The International Chronostratigraphic Chart (ICC), as the basis of the International Geological Time Scale, is the primary product of the International Commission on Stratigraphy (ICS), itself the principal commission of the International Union of Geological Sciences (IUGS). The ICC represents a sustained and concerted effort by Earth scientists worldwide to produce a temporal correlation framework that is both informative and practical. As with the International Stratigraphic Guide (Hedberg 1976, Salvador 1994, Murphy et al. 2021) published by the ICS Subcommission on Stratigraphic Nomenclature (ISSC), the ICC is designed to serve the broad scientific community effectively and efficiently. Inspired by the model provided by the Committee on the Silurian-Devonian Boundary (McLaren et al. 1977), the ICS established rules to ensure a consistent and objective approach to scientific procedures in implementing a common chronostratigraphic language (Cowie et al. 1986, Remane et al. 1996). While these rules have encouraged discussion, openness, and objectivity, tensions remain in some areas where compromises have not yet been achieved. We review here one such case concerning the subdivisions of the Cenozoic Era into subseries/subepochs, in which strong opinions have hindered the integration of Cenozoic chronostratigraphy into the accepted standard. In light of long historical precedent, logical consistency with units in the Neogene and Quaternary Cenozoic systems/ periods, broad applicability across marine, terrestrial and transitional strata, and wide acceptance and use by the Cenozoic Earth Sciences community, it is clear that Paleogene subseries/subepochs should be included in the ICC.

A look back at the first contributors to this journal.

We define 17 African land mammal ages, or AFLMAs, covering the Cenozoic record of the Afro-arabian continent, the planet’s second largest land mass. While fossiliferous deposits are absent on the eroded plateau of the continent’s interior, almost 800 fossil genera from over 350 locations have now been identified in coastal deposits, karst caves, and in the Neogene rift valleys. Given a well-developed geochronologic framework, together with continuing revision to the fossil record—both stimulated by the story of human evolution in Africa—and also to compensate for the variation in fossil ecosystems across such great distances, the AFLMAs are biochronological units defined by type localities, and not biozones to be recognized by the occurrence of certain genera. Disparities are notable: Africa is the highest of all continents, but almost every Paleogene locality was formed at sea level; the fossil record of its great rainforest ecosystem remains virtually unknown; and the Paleogene fauna is relatively isolated, whereas the Neogene begins with open exchange with Laurasia following the Tauride collision, with a simultaneous opening of the East African rift valleys in which the newly revolutionized fauna is abundantly preserved. Notably, the continent-wide and comprehensive documentation of the African mammalian record reveals an unparalleled rate of transformation in the hominin lineage, unmatched by any other group, in response to the Neogene expansion of the open-country ecosystem.

The formal recognition of Quaternary as a Period/System was approved by JUGS in June 2009, in accordance with a proposal originated by INQUA. There are reasons to believe that this will have destabilizing consequences for the geological time scale. Until now, the primary divisions of the stratigraphic record, at the Period level and above, have been based on the progressive change of Earth's biota. The Quaternary, on the other hand, is a paleoclimatic concept based on glacial-interglacial variability, expressed in lithological change. The JUGS vote holds that this paradigm now supersedes the biochronological identity of the Neogene Period/System. Furthermore, to accomodate the most recent INQUA opinion about "when the Ice Ages began", the ICS agreed to relocate the base of the Pleistocene to 2.59 Ma from 1.81 Ma, enlarging the epoch by 43% and again without regard for its original paleontological definition, or for the vast literature in other fields of Pleistocene research. If history is a guide, the resulting disruption in late Cenozoic marine and vertebrate paleontology, human evolution, paleoceanography and paleoclimatology will be widely resisted, with potential impact on the authority of JUGS. The consequence of abandoning basic principles in order to satisfy the interest of a special group deserves a wider consideration than it has so far received.

It has been recommended that geological time be described in a single set of terms and according to metric or SI (“Système International d’Unités”) standards, to ensure “worldwide unification of measurement”. While any effort to improve communication in scientific research and writing is to be encouraged, we are also concerned that fundamental differences between date and duration, in the way that our profession expresses geological time, would be lost in such an oversimplified terminology. In addition, no precise value for ‘year’ in the SI base unit of second has been accepted by the international bodies.Under any circumstances, however, it remains the fact that geological dates – as points in time – are not relevant to the SI. Known dates may define durations, just as known durations may define dates, or dates may simply be punctual references that support historical narratives, but dates are not quantities. Furthermore, dates, as datum points, belong to a specific type of guiding information that is in constant use not only by the disciplines that explore the unwritten past, but in the physical sciences and engineering as well. Accordingly, we recommend a new standardization of the distinction between geohistorical date, in years before present expressed in ‘annus’, symbol ‘a’,with the multiples ‘ka’, ‘Ma’, and ‘Ga’ for thousands, millions and billions of years ago, according to a convention that has been very widely adopted during the last 30 years, and geohistorical duration, expressed in ‘year’, symbol ‘yr’, with multiples ‘kyr’, ‘Myr’ and ‘Gyr’, respectively, as the most appropriate among the various formats in the current literature. Agreement on these two sets of terms throughout the wide community that deals with paleochronology would remove a false impression of improvisation and uncertainty as to appropriate terminology, and would lead to more effective communication in areas where a simplified but needlessly SI-conisistent terminology would be less, not more useful.

Removing the Tertiary and Quaternary Periods whilst conserving the Paleogene and Neogene Periods in The Geological Timescale 2004 caused a storm of protest. One response was to advocate restoring an enlarged Quaternary and consigning the Neogene to a minor role within the Tertiary. Amongst an array of practical, traditional, sentimental and anthropocentric reasons for this response, the one hard-core justification was that the rigidly nested hierarchy of the geological timescale must be preserved.The central objective of this paper is conserving the historically legitimate, Miocene-present, Neogene Period and System. There are two options for conserving the Quaternary concurrently with the Neogene: (i) an inclusive compromise in a flexible hierarchy, and (ii) an upgrading of Pliocene and Pleistocene divisions to the level of epoch. In the inclusive compromise there coexist alternative pathways through the hierarchical ranks. Thus geohistorians and biohistorians have two options for traversing the hierarchy from era to age, as in this example using the hierarchical positioning of the Calabrian Age and Stage:either Cenozoic [era] <-> Neogene [period] <-> Pleistocene [epoch] <-> Calabrian [age],or Cenozoic [era] <-> Quaternary [subera] <-> Pleistocene [epoch] <-> Calabrian [age].We reaffirm that the inclusive compromise is entirely viable. In so doing we (i) challenge the necessity of the rigidly nested hierarchy, which should be capable of a little flexibility; (ii) reject all analogies of the arbitrary and conventional chronostratigraphic hierarchy with three natural biological hierarchies; (iii) reaffirm the integrity of the Neogene extending to the present; and (iv) see no reason to doubt the harmonious coexistence of the two options preserving the Quaternary and Neogene traditions in an orderly working and stable time scale.In the alternative schema conserving the Neogene, divisions of the Pliocene and Pleistocene are upgraded, so that the Late Pleistocene, Early Pleistocene and Late Pliocene Epochs comprise the Quaternary Subperiod, itself equivalent to Late Neogene. The inflexibly nested hierarchy is preserved but the Tertiary is lost. (C) 2009 Elsevier B.V. All rights reserved.

The International Commission on Stratigraphy (ICS) together with its subcommissions on Neogene Stratigraphy (SNS) and Quaternary Stratigraphy (SQS) are facing a persistent conundrum regarding the status of the Quaternary, and the implications for the Neogene System/Period and the Pleistocene Series/Epoch. The SQS, in seeking a formal role for the Quaternary in the standard time scale, has put forward reasons not only to truncate and redefine the Neogene in order to accommodate this unit as a third System/Period in the Cenozoic, but furthermore to shift the base of the Pleistocene to c. 2.6 Ma to conform to a new appreciation of when “Quaternary climates" began. The present authors, as members of SNS, support the well-established concept of a Neogene extending to the Recent, as well as the integrity of the Pleistocene according to its classical meaning, and have published arguments for workable options that avoid this conflict. In this paper, we return to the basic principles involved in the conversion of the essentially marine biostratigraphic/ biochronologic units of Lyell and other 19th-century stratigraphers into the modern hierarchical arrangement of chronostratigraphic units, embodied in the Global Standard Stratotype-section and Point (GSSP) formulation for boundary definitions. Seen in this light, an immediate problem arises from the fact that the Quaternary, either in its original sense as a state of consolidation or in the more common sense as a paleoclimatic entity, is conceptually different from a Lyellian unit, and that a Neogene/Quaternary boundary may therefore be a non sequitur. Secondly, as to retaining the base of the Pleistocene at 1.8 Ma, the basic hierarchical principles dictate that changing the boundary of any non-fundamental or “higher" chronostratigraphic unit is not possible without moving the boundary of its constituent fundamental unit. Therefore, to move the base of the Pleistocene, which is presently defined by the Calabrian GSSP at 1.8 Ma, to be identified with the Gelasian GSSP at 2.6 Ma, requires action to formally redefine the Gelasian as part of the Pleistocene. Finally, it is important to keep in mind that the subject under discussion is chronostratigraphy, not biostratigraphy. Both systems are based on the fossil record, but biostratigraphic units are created to subdivide and correlate stratigraphic sequences. The higher-level units of chronostratigraphy, however, were initially selected to reflect the history of life through geological time. The persistence of a characteristic biota in the face of environmental pressures during the last 23 my argues strongly for the concept of an undivided Neogene that extends to the present. Several ways to accommodate the Quaternary in the standard time scale can be envisaged that preserve the original concepts of the Neogene and Pleistocene. The option presently recommended by SNS, and most compatible with the SQS position, is to denominate the Quaternary as a subperiod/subsystem of the Neogene, decoupled from the Pleistocene so that its base can be identified with the Gelasian GSSP at c. 2.6 Ma. A second option is to retain strict hierarchy by restricting a Quaternary subperiod to the limits of the Pleistocene at 1.8 Ma. As a third option, the Quaternary could be a subera/suberathem or a supersystem/ superperiod, decoupled from the Neogene and thus with its base free to coincide with a convenient marker such as the base of the Pleistocene at 1.8 Ma, or to the Gelasian at 2.6 Ma, as opinions about paleoclimatology dictate. If no compromise can be reached within hierarchical chronostratigraphy, however, an alternative might be to consider Quaternary and Neogene as mutually exclusive categories (climatostratigraphic vs. chronostratigraphic) in historical geology. In this case, we would recommend the application of the principle of NOMA, or Non-Overlapping Magisteria, in the sense of the elegant essay by the late Stephen J. Gould (1999) on the mutually exclusive categories of Religion and Science. In this case the Quaternary would have its own independent status as a climatostratigraphic unit with its own subdivisions based on climatic criteria.

Early Miocene fossils from Rusinga Island, Kenya, provide some of the best evidence for catarrhine evolution and diversification, and, together with more than eighty-five other mammalian species, form an important comparative reference for understanding faunal succession in East Africa. While there is consensus over the stratigraphic position of most of Rusinga's volcaniclastic deposits, the lacustrine Kulu Formation has been placed in various parts of the geological sequence by different researchers. To resolve this discrepancy, we conducted detailed geological analyses which indicate that the Kulu Formation was formed in the Early Miocene during a period of volcanic inactivity and subsidence following the early, mainly explosive hyper-alkaline phase of the Kisingiri complex and prior to the final eruptions of nephelinitic lavas. The underlying Hiwegi and older formations were locally deformed and deeply eroded before sedimentation began in the Kulu basin, so that the Kulu sediments may be significantly younger than the 17.8Ma Hiwegi Formation and not much older than the overlying Kiangata Agglomerata-Lunene Lava series, loosely dated to ca. 15Ma. The overall similarities between Kulu and Hiwegi faunas imply long-term ecological stability in this region. Our stratigraphic interpretation suggests that the Kulu fauna is contemporaneous with faunas from West Turkana, implying that differences between these assemblages—particularly in the primate communities—reflect paleobiogeographic and/or paleocological differences. Finally, the position of the Kulu Formation restricts the time frame during which the substantial faunal turnover seen in the differences between the primate and mammalian communities of Rusinga and Maboko Islands could have occurred.

In 2004, the Quaternary was deliberately eliminated as a formal chronostratigraphic unit from the standard Geological Time Scale (GTS) while the Neogene extended to the Recent. This extended Neogene was not a spontaneous undertaking by the Neogene community. It is rooted in a strong and long-standing tradition in the study of especially the marine stratigraphic record.The original definition of the Neogene by Hornes in 1853 included stratigraphic units that are now considered middle Pleistocene in age, but is ambiguous with regard to its upper limit. Nevertheless the concept of an extended Neogene was incorporated in a number of time scales but was not widely employed until it was firmly adopted by marine stratigraphers when they started to explore the deep marine record of the Cenozoic in the middle of the 20(th) century.As such the extended Neogene is found in the original codification and subsequent modifications of all standard microfossil zonal schemes with N(eogene) zones continuing up to the Recent. Moreover the extended Neogene was generally accepted by the DSDP and ODP community and incorporated in widely used integrated - magnetobiochronostratigraphic - time scales and in prominent textbooks dealing with Earth history. It has been likewise accepted by vertebrate paleontologists. The concept of an extended Neogene also stood at the base of the recommendations for defining the Pliocene/Pleistocene (= Tertiary/Quatemary) boundary that originated from the 1948 International Geological Congress (IGC) in London.The continuous deep marine archive is most suitable for the formal definition of global chronostratigraphic units to be incorporated in the standard GTS. Clearly this marine standard is pre-eminently exemplified by the Neogene but is at odds with the dominantly continental-based Quaternary. In fact, the detailed study of the marine Neogene has revolutionized chronostratigraphic thinking during the last several decades. It has led to a stable astronomical-tuned Neogene time scale with a fully integrated magnetobiochronostratigraphic framework via first-order correlations. This innovative approach further resulted in re-emphasizing the usefulness of the unit stratotype concept, in the potential introduction of orbital controlled cycles as formal chronostratigraphic units of minor rank (chronozones) and in the inter-calibration of astronomical and radio-isotopic time. For all these reasons, the term Neogene should remain attached to the extended concept of 23-0 Ma. Furthermore, if nomenclature reflects geological thinking, understanding and practice of Earth history, the truncation of the Neogene at 2.6 Ma would introduce an artificial division, especially when looking from the marine perspective. This would prevent scientific communities who deal with Earth history beyond the last 2.6 myr from correctly expressing the continuity of the evolutionary, oceanographic, climatic, and tectonic dynamics over the last 23 my.

The GSSP for the base of the Eocene Series is located at 1.58 m above the base of Section DBH in the Dababiya Quarry, on the east bank of the Nile River, about 35 km south of Luxor, Egypt. It is the base of Bed I of the Dababyia Quarry Beds of the El Mahmiya Member of the Esna Formation, interpreted as having recorded the basal inflection of the carbon isotope excursion (CIE), a prominent (3 to 5%) geochemical signature which is recorded in marine (deep and shallow) and terrestrial settings around the world. The Paleocene/Eocene boundary is thus truly a globally correlatable chronostratigraphic level. It may be correlated also on the basis of 1) the mass extinction of abyssal and bathyal benthic foraminifera (Stensioina beccariiformis microfauna), and reflected at shallower depths by a minor event; 2) the transient occurrence of the excursion taxa among the Planktonic foraminifera (Acarinina africana, A. sibaiyaensis, Morozovella allisonensis); 3) the transient occurrence of the Rhomboaster spp. - Discoaster araneus (RD) assemblage; 4) an acme of the dinoflagellate Apectodinium complex. The GSSP-defined Paleocene/Eocene boundary is approximately 0.8 my older than the base of the standard Eocene Series as defined by the Ypresian Stage in epicontinental northwestern Europe.

The advances in information handling that are made possible by digitization force us to consider whether the existing procedures for updating and using the standard Geological Time Scale, based on printed books, may be obsolete. Not only does print publishing require expensive investment, but the publication process imposes limits on participation and distribution, as well as setting a deadline on improvement. In addition, digitization means that the way we use the information is no longer limited to what can be done with glyphs on paper. In this report we consider some aspects of the inevitable migration of the Geological Time Scale (GTS) into digitized formats. On one hand we envisage the organization and design of a dynamically interactive, community-based consensus GTS on the internet, in open public access for worldwide use. On the other hand, the complete dataset from the last published time scale, the “GTS2004” (Gradstein, Ogg and Smith 2004a) is already available in digital form, and has been used to generate custom visualizations in TimeScale Creator, a machine resident application. The migration of the GTS2004 dataset to the internet, as the basis for a community consensus GTS, would greatly facilitate the improvement of the dataset through user interaction. It would also transform the Geological Time Scale from a shelf reference, or a computer program, to an integrated worldwide resource in geoscience research, education, and public programming.

The long controversy over the term ‘Quaternary' as a chronostratigraphic unit may be reaching an apotheosis, judging from recent papers (Pillans and Naish, 2004; Gibbard et al., 2005; and referencest herein). The debate is no longer centered on whether there should be a place in the geological time scale for a unit termed ‘Quaternary'-despite its dubious past, it cannot be denied that a large body of earth-historical research is strongly identified with this term. The challenge now concerns an appropriate rank and definition of Quaternary with regard to other chronostratigraphic units. Several options have been proposed (Pillans and Naish, 2004), and Gibbard et al. (2005) encourage a debate on these before decision is reached. In this brief note, we describe an arrangement not previously considered that seems advantageous. It is instructive, however, to first review the Pleistocene Series and Neogene System, the two units that are directly affected by introduction of the Quaternary into the chronostratigraphic hierarchy.