PALYNOLOGY OF THE CAMBRO-ORDOVICIAN TRANSITION AT QUEBRADA DE MOYA, EASTERN CORDILLERA, ARGENTINA. This contribution documents the presence of acritarchs and related forms in the Casa Colorada and Alfarcito formations cropping out at the Quebrada de Moya in the Quebrada de Humahuaca, Jujuy province, Northwest Argentina. The taxonomic composition and the biostratigraphic distribution of taxa allows to define three palynological assemblages. The first is located in the lower part of the Casa Colorada Formation and records a restricted diversity with poor preservation. However, it contains simple spheromorphs (Leiosphaeridia, Lophosphaeridium, Saharidia), indicating a shallow-marine conditions, coincident with the sedimentological characterization of strata. The following assemblage was recovered from the middle section of the Casa Colorada Formation and includes a more diversified microflora with Vulcanisphaera africana, Cristallinium cambriense, Cymatiogalea velifera, among others, that have been assigned with the early mentioned assemblage to the Upper Cambrian. The third assemblage was located in the upper sector of the Casa Colorada Formation and the Alfarcito Formation, and comprises several species, among which Buedingiisphaeridium tremadocum, Cymatiogalea membranispina, Polygonium symbolum are indicative of a Tremadocian age. Palynological data suggests an Upper Cambrian age for the two lower associations (lower and middle sector of the Casa Colorada Formation), and an Early Ordovician age for the upper association (uppermost sector of the Casa Colorada and Alfarcito formations), in concordance with other shelly fauna mentioned for the units. The position of the boundary between the Cambrian and Ordovician System in the Quebrada de Moya is inferred in the uppermost part of the Casa Colorada Formation.