Geomorphological landmarks of the eastern romanian plain Holocene evolution
Grecu, F.; Sacrieru, R.; Ghita, C.; Vacaru, L.
published: Jun 1, 2009
ArtNo. ESP023105301006, Price: 29.00 €
The geomorphological evolution of the Romanian Plain was a subject very debated among Romanian geomorphologists and geologists. The Holocene represents the final stage in the evolution of the plain and during that period the hydrographical network settled. The Holocene is the time when the subsidence plain was formed, which is the recent most morphogenetic type of plain.The main goal of the present study is to describe the Holocene geomorphological forms and processes and to differentiate them from the older Pleistocene ones (Grecu et al. 2006). Another goal is to correlate the geomorphological moments of evolution with the characteristic climate features, the biogeographical features and the level variations of the Black Sea during that period.The Danube and all its tributaries in the Romanian Plain (especially those in its eastern part) were influenced by the level variations of the Black Sea. During postglacial transgression, the rivers would reach a new equilibrium profile. Alluvial deposits occurring on the river beds, blocked the river mouths of some autochthonous streams in the plain, tributaries of the Danube (the Mostistea, Galatui, etc.), or tributaries of some large rivers (the Ialomiţa and the Buzau), forming river lagoons. Most probably, the formation of river lagoons started simultaneously with the formation of the first lobes in the Danube Delta 5200 years ago (Giosan et al. 2006). As there were more than 30 river lagoons in the eastern part of the Romanian Plain, the latter was also named the Lagoon Plain (Posea 2002). The morphological and morphometrical features of river lagoons, as well as their connections with the Pleistocene terraces of the Danube are analysed in several case-studies: Mostistea, Galatui and Comana.Typical of the Holocene are the changes in the flow of the different tributaries of the Danube: the Dambovita, Ialomita, Buzau, Ramnicu Sarat, Milcovand Putna. Some authochthonous streams in the Eastern Romanian Plain (the Calmatui and the Mostistea) developed on the abandoned channels of the major Carpathian rivers. What caused it are tectonic or climate-related events, and they have hydrological implications. Variations in the river course could have taken place during some exceptional floods, most probably after the climatic optimum. There is evidence of these extreme events on the lower course of the Putna and the Siret (Roman 1986). The sub-fossil trees identified in the two river beds can help us outline the succession of the phytogeographical stages specific to the Holocene.Subsidence plains were formed exclusively during the Holocene by local negative tectonic movements of 7-8 mms/year, which still occur nowadays (van der Hoeven et al. 2005). The plains were the latest lacustrine sedimentary basins. The paper analyses the relations between the lacustrine units and the Danube (the main collector), on the one hand, and the Black Sea, on the other. The question is whether these lakes were permanently and directly connected with the Black Sea or not. Nowadays subsidence plains are areas prone to flooding during exceptionally high waters (1970, 1975, 2006).