Tracing the origin of Lago Mare biota: Ostracods and mollusks from the late Neogene of the Slavonian mountains in the southern Pannonian Basin (NE Croatia)

Abstract

Lake Pannon was a huge central European, long-lived endorheic lake occupying the Pannonian Basin System during the late Neogene. The benthic fauna of this originally sparsely populated brackish lake went through a spectacular adaptive radiation leading to a great number of autochthonous species. Although largely endemic, some of these species are excellent stratigraphic markers of the Lago Mare interval in the Mediterranean Basin. This situation apparently reflects a short-termed unidirectional migration-wave in the latest Miocene. The latter interval marks the final phase of a major environmental perturbation followed by a massive evaporite deposition termed the Messinian Salinity Crisis. The Section Bozara, located in the southern Pannonian Basin at the southern slopes of Mt. Papuk, bears a well-preserved benthic fauna representative of Lake Pannon. It is embedded into a 25-m-thick succession of alternating mud and sand packages. We detected therein 25 ostracod and 18 mollusk taxa enabling, along with a sedimentary facies analysis, an integrated evaluation of the depositional setting, biostratigraphic position, and paleogeographic distribution pattern. Accordingly, the depositional environment shows a shallowing upward trend from deep-water sublittoral and distal prodelta settings to deltaic high-energy littoral conditions. The biostratigraphic markers, such as the bivalve Rhombocongeria rhomboidea (Hörnes, 1867) and the ostracod Caspiocypris pontica (Sokač, 1972), constrained its stratigraphic position to the Portaferrian interval (8.0–4.5 Ma). Of 16 ostracod taxa determined at the species level, 10 are shared with the Eastern Paratethys, whereas only 3 are present in the Mediterranean Lago Mare deposits as well. In contrast, among 12 corresponding mollusk taxa, only 4 are known from the Eastern Paratethys, all being absent in the Lago Mare interval. Such a paleobiogeographic pattern suggests that the time window of the outflow event from Lake Pannon into the Eastern Paratethys was not synchronous with, but must have preceded, the hypothetic Eastern Paratethys drainage event generating the Lago Mare depositional conditions in the Mediterranean Basin.