Early Cretaceous Volcanism and Its Control on Tectonic Framework in the Santos Basin, Offshore Brazil

The Santos Basin is a globally hydrocarbon exploration hotspot. In the past decade, a large number of major discoveries have been made in pre-salt plays in ultra-deepwater areas of the Santos Basin. The current drilling and seismic data in the Santos Basin record at least five stages of magmatic activity, forming two types of basic igneous rocks, namely, flooding facies basalt and intrusive facies diabase. Three periods of magmatic eruption activities during the early Cretaceous were recorded in the pre-salt lacustrine strata. According to the spatial development characteristics of volcanic rocks, two types of volcanic edifices can be identified, namely, fissure-type and central-type. Among them, fissure-type volcanic edifices are distributed along faults with a wide range of distribution, which are the main types of volcanic edifices in the basin. While the central-type volcanic edifices are characterized by small-scale volcanic conduit facies. According to the depositional environment, it can be further divided into subaqueous effusive facies (the second stage of igneous rocks, such as the basalt developed in the same period of the deposition of the Itapema Formation in the northeast oil field of the East High), subaerial effusive facies (the third stage of basalt during the period of deposition of the Barra Velha Formation of the third stage in the southwest basin, which is mainly formed in the Central High inside the Central Sag) and transitional effusive facies. According to the integrated interpretation of gravity, magnetic and seismic data, it is pointed out that strike-slip faults and extensional faults control the spatial distribution of pre-salt igneous rocks in the Santos Basin, while the large-scale volcanic edifices control the tectonic framework of the basin. The volcanic rocks developed on a large scale in the first and third stages have significant constructive effects on the paleogeomorphology of carbonate build-up at the end of the rift stage and sag stage, and ultimately control the distribution of favorable reservoir facies belts of lacustrine carbonate rocks.