Banca de DEFESA: João Pedro Santos de Brito

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : João Pedro Santos de Brito
DATE: 08/12/2023
TIME: 09:00
LOCAL: Sala de videoconferência e Teams
TITLE:

U-Pb Dating of Pre-salt Carbonate Rocks: Implications for the Geological History of the Santos Basin.

KEY WORDS:

U-Pb resetting; Carbonate dating; Barra Velha Formation; Fluid-rock interaction.

PAGES: 145
BIG AREA: Ciências Exatas e da Terra
AREA: Geociências
SUBÁREA: Geologia
SUMMARY:

The Pre-salt carbonates and their unique characteristics represent a challenge for understanding depositional and diagenetic processes related to these rocks. Even the Barra Velha Formation's chronology is controversial, whether it was deposited during Barremian and Aptian times. To constrain the chronology of depositional and diagenetic processes related to the Upper Barra Velha carbonates and also to understand how the U-Pb isotopic system works in carbonates, this study presents an integrated study of conventional petrography, QEMSCAN imaging, and in situ U-Pb dating of carbonate samples from three wells (3-BRSA-923A-SPS, 9-BRSA-928-SPS, and 7-SPH-6-SPS) of the Sapinhoá field, located in the central part of the Santos Basin. Ages obtained in this study coincide with regional tectonic and thermal events that affected the Santos Basin. These events have geochronological ages of ~ 127/125 Ma, ~ 116/114 Ma, and ~ 105/100 Ma. A local influence of the geological and structural contexts of the analyzed particles was also detected, since the pattern of ages obtained in each well was different from the other. For instance, the calcite primary particles from the well 9-BRSA-928-SPS underwent U-Pb post-depositional resetting, which resulted in younger post-depositional ages of ~ 106 Ma for these particles. Instead, the calcite primary particles from the 7-SPH-6-SPS well preserved older ages of ~115 Ma. This different age behavior may be explained by different magmatic, hydrothermal, structural, or stratigraphic contexts acting on the studied wells. The dolomites, compared to calcite particles, showed that the geochronological resetting of the particles may not be a pervasive effect but may depend more on fluid-rock interaction and physical properties of the particles, such as porosity and permeability. This was observed hence the non-porous and non-permeable dolomitic aggregates were not affected by U-Pb geochronological resetting. Indeed, primary microcrystalline and fine dolomite rhombs recorded the first direct Barremian ages for the Barra Velha carbonates, providing a Barremian depositional age of the Upper Barra Velha Formation. Otherwise, microcrystalline pseudomorphic dolomites and calcite particles underwent U-Pb resetting caused probably by fluid-rock interactions and thermal effects. Concerning the dolomite ages, they were separated in pre-silicification and post-silicification dolomites. Pre-silicification dolomites occur as Barremian-Aptian microcrystalline to very fine laminated dolomite rhombs, as ~115 – 109 Ma fine rhombohedral dolomite crystals that are the product of pervasive dolomitization, and as pseudomorphic microcrystalline dolomites that underwent U-Pb resetting related to an Albian-Cenomanian silicification event. Post-silicification dolomites have ages of ~ 100 Ma and are represented by later diagenetic cements such as blocky dolomite and saddle dolomite. The saddle dolomite temporally limits a silicification event as older than 100 Ma.

COMMITTEE MEMBERS:
Externo à Instituição - CRISTIANO DE CARVALHO LANA - UFOP
Interna - 1658822 - LUCIETH CRUZ VIEIRA
Externo ao Programa - 3340609 - MARCIO VINICIUS SANTANA DANTAS - nullPresidente - 418662 - ROBERTO VENTURA SANTOS