A deep seimic reflection line in the Danish Central Graben

Abstract

Results are presented from a deep seismic reflection line, recorded to 16 seconds trave1 time, across the Coffee Soil Fault in the southern part of the Danish Central Graben. Data processing has been focused on the deeper parts of the sedimentary sequences, the crystalline crust and the crust-mantle boundary. Depth migration is performed down to 15 km depth, and time migration is performed on the entire section. The Coffee Soil Fault is clearly imaged as a normal fault dipping about 45" from about 2.5 to 9 km depth. Interpretation of the sedimentary sequences is constrained by well data and shows an almost uniform 2 km thick unit of post-chalk deposits. The thickness of the Mezosoic sequences is to a large extent controlled by faulting and highly influenced by movements of Zechstein salt. They exceed 4 km of thickness in the halfgraben immediately west of the Coffee Soil Fault. Large block-faulted pre-Zechstein units of more than 2 km thickness are seen indicating a total depth of at least 8 km to the crystalline basement. The crystalline crust is generally non-reflective. Around 11 seconds two-way trave1 time (about 28 km depth) reflectivity interpreted as the crust-mantle boundary (Moho) is observed. Comparison with other deep seismic profiles across the Central Graben is taken to indicate a local crustal thinning by a factor of 1.5 associated with graben formation by extension.