Downloaded from http://sp.lyellcollection.org/ by guest on October 26, 2013 Geological Society, London, Special Publications Online First The term 'Anthropocene' in the context of formal geological classification P. L. Gibbard and M. J. C. Walker Geological Society, London, Special Publications, first published October 25, 2013; doi 10.1144/SP395.1 Email alerting click here to receive free e-mail alerts when service new articles cite this article Permission click here to seek permission to re-use all or request part of this article Subscribe click here to subscribe to Geological Society, London, Special Publications or the Lyell Collection How to cite click here for further information about Online First and how to cite articles Notes © The Geological Society of London 2013 The term ‘Anthropocene’ in the context of formal geological classification P. L. GIBBARD1* & M. J. C. WALKER2 1Department of Geography, Cambridge Quaternary, University of Cambridge, Cambridge CB2 3EN, UK 2School of Archaeology, History and Anthropology, Trinity Saint David, University of Wales, Lampeter SA48 7ED, UK *Corresponding author (e-mail: [email protected]) Abstract: In recent years, ‘Anthropocene’ has been proposed as an informal stratigraphic term to denote the current interval of anthropogenic global environmental change. A case has also been made to formalize it as a series/epoch, based on the recognition of a suitable marker event, such as the start of the Industrial Revolution in northern Europe. For the Anthropocene to merit formal definition, a global signature distinct from that of the Holocene is required that is marked by novel biotic, sedimentary and geochemical change. Although there is clear evidence of anthropogenic effects in geological sequences, it is uncertain whether these trends are suffi- ciently distinct, consistent and dated for the proposal for a Holocene/Anthropocene boundary to be substantiated. The current view of the Earth-Science community is that it should remain infor- mal. For formal definition a Global Stratigraphic Section and Point (GSSP) is required. Adoption of the term ‘Anthropocene’ will ultimately depend on recognition of a global event horizon. Without this, there is no justification for decoupling the Anthropocene from the Holocene. If the Anthropo- cene is deemed to have utility, it should be as an informal historical designation rather than a for- mally defined stratigraphic unit (of whatever status) within the geological timescale. The ‘Anthropocene’ (meaning anthro¯pos ‘human palaeoenvironmental reconstructions. These anthro- being’ and kainos ‘new’) is a term that has pogenic effects, which have reached significant become increasingly widely used since it was first levels during the last few centuries, and particularly proposed by Paul Crutzen & Eugene Stoermer since the Industrial Revolution in northern Europe, (2000) to denote the present time interval, in have resulted in marked changes to the Earth’s which many geologically significant processes and surface. Indeed, almost every aspect of the contem- conditions have been, and continue to be, pro- porary global environment is now modified, or at foundly altered by human activities. Processes least influenced, by human activity (Crossland include changes in erosion and sediment transport 2005; Zalasiewicz et al. 2010; Steffen et al. 2011). resulting from agriculture and urbanization, and There is a body of opinion within the geological variations in the chemical composition of the atmos- community that this accelerated human impact phere, oceans and soils, with notable perturbations may be reflected in the recent stratigraphic record, in element cycling, such as carbon, nitrogen, phos- and that the anthropogenic effect can be dis- phorus and various metals. Changes in environmen- tinguished from natural ‘background’ conditions tal conditions generated by these various processes (Zalasiewicz et al. 2008). Although the term include global warming, ocean acidification and Anthropocene was initially invoked informally to coastal eutrophication and ensuing anoxia; habitat describe this period of expanding human influence loss, species range shifts and extinctions; and glob- on the global environment (Crutzen 2002), and ally significant physical and chemical changes, was apparently suggested by chance (Steffen et al. including cryospheric loss, ozone depletion and 2004), it is increasingly being applied to the recent accelerating eustatic sea-level rise (e.g. Orr et al. geological record, where the term is viewed, by 2005; Nicholls et al. 2007; Chen et al. 2011; Urban some, as being equivalent to those used as series- et al. 2012). status subdivisions of the Cenozoic Erathem (‘recent The increasing prominence of humans dur- life’), notably the Pleistocene and Holocene. ing the present (Holocene Series/Epoch) intergla- An important consequence of the recognition of cial has been marked by a progressive increase the increasing intensity of human impact on the in their effect on the natural environment and its natural environment, and its possible manifestation processes, and this has long been recognized in in the geological record, has been the initiation of From:Waters, C. N., Zalasiewicz, J. A., Williams, M., Ellis,M.A.&Snelling, A. M. (eds) A Stratigraphical Basis for the Anthropocene. Geological Society, London, Special Publications, 395, http://dx.doi.org/10.1144/SP395.1 # The Geological Society of London 2013. Publishing disclaimer: www.geolsoc.org.uk/pub_ethics P. L. GIBBARD & M. J. C. WALKER discussions to determine whether the stratigraphic to form a parallel, numerical timescale based on signature of the Anthropocene is now sufficiently years. Chronostratigraphical divisions are ‘time/ clearly defined to warrant its formal definition as a rock’ units, that is they refer to the sequence of new period of geological time (Zalasiewicz et al. rocks deposited during a particular interval of 2011a, b). This is currently being considered by time. Geochronological divisions are the corre- a Working Group of the Subcommission on Qua- sponding intervals of (continuous) geological time. ternary Stratigraphy (SQS). In the meantime, a sep- Thus, it can be said that rocks of the Quaternary arate Working Group of the SQS, jointly with System were deposited during a time interval INTIMATE (integration of ice-core, marine and called the Quaternary Period. terrestrial records), has been examining the case In conventional stratigraphic practice, it is for a formal subdivision of the Holocene Series/ generally accepted that chronstratigraphical and Epoch (M. J. C. Walker et al. 2012). In the light geochronological boundaries should, as far as of a possible conflict between the two groups, possible, be defined in continuous sedimentary the Holocene working group has not considered sequences. Ideally, such sequences preserve mul- the Anthropocene question. Nevertheless, they tiple lines of evidence (multi-proxy records) and, acknowledge that although there is a clear distinc- in particular, continuous sedimentation spanning tion between these two initiatives, the Holocene the boundary itself, that is, excluding time gaps. subdivision being based on natural climatic/ This continuity offers the opportunity for identify- environmental events and the concept of the ing, inter alia, palaeontological, isotopic, chemical Anthropocene focusing on the human impact on and palaeomagnetic changes, and therefore enables the envi-ronment, there may indeed be areas of the boundary to be identified as precisely as possible overlap. We return to the subdivision of the Holo- within the limits of the evidence contained within cene below. the sequence. Throughout the Phanerozoic, this In this paper we consider the designation of the approach provides not only a basis for accurately Anthropocene as a formal time-stratigraphic unit delimiting a boundary, but also a means by which against the background of these ongoing discus- that horizon can be extended beyond the stratotype sions. We examine the term Anthropocene in the locality for purposes of correlation. context of the formal definition of geological time- The recommendations of the International Stra- scale units, particularly in relation to the require- tigraphic Guide (Hedberg 1976; Salvador 1994) ment for relating such units to unequivocal Global require that all major chronostratigraphical subdivi- Stratotype Section and Point (GSSP, ‘golden sions are defined with reference to boundary strato- spike’) localities, and we also evaluate the potential type localities in sediment reference sequences. value and utility of defining the episode of recent These are designated GSSPs, or ‘golden spikes’, human activity as a new stratigraphic unit within and form the basis for the division of geological the geological timescale (GTS). time in the internationally sanctioned GTS. This is the responsibility of the International Commis- sion on Stratigraphy (ICS), which is a constituent Stratigraphic procedures and the group of the International Union of Geological geological timescale Sciences (IUGS), the body that directs all aspects of global geoscience. The role of the ICS is to The stratigraphy of geological sequences is the formulate the subdivision, classification and deter- foundation upon which the discipline of historical mination of geological time, that is, chronostrati- geology, and therefore the accurate reconstruction graphy and geochronology. The ICS operates of Earth history, depends. It is concerned with all through subcommissions, each associated