Abstract
Abstract. The sedimentary architecture at continental margins reflects the interplay between the rate of change of accommodation creation (δA) and the rate of change of sediment supply (δS). Stratigraphic interpretation increasingly focuses on understanding the link between deposition patterns and changes in δA∕δS, with an attempt to reconstruct the contributing factors. Here, we use the landscape modelling code pyBadlands to (1) investigate the development of stratigraphic sequences in a source-to-sink context; (2) assess the respective performance of two well-established stratigraphic interpretation techniques: the trajectory analysis method and the accommodation succession method; and (3) propose quantitative stratigraphic interpretations based on those two techniques. In contrast to most stratigraphic forward models (SFMs), pyBadlands provides self-consistent sediment supply to basin margins as it simulates erosion, sediment transport and deposition in a source-to-sink context. We present a generic case of landscape evolution that takes into account periodic sea level variations and passive margin thermal subsidence over 30 million years, under uniform rainfall. A set of post-processing tools are provided to analyse the predicted stratigraphic architecture. We first reconstruct the temporal evolution of the depositional cycles and identify key stratigraphic surfaces based on observations of stratal geometries and facies relationships, which we use for comparison to stratigraphic interpretations. We then apply both the trajectory analysis and the accommodation succession methods to manually map key stratigraphic surfaces and define sequence units on the final model output. Finally, we calculate shoreline and shelf-edge trajectories, the temporal evolution of changes in relative sea level (proxy for δA) and sedimentation rate (proxy for δS) at the shoreline, and automatically produce stratigraphic interpretations. Our results suggest that the analysis of the presented model is more robust with the accommodation succession method than with the trajectory analysis method. Stratigraphic analysis based on manually extracted shoreline and shelf-edge trajectory requires calibrations of time-dependent processes such as thermal subsidence or additional constraints from stratal terminations to obtain reliable interpretations. The 3-D stratigraphic analysis of the presented model reveals small lateral variations of sequence formations. Our work provides an efficient and flexible quantitative sequence stratigraphic framework to evaluate the main drivers (climate, sea level and tectonics) controlling sedimentary architectures and investigate their respective roles in sedimentary basin development.
Highlights
Since its introduction in 1970s, sequence stratigraphy has been widely used to interpret depositional architectures in terms of variations in eustatic sea level or relative sea level (Vail et al, 1977a; Pitman, 1978; Posamentier et al, 1988; Posamentier and Vail, 1988; Jervey, 1988)
An oblique prograding clinoform develops due to the falling eustatic sea level, with strata toplapped by a subaerial unconformity (SU). This subaerial unconformity terminates downdip at the offlap-break at 4.0 Myr and it transfers to a marine correlative conformity (CC∗), which together forms a sequence boundary (Fig. 5a)
We analysed the predicted stratigraphic architecture based on observations of shelf-edge or offlap break trajectory, stratal terminations and stratal geometries, following the workflow of two stratigraphic interpretation approaches: the trajectory analysis and the accommodation succession method
Summary
Since its introduction in 1970s, sequence stratigraphy has been widely used to interpret depositional architectures in terms of variations in eustatic sea level or relative sea level (i.e. accommodation) (Vail et al, 1977a; Pitman, 1978; Posamentier et al, 1988; Posamentier and Vail, 1988; Jervey, 1988). With recognition of the role of sediment supply in affecting stratal stacking patterns, the rate of change of accommodation creation (δA) versus the rate of change of sediment supply (δS) – the δA/δS ratio – has been widely accepted as the main control of sequence formations (Schlager, 1993; Muto and Steel, 1997; Catuneanu et al, 2009; Neal and Abreu, 2009; Neal et al, 2016). The inherent difficulties in accurately describing accommodation and reconstructing sediment supply limit the quantification of the δA/δS ratio and, as a result, the practical application of the δA/δS concept in stratigraphic interpretations (Muto and Steel, 2000; Burgess et al, 2016)
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