Quantitative Biostratigraphy—achieving Finer Resolution in Global Correlation

Abstract

▪ Abstract The fossil record preserves a wide range of events that might be used to build timescales and correlate strata from place to place. The events include the originations and extinctions of species, the occurrence of distinctive faunal assemblages, magnetic field reversals, changes in ocean chemistry, and volcanic ash falls. The fundamental task is to determine the global sequence of all these events. Modern computer algorithms can build high-resolution timescales by sequencing and calibrating thousands of such events from hundreds of localities. Each successful sequencing algorithm can be understood in terms of a simple two-dimensional visual device. Graphic correlation, permutable sequences, permutable matrices, and slotting devices are each suited to a different data problem, such as contradictory evidence of sequence, a lack of information about sequence, or uncertain correspondence of events. Algorithms based upon permutable sequences and evolutionary programming heuristics have the flexibility to optimize sequences with a wide variety of event types and data problems; they are slower than the more narrowly tailored methods. All methods will be challenged to keep pace with the amount of biostratigraphic information that is accumulating in the latest generation of shared databases. Currently, it is possible to sequence sufficiently large numbers of events to imagine a potential resolution of 10,000 to 50,000 years over time spans on the order of 50 to 100 million years. The actual resolving power is less because the solutions to these sequencing problems are not unique. Multiple equally good solutions typically emerge and, to extract a consensus sequence with which all solutions agree, some runs of events must be collapsed into unresolvable clusters. Nevertheless, quantitative methods have been shown to improve resolution up to tenfold over traditional methods that discard many potentially useful events.

Strata and time: probing the gaps in our understanding

“…CONOP is a generalization to many dimensions of Shaw's (1964) bivariate graphic correlation approach, allowing the simultaneous comparison of event sequences from many sections. The result is a composite sequence of events for which the net misfit with all contributing sections is minimized, but no information is discarded or ignored (Sadler 2004;). An example is the graptolitebased chronostratigraphic scale for the Ordovician and Silurian (Sadler et al 2009) with its estimated tenfold improvement in resolving power over conventional zonal schemes.…”

Ammonoids and Quantitative Biochronology—A Unitary Association Perspective

“…In addition to these direct applications, such biozonations are also of primary importance for reconstructing changes of taxonomic diversity in time and space, especially in relation with mass extinctions and recoveries (e.g., Brayard et al 2009b;Brühwiler et al 2010). To achieve these goals of accuracy and precision, a number of quantitative biochronological methods have been developed during the last decades (Hay and Southam 1978;Guex 1979;Cubitt and Reyment 1982;Gradstein et al 1985;Boulard 1993;Sadler 2004;Gradstein 2012). All these methods utilize strict and well-defined algorithms that allow not only the processing of large datasets but also to test the reliability of the underlying methods with sets of either real or simulated data of different quality.…”

No Major Stratigraphic Gap Exists Near the Middle-Upper Pennsylvanian (Desmoinesian-Missourian) Boundary in North America

“…In those cases, biostratigraphic correlation is more precise if it relies on the sequence of first and last appearance data of those taxa common to both areas (Blake et al, 2002;Pfefferkorn, 2003;Sadler, 2004), and eliminates taxa that have shown slow migration over time (Laveine et al, 2000;Blake et al, 2002) or regional extirpation ).…”