Conference:
EEDEN, Dinoflagellate cysts: promising markers of Mediterranean–Paratethys relationships, Workshop, 17-20 April 2004, Lyon, France.
Author:
Speranta-Maria Popescu.
Abstract:
After being isolated from the Mediterranean Sea, Paratethys evolved towards brackish conditions. Sea-Surface salinity progressively decreases from West to East. Release in Alpine orogeny (Dinarids, Carpathians, Caucasous) and coeval global sea-level rise may have caused some brief connections between Paratethys and the Mediterranean Sea. Variability in salinity (i.e. a progressive decrease interrupted by some increases during brief connection events) induced repetitive environmental stress superimposed to the climate evolution (from subtropical-tropical conditions in the Mid-Miocene to warm-temperate ones in the Mid-Pliocene). Dinoflagellates are among the most reliable indicators of such events because living in abundance in the surface waters, being in addition outstandingly adaptable. Marine palaeoenvironments are well-reconstructed on the basis of dinoflagellate cysts (salinity, temperature, currents). Such a tool is difficult to use in low salinity basins because of the appearance of many morphotypes that have been often described as new genera, species or subspecies, being generally devoid of any modern ecological reference. Studies both on old (Late Miocene – Early Pliocene) and recent (Holocene) sediments from Black Sea cores (DSDP 380A and BLKS 98-10 sites respectively) have evidenced appearance of similar morphotypes under environmental stress conditions. Cysts of endemic species from Paratethys, such as Spiniferites cruciformis, Pyxidinopsis psilata, and Galeacysta etrusca show morphological changes concerning shape, size, sculpture, type of archeopyle (one or two plates), shape of the veil. They may be related to climatic changes. Cysts of marine species show important morphological when entering low salinity basins, such as development of reduced processus (up to a bowl shape for Lingulodinium machaerophorum), of a coarse sculpture or acquisition of a more or less perforated veil connecting base of processus. In addition, cruciform bodies appear as an adaptation to low salinity. Morphological similarities concern the following species: (1) Spiniferites cruciformis(morphotypes with a veil), Pterocysta cruciformis, Seriliodinium explicatum, Spiniferites balcanicus, Romanodinium arveolatum, Galeacysta etrusca; (2) Achomosphaera andalusiensis, Spiniferites galeaeformis, Spiniferites andalusiensis, Spiniferites maisensis; (3) Tectatodinium pellitum, Pyxidiniopsis pastiliformis, Pyxidiniopsis psilata. Were such important morphological changes caused by an adaptation (even evolution) or only an accommodation to new environmental conditions? The question results from the simultaneous occurrence of these morphotypes during environmental crises.