Oil company geologist helps find new asteroid crater

From Australian National University Sciencewise Magazine

A big impact on climate: Examining a new asteroid crater found in the Timor Sea

Article Illustration

The newly discovered impact feature lies near the Ashmore Reef in the Timor Sea north west of Australia

As new land-based oil deposits become increasingly scarce, oil companies have turned to the seabed in search of new reserves. The drilling and seismic surveying often find oil, but occasionally they turn up something far more interesting, at least from a scientific perspective.

This was exactly what happened when oil company geologist Dariusz Jablonski of Finder Exploration was conducting seismic surveys in areas straddling the Ashmore Platform and Browse Basin north of Australia. His results led him to suspect the existence of a large impact feature so Dariusz contacted Dr Andrew Glikson at ANU who is a specialist in the study of extraterrestrial impacts. Dr Glikson was asked to study cuttings from the Mount Ashmore-1B well and investigate whether there was indeed evidence for an ancient impact structure.

But how exactly does a scientist go about determining if a 35 million years old structure deep below both rock and sea is indeed impact related?

‘It’s a process of elimination,” Dr Glikson explains, “Essentially we look at all plausible explanations and eliminate them one by one. But the process can be difficult depending on the type of rocks in that particular area.”

When an impact occurs in Igneous or Metamorphic Rocks it’s usually possible to see tell-tale crystallographic fracture planes under the microscope. These particular structures known as planar deformation features (PDFs) only form due to high velocity shock imparted by an impact but can’t form due to volcanic explosition, which makes them a “fingerprint” for impacts. However in the sedimentary rocks that are commonly found under the sea the high concentration of volaltiles – mainly water and carbon dioxide – makes it much less likely that PDFs will form, so scientists have to look for other clues.

 

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Planar deformation features (PDFs) as seen in this microscope image, are a strong geological fingerprint for impacts in igneous and metamorphic rocks. However, when the impact occurs in sedimentary rocks (as is the case with the Mount Ashmore Dome) differences in the physical and chemical properties of these rocks mean PDFs are rarely seen.

 

Two candidates for non-impact explanations of dome structures are volcanism and salt domes. Salt domes are created when restricted marine basins have a cyclical evaporation causing salt and gypsum to be deposited over many centuries. As time progresses these salt deposits can become covered in layers of sediment. However because the salt is less dense than the sedimentary rock that forms over it, it has a tendency to rise up through the rocks above like a bubble.

 

Article Illustration

Seismic section through the Mount Ashmore Dome

 

“The Mount Ashmore feature extends far too deep into the crust to be a salt Dome and has a basement rise underneath it, “Dr Glikson says, ”In the seismic profiles we can see a number of features deep below that are not consistent with such an explanation. We also see no indication of igneous material in the drill core, which makes a volcanic explanation unlikely. So what we’re left with is an impact explanation.”

“At the time of the impact the ocean would have been a few hundred metres deep” Dr Glikson adds, “But when you’re talking about large impacts, the presence of a relatively small amount of water is not a major factor in attenuating the impact.”

Only very low angle impacts which plunge into deep water may be slowed down.  When a large mass of a hard material like silicate rock or iron hits the Earth the tremendous kinetic energy is converted into thermal energy at the end of its trajectory. This releases a vast amount of heat in a very small time, melting the rocks and vaporising the solid mass into a series of hot gasses such as CO2, water and silicate vapour. The process involves a rapid and enormous increase in volume, perhaps analogous to an underground nuclear detonation.

You can see clear evidence of this impact explosion mechanism for yourself if you look at the moon through a small telescope. The many thousands of asteroids and comets that have hit the moon over the last 4 billion years came in at every possible angle. If you imagine throwing stones into mud, the ones that hit at a grazing angle leave long elliptical indentations and it’s actually quite difficult to create a circular carter. However when you look at the moon, all the craters and basins are essentially perfect circles.

The explanation of this is that when an asteroid hits a planetary sized body, the initial crater (which may be elongated) is wiped out a few milliseconds later by the explosive release of kinetic energy. This explosion creates an essentially spherical impact feature. So all the craters on the moon are perfectly round despite the variety of impact angles.
There is a rule of thumb that says that the diameter of a particular crater sill will be about 10 to 20 times larger than the impactor that caused it. “The minimum size of the Mount Ashmore dome, which represents elastic rebound doming of the Earth’s crust triggered by the impact, is 50 kilometers at the base, but the full size of the impact crater – not yet defined – may be significantly larger” Dr Glikson says. “This would suggest that the asteroid that created the structure was at least 5 kilometers across.”

The impact of such a large asteroid throws up vast amounts of dust and fine particulate matter into the upper atmosphere. This reflects sunlight resulting in a significant, though temporary cooling of the planet. Although a single massive impact could create this effect, a series of smaller ones close together in time may have a bigger and more prolonged effect. Despite the fact that asteroid impacts are very infrequent, clusters of asteroid impacts have occurred several times through the history of Earth.

Relatively small objects like asteroids that orbit the Sun are very strongly influenced by the gravity of massive planets, in particular Jupiter. Astronomers believe that perturbations caused by Jupiter’s gravity either prevented a planet forming from the debris between Mars and Jupiter or even tore it apart. This perturbation coupled with gravitational attraction between different asteroids means that many of them orbit in loose clumps. The implications for the Earth being, that if one member of such a clump hits the Earth many of the others may also do so within a few orbits, creating an impact cluster. Scientists know that there have been a few such clusters of impacts throughout the history of the Earth. There are a number of impact features around the world that, like the Mount Ashmore dome, are about 35 million years old suggesting the newly discovered dome is part of this impact cluster.

“Around the same time as the Mount Ashmore impact, a 100 kilometer wide asteroid impact structure formed in Siberia, and another measuring 85 km in diameter in Chesapeake Bay, off Virginia, in the United States.  Likewise a large field of tektites – molten rock fragments splashed by impact – fell over northeast America. This defined a major impact cluster across the planet,” Dr Glikson says.

This impact cluster would have contributed significantly to a global cooling in so far as it may have triggered the opening of the Drake Passage between Antarctica and South America. The opening of the Drake Passage allowed continuous circulation of the circum-Antarctic ocean current, isolating the Antarctic continent from warm mid-latitude currents and allowing the onset of its large ice sheet, which acts as a ‘thermostat’ for the Earth’s climate.” Dr Glikson explains.

 

Article Illustration

Looking at the Earth from the South Pole, the broken land connection between Antarctica and South America can clearly be seen, forming the Drake Passage. Thanks to this passage continuous ocean current circulation around the Antarctic continent became possible about 34 million years ago

 

The opening of the Drake Passage and the impact may have occurred around the same time purely by coincidence. However it’s also possible that the disturbance of the crust caused by such massive impacts may have nudged the existing tectonic movements into action. A bit like kicking a boulder on a hill. The kick isn’t enough to move the boulder far but it can give it the tiny extra impetus it needs to start and gravity will do the rest.

“We really don’t know for certain if there’s any causal relationship between the impact cluster and the opening of the Drake Passage,” Dr Glikson says, “But what we do know with certainty is that impact clusters have had and may continue to have, profound implications for life on planet Earth.”

h/t to WUWT reader “scarlet pumpernickel”

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15 Responses to Oil company geologist helps find new asteroid crater

  1. AleaJactaEst says:

    very similar to the discovery, again during exploration seimic shooting, of the Yucatan peninsula event which is thought to have been analogous with the KT boundary (Cretaceous/Tertiary) and the extinction of the dinosaurs

    http://miac.uqac.ca/MIAC/chicxulub.htm

    Big Oil do have a great deal to offer the world.

  2. Malaga View says:

    Thank you… what a wonderful post… a real pleasure to read and inwardly digest… and an opportunity to consider plate tectonics and the concept of an expanding earth based upon the accretion of extraterrestrial matter.

  3. Bill Illis says:

    With the other two 5 km asteroid strikes right at this time, Cheasapeake Bay and Popigai in Russia (dated at 400,000 years apart), another one of the same size around the same time starts to suggest a bigger asteroid that broke-up as the source.

    Graphic of the continental alignment and ocean currents around Australia and Antarctica right at this time (Bijl 2009). We can see the impact site was on the wrong side of Australia to open up the Drake Passage or start-up the Antarctic Circumpolar Current. Antarctica iced over about 33.5 million years years ago so it was quite some time after the impact.

    http://img35.imageshack.us/img35/8862/antoceancurrents35m.jpg

  4. Douglas Dc says:

    So a relatively quick catastrophe-changing the planet quickly.Hmmm. Where have I heard that before?
    Trouble is, we have the ability to stop or mitigate a strike before it happens,
    but we ( NASA) have to reach out to Muslim countries first, and chase Chimeras
    of the AGW kind.
    I may be Russia and China that saves US from the “Big Rock”…

  5. Gareth says:

    “The explanation of this is that when an asteroid hits a planetary sized body, the initial crater (which may be elongated) is wiped out a few milliseconds later by the explosive release of kinetic energy. This explosion creates an essentially spherical impact feature. So all the craters on the moon are perfectly round despite the variety of impact angles.”

    Amongst the many things in this article that I did not know, the above is the most fascinating.

    Thanks Anthony and scarlet pumpernickel!

  6. Thanks for being this to our attention. I find these things fascinating, always have. In the late 80’s I did some work on the middle Cretaceous Steen River structure in northwestern Alberta. One of my associates that was sitting the discovery well, well before I had a chance to look at the data. It too was found by oil exploration and instead of being covered by water, is covered by ±80 million years of sediment. Numerous other impact structures are known around the world. The best know have strong surface expressions. These that are covered by water or sediment obviously less so.

    When it comes to the earth and especially the oceans we still have an enormous body of ignorance to learn about.

  7. jmc says:

    Looking for oil in places that were never covered by forests means they believe in the abiogenic petroleum origin?
    http://en.wikipedia.org/wiki/Abiogenic_petroleum_origin

  8. paulhan says:

    Looking at that photo of Antarctica, it actually looks like something scored the Earth between it and South America. I can see what looks like two ridges with a roundy bit at the end as if a huge asteroid hit it at an acute angle. Great article.

  9. John F. Hultquist says:

    jmc says:
    October 9, 2010 at 10:44 am
    Looking for oil in places that were never covered by forests means they believe in the abiogenic petroleum origin?

    No, I don’t think so.

    http://www.geoexpro.com/geoscience/rich-petro/

  10. Jimmy Haigh says:

    Some guys I worked with in Aberdeen found one in the North Sea a few years ago:

    http://en.wikipedia.org/wiki/Silverpit_crater

    This one happened at the Cretaceous/Tertiary boundary. Some workers think it’s a salt disollution feature but my first impression when I saw it was that it was a meteorite impact.

  11. Louis Hissink says:

    The Mount Ashmore Dome has the appearance of a mantle plume structure, suggesting it has origins deeper in the mantle rather than from a surface impact. A recent paper by Medvedev in New Concepts in Global Tectonics discusses this idea for more recent impact structures (Current issue embargoed for 2 issues).

    I wonder if the are seismic profiles across other impact structures elsewhere for comparison?

  12. davidmhoffer says:

    Odd that on a blog like this the most interesting (in my opinion) remark seems to have gone unnoticed:

    ” isolating the Antarctic continent from warm mid-latitude currents and allowing the onset of its large ice sheet, which acts as a ‘thermostat’ for the Earth’s climate.” Dr Glikson explains.”

    Would be most interesting to have Dr. Glikson expand on that…

  13. anna v says:

    I decided to respond and say that I think it was read with interest and it informed us both about methods unknown andn speculations of asteroid impacts. I believe most readers felt no need to respond because there is nothing controversial.

  14. Bill Illis says:

    davidmhoffer says:
    October 9, 2010 at 7:17 pm
    Odd that on a blog like this the most interesting (in my opinion) remark seems to have gone unnoticed:

    ” isolating the Antarctic continent from warm mid-latitude currents and allowing the onset of its large ice sheet, which acts as a ‘thermostat’ for the Earth’s climate.” Dr Glikson explains.”

    Would be most interesting to have Dr. Glikson expand on that…
    ———————–

    The exact date this happened was 33.6 million years ago. In a little more than 100,000 years, Antarctica went from a continent with a few mountain glaciers and very cold winters but warm enough summers that most of the snow melted, to a continental ice sheet where the glaciers extended onto the continental shelves.

    Global temperatures fell by 2.0C as a result. If one calculates the extra amount of sunshine that all this new glacier reflected back to space (versus how much a cold winter Antarctica would have reflected before), it is just enough to drop global temperatures by 2.0C.

    Ocean currents at 35 million years ago – note how the ocean gyres are circulating in warmer ocean water from the tropics around the three continents which are mostly linked together at least in terms of continental shelves and deep ocean current possibilites.

    http://img35.imageshack.us/img35/8862/antoceancurrents35m.jpg

    By 33.6 million years ago, enough separation occured between Australia and Antarctica – South America and Antarctica that the Circumpolar Current started up isolating Antarctica in an extreme polar climate and it rapidly glaciated over – shown in the modern configuration.

    http://polardiscovery.whoi.edu/antarctica/images/antarctica-circulation-en.jpg

    CO2 over the period in question – 1400 ppm – and it stayed at this level for another 2.0 million years before starting the fall toward 280 ppm which it reached at 24 million years ago.

    Just before CO2 finally reached 280 ppm and was still falling, Antarctica suddenly warmed up again and the glaciers melted back by about half. Global temperatures increased again. This warming was probably caused by that unusual area in the Drake Passage noted above – between South America and Antartica which is really a tectonic plate feature – there are dozens of small cratons that get jostled around between the two larger tectonic plates.

    At 25 million years ago, the Antarctic Circumpolar Current became cut-off in the Drake Passage area and it didn’t really fully open up again until about 8 million years ago or even 3.0 million years ago and Antarctica fully iced over again.

    http://img25.imageshack.us/img25/8785/drakepassagerestricted.jpg

    Note – no change in CO2 levels was required to explain these events and CO2 levels actually acted in the opposite direction to the formation and melting of ice on Antarctica. Very simple and well-studied example of how continental drift and the resulting ocean currents affect the global climate.

  15. John Kehr says:

    35 Million years ago is very important date to remember. That is how long Antarctica has been frozen over. The sea levels dropped globally as the average global temperature plummeted.

    When warmists start spouting about Antarctica melting, ask them about Antarctica freezing solid when the Earth had HIGHER levels of CO2 (near 800 ppm) and the average temperature of the Earth was about 7C warmer than it is now. It still froze solid. It has had continuous ice sheets for more than 34 million years. It has been frozen solid for the past 12 million years.

    Arguing AGW is one thing, saying it will melt Antarctica is absolute folly.

    John Kehr
    The Inconvenient Skeptic

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