Palynology of the Las Curtiembres Formation (Upper Cretaceous), Salta Group basin, Argentina

NARVÁEZ, P.L; SABINO, I.F.; DAMIANI, S.

Mendoza

Congreso; Gondwana 12; 2005

Centro de Investigaciones Geológicas-CONICET-UNLP

The first palynologic record given for the Las Curtiembres Formation (Salta Group basin, Pirgua Subgroup) in this contribution, provides a better understanding of the paleoenvironmental conditions at the final stage of Gondwana in northwestern Argentina. The first palynologic record is given for the Las Curtiembres Formation (Pirgua Subgroup). The material was collected from the type area of the Morales Member (Salfity and Marquillas, 1994; nom. subst. Sabino, 2004) near the Morales bridge in the Las Conchas creek (Alemanía depocenter of the Salta Group basin). The Morales Member which is known for its fossil pipid frogs that appear together with bad preserved plant remains (Reig, 1959) and clupeiform fish (Báez, 1981), is in the upper section of the Las Curtiembres Formation. Its deposits were accumulated during the climax of the synrift stage of the Salta Group basin and are contemporary with the effusions of the Las Conchas Basalt, dated 77±5 Ma (K/Ar; Valencio et al. 1976). The Morales Member is a lacustrine deposit of the second flooding event of the Salta Group basin (Sabino, 2004; Marquillas et al., 2005). It is composed of micritic limestones intercalated with green to brown-reddish pelites and whitish sandstones, sometimes with some levels of chert and volcaniclastic deposits (Sabino, 2004). The palynologic assemblage is characterized by a prevalence of species that belong to the Ephedrales: Ephedripites spp., Gnetaceaepollenites spp. and Singhia sp. The other gymnospermous species found in the Las Curtiembres Formation are: Araucariacites sp., Cycadopites sp. and Classopollis sp. The angiospermous pollen is represented by Ailanthipites sp., Liliacidites variegatus, Peninsulapollis gilli, Rousea patagonica, Striatopollis sp. and Tricolpites reticulatus. The pteridophyte spores are poorly represented by Deltoidospora minor and Gemmatriletes sp., and a unique fungal spore was found (Diporisporites oblongatus). The abundance and diversity of Ephedrales would indicate semiarid conditions and a warm-dry paleoclimate at the moment of deposition. Peninsulapollis gilli is a chronostratigraphic indicator of a Campanian-Maastrichtian age (Baldoni and Askin, 1993; Papú, 2002).