Some personal thoughts on stratigraphic precision in the twentieth century

Abstract

AbstractSurprisingly, most of the major elements of today’s stratigraphic column were in place by 1850. By then, the ideas that stratigraphy concerned geological time relations, and that a palaeontological identity of ‘best’ fossils (like ammonites) was an indication of time-equivalence, were starting to be accepted. By 1900, thanks to the work of people like Henry Shaler Williams (USA) and Sydney Savory Buckman (UK) stratigraphy was starting to concern itself with the precision with which biochronological time-scales could be created, especially in the Jurassic. By then, Buckman had demonstrated the great extent to which particular lithologies could cross time-lines and equally how well such rapidly evolving fossils as ammonites could be used to discriminate time. But from 1960, facing new demands for energy, and the growth of new ‘earth science’, focussing on numerical methods in geophysics and geochemistry using computers, such field-based ‘historical geology’ was progressively perceived as boring, out-dated, and expensive. Many new techniques, which ignored, or worse, assumed time-equivalence, now evolved. Fossils by their unique nature had given unique signatures to discriminate time. But some of the new methods relied on binary repetitions, not unique to time, and may suggest a false precision. This paper attempts a, now near-impossible, investigation of the temporal precisions that stratigraphic methods, both old and new, might attain. It concludes that we need to pay greater attention to the incompleteness of the stratigraphic record and to the chronological precision with which we can investigate that record. It now seems almost axiomatic that the harder you look at a rock the more incomplete the record of its stratigraphy appears to become.