Understanding the variability of sedimentary basin’s gravity response through stratigraphic modelling

Summary

It is well known that inversions of gravity data are non-unique and this means that if one model can be found that fits data then there is also a set of alternative models that fit the data equally well. This non-uniqueness also extends to the choice of model parameterisation, a voxelised model is likely to explain the data as well as a model with layers with constant density and variable thickness.

A practical consequence of the non-uniqueness of gravity inversions is that a measured gravity response above a sedimentary basin can be explained by (1) sediments with constant densities above a highly heterogeneous basement or by (2) a basement with a constant density combined with variations of densities within the sedimentary strata. Understanding the sedimentary cover’s gravity response and its variability is therefore central to localise the cause for anomalies in the observed gravity response particularly in the context of whether or not they are caused by density anomalies in the basement or the sediment cover.

Here, we use stratigraphic modelling to assess the variability of sedimentary strata’s gravity response. We employ process-based numerical simulations to generate density distributions and focus on geologically plausible models. Results from a study of a 2D section in the Northern Carnarvon basin (offshore of north-western Australia) show that even with a wide range of input parameters for the stratigraphic models, the gravity response has a limited variability when compared with the gravity response of a model where the subsurface density distribution and its uncertainty is parameterised using voxels or layers. Further to this, our numerical experiments provide insight into the global sensitivity of the gravity response to stratigraphic model parameters. We find that the gravity response is most sensitive to parameters related to creation and filling of the accommodation space.

• Undercover Resources
• Gravity Modelling
• Stratigraphic Modelling
• Geological Realism