Pre-drill predictions of basin-fill strata, in the absence of substantial supporting data, have been a key objective of seismic and sequence stratigraphic methods including global sea-level curves since the original concepts of sequence stratigraphy were copied from outcrop-based approaches and applied to newly-developed seismic methods in the late 1970s. Despite much hyperbole, it is doubtful this objective has yet been achieved, for two key reasons.
Firstly, stacking patterns and spatial distribution of strata, including key source rock, reservoir and seal elements of petroleum systems are most likely controlled by multiple complex factors, not just accommodation variations. This point has been made numerous times, including cautionary comments by the geologists who originally developed the key sequence stratigraphic ideas. This evidence for multiple controls means the assumption of dominant accommodation control underpinning prediction of strata based on a eustatic of even a relative sea-level curve is unlikely to be reliable.
Secondly, it is very unlikely, based on currently available evidence, that any published sea-level curves are sufficiently accurate models of eustatic sea-level history to reliably constrain even part of the accommodation control that forms one single element of the multiple controls on any basin-fill. This is because a comparison of the various published sea-level curves shows very clearly that they all differ, not all of them can therefore be correct, and quite possibly none of them are.
Are none of the curves correct?
A conclusion that none of them are likely to be correct is also supported by consideration of the methods used to construct the curves, all of which contain substantial uncertainty. Perhaps the most obvious examples are eustatic curves derived from studies of stratal onlap at multiple single locations through time, or even over regional studies, which are unlikely to yield accurate eustatic history because of the multiple control problem; local and regional tectonic processes cause vertical displacements everywhere and temporally variable sediment supply also control potentially diagnostic stacking patterns.
Other methods are similarly problematic, including the reconstruction published by Van der Meer and Wilkinson recently that prompted this response; strontium curves clearly do not record eustatic sea-level change directly, and the assumptions required to convert a strontium isotope curve into a eustatic sea-level curve are so substantial that the related uncertainty, if robustly calculated, seems likely to substantially reduce any predictive power. Qualitative comparison with interpreted sea-level history from specific basin fill examples lack sufficient rigour to be a robust test of predictive power.
Hard work
Given all these challenges, how can we make progress predicting basin fill in a useful way? The simplest answer is, of course, acquire sufficient data to reduce uncertainty to the required level. This may be expensive but perhaps still less expensive than poor predictions. Robust quantitative analysis of the various published eustatic curves might improve understanding and prediction by elucidating exactly how and perhaps then why they are different. Accepting that multiple controls operate, and developing methods to make predictions accounting for this is also likely to be useful. Analysing multiple stratal controls using more rigorous quantitative and probabilistic approaches, and using ever-increasing computation power to compute and analyse constrained multiple scenario forward models are also promising methods.
In summary, using eustatic curves to predict unknown basin fill may be quick, easy, and therefore seductive, but it is unlikely to be correct. Other methods require more work, but robust prediction is worth the hard work.
References
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