This page lists the definitions of the major global stratigraphic divisions of the Quaternary System/Period. A brief history of the definitions of the Quaternary and Pleistocene is provided first, then a synopsis of GSSPs sanctioned to define the Quaternary and its subdivisions, and finally a listing of official auxiliary stratotypes designated to support these GSSPs. For the Anthropocene, a presently unofficial but proposed series/epoch that would terminate the Holocene, see here.
The current IUGS-ratified timescale for the Quaternary System/Period (July 2022). The age, location and primary guide for each GSSP is also included. The Upper/Late Pleistocene Subseries/Subepoch is ratified in name only, pending its definition and that of its corresponding stage by GSSP. Abbreviations: “b2k” = before the year 2000. ka = thousands years before present. Ma = millions of years before present.
History of Quaternary and Pleistocene definitions
The terms Quaternary and Pleistocene have long and varied histories. The Quaternary was effectively introduced by the Italian mining engineer Giovani Arduino in defining a “fourth order” (quarto ordine) in his subdivision of strata in the Venetian and Tuscan regions of Italy (Arduino, 1760; Vaccari, 2006; Gibbard, 2019). Desnoyers (1829) is credited with being first to use the specific term Quaternaire, which he used unequivocally to distinguish from the Tertiary (Head and Gibbard, 2015a).
Charles Lyell in 1839 introduced the term Pleistocene (Greek, pleīstos, most; and kainos, recent) as a substitute for his Newer Pliocene (Lyell 1839, p. 621) but in 1863, he proposed abandoning Pleistocene altogether on grounds that Forbes (1846) had popularized this term not in the sense of Lyell’s Newer Pliocene but almost precisely with reference to the subsequent interval of time for which Lyell was now introducing the term Post-pliocene (Lyell 1863, p. 6). Lyell had by 1865 conceded that if the term Pleistocene continued to be used, then it should not be as originally intended but in place of his “Post-pliocene” (Lyell 1865, footnote to p. 108). By the time Lyell had unconditionally accepted the Pleistocene in place of his Post-pliocene (Lyell 1873, p. 3, 4), this suggestion had already been generally adopted (Head, 2021).
The linkage between the base of the Pleistocene and that of the Quaternary became established over time, and was reaffirmed during the 18th International Geological Congress in London in 1948, where it was agreed to place the “Pliocene–Pleistocene (Tertiary–Quaternary) boundary … at the horizon of the first indication of climatic deterioration in the Italian Neogene succession.” (King and Oakley, 1949, p. 186; see Head and Gibbard, 2015a).
A brief history of Quaternary chronostratigraphic divisions since 1982 as depicted in the Geological Time Scale (GTS) publications of Harland et al. (1982, 1989) and Gradstein et al. (2004, 2012, 2020). Reproduced from Gibbard and Head, 2020, fig. 30.1.
Nonetheless, in 2004 the Quaternary as an official unit was eliminated from the Geological Time Scale and the Neogene extended to the present day (Gradstein and Ogg, 2004; Gradstein et al., 2004, 2005), with the Quaternary appearing as an unofficial unit with its base decoupled from that of the Pleistocene and aligned with that of the Gelasian Stage, then the uppermost stage of the Pliocene.
Following a long interval of impassioned discourse, the matter was eventually resolved on 29 June with the Executive Committee of the International Union of Geological Sciences (IUGS) ratifying a decision by the International Commission on Stratigraphy (ICS) that the base of the Quaternary System/Period be defined by the GSSP at Monte San Nicola, Sicily, Italy; and that the base of the Pleistocene Series/Epoch be lowered to the same level.
This decision was a natural consequence of several facts: 1) alignment of the base of the Quaternary with that of the Gelasian Stage had become uncontested; 2) an earlier IUGS-sanctioned timescale chart by Remane (2000) had included the Quaternary as an official system/period; 3) the base of the Pleistocene Series/Epoch required lowering to that of the Quaternary System/Period to maintain time scale hierarchy; 4) the Subcommission on Quaternary Stratigraphy had the greater authority over the base of its own time interval given that any unit of the geological time scale is defined by its base alone – its top being defined by the base of the superjacent unit. The following selected literature describes in detail the events and decisions reported briefly above: Head et al. (2008a, 2019), Gibbard and Head (2009a, b, c; 2020), Gibbard et al. (2010), and Head and Gibbard (2015a).
Global boundary Stratotype Sections and Points (GSSPs) and official subdivisions of the Quaternary
GSSPs for the Quaternary System/Period: Monte San Nicola, near Gela, Sicily, Italy (Quaternary System/Period, Pleistocene Series/Epoch, Lower/Early Pleistocene Subseries/Subepoch, Gelasian Stage/Age), Vrica, Calabria, Italy (Calabrian Stage/Age), Chiba, Chiba Prefecture, Boso Peninsula, Japan (Middle Pleistocene Subseries/Subepoch, Chibanian Stage/Age), NorthGRIP2 (NGRIP2), Greenland (Holocene Series/Epoch, Lower/Early Holocene Subseries/Subepoch, Greenlandian Stage/Age), NorthGRIP1 (NGRIP1),Greenland (Middle Holocene Subseries/Subepoch, Northgrippian Stage/Age), KM-A speleothem, Mawmluh Cave, Meghalaya State, India (Upper/Late Holocene Subseries/Subepoch, Meghalayan Stage/Age). Credits: Mollweide projection by Strebe.
Quaternary System/Period, Pleistocene Series/Epoch, Lower/Early Pleistocene Subseries/Subepoch, and Gelasian Stage/Age
The Monte San Nicola section, near Gela, in Sicily, Italy – the GSSP for the Gelasian Stage, Pleistocene Series, and Quaternary System is placed at the base of the marly layer conformably overlying the sapropelic Nicola bed. The position of the GSSP is indicated by an arrow. The GSSP has an age of 2.58 Ma. Photograph: M.J. Head (May 2022).
Close-up of the Monte San Nicola section showing the GSSP for the Gelasian Stage, Pleistocene Series, and Quaternary System. The position of the GSSP is indicated by an arrow. Photograph: M.J. Head (May 2022).
Locality of GSSP: Monte San Nicola, near Gela, Sicily, Italy: 37°8′45.64′′N, 14°12′15.22′E.
Stratigraphic position of GSSP: base of the marly layer immediately overlying the prominent sapropelic bed known as the Nicola bed. Boundary interval occurs within marly-silty deposits of the Monte Narbone Formation.
Depositional environment of GSSP interval: a slope-basin setting at a water depth of 500–1000 m (Rio et al., 1994). The sedimentation rate at the GSSP interval is 6.1 cm/kyr (Hilgen, 1991, fig. 8).
Date of ratification: for the Gelasian Stage in August, 1996 (Rio et al., 1998), for the Pleistocene Series and Quaternary System on 29 June 2009 (Gibbard and Head, 2010), and for the Lower Pleistocene Suberies on 30 January 2020 (Head et al., 2021).
Age of GSSP: Astronomically tuned at 2.58 Ma (Gibbard and Head, 2009, 2010) on the assumption that the mid-point age of the Nicola bed is 2.588 Ma (Lourens et al., 1996a) and that the Nicola bed has a duration of 7–10 kyr: the GSSP is therefore about 3.5–5.0 kyr younger than the midpoint age, rounding down to 2.58 Ma.
Local / regional marker horizon: the Nicola bed, which corresponds to small-scale cycle 119 at Monte San Nicola (= Rossello composite section cycle number 119), and to Mediterranean Precession-Related Cycle (MPRC) 250 (Hilgen, 1991). It is the highest in a cluster of six sapropels (cluster A) occurring at a time of maximum eccentricity (Rio et al., 1994), and represents the greatest summer insolation in this eccentricity cluster, explaining its prominence.
Global correlation: The Nicola bed coincides with an obliquity maximum, representing MIS 103. The GSSP is close to the Gauss–Matuyama reversal, either coinciding with it or occuring slightly above (Head, 2019; contra Rio et al., 1998). The best independent estimate for the age of the directional midpoint of the Gauss–Matuyama reversal is ∼2.587–2.581 Ma (Head, 2019).
Comments: The Gelasian GSSP has been reviewed by Head (2019). The Monte San Nicola succession (at the type section and the Mandorlo section) was recently reexamined by Capraro et al. (2022). A high-resolution reexamination of the type section across the GSSP interval is the focus of the GELSTRAT, an INQUA–SQS initiative to improve the global correlation potential of the GSSP.
Access: The site is somewhat remote. Access requires permission of the landowner.
The Vrica section near Crotone, Calabria, southern Italy – the GSSP for the Calabrian Stage and Lower Pleistocene Subseries. The GSSP is placed at the base of the marine claystone conformably overlying sapropelic bed ‘e’, indicated by an arrow in the closeup of the section in (b). Photograph by Ilka Von Dalwigk (June 2000); supplied by Luca Capraro. Reproduced from Head (2019, fig. 5).
Locality of GSSP: Vrica, Calabria, Italy: 39°02’18.61″ N, 17°08’05.79″ E, some 4 km south of the town of Crotone.
Stratigraphic position of GSSP: base of the marl bed immediately overlying sapropel ‘e’, as identified in a succession of dark grey or blue-grey silty marls.
Depositional environment of GSSP interval: deposited at a water depth in excess of 500 m (Pasini and Colalongo, 1997). Sedimentation rates are ~29 cm/kyr at around the GSSP interval (Suc et al., 2010).
Date of ratification: the GSSP previously defined the base of the Pleistocene, as ratified on 31 May, 1985 (Aguirre and Pasini, 1985; Bassett, 1985); presently defines the base of the Calabrian Stage (second stage of the Lower Pleistocene), as ratified on 5 December 2011 (Cita et al., 2011).
Age of GSSP: sapropelic bed ‘e’ has a midpoint astronomical age of 1.806 Ma (Lourens et al., 2005) but allowing for the delay in deposition of the overlying claystone, the GSSP is dated to 1.80 Ma (Cita et al., 2012).
Local / regional marker horizon: sapropelic bed ‘e’ is assigned to MPRS 176 (Lourens et al., 1996b).
Global correlation: The GSSP coincides with the transition from MIS 65 to 64, and is ∼8m below the observed top of the Olduvai Subchron, although diagenetic overprinting prevents a more precise estimate of this polarity reversal (Roberts et al., 2010). Nonetheless, the top of the Olduvai Subchron elsewhere is within MIS 63, and highly resolved North Atlantic records suggests that the GSSP is ∼20 kyr older than the top of the Olduvai Subchron (see Head, 2019 for dicussion).
Comments: In its original role in defining the base of the Pleistocene, the Vrica GSSP was selected to mark the first appearance of “northern guests” in the Mediterranean, as recommended at the 1948 International Geological Congress in London; although these have since been recorded below the GSSP level, having entered the Mediterranean at various times (Pasini and Colalongo, 1997; Gibbard and Head, 2010; Head, 2019).
Access: The GSSP occurs within a badlands topography, and is freely and easily accessible (Cita et al., 2008).
Middle Pleistocene Subseries/Subepoch and Chibanian Stage/Age
The Chiba section, Chiba Prefecture, Japan – the GSSP for the Chibanian Stage and Middle Pleistocene Subseries. The GSSP is placed at the base of the Byk-E tephra bed (orange star in b). (a) Overview of the Chiba section. The yellow line indicates the Byk-E tephra bed and GSSP horizon. (b) and (c) Details of the Byk-E tephra bed. The length of rule (b) is 2.0 m. Credits: a, b, from Suganuma et al. (2021, fig. 10); c, photograph by M.J. Head.
Locality of GSSP: Chiba section, Chiba Prefecture, Boso Peninsula, east-central Japan: 35°17’39.6” N, 140°08’47.6” E.
Stratigraphic position of GSSP: base of the Ontake-Byakubi-E (Byk-E) tephra bed, a regional marker. The GSSP section outcrops along the Yoro River, and is dominated by bioturbated, hemipelagic, silty beds within the Kokumoto Formation of the Kazusa Group (Suganuma et al., 2021).
Depositional environment of GSSP interval: open-ocean continental slope setting under generally stable conditions; facing the Pacific Ocean. Water depths may have exceeded 800 to 1000 m based on the trace fossil association. The Chiba composite section represents transgressive and highstand systems tracts. Sedimentation rates are ~89 cm/kyr across the GSSP interval (Suganuma et al., 2021).
Date of ratification: for both the Chiba Stage and Middle Pleistocene Subseries, on January 17, 2020 (Suganuma et al., 2021).
The GSSP plaque at the Chiba section, Japan. Photo: M.J. Head.
Age of GSSP: astronomically dated at 774.1 ± 5.0 ka (Suganuma et al., 2018, 2021). The Byk-E tephra bed has a U-Pb zircon age of 772.7 ± 7.2 ka (Suganuma et al., 2015).
Local / regional marker horizon: Byk-E tephra bed.
Global correlation: The GSSP is 1.1 m below the directional midpoint of the Matuyama–Brunhes paleomagnetic reversal which serves as the primary guide to the GSSP. This directional midpoint has an astronomical age of 772.9 ± 5.4 ka, with a reversal duration of up to ~ 2 kyr (Head, 2021). The GSSP is therefore ~1200 years older than the Matuyama–Brunhes reversal. The GSSP occurs near the top of MIS 19c and is therefore close in age to glacial inception which is indicated by the MIS 19c–b boundary (Suganuma et al., 2021; Head, 2021).
Comments: As a practical measure for global correlation, the Early–Middle Pleistocene boundary aligns with a major paleomagnetic boundary, the Matuyama–Brunhes reversal. But it also occurs within the Early–Middle Pleistocene transition (1.4–0.7 or 1.4–0.4 Ma; Head, 2021) and is therefore associated with a fundamental shift in Earth’s history from a 41-ky to quasi-100-ky orbital rhythm, and increases in the amplitude of climate oscillations, long-term average global ice volume, and asymmetry in global ice volume cycles. This shift caused progressive and fundamental physical, chemical, climatic, and biotic adjustments to the planet (Head and Gibbard 2015b).
Access: The Chiba section is on land protected from development and has easy and free access.
Upper/Late Pleistocene Subseries/Subepoch
Comments: The Upper Pleistocene Subseries was ratified in name only on 30 January, 2022 (Head et al., 2021). This completed the official tripartite division of the Pleistocene into subseries. The base of the Upper Pleistocene has long been linked with the base of the Last Interglacial, and at the 12th INQUA Congress in Ottawa in 1987, a proposal was approved to use the base of MIS 5 (Termination II) as the primary guide for the boundary (Anonymous, 1988; Richmond, 1996).
The definition of a GSSP for the Upper Pleistocene Subseries and its corresponding stage is in progress. Two prospective candidate GSSPs have been advanced: the Fronte Section, near Taranto, Apulia, southern Italy (Negri et al., 2015), and the EPICA Dome C ice core in Antarctica (Head, 2019). A provisional age of ~129 ka relating to significant warming at the beginning of the Last Interglacial is given for the base of the Upper Pleistocene Subseries (Head et al., 2021).
Holocene Series/Epoch and its official subdivision
The term ‘holocène’, from the Ancient Greek holos and kainos meaning ‘entirely (wholly) recent’, was introduced by the French zoologist and paleontologist Paul Gervais (1867–1869, p. 32) for the warm episode that followed the last glacial period. It entered the international lexicon as ‘holocènes’ during the Second International Geological Congress (IGC) held in Bologna in 1882, and a ‘Holocenian’ Stage was proposed by the Portuguese Committee for the Third IGC in Berlin in 1885 (Head, 2019). The term replaced ‘Recent’ (Lyell, 1833, p. 52) which is not an official chronostratigraphic term.
The GSSP for the Holocene Series/Epoch was officially ratified on 8 May 2008 (Head and Gibbard, 2015a), based on a proposal of the Joint Working Group of the North Atlantic INTIMATE programme (Integration of ice-core, marine and terrestrial records: INQUA project 0408) and the SQS (Subcommission on Quaternary Stratigraphy) which had been established in 2004 (Walker et al., 2009). The GSSP was defined in the NGRIP2 ice core (the earlier NGRIP1 ice core having not penetrated the base of the Holocene; Walker et al., 2019, p. 177) but without an accompanying stage/age. This irregularity was not rectified until 10 years later with the official subdivision of the Holocene. The GSSP is described below.
The Holocene Series/Epoch is subdivided into the Greenlandian, Northgrippian and Meghalayan stages/ages and their corresponding Lower/Early, Middle, Upper/Late subseries/subepochs (Walker et al., 2018, 2019). This subdivision was ratified on 14 June 2018. The formalization process was long, rigorous and consultative, beginning with the publication of a discussion paper (Walker et al., 2012) and further deliberation and voting within the SQS in 2015 that recommended this subdivision. Ratification was in fact delayed because the rank of subseries did not then have official status within the geological time scale (see Head et al., 2017), matters being resolved only by ratification of the Holocene subdivisional proposal itself (Head et al., 2021).
It should be noted that an early/middle/late subdivision for the Holocene had been in widespread use since the 1970s. There are no major step-changes in the evolution of Holocene climate, so the continuance of this terminology primarily reflected the desire for increased precision in communication. The 4.2- and 8.2-ka climatic events were simply chosen as convenient and globally correlatable markers for a more-or-less equally spaced tripartite formal subdivision, thereby removing ambiguity in the application of these positional terms (Walker et al., 2018, 2019). The definition of corresponding stages / ages followed requirements of the geological time scale.
Holocene Series/Epoch, Lower/Early Holocene Subseries/Subepoch, and Greenlandian Stage/Age
NorthGRIP2 (NGRIP2) ice core, Greenland – GSSP for the Greenlandian Stage, Lower Holocene Subseries, and Holocene Series. This visual image is ’reversed’ to show clear ice as black and impurities including micrometre-sized dust particles approaching white. This results in an essentially seasonal signal revealing annual banding in the ice. The GSSP is at 1492.45 m depth in this core. From Walker et al. (2009, fig. 4).
NorthGRIP2 (NGRIP2) ice core, Greenland – GSSP for the Greenlandian Stage, Lower Holocene Subseries, and Holocene Series. a) shows the oxygen isotope record across the Pleistocene–Holocene boundary, and b) high-resolution multi-parameter record: δ18O, electrical conductivity (ECM), Na+ concentration, dust content, and a sharp decline in deuterium excess at the GSSP indicating rapid warming. Modified from Walker et al. (2009, fig. 5).
Locality of GSSP: NorthGRIP (NGRIP)2 ice core (where GRIP = Greenland Ice Core Project) from central Greenland: 75.10°N, 42.32°W.
Stratigraphic position of GSSP: 1492.45m depth.
Depositional environment of GSSP interval: Greenland ice sheet.
Repository of GSSP: NGRIP cores are archived at the Ice Core Repository, Centre for Ice and Climate, The Niels Bohr Institute, University of Copenhagen, Denmark.
Date of ratification: 8 May, 2008 for the Holocene Series GSSP (Head and Gibbard, 2015a), 14 June 2018 for the Greenlandian Stage and Lower Holocene Subseries utilizing the same GSSP (Walker et al., 2018, 2019).
Age of GSSP: 11,700 yr b2k (before 2000 CE) based on multi- parameter annual layer counting with a maximum counting error of 99 yr (equivalent to 2σ) (Walker et al., 2008, 2009).
Local / regional marker horizon: The GSSP occurs 1.5 cm above the base of an interval of clear ice in the NGRIP2 core core. It coincides with a sharp decline in deuterium excess values, representing an interval of just 1–3 years, which is interpreted as reflecting a rapid retreat of the oceanic polar front in the North Atlantic which serves as the source of moisture for precipitation over central Greenland. Paradoxically, rapid warming causing this retreat led the moisture source to shift northwards where surface waters were cooler, hence a sharp decline (a “cooling” signature) in the deuterium excess values (Walker, 2008, 2009). Supporting signals are a short-term shift to heavier δ18O values (but longer-term shift to lighter δ18O), shifts in other chemical proxies, a trend towards lower dust concentrations, and a sharp increase annual ice-layer thickness (Walker et al., 2008, 2009).
Global correlation: Conspicuous rapid warming that marks the end of the last cold episode (Younger Dryas Stadial / Greenland Stadial 1) of the Late Pleistocene.
Comments: This is the first GSSP ever to be located in an ice core, a practice continued with the Northgrippian GSSP (below).
Access: NGRIP cores may be accessed with permission of the curator, Ice Core Repository, University of Copenhagen.
Middle Holocene Subseries/Subepoch, and Northgrippian Stage/Age
NorthGRIP1 (NGRIP1) ice core, Greenland – GSSP for the Northgrippian Stage and Middle Holocene Subseries. a) shows the water oxygen isotope record in both GRIP and NGRIP1 Greenland ice cores, where the arrow marking the 8.2 ka climate event has a duration from ~8300 a b2k (1234.78 m) to ~8140 a b2k (1219.47 m). b) Electrical conductivity measurements (ECM) reveal a distinct acidity double peak, most probably caused by an Icelandic volcano. This peak is dated on the GICC05 timescale to 8236 a b2k (8186 cal a BP), and is the primary marker for the GSSP which is indicated by the dashed vertical line (after Walker et al., 2012, 2018, 2019).
Locality of GSSP: NorthGRIP (NGRIP)1 ice core from central Greenland: 75.10°N, 42.32°W.
Stratigraphic position of GSSP: 1228.67 m depth.
Depositional environment of GSSP interval: Greenland ice sheet.
Repository of GSSP: NGRIP cores are archived at the Ice Core Repository, Centre for Ice and Climate, The Niels Bohr Institute, University of Copenhagen, Denmark.
Date of ratification: 14 June 2018 (Walker et al., 2018).
Age of GSSP: 8236 yr b2k with a maximum counting error of 47 yr; based on the counting of annual ice layers in the DYE-3 core in southeastern Greenland where high ice accumulation rates have led to the best resolved time scale of all the Greenland ice cores for this interval (Walker et al., 2018).
Local / regional marker horizon: an electrical conductivity double peak probably representing a volcanic eruption in Iceland and which can be correlated to other Greenland ice cores. The GSSP is placed in the middle of this double peak (Walker et al., 2018, 2019).
Global correlation: the 8.2‐ka climatic event, represented by cooling in the Greenland ice core record, and near-global in extent. In the NGRIP1 ice core, cooling (of ~5 °C) is indicated by a conspicuous shift to more negative δ18O and δD values; by declines in ice‐core annual layer thickness and deuterium excess; by a substantial, sudden and short‐lived minimum in atmospheric methane (a global event); and by a subsequent increase in the atmospheric content of CO2 (Walker et al., 2018, 2019). The 8.2 ka climatic event is recognized widely in an array of climate proxies, and therefore serves as the primary correlation event for this GSSP.
Comments: The 8.2 ka climatic event appears to reflect the interruption of North Atlantic Deep Water formation, and its associated northward heat transport, by catastrophic meltwater release from glacial lakes Agassiz and Ojibway into the North Atlantic during wastage of the Laurentide Ice Sheet, as well as meltwater contributions from elsewhere (Walker et al., 2018).
Access: NGRIP cores may be accessed with permission of the curator, Ice Core Repository, University of Copenhagen.
Upper/Late Holocene Subseries/Subepoch, Meghalayan Stage/Age
Speleothem KM-A from the Mawmluh Cave, State of Meghalaya, India – GSSP for the Meghalayan Stage and Upper Holocene Subseries. A) the speleothem KM-A with the position of the 4.2 ka climate event which is the primary guide to the GSSP. The speleothem is ~308 mm long. B) a) precise location of the GSSP, b) Oxygen isotope record of speleothem KM-A across the GSSP interval showing the precise position of the GSSP. The GSSP occurs at the approximate mid-point between the onset of the 4.2 ka climate event and its intensification (marked by the shaded rectangle). c) an inverted δ13C tree ring record from northern Finland as a proxy for wetter conditions, and the most northerly expression yet documented for the 4.2 ka event (from fig. 1 of Helama and Oinonen, 2019). Based on Walker et al. (2019, fig. 5) and Head (2019, fig. 12).
Speleothem KM-A is on permanent display in the museum of the Birbal Sahni Institute of Palaeosciences, Lucknow, India. This is the only GSSP at present that can be displayed in a museum without refrigeration.
Locality of GSSP: KM-A speleothem obtained from Mawmluh Cave, near the town of Sohra (Cherrapunji), State of Meghalaya, northeastern India. Cave entrance: 25°15’44”N; 91°42’54”E.
Stratigraphic position of GSSP: 7.45 mm depth in speleothem KM-A (Head, 2019).
Repository of GSSP: Birbal Sahni Institute of Palaeosciences (BSIP), Lucknow, Uttar Pradesh, India.
Date of ratification: 14 June 2018 (Walker et al., 2018).
Age of GSSP: 4.200 ± 30 ka before the year 1950 CE (= 4.250 ± 30 ka), a modelled age based on a Monte Carlo fitting procedure through 12 U-Th dates. The analytical uncertainty on those two U-Th dates closest to the GSSP (3654 and 4112 yr BP) are 20 and 30 years respectively. The KM-A record shows linear growth rates across the GSSP interval which provides further confidence in the age of the GSSP and onset and duration of the 4.2 ka event (Berkelhammer et al., 2012; Walker et al., 2018).
Local / regional marker horizon: The GSSP is characterised geochemically (rather than physically) by its stable oxygen isotope record in the KM-A speleothem which captures the 4.2-ka climatic event in full. The event is expressed by a shift to heavier isotopic values that reflect an abrupt decline in precipitation as the monsoon across the Indian sub-continent and southeast Asia weakened. The GSSP (4200 ± 30 years) is placed at the approximate midpoint between the onset (4303 ± 26 years) and intensification (4071 ± 31 years) of the 4.2-ka event as recorded in the KM-A speleothem. (Walker et al., 2018).
Global correlation: The 4.2 ka climatic event represents a significant reorganisation of oceanic and atmospheric circulation, and is recorded from North America and Europe, through West Asia to China; and from Africa, Andean-Patagonian South America, Antarctica and the central North Pacific. Most mid- and low-latitude records indicate a two to three century aridification event (Walker et al., 2018), but some locations show a shift to wetter conditions, as with a composite δ13C tree-ring record from northern Finland that registers increased cloudiness (Helama and Oinonen, 2019). In lower latitudes, the event represents a weakening or deflection of the East Asian and Indian summer monsoons.
Comments: Aridification in many low-latitude regions during the 4.2 ka climatic event led to profound societal changes in Spain, Greece, Palestine, Egypt, Mesopotamia, the Indus Valley and the Tibetan Plateau, the regions of the Yangtze and Yellow River and North China, in central Africa, the American Southwest, and the Yucatan (Walker et al., 2018 and references therein). This event was therefore global or near global in extent, short-lived and near isochronous, providing a practical time line with which to define the Upper Holocene, while intersecting meaningfully with archaeological and historical time scales.
Access: Those wishing access should contact the Director, Birbal Sahni Institute of Palaeosciences.
Auxiliary stratotypes assist in extending the knowledge of a Global boundary Stratotype Section and Point (GSSP) between continents, biogeographic provinces, climatic zones, depositional facies and preservational states (Head et al., 2022). They are always subordinate to GSSPs. Auxiliary stratotypes have presently been defined only for the Holocene and its subdivisions, although work is ongoing to define additional auxiliary stratotypes for the Quaternary.
Auxiliary stratotypes for the Quaternary System/Period have been designated to support several GSSPs. Holocene Series/Epoch, Lower/Early Holocene Subseries/Subepoch, and Greenlandian Stage/Age: Eifelmaar lakes (Lake Holzmaar and Meerfelder Maar), Germany; Splan Pond, eastern New Brunswick, Canada; Lake Suigetsu, western central Japan; Lake Maratoto, northern North Island, New Zealand; and Cariaco Basin off Venezuela. Middle Holocene Subseries/Subepoch, Northgrippian Stage/Age: Gruto do Padre speleothem, Bahia State, Brazil. Upper/Late Holocene Subseries/Subepoch, Meghalayan Stage/Age: Mount Logan plateau ice field, Yukon, Canada. Credits: Mollweide projection by Strebe.
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