Anthropocene: its stratigraphic basis

As officers of the Anthropocene Working Group (AWG; J.Z. and C.W.) and chair of the Subcommission on Quaternary Stratigraphy (SQS; M.J.H.) of the International Commission on Stratigraphy (ICS), we note that the AWG has less power than Erle Ellis and colleagues imply (Nature 540, 192–193; 2016). Its role is merely advisory — to evaluate the Anthropocene as a formal unit in the geological timescale. Proposals must pass scrutiny by the AWG, the SQS and the ICS before being ratified by the Executive Committee of the International Union of Geological Sciences

Humans as the third evolutionary stage of biosphere engineering of rivers

We examine three fundamental changes in river systems induced by innovations of the biosphere, these being: (1) the evolution of oxygenic photosynthesis; (2) the development of vascular plants with root systems; and (3) the evolution of humans. The first two innovations provide context for the degree of human-induced river change. Early river systems of the Precambrian Archean Eon developed in an atmosphere with no free oxygen, and fluvial sediments accumulated ‘reduced detrital’ minerals. By 2.4 Ga the evolution of oxygenic photosynthesis produced an oxygenated atmosphere and ‘reduced detrital’ minerals mostly disappeared from rivers, affording a distinct mineralogical difference from subsequent fluvial deposits. Rivers of the Precambrian and early Phanerozoic were dominantly braided, but from 0.416 Ga, the evolution of vascular plants with roots bound floodplain sediments and fostered fine-grained meandering rivers. Early meandering river deposits show extensive animal activity including fish and arthropod tracks and burrows. Homo sapiens, appearing about 150 ka BP, has, in recent millennia, profoundly modified river systems, altering their mineralogical, morphological and sedimentary state. Changes in sediment fluxes caused by human ‘reverse engineering’ of the terrestrial biosphere include deforestation, irrigation and agriculture. Sediment retention has been encouraged by the construction of dams. Modern river systems are associated with extensive human trace fossils that show a developing complexity from ancient civilizations through to megacities. Changes induced by humans rank in scale with those caused by earlier biosphere innovations at 2.4 and 0.416 Ga, but would geologically soon revert to a “pre-human” state were humans to become extinct.This is the author accepted manuscript. The final version is available from Elsevier at http://www.sciencedirect.com/science/article/pii/S2213305415000089

Evidence for a stratigraphic basis for the Anthropocene

The Anthropocene was proposed as a term (Crutzen and Stoermer 2000) before consideration was given to the nature of the key signatures, contrasting with standard procedures for defining such units. The term is being widely used in both popular and scientific publications before a decision is made as to whether it warrants formalisation and definition of a Global Stratigraphic Section and Point (GSSP). The deliberate human modification of the landscape and its subsurface, and the creation of human-generated novel sedimentary deposits, minerals, and landforms, are characteristic features of the development of Earth’s surface and near surface, which has accelerated in the past two centuries. The large-scale intentional excavation, transportation, and deposition of mixtures of rock and soil to form anthropogenic deposits and landforms represent a new geological process that could be used as a diagnostic signature of the Anthropocene

Integrated stratigraphical study of the Rhuddanian-Aeronian (Llandovery, Silurian) boundary succession in the Rheidol Gorge, Wales:A proposed Global Stratotype Section and Point for the base of the Aeronian Stage

The Rheidol Gorge section, approximately 17 km east of Aberystwyth, mid Wales, exposes a ca. 20 m-thick succession of Llandovery (Silurian) strata from the upper Rhuddanian Pernerograptus revolutus Biozone through the lower Aeronian Demirastrites triangulatus Biozone and basal Neodiplograptus magnus Biozone. The section records deposition under a range of bottom-water oxygenation states. The Rhuddanian-Aeronian boundary is located 0.8 m above an abrupt lithological change from predominantly organic-poor, bioturbated `oxic' mudrocks to an interval of black, richly graptolitic `anoxic' shales. The graptolite fauna through the boundary interval, including the local lowest occurrence of D. triangulatus, allows precise correlation with other parts of the world. Graptolite assemblages indicative of separate divisions in the underlying revolutus Biozone and of the lower and upper parts of the triangulatus Biozone are also present. Chitinozoans are relatively well preserved in the section and indicate the Spinachitina maennili Biozone throughout the boundary interval, as is widely the case. The results of carbon isotope analyses from organic matter indistinctly show the weak interval of positive shift in d13C org values through the Rhuddanian-Aeronian boundary interval, as observed globally, though local or regional processes appear largely to overprint the global signal. Overall, the excellent biostratigraphical record, well-documented local and regional stratigraphical context, historical significance, as well as easy access and assured longterm preservation, mean that the Rheidol Gorge section can be proposed as a strong candidate for a new Global Stratotype Section and Point for the base of the Aeronian Stage.. Silurian, Llandovery, Rhuddanian, Aeronian, Global Stratotype Section and Point, Graptolites, Chitinozoa, Carbon Isotope

Can nuclear weapons fallout mark the beginning of the Anthropocene Epoch?

Many scientists are making the case that humanity is living in a new geological epoch, the Anthropocene, but there is no agreement yet as to when this epoch began. The start might be defined by a historical event, such as the beginning of the fossil-fueled Industrial Revolution or the first nuclear explosion in 1945. Standard stratigraphic practice, however, requires a more significant, globally widespread, and abrupt signature, and the fallout from nuclear weapons testing appears most suitable. The appearance of plutonium 239 (used in post- 1945 above-ground nuclear weapons tests) makes a good marker: This isotope is rare in nature but a significant component of fallout. It has other features to recommend it as a stable marker in layers of sedimentary rock and soil, including: long half-life, low solubility, and high particle reactivity. It may be used in conjunction with other radioactive isotopes, such as americium 241 and carbon 14, to categorize distinct fallout signatures in sediments and ice caps. On a global scale, the first appearance of plutonium 239 in sedimentary sequences corresponds to the early 1950s. While plutonium is easily detectable over the entire Earth using modern measurement techniques, a site to define the Anthropocene (known as a Ògolden spikeÓ) would ideally be located between 30 and 60 degrees north of the equator, where fallout is maximal, within undisturbed marine or lake environments

The Great Acceleration is real and provides a quantitative basis for the proposed Anthropocene Series/Epoch

The Anthropocene was conceptualized in 2000 to reflect the extensive impact of human activities on our planet, and subsequent detailed analyses have revealed a substantial Earth System response to these impacts beginning in the mid-20th century. Key to this understanding was the discovery of a sharp upturn in a multitude of global socio-economic indicators and Earth System trends at that time; a phenomenon termed the ‘Great Acceleration’. It coincides with massive increases in global human-consumed energy and shows the Earth System now on a trajectory far exceeding the earlier variability of the Holocene Epoch, and in some respects the entire Quaternary Period. The evaluation of geological signals similarly shows the mid-20th century as representing the most appropriate inception for the Anthropocene. A recent mathematical analysis has nonetheless challenged the significance of the original Great Acceleration data. We examine this analytical approach and reiterate the robustness of the original data in supporting the Great Acceleration, while emphasizing that intervals of rapid growth are inevitably time-limited, as recognised at the outset. Moreover, the exceptional magnitude of this growth remains undeniable, reaffirming the centrality of the Great Acceleration in justifying a formal chronostratigraphic Anthropocene at the rank of series/epoch

Integrated stratigraphic study of the Rhuddanian-Aeronian (Llandovery, Silurian) boundary succession at Rheidol Gorge, Wales : a preliminary report

Rheidol Gorge, approximately 17 km west of Aberystwyth, mid Wales, exposes a continuous succession of strata from the middle part of the upper Rhuddanian Coronograptus Cyphus Biozone through the lower Aeronian Demirastrites triangulatus (= Monograptus triangulatus) Biozone. Parts of the Aeronian succession are well known for their beautiful lower Aeronian graptolites preserved as pyrite internal moulds. We measured this section and sampled for graptolites, palynomorphs, and for lithological and geochemical analyses. One of our objectives was to assess the section for its suitability as a candidate for a new Global Stratotype Section and Point for the base of the mid-Llandovery Aeronian Stage. The succession alternates between bioturbated grey mudstones lacking in graptolites and laminated, graptolitic black shales. The black shales commonly show thin, interbedded siltstones. The grey mudstones are interpreted to represent deposition under oxic to dysoxic conditions, the black shales an anoxic seafloor environment. The strata have undergone low-grade metamorphism, commonly with a weakly to moderately developed cleavage, and the graptolites often show ductile and/or brittle deformation. Strate of the middle to upper cyphus Biozone are c 10.2 m thick and yield graptolite faunas of varying diversity and preservation quality. 0.8 m below the base of the D. triangulatus Biozone there is a change from predominantly organic-poor mudrocks with interbeds of darker shales with sparse graptolites to an interval of predominantly black shales with a relatively rich graptolite fauna. The graptolites in the black shale interval, which spans the zonal boundary, are flattened or in partial relief, commonly deformed, and the strata tend to break along cleavage rather than bedding planes. Nevertheless, a distinctive graptolite fauna occurs through the boundary interval that allows good correlation with successions in other parts of the world. The base of the D. triangulatus Biozone is marked by the first appearance of D. triangulatus. Other species first appearing just below the base of the D. triangulatus Biozone that are useful for international correlation include Pristiograptus concinnus and Pseudorthograptus finneyi. Strata rich in well-preserved, pyritic graptolites become common about 2.3 m above the base of the triangulatus Biozone. Chitinozoans are poorly to moderately well preserved in the section and indicate the Spinachitina maennili Biozone through the boundary interval, without any significant faunal changes, as is the case in many other parts of the world

Epochs, events and episodes: Marking the geological impact of humans

Event stratigraphy is used to help characterise the Anthropocene as a chronostratigraphic concept, based on analogous deep-time events, for which we provide a novel categorization. Events in stratigraphy are distinct from extensive, time-transgressive ‘episodes’ – such as the global, highly diachronous record of anthropogenic change, termed here an Anthropogenic Modification Episode (AME). Nested within the AME are many geologically correlatable events, the most notable being those of the Great Acceleration Event Array (GAEA). This isochronous array of anthropogenic signals represents brief, unique events evident in geological deposits, e.g.: onset of the radionuclide ‘bomb-spike’; appearance of novel organic chemicals and fuel ash particles; marked changes in patterns of sedimentary deposition, heavy metal contents and carbon/nitrogen isotopic ratios; and ecosystem changes leaving a global fossil record; all around the mid-20th century. The GAEA reflects a fundamental transition of the Earth System to a new state in which many parameters now lie beyond the range of Holocene variability. Globally near-instantaneous events can provide robust primary guides for chronostratigraphic boundaries. 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

The Anthropocene is a prospective epoch/series, not a geological event

The Anthropocene defined as an epoch/series within the Geological Time Scale, and with an isochronous inception in the mid-20th century, would both utilize the rich array of stratigraphic signals associated with the Great Acceleration and align with Earth System science analysis from where the term Anthropocene originated. It would be stratigraphically robust and reflect the reality that our planet has far exceeded the range of natural variability for the Holocene Epoch/Series which it would terminate. An alternative, recently advanced, time-transgressive ‘geological event’ definition would decouple the Anthropocene from its stratigraphic characterisation and association with a major planetary perturbation. We find this proposed anthropogenic ‘event’ to be primarily an interdisciplinary concept in which historical, cultural and social processes and their global environmental impacts are all flexibly interpreted within a multi-scalar framework. It is very different from a stratigraphic-methods-based Anthropocene epoch/series designation, but as an anthropogenic phenomenon, if separately defined and differently named, might be usefully complementary to it