Stratigraphy and Eruption Styles of Cretaceous Volcanism in the Santos Basin (Brazil): Preliminary Insights

Petrographic analyses of forty-five volcanic rock samples from seven wells in the Santos Basin were conducted to investigate lithofacies distribution, eruptive styles, and petroleum system implications from the Aptian Barra Velha Formation to the Turonian– Maastrichtian Itajaí-Açu Formation. Six lithofacies were identified, including coherent basaltic lava flows, autobreccias, peperites, and lithic, vitric, and crystal tuffs. Lava flows composed mainly of plagioclase and augite (± olivine), commonly displaying amygdales and secondary alteration to chlorite, zeolites, calcite, and palagonite, dominate the early pre-breakup intervals. Younger post-breakup units are characterized by abundant volcaniclastic deposits and intense palagonitisation. Integrated petrographic and stratigraphic data indicate a temporal transition from predominantly subaerial Hawaiian and Transitional volcanism during the rift and post-rift stages to subaqueous Surtseyanstyle hydromagmatic activity during the drift phase, strongly influencing reservoir heterogeneity, porosity evolution, and seal development within the basin.