Natural sampling and aliasing of marine geochemical signals

It is well known that the sedimentary rock record is both incomplete and biased. Correlation between geographically distinct records is problematic in the absence of absolute age constraints, which can profoundly affect interpretations of geological and geochemical data. We use a computational process model to create canonical examples of carbonate-siliciclastic stratigraphic cross-sections from oscillatory overall-rising and -falling sea level, in which we can quantify how spatial and temporal geochemical records are biased by the inherent processes of marine sedimentation and preservation. Sedimentary hiatuses are shown to span ~50 to 95% of geological time, and even in these simple cases, infinitely dense sedimentology and geochemical data collected along spatial transects crossing the geological strata are shown to confound expert interpretations of paleo-environmental signals. Observations of secular variation of inferred paleo-environmental changes are shown to be irreversibly disguised as lower frequency signals by an aliasing effect, caused by cyclical and multiscale relative sea-level changes. Nyquist’s theorem correctly predicts their biased signatures, proving that aliasing is caused by natural geological processes. Both effects are compounded by finite spatial sampling intervals adopted in practice, illustrated using real data case studies. These combined effects imply (a) that deeper marine records are significantly more likely to provide unaliased environmental signatures, and (b) that careful sedimentological field observations still allow such records to be correctly correlated in age given aliased shallow marine intervals.