On the Quaternary

The word 'Quaternary' is commonly used to indicate a youngest period of geological time (ending with the present), that saw severe climatic oscillations between glacials (ice-ages) and interglacials. As such, the Quaternary is also used in formal stratigraphic terminology, at SUBERA hierarchical level. Formal stratigraphy requires it to have a defined basal point in the geological rock-record (a type section) somewhere in the world. Traditionally it includes the Holocene and Pleistocene Series, that have their own defined basal points [called GSSP's, see the ICS site www.stratigraphy.org; see the SQS site www.quaternary.stratigraphy.org.uk ].

As knowledge on the Quaternary period and the preceding Tertiary increased during the 20th century, it was realised that the global ice-ages mainly reflect glaciation/deglaciation cycles at the northern hemisphere (North America, Greenland, Northerly Europe, Alps). The classic ice ages from Europe and America, are now known to comprise ~10 glacial-interglacial cycles of each roughly 100-ka length, a situation that set on about 1 million years ago. Before this time, glaciations were less severe, but nevertheless, there were several episodes of incidental widespread glaciation, e.g. around ~1.8 and around ~2.5 million years ago.

Formal status (dd. January 2010)

Based on the above facts, several lines of reasoning compete and have lead to alternative definitions for the base of the Pleistocene and the base of the Quaternary. Sharp debate on this topic is very much ongoing and involves the organisations INQUA (its commission on Statigraphy and Geochronology) and IUGS (its International Commission on Stratigraphy). Both organisations are keen to put formal use of stratigraphy on the agenda. When the IUGS abandoned the Tertiary as a formal stratigraphic term (replaced by Paleogene and Neogene), this flagged the Quaternary as remaining 'anachronistic' terminology. Hence, the Neogene was proposed to subhume the Quaternary (in 2003-2005). By many in the Quaternary community however, such is seen as an attack on their identity. Also from a pragmatic viewpoint, it would harm to drop widely known terminology, especially for terrestrial geology and climate change research communities. Hence, with hindsight, in 2006 the IUGS has stated it has not dropped the term Quaternary, and that it no longer intended to do so. INQUA and IUGS(ICS) remained in the process to formally redefine the stratigraphical status, preparing votings on INQUA and IUGS congresses. In 2009 the base of the base Quaternary = base Pleistocene at 2.6 Ma was formally ratified. Details here.

Daily practice

In practice [e.g. legends of official geological maps, common use in academic publications] the base of the Quaternary and the base of the Pleistocene has been put at ~1.8 and at ~2.6 Ma, depending on what country one lives in, in what subdiscipline/institute one received academic training (terrestrial, marine, palynology, computer modelling, physics), and how formal-aware one is when applying terminology from stratigraphy. Focus and scope differ between disciplines and this extends to viewpoints on stratigraphy. If one is interested in long term climate oscillation as recorded in deep sea sediments and fossils therein, the Quaternary and Upper Tertiary do not differ that much and what difference is there develops gradually, justifying to see Tertiary and Quaternary as a continuum (Neogene). If one is interested in spreads of sand and gravel mapped across terrestrial Europe and fossils and artefacts therein, the areal preservation effect makes the Quaternary stand out considerably and justifies to see it as a seperate unit (base Pleistocene at 2.6 Ma). Compromised terminology such as Plio-Pleistocene and Plio-Quaternary has also been used. References to absolute dating and/or marine isotope stages usually clarify what exactly is meant, but in principle the status of the base of the Quaternary ought be properly defined.

In the Netherlands, terrestrial geologists and the National Geological Survey put the base at ~2.6, whereas marine geologists working at the Tertiary/Quaternary transition prefer the term Neogene and within the Neogene have the Pliocene/Pleistocene boundary at ~1.8. The latter was long the formal base of the Pleistocene, following a London 1948 IUGS congress vote.

In 2007 the IUGS' ICS has voted to (re)define the Quaternary to begin at 2.6 Ma. It is to subhume the Gelasian stage (2.6-1.8 Ma - which had been the uppermost Pliocene before) ) into the Pleistocene so that the base Pleistocene equals base Quaternary. INQUA discussed this at their Cairns conference in 2007, and IUGS' ICS discussed it in 2008 at the IGC conference in Oslo and ratified the descision in 2009.

The paragraphs below, on a Quaternary redefinition proposal and polling in 2006, are kept here for archiving reasons only.

INQUA-NL response on 2004-2006 redefinition polls

In an attempt to settle the stratigraphic position, in 2006 it was proposed to formalise parrallel usage of the terms Quaternary and Tertiary (at SUBERA level) and Neogene - Paleogene (at SYSTEM level); with the Tertiairy-Quaternary boundary at ~2.5 Ma, and the Neogene running from base Miocene towards the present (thus extending it to the slot of the Quaternary system). This would abandon the linkage of base Pleistocene = base Quaternary. This would bring back 'Tertiary' in official terminology. This would not change anything in the status quo regarding the official ~1.8 and unofficial alternative usage of ~2.5 for the base of the Pleistocene. Through various journals, INQUA called its national members to respond to this proposal. In practice, the proposal offers workers the simple choice to use 'Upper Neogene (last 5 Ma)' or 'Quaternary (last 2.5 Ma) ' or 'Pleistocene (last 1.8 Ma)' to define the period they are working on, depending on how far back in time their stories go. The Quaternary subera would be the first subera that has its basal boundary conincide with a subseries/stage (Gelasian, within the Upper Pliocene), instead of a series (Pleistocene). This could be seen as inconsistency, and there was fear that the subera hierarchical level in practice would be scapegoated in stratigraphic tables that try to capture the full range of geological time. Considering the above, the INQUA-Netherlands committee replied with > THIS LETTER <.

From: INQUA Committee The Netherlands
Date: Leiden, 17 February, 2006

Dear Colleagues,

The board of the INQUA Committee The Netherlands (8 members) discussed, during their meeting of the 1st of February 2006, the issue about the status of the Quaternary in the new Geological Time Scale (GTS). We discussed in particular the proposal communicated by the President of INQUA with the following definition of the Quaternary: the Quaternary is a Sub-Erathem/Sub-Era correlative with the upper part of the Neogene System/Period and with a lower boundary coincident with the base of the Gelasian Stage (2.6 Ma).

The board is unanimously in its desire to keep Quaternary as a formal unit with a clear definition and a clear status. Important is also that Quaternary should be included and visible in stratigraphical charts and geological timetables. The members of the board are of the opinion that it is most important to end the ongoing debate and to come to a final decision. To postpone the discussion to the 2007 INQUA Congress is no option for the majority of the board members. A requirement is, however, that the final decision will be supported by a vast majority of the scientific community. If that requirement can be fulfilled and the debate can come to an end by accepting the proposal put forward by the President of INQUA, the majority (5 of 8 members) supports the proposal for a definition of the Quaternary as given above and to eliminate the Quaternary as a System/Period. However, for three out of eight members this is not acceptable.

In a country such as the Netherlands it is often the majority that decides and in this case the majority supports INQUA�s proposal. We realise that the issue is a difficult one and whatever will be decided before the INQUA meeting in 2007, we think it is important to use the 2007 INQUA congress to create support for the decision.

Yours sincerely

Thijs van Kolfschoten

For further information, background, debate-history etc. see: www.quaternary.stratigraphy.org.uk

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