CONSEQUENCES OF A CHANGE TO THE GEOLOGIC TIMESCALE – DOES THE INCREASED DURATION OF THE QUATERNARY PERIOD AFFECT THE GEOSCIENCES?

A question that must be considered for changes to internationally recognized geologic timescales is – does a major change serve the geosciences community as a whole as opposed to serving specific disciplines of our science? Arguments to retain the base of the Quaternary System coincident with the base of the Calabrian Stage of the Pleistocene Series (1.806 Ma) failed when in 2009 the International Commission on Stratigraphy redefined the base of the Quaternary coincident with the base of the Gelasian Stage (2.58 Ma), formerly the uppermost stage of the Pliocene. The type section moved from Vrica, Italy where the base of the Quaternary was marked by sediments that record cooling waters in a marine environment, to Monte San Nicola, Sicily. Changing this important boundary increased the duration of the Quaternary Period by 43 percent. Although not unanimous, many North American geologists were taken aback by this change and wondered how the science and geologic maps completed before this change would be affected and how we would adapt. The USGS Geologic Names Committee had decided in 2007 to adopt the international standard for chronostratigraphic units, and therefore, have lowered the position and age calibration of the base of the Quaternary in 2010 to be consistent with the international community. However, this change has caused issues in consistency of communication for scientists who work in the Pliocene and Pleistocene as well as geologic mappers whose Pliocene units are now Pleistocene or uncertain. The timescale should be as consistent as possible. Changes should be based on the rock record as our evidence and basis for chronology. If a standard is established and does not show major problems, it should be used until such time it is deemed “broken.” Changes to the timescale should not be made to satisfy one avenue of science without due consideration of consequences to others. The change in the definition of the base of Quaternary three years ago gives us examples of the unintended consequences of major changes to the geologic timescale.