Freshwater Algae From the Upper Triassic Cuyana Basin of Argentina: Palaeoenvironmental Implications

Abstract

Diverse freshwater aquatic palynomorphs are present among rich terrestrial palynofloras from the upper part of the Potrerillos and Cacheuta formations outcropping in the Cuyana Basin at the southern extremity of the Precordillera of Argentina. The Potrerillos ⁄ Cacheuta sequence includes fluvial, deltaic and lacustrine facies deposited in the early Late Triassic fault-bounded syn-rift Cacheuta hemigraben. The phytoplankton described and illustrated consist of representatives of colonial chlorococcalean algae belonging to the Hydrodictyaceae (Plaesiodictyon) and Botryococcaceae (Botryococcus), a diverse group of Zygnemataceae zygospores, a freshwater dinoflagellate cyst (Bosedinia) and acritarchs (sphaeromorphs). Zygnematacean zygospores are represented by species of Gelasinicysta?, Lecaniella, Mougeotia, Ovoidites, Peltacystia and Schizocystia. Of these, Gelasinicysta? cuyanensis sp. nov. is newly described. Quantitative analysis of the palynofloras permits interpretation of changes in the local vegetation and phytoplankton communities controlled by changes in environmental setting. Two algal associations are recognized as belonging to different stages in the evolution of the basin. Diverse zygnematacean assemblages along with hydrodictyacean, botryococcacean and leiosphere ⁄ sphaeromorph algae are common in fluvialdeltaic environments of the upper part of the Potrerillos Formation and the lowermost part of the Cacheuta Formation. Higher in the sections (in the Cacheuta Formation) Botryococcus dominates, in association with amorphous kerogen, representing deposition in a relatively deep, quietwater, lacustrine environment where anoxic conditions prevailed. In the Cacheuta hemigraben the lacustrine shales have average TOC values of 4 per cent (locally reaching 20 per cent), with some terrigenous components (Type II ⁄ III kerogen), but dominant amorphous, algal-like, organic matter (Type I ⁄ II kerogen). Oils derived from these source rocks are predominantly waxy.

First occurrence of charophyte algae from a Triassic Paleolake in Argentina and their paleoenvironmental context

“…In Argentina, several micropaleontologic investigations have been carried out in continental sediments of the Triassic (Ottone et al, 2005;Ottone and Mancuso, 2006;Zavattieri and Prámparo, 2006). Despite this, charophytes have not been described in this sedimentary context probably because previous studies have only focused on palynologic or sedimentologic research.…”

Catálogo de ejemplares tipo de las Colecciones Paleontológicas del Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales (IANIGLA), Mendoza, Argentina

“…Paratipo: MPLP 9041 A4/2H:15.1/93.1 (Volkheimer, 2010 Género Gelasinicysta Head, 1992 Gelasinicysta? cuyanensis Zavattieri & Prámparo, 2006 (Figura 4A) Diagnosis (Zavattieri & Prámparo, 2006;p. 1196): Espora compuesta por dos mitades unidas por una sutura ecuatorial irregular, no claramente visible.…”

“…Holotipo: MPLP 7143B, H32 ⁄ 2 (Zavattieri & Prámparo, 2006: P. 1197Lámina 2, Figuras 1-3). Localidad tipo: Puesto Míguez, sur Cerro Cacheuta, provincia de Mendoza, Argentina.…”

Fossil zygospores of Zygnemataceae and other microremains of freshwater algae from two Miocene palaeosinkholes in the Opole region, SW Poland

“…Diagonalites-like microfossils are usually related to the zygospores of extant Mougeotia laetevirens (A.Braun) Wittrock (van Geel & van der Hammen 1978, van Geel et al 1981, Lyubomirova & Rundina 1993, Zippi 1998, Zavattieri & Prámparo 2006, but they are also morphologically close to zygospores of other Mougeotia species of section Mesocarpus (e.g. M. acadiana Transeau and M. varians (Wittrock) Czurda).…”