3-D Visualization and Interpretation of Branching Unconformities

Wirth, Bastian, Stefan Back, Peter Kukla, RWTH Aachen University, Aachen, Germany

This study concerns the detailed analysis of the three-dimensional morphology of later­ally amalgamated unconformities on 3D seismic data. The study area covers a block of 10 x 15 km in a Jurassic to Cretaceous rift system in the West Netherlands Basin. Syn- and postrift sequences are characterized by a multi-phase unconformity development in a fluvial to shallow marine depositional setting.

The approach presented comprises 1) the mapping of unconformities by picking seis­mic boundary surfaces that are defined by reflection discontinuities, and 2) an integrated analysis of lap surface geometry, subsidence development and hiatus maps. Our interpreta­tion results show a distinct contrast in unconformity character between structural highs and basinal areas: discontinuity surfaces on structural highs are generally represented by angu­lar contacts, reflecting major material removal during a multistage erosional history. Unconformity surfaces of the basin areas are predominantly lapsurfaces, often lacking ero­sional truncation. Both areas are linked by a transition zone, in which discontinuity surfaces onlap stepwise on older unconformities and converge towards structural highs, accompa­nied with an increase in unconformity diachronism.