Conference:
Monsoon workshop, 26 October, 2001, University Paris Sud, Paris, France.
Author:
Speranta-Maria Popescu.
Abstract:
High-resolution pollen analyses on the lignite-clay Lupoaia section (from 4.9 to 4.3 Ma) in southwestern Romania provide an accurate record of the Lower Pliocene vegetation changes in the Danube paleodelta environment close to the Carpathians. Many major fluctuations concern thermophilous trees vs. altitudinal trees (chiefly in agreement with lignite-clay alternations) and have been referred to changes in temperature. Thanks to a reliable magnetostratigraphic calibration of the section, such changes are to be linked to eccentricity cycles, that provides a more precise chronologic control to the section (Popescu, in press). In addition, regular secondary fluctuations occur which oppose swamp trees (as most of the Taxodiaceae) to marsh herbs (as Cyperaceae). They evoke the present-day landscape of the Mississippi delta where swamp forests (constituted by Taxodium distichum mainly) are in competition with herbaceous marshes (made of Cyperaceae as Mariscus jamaicensis in addition to some Cyrillaceae and Myrica). The latest require significantly more water than the swamps (Roberts, 1986). These plant environments cause two kinds of lignite deposition that have been also identified in the Lupoaia section (Ticleanu and Diaconita, 1997). According to the chronologic frame previously defined, it is possible to evidence a precession forcing for these alternations. Minima in precession probably caused increasing rainfall over the region and expansion of marshes. So, it is suggested that during Lower Pliocene the West Asian monsoon influenced climate of the northeastern Mediterranean region.