Trajectory analysis: concepts and applications

Abstract

Shoreline and shelf‐edge trajectories describe the migration through time of sedimentary systems, using geomorphological breaks‐in‐slope that are associated with key changes in depositional processes and products. Analysis of these trajectories provides a simple descriptive tool that complements and extends conventional sequence stratigraphic methods and models. Trajectory analysis offers four advantages over a sequence stratigraphic interpretation based on systems tracts: (1) each genetically related advance or retreat of a shoreline or shelf edge is viewed in the context of a continuously evolving depositional system, rather than as several discrete systems tracts; (2) subtle changes in depositional response (e.g. within systems tracts) can be identified and honoured; (3) trajectory analysis does not anticipate the succession of depositional events implied by systems‐tract models; and (4) the descriptive emphasis of trajectory analysis does not involve any a priori assumptions about the type or nature of the mechanisms that drive sequence development. These four points allow the level of detail in a trajectory‐based interpretation to be directly tailored to the available data, such that the interpretation may be qualitative or quantitative in two or three dimensions. Four classes of shoreline trajectory are recognized: ascending regressive, descending regressive, transgressive and stationary (i.e. nonmigratory). Ascending regressive and high‐angle (accretionary) transgressive trajectories are associated with expanded facies belt thicknesses, the absence of laterally extensive erosional surfaces, and relatively high preservation of the shoreline depositional system. In contrast, descending regressive and low‐angle (nonaccretionary) transgressive trajectories are associated with foreshortened and/or missing facies belts, the presence of laterally extensive erosional surfaces, and relatively low preservation of the shoreline depositional system. Stationary trajectories record shorelines positioned at a steeply sloping shelf edge, with accompanying bypass of sediment to the basin floor. Shelf‐edge trajectories represent larger spatial and temporal scales than shoreline trajectories, and they can be subdivided into ascending, descending and stationary (i.e. nonmigratory) classes. Ascending trajectories are associated with a relatively large number and thickness of shoreline tongues (parasequences), the absence of laterally extensive erosional surfaces on the shelf, and relatively low sediment supply to the basin floor. Descending trajectories are associated with a few, thin shoreline tongues, the presence of laterally extensive erosional surfaces on the shelf, and high sediment supply to basin‐floor fan systems. Stationary trajectories record near‐total bypass of sediment across the shelf and mass transfer to the basin floor.

Depositional evolution of a progradational to aggradational, mixed-influenced deltaic succession: Jurassic Tofte and Ile formations, southern Halten Terrace, offshore Norway

“…In addition, the occurrence of coarse sand grains and granules beneath the erosion surface (in well 6407/6-5) suggests proximity to a contemporaneous coastline with coarse-grained fluvial sediment input. Hence, a forced regressive shoreline interpretation is proposed, in which prograding deltas followed a descending regressive trajectory (Posamentier and Morris, 2000;Helland-Hansen and Hampson, 2009;Prince and Burgess, 2013). In contrast, those locations comprising gradual coarsening upward facies successions ( Figure 10H) record ascending regressive shoreline trajectories.…”

Towards a sequence stratigraphic solution set for autogenic processes and allogenic controls: Upper Cretaceous strata, Book Cliffs, Utah, USA

“…at a shoreline or shelf edge), to define trajectories for such palaeo-geomorphological features (HellandHansen & Martinsen 1996;Helland-Hansen & Hampson 2009). These two approaches do not anticipate a fixed succession of stratal architectures (in contrast to the succession of systems tracts associated with a sinusoidal relative sea-level curve), and they allow aspects of stratal architecture to be quantitatively estimated if due care is exercised in choosing a reference datum surface(s) and accounting for compaction (Løseth et al 2006;Helland-Hansen & Hampson 2009;Prince & Burgess 2013). The application of shoreline trajectory to characterize shallow-marine stratigraphic patterns (e.g.…”

Seismic expression of depositional elements associated with a strongly progradational shelf margin: northern Santos Basin, southeastern Brazil

“…Although sand transport to the deep-sea is favored by forced regressions (e.g., Muto & Steel, 2002;Helland-Hansen & Hampson, 2009), occurrence and volume of turbidites are not exclusively controlled by base-level falls (e.g., Burgess & Hovius, 1998;Carvajal & Steel, 2006;Dixon et al, 2012;Safronova et al, 2014;Berton & Vesely, 2016). Turbidites were identified in all seismic facies associations formed during base-level falls, but they are more frequently observed on the bottomset of clinoforms from association 1, in which well-developed shelf-margin deltas/shoreface deposits occur (Figs.…”