CONICET | Buscador de Institutos y Recursos Humanos

The distribution and diversity of marine palynomorphs, such as acritarchs and chlorophytes, and terrestrial palynomorphs, such as miospores, are controlled mainly by palaeonvironmental and palaeogeographical conditions. Recently, global patterns of organic-walled phytoplankton were illustrated for the late Silurian to earliest Devonian based on data from different stratigraphic sections and palaeocontinents. Here we analyze the Silurian and the Early Devonian diversity in the Argentinean Precordillera, Central Andean, and Chacoparanense basins. The evolution of the diversity is evaluated in a wellconstrained biostratigraphic framework, bearing in mind local palaeoenvironmental conditions and changes within each basin. Taking into account updated published and unpublished data from well-dated sections, if possible, the biodiversity of Silurian phytoplankton seems to increase upwards, reaching its maximum peak during the Ludlow. However, palynomorphs are scantily recorded in Wenlockian strata, and the supposed Pridolian layers are not confidently well-dated. The first record of trilete spores in Argentina is Ludlovian in age, around 30 million yr later than their first incoming during the Late Ordovician. Palynomorphs diversity rise at the Early Devonian, turning the diversity of miospores greater than that of the marine phytoplankton. We interpret possible discrepancies in biodiversity trends of organic-walled phytoplankton between Argentina and other regions, as related to the quantitatively and qualitatively disparity of data, as well as the lack of rigorous biostratigraphic and palaeonvironmental assessments of the Argentinean basins. In addition the palaeogeographic location of the Precordillera and the Central Andean Basin, along the active margin of Gondwana with particular geodynamic conditions, is considered.