Abstract
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 relates to those imaged 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 (22x0.25 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.
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.
| Original language | English |
|---|---|
| Pages (from-to) | 193-209 |
| Number of pages | 17 |
| Journal | Journal of the Geological Society |
| Volume | 175 |
| Issue number | 2 |
| Early online date | 1 Dec 2017 |
| DOIs | |
| Publication status | Published - Mar 2018 |
Bibliographical note
Acknowledgements: We thank reviewers Craig Magee and MurrayHoggett for considerate and insightful reviews that considerably improved this
manuscript. The LIDAR data were acquired by Julien Vallet and Samuel Pitiot of
Helimap Systems. We acknowledge NORSAR for an academic licence of the
seismic modelling software SeisRoX, which was used to generate synthetic
seismograms in this study, and NORSAR-2D, which was used for analysis of
seismic propagation through the overburden models. The virtual outcrop was
visualized and interpreted using LIME (http://virtualoutcrop.com/lime). We also
acknowledge Tore Aadland for writing invaluable scripts used for import of the
outcrop models to seismic modelling software, and Gijs A. Henstra and Björn
Nyberg for assistance in the field.
Funding: Funding for data acquisition was provided from the Research
Council of Norway through the PETROMAKS project 193059 and the FORCE
Safari project. Funding for data analysis and modelling was provided from
PETROMAKS through the Trias North project (234152).