Cyclostratigraphy at a tipping point

Abstract

There are key patterns of variation in the (litho-) stratigraphical record, which, with advances in computing technology in recent decades, have become amenable to objective numerical analysis. This research has chiefly focused on the search for spatially regular cycles in the sedimentary rock record, since there are theoretical grounds for believing that these would be periodic and thus provide a means of time-calibrating the stratigraphical records in which they occurred. Less popular lines of research consider the scaling relationships of the tangible, measurable sedimentary rock layers, and of the hiatuses, individually of indeterminate length, that punctuate these layers. Objective source data for all these analyses is provided, on limited (usually decametre) scales, by detailed lithological logging, sampling and dating of sections provided by exposures and cores. An objective global lithostratigraphical database, with larger, kilometre scales, is provided by the widespread practice of electric (wire-line) logging of deep wells. This involves measurement, at 6-inch (~15 cm) depth intervals of lithology-related petrophysical properties. Rapid desk top computer analysis of the hundreds or thousands of readings that comprise these two data series, searches for patterns of variation. This review considers the published evidence for ‘ubiquitous’ cyclicity and its use in chronostratigraphy, despite the contrary claims that stratigraphical records are predominantly random in character.