Origin and sedimentary evolution of SW Gondwana mega-lakes

Abstract

During the late Permian, a large part of the southwest of the supercontinent Gondwana was covered by a mega-lake formed by the entrapment of the epicontinental sea existing since the Ordovician. The subduction of the oceanic plate and the collision of the Patagonian micro-continent against Gondwana, led to the closure of the connection between the Paraná Basin and Panthalassa, modifying ocean circulation patterns and the climate of this part of the planet. Synchronously with these events, the deposition of the mixed succession (siliciclastic-carbonate) of the Passa Dois Group (Brazil) and the Mangrullo, Paso Aguiar, Yaguarí (Uruguay), Huab and Gai-As formations (Namibia) occurred. To date, it is unknown whether the Permian units of the Paraná and Huab basins recorded the passage of the Paleozoic and Mesozoic eras, but the isolation of the basins, the high degree of endemism of the populations and the recurrent ecologically stressful conditions of the body of water possibly made the biggest mass extinction event has left very particular traces in the sedimentary and paleontological record of this mega-lake, given that lake environments are considered excellent holders of physical, chemical and biological indicators of climate change. Thus, the existence of a continental-scale lake in the interior of Gondwana represents an excellent opportunity to explore and better understand the climatic, geochemical and bioevolutionary consequences of the largest mass extinction event of the Phanerozoic in systems developed in continental environments. However, the heterogeneity of information in the South American and African successions, the scarcity of stratigraphic correlations on a basin scale, and the limitation in geochronological, paleoclimatic and paleogeographical data, make it impossible to precisely define the climatic, tectonic and eustatic conditions that acted during the generation of the Permian mega-lake. Given this scenario, this project intends to carry out a detailed multi-proxy analysis of the deposits of the Serra Alta, Corumbataí, Teresina (Paraná Basin, Brazil), and Gai-As (Huab Basin, Namibia) formations, seeking to understand the origin and evolution of the continental-scale lacustrine system, the autogenic and allogenic controls on sedimentation, as well as the paleogeographic and paleoclimatic reconstruction of the interior of Gondwana. By using established investigative techniques, this research aims to contribute to the understanding of little-known depositional systems (i.e., mega-lakes), also seeking to adjust the chronostratigraphic relationships of the Permian units on a continental scale. In an innovative way, the application of unusual analytical techniques in the deep geological record, such as the magnetic and geochemical susceptibility of major and trace elements as paleoenvironmental proxies in siliciclastic rocks, will seek to track the climatic and environmental changes that preceded or acted during the ecological crisis from the end of the Permian period.