No abstract

In oshore Brunei, the Baram delta displays Pliocene to recent gravitational deformations on top of the overpressured Setap Shales. We use the limit analysis, implemented in SLAMTec, to constrain their kinematics and propose rst-order values of compatible pore pressures. Using the critical Coulomb wedge theory, we conrm that extreme overpressure are needed to account for the gravitational deformations currently observed in the delta. SLAMTec simulations quantify the role of the migration of the deltaic system on the deformations and suggest that this overpressure has existed since the initiation of the gravity-driven system. An inverse analysis is performed to identify the uid overpressure and sedimentation pattern that best reproduces the forward structural model. This inverse approach validates the proposed kinematics, since we can reproduce quantities describing the structural style with overpressure coherent with the present-day observations. It points out the existence of key events explaining the structural interpretations, which leads to propose new kinematic models enriched with compatible pore pressure and sedimentation rates. This mechanical study highlights how mechanical modelling helps design a cross-section with an appropriate kinematics based on mechanical solutions and discuss on the basis of objective mechanical criteria the ranges of pore pressure consistent with a prescribed structural evolution.

Using the geologist’s interpretation of 6 published balanced cross-sections in the fold and thrust belts of the northwestern Mediterranean, a comparative analysis of the interpreted subsurface structural architecture is used to address the links between the structural style and the mechanics of fold and thrust emplacement. For each cross-section example, the geo-dataset and the methods used by the interpreters are different in quantity and quality. Here we have examined how useful is the content of information of each cross-section to constrain the structural evolution scenario. Each interpretation is examined according to considerations of the mechanics of sedimentary basin deformation and how uncertain is the extrapolation of fault trajectory at depth. It is shown that each case reveals a particular type of structural style: thin-skin or thick skin tectonics, fault-related folding, pre-existing fault pattern. The present structural analysis is used to determine for each cross-section the nature of the mechanical problem to address that will reduce uncertainty on the geologic scenario reconstruction. The proposed mechanical boundary conditions could serve to develop analog or numerical models that aim at testing the mechanical validity of the structural scenario of fold and thrust emplacement.