SEQUENCE OF DEFORMATION AT THE FRONT OF AN OROGEN: LUBLIN BASIN CASE STUDY (POLAND)

Abstract We provide a detailed description of a late Carboniferous fold-and-thrust belt in the Lublin Basin based on seismic lines, including new, high-resolution acquisitions, and legacy borehole and gravimetric data. A series of regional cross-sections integrate results of the joint seismic-borehole-gravimetric interpretation. Cross-section restoration provides estimates of the minimum incremental and total shortening and reveals its along-strike variations. The Lublin Basin straddles a leading edge of the Variscan orogen and its undeformed foreland; therefore, it experienced only a minor deformation. It preserves a fossilised record of early phases of shortening: seismic scale, bivergent intra-formational thrusts and folds in horizontal strata that were later passively rotated by subsequent folds developed above a regional decollement. Lateral variations of deformation styles – from displacement of the entire basin with little internal deformation to dispersion of shortening by numerous contractional structures – is attributed to along-strike changes in lithology and thickness of the Silurian detachment horizon. Lateral change of detachment strength is quantified using the critical wedge theory. Our observations deliver a new perspective on factors controlling the localization of incipient structures, their differentiation as a function of detachment strength and interplay between folding and thrusting along a leading edge of an orogenic system.