Stromatolitic and Trace Fossils Community of the Cerro Victoria Formation, Arroyo del Soldado Group (Lowermost Cambrian, Uruguay)

The Cerro Victoria Formation of the Arroyo del Soldado Group (Uruguay) comprises 400 m of mainly stromatolitic, micritic and oolitic limestones. In this low-diversity stromatolite paleocommunity, moundlike and planar laminites dominate, but columnar forms, ooids and pisoids occur as well. Stromatolites played a major role in the construction of the carbonate ramp, which developed onto a passive (eastern) margin of the Río de la Plata Craton. A paleobiological reconstruction of the stomatolite community, which includes subtidal, intertidal and supratidal environments, is presented. A low-diversity trace fossil association, dessignated as “Thalassinoides-Gyrolithes-Palaeophycus” assemblage, is preserved in syngenetic concretions. The stromatolite community, ichnofossil assemblage and ichnofabrics are typical for the lowermost Cambrian, corroborating earlier age estimations. The unit represents a shallowing-upward sequence deposited under predominantly subtidal, normal marine, high energy conditions. Tropical climate prevailed, as shown by thick carbonate deposits, evaporitic minerals (halite, gypsum) and abundance of ooids. The Cambrian of western Gondwana is characterized by scarcity of carbonate ramps. This was mainly determined by high siliciclastic input related to erosion of the Pan African-Rio Doce orogenic belts. Carbonate ramps developed in blocks located at tropical paleolatitudes and characterized by low clastic input, such as the Nico Pérez Terrane and Argentine Precordillera.