Abstract: Syn-Rift Submarine Canyon Development on the Margin of the Sogn Graben, Northern North Sea, Norway

Andreas Hoeie, Bjoern Egil Knudsen, Stefan Nilsson

Several submarine erosional features of Late Jurassic to Early Cretaceous age are observed on seismic data along the eastern margin of the Sogn Graben. In an area 50 km north of the giant Troll gas field, these features are particularly well defined by a high quality 3-D seismic data set.

Two major Upper Jurassic east-west trending canyon systems have been mapped crossing the dominant north-south striking fault systems. The erosional features are typically 1.5-2.5 km wide and 150-500 meters deep. The canyons are incised into the shallow to offshore marine sediments of Oxfordian to Bathonian age. Both canyon systems include two distinct phases of incision and sediment fill. The erosion is dominantly of submarine origin, and observation of compaction-related geometries and reservoir pressure indicate that the canyons are mainly filled with sealing clays. Based on structural geological considerations, the first (?early Kimmeridgian) and second (?late Volgian) incision phases are interpreted to coincide with early syn-rift and main syn-rift events, respectively.

The absence of deep incision features within the underlying marine to marginal marine pre-rift section is in marked contrast to canyon development within the syn-rift package, and serves to emphasize the importance of tectonics as a whole for the development of submarine erosional features in this area. Even though the incisional phases could have been initiated by eustatic sea level variations, tectonically generated relief and related slope instability is considered the main cause for the generation of the canyon systems.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994