Item

Abstract

Gas and fluid dynamic processes in the Mesozoic to recent strata of the southern slope and center of the Norwegian Trench (Skagerrak) have been analyzed by high-resolution multi-channel seismic data collected with a watergun as the seismic source on board of RV Heincke in spring 2003. Three profiles across the southern slope and the center of the trench and four profiles cover the north-eastern termination of the trench. The data resolve the Quaternary succession and the subcropping Mesozoic strata. The separating unconformity shows a typical cuesta topography, caused by glacial erosion. On the slope, contourite drifts are present. Above a water depth of approximately 400 m internal reflections of the Quaternary are obscured by acoustic turbidity. Particularly, phase reversed bright reflections occurring in the entire Lower Jurassic to Upper Cretaceous succession suggest the presence of fluids therein. Sea-floor pockmarks have been observed on the southern slope and in the center of the trench. Both slope and trench pockmarks are vertically correlated with the sub-crop of fluid charged Mesozoic rocks beneath, which indicate lateral fluid escape from porous Mesozoic rocks. Fluids that migrate towards a slope pockmark are capable to wash out gas from the Quaternary, leaving gas free patches behind. Since no thermogenic gas has ever been measured in core samples from the slope and trench, freshwater seepage is a possible explanation. In this case the water outflow might represent artesian springs.