Clinoforms, Clinoform Trajectories and Deepwater Sands
Ron Steel, Torben Olsen, 2002. "Clinoforms, Clinoform Trajectories and Deepwater Sands", Sequence Stratigraphic Models for Exploration and Production: Evolving Methodology, Emerging Models and Application Histories, John M. Armentrout, Norman C. Rosen
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Sedimentary prisms build out from the margins of most types of sedimentary basin where there is significant differential subsidence. Clinoforms are the large-scale (hundreds of meters), time-line expressions of discrete phases of aggradation and accretion within these prisms. The sigmoidal clinoforms are surfaces of dynamic equilibrium that are created and maintained by sediment aggradation to form topsets and then sediment by-pass through the topsets onto the accreting deepwater slope and beyond (Swift and Thorne, 1991). It is argued, on this basis, that the topset surface of such large-scale clinoforms is referred to as a morphological ‘shelf’ and that the upper rollover of the clinoform is referred to as the ‘shelf-slope break.’ Such features form at the supply margins of many types of basin where there is a water depth of at least several hundred meters and are not restricted to continental margins.
The geometry and internal architecture of individual clinoforms, or groups/sets of clino-forms, can be used to predict how sediment budgets have been partitioned between the shelf and deepwater areas beyond the shelf break. The architecture of individual clinoforms (time scale of several 100ky), mainly the degree of shelf-edge incision and the degree of slope disruption, can indicate whether or not significant volumes of sand have been delivered beyond the shelf margin. Another method of prediction makes use of the ‘trajectory’ of the shelf margin on time scales of 1Ma or more; i.e., how the break-of-slope of successive clinoforms stack with respect to each other. High-angle trajectories generally imply preferential sediment storage on the shelf and coastal plain, whereas low-angle or falling trajectories involve erosion and sediment by-pass to the deepwater slope and basin floor. These concepts are illustrated from well-exposed clinoforms and clinoform sets within a shelf margin that has migrated and accreted some 30 km during an interval of some 6 Ma, in the Central Basin of Spitsbergen.