Poster:
32nd International Geological Congress, Florence (Italy), 20-28 August, 2004, Session 322- T26.01.
Author:
Speranta-Maria Popescu.
Abstract:
High-resolution palynological analysis has been performed on five well-dated Early Pliocene sections from southeastern Europe: Hinova, Valea Visenilor, Husnicioara and Lupoaia in the Dacic Basin (southwestern Romania), DSDP Site 380A (Black Sea) which also includes latest Miocene sediments (Messinian). Pollen floras show how this region was relatively protected from floristic extinctions which occurred in Europe during the Late Pliocene and the Quaternary because of glacial-interglacial cycles. A noticeable effect of Asian monsoon has probably encouraged persistence in this area of some themophilous species up today. Altitudinal forest belts have been reconstructed on the southern Carpathians. Palaeo-Danube delta was rich in swamps inhabited by Taxodiaceae forest and marshes occupied by grasses (Cyperaceae) as today in Florida and Mississippi delta. The descent of the altitudinal gymnosperm belts is evidenced in relation with each “cooling” with respect to eccentricity 100 kyrs cycles. On contrary, warmer phases forced development of thermophilous trees and lignite deposition. Asian monsoon probably controlled opposing development of swamps and marshes with respect to precession 20 kyrs cycles. Precession minima (monsoon enhancement) advantaged marshes which require more humidity than swamps. A comparison is possible with the Mediterranean sapropels, the forcing of which being also the precession rhythm. This suggests the establishment in Early Pliocene of a longitudinal gradient over the Mediterranean region. As today, a strong contrast separated vegetation features from Dacic and Pontic realms. In the latter, thermic cycles forced competition between thermophilous trees and Artemisia steppes, the early development of which announces their forthcoming development over the whole Mediterranean region in relation with earliest glacials (2.6 Ma). Such high-resolution pollen analyses provide a very detailed climatic record for the region with respect to global climatic changes between 6 and 3.8 Ma. Resolution of pollen records reaches that of reference δ18O curves. So, weak variations in temperature and humidity occurring during the warm Pliocene will be more understood as well as their effects on the vegetation. The European Pliocene climatostratigraphy is confirmed and Central Paratethyan deposits receive for the first time a reliable cyclostratigraphy. Relationships will be easier with the reference Mediterranean marine sections. Consequences of the Mediterranean Sea desiccation (Messinian salinity crisis: 5.7-5.32 Ma) over the Black Sea have been evidenced: they concern both coastal vegetation and dinoflagellate assemblages. A new idea of Mediterranean Sea – Central Paratethys relationships is proposed for a better explanation of the events bordering the salinity crisis.