Control of mechanical stratigraphy on the stratified style of strike-slip faults in the central Tarim Craton, NW China

Abstract

The large-scale (tens to hundreds of kilometers long) but small-displacement (<2 km) strike-slip faults in the Shunbei region of the Tarim Basin, NW China, provide an opportunity to document the role of mechanical stratigraphy in an intracratonic strike-slip situation. Uniaxial compression test results and dipole acoustic logging data illustrate that the lower Paleozoic mechanical profile in the Shunbei region consists of 2 incompetent layers (middle Cambrian and Upper Ordovician) and 3 competent layers (Sinian–lower Cambrian, upper Cambrian–Middle Ordovician, and Silurian). Borehole and high-resolution 3D seismic data illustrate that the 3 competent layers are characterized by low-amplitude folds and isolated brittle faults. The discrete element method (DEM) modeling results indicate that mechanical stratigraphy is an important factor controlling the soft-linked faulting style that is independent of multiphase deformation. A pre-existing structure promotes the formation of narrow and localized fault zones. The early–middle Silurian evolution of the Shunbei No. 1 fault zone reflects a classic stratigraphically decoupled deformation model: the middle fault arrays (upper Cambrian–Middle Ordovician layers) and en echelon normal faults (Silurian layer) synchronously experienced left-lateral slip. These two styles of faulting have different geometries (fault dips, slips, and arrangements) but are kinematically coupled and genetically related. This proposed deformation model provides mechanical support to document deeply buried structures by characterizing genetically related shallow structures, which may be widely employed as multiphase inheritance structures with mechanical stratigraphy. We also point out that vertical fault connectivity is a key research aspect of hydrocarbon exploration in the Shunbei oilfield.