Séminaire de Fabricio Caxito

Résumé :

The influence of mountain ranges on the climate, oxygenation and cycle of elements such as carbon and phosphorus on the planet is a subject of much debate in the current scientific literature. The weathering of high relief areas consumes CO₂, one of the main greenhouse gases, modulating the planet’s climate, and the erosion and transport of large quantities of sediments can cause the burial of organic carbon, generating an excess of O₂ that does not react back to form carbon dioxide, thus indirectly causing the oxygenation of the oceans and atmosphere. In addition, the erosion of mountain ranges can supply important nutrients, such as phosphorus, to adjacent basins, promoting changes in biogeochemical cycles and trophic chains. Using several proxies for the redox and nutrient conditions of the ancient basins of the paleocontinent Gondwana preserved in South America, it is possible to detect moments in which these variations were both beneficial and deleterious to the ecosystems. During the amalgamation of the paleocontinent in the Brasiliano Orogeny (630-500 Ma), for example, the Corumbá Basin, which was located on its edge, experienced an influx of oxygen coinciding with the building of the mountain range and the emergence of organisms that demonstrate high motility on the ocean floor as demonstrated by trace fossils, indicating advanced aerobic metabolism. In the interior of the continent, however, the observed effect is the opposite, with the Bambuí Basin, of similar age, becoming surrounded by mountain ranges that allowed an enormous influx of nutrients and possibly caused a eutrophication effect, culminating in toxic conditions for the complex life forms of the Ediacaran/Cambrian transition. In the Phanerozoic, a similar effect that led to anoxic conditions in the Irati-Withehill Sea during the Permian (ca. 277 Ma) can be detected through several proxies, such as iron speciation, carbon and nitrogen isotopes. The examples of the basins of the paleocontinent Gondwana demonstrate the complexity of interactions between the different terrestrial spheres and the importance of their study together for understanding the linked evolution of life and the Earth over geological time.