The Río Blanco Basin is located in western Argentina (La Rioja and San Juan provinces) and comprises the Angualasto Group defined by Limarino and Césari (1992). This Early Carboniferous unit includes, among others, the Malimán and Cortaderas Formations, both represented at its type locality (La Cortadera creek).
These sequences are characterized by predominant marine sedimentation (Lopez Gamundi et al , 1987). The outcrops of the Malimán Formation in La Cortadera creek, reach a thickness of 1188 m, unconformably overlying the Devonian Chigua Formation, and have an abundant record of plant remains (Frenguelli, 1954; Menéndez, 1965; Azcuy et al ., 1980; Césari, 1988; Sessarego and Césari, 1989; Arrondo et al ., 1991). This paleoflora was referred to the Archaeosigillaria-Frenguellia Biozone and an Early Carboniferous age was suggested (Sessarego and Césari, 1989). Césari and Limarino (1995) recorded a rich palynological association from the Malimán Formation and proposed a Tournaisian age for this sequence. These assemblages, deposited on a low energy marine plataform, are characterized by the presence of smooth, verrucate and cingulizonate spores, along with scarce acritarchs. The invertebrate association was studied by Amos, 1958; Amos et al. , 1973 and Antelo, 1969, and a marine biozone named Protocanites (González, 1981) or Fauna Malimaniana (González, 1993) was defined and regarded as Tournaisian in age. Later, Sabattini et al . (2001) proposed a new bioestratigraphic zone: Protocanites scalabrinii-Paurohynchia chavelensis , suggesting an Early Carboniferous age for the unit. Recently, Rodríguez Amenabar et al . (2003) recognized Devonian reworked specimens in the palynological assemblages from the basal conglomerates of the Malimán Formation.
The Cortaderas Formation is 1160 m thick in its type locality, and unconformably overlies the Malimán Formation. This unit was originally regarded as Late Carboniferous-Permian by Scalabrini Ortiz (1970, 1973), and was assigned to the Early Carboniferous on the basis of palynological data by Limarino and Césari (1992). According to these authors, its sedimentation occurred mainly during the Early Carboniferous, but they also suggested that its upper levels most probably could reach the Late Carboniferous. Carrizo (1990) reported the Late Carboniferous NBG Biozone at the top of this Formation, while Césari and Limarino (1993) described palynological associations including continental and marine species from the lower and middle sections of this unit.
The aim of the present paper is to describe, illustrate and revise some trilete spore species that are characteristic components of the Malimán and the Cortaderas Formations. All species described here, with exception of D. corrugata (restricted to Cortaderas Fm.) appear in all the sequence. At present it is assumed that these species are authochthonous.