干旱区生态环境知识资源中心

Fossil microfloral assemblages from five sedimentary successions of the Dacian Basin (Eastern Paratethys) are used to reconstruct the palaeovegetation and palaeoclimate of SE Romania during the Late Miocene to Early Pliocene (regional stages Khersonian, Meotian, Pontian, and Dacian). The studied microfloras were deposited under brackish to freshwater conditions in a fairly distal area of the Dacian Basin and are interpreted to reflect changes in the terrestrial ecosystems at a regional scale. The results show that the vegetation dynamic of the area was driven by the interplay of palaeogeographical and climatic changes. Broadleaved deciduous trees characteristic of temperate climatic regimes and a variety of gymnosperms dominated the vegetation during the Khersonian and the Meotian. This type of vegetation underwent a gradual decline throughout the studied time span, probably associated with a long-term cooling and drying trend. Thermophilous taxa were virtually absent in the area, with the exception of Engelhardia and Taxodioideae, which probably inhabited lowland swamp forests. The effect of an arid phase, which had its acme during the late Khersonian and extended, in an attenuated mode, during the earliest Meotian, is reflected in the palynological assemblages. This event resulted in the development of a xeric flora including Ephedra and Lygeum. The latter genus is cited for the first time in the Neogene flora of the Eastern Paratethys. Although mesic herbaceous taxa generally occur in low numbers throughout the successions, its signal becomes more relevant in the Pontian, suggesting drier conditions favourable for open ecosystems to develop. During the Dacian substage, the transition from brackish to freshwater settings in the basin favoured the development of shallow, freshwater marshes and led to the spread of a diverse hygrophytic flora. At the same time, a significant increase in Celtis pollen is interpreted to represent increased seasonality of precipitation.