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Understanding ‘event stratigraphy' in the context of Anthropocene chronostratigraphic definition
Colin Waters  1@  , Mark Williams  1@  , Jan Zalasiewicz  1@  , Simon Turner  2@  , Martin J. Head  3@  , Scott Wing  4@  , Anthony Barnosky  5@  , Michael Wagreich  6@  , Jens Zinke  7@  , Colin Summerhayes  8@  , Andrew Cundy  9@  , Barbara Fiałkiewicz-Kozieł  10@  , Reinhold Leinfelder  11@  , Peter Haff  12@  , John Mcneill  13@  , Neil Rose  2@  , Irka Hajdas  14@  , Francine Mccarthy  3@  , Alejandro Cearreta  15@  , Agnieszka Gałuszka  16@  , Jaia Syvitski  17@  , Yongming Han  18@  , Zhisheng An  18@  , Ian Fairchild  19@  , Juliana Ivar Do Sul  20@  , Catherine Jeandel  21@  
1 : School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester LE1 7RH
2 : Environmental Change Research Centre, Department of Geography, University College London, Gower Street, London WC1E 6BT
3 : Department of Earth Sciences, Brock University, 1812 Sir Isaac Brock Way, St. Catharines, Ontario L2S 3A1
4 : Department of Paleobiology, Smithsonian Museum of Natural History, 10th Street and Constitution Avenue, NW, Washington, DC 20560
5 : Department of Integrative Biology, University of California, Berkeley, CA 94720
6 : Department of Geology, University of Vienna, A-1090 Vienna
7 : School of Geography, Geology and the Environment, University of Leicester, University Road, Leicester LE1 7RH, UK
8 : Scott Polar Research Institute, Cambridge University, Lensfield Road, Cambridge CB2 1ER
9 : School of Ocean and Earth Science, University of Southampton, National Oceanography Centre, Southampton
10 : Biogeochemistry Research Unit, Institute of Geoecology and Geoinformation, Adam Mickiewicz University, Krygowskiego 10, Poznań
11 : Department of Geological Sciences, Freie Universität Berlin, Malteserstr. 74-100/D, 12249 Berlin
12 : Nicholas School of the Environment, Duke University, 9 Circuit Drive, Box 90238, Durham, NC 27708
13 : Georgetown University, Washington, DC
14 : Laboratory of Ion Beam Physics, ETH Otto-Stern-Weg 5, 8093 Zurich
15 : Departamento de Geología, Facultad de Ciencia y Tecnología, Universidad del País Vasco UPV/EHU, Apartado 644, 48080 Bilbao
16 : Geochemistry and the Environment Division, Institute of Chemistry, Jan Kochanowski University, 7 Uniwersytecka St, 25-406 Kielce
17 : INSTAAR and CSDMS, University of Colorado, Boulder, CO
18 : State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710061
19 : School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT
20 : Leibniz Institute for Baltic Sea Research Warnemüende (IOW), Rostock
21 : LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS, 14 avenue Édouard Belin, 31400 Toulouse
LEGOS, Université de Toulouse, CNES, CNRS, IRD, UPS

The Anthropocene Working Group of the Subcommission on Quaternary Stratigraphy is working towards formally defining an Anthropocene epoch/series, and its associated age/stage commencing in the mid-20th century. The proposal will recommend that the Anthropocene be constrained by a Global boundary Stratotype Section and Point (GSSP) in a sediment core and supported by several Standard Auxiliary Boundary Stratotypes (SABSs) that permit correlation of the base of the Anthropocene into many of the diverse depositional environments in which it is clearly recorded. Global correlation is achieved using the many geosignatures of the Great Acceleration Event Array (GAEA: Head et al., 2022a, 2022b; Waters et al., 2022). We evaluate recent proposals that the Anthropocene should be an informal ‘event' characterised as an interdisciplinary, time-transgressive concept extending over tens of millennia and still ongoing, and not based exclusively on the stratigraphic record. We provide analysis of ‘events' in geological history and scrutinize their definition.

We investigate how concepts of events and episodes should be more rigorously applied and how events can be used as suitable guides for chronostratigraphic boundaries, using analogous Quaternary and deeper-time examples. We recognise events as associated with rapid rates of process change over brief time intervals and distinguish between global phenomena that represent an Earth System state-shift, e.g. large bolide impacts or Snowball Earth terminations, and local to global phenomena that do not alter the functioning of the Earth System, e.g. tsunamis. Episodes, in the informal use of the term, are by contrast long-lived phenomena, markedly time-transgressive with slow rates of process change. These too can be differentiated between episodes that cause state-shifts (e.g. the effects of very large igneous provinces such as the Siberian Traps on climate, oceans and biota) and those that have more modest and reversible impacts (e.g. changes in orbital parameters amplified by other Earth effects that cause the glacial-interglacial oscillation). Time resolution interacts with perceived suddenness and consequently samples closely spaced in time may reveal events that are embedded within episodes.

In the context of human impacts on stratigraphical successions, we recognise an extensive time-transgressive ‘episode' related to the global record of all geologically significant anthropogenic change, termed the Anthropogenic Modification Episode (AME). Nested within the AME are many brief and geologically correlatable events. The most notable is the GAEA, an array of global anthropogenic signals recorded in mid-20th century deposits, e.g.: onset of the radionuclide ‘bomb-spike'; appearance of microplastics, novel organic chemicals and fly ash particles; marked changes in patterns of sedimentary deposition, and in heavy metal contents and carbon/nitrogen isotopic ratios; and biotic changes leaving a global fossil record. These events include short-duration signals that returned to pre-1950 levels within a few decades, as well as signals that will persist for millennia or will be permanent (e.g. significant reconfiguration of ecosystems including extinctions).

Given the intensity, magnitude, planetary significance and global isochroneity of the GAEA, it provides a suitable level for recognition of the base of the Anthropocene as a series/epoch (Waters et al., 2023). The chronostratigraphic Anthropocene, defined in strict accordance with ICS approved nomenclature and procedures, provides a clear and stable meaning to stratigraphic use of the term “Anthropocene”.

References

Head, M.J., Zalasiewicz, J.A., Waters, C.N. et al. 2022a. The proposed Anthropocene Epoch/Series is underpinned by an extensive array of mid-20th century stratigraphic event signals. Journal of Quaternary Science 37(7), 1181–1187.

Head, M.J., Zalasiewicz, J.A., Waters, C.N.et al. 2022b. The Anthropocene is a prospective epoch/series, not a geological event. Episodes https://doi.org/10.18814/epiiugs/2022/022025

Waters CN, Williams M, Zalasiewicz J. et al. 2022. Epochs, events and episodes: marking the geological impact of humans. Earth-Science Reviews 234: 104171 https://doi.org/10.1016/j.earscirev.2022.104171

Waters, C.N., Turner, S.D., Zalasiewicz, J. and Head, M.J. (eds) (2023) Candidate sites and other reference sections for the Global boundary Stratotype Section and Point (GSSP) of the Anthropocene Series. The Anthropocene Review https://doi.org/10.1177/20530196221136422


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