Thickness of the stratigraphic record of Britain: How the fidelity of geological and fossil data is unrelated to rock quantity

Abstract

The sedimentary-stratigraphic record is the principal repository of empirical historic evidence for evolution and deep time environments. However, the record has a temporal incompleteness and inconsistency to its extensive quantity, driven by the spatial heterogeneity of deposition and erosion. This is argued to bias intensive fossil records, with correlations apparent between fossil diversity and mapped rock area from different intervals. However, mapped rock area is a poor proxy for strata accessible for fossil studies because most is concealed. Additionally, spatially diminutive older rocks commonly sample a greater stratigraphic transect per unit exposure area than widespread younger rocks because the tectonic forces that drive recycling additionally result in tilting. We calculate observable vertical stratigraphic thickness throughout geologic history for southern Britain and show that potential sample availability increases with age, in contrast to general models of rock survivorship. Using this subsample of the sedimentary-stratigraphic record as a calibration sample for the global record, we find no correlation between available stratigraphic thickness and palaeobiodiversity, except in flat-lying strata. We demonstrate instances where the first occurrences of fossil genera appear robust because there is high availability of suitable host rock pre-dating them. Our work suggests that preservation biases induced by variability in rock quantity have been significantly overstated and that local tectonic history renders different regions as stratigraphic hotspots for specific intervals, in which intensive high-veracity fossil records have exceptional value for elucidating global trends and timing in evolutionary history. The British non-marine Palaeozoic record is highlighted as such an example, with high-fidelity palynological records of plant evolution and ichnological records of animal terrestrialization.