Seismic amplitude and attribute data from Mesozoic strata in the Skagerrak (Danish-Norwegian North Sea): Indicators for fluid migration and seal bypass systems.

The Skagerrak builds the transition from the exposed Palaeozoic basement of South Norway to thick Mesozoic to Cenozoic sediments covering Danish Jutland. It states the southern Norwegian Trench, and comprises from W to E the Mesozoic Farsund Basin, the northernmost sector of the Sorgenfrei-Tornquist Zone and the Palaeozoic Skagerrak Graben. Over the past decades, fluid escape structures at the southern Skagerrak Shelf and in the central Norwegian Trench were investigated and layer-parallel fluid migration from Mesozoic rocks was suggested. However, a fluid source or a corresponding migration system of the fluids has not been proposed yet. In this study, a joint interpretation of seismic imagery and seismic attributes reveals fluid indications and migration systems in the Farsund Basin and the central Skagerrak. We propose that source rocks of the Lower Jurassic Fjerritslev Formation generated thermogenic fluids in the Farsund Basin as well as in the Fjerritslev Trough. For the central Skagerrak, a time-structure map of the base of the F-III member of the Fjerritslev Formation shows that these fluids could migrate upward forced by buoyancy and partially bypassed by faults, and seep out in the Norwegian Trench. Furthermore, we propose that fluid escape structures on the southern shelf were likely caused by seepage of biogenic fluids under bottom current action. Image 1 • Seismic amplitudes and attributes reveal fluid migration paths and seal bypasses. • Fluids escaping in the central Norwegian Trench are of thermogenic origin. • Fjerritslev Formation (F-III/IV) is likely the kitchen in the Fjerritslev Trough. • The Holocene sediments act as thickness-depending sealing. • Fluids escaping on the Skagerrak shelf are of biogenic origin. [ABSTRACT FROM AUTHOR]