Seismic interpretation of sill complexes in sedimentary basins: implications for the sub-sill imaging problem

Application of 3D seismic reflection data to igneous systems in sedimentary basins has led to a revolution in the understanding of mafic sill complexes. However, there is considerable uncertainty on how geometries and architecture of sill complexes within the subsurface actually relates to geometries in seismic reflection data. To provide constraints on how sill complexes in seismic data should be interpreted, we present synthetic seismograms generated from a seismic-scale (22 x 0.25 km) outcrop in East Greenland constrained by abundant field data. This study highlights how overlying igneous rocks adversely affect imaging of underlying intrusions and rocks by decreasing seismic amplitude, frequency and making steeply dipping features near-impossible to image. Furthermore, seismic modelling in this study shows that, because of the high impedance contrast between siliciclastic host rock and dolerites, very thin (1-5 m) intrusions should in principle be imaged in reflection seismic data at 3 km depth. However, comparison with actual seismic data with well data shows significant amounts of unimaged sill intrusions, and this is likely due to limited seismic resolution, overburden complexity, inadequate velocity-models, and interference between reflections from closely spaced sills and sill splays. Significant improvements to sill imaging and interpretation could be made by better predicting occurrence and geometry of sill intrusions and including these in velocity models.