Salt Tectonics Controlling Sedimentation in Deepwater Settings: An Example from Santos Basin, Southeast Brazil

Alexandre S. Castro and Michael Holz
UFRGS - Rio Grande do Sul University and PETROBRAS - Petroleo Brasileiro S.A, Porto Alegre, Brazil

Salt tectonics has been recognized as an important control to the petroleum system in many active petroleum provinces worldwide, such as the Gulf of Mexico and South Atlantic marginal basins. It is responsible not only for the creation of structural closures, but also for modifying the thermal profiles, creating fluid pathways and acting as seal to hydrocarbons in a variety of structural and stratigraphic situations.

The Santos sedimentary basin is located at southeastern Brazilian passive margin. In this sedimentary basin thick evaporitic deposits of Early Cretaceous age deformed to create impressive structures such as pillows, diapirs and walls on the slope and deep-water depositional settings. These structures created preferential areas of sedimentation which act as depositional barriers or pathways in different periods of basin evolution.

We interpreted several 2D seismic profiles using integrated structural and stratigraphic approaches to understand the timing of salt migration and the sedimentary filling in this area.

The seismic stratigraphic method was used to define the key surfaces and reflection terminations which define several deep-water depositional sequences that can be mapped throughout the deformed and the undeformed regions of the basin. The external and internal characteristics of these sequences reflect the different moments of salt evolution in the studied area.

The fault patterns were also mapped and correlated to identify periods of structural instability of the slope deposits due to the growth of salt structures.

The use of this integrated approach allowed the identification of the main pulses of sediment input and salt movement. This kind of information is vital to define the best prospects of salt-controlled minibasins.