Ground-penetrating radar imaging of carbonate mound structures and implications for interpretation of marine seismic data

Images of carbonate mound structures in Denmark and Sweden are obtained from ground-penetrating radar (GPR) reflections and outcrop analysis. The GPR data are collected in limestone quarries and provide a depth penetration of about 10 m (33 ft) and a vertical resolution of about 0.5 m (1.6 ft). The mounds are part of the northwest European Upper Cretaceous-Danian (lower Paleocene) Chalk Group, and they are similar to each other in terms of architecture, spatial distribution, and size, with widths and lengths of 30-60 m (100-200 ft) and heights of 5-10 m (16-33 ft). Seismic reflection images from the sea of Kattegat between Sweden and Denmark and the North Sea show large (∼500-1000-m [∼1640-3280-ft]-wide and ∼50-100-m [∼160-330-ft]-high) moundlike carbonate structures. Interpretations of such large mounds conflict with the GPR and outcrop observations. We address these conflicting observations. We construct realistic reference models of carbonate mound complex geometries based on the results of the GPR measurements and outcrop analysis and calculate synthetic seismic sections for the models. The modeling results show that the size of individual mounds is below the seismic resolution of 10-25 m (33-82 ft), and that interference effects caused by stacks of mounds may explain the observed large moundlike structures. Our findings are important for the interpretation of seismic images of carbonate mound structures. Carbonate mound buildups may form traps, and correct seismic interpretation of mound complex geometry may be essential for evaluation of the nature and reservoir potential of such structures.