Will Drilling Project in Petrified Forst Settle Long Norian "Dispute?"

Tourists flock to Petrified Forest National Park in Arizona to marvel at great glittering logs of petrified wood. But geologists hope to flock there this month in search of something less visible and more scientifically significant: a core obtained by drilling half a kilometre into rock more than 200 million years old.

Drillers will spend several weeks boring through layers of rock that house the fossils of tiny early dinosaurs and giant crocodile-like phytosaurs, as well as the leaves and pollen of an entire fossilized ecosystem. The goal of the US$970,000 drilling project is to stitch together a complete picture of most of the middle and late Triassic period, a turbulent interval that saw both a mass-extinction event and the emergence of dinosaurs. Geoscientists hope to use the decay of radioactive uranium in layers of volcanic ash in the core to precisely date events between about 205 million and 235 million years ago, just before the supercontinent Pangaea began to break apart.

“It’s a unique opportunity to put together a coherent time framework for a critical part of the Triassic,” says John Geissman, a geologist at the University of Texas at Dallas and one of the project’s leaders. “Sure, we have other continental Triassic records, but the Petrified Forest area is pretty darn good when it comes to details.”

The Petrified Forest effort has been years in the making. It is a follow-up to a project in which a Triassic core was drilled from New Jersey’s Newark sediment basin between 1990 and 1993 (ref. 1). That project aimed to tease out changes in the amount of sediment that was deposited as Earth went through cyclical shifts in the shape of its orbital path around the Sun. “If we can show that the Newark timescale is correct, we can empirically calibrate the Solar System’s behaviour,” says Paul Olsen, a geologist at the Lamont–Doherty Earth Observatory in Palisades, New York, and a member of the project team. “That’s probably the most exciting aspect for me.”

The effort, funded by the US National Science Foundation and the International Continental Scientific Drilling Program, might also help to resolve a simmering dispute. Comparisons of the Newark data with data from Triassic rocks in the Mediterranean have led some researchers to suggest radically revising the period’s history. This reworking would lead to one subdivision — the Norian stage — taking up nearly half of the entire Triassic period, drastically changing dates of key evolutionary events, including the emergence of certain dinosaurs.

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