Development of transient carbonate ramps in an evolving foreland basin
V. Cosovic, E. Mrinjek, W. Nemec, J. Spanicek and K. Terzic
Journal name: Basin Research
Issue: Vol 30, No 4, August 2018 pp. 746 - 765
Info: Article, PDF ( 15.4Mb )
This study of Eocene carbonate succession in the Dinaric Foreland Basin of northern Dalmatia, Croatia, integrates palaeontological and sedimentological data to document a range of carbonate ramps formed intermittently during the basin tectonic development. The end-Cretaceous basal erosional unconformity records the coupling of Adria and Eurasia crustal plates, with an antiformal uplift along their suture zone. The overlying late Ypresian carbonate ramp, spanning biozones SBZ 11–12, developed on the forebulge flank of a shallow-marine early synclinal basin. Basal grainstone/ packstone facies, dominated by encrusting foraminifers with alveolinids and miliolids, pass upwards into packstones dominated by miliolids and rotaliids with bryozoan and echinoid fragments, indicating an increased bathymetry of the retreating forebulge flank. Deposition of grainstone facies preceded an end-Ypresian (SBZ 12/13 transition) subaerial exposure due to post-subductional isostatic uplift. The younger, middle to late Eocene carbonate ramps (SBZ 13–19) formed episodically as perched isolated features on blind-thrust anticlines in a bathymetrically diversified wedge-top basin, where phases of clastic and skeletal biogenic sedimentation alternated due to disharmonic thrusting and relative sea-level changes. Clastic sedimentation reflects anticline crest erosion and a forced-regressive progradation of gravelly foreshore and sandy shoreface facies over heterolithic offshore- transition and muddy offshore facies on the anticline flank. Biogenic sedimentation represents inner- to middle-ramp environments, with the latter terminating bluntly in muddy offshore environment. An outer-ramp environment, known from classic ramp models, was lacking due to bathymetric threshold. Analysis of larger benthic foraminifers (LBF), as biostratigraphic age indicators and palaeobathymetric proxies, helped distinguish systems tracts and determine their time span. A comparison of local and global sea-level changes allowed the interplay of tectonic and eustatic forcing to be deciphered for the study area.