Controls on the stratigraphic architecture of shallow marine systems in syn-rift basins

Rift basin-fills preserve complicated stratigraphic architectures due to temporally- and spatially-variable interactions of base level, tectonics and sedimentation. This work aims to reduce uncertainty, and improve interpretations and predictions of shallow marine, syn-rift stratigraphy around normal fault blocks, by: i) accounting for architectural complexities arising from along-strike variability in allogenic controls; ii) deconvolving control signals from the depositional record; iii) using quantitative data, techniques, classification and modelling; and iv) proposing an alternative stratigraphic framework to the ratio of accommodation to supply (δA/δS) for tectonically-active basins. Novel geometric and volumetric, 3D approaches are utilised through numerical modelling (new sequence stratigraphic forward model, ‘Syn-Strat’), field and subsurface analysis. Detailed assessment of field data and UAV photogrammetry-based 3D outcrop models is undertaken of coeval and adjacent exposed fan deltas and their interfan area (Gulf of Corinth Greece), and of 3D seismic data imaging footwall-, hangingwall- and axially-derived depositional systems in the subsurface (northern Carnarvon Basin, NW Shelf, Australia).
Tectono-sedimentary models are improved through this work by: better constraints of key surface diachroneity; understanding the relative contribution and interactions of multiple sedimentary systems within a basin; consideration of along-strike depositional system asymmetry and sediment routing; and a 3D approach. Documenting along-strike variability of stratigraphic architecture in rift basin enables control signals to be deconvolved and quantified. The ‘non-unique solutions’ theory is only arguable in cases with one-dimensional data and limited regional knowledge. By using a multi-system, along-strike distributed approach with interpretation and modelling based on geological rules, it is possible to invert the stratigraphic record. Several flaws in the δA/δS ratio are highlighted, and a new framework (δAI/δAR) is proposed, which is unbiased, inclusive of all control parameters and possible recorded outcomes. This new approach better allocates time across surfaces and strata in the depositional record, and is applicable to global rift basin analysis.