Hybrid compactive faults formed during burial in micritic limestone (Montpellier area, France)

Detailed fieldwork, analyses including SEM and EBSD investigations, and dynamic inversion method are used to describe and propose a conceptual model for the formation of compactive faults related to burial in micritic lacustrine-palustrine limestones (Eocene, Pyrenean foreland basin, South of France). These faults are characterized by sinuous shape, no calcite precipitation and no macroscopic fault core evidencing their development in poorly consolidated sediments. The fault pattern is composed of two sub-synchronous systems of conjugate meter-scale faults (a normal-sense system and a strike-slip system), each one with high dihedral angle (130°) and sometimes showing continuity between faults of both sets. Their pervasive distribution, angle relative to the maximum principal stress direction, incipient shear-offset, porosity reduction, their crystallographic preferred orientation, and the “ridge and groove” morphology of their slickenside, all argue for a hybrid compactive and shear deformation process combining disaggregation, comminution, and pressure-solution-recrystallization processes. A conceptual model using estimated stress path and theoretical yield envelope is proposed to explain their formation along the end cap part during early burial and compaction of the limestone beds. The slope to the South associated to the syn-sedimentary basin flexure is proposed to trigger their specific pattern.