Ontario lake to be studied by Brock-led team as possible geologic time reference site

A group of researchers are hoping Crawford Lake in Milton will help confirm a new episode in the world’s geological time scale.

The Brock University-led team of scientists has identified the Halton region lake as a possible location to define a new geologic epoch called the Anthropocene.

On Tuesday, Aug. 14, Professor of Earth Sciences Francine McCarthy and researchers from Brock, Carleton and McMaster will collect sediment layers spanning the last millennium from the basin of Crawford Lake.

If they find what they’re looking for in these sediments, the research team will make a submission to the Anthropocene Working Group (AWG), an international group charged with evaluating proposals on where evidence of the Anthropocene can be best seen.

To define a new geologic epoch, scientists must establish a “golden spike,” an internationally agreed-upon location with a reference point in a section of rock or sediment layers that signals the beginning of a new episode in the geologic time scale.

McCarthy and colleagues are setting out to prove that the 22-metre-deep Crawford Lake should be that “golden spike.”

“The lake is small but very, very deep,” says McCarthy, who has been conducting research at Crawford Lake for decades. “The waters don’t get oxygenated all the way to the bottom and that lack of oxygen makes preservation ideal.”

Because the lake is in a protected conservation area, it has been an ideal location for other studies over the years. Having the core recovered from the lake on Tuesday be designated as a golden spike would mean “scientists from around the world would come to Crawford Lake to see the defining area,” says McCarthy.

If the AWG were to vote in favour of using the lake, the proposal would then be evaluated by the International Subcommission on Quaternary Stratigraphy, chaired by Brock Professor of Earth Sciences Martin Head.

Head, who is also a member of the AWG, says the calm and anoxic bottom waters of Crawford Lake have produced layers each year that give a very clear geologic record.

These layers result from the accumulation of dark organic matter after organisms in the upper water column die and tiny calcite crystals that gradually sink to the lake bed.

“This is essential for any site being considered in defining the base of the Anthropocene,” says Head. “The big question is whether Crawford Lake has a plutonium fallout signal.”

Researchers use the presence of plutonium 239 — an isotope released during the detonation of nuclear weapons — as a mark of time.

“The rise of plutonium 239 in the early 1950s seems to give the best global signal,” says Head. “It arises from increasing aboveground nuclear weapons testing at this time and declined in the early 1960s with the Partial Test Ban Treaty in 1963.”

The AWG considers some point during the mid-20th century to be the best starting point for the Anthropocene, a suggested new geological epoch distinct from the Holocene in which we are currently officially living.

This distinctiveness arises from the fact that human activities have shifted the way our planet is now behaving as an integrated system, says Head.

This shift is known as the Great Acceleration, a mid-20th century phenomenon associated with global industrialization, commercialization and energy use.

“Plutonium 239 could be a very convenient geological marker for this Earth systems shift,” says Head.

What: Drilling of bottom of Crawford Lake by Brock-led geological research team

When: Tuesday, August 14, noon to 4 p.m.

Where: Crawford Lake Conservation Area, 3115 Conservation Rd., Milton. Ask for directions at the interpretive centre.

Who: Brock Professors Francine McCarthy, Martin Head and Michael Pisaric; Carleton Professor Timothy Patterson; McMaster Professors Joe Boyce and Eduard Reinhardt.

Why: To investigate and potentially propose a site that would define the Anthropocene epoch.

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