1 - Introduction

1The Quaternary is youngest in a four-cycle division of earth history proposed by G. Arduino in 1759 (Arduino, 1760). Although he never used the term “quaternario”, referring instead to his “fourth order” (Schneer 1969; Ellenberger 1994, p. 261; Vaccari, 2006), his concept was reinvoked by J. Desnoyers (1829) to encompass Tertiaire récent, and finally defined by H. Raboul (1833, p. 1-2) as “la période dont les terrains sont caractérisés par les espèces animales et végétales semblables aux êtres actuellement vivants dans les mêmes lieux”. This term has continued in use to the present day. Until the events reported here, the official status of the Quaternary was that of period/system with a base at 1.8 Ma (Cowie & Bassett, 1989; Remane, 2000; Head, Gibbard & Salvador, 2008a, Fig. 1B). Nonetheless, the Quaternary was omitted from the influential time scale of Gradstein et al. (2004, Fig. 1A) because, they argued, the term represented an outdated concept. This action immediately sparked vigorous debate about the nature, duration and chronostratigraphical status of the Quaternary. Indeed, the recent time scales of Gradstein et al. (2004, 2005), while officially sanctioned by neither the International Commission on Stratigraphy (ICS) nor the Inter-national Union of Geological Sciences (IUGS), have stimulated productive discussions about the status of the Quaternary, and indeed its equally legitimate sister, the Tertiary.

2Recent proposals regarding the status of the Quaternary have included treating it as an informal chronostratigraphic unit, and formally as a sub-period, period, or subera (see Pillans and Naish, 2004; Gibbard et al., 2005; Aubry et al., 2005; Walsh, 2006; Bowen and Gibbard, 2007; and Pillans, 2007 for reviews). Objections to its classification as an informal term include its precise, formal and widespread use in the literature and among technological as well as scientific communities (Salvador, 2006a, b). Claims based on historical interpretation that the Neogene Period should extend to the present day, thereby rendering the term Quaternary superfluous (e.g., Berggren, 1998; Aubry et al., 2005; Lourens et al., 2005), have been refuted (Walsh, 2006, 2008). Proposals for both sub-era and sub-period status denied the Quaternary its ubiquitous usage, and failed to respect the hierarchical nature of the stratigraphic time scale, when adopting a 2.6 Ma inception for the Quaternary.

3Following the largest survey of researchers’opinions ever undertaken, the International Union for Quaternary Research (INQUA) jointly with SQS, in March 2006 notified the ICS of its requirements: that the Quaternary be of period status with its base at the GSSP of the Gelasian Stage (2.6 Ma), and that the base of the Pleistocene should also be lowered from 1.8 Ma to coincide with that of the Quaternary. In May 2007, the ICS voted in favour of the INQUA proposal, but the International Union of Geological Sciences (IUGS), while approving the ICS’s request to accept the Quaternary as a formal period, noted in correspondence to the ICS (in May 2007) that the base of the Pleistocene could not be moved until a 10-year moratorium had expired (in January 2009). This had come about because the IUGS (but not the ICS) had voted in January 1999 to uphold the base-Pleistocene GSSP after a joint Quaternary-Neogene task group reconsidering the level of the Pliocene-Pleistocene boundary was unable to reach a supermajority (60 %) recommendation (Remane and Michelsen, 1998). The IUGS imposed a 10-year moratorium on the earlier base-Pleistocene decision, thereby delaying further consideration of a definition for the Quaternary and associated shifting of the Gelasian Stage to the Pleistocene until after January 2009. This was the situation before the most recent voting round that was completed on 22 May 2009.

4A difficulty that hindered all discussions concerning the definition and duration of the Quaternary has been the 1985 decision to place the Pliocene-Pleistocene boundary near the top of the Olduvai Subchron. This boundary, dated astronomically at 1.806 Ma (Lourens et al., 2005), was defined by a global stratotype section and point (GSSP) at Vrica in Calabria, south-eastern Italy (Aguirre and Pasini, 1985; Cita, 2008), and reaffirmed by the IUGS in 1999 in spite of numerous objections (Partridge, 1997; Suc et al., 1997; Gibbard et al., 2005; Bowen and Gibbard, 2007). Among these was that funda-mental geological changes did not take place at or even near the chosen boundary. Indeed, some of the so-called “northern guests”, cold-tolerant migrants into the Mediterranean used as indicators of cooling at the boundary (Aguirre and Pasini, 1985), have since been found to have arrived in the Mediterranean earlier than 1.8 Ma (e.g. Aiello et al., 1996): an age of c. 2.5-2.7 Ma is more appropriate (e.g. Suc et al., 1997). It is now well known that major cooling events in the Mediterranean occurred between about 2.8 and 2.5 Ma (e.g. Versteegh, 1997; Monegatti and Raffi, 2001; Roveri and Taviani, 2003), which coincide with the widely agreed base of the Quaternary.

5This was the basis for the repeated and longstanding demands from the Quaternary community for lowering the basal boundary of both the Quaternary and the Pleistocene when the current round of discussions were initiated at the 33^rd International Geological Congress (IGC) held in Oslo, August 2008. There was overwhelming support for the Quaternary to be recognised as a full period/system extending from 2.6 Ma to the present day, and that the base of the Pleistocene be lowered to that of the Quaternary in order to maintain hierarchy (Ogg and Pillans, 2008; Head et al. 2008a).

2 - Base of the Quaternary

6While the Quaternary is generally characterised by widespread Northern Hemisphere mid-latitude glaciation, cooling was both global and episodic. Multiple major cooling phases occurred between 2.8 and 2.4 Ma (MIS G10 to MIS 96), and their expression varied according to region (North Atlantic ice-rafted debris at 2.74 Ma, loess-palaeosol accumulation in China at 2.6 Ma, severe cooling in NW Europe at 2.54 Ma, incoming sub-Antarctic molluscs to Wanganui Basin in New Zealand at 2.4 Ma [Pillans and Naish, 2004]). No single global event emerges as triggering the change. Given that boundaries must be recognised unambiguously and widely, it was noted that the Gauss-Matuyama polarity boundary at 2.581 Ma (or 2.610 Ma, with a transition of 1.5 kyr, according to Deino et al., 2006), falls near the mid-point of this interval of global cooling. The base of the Gelasian Stage, defined by a GSSP at Monte San Nicola in Sicily, has an astrochronological age of 2.588 Ma. It corresponds to MIS 103 and is located about 1 m (20 kyrs) above the Gauss-Matuyama boundary (Rio et al., 1998). Given the close proximity of this existing GSSP to the Gauss-Matuyama boundary, and its calibration to the astrochronological time scale, the base-Gelasian GSSP is evidently well characterised also to define the base of the Quaternary.

3 - Formal proposals

7Following public discussions at the Oslo IGC in 2008, the incoming ICS President, Stanley Finney, asked each of the competing proponents, the Subcommissions of Quaternary and Neogene Stratigraphy (SQS, SNS) to submit formal proposals on which the ICS voting membership could comment and ultimately vote.

8The “formal request to ICS that the base of the Quaternary System/Period be lowered to the Gelasian Stage GSSP (at 2.588 Ma), and that the base of the Pleistocene Series be lowered to the same position”, submitted by Philip Gibbard & Martin J. Head on 1 September 2008 on behalf of the Subcommission on Quaternary Stratig-raphy is given in Box 1 and Fig. 1.

9A competing proposal was submitted on behalf of the Neogene Subcommission by Frits Hilgen in November, 2008 which effectively split the Pliocene Series into two parts: a Lower Pliocene Series that was excluded from the Quaternary, and an Upper Pliocene Series included within a Quaternary Subperiod (Box 2: Fig. 2A).

10Curiously the “Neogene” proposal reinvoked a request already rejected by the IUGS in May 2007 since it suggested that the Quaternary be classified as a subdivision of the Neogene Period. An alternative proposal advanced by the Neogene community (Aubry et al., in press; Fig. 2B) assigned the Quaternary as Sub-erathem/Sub-era, although this proposal was ulti-mately not included in the vote. Both proposals (Fig. 2A and B) show the Neogene Period extending to the present day. Yet more surprisingly, the SNS on the 20^th March 2009, just days before ICS voting was due to commence, asked to withdraw its proposal(s) in favour of one that excluded the Quaternary completely, essentially returning to the proposal of Gradstein et al. (2004; Fig. 1A). In view of the short notice given, this request was not granted. However, it is probable that any of the SNS Neogene proposals, had they been accepted by the ICS membership, would have been rejected by IUGS, further delaying final settlement of the controversy.

11Following submission of these proposals, they, together with supporting documentation (a total of 27 documents), were circulated to the ICS voting membership (comprising 18 individuals, the chairs of the subcommis-sions and the ICS officers). The full documentation can be viewed on the ICS (www.stratigraphy.org) and SQS (www.quaternary. stratigraphy.org.uk) websites.

4 - Recommendation

12In the “Quaternary” proposal, the Quaternary Period/System, Pleistocene Epoch/Series, and Gelasian Age/Stage share the same GSSP at the base-Gelasian, which is dated at 2.588 Ma. The Holocene had already been regarded officially as an epoch distinct from the Pleistocene, in recognition of the fundamental impact made by modern humans on an otherwise unremarkable interglacial (Walker et al., 2008, 2009). Consequently the terms Pleistocene and Quaternary are both essential. However, on hierarchical considerations, the ICS supported SQS’s and INQUA’s recommendation to lower the Plio-Pleistocene boundary while accepting that the Vrica GSSP continues to define the base of the Calabrian Stage (Cita et al., 2008). The SQS accepted the Gelasian Stage as a useful and already familiar term, and by extension generally supports use of the provisional large-scale (“super-”) stages Calabrian, Ionian, and Tarantian (Cita et al., 2006, 2008; Cita, 2008). The proposed scheme (Fig. 1C) met INQUA requirements, obeyed the principles of a hierarchical time scale, and respected historical precedents and established usage for the term Quaternary.

5 - Voting

13The first-round ballot was sent out on 23 March 2009 with 30 days allowed for voting. The first ballot listed the “status quo” (i.e. the Quaternary /Pleistocene defined at 1.8 Ma), “Quaternary”, and “Neogene” proposals to which each voting member was required to vote yes, no, or abstain on each proposal. Those proposals receiving a majority of affirmative votes on the ballots submitted, if more than one, were to be listed on a second-round ballot.

14In the second round of voting, each member was directed to vote in favour of only one of the proposals or to abstain. The proposal receiving the majority of votes would then be subject to a third-round ballot on which there would be only one proposal, if necessary. For the proposal that then received at least a 60 % majority of “yes” votes, a formal decision will have been made, and it would be forwarded to the IUGS for formal ratification.

15If only one proposal received a majority of “yes” votes on the first round, then it would stand alone on a second-round ballot for approval by a 60 % majority (S. Finney, written communication 23 March, 2009).

16The results of the first ballot were announced on 22 April and are given in Table 1. Only the Quaternary proposal received a majority of affirmative votes, causing the ballot for the second round of voting to include only the Quaternary proposal. It needed to receive at least a 60 % majority of “yes” votes among the ballots submitted for it to be approved by ICS and

17Table 1. Results of the first round of voting by ICS members. All ballots received and votes compiled on 22 April, 2009 by S. Finney. The Quater-nary proposal received a 72 % majority of “yes” votes. The “Status Quo” and “Neogene” proposals failed to receive a majority of “yes” votes. Therefore, the second round of voting included only the “Quaternary” proposal. Abbreviations: Sec. Gen = Secretary General; Strat. Classif. = Stratigraphic Classification; Strat. Inf. Serv. = Stratigraphic Information Service.

18Tableau 1 : Résultats du vote des membres de l’ICS du premier scrutin. Tous les bulletins ont été reçus et dépouillés par S. Finney le 22 Avril 2009. La proposition des quaternaristes a été approuvée à la majorité avec 72 % de votes favorables. Les propositions du « Statu Quo » et du Néogène n’ont pas été créditées d’un vote majoritaire favorable. En conséquence le deuxième tour de scrutin a porté seulement sur la proposition des quaternaristes. Abréviations : Sec. Gen = Secrétariat Général ; Strat. Classif. = Classification Stratigraphique ; Strat. Inf. Serv. = Service d’Information Strati-graphique.

19Table 2. Results of the second round of voting by ICS members. All ballots received and votes compiled on 22 May, 2009 by S. Finney. The “Quaternary” proposal was approved by an 89 % majority “yes” vote.

20Tableau 2 : Résultats du second tour de scrutin des membres de l'ICS. Tous les bulletins ont été reçus et dépouillés par S. Finney le 22 avril 2009. La proposition des quaternaristes a été approuvée à la majorité avec 89 % de votes favorables.

21forwarded to the IUGS Executive Committee for ratifica-tion. A deadline of 22 May 2009 was set for the return of second-round ballots (S. Finney, written communication, 22 April, 2009).

22The results of the second ballot were announced on 20 May and are given in Table 2. S. Finney (written communication, 21 May, 2009) commented “The Quaternary proposal was approved by an 89 % majority yes vote. The Quaternary proposal will now be forwarded to the IUGS Executive Committee for ratifica-tion.” Ratification is the final stage in the process. Once the proposal has been ratified by the IUGS Executive Committee, the definition is finally officially accepted. There can be no modification of this decision and there is a moratorium on changes or challenges to the definition of 10 years (i.e. January 2019).

23ACKNOWLEDGEMENTS

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