Subdivision of the Quaternary System: formal subseries and new corresponding stages for the Pleistocene and Holocene

Abstract

<p>The Holocene and Pleistocene series/epochs have each long been divided into Early, Middle and Late subseries/subepochs, although their formalization had been complicated by the hitherto absence of this rank from the International Chronostratigraphic Chart.  On 14th June 2018, the Holocene was formally subdivided into the Greenlandian, Northgrippian and Meghalayan stages/ages and their corresponding Lower/Early, Middle, Upper/Late subseries/subepochs, each defined by a Global Boundary Stratotype Section and Point (GSSP). The GSSP for the lowermost stage, the Greenlandian, is that of the Holocene as previously defined in the NGRIP2 Greenland ice core, and dated at 11,700 yr b2k (before 2000 CE). The GSSP for the Northgrippian is in the NGRIP1 Greenland ice core, and dated at 8236 yr b2k, whereas that for the Meghalayan is located in a speleothem from Mawmluh Cave, Meghalaya, northeast India with a date of 4250 yr b2k (Walker et al., 2018).  The Pleistocene Series/Epoch of the Quaternary System/Period has been divided unofficially into three subseries/subepochs since at least the 1870s.  On 30th January 2020, two proposals were ratified: 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.  The Middle Pleistocene and its corresponding Chibanian Stage/Age had meanwhile been formalized on January 17, 2020 with a GSSP in the Chiba section, Japan.  The GSSP is placed 1.1 m below the directional midpoint of the Matuyama–Brunhes Chron boundary, at the base of a regional lithostratigraphic marker, the Ontake-Byakubi-E tephra bed, in the Chiba section. The GSSP has an astronomical age of 774.1 ka and is placed just below the top of Marine Isotope Substage 19c.  These ratifications nominally complete the official division of the Quaternary into subseries/subepochs, although the Upper Pleistocene and its corresponding stage remain to be defined by GSSP.  The Anthropocene is currently an unofficial unit, while analysis of potential candidate GSSP locations is progressing in preparation for a formalization proposal.  If approved, it would terminate the Holocene at around the year 1952, assuming it is defined at series/epoch rank.</p><p>Head, M.J., Pillans, B., and Zalasiewicz, J.A., in press. Formal ratification of subseries/subepochs for the Pleistocene Series/Epoch of the Quaternary System/Period. Episodes</p><p>Suganuma, Y., Okada, M., Head, M.J., et al., in press. Formal ratification of the Global Boundary Stratotype Section and Point (GSSP) for the Chibanian Stage and Middle Pleistocene Subseries of the Quaternary System: the Chiba Section, Japan.  Episodes</p><p>Walker, M., Head, M.J., Berkelhammer, M. et al., 2018.  Formal ratification of the subdivision of the Holocene Series/Epoch (Quaternary System/Period): two new Global Boundary Stratotype Sections and Points (GSSPs) and three new stages/subseries. Episodes 41(4): 213–223. </p>