|
Evy Glørstad-Clark, University of Oslo (Norway)
Jan Inge Faleide, University of Oslo (Norway)
Johan Petter Nystuen, University of Oslo (Norway)
Karen Leever, University of Oslo (Norway)
|
|
We present a sequence stratigraphic framework of the Norwegian Barents Sea from seismic and well data as a part of the PETROBAR project (Petroleum-related regional studies of the Barents Sea region). First, we defined and mapped out regionally identifiable seismic units without applying the surfaces into a rigid, predetermined sequence stratigraphic classification system. Then, we established a hierarchy of sequence boundaries based on the regional implications and magnitude of change of accommodation space between the different boundaries. Megasequences are the highest order, recording discrete, major phases of basin evolution. We recognize five megasequence boundaries, representing major events in the tectonic evolution of the region from the Caledonian to present. We then focus on the Triassic succession as an example of how to further analyze and subdivide one megasequence based on facies analysis of 2D seismic data constrained by well data.
We subdivide the Triassic succession into 5 second-order sequences separated by maximum flooding surfaces. The Mesozoic succession in the Barents Sea was deposited in a shallow epicontinental seaway, and relative sea level variations relocated the shoreline significantly, alternately submerging or exposing large areas of the shelf over distances of several hundred kilometers. Time-thickness maps of the Triassic sequences illustrate the changes in depocenters through time and the gradual infill of preexisting topography in the basin. The three lower sequences exhibit an eastward thickening towards the main sediment source area with marine onlap onto highs in the basin (e.g., Loppa High). The main depocenter in the earliest Triassic was at the Finmark and Bjarmeland platforms, with sediment thicknesses decreasing towards the west and northwest. Seismic facies mapping reveals multiple source areas for lower Triassic deposition, with clinoforms prograding out from the Fennoscandian Shield in the south in addition to the main Uralian system in the east and southeast. The main focus of deposition shifted from Ladinian time, with a significant westward and northwestward thickening of sequences, indicating reduced accommodation space to the south and east. Based on the observed clinoforms, a change in water depths also occurred, with a gradual shallowing upwards during the Triassic. The Middle-Upper Triassic is characterized by more parallel seismic reflection patterns, but we observe clinoforms north of 76° N prograding from the southeast. We also interpret clinoforms prograding from west to east in the Loppa High region, representing a new source area from Greenland. Within each sequence, maximum progradation and retrogradation is mapped out and discussed in terms of reservoir, seal and source rock development.
|
