Macrocystella? durandi sp. nov. (Echinodermata, Rhombifera) y el registro del género Macrocystella en la cuenca cambro-ordovícica del norte argentino

The new species Macrocystella? durandi n. sp. is characterized for the Tremadoc of Northern Argentina, and six new localities bearing the genus Macrocystella CALLAWAY within the A rgentine Cordillera Oriental are introduced. The fossiliferous material comes from shale and sandstone levels of the Casa Colorada, Alfarcito, Rupasca and Saladillo Formations (Santa Victoria Group), that crop out in different localities of the Quebrada de Humahuaca (Jujuy Province), and the Angosto de la Quesera (Salta Province). The biostratigraphic framework of the fossils is also given, showing the oldest record of Macrocystella CALLAWAY in the Upper Cambrian of the Casa Colorada Fo rmation at the locality of Pintayoc, north of Humahuaca town (Jujuy Province). A discussion on the taxonomy of the genus is given, analysing the information published until now within the Argentine-Bolivian cambro-ordovician basin. Macrocystella? durandi n. sp. differs from the rest of the species of Macrocystella? by its delicate ornamentation on the thecal plates, with fine and numerous folds, as well as by the possible pectinirrombs developed on some fields between the main (axial and radial) folds

Regional implications of U-Pb zircon ages from rhyolitic pebbles of Suncho Formation conglomerates, northern Sierras Pampeanas (NW Argentina)

Conglomerates are scarce in the Neoproterozoic/Cambrian strata of the South American Central Andean Basin. In NW Argentina, unusual conglomerates within meta-psammites of the Suncho Formation contain rhyolite clasts that yielded 524.9 ± 1.12 Ma and 525.1 ± 1.3 Ma LA-ICP-MS U-Pb zircon ages. These ages coincide with the reported youngest age populations obtained from detrital zircons in the host rocks. The new geochronological data, the regional geology and published data suggest that the source areas of these pebbles were located to the NE and E of the Suncho Formation, which may include some reworked older sedimentary levels of the Puncoviscana Formation. The origin of the Suncho conglomerate is linked to Pre-Tilcaric magmatism which closed the Pampean Cycle, whose ages are in the range 541-517 Ma. The match between the radiometric data and the age provided by the Oldhamia trace fossils with both sedimentary and magmatic events occurring during the Terreneuvian - Series 2 time span ("lower Cambrian") is here emphasized. Considering that the dated rhyolite clasts were derived from magmatic rocks, a Puncoviscana active margin can be proposed as their source, and an active margin setting is proposed for Puncoviscana in this part of the western margin of South America. The knowledge of unusual facies within the Neoproterozoic/Cambrian sequences in the South American Andes provides a better understanding of the geology of little known areas in the western protogondwanan margin. © 2015 E. Schweizerbart'sche Verlagsbuchhandlung, Stuttgart, Germany