Application of the ADS method to predict a “hidden” basal detachment: NW Borneo fold-and-thrust belt

The NW Borneo margin is characterized by a complex deepwater fold-and-thrust belt. Despite previous studies, the definition of a univocal detachment level for folding and thrusting is still lacking. The area-depth-strain (ADS) method can be used to determine the location for a detachment in areas lacking data, and to balance geological cross sections. This study applies the ADS method to the central part of the NW Borneo fold-and-thrust belt to predict a structurally conclusive detachment level in an area lacking a seismic detachment reflection. Seismic interpretations were completed after the ADS-determination of the basal detachment, providing input for a 2D sequential restoration that delivered values on shortening distribution and shortening rate. The kinematic and mechanic analyses presented, document that the central part of the NW Borneo fold-and-thrust belt is affected by both, near- and far-field stresses, and that the far-field crustal shortening component becomes more important northward. This work demonstrates that the ADS method can be effectively applied in fold-thrust belt settings with limited information on the detachment, supports in a quantitative way the tectonic and stratigraphic interpretation of seismic-reflection data and provides a robust structural base for the restoration of balanced cross-sections, including the reconstruction of syn-kinematically eroded stratigraphy.