The varved succession of Crawford Lake, Milton, Ontario, Canada as a candidate Global boundary Stratotype Section and Point for the Anthropocene series

Abstract

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed as the Global boundary Stratotype Section and Point (GSSP) for the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with fallout from nuclear and thermonuclear testing—239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, unusual in a meromictic lake, inhibits the mobilization of 239Pu, the proposed primary stratigraphic guide for the Anthropocene.

Candidate sites and other reference sections for the Global boundary Stratotype Section and Point of the Anthropocene series

“…In the Sihailongwan Lake core, statistical analysis of all measured proxies identified a 1954 change point, but the rapid increase in 239+240 Pu activities at 88 mm (1953 CE) was selected as the preferred GSSP level (Han et al, 2023), supported by rapid increase in radioactive 129 I concentrations from ~1950; alternatively, the base of the lowermost dark-yellow lamina at 85 mm (1955–1956) forms a prominent lithological boundary. For the Crawford Lake core, the GSSP is proposed at 15.6 cm depth, at the base of the calcite lamina deposited in the summer of 1950 CE, selected because of the rapid rise in key markers between 1950 and 1954 and in particular the primary guide of 239+240 Pu having a significant initial upturn at ~1950 CE (McCarthy et al, 2023). A prominent triplet of laminae mark the summers of 1956, 1957 and 1958 CE, with the proposed GSSP located near the base of a ~1-cm-thick interval below in which there are weakly perceptible white laminae.…”

“…The Crawford Lake, Ontario site, discussed by Waters et al (2018), is detailed by McCarthy et al (2023) with new data from five cores collected in 2019. Originally investigated to demonstrate the sporadic occupation by pre-European indigenous peoples and subsequent colonisation by Europeans, the new study has provided a wider range of proxies (not just those indicative of agricultural change) and a more detailed investigation of the younger part of the succession.…”

The Anthropocene as an epoch is distinct from all other concepts known by this term: a reply to Swindles et al. (2023)

“…Within this event array, the primary guide to the Global boundary Stratotype Section and Point is likely to be the plutonium isotopic signal, which reflects nuclear weapons testing from 1945 onwards (Waters et al, 2015(Waters et al, , 2019. This signal has a detectable global upturn in the stratigraphic record beginning around and soon after the year 1950 (Han et al, 2023;McCarthy et al, 2023;Waters and Turner, 2022;Waters et al, 2023;Fig. 1) and in a range of stratigraphic settings.…”

The Anthropocene's stratigraphic reality and the humanities: a response to Finney and Gibbard (2023) and to Chvostek (2023)

“…Geologist Francine McCarthy and her team, building on the work led by Jock McAndrews going back to the 1970s (Roberts, 2014), engaged with First Nation peoples and other constituencies as they explored the evidence (McCarthy in Thomas, ed., 2022). Their core samples reveal not only the gentle changes of the Holocene when indigenous people lived in the area from the 13th to the 15th centuries, but also the abrupt developments of the Anthropocene (McCarthy, Patterson, et al, 2023). This is another example of the approach Chvostek calls for.…”