How post-salt sedimentation rates control the thermal evolution of salt-bearing margins: The interplay between thermal blanketing and salt effects

Salt rich margins are characterised by complex structural and thermal regimes due to the high thermal conductivity of evaporites (~6.5 Wm^-1K^-1) and their interaction with the insulating sedimentary cover (~2.0 Wm^-1K^-1). Observational evidence and well data demonstrate the existence of thermal anomalies in proximity to salt structures in salt-bearing basins. Furthermore, these rocks exhibit extremely low viscosity and an absence of shear strength, thus allowing for the occurrence of highly non-linear salt tectonics, otherwise referred to as halokinesis. While the structural mechanics of halokinesis are well-documented, the dynamic feedback between sedimentation rates, salt geometry, and the basin's thermal evolution remains under-explored in geodynamic models.

In this work, we investigate this interplay using a 2D thermo-mechanical numerical code (Mandyoc). A rifted margin was modelled under three post-salt sedimentation rates, with realistic salt thermal properties being compared against control scenarios where salt is thermally equivalent to the crust. Our models replicate the expected behaviour of the salt tectonics, with depocentre migration, diapirism, nappes and welds. The structures in the sediments are marked by extension in the proximal domain, and compression in the distal domain. The results obtained demonstrate that the thermal field is strongly affected by the sedimentation rate, since it is the primary cause of halokinesis. 

In low sedimentation regimes, the effect of the salt high conductivity dominates. Diapirism and allochthonous nappes efficiently conduct heat to the surface, cooling the sub-salt section and depressing isotherms, potentially retarding source rock maturation. In the moderate sedimentation rate scenario, the salt movement creates more complex structures and the isotherms are modified depending on the structure thickness and range. In a high-sedimentation regime, the rapid progradation suppresses vertical salt tectonics and creates a thick, low-conductivity clastic wedge. In this instance, the sedimentary blanketing effect is more significant than the salt cooling effect, which results in heat trapping and accelerated thermal maturation in the pre-salt layers.

Our findings point that the salt layer acts not only as a structural seal or a detachment layer but as a dynamic thermal modulator. The effectiveness of the salt as a "radiator" is strictly controlled by the competition between the halokinesis and progradation rate. Disregarding this coupling in basin modelling may lead to significant misinterpretations of the oil maturation window and the thermomechanical evolution of the distal margin.

This work has been by Petrobras Project 2022/00157-6 and has been financially supported by the Human Resources Program of the Brazilian National Agency for Petroleum, Natural Gas, and Biofuels – PRH/ANP43 (2025/21407-9). We also would like to express our fully gratitude to Leonardo M. Pichel and the Bergen Research Group because of its extensive collaboration with us.