La cuenca neoproterozoica-eocámbrica en el NOA: sedimentología y ambientes de depósito de secuencias con icnofósiles, nuevas perspectivas.

VANINA LÓPEZ DE AZAREVICH; FLORENCIA G. ACEÑOLAZA; GUILLERMO F. ACEÑOLAZA,; RICARDO H. OMARINI; MIGUEL AZAREVICH

Relatorio XIII Reunión Argentina de Sedimentología

SCS Publisher

Lugar: Salta; Año: 2012; p. 119 - 132

In NW Argentina, the Neoproterozoic-Eocambrian sequences that include an important ichnofossil record arefilites, shales, quartzites and grauvackesof the Puncoviscana Formations.l., deposited in a shallow marine basinwithtidal flats and foreshore to distal platforms (less than 200 meters-deep). Primary sedimentary structures such aslinguoid, interference and double crested ripples, hummocky cross stratification, flasser and ondulitic stratification,rill marks, exposed surfaces, tidal rhythmites, as well as photic zone related microbial mats and algae activity, confirman inter- to sub-tidal deposition influenced by tides, waves and storms. At the moment, no turbidite sequences werefound in the studied localities of Rancagua, Palermo Oeste, Km 13, Bárcena, Purmamarca, Tilcara, Quebrada delToro, Muñano, Tastil, San Antonio de los Cobres. They contain Nereites and Oldhamia ichnoassociations thatsuggest an Upper Ediacara to Early Cambrian (Terraneuvian - Series 2?) age of deposition. Earliest depositional ageis also confirmed by U/Pb zircon age obtained from magmatic rocks that intrude or interlayered the sedimentarysequence (563 to 517 Ma).Analyses of astronomic periods obtained from tidal rhythmites allowed to adjust, fromanother point of view, the relation between astronomic, sedimentary and biologic processes occurred at global scalein the temporal range of deposition (Neoproterozoic-Eocambrian). It implies that an important decrement in theMoon retreat during the Neoproterozoic-Cambrian transition influenced in more stable and lowertides and benignconditions for the Cambrian Explotion. Geotectonic interpretations of the Puncoviscana basin developed at thepresent are based on petrologic, geochemical and geochronological data, but lack of the appropriate sedimentologicalcontext that allow an adjust evaluation the geodynamic configuration from the initial rifting occurred during Rodiniafragmentation.