CONICET | Buscador de Institutos y Recursos Humanos

The Sierra de Zenta (Eastern Range of Salta and Jujuy) displays a remarkable sequence of Ordovician strata dominated by sandstones (calcareous levels and shell beds are rare), displaying an important fossiliferous association. The presence of palynomorphs, trilobites, graptolites, conodonts, brachiopods, ostracods, nautiloids and trace fossils contributes to a better understanding of the biostratigraphy of a large area in NW of Argentina. This contribution particularly focuses the central sector of Zenta Range, between Abra Llana and Abra Buey Ojo, where we have recognized a thick sandy sequence of sandstones deposited on a relative shallow shoreface setting (Lower shoreface / transition / Upper shoreface). Among the recognized acritarchs we mention: Acanthodiacrodium crassus, Coryphidium bohemicum, Cristalliniun dentatum, C. miladae-tadla, Cymatiogalea granulata, C. messaoudensis var. messaoudensis, Dactylofusa velifera, Eisenackidium orientalis, Ericanthea pollicipes, Eupoikilofusa striatogranulata, Ferromia pelita, Leiofusa tumida, Picostella turgida, Polygonium gracile, Stellechinatum uncinatum, Stelliferidium stelligerum, Vavrdovella areniga, chitinozoans: Eremochitina sp. and Euconochitina sp., prasinophytes: Cymatiosphaera sp., Leiosphaeridia sp., Pterospermella sp. and few unrecognizable criptospores. The sequence displays a coarsening upward grain and strata arrangement, with increasing bioturbation and the presence of sporadic shell beds. Graptolites (assigned to Baltograptus sp., Didymograptus sp., Expansograptus sp. and Tetragraptus sp.) and the trilobite Thysanopyge were recognized as well, associated to the early mentioned levels. The fossiliferous association suggests a Floian age for the sequence, which allows a correlation to those strata cropping out in the middle part of the Abra de Zenta, Los Colorados (Jujuy) and Pascha ? Incamayo (Salta) localities