Kinematic Evolution of Layered Aptian Salt in the Northern Santos Basin: Insights from 3D Seismic Data

Salt tectonics is a three-dimensional and time-dependent process strongly influenced by intra-salt heterogeneity and base-salt relief. This study investigates the geometry, internal deformation, and kinematic evolution of layered Aptian salt structures and associated minibasins in the northern Santos Basin, offshore Brazil, using a ca. 3,700 km² post-stack depth-migrated (PSDM) 3D seismic dataset (Franco–Iara survey). Seismostratigraphic analysis enabled the identification of five key seismic surfaces and four chronostratigraphic units within the salt and post-salt succession. Top- and base-salt horizons were mapped across the entire area, while intra-salt reflectors were interpreted in cross-sections to characterize internal deformation, including folds, faults, and shear zones. Salt bodies were classified in terms of their external geometry, maturity, and kinematics based on plan-view and cross-sectional morphology, top-salt concordance, and autochthonous versus allochthonous character. The Aptian layered salt displays strong thickness variations, ranging from ~120 m underneath minibasins to >3.4 km within diapirs. Salt structures include walls, stocks, and anticlines, commonly affected by intra-salt shear-zones and/or faults, and exhibit a basinward decrease in diapir maturity. The Northern Domain of the studied area is dominated by E–W-oriented discordant structures (salt walls and stocks) with E-W upright intra-salt folds and thrusts in their upper most heterogeneous portion that indicate salt transport from north to south. The Northern Domain also displays salt welds, eroded culminations, and features indicative of extensional diapir collapse (e.g., mock-turtle anticlines). In contrast, the Southern Domain is dominated by concordant salt structures, N–S-trending salt anticlines with intra-salt asymmetric fold-and-thrust systems indicating transport from west to east. Base-salt mapping reveals a non-planar surface with dip angles up to ~30°, defining structural highs and lows that exert a first-order control on minibasin localization and salt migration pathways. The spatial correlation between base-salt relief, salt structures, and minibasin architecture supports a conceptual model for the evolution of salt tectonics in the area. Spatiotemporal variations in salt deformation reflect changes in sedimentary loading and transport directions during the Albian–Maastrichtian, followed by waning salt tectonic activity in the Cenozoic. These results highlight the strong coupling between layered salt rheology, base-salt relief, and minibasin evolution, providing new 3D insights into salt tectonic processes in passive margin basins. Understanding salt tectonics in heterogenous settings is critical not only for the oil and gas industry, where salt provides an effective regional seal, but also for emerging energy-transition applications, including subsurface carbon capture and storage.