Ediacaran in Uruguay: Facts and controversies

摘要

The Ediacaran of Uruguay has been regarded as containing a significant geological and paleontological record, which would make these successions critical to unraveling diverse aspects regarding the assembly of southwestern Gondwana and to understanding the conditions surrounding the rise of animal life in a period punctuated by drastic paleoenvironmental changes. However, a review of currently available data leads to the conclusion that, although variable, the stratigraphy, distribution and age of these units remain ambiguous. The same is true for existing basin models and tectonic evolution, which show different and sometimes contradicting supporting evidence. Here, we propose that the Ediacaran record consists of the Maldonado Group (Playa Hermosa, Las Ventanas and San Carlos formations), and the Tacuari, Barriga Negra, Rocha and Sierra de Aguirre formations. The Arroyo del Soldado Group (Yerbal, Polanco Limestones and Cerro Espuelitas formations) and the Arroyo de la Pedrera Group (Piedras de Afilar and Cerro Victoria formations) were likely deposited between 700 and 1000 Ma. The best available radiometric age constraints indicate intense magmatic-tectonic activity occurred between 600 and 560 Ma, incompatible with previous models suggesting a stable, Atlantic-type passive margin on this portion of southwestern Gondwana. Further research is needed in order to firmly establish a consistent litho- and chronostratigraphic framework; particularly, before attempting any regional or global correlation, and inferences on global paleoenvironmental and paleobiological events.