Abstract
The Puncoviscana Formation (s.l.) comprises a few thousand meters of mainly low-grade metamorphosed sedimentary rocks. These are dominated by mudstones, slates, and sandstones cropping out extensively in the Eastern Cordillera of NW Argentina. The formation is known by its ichnofossils, that include a variety of ichnotaxa such as Asaphoidichnus, Cochlichnus, Didymaulichnus, Dimorphichnus, Diplichnites, Glockerichnus, Helminthoidichnites, Helminthopsis, Monomorphichnus, Nereites, Oldhamia, Planolites, Protichnites, Protopaleodictyon, Protovirgularia and Treptichnus, among the most remarkable ones. The record of recurrent wrinkle structures and palimpsest ripples suggest the presence of microbial matgrounds and biofilms in different localities of NW Argentina. These have been regarded in the literature as important elements of paleoenvironments during the Vendian-Tommotian transition. Three associations have been recognized within the unit. These are the Beltanelliformis, Nereites and Oldhamia, associations, characterized by a distinct spatial distribution. They appear in NW Argentina as elongated bands (NE-SW general direction), representing different temporal steps in the Precambrian-Cambrian transition of the region. We describe an ichnoassociation represented by Helminthopsis isp., Treptichnus cf. aequalternus Schlirf, Monomorphichnus isp., comparable to an enigmatic “annelid tube” regarded as Sphenotallus? sp., and several undifferentiated microbial structures for one locality of “ Beltanelliformis association” at La Higuera outcrops (Province of Tucumán). The early-referred association is included in highly folded heterolithic facies, characterized by a alternate succession of greenish-grayish fine/mid sandstones and slates. All new data on the biostratigraphy of the Precambrian-Cambrian transition in NW Argentina, contribute to a better understanding of sequences, and to the evolution of the Early Paleozoic basins of the South American margin.
Published Version
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