Palynological assemblages present in Los Monos (Devonian) and Itacua (Early Carboniferous) formations at Balapuca (Tarija basin), southern Bolivia. Part 2. Itacua Formation assemblages and stratigraphical interpretation and chronology of the Los Monos and

Abstract

The palynological result of three fertile samples of the Itacua Formation is presented. This unit crops out at Balapuca located in the Bolivian margin of the Bermejo river, in the mountain range of San Telmo. The stratigraphic extension of the species determined in this association allowed the identification of two sets of palynomorphs, one indigenous, composed of 61 species of spores and few colonies of Botryococcus, and another set of reworked species, composed by spores, acritarchs, prasinophytes, chloroficean algae, cryptospores and chitinozoans, mostly coming from the Devonian layers and subordinated spores of the Tournaisian (Carboniferous) ones. Two indigenous spore species are proposed as new Palinoestratigrafía de la Formación Itacua, Bolivia. Parte 2 combinations. The stratigraphical distribution of indigenous key species allowed assigning this association to the early Visean (Early Carboniferous). This is the first work where indigenous palynomorphs of this age are illustrated along with a selection of reworked species, and are obtained of an in situ deposit of the Itacua Formation cropping out in the southern Tarija Basin. Based on the age attributed to the Los Monos and Itacua formations in this study, a hiatus is defined between them, characterized by an erosive phase during the Frasnian-Tournaisian and, another non-depositional hiatus identified in the latest Famennian ('Strunian'). This is interpreted from the presence/absence of reworked species with restricted stratigraphical range in the Itacua Formation assemblage. On the other hand, the Machareti Group overlies this unit, and it was dated as early Late Carboniferous based on palynology. Between both units, a new hiatus that spans the late Visean-Serpukhovian partly interpreted as non-depositional is registered. In addition, a discussion about a possible tectonic and glacioeustatic origen for both hiatus is included.