Thursday, September 24, 2009

Phew! We Finally Know When the Quaternary Period Began

Its official. The Quaternary now begins 2.58 Million years ago. Everyone knew the Quaternary corresponded with the ice ages but there was doubt on which geological horizon to use as a base.

In June 2009, the Executive Committee of the International Union of Geological Sciences (IUGS) formally ratified a proposal by the International Commission on Stratigraphy to lower the base of the Quaternary System/Period to the Global Stratotype Section and Point (GSSP) of the Gelasian Stage/Age at Monte San Nicola, Sicily, Italy. The Gelasian until then had been the uppermost stage of the Pliocene Series/Epoch. The base of the Gelasian corresponds to Marine Isotope Stage 103, and has an astronomically tuned age of 2.58 Ma. A proposal that the base of the Pleistocene Series/Epoch be lowered to coincide with that of the Quaternary (the Gelasian GSSP) was also accepted by the IUGS Executive Committee. The GSSP at Vrica, Calabria, Italy, which had hitherto defined the basal boundary of both the Quaternary and the Pleistocene, remains available as the base of the Calabrian Stage/Age (now the second stage of the revised Pleistocene). In ratifying these proposals, the IUGS has acknowledged the distinctive qualities of the Quaternary by reaffirming it as a full system/period, correctly complied with the hierarchical requirements of the geological timescale by lowering the base of the Pleistocene to that of the Quaternary, and fully respected the historical and widespread current usage of both the terms 'Quaternary' and 'Pleistocene'.

Confused? Me too!

What that means is that earth history can be subdivided into geological time units like the Quaternary based on some natural break in earth conditions. That break should be one of geological significance and one which is easily recognizable all over the world. In this case that break is the beginnings of the global ice ages at around 2.58 Million years ago and it is best represented by the geological section in San Nicola Italy which is being used as the standard or type section. A type section contains a continuous sequence of rock / sediment spanning the break. The base of the new geological time unit can thus be clearly highlighted in the rock record at the type section.  Sections marking the beginnings of the ice age are found elsewhere too but it may be exceptionally well preserved at the type section.

Science Daily has the press release.


  1. The poor Pliocene! They just take more and more of it until there will be no Pliocene left....

  2. Now all we have to do is bring back the Primary and the Secondary! :)

  3. good thought Garry.

    hypocentre- yeah I've been wondering why the term Quaternary has stuck around for so long?!

  4. Thank You for the explanation in plain English!!!

  5. Good summary! And I keep wondering about the Pliocene, also.

  6. Silver Fox- we will have to await on the fate of the Pliocene. I guess nomenclature / classification of any kind is always contentious. Placing entities / objects in their natural order and hierarchy is fundamental to further efforts so these fields tend to be the most rancorous.