Carbonate ramp evolution during the Late Oligocene (Chattian), Salento Peninsula, southern Italy

Oligocene carbonate ramps and platforms are widespread and though they are important carbonate reservoirs, detailed studies on the facies organization, platform type and internal architecture are scarce. Within this context, the Chattian carbonate units cropping out in Salento (southern Italy) allow detailed study of the distribution of skeletal components and facies architecture. The lower Chattian Castro Limestone, previously considered as a fringing reef, is reinterpreted as a distally steepened ramp with a distal talus induced by a paleo-escarpment in the substrate. Epiphytic biota and sediment dweller organisms thriving in seagrass meadows dominated production in the shallow-water euphotic zone. Seawards, large rotalid foraminifers dominated a detritic mesophotic zone. Near the edge of the escarpment, also in the mesophotic zone, luxurious growth of corals built discrete mounds with no evidences of wave-resistant growth fabrics. Basinward, 25° to 30° dipping clinobeds abut against the escarpment where coral rudstone/floatstone textures resulted from downfall of corals and sediments. The upper Chattian Porto Badisco Calcarenite represents a homoclinal ramp dominated by packstone textures. In the euphotic inner ramp, autochthonous biota suggests the occurrence of extensive seagrass meadows. Basinward, large rotalid packstone and small coral mounds developed in mesophotic conditions, and rhodolithic floatstone to rudstone and large lepidocyclinid packstone characterize the sediments of the deeper oligophotic zone. Comminuted skeletal debris, depleted of light-dependent organisms, typifies deposition in the dysphotic/aphotic zone. In both examples, the middle ramp (meso-oligophotic zones) was the most prolific in terms of carbonate production, whereas shallow-water seagrass-related production (euphotic) was much less important. Corals built mounds, also in the mesophotic zone but never reached sea level. Hydrodynamic conditions in the meso-oligophotic zone are better explained by breaking of internal waves, and their induced up- and down-slope currents, instead of the surface storm waves.