Abstract

ZAVATTIERI, Ana María  and  ROJO, Leandro David. Microfloristic study of the Potrerillos and Cacheuta Formations (Triassic), south of Cacheuta hill, Mendoza, Argentina. Part 2. Ameghiniana [online]. 2005, vol.42, n.3, pp.513-534. ISSN 1851-8044.

The Triassic continental sequences exposed at two sections south of cerro Cacheuta, Cuyana Basin, contain diverse microfloristic assemblages from the Potrerillos and Cacheuta Formations. In this second part, 43 species of gymnospermous pollen grains are listed and illustrated. Ten species belonging to the genera Brachysaccus , Podocarpidites , Lunatisporites , Protohaploxypinus , Steevesipollenites , Striatoabieites , Peroaletes and Cycadopites are new records for Argentina. Abundant freshwater green algae communities are also present in both units, included members of Chlorococcales from Botryococcaceae, Hydrodictyaceae and Zygnemataceae. Plaesiodictyon mosellanum Wille is first recorded in Cuyana Basin. Peltacystia and Ovoidites are new genera for the Argentinian Triassic. A complete list of microfloristic taxa distributed in both formations is presented, stratigraphically relocating those of the "Minas de Petroleo Beds" previously known microflora. Highly diverse gymnospermous pollen grains dominate the assemblages and are compared with the known gymnospermopsida components of the megaflora. Quantitative features within the microfloral successions appear to reflect environmental shifts associated with the evolution of the coal and clastic facies through the Triassic local deposition. Therefore, it is suggested that the microfloras are facies-controlled and they reflect elements of basically contemporary floras. The chronostratigraphic distribution of selected species and cosmopolitan Triassic elements support an Early Late Triassic age for the studied microfloras. In terms of the known Gondwanan Triassic palynostratigraphy, the microfloras of the Cacheuta sections can be correlated to Ipswich Microflora. They represent floral communities of temperate to warm temperate climate, highly seasonal and locally humid.

Keywords : Palynology; Potrerillos and Cacheuta Formations; Triassic; Mendoza; Argentina.