EARLY OLIGOCENE PALEOCLIMATE IN SOUTHEAST BULGARIA - A STUDY BASED ON PRELIMINARY PALEOBOTANICAL DATA FROM USTREN (EAST RHODOPES MTS.)

The Bulgarian paleobotanical record provides important clues about the Paleogene vegetation and climate of the Tethyan Archipelago coastal areas of the evolving Eastern Paratethys. First results from a palaeoclimatic survey over a leaf flora discovered in an Oligocene volcano-sedimentary sequence, close to the village Ustren (East Rhodopes Mts., South-East Bulgaria) allow for a detailed reconstruction. The fossil flora is of late Oligocene age (ca. 32 Ma) as proved by isotope dating. Due to its specific palaeogeographical settings, this newly-discovered “volcano flora” provides insight into the vegetation cover of the uplands while most of the other localities of the area reflect the wetland vegetation widespread in the sedimentary basins.

In this contribution, we focus on regional provenance of Nearest Living Relatives (NLRs) of the taxa recorded, and on their palaeoclimatic interpretation using Coexistence Approach (CA). Up to now, 24 different fossil taxa were identified. To most of them NLRs can be assigned with sufficient accuracy. It is shown that the majority of these NLRs are presently native to Southeast Asia and to Central America, respectively. In rarer cases, the NLRs of the Ustren palaeoflora now exist as relics on the Canary Isles, and in Southeast North America. Our results testify the close relationship between the European Paleogene flora and the recent, natural vegetation in Southeast Asia and Central America. Paleoclimate analysis revealed warm temperature, humid conditions, with mean annual temperature above 17 °C, and cold month mean over 10 °C as suggested by the presence of palms (Phoenix, Sabal) and warmth-loving angiosperms such as Persea and Ficus. As regards precipitation annual rates over 1,000 mm are probable (presence of Neolitsea/Lauraceae and Eurya/Theaceae). According to our data, seasonality of rainfall was only moderate, so a Cfa-type climate can be inferred.