Abstract

OTTONE, Eduardo G.; MANCUSO, Adriana C.  and  RESANO, Magdalena. Miospores and chlorococcalean algae from the Los Rastros Formation, Middle to Upper Triassic of central-western Argentina. Ameghiniana [online]. 2005, vol.42, n.2, pp.347-362. ISSN 1851-8044.

Lacustrine strata of the Los Rastros Formation (Middle to Upper Triassic) at Río Gualo section (La Rioja province), yield a distinctive palynological assemblage of miospores and chlorococcalean algae. The miospore association is characterized by a relative abundance of corystosperm pollen grains with subordinate inaperturates, diploxylonoid disaccates, spores, monocolpates, monosaccates and striate pollen grains. The phytoplankton are mostly represented by Botryococcus but also by Plaesiodictyon , a form probably related to the Hydrodictyaceae. Geological data and variations in phytoplankton content indicate that the lacustrine system probably evolved from a stretcht of freshwater with eutrophic conditions, into a body with oligotrophic conditions through the middle and upper part of the Río Gualo section. The genus Variapollenites is emended in order to amplify its original diagnosis.

Keywords : Argentina; Triassic; Miospores and chlorococcalean algae; Systematics; Lacustrine environment.