Current official status of Quaternary on International Stratigraphic Chart

Posted by James Ogg 16 Jul 2004 13:02:40

15 July 2004
(This was an attachment sent to all individuals who forwarded messages to ICS in response to John Clague's appeal for input. It was suggested that I should post a version on this discussion site.)

Dear Quaternary stratigraphers and others interested in divisions of Cenozoic,

Thank you for the flood of well-presented arguments and concerns about re-instating Quaternary as an official unit of the international geologic time scale.
I have assembled portions of your comments into a compact document to indicate both the unity and the diversity of opinions. Felix Gradstein, the ICS chair, is at sea until 5 August, and I will forward the summary to him.

Several of your comments seem to implicitly assume that the “Quaternary” was a formal unit of the international geological time scale, and that the ICS had taken a sudden unilateral decision to remove it. Therefore, we would like to clarify the status according to decisions made during 1983-1985, and re-confirmed in 1998 by special joint ICS-INQUA working groups to establish the base-Pleistocene GSSP. The International Stratigraphic Chart reflects these decisions, which were made before the present ICS chairs and other officers were selected.

The definition and status, if any, of the “Quaternary” had been left in limbo for 20 years after the statement by the joint working group -- Please note the important phrase below:

From Aguirre, E. and Pasini, G., 1985:
This base-Pleistocene GSSP boundary ratification is “isolated from other more or less related problems, such as … the status of the Quaternary within the chronostratigraphic scale”
(excerpt from: The Pliocene-Pleistocene boundary. Episodes, 8: 116-120 = official publication by the special joint INQUA-ICS working group of the base-Pleistocene GSSP decision)

There are two relevant points concerning the Neogene and the Quaternary which do not appear to be widely known:

1. Base-Pleistocene GSSP did NOT define the base of the Quaternary
The decision by the joint INQUA-ICS working group to assign the GSSP at Vrica in Sicily for the base of the Pleistocene near the top of the Olduvai subchron (1.8 Ma) was ratified by IUGS in 1983. This working group had specifically omitted any indication that the base of the “Quaternary” concept would coincide with the base of the Pleistocene.
In 1998, another joint ICS-INQUA working group debated lowering the base-Pleistocene to about 2.6 Ma (and to another geographic location). The Vrica GSSP was upheld by a majority. As in 1983, the official voting documents did not mention “base-Quaternary”. Indeed, it seemed from the supplementary document package that accompanied the voting that a number of members of INQUA did not want a base-“Quaternary” defined as at the ratified and re-confirmed base-Pleistocene level. Therefore, neither of the GSSP ratifications and publications indicates that the base-Pleistocene should be synonymous with a base-Quaternary.

2. Cenozoic currently has only two defined periods – Neogene & Paleogene
When the “Tertiary-Quaternary” periods of the Cenozoic were replaced by the “Paleogene-Neogene” periods, there was no indication that there would be a “Neogene-Quaternary” boundary. The 1983/1985/1998 decisions by the ICS/INQUA boundary committees to omit any decision on “the status of Quaternary within the chronostratigraphic scale” (as quoted at top of this page) seemed to validate the Neogene/Paleogene division of the Cenozoic. According to the Neogene concept – both historic usage and current concept – the Neogene period extends to the present. The boundary between Neogene and Paleogene periods/systems is defined and ratified by the base-Miocene GSSP.

Importance of Brad Pillan’s proposal
According to the 1983-1985 decisions (and reconfirmation in 1998), the “Quaternary” is neither defined, nor has an official chronostratigraphic status.
Brad Pillan’s proposal seeks to rectify both issues – (1) defining the span and lower boundary of Quaternary (which will overlap the upper third of the Pliocene Epoch), and (2) proposing that it be a unique “sub-period” within the Neogene. The latter chronostratigraphic classification is somewhat analogous to the international compromise that divided the Carboniferous period into the sub-periods of Mississippian and Pennsylvanian.

Sincerely,
James Ogg
Secretary-General (appointed in 2000)
International Commission on Stratigraphy of IUGS

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Some other comments (as James Ogg, not the ICS secretary):

Usage of alternative chronostratigraphic terms, even those with accepted definitions, is quite common in literature and regional geologic maps, but these are not part of the ratified International Stratigraphic Chart. Examples include “Emsian”, “Tertiary”, “Neocomian”, “Volgian”, “Portlandian”, “Westphalian”, “Ashgill”, “Cincinnatian” and “Hadean”; and I just finished editing a listing of nearly 200 such terms for the American Geological Institute dictionary.
However, in contrast to these other terms, it seems that the term “Quaternary” generates a more widespread demand for formalization and inclusion in some form on the International Stratigraphic Chart. Deciding on its formal definition (lower boundary, span) should be the duty of INQUA. Deciding among options of assigning a formal chronostratigraphic rank, if any, to “Quaternary” should be a joint voting and recommendation by INQUA and ICS, which would then be submitted to IUGS for potential ratification.

At present, it seems that there are two usages of “Quaternary” – one is exactly equivalent to the Holocene and Pleistocene epochs, the other version includes the upper third of the Pliocene epoch. According to the Stratigraphic Guide principles of hierarchy, a higher-rank unit should not cut across formalized and ratified lower-rank units. There is no problem defining Quaternary to span a larger interval. However, if an expanded “Quaternary” definition is also to become a formal chronostratigraphic unit within the Cenozoic hierarchy, then either that principle in the Stratigraphic Guide would need to be revised through international agreement, or the definitions of Pliocene and Pleistocene that are engrained in the literature of the past 20 years would need to be adjusted (50% expansion of Pleistocene Epoch, 25% reduction of Pliocene Epoch). It should be noted that the definition of the Pleistocene Epoch was re-confirmed by ICS/IUGS in 1998, during a voting process that also involved equal participation of INQUA. At this point, the ICS executive is reluctant to again re-open that volatile epoch boundary debate, but would prefer that emphasis be placed on achieving formal subdivision of the remaining Cenozoic stages and epochs (e.g., the Holocene is the only Cenozoic epoch that lacks a formal definition).

It seems appropriate for INQUA, not ICS, to officially propose: (1) a formal definition for the span of the Quaternary, and separately, (2) preferred ordering of options for the rank of such a Quaternary within the chronostratigraphic scale. Note that this Quaternary discussion should also receive advice from the geologic surveys of different nations, because a formal definition for Quaternary (as opposed to its present vague usage by many field geologists) has major implications for the units on geologic maps.
Then, it will be the role for ICS members to vote and advise IUGS on both aspects (lower boundary, chronostratigraphic rank). The IUGS would make the formal decision (presumably in collaboration with INQUA) on the divisions of the Cenozoic portion of the International Stratigraphic Chart.

Sincerely,
Jim Ogg

P.S. – At the Florence IGC, there will be an open official ICS meeting that will discuss many issues of the International Stratigraphic Chart, including the Quaternary. This meeting (listed as a workshop in order to have a longer block of time) will be on Thursday, 26 August. The current agenda plans an open discussion of Quaternary and possible procedures for an INQUA-ICS-IUGS decision process.