Late Syn-Rift and Post-Rift Slope-to-Basin-Floor Depositional System, Lower Cretaceous, Oseberg Area, Norwegian North Sea

Anna-Jayne Zachariah
University of Manchester, Manchester, United Kingdom

Lower Cretaceous deep-water deposits within the North Sea are poorly understood due to deep burial depths, low seismic resolution and limited well control. This paper highlights the seismic geomorphologies present within the Lower Cretaceous system of Oseberg, and attempts to quantify the architectural elements and sedimentary processes active in this system. Analogues are used to predict the sedimentary processes and geomorphologies hidden below seismic resolution.

The study area is located on a major transfer zone and collapsed rift shoulder in the North Viking Graben. It is 33 by 25 km and dominated by regional N-S and minor E-W striking faults. The Lower Cretaceous section lies unconformably on Upper Jurassic stratigraphy and is a late syn-rift to early post-rift basin infill. In the deepest part of the basin the succession is ca. 600 m thick, where as on the shelf it is ca. 100 m thick.

Key seismic surfaces have been mapped and isopachs reveal depositional systems in the south and the north-west. 3D volume visualisation reveals that depositional systems occupy topographic lows and have lens-shaped geometries. The sediment pathways that fed the systems appear ‘channelised' and are confined by the underlying late Jurassic fault geometry. Well penetrations from structural highs adjacent to the basin, display erosional breaks at stratigraphic intervals which signify periods of regional sandstone deposition. It is anticipated that the sediments in the down-dip location are sourced from the missing up-dip stratigraphy.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005