3D - Denmark, Dinosaurs & Death

If BBC can walk with Dinosaurs, so can we, and nothing extraterrestial is too large or too small for us to explore.
By Ole Nielsen, Brussels.

  1. Danish dinos, iridium and K-T boundary
  2. Deccan Plateau basalts of western India
  3. Dinos, Bucky Balls, the greatest mass extinction ever and the P-T boundary

Why?

As a Dane I would of course like to show you that Denmark has the most important, spectacular and famous geology in the world. The most popular geological theme today seems, however, to be Dinosaurs, and we haven’t found many dinosaurs in Denmark, not dead ones at least. Nevertheless let this be the story of the beginning and the end of the dinosaurs, or to talk bio-stratigraphy, the beginning and the end of the Mesozoic.

Why did the dinosaurs die out? That is a question that has raised a lot of discussion, and thereby luckily has lead to a lot of research.

When did the dinosaurs die out? They died out together with a lot of other living organisms about 65 million years ago in the second largest mass extinction we have seen on earth. The largest mass extinction ever happened about 250 million years ago. These two mass extinction events mark the beginning and the end of the Mesozoic Era or “Age of Dinosaurs” (The Triassic, Jurassic and Cretaceous periods).

Stevns
Stevns

Dinosaurs, iridium and the K-T boundary

Some twenty years ago the well-known physicist and Nobel Price winner (for physics in 1968) Louis Alvarez (1911-1988) from the University of California at Berkeley thought he knew why the dinosaurs died out. He was convinced that the cause was an explosion of a supernova. If so he would expect a higher concentration of the very rare plutonium at the so-called K-T boundary, which is the boundary between the end of the Cretaceous period and the beginning of the Tertiary period. He went out into the field to prove it together with his son Walter Alvarez, who was a geologist, and they started looking at the boundary layer near the town of Gubbio in Italy. To their surprise they found no plutonium, but an important enrichment of iridium, exactly in the boundary layer.

As cosmic matter has higher iridium concentrations than terrestrial materials Alvarez concluded that the iridium was due to a large meteoritic impact 65 million years ago, and he and his team was quick to publish the findings [1] in 1980.

Geologists all over the world rushed to their nearest exposure of the K-T boundary to look for iridium.

One such place is Stevns Klint in Denmark, where a thin clay layer, the so-called Fish Clay, between Maastrichtian chalk and Danian Cerithium Limestone, marks the Maastrichtian-Danian interval. A lithostratigraphy of this interval had been published in 1973 [2], where the authors identified a Ni-anomaly in the Fish Clay. The background iridium level is typically around 0.3 ppb. At Gubbio the concentration was 9 ppb, but at Stevns Klint it was as high as 160 pbb. Measurements around the world at the K-T boundary – at more than 100 locations - confirmed the anomaly. In Spain it went up to 450 pbb.

Other peculiarities at the boundary seemed to confirm the impact theory as well, but where was the crater? If Alvarez was right the meteorite would have had a 10 km diameter and produced a crater 200 km in diameter. It could of course be in the sea or have disappeared at a destructive plate margin. In the 1990’s however researchers discovered a subsurface crater that fulfilled all the criteria in Yucatan Peninsula, Mexico, at Chicxulub. Now after more than 3000 professional papers on the subject since the first paper in 1980 most geologists agree that the impact did occur, and that the time was right – but was this the cause of the mass distinction? It is a popular belief, but at least one other competing theory is still in the running.

Dinos
Dinos

The Deccan Traps and the mantle plume theory

The volcano eruptions theory is more down to earth - literally. Eruptions from a large volcano could also block the sun and cause serious global climate change. The Deccan Traps lava fields around Bombay in India still cover an area about the size of Western Europe, and would originally have covered most of India with thickness of up to a few kilometres. The basaltic lavas erupted when India on its way to its present position passed over the hot spot where Reunion Island is today (the Piton de la Fournaise volcano).

New strong evidence for this theory was published last year by a group of French scientists [3]. They made a detailed section of the main lava pile and found that the age varied from 65.4 (± 0.7) for five lava flows near the base of the section to 65.2 (± 0.4) million years for a dyke crossing some of the formations just below the topmost formation (but not the uppermost formation itself). Their conclusion was that at least 1800 of the 2500 m basalt were erupted within 1 million years or probably less at the K-T boundary. The amount of CO2, dust and ash in the atmosphere would have been catastrophic, triggered greenhouse warming, and made food chains collapse.

Could mantle plume eruptions also be (partly) responsible for the mass extinction at the P-T boundary? The mother of all mass extinctions, an extinction that through the shock it caused to the wildlife set the stage for the evolution of dinosaurs.

The most voluminous eruption of continental flood basalt occurred in Siberia (at the edge of supercontinent Pangea), it is argued at the time of the Permian-Triassic extinction. It seems in fact that a number of superplumes recorded by continental floods may correlate with corresponding mass extinctions.

Does that mean that we can dismiss the impact hypothesis? According to a team of scientists from Washington University, NASA’s Ames Research Centre and Goddard Space Flight Centre [4] the answer is NO!

Bucky Balls

The iridium concentration at the P-T boundary is much smaller than at the K-T boundary. What is worth looking at, however, is an astounding concentration of “Bucky Balls”.

bucky ball
Bucky Ball: Buckminsterfullerenes

Bucky Balls, short for Buckminsterfullerenes, were discovered in 1985 by Robert F. Curl, Harold W. Kroto and Richard E. Smalley and named after Buckminister Fuller. They are naturally occurring stable forms of pure carbon, C60, where hexagons and pentagons of carbon link together in a coordinated fashion to form a hollow cluster with bonding strains equdistributed among 60 carbon atoms, so that it reminds of a football. (In 1996 the three chemists were awarded the Nobel Prize in Chemistry for their discovery of fullerenes).
The drawing shows C60 with carbon atoms as red dots. Later a whole family of fullerenes were discovered – C70, C84, as small as C28, and I gather by now up to C400.

The Bucky Ball or fullerene molecules found at the P-T boundary must be extraterrestrial, because of the exceptional composition of helium isotopes encapsulated within the hollow balls – nearly exclusively 3He, and not, as usually on earth, mainly 4He with only a little 3He.

A carbon star is, according to Luann Becker, the only place where these gas filled fullerenes could have been formed under extreme high temperatures and high gas pressure outside our solar system.

The scientists think that the celestial body that slammed into the Earth was about the same size as the Yucatan asteroid, which means between 6 and 12 km in diameter. Becker and her team reckon however that the two bolides were of different composition.

It is more difficult to find rocks from the P-T boundary than from the K-T boundary (because of the difference in age – respectively 250 and 65 million years old), but rocks containing Bucky Balls with gas traces have been sampled at different places in Japan, China and Hungary.

Where is the Crater?

Find out and become famous! But beware; a subduction zone has probably consumed it. The crater is certainly not in Denmark anyway, so let’s finally get back to the K-T boundary.Where can the K-T boundary be seen in Denmark and what does it look like?
I shall try to answer these questions in a coming article on this website

In the meantime I recommend a review of impact effects (concentrating on the K-T event) written by David A. Kring [5] in GSA Today, August 2000, and available on the Web at:

http://www.geosociety.org/pubs/gsatoday/gsat0008.htm

References

[1] ALVAREZ, L.W., ALVAREZ, W., ASARO, F. AND MICHEL, H.V. (1980). Extraterrestrial cause for the Cretaceous-Tertiary extinction, Science, vol. 208, 1095-1108.

[2] CHRISTENSEN, L. ET AL. (1973). Sedimentology and depositional environment of Lower Danian fish clay from Stevns Klint, Denmark. Bulletin of Geological Society Denmark 22, 193-212.

[3] HOFMANN, C., FERAUD, G. & COURTILLOT, V. (2000). 40AR/39AR dating of mineral separates and whole rocks from the Western Ghats lava pile: further constraints on duration and age of the Deccan traps. Earth and Planetary Science Letters 180, 13-27.

[4] Luann BECKER, Robert J. POREDA, Andrew G. HUNT, Theodore E. BUNCH, and Michael RAMPINO (2001). Impact Event at the Permian-Triassic Boundary: Evidence from Extraterrestrial Noble Gases in Fullerenes. Science Feb 23 2001: 1530-1533.

[5] Kring, D.A. (2000). Impact Events and Their Effect on the Origin, Evolution, and Distribution of Life, GSA Today, vol. 10, no. 8, August 2000.

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