BIOCHRONOLOGY

Underlain by biotic evolution, biochronology has played a critical role in the development of Earth Sciences. Intertwined with early attempts at chonostratigraphic classification it lies at the origin of most of the chronostratigraphic terms in use today down to the level of epoch. A central component of the modern Phanerozoic time scale, it was also the very first embodiment of a time scale, providing an initial glimpse into the strength of estimated numerical dates. Subsequent integration with geomagnetic polarity history, and then astrochronology, has resulted in an unprecedented increase in temporal resolution, now reaching a precision of ~half a precessional cycle (~10 kyr). Further, diachrony (that has plagued biostratigraphy) is being measured, which decreases the uncertainty inherent to biochronology, making it competitive with other methods of dating rocks.

Today biochronology occupies a central role in historical geology not least because it is the most immediate means of determining the rates at which geological (including evolutionary) processes develop, enabling a basis for future scenarios. However, as yet, the discipline has had very little input in the domain of sequence stratigraphy, which has not incorporated biochronology to analyze stratigraphic sequences in a dynamic temporal context. Based on examples from the Gulf of Mexico we show that biochronology has the capability to help sequence stratigraphy resolve the fundamental problem of the relationship between strata along sequence boundaries, from the shallow subaerial unconformity to the deeper water stratal conformity (i.e., concordance), and, thereby, assist in the determination of the forcing mechanism on stratigraphic architecture.