The magnitude of fracturing of the country rocks in the Manicouagan structure increased towards the centre of the crater, the point of maximum shock effect. The fragmentation increased to where the energy from the impact caused the rocks to melt. These melted rocks remain today as the central peak of the crater (the island in the image). The “smaller” fragmented rocks surrounding the “melt rock” central peak were easily evacuated by glaciation and erosion. The annular moat around the Manicouagan central peak is what remains after the country rocks that experienced “maximum” fracturing were removed. This circular moat is an impact indicator.

 I feel very fortunate to document this specimen as I do not know of another shatter-cone from Manicouagan in any other collection. Unfortunately, weight constraints with the loading of the canoe prevented me from returning with shatter-cones (rocks don’t float).

The passage of the shock wave through the rock changes the structure of some of the enclosed minerals. IE: change is possible in the feldspar mineral plagioclase. The shock wave can break down the structure of the mineral, changing parts of it into a diapletic glass (glass formed at high-pressure in the solid-state) which is isotropic, or uniform in all directions. This photograph of a thin slice of plagioclase, 0.03 millimetre thick, is seen here in cross-polarised light, with a ‘sensitive tint’ plate. The original plagioclase is coloured yellow and the shock-changed mineral is purple. This sample is from the Manicouagan impact crater. (Courtesy Denis W. Roy & MIAC).

¹ STOKES LAW: If the particles are falling in the viscous fluid by their own weight due to the Earth’s gravity, then a terminal velocity, also known as the settling velocity, is reached when this frictional force combined with the buoyant force exactly balance the gravitational force. The resulting settling velocity (or terminal velocity) is given by:

V_s = ( 2 (ρ_p – ρ_f ) / 9 η ) g R² where:

• V_s is the particles’ settling velocity (m/s) (vertically downwards if ρ_p > ρ_f, upwards if ρ_p < ρ_f ),
• R is the radius of the spherical object (in metres),
• g is the Earth’s gravitational acceleration (m/s²),
• ρ_p is the mass density of the particles (kg/m³),
• ρ_f is the mass density of the fluid (kg/m³), and
• η is the fluid’s viscosity (in [kg m^-1 s^-1]).

I mentioned earlier that it is not recommended to do this trip by canoe (as we did). The waves on the annular moat and in Memory Bay can reach dangerous heights very quickly. On our final day in the impact structure we were returning to our starting point in Kauashapishkau Bay in a semi-calm wind. But within 20 minutes the wind had increased from under 10 kts to greater than 30 kts! We had to perform an emergency beaching on an island 1/3 of the way across the annular moat.

We made it onto the beach by surfing the waves! It was fortunate that Eric was an experienced white water canoe operator, as we may have otherwise been dumped. Here, we had just started a fire to dry ourselves off.

We will be marooned here for 22 hours waiting for the winds to subside. So, what to do until the wind subsides? Why, explore of course!

We eventually made it off the island at 5AM the next morning. Within 15 minutes of waking up during a wind lull, we had struck camp and were paddling for dear life for the eastern shore of the annular moat! We made it back across the reservoir without incident in under three hours. We had a great tail wind. What an adventure!! It was surreal later that morning eating our hot egg and bacon breakfast in a restaurant and realizing that just hours ago we were marooned without any idea of how long it would be until we could get back to the main land.

5. MANICOUAGAN IMPACT EJECTA

The fireball generated by the impact probably expanded as far as the present location of New York City. The impact also triggered powerful seismic events and ejected material out of the atmosphere. The ejected material was sent on a ballistic trajectory around the earth. Like the Chicxulub impact, the Manicouagan impact left behind a global geochemical signature in the rock record.

As a result of the Manicouagan impact, molten rock and dust from this bedrock left a thin layer of glass beads and shattered mineral grains in a rock deposit in the United Kingdom.

Dating of this UK deposit connected it to Manicouagan precluding most of the European impact sites nearby as the source of the deposit layer.

 

 

European Space Agency: [SELECTED QUOTES]The documented late Triassic spherule layer of SW England deposit (illustrated here) contains an abundance of spherules, common shocked quartz and a suite of accessory minerals believed to have been derived direct from the impact site. These include garnets, ilmenites, zircons and biotites. Garnets and ilmenites are highly fractured, and biotites show prominent kink bands indicative of shock.

The time of the deposit was determined by noting the decay of radioactive potassium in the spherule layer and dates at 214 ± 2.5Ma. This is comfortably within the date of the late Triassic Manicouagan impact event.
Single grain K-Ar ages for the biotites are in the range 700-1100Ma which are superficially similar to the Grenville rocks around the Manicouagan impact site. Given the geometry of the contemporaneous Triassic continental assembly, the contact point of the impactor was only 20 crater diameters from the site of deposition of this ejecta layer. (Thackrey et al 2006) [SELECTED QUOTES]

A distal impact deposit has recently been reported from a location near Bristol, England. The 0-15 cm thick, discontinuous layer is of Late Triassic age and occurs in a sequence of red calcareous mudstones deposited unconformably on Carboniferous limestone, in a semi-arid, continental environment. It consists of closely packed, millimetre sized green spherules, composed of a green clay surrounding a calcitic or hollow core. They have been inferred to be diagenetically altered type I spherules, formed from quenched impact-melt droplets, deposited aerially from an expanding impact ejecta curtain. The stratum, with a reported 39Ar – 40Ar age of approximately 214 Ma, is coincident with the age of two known impact craters from the Late Triassic, Manicouagan in Canada and Rochechouart in France. The focus of the present study is to determine if a meteoritic component and projectile type can be identified from this impactoclastic air-fall bed and adjacent strata, using a combination of geochemical analyses – chromium isotope systematics, siderophile and platinum group elemental ratios. In particular, we have developed a new method for the isolation and concentration of chromium, following sample dissolution. Chromium isotope ratios are determined using a multiple collector, inductively coupled plasma, mass spectrometer (MC-ICP-MS) for which the conditions have been established to obtain high precision ratio measurements. ( AMORet al 2005)

A Late Triassic Impact Ejecta Layer in Southwestern Britain

Gordon Walkden ^1*, Julian Parker ¹, Simon Kelley ²

¹ Department of Geology and Petroleum Geology, Kings College, University of Aberdeen, Aberdeen AB24 3UD, UK.
² Department of Earth Sciences, Open University, Milton Keynes MK7 6AA, UK.

^* To whom correspondence should be addressed. E-mail: spherules@abdn.ac.uk.

Despite the 160 or so known terrestrial impact craters of Phanerozoic age, equivalent ejecta deposits within distal sedimentary successions are rare. We have recognized a Triassic deposit in southwestern Britain that contains spherules and shocked quartz, characteristic of an impact ejecta layer. Inter- and intragranular potassium feldspar from the deposit yields an Ar-Ar age of 214 ± 2.5 million years old. This is within the age range of several known Triassic impact craters, the two closest of which, both in age and location, are Manicouagan in northeastern Canada and Rochechouart in central France. The ejecta deposit provides an important sedimentary record of an extraterrestrial impact in the Mesozoic that will help to decipher the number and effect of impact events, the source and dynamics of the event that left this distinctive sedimentary marker, and the relation of this ejecta layer to the timing of extinctions in the fossil record.

*******************************

Asteroid impacts may not always cause mass extinctions, say geologists in the US. They believe that the the impact that created the 100-kilometre Manicouagan crater in Quebec did not coincide with any extinction event.

Some scientists had claimed the Manicouagan impact occurred at the same time as the mass extinctions which ended the Triassic period about 202 million years ago. But Joseph Hodych and G. Dunning of Memorial University of Newfoundland in St John’s have now dated zircon crystals from the site. They find them to be 214 million years old.

Evidence that the impact of an asteroid caused the mass extinctions at the end of the Cretaceous period 65 million years ago made many geologists suspect that a similar impact at the end of the Triassic period caused the mass extinctions then. The Manicouagan crater, one of the largest impact structures on the Earth’s surface, was an obvious candidate for the impact site. Previous estimates of its date came with errors that were large enough to overlap with the boundary between the Triassic and Jurassic periods.

The best evidence for an impact at the end of the Triassic was reported by David Bice of Carleton College in Northfield, Minnesota, in late 1990. At the Triassic-Jurassic boundary in Italy, he found ‘shocked’ quartz grains, which are considered evidence of an impact. Bice and others believed that the extinctions occurred rapidly.

Hodych and Dunning’s date, obtained by analysing uranium and lead isotopes, is the most precise yet (Geology, January, p 51). Bice remains unconvinced.

From issue 1807 of New Scientist magazine, 08 February 1992, page 23

6. STRATIGRAPHIC RECORD IN THE FUNDY RIFT BASIN OF THE MANICOUAGAN IMPACT

The impact did trigger a powerful seismic event as Lawrence Tanner from Bloomsburg University recently discovered in a deformed zone of the Fundy Rift Basin. “There have been previous reports attempting to link paleoseismicity, as recorded by soft-sediment deformation features, to impacts,” Tanner explained. “But this is the first instance of linking the Manicouagan impact to the stratigraphic record. The Fundy rift Basin experienced a substantial period of volcanic activity at the time of the Manicouagan impact.

ABSTRACT
The terrestrial redbeds of the Blomidon Formation were deposited in the Fundy rift basin during Norian to Hettangian time. A 10-m-thick zone of intensely deformed strata that occurs near the base of the formation is characterized by rubblization and step-wise faulting. Correlation of this zone basin-wide indicates that it is a record of a very powerful paleoseismic event. The greater thickness of the deformed zone in proximity to the border fault, the Minas Fault Zone (MFZ), indicates that movement of the MFZ was the immediate cause of this paleoseismicity. The presence in strata just above the deformed zone of quartz grains displaying features of shock metamorphism raises the intriguing possibility that reactivation of the MFZ was triggered by a bolide impact. (Tanner 2002)

The ~100 km-wide Manicouagan impact structure in northeastern Canada, 700 km from the Fundy rift basin, is one of the largest well-documented impact sites. Once considered a candidate for the cause of the end-of-Triassic extinctions, U-Pb zircon dating of the impact melt establishes the age of the impact as much earlier Norian, approximately coeval with the seismic deformation of the Blomidon Formation. Stratigraphic constraint of the age of the impact allows an accurate assessment of the effects of this event on biota.  (see – David E. Brown ET AL 2018 and Onoue 2012 above)The impact did trigger a powerful seismic event as Lawrence Tanner from Bloomsburg University recently discovered in a deformed zone of the Fundy Rift Basin. “There have been previous reports attempting to link paleoseismicity, as recorded by soft-sediment deformation features, to impacts,” Tanner explained. “But this is the first instance of linking the Manicouagan impact to the stratigraphic record. I made the association between the impact and paleoseismicity in the Fundy Rift Basin, a sedimentary basin 700 km away from the impact site, and went looking for shocked quartz grains. Finding them allows us to place this impact into a stratigraphic context and look elsewhere to see if there are any significant biotic effects. So far, there don’t seem to be any.” The Fundy rift Basin experienced a substantial period of volcanic activity at the time of the Manicouagan impact. (GEOLOGICAL SOCIETY OF AMERICA 2002)

7. NOTES

EARTH SCIENCE PICTURE OF THE DAY

• • MANICOUAGAN – BRECCIA
  • MANICOUAGAN – IMPACT MELT

 

RASC 150 

Components of the RASC Sesquicentennial Logo:

The aurora borealis is a quintessentially Canadian space-weather phenomenon, one shared with other high latitude cultures. RASC members have contributed to the scientific, historical, and artistic investigation of the northern lights, and have promoted their recreational enjoyment.

The Manicouagan astrobleme (214 ± 1 Ma) represents the major discovery of sites of impact cratering in the Canadian Shield, an effort pioneered by astrophysicists and geophysicists at the Dominion Observatory (ca. 1950-), many of whom were RASC members. This world-impacting research played a crucial role in changing scientific and popular perceptions of crater-forming mechanisms, solar-system history, and planetary geology. The representation of the crater also acknowledges Canadian excellence in meteor dynamics, meteorite petrology, meteorite curation, and the RASC’s long-standing interest in such work.

The stars represent the major Canadian contributions to stellar spectroscopy done at the Dominion Observatory, the Dominion Astrophysical Observatory (also see this), the David Dunlap Observatory,(additionally refer to this) and elsewhere (ca. 1905-), whose major contributors were also RASC members (such as J.S. Plaskett [1865-1941], the first Canadian astrophysicist of international repute). The stars also symbolize the asteroseismology, exoplanet transits and eclipses, and investigations into stellar variability through precise photometry achieved by the Microvariability and Oscillations of STars space telescope(MOST, 2003-).

The globular cluster recognizes the field of Helen Sawyer Hogg‘s (1905-1993) greatest scientific contributions (ca. 1926-ca. 1993), and the Helen Sawyer Hogg Telescope (HSHT) at the University of Toronto Southern Observatory at Cerro Las Campanas, one of Canada’s first ventures (1971-1997) in exploring off-shore astronomical installations, which has born lasting fruit in international cooperative installations exploring the full range of astrophysical phenomena, such as the Canada-France-Hawaii Telescope (CFHT, 1979-), the James Clerk Maxwell Telescope (JCMT, 1986-2015 [period of direct Canadian involvement & funding]), the Gemini Telescopes (North 1999-, South 2000-), the Atacama Large Millimetre Array (ALMA, 2011/2013-), the Square Kilometre Array (SKA, 2020-), and the Thirty Metre Telescope (TMT, ca. 2022-).

The spiral galaxy represents both the work of Canadian observational cosmologists (e.g., Sidney van den Bergh‘s classification of Galaxy morphology, Laura Ferrarese‘s work on the morphology & dynamics of early type galaxies), as well as the efforts of amateur Canadian observers of deep-sky objects (DSOs), and imagers.

The comet stands for the contributions to cometography by Canadian comet discoverers, such as David Levy, Rolf Meier, and Chris Wilson.

The Moon symbolizes an object important for first nations’ calendrics, and the earliest recorded observations by Europeans in Canada (17th century lunar reports, and lunar eclipse reports). The Moon together with the stars symbolizes the practice of navigational astronomy on land and water, which was crucial to the formation of Canada. Finally, the Moon is as popular an object for RASC members to share with the public when doing outreach as it was 150 years ago.

R.A. Rosenfeld

RASC AstroNotes Article (September 2010)

from (AstroNotes October 2010😉 – I included the geology from our exploration of the Manicouagan Impact Crater as examples for “Identifying Impact Craters/Structures”.

~214 Ma – LATE TRIASSIC EXTINCTION

Scientists reported in the journal Nature today (March 13, 1998) that they had found evidence of a chain of five craters formed 214 million years ago that was likely due to pieces of a comet crashing into the Earth’s surface, similar to the Comet Shoemaker-Levy 9 impact on Jupiter in 1994. The craters no longer appear to be in a straight line due the shifting of the Earth’s continents due to plate tectonics. Two of the craters, Manicouagan and Saint Martin, are in Canada (Quebec and Manitoba, respectively). The other three craters are Rochechouart in Europe, Obolon in the Ukraine and Red Wing in Minnesota. The impacts appeared to occur at the Norian stage of the Triassic period, about six million years after a mass extinction that wiped out 80% of all the species on Earth, but the ages of all the craters are uncertain enough to include this extinction (from ScienceWeb Daily).

Abstract:

The 34-million-year (My) interval of the Late Triassic is marked by the formation of several large impact structures on Earth. Late Triassic impact events have been considered a factor in biotic extinction events in the Late Triassic (e.g., end-Triassic extinction event), but this scenario remains controversial because of a lack of stratigraphic records of ejecta deposits. Here, we report evidence for an impact event (platinum group elements anomaly with nickel-rich magnetite and microspherules) from the middle Norian (Upper Triassic) deep-sea sediment in Japan. This includes anomalously high abundances of iridium, up to 41.5 parts per billion (ppb), in the ejecta deposit, which suggests that the iridiumenriched ejecta layers of the Late Triassic may be found on a global scale. The ejecta deposit is constrained by microfossils that suggest correlation with the 215.5-Mya, 100-km-wide Manicouagan impact crater in Canada. Our analysis of radiolarians shows no evidence of a mass extinction event across the impact event horizon, and no contemporaneous faunal turnover is seen in other marine planktons. However, such an event has been reported among marine faunas and terrestrial tetrapods and floras in North America. We, therefore, suggest that the Manicouagan impact triggered the extinction of terrestrial and marine organisms near the impact site but not within the pelagic marine realm (Onoue, Tetsuji, October 2012).

Summary of impact structures in the Late Triassic.

December 2017
Conference: 53rd Annual GSA Northeastern Section Meeting – 2018
Lawrence H Tanner, Michael J. Clutson, David E. Brown

2021 December Update: A possible explanation for Manicouagan NOT being related to an extinction event.

Meteorites that produce K-feldspar-rich ejecta blankets correspond to mass extinctions

M.J. Pankhurst, C.J. Stevenson and B.C. Coldwell

Abstract:

Meteorite impacts load the atmosphere with dust and cover the Earth’s surface with debris. They have long been debated as a trigger of mass extinctions throughout Earth history. Impact winters generally last <100 years, whereas ejecta blankets persist for 10³ –10⁵ years. We show that only meteorite impacts that emplaced ejecta blankets rich in K-feldspar (Kfs) correlate to Earth system crises (n = 11, p < 0.000005). Kfs is a powerful ice-nucleating aerosol, yet is normally rare in atmospheric dust mineralogy. Ice nucleation plays an important part in cloud microphysics, which modulates the global albedo.

A conceptual model is proposed whereby the anomalous presence of Kfs post impact is posited to have two key effects on cloud dynamics:

(1) Kfs reduces the average albedo of mixed-phase clouds, which leads to a hotter climate; and

(2) Kfs weakens the cloud albedo feedback mechanism, which increases climate sensitivity.

These mechanisms offer an explanation as to why this otherwise benign mineral is correlated so strongly with mass extinction events: every Kfs-rich ejecta blanket corresponds to a severe extinction episode over the last 600 myr. This model may also explain why many kill mechanisms only variably correlate with extinction events through geological time: they coincide with these rare periods of climate destabilization by atmospheric Kfs.

8. REFERENCES

[see – METEORITE]

Kenneth Amor, Stephen P. Hesselbo, Don Porcelli, Scott Neil Thackrey, John Parnell, A Precambrian proximal ejecta blanket from Scotland GEOLOGY, April 2008

AMOR, Kenneth, HESSELBO, Stephen P., and PORCELLI 2005, GEOCHEMICAL ANALYSIS OF A LATE TRIASSIC DISTAL IMPACT EJECTA LAYER FROM SW ENGLAND. Donald Department of Earth Sciences, University of Oxford.

Brent Dalrymple, Radiometric Dating Does Work! Reports of the National Center for Science Education

M.H.L. Deenen, M. Ruhl, N.R. Bonis,W. Krijgsman, W.M. Kuerschner, M. Reitsma, M.J. van Bergen, A new chronology for the end-Triassic mass extinction. Earth and Planetary Science Letters 2009.

Dence, M.R., Bunch T.E. Cohen A.J. NATURAL TERRESTRIAL MASKELYNITE, THE AMERICAN MINERALOGIST 1967

Dence, M. R. 1976 The Manicouagan impact structure. NASA Spec. Pub.

Kord Ernstson, Gravity surveys of impact structures 2009

French, Bevan M. 1998. Traces of Catastrophe, A handbook of Shock-Metamorphic effects, Lunar and Planetary Institute.

R. A. F. Grieve et al , Manicouagan Impact Melt, Quebec, 1, Stratigraphy, petrology, and chemistry  1978

Haskin, L et al 1998, The case for an Imbrium origin of the Apollo thorium-rich impact-melt breccias. Meteoritics & Planetary Science, vol. 33, no. 5, pp. 959-975.

Murtaugh, J.G. 1972, Shock metamorphism in the Manicouagan cryptoexplosion structure, Quebec. Proc. 24th Int. Geol. Congr.

O’Dale, C.P. 2006; Manicouagan Impact Structure

Onoue T. et al; Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic. National Academy of Sciences, 2012

Onoue T. et al; Bolide impact triggered the Late Triassic extinction event in equatorial Panthalassa. Scientific Reports, 2016

Tetsuji Onouea, et al; Deep-sea record of impact apparently unrelated to mass extinction in the Late Triassic. Rutgers University/Lamont-Doherty Earth Observatory, Palisades, NY, October 3, 2012

Orphal, D & Schultz, P, An alternative model for the Manicouagan impact structure. Proc Lunar Planet Sci Conf 1978.

Simonds, C.H. et al 1976, Thermal model for impact breccia lithification: Manicouagan and the moon. Proc. Lunar Sci. Conf. 7th (1976) p. 2509-2528.

Smith, R. Dark days of the Triassic: Lost world – Did a giant impact 200 million years ago trigger a mass extinction and pave the way for the dinosaurs? NATURE 17 Nov. Vol#479 2011.

Tanner, Lawrence Synsedimentary seismic deformation in the Blomidon Formation (Norian-Hettangian), Fundy basin, Canada 2006, The Triassic-Jurassic Terrestrial Transition

L. M. Thompson, J. Brown and J. G. Spray, SHATTER CONES, SHOCK ATTENUATION AND FELDSPARS: MANICOUAGAN IMPACT STRUCTURE, CANDA. 79th Annual Meeting of the Meteoritical Society (2016)

Earth Impact Database