Palaeoenvironments on a Middle Eocene carbonate ramp in the Vértes Mountains, Hungary

Eocene sediments of the Hungarian Paleogene Basin – located on the Northern margin of the Tethys – unconformably overlie Mesozoic rocks, which were uplifted during Late Cretaceous to Early Eocene time. In the Vértes Mountains, there was a Bartonian, narrow, low-angle subtropical carbonate ramp with 40-50 m thick limestone (Szőc Limestone Formation) directly covering the karstic surface of Triassic limestone and dolomite. Ramp sediments were overlain basinward by Upper Lutetian - Bartonian brackish and normal marine deposits. Seven facies were distinguished by semi-quantitative microfacies analysis of Szőc Limestone. The inner ramp is represented by four facies: (1) extraclast rudstone to extraclast-bioclast floatstone (basal beds of Szőc Limestone), (2) bioturbated foraminifer-mollusc-echinoderm packstone/grainstone (interpreted as sea-grass meadow), (3) skeletal grainstone (bioclastic sand shoals), and (4) Nummulites perforatus rudstone/packstone (Nummulites banks). On the mid-ramp, larger foraminiferal floatstone and red algal facies with 3 subfacies – coral-algal boundstone (small patch reefs), larger foraminiferal-red algal and larger foraminiferal-rhodolith floatstones – were recognized. The lower mid-ramp to upper outer ramp is characterized by glauconitic larger foraminiferal grainstone (bioclastic sand deposition effected by currents). All facies record normal marine conditions. Main palaeoecological parameters influencing palaeoenvironments were hydrodynamic energy, depth, light conditions, substrate and nutrient availability