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Catastrophes and Prehistory


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Troy Exeter
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« Reply #15 on: March 18, 2007, 10:24:44 pm »

Update on the possible Falkland craters.

In his book "Rogue asteroids and doomsday comets" Duncan Steel refers to investigations by Michael Rampino (then at the Goddard Institute of Space Studies): "The appropriate antipodal point to Siberia (Siberian Traps 250Ma) is
the Falkland plateau off Tierra del Fuego... on that plateau Rampino has identified two sub-oceanic circular basins with diameters of about 300km and 200km respectively. Dating the rocks indicates the same age as the Late Permian Extinction." He cites a Rampino paper in the book "Hazards due to Comets and Asteroids" called "Extraterrestrial impacts and mass extinctions" - this may contain more information.
I cannot find any recent references to this subject. It seems that the same issues that delayed discovery of Chicxulub are occurring in the case of the Falkland Plateau - commercial and political sensitivities. The area has potential oil reserves and is also very sensitive politically. Altimetry map of the Falkland Plateau from Delft Institute for Earth-Oriented Space Research.
CCNet 21 Oct 1999
(1)With reference to Michael Paine's communication (CCNet 20.10.1999), several indicators exist for extraterrestrial impacts contemporaneous with the Permian-Triassic boundary - which saw the largest extinction recorded in Earth history - including:
 1.  Araguainha impact structure, Brazil - ~247 +/-5.5 Ma; D=40 km (see R.A.F. Grieve's crater listing).
2.  Lorne Basin - New South Wales - a candidate P-T boundary impact  structure, 35x30 km large (Tonkin, P.C., 1998, Aust. J. Earth Sci.  45, 669-671).
3.  shock features in quartz (PDF) along the P-T boundary in Antarctic  and New South Wales (Retallack G.J., Geology, Jan. 1999; for other  references re-P-T boundary conditions refer to Retallack and Krull, 1999, Aust. J. Earth Sci. 46:785-812.
4.  Weak Ir anomalies reported from China and Japan, remaining  unconfirmed due to possible analytical problems.
On the basis of known stratigraphic constraints, more than one impact structures may prove to be of a P-T boundary age by future isotopic age studies. The Falkland structure (M.R. Rampino) and Bedout structure (off
NW Australia, J.D. Gorter) are only candidate P-T impact structures inferred from geophysical and in the latter case drilling data, as yet unconfirmed and undated. As yet the magnitude of the confirmed impact/s is not large enough to link them to the P-T boundary extinction and/or as triggers of the Siberian volcanic traps (248.4+/-2.4 Ma), although it
is definitely possible further crater/s identification and isotopic dating may shed light on these questions.

Andrew Glikson, Research School of Earth Science,Institute of Advanced Studies, Australian National University

(2) POSSIBLE FALKLAND IMPACT STRUCTURE
There is a large, circular gravity anomaly on the Falkland Plateau that resembles anomalies associated with large impact craters.  It is quite large; greater than 200 km in diameter.

The basin that is indicated could be Late Paleozoic or Early Mesozoic in age, but not much more is known about it. Recent papers have suggested that it is of tectonic origin, but more study is needed.

I suggested that it might be an impact structure, and should be more closely studied back in 1992.

Dr. Michael R. Rampino


See also Duncan Steel's book "Rogue asteroids and doomsday comets"



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