The role of the Eocene larger benthic foraminifera in evolution of transient ramps in Dinaric Foreland Basin

In the study of Eocene carbonate succession in the Dinaric Foreland Basin (northern Dalmatia, Croatia), integrated palaeontological and sedimentological data document a range of successive carbonate ramps formed intermittently during the basin tectonic evolution and progressive contraction. The late Ypresian Foraminiferal Limestones are overlain unconfortably by a succession of early Lutetian limestones, the Upper Nummulitic Limestone or Lithotamnium Limestones. The study of Larger benthic foraminifers (LBF) is important in the sequence-stratigraphic analysis of the sedimentary succession, particularly in the distinction and timing of its component systems tracts. The bathymetric assessment based on LBF has made it clear that these biogenic limestones signify an increase of water depth and hence belong to the transgressive tract. The late Ypresian Foraminiferal Limestone, rich in alveolinids, conical agglutinated foraminifers and complex miliolids, was deposited during a global sea-level highstand and this early period of low-rate foreland subsidence well-balanced by the rate of organic productivity. The slight bathymetric fluctuations indicated by facies changes in the lower part of this succession seem to reflect the eustatic cycles Yp8–10 (sensu Snedden & Liu, 2010), the end-Ypresian emergence of the carbonate ramp at the highstand peak of cycle Yp10 was clearly caused by local tectonics. The eustatic signal becomes far less recognizable in the Lutetian to Priabonian part of the stratigraphic succession, where the local changes of relative sea level are mainly opposite to the eustatic ones. Nummulitids, asterigerinids, silvestriellas and different genera of encrusting foraminifers were dominant constituents in LBS assemblages along with corallinaceans. The late Ypresian carbonate-ramp deposits were developed on the retreating forebulge flank of a shallow-marine early foredeep basin. The younger, middle to late Eocene carbonate ramps formed episodically as perched isolated features on blind-thrust anticlinal ridges in a bathymetrically diversified wedge-top basin, where phases of biogenic and clastic carbonate sedimentation alternated due to disharmonic thrusting and frequent sea-level changes.