Clinoform stacking patterns, shelf-edge trajectories and facies associations in Tertiary coastal deltas, offshore Norway: Implications for the prediction of lithology in prograding systems

摘要

Regional uplift of Scandinavia in the Late Cenozoic resulted in widespread deltaic shelf progradation on the mid-Norwegian continental shelf This deltaic complex, called the Molo Formation, is readily recognised on seismic cross-sections by a series of high angle, westward prograding clinoforms. High quality three-dimensional seismic data allow for the detailed mapping of parts of this deltaic-complex. Recent advances in the field of three-dimensional seismic imaging have led to an increased ability to interpret depositional sedimentary environments from seismic attribute maps and time-slices. Seismic interpretation combined with seismic attribute mapping of selected clinoforms has allowed for the identification of a variety of depositional environments along the depositional profile. The shelf-edge trajectory concept is used in conjunction with high quality three-dimensional seismic data to determine the existence of a relationship between varying rates and directions of shelf-edge progradation, depositional environments encountered in the coastal-plain/shelf environment, and the character and geometry of slope/basin-floor deposits. Steep-positive shelf-edge trajectories, indicating an increased rate of aggradation, appear to be associated with barrier/lagoonal deposits in the lower coastal plain. Flat-negative (forced regressive) shelf-edge trajectories are associated with topset truncation and slumping at the shelf-edge. Strongly negative (forced regressive) shelf-edge trajectories are associated with bypass of the shelf and slope, and the deposition of basin-floor fan deposits. Low angle-positive shelf-edge trajectories are associated with the preservation of fluvial depositional systems with meandering channel-belt geometries behind the shelf-break and the deposition of lobate deltas at the shelf-edge.