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Depositional history of the Paleogene Adriatic carbonate platform

The Paleogene Adriatic carbonate platform (PgAdCP), existed within the Central Tethys (around 32 N palaeolatitude) from the Paleocene (Danian) to the late Middle Eocene (Bartonian). Its depositional history differs from the stages-pattern recognized in the platformal development in the Tethys region in the Pyrenees and Egypt (Scheibner & Speijer, 2007). In the Adriatic, the shallow-marine carbonate regime is composed of various facies types which are defined upon the larger benthic foraminiferal associations and sedimentary structures. These facies are grouped into and record temporal and spatial demise of certain ecological conditions. Sedimentation within each zone started with restricted, marginal marine, paralic and pallustrine carbonates, that we consider as the initially phase to gaining full marine conditions. Once the marine regime was obtained, the shallow-marine settings supported the development of diverse and abundant foraminiferal assemblages. The biota suggests that platform jumped into the third Tethyan stage even though sedimentation started in SBZ1 (Serra-Kiel et al., 1998) and lasted until SBZ 9 (BiosZ 2), in SBZ 2 until three main biosedimentary units, BiosZ 2 to BiosZ 4 (Drobne 2003, Drobne et al., 2008). These zones followed one upon another in a step-wise geographic pattern SBZ 12 (BiosZ 3), and in SBZ 11 to SBZ 14 (BiosZ 4). Interestingly, the second Tethyan stage, coralgal facies, is recorded within the NW margin in the BiosZ 2 area only. The characteristics that differ the Pg AdCP from others are: (1) a reduced species richness in the Paleocene succession (3 assilinid species in Paleocene) ; (2) less diversified Eocene foraminiferal assemblages (eg. 8 species of Nummulites in the early Eocene and 12 species from the middle Eocene, Pavlovec 2003 vs. 76 for early and 62 for middle Eocene, Less 1998), (3) absence of some taxa (Spiroclypeus sp., Heterostegina sp., Pellatispira sp.) ; (4) absence of encrusting foraminifera ; (5) the regularity in occurrences of certain larger foraminiferal groups: complex miliolids and agglutinated conical forminiferas characterize the beginning of platform regime, which gave way to alveolinids, orbitolitids and nummulitids assemblages, and which eventually were replaced by operculinids and orthophragminids ; (6) concurrence of BiosZ 3 with Alveolina histrica lineage and Alveolina levantina lineage with BiosZ 4.

Paleogene; Foraminifera; Adriatic carbonate platform

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