Caracterização do evento climático MTPE (Máximo Termal do Paleoceno-Eoceno) nas Bacias de Mucuri e Espírito Santo à margem leste brasileira e sua possível relação com o magmatismo de Abrolhos

Abstract

This work related the global warming event that occurred roughly 56 million years ago (PETM – Paleocene–Eocene Thermal Maximum) with the magmatism in the Abrolhos volcanic complex (AVC). For that purpose, seismic and magnetometric techniques, well and isotopic geochemical data have been used. In the northeast part of the basin circular structures were identified and interpreted as the laccolith of the AVC. An interpretation of other circulars structures, such as salt dome, hydrothermal vents complexes, and forced fold was carried out. The salt dome occurs in the central part of the area, and it is characterized by its magnificence. It is about ~3 km long. The formation of the salt dome was associated with an igneous activity because of the presence of the intrusive rocks into the salt layer and in the base; or because of the forces of buoyancy, caused by the weight of the igneous rocks. By utilizing indirect dating, based on stratigraphic relationships, more specifically in filling in onlap, it was possible to assume a Neogene period for the end of the action of the dome structure. This assumption indicates that the AVC activity may have occurred at much more recent ages than those already described. According to the stratigraphic relations and lithological data, the hydrothermal vents complexes were formed from the process of degassing due to the intrusion of igneous rocks in shales rich in organic matter. The hydrothermal activity occurred in the PETM interval. Using the δ13CTOC, associated with biostratigraphy, the CIE anomaly was identified, which marks the passage of the Paleocene / Eocene. The geochemical dates indicated that there was a release of the 0.09 x 1018g (or 0.09 Eg or 0.09 Tt) of the methane into the atmosphere due to igneous intrusions in the study area. By means of the isotopic mass balance, the value of the 3.4 x 1018g was obtained and it was necessary for the -2.9 ‰ anomaly to form, which was recorded in well 1-BRSA-819A-ESS. Although the calculated value of methane released is lower than what it would be necessary for the formation of the CIE anomaly, the area studied is much smaller than the entire CVA coverage area. Therefore, there is a possibility that the amount of methane exhaled was approximately 300 times greater. That is a considerable amount that may have contributed, together with the other North Atlantic basins, to the release of greenhouse gas into the atmosphere and the formation of the hyperthermal event PETM.