagoonalenvironment. The hyaline SBF and encrusting benthic foraminifera biofacies (BF2) developed in a shallow water,inner-ramp environment, and is related to a vegetated seafloor. The nummulitid biofacies (BF3) indicates a moderatelyhigh energy, shallow water environment, whereas the comminuted bioclasts and nummulitid biofacies(BF4) corresponds to a low-energy, shallow water environment, and both deposited in inner-to-middle ramp settings.The nummulitid and orthophragminid biofacies (BF5) indicates a moderate energy environment, depositedin middle ramp settings. The nummulitid and serpulid biofacies (BF6) consists of transported material from theinner ramp deposited in middle ramp settings. The orthophragminid and nummulitid biofacies (BF7) indicates abelow-wave base, outer shelf setting and the planktic foraminifera biofacies (BF8), recorded in the TransitionalBeds, indicates a hemipelagic environment. Based on the foraminiferal counting, quantitative parameters such asthe orthophragminids/nummulitids ratio, the planktic/benthic foraminifera ratio, and the hyaline/porcelaneousforaminifera ratiowere calculated. These parameters indicate that the succession formed along a distally steepenedramp profile, showing a progressively tectonically-controlled deepening of the depositional environment, culminatingwith the final drowning of the carbonate ramp. Quantification serves as a crucial instrument for a preciseand reliable palaeoenvironmental reconstruction, allowing the comparison amongst different successions.