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NZ ideal location to resolve dinosaur debate - 03/05/1998

New Zealand scientists are leading an international team in a study of New Zealand rocks and fossils to try and find out what killed the dinosaurs 65 million years ago.

The scientists are confident that a study of marine and freshwater sedimentary rocks and the fossils they contain will improve understanding of the dramatic extinction of many species at the end of the Cretaceous era.

Most scientists now accept that a 10km-diameter meteorite crashed to earth in the area of modern Mexico at the end of the Cretaceous era and caused a global catastrophe which wiped out the dinosaurs and many other groups of animals and plants.

But geologists and paleontologists are divided on this theory because although they accept the evidence for a meteorite impact, they are not convinced that it actually caused the extinctions. The theory doesn't explain why some groups of animals went extinct and others didn't or why some extinctions, such as the dinosaurs, appear to have occurred gradually over the last few million years of the Cretaceous era.

The New Zealand-led team has set out to establish the role that gradual processes, such as climate change, may have played in the changes in fossil assemblages across the narrow band of sedimentary strata that separates the Cretaceous and Cenozoic eras. This sedimentary horizon is called the K-T boundary in the geological literature; "K" being the standard abbreviation for the Cretaceous era, and "T" standing for tertiary, a now out-dated alternative for the Cenozoic.

The team is led by Chris Hollis, a paleontologist with the Institute of Geological & Nuclear Sciences Limited.The three-year research project is funded by the New Zealand government-sponsored Marsden Fund, which supports long-term, internationally-important, "blue-sky" research.

The scientists will begin by examining fossils and ancient sediments from a wide range of New Zealand sites.

'' New Zealand is ideally located to resolve this debate,'' Dr Hollis says.'' Although several thousand kilometres from the Yucatan Peninsula, Mexico, where scientists believe the meteorite impact site to be,"(See Smithsonian Institution on-line exhibit "Blast From The Past") debris from the impact appears to be abundant in several sites in Marlborough, at the northern tip of the South Island. ''

The ancient dust in the K-T boundary layer in coastal Marlborough has extremely high levels of elements such as iridium and palladium, which are much more abundant in meteorites than in possible sources on earth, as well as containing mineral grains bearing the tell-tale signs of impact fracture.

'' More significantly for our study though, New Zealand has the only southern hemisphere record of the extinction event across a wide range of environments,'' Dr Hollis says.

'' This gives us the opportunity to compare changes in plants and animals across an environmental profile from terrestrial swamp to continental shelf to deep ocean. In this way we can find out if the changes really were instantaneous, as we'd expect from a sudden global catastrophe, or progressive, perhaps affecting the ocean environments first and later affecting the terrestrial realm, as we might expect from more gradual climate changes.''

The researchers also want to find out why some fossil studies suggest extinctions in New Zealand were less severe than in the equatorial and northern hemisphere areas.

" It is crucial to discover if these global variations have purely earth-bound causes or are due to the effects of the meteorite impact being more complex that initially predicted. Such findings will lead to better understanding of how the earth's ecosystems might respond to future catastrophes of this kind."

Contact: Chris Hollis

QUESTIONS COMMONLY ASKED ABOUT THIS PROJECT:

How do you know where to look?

Geologists have been mapping the rock sequences in New Zealand for over a hundred years and with the aid of paleontologists have worked out the general age of most sedimentary strata in the country. The precise location of the K-T boundary has been worked out in several areas by detailed studies of microfossils undertaken largely by members of the current project working at GNS (Percy Strong, Graeme Wilson, Ian Raine and Chris Hollis).

Microscopic fossils of marine plankton (foraminifera, dinoflagellates, radiolaria) and terrestrial spores and pollen show either dramatic or subtle changes in species content at the boundary which allow us to pinpoint the boundary. Subsequent studies of the boundary clay layer have confirmed the location in many sites by the presence of abundant iridium, and other materials of presumed meteorite origin found in K-T boundary clays the world over.

What are you looking for, and how difficult are they to find?

We are looking for fossils and other sedimentary or chemical signals of environmental change. New Zealand doesn't have a good record of large fossils, such as dinosaur or mammal bones, ammonite or other shellfish, but we have an extremely good fossil record of microfossils (see above).

We have carefully selected places in New Zealand in which the K-T boundary is already well-defined and the microfossil content is known in general terms. The value of microfossils as opposed to bigger fossils is that they occur in great numbers and diversity in the appropriate sort of rock. A thumb-sized piece of limestone from the K-T boundary strata in Marlborough for instance will contain thousands of foraminifera and radiolarians and hundreds of dinoflagellates representing about two hundred separate species.

Will you be digging deep beneath the earth's surface or are you concentrating on ancient layers that are exposed?

In some cases we will be looking at rock samples collected by drilling into the earth, but most of our collections will be made along streams or shore platforms. Because New Zealand is so active geologically, rocks of Cretaceous and early Cenozoic age have been already rucked up by earthquakes, so that their layers now lie almost vertically rather than horizontally as they were when they were originally deposited. So a small stream cutting can contain vertical layers representing several million years of late Cretacaeous and early Cenozoic time.

What laboratory techniques are involved in analysing your samples?

Getting the fossils out of the rocks can be difficult. Sometimes we can just crush the rock into small pieces and wash it through a small sieve using warm water and detergent. Other times we have to use dangerous acids to preferentially dissolve the rock and leave the fossils. Once extracted the fossils must be identified under a microscope , sometimes using a scanning electron microscope. We then have to count them so that we can compare changes in populations over time (just like with humans, we call such work, "census studies").

Other members of the team will be looking at the chemical composition of the rocks. Study of changes in the relative abundance or carbon and oxygen isotopes will provide a guide to climate changes. Study of complex carbon compounds called biomarkers will tell us more about the changes in life forms that don't preserve as fossils.
Has this type of study been attempted in other countries?

There have been many studies of the rocks and fossils across individual K-T boundary rock sequences. But this is the first study worldwide, as far as we are aware, of a suite of sequences representing an environmental profile.

Why is it so important to have the "meteorite layer" in the New Zealand rocks?

Working on strata where the "meteorite dust" has been identified is very important because we are trying to distinguish the effects of a sudden event from those caused by gradual processes. So we have to be sure we have the record of the meteorite layer in the strata so as to be confident we have a pretty continuous record of the first few thousands of years after the meteorite impact. In many areas in New Zealand and overseas the boundary layer and the earliest Cenozoic strata are missing, so a gradual change over this interval will appear like a sudden change.