On January 17, 2020, the Executive Committee of the International Union of Geological Sciences on January 17, 2020 ratified the Global Boundary Stratotype Section and Point (GSSP) defining the base of the Chibanian Stage/Age and Middle Pleistocene Subseries/Subepoch at the Chiba section of the Chiba composite section, Japan. The Chiba composite section is a continuous and expanded marine sedimentary succession in the east-central Japanese archipelago facing the Pacific Ocean. It contains well-preserved pollen, marine micro- and macrofossils, a tightly-defined Matuyama–Brunhes (M–B) paleomagnetic polarity boundary, two geomagnetic field paleointensity proxies, and numerous tephra beds, allowing the establishment of a robust and precise chronostratigraphic framework. Its open-ocean continental slope setting has captured both terrestrial and marine environmental signals from upper Marine Isotope Stage (MIS) 20 to lower MIS 18. The M–B reversal serves as the primary guide for the Lower–Middle Pleistocene boundary, yielding an astronomical age of 772.9 ka. The GSSP is positioned 1.1 m below the directional midpoint of the reversal, at the base of a regional lithostratigraphic marker, the Ontake-Byakubi-E (Byk-E) tephra bed, in the Chiba section. The GSSP has an astronomical age of 774.1 ka and occurs immediately below the top of Marine Isotope Substage 19c (Suganuma et al., 2021, Episodes, online).
On 30th January, 2020, the Executive Committee of the International Union of Geological Sciences ratified two proposals approved by the International Commission on Stratigraphy formalizing: 1) the Lower Pleistocene Subseries, comprising the Gelasian Stage and the superjacent Calabrian Stage, with a base defined by the GSSP for the Gelasian Stage, the Pleistocene Series, and the Quaternary System, and currently dated at 2.58 Ma; and 2) the term Upper Pleistocene, at the rank of subseries, with a base currently undefined but provisionally dated at ~129 ka (Head, Pillans & Zalasiewicz, 2021, Episodes, online). The Middle Pleistocene Subseries is defined by the recently ratified GSSP for the Chibanian Stage currently dated at 0.774 Ma (Suganuma et al., 2021, Episodes, online; and see above). These ratifications complete the official division of the Pleistocene into three subseries/ subepochs, in uniformity with the similarly subdivided Holocene Series/Epoch. The Upper Pleistocene Subseries is an official ratified term but its base is presently undefined. Historically, this base aligns approximately with the base of Marine Isotope Substage 5e. The definition of the base of Upper Pleistocene Subseries and its corresponding stage by GSSP is now a priority of the SQS.
On June 14, 2018, the Executive Committee of the International Union of Geological Sciences (IUGS) ratified the subdivision of the Holocene Series/Epoch as follows:
Lower/Early Holocene Subseries/Subepoch = Greenlandian Stage/Age with a base dated at 11,700 years b2k (before 2000 AD). GSSP = NGRIP2 Greenland ice core.
Middle Holocene Subseries/Subepoch = Northgrippian Stage/Age with a base dated at 8236 years b2k. GSSP = NGRIP1 Greenland ice core.
Upper/Late Holocene Subseries/Subepoch = Meghalayan Stage/Age with a base dated at 4250 years b2k. GSSP = a speleothem (specifically a stalagmite) from Mawmluh Cave, Meghalaya, northeast India.
Full details are published in Walker et al. (2018 online) in the IUGS journal Episodes, available here.
The above subdivision has no bearing on the Anthropocene, which remains an undefined unit under active investigation by the SQS Anthropocene Working Group.
ACKNOWLEDGEMENTS: These definitions originate with an initiative by Phil Gibbard (then Chair of SQS) in 2010 to establish a joint SQS/INQUA Working Group to examine the case for formal subdivision of the Holocene. Mike Walker led this Working Group and fronted the ensuing proposal (see also the discussion paper by M.J.C. Walker et al., 2012, Journal of Quaternary Science, 27: 649–659). The proposal was recommended by the SQS voting membership in 2016 and approved by the ICS in 2018. It was ratified by the IUGS Executive Committee on 14 June 2018. The IUGS ratification letter is here. A letter from Allan Ashworth, President of INQUA, thanking INQUA for its support, is here. David Harper, Chair of ICS, Phil Gibbard, Secretary General of ICS, and Stan Finney, Secretary General of the IUGS, all provided invaluable support during the long process of approval and ratification.
Chair: David Harper, University of Durham, UK
Vice Chair: Brian Huber, Smithsonian Institution, USA
Secretary-General: Philip Gibbard, University of Cambridge, UK
Past Chair: Stan Finney, California State University, USA
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A special volume of Quaternary International, edited by Mathieu Duval et al. and focused on the Early-Middle Pleistocene transition, has now been published. It is based on the SQS-SACCOM-ESF sponsored meeting “The Early-Middle Pleistocene transition: significance of the Jaramillo Subchron in the sedimentary record” held in Burgos, Spain, 2013. The 18 contributions are now available here.
Another special volume of Quaternary International, edited by Martin J. Head, Philip L. Gibbard, and Thijs van Kolfschoten, and dealing with the formal subdivision of the Quaternary, is also now published. It is based on an SQS-SACCOM sponsored symposium “The Quaternary System and its formal subdivision” held during the STRATI 2013 conference in Lisbon. The 13 contributions are now available here.