[meteorite-list] Holocene Start Impacts: EP Grondine: Rich Murray 2009.10.15

From: Rich Murray <rmforall_at_meteoritecentral.com>
Date: Thu, 15 Oct 2009 00:27:59 -0600
Message-ID: <0BEC316015F04C90B564F3BED37D1D5C_at_ownerPC>

Re: [meteorite-list] Holocene Start Impacts: EP Grondine:
Rich Murray 2009.10.15
___________________________________________________

Hello all,

I'm glad to see a new consensus rapidly evolving re widespread
Holocene Start impacts from myriad fragments of an 13 Ka BP
ice comet.

On Sept 9, 2009,

Jason Utas posted, "...There are quite literally hundreds
(if not thousands) of elongate depressions that are quite easily
visible from the air... literally thousands of square kilometers...."

Darren Garrison agreed, "...Sounds a lot like
Carolina Bays to me."

These impact features may be found in most parts of the world
with Google Earth and Google Maps.

I have intriguing samples from sites in New Mexico and Kauai.

nanodiamond evidence for 12,900 BP Clovis extinction impact,
Santa Rosa Island, discussion on Scientific American website,
Carolina Bay type craters east of Las Vegas, NM:
Rich Murray 2009.07.24
http://rmforall.blogspot.com/2009_06_01_archive.htm
Friday, July 24, 2009
http://groups.yahoo.com/group/AstroDeep/28

Here are the Windows/Linux keyboard commands that make it
easy to "fly" easily, creating an intuitive 3D grasp
of the landscape -- my laptop runs at 1 GHZ with a graphics
card, Windows Vista, Firefox, and 3 GB RAM:

Full screen mode: F11
Lat/Long grid: Ctrl L
Slow movement down: add Alt before other keys
Zoom in, out: PgUp, PgDn keys
Move left, right, forward, back: arrow keys
Tilt view up, down: Shift down arrow, up arrow
Rotate view in circle clockwise, counterclockwise:
Shift right arrow, left arrow
Tilt up towards horizon, down towards directly below:
Shift down arrow, up arrow
Stop, start movement: space bar
Look in any direction: Ctrl, left mouse button and drag
New placemark: Ctrl Shift P
To delete or rewrite a placemark title,
right click it and select Properties
Reset view to north as forward: n
Reset tilt to top-down view: u
Select Tools to select Web to return to your other screens

It's easy to look down about 45 degrees while moving straight
ahead in any direction at an eye elevation of 1-200 km,
scanning a straight strip half-way around the world,
stopping to placemark, examine, and measure any features.

I here list a few of over 100 .1-.5 km shallow
[oblique low velocity ice impacts] craters ,
Bajada del Diablo, Argentina (.78-.13 Ma BP)
[-42.87 -67.47] Rogelio D Acevedo et al,
Geomorphology 2009 Sept:

[ my notes ]
over100 almost circular, crater-type structures with diameters
ranging from 100 to 500 m in width and 30 to 50 m in depth.

three separated impact crater fields, formed simultaneously
on a Miocene basaltic plateau and Pleistocene pediments,
later eroded by Late Pleistocene fluvial processes,
thus three major separate areas.

Crater structures are similar in both target rocks,
although showing different behavior in relation to rock type.
They are simple rings, bowl-shaped with raised rimrock.
Basaltic boulders have been deposited as a ring-shaped pile
and the ejecta are found towards the NE flanks.
The craters present a hummocky bottom, with dry ponds
and lakes in the center, but they do not show raised central peaks.
The rocks within the craters have strong, stable magnetic signature.
No meteorite fragments or other diagnostic landmarks are found.
The craters have been partially filled-in by debris flows
from the rim and wind-blown sands in recent times.
The origin of these crater fields may be related to multiple
fragmentation of one asteroid which broke up before impact,
perhaps traveling across the space as a rubble pile.
When entering the Earth atmosphere, the impacting fragments
were at an estimated shallow input angle
between 15? to 25? from the horizontal.
Alternatively, multiple collisions of comet fragments
could explain the formation of these crater fields.
The layout of the ejecta that moves preferably in the downrange
direction indicates a high velocity impactor
coming from SW towards NE.
Based on field geological and geomorphological data,
the age of this event is estimated to be from the
late Pliocene-early Pleistocene and the late Pleistocene,
most likely early-middle Pleistocene (i.e., 0.78-0.13 Ma ago).

Area 1 -42.80 -67.42
Area 2 -42.85 -67.72
Area 3 -42.97 -67.71.

The central dots seen from above on most of the 66 craters
are dry lake surfaces.

For the 18 craters found on top of the Miocene basaltic
plateaus (volcanic mesas), including craters A, B, C, G
in the oblique 3D view in Fig. 5, no meteorite fragments
or other megascopic diagnostic landmarks have been
found among the boulders and pebbles of vesicular basalt.
Chemical tests found some Ni in the bottom sands and silts
of two horseshoe-shaped craters A and A', while X-ray
diffraction found magnetite and petrogenic silicates, and
maybe taenite, a rare Fe-Ni mineral.

Craters on the pediment surface have hummocky
bottoms with dry ponds and salt lakes in the centers,
and were later dried and filled up with gravel and
sand, from debris flows from the rim and wind-blown
sands, and so are often hard to see. Ejecta is often
strongly marked in views from above.

The entire crater field seems not elliptical, but chaotic.
The lack of meteoritic fragments suggests vaporization
of the object from very high temperatures during a
hypervelocity impact.
A rubble-pile would fragment greatly in the air
before ground impact.

Possibly, and more likely, a small comet nucleus,
several hundred meters in diameter, formed by water
and carbon dioxide ice, with a small fraction of rocky matter,
generally very fragile, would also fragment
into hundreds of pieces in the air before ground impact,
leaving no physical traces behind.

The vaporization from impact makes a nearly spherical
expanding envelope of hot gas, creating fairly round craters.

Research was funded by CONICET and The Planetary
Society, Pasadena, California. Dr. William McDonald,
State University of NY at Binghamton, visited Ushuaia.
[ end of summary notes]

I list some here with decimal degrees, and widths,
lowest crater depth, and highest ejecta or terrain in km.
Google Earth and Maps has about the same quality and
resolution as their photos, about 1 m, enough to see
2 ruts in a dirt road, but not enough to tell a car from
a bush, boulder, or hole.

The first 5 are on grey basalts and trachybasalts.

C -42.788574 -67.548570 .860 km deep, .894 N ejecta,
W edge eroded [ Fig. 4, 5 ]

D -42.785062 -67.533669 .278, .850, .873, S edge eroded
[ both Fig. 4]
D' -42.782352 -67.535068 .219, .868, .875

G -42799292 --67.526446 .291, .779, .804, S edge eroded
[ Fig. 4, 5 ]

H -42.770845 -67.538997 .168, .917, .923

The next 5 are on sandstones and conglomerates.

A -42.808171 -67.436316 .220, .648, .653
[ on the right (E) in Fig. 4, 5 ]

A' -42.807212 -67.441747 .165, .654, .656
[ on the left (W) in Fig. 4, 5 ]

B -42.805004 -67.505493 .351, .683, .707
[ both Fig. 4, 5 ]
B' -42.809174 -67.503760 .271, .681, .683

E -42.791507 -67.489361 .355, .681, .687

Google Earth does show color in this bleak badlands.
Processing the color data may be helpful.

In the region, I soon found:

R1 -42.768 -67.484 green pond .5 km, .695 high
on eroded slope 2 km E of H, 3 NNW of E,
while 6.84 km NNE is

R2 -42.708 -67.484 dry white eroded lake 1.4X.6, .497 high,
slopes WE .545-.500

Erosion, possibly from immediate catastrophic regional floods,
similar to glacial volcanic debris flows, mudflows, outburst floods,
and lahars, can follow and alter craters and impact shocked
bedrock, concentrating minerals, and evolving oriented lakes
and features.

Could much of this be from the 12,950 BP Younger Dryas start?

Could the white minerals, common in various depressions
on high durable surfaces, derive largely from the impactors?

R3 -42.729681 -67.686537 lake 1.11X.46, 1.082, 1.095
Quinelaf Eruptive Complex. Final basic lavas facies [Fig. 2]

p 60 4.1 Quinelaf eruptive complex
"...On the basis of several radiometric datings, Ardolino (1981)
identified that the latest volcanic activity of this trachytic unit
(the Final Lava Facies) took place in the Miocene."

R4 -42.143501 -67.686537 lake 1.16X.60, 1.486, 1.542,
cluster

R5 -41.474665 -67.912145 3.0 round,
flat shallow 1.3 white core, .968, 1.167 1km N
also 1.2X.6 on SW rim,
5 km E of Rd 8 ns, 28 km N of Rds 5 and 7.
1X.5 green farm on NW rim of white core, with road.
Part of a regional crater field on a dark, incised plateau --
the edges are dark layers .1 km deep at least.


Let's do a little back of the envelope estimate of how much
a single sizable ice comet could achieve.

Let the target be the entire sphere of sea and land of
all Earth, 5.1 x 10E8 km**2 = 500,000,000.

We consider 0.01 MT = 10 KT TNT impact energy per km**2,
which would be 5.1 x 10E6 MT -- half the 10 km
iron Chicxulub impact level of 1 x 10E7,
which 65 million years ago
vaporized a mile of sea and bedrock limestones, spewing
white hot debris far into space and all over the globe,
setting wildfires everywhere, generating enough smoke
and dust to turn day into frigid night, followed by
long, torrential rains of nitric and sulfuric acid -- so
goodbye dinosaurs and most other species.

But a largely ice comet, bearing any percentage of
fairly ordinary minerals, is very different. Very weak,
perhaps only a rubble pile, it will fragment into many
pieces from gravitational stesses as it nears Earth.
The pieces will impact not just a single point, but
a continental region, entering the atmosphere over
a period of hours, and the fragments will fragment
80 miles up, and their fragments will fragment and
so on, until there are many air bursts, at various heights,
shining much of the energy back into space, while
flash heating and blasting the Earth below. Some
fragments, perhaps with iron and nickel or rock,
perhaps with high amount of minerals, probably
many as ice, water, or complex superpressure clouds
of high temperature steam, will impact.

Larger objects, less slowed by air resistance, will
go further and land quicker, with the smaller ones
slowing and falling to both sides behind the initial
strikes, forming a long elliptical cluster.

But there are many variations. Large objects
entering the atmosphere will have greater air
resistance and drag on their lower surface,
inducing spin forward in the direction of movement.
This forward spin will create lift, keeping the
fragment in flight longer, while reducing its velocity.
Spin will spread the heat and pressure of air resistance
more evenly over the whole surface of the object,
delaying fragmentation and melting. Slower
velocity allows time for melting and vaporization
to change its shape, perhaps becoming more
streamlined, while the surrounding layer of water
and steam reduces air resistance
and the rate of heating, while giving the body
more time to slow down.

Some may simply come down with a low-speed
plop, while some may glide almost gracefully into
a very low angle impact. The speed and angle
of impact determines how explosive it is:

1. Just a plop -- leaving a hill, ridge, parallel ridge,
fan of ridge lobes, ring, or long oval of mineral
deposits and some displaced ground
earth, rock, and water.

2. Enough energy to melt all its ice -- might look
much like case 1, but with greater distances
and lower heights, along with more obvious
flooding and splashing.

3. Enough energy to vaporize all the ice --
in addition to any water and high pressure
superheated steam already coming with the
object, along with contributions of ice and water
on and in the ground, could in a low-angle
impact cause the bottom contact side of the
object to evolve a "pancake" of very high
pressure superheated steam under it, moving
forward and growing as the whole object
is converted into steam, so that huge pressures are
created on the ground, while the escaping
steam all around creats a focused blast that
levels the ground widely and leaves a small rim,
with mostly forward shallow trenches in one,
two, or many more directions. The steam
pancake may enable the impact process to
continue forward for much longer distances, creating
one or more trenches of various sizes and depths,
often expanding like a fan or triangle from the
point of impact. I call these features "pawprints".

Spinning around along the direction of travel
may create impacts that are much deeper on one side
or the other.

The hydrodynamics are very complex. There could
be directed jets of steam that, like shaped explosive
charges, penetrate surprisingly deeply into ice,
water, earth, or rock, or jet pairs in opposite
directions or in a forward V pattern.

These cases consider relatively low velocities,
in the range of 5 km/sec, mainly at angles of
approach at the ground of 5 to 30 degrees.
The most probable angle from space is 45 degrees,
but ice meteors and their fragments may tend
to curve into lower angles near the ground.

Thus, in comparison to iron or stone impacts,
the pressures of impacts are much lower,
with little penetration of the surface, and much
less excavation, ejection, and vaporization of
surface water, ice, soil, and rock.

Tests have shown that oblique, low angle impacts
on ice as thick as the diameter of the fragment
will cause little damage to surfaces under the ice.

A very helpful line of evidence comes from the
mineral layers and coatings blasted onto exposed
bedrocks or rocks blasted through the high pressure,
superheated steam, carrying minerals as gases,
molted nano and microdrops, hot dusts, and a
variety of larger framents. The steam's pressure
and temperature would change rapidly with its
overall expansion, or momentarily increased pressures
and temperatures upon impact with surfaces or
flying objects. A huge varity of often durable
coatings would be created, adding to any
effects on surfaces and objects from initial
radiant heat and blast from the impact.
Natural would be common white minerals
(sodium chloride, silicon dioxide,
calcium carbonate, sodium sulfate,
titanium dioxide, etc.), grey hematite,
red iron oxide, black manganese oxide,
and perhaps boron minerals.

I have specimens of rocks from crater fields
in New Mexico and Kauai with these coatings,
as thick as 6 cm. The initial layers of reddish
to black color are often named "desert varnish",
and can evolve slowly over thousands of years
of wet and dry climate from accumulated dust,
water deposition, and microorganism activity.
White coatings are often described as caliche.
Water and wind, of course, will rework and
widely redistribute minerals from ice impacts.

I welcome specific critical feedback.

Rich Murray 505-501-2298 rmforall at comcast.net
1943 Otowi Road, Santa Fe, NM 87505


----- Original Message -----
From: "E.P. Grondine" <epgrondine at yahoo.com>
To: <meteorite-list at meteoritecentral.com>
Sent: Tuesday, October 13, 2009 2:02 PM
Subject: [meteorite-list] Holocene Start Impacts


E.P. Grondine
Man and Impact in the Americas
 ______________________________________________
http://www.meteoritecentral.com
Meteorite-list mailing list
Meteorite-list at meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list

 2009 FALL AGU San Francisco, CA
Field-Analytical approach of land-sea records for elucidating
the Younger Dryas Boundary syndrome
SECTION/FOCUS GROUP:
Paleoceanography and Paleoclimatology (PP)
SESSION: Younger Dryas Boundary:
Extraterrestrial Impact or Not? (PP15)
AUTHORS (FIRST NAME, LAST NAME):
Thierry Ge 1,
Marie-Agnes Michele Courty 2, [ see also:
http://www.springerlink.com/content/x344w32523h00q43/
http://www.cprm.gov.br/33IGC/1345536.html
http://en.wikipedia.org/wiki/Marie-Agn%C3%A8s_Courty
http://www.futura-sciences.com/fr/news/t/terre-3/d/un-asteroide-a-t-il-percute-la-terre-il-y-a-4000-ans_10148/ ]
Francois Guichard 3.
INSTITUTIONS (ALL):
1. Geoarcheology, INRAP, Pessac, France.
2. Prehistory, IPHES-ICREA, CNRS-MNHN,
Tarragona, Spain.
3. Paleoocenography, CNRS-CEA UVSQ,
Gif-sur-Yvette, France.

 Linking lonsdaleite crystals, carbon spherules and diamond
polymorphs from the North American dark layers
at 12.9 cal yr B.P. to a cosmic event has questioned
the nature and timing of the related impact processes.

A global signal should trace the invoked airshocks and/or
surface impacts from a swarm of comets
or carbonaceous chondrites.

 Here we report on the contextual analytical study of debris fall
events from three reference sequences of the Younger Dyras
period (11-13 ka cal BP):

 (1) sand dune fields along the French Atlantic coast at the
Audenge site;

(2) A 10 m record of detrital/bioorganic accumulation in the
southern basin of the Caspian Sea with regular sedimentation rate
(0.1 to 3 mm per year) from 14 to 2-ka BP cal;

(3) the Paijan sequence (Peruvian coastal desert) offering
fossiliferous fluvial layers with the last large mammals and
aquatic fauna at 13 ka BP sealed by abiotic sand dunes.

 The three sequences display one remarkable layer of exogenous
air-transported microdebris that is part of a complex time series
of recurrent fine dust/wildfire events.

The sharp debris-rich microfacies and its association to ashes
derived from calcination of the local vegetation suggest
instantaneous deposition synchronous to a high intensity wildfire.

The debris assemblage comprises microtektite-like
glassy spherules, partly devitrified glass shards,
unmelted to partly melted sedimentary and igneous clasts,
terrestrial native metals, and carbonaceous components.

The later occur as grape-clustered polymers,
vitrified graphitic carbon, amorphous carbon spherules
with a honeycomb pattern, and
green carbon fibres with recrystallized quartz and metal blebs.

Evidence for high temperature formation from a
heterogeneous melt with solid debris and volatile components
derived from carbonaceous precursors supports an impact
origin from an ejecta plume.

The association of debris deposition to total firing would trace
a high energy airburst with surface effects of the fireball.

In contrast, microfacies and debris composition of the
recurrent fine dust/wildfire events would trace a series
of a low energy airburst.

Their record is expressed in the Audenge sequence by a series
of water-laid laminae of charred pine residues formed of
carbonaceous spherules wrapped by carbonaceous polymers
that includes lonsdaleite crystals as detected by high resolution
in situ micro-Raman analysis.

This association suggests recurrent flash forest wildfires ignited
by hot spray of carbon-rich debris, followed by heavy snow falls.

The record from the Peruvian desert suggests a possible linkage
between the repeated debris fall/wildfires during the Younger
Dryas and the following irreversible aridity along the Peruvian coast.

In contrast the Caspian record of the Younger Dryas period
indicates more gradual changes, possibly buffered by the
hydrological functioning of the Caspian sea in a complex region.

The Audenge context offers the amplified signal needed to
understand at local to global scales the spatio-temporal pattern
of impact-airburst events.

 KEYWORDS:
[4901] PALEOCEANOGRAPHY /
Abrupt/rapid climate change,
[1029] GEOCHEMISTRY /
Composition of aerosols and dust particles,
[4924] PALEOCEANOGRAPHY / Geochemical tracers,
[5420] PLANETARY SCIENCES: SOLID SURFACE
PLANETS / Impact phenomena, cratering.

Previously Presented Material:
Original results, never presented, never published

http://www.mail-archive.com/meteorite-list at meteoritecentral.com/msg77749.html

[meteorite-list]
Younger Dryas Impact hypothesis GSA and AGU Abstracts
Paul H.
Sun, 13 Sep 2009 05:06:43 -0700

The GSA abstracts can be found in
"T94. Impact Cratering from the Microscopic
to the Planetary Scale II
(GSA Planetary Geology Division;
International Continental Scientific Drilling Program [ICDP];
GSA Sedimentary Geology Division;
GSA Structural Geology and Tectonics Division;
GSA Geophysics Division;
Paleontological Society;
GSA International Division) at:

http://gsa.confex.com/gsa/2009AM/finalprogram/session_25177.htm

The abstracts are:

1. Dryas. Pinter, N., A. C. Andrew, and D. Ebel, 2009,
Extraterrestrial and Terrestrial Signatures at the Onset of
the Younger Geological Society of America Abstracts with
Programs.

http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_162563.htm

2. Holliday, V. T., and D. J. Meltzer, 2009,
Geoarchaeology of the 12.9ka Impact hypothesis.
Geological Society of America Abstracts with Programs.

http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_160959.htm

3. Paquay, F., S. Goderis, G. Ravizza, and P. Claeys, 2009,
No evidence of of extraterrestrial geochemical components at the
Bolling-Allerod/Younger Dryas Transition.
Geological Society of America Abstracts with Programs.

http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_163154.htm

4. Surovell, T. A., and V. T. Holliday, 2009,
Non-Reproducibility of Younger Dryas Extraterrestrial
Impact Results
Geological Society of America Abstracts with Programs.

http://gsa.confex.com/gsa/2009AM/finalprogram/abstract_163912.htm

PDF files of various papers by Dr. V. T. Holliday can be
found beneath "Publications of Vance T. Holliday" at:

http://www.argonaut.arizona.edu/holliday.htm

This includes:

Vance T. Holliday, David A. Kring, James H. Mayer, and Ronald J.
Goble, Age and effects of the Odessa meteorite impact, western Texas,
USA. Geology. vol. 33, pp. 945-947. at:

http://www.argonaut.arizona.edu/articles/holliday_etal2005.pdf

The Abstracts to the 2009 American Geophysical Union
presentations for
"PP15: Younger Dryas Boundary: Extraterrestrial Impact
or Not?"
have not been posted yet.
Eventually, they should appear at:

http://www.agu.org/meetings/fm09/program/scientific_session_search.php?show=detail&sessid=388

According to George Howard,
http://www.georgehoward.net/clovis_comet_at_fall_2009_agu.htm ,
the titles of the accepted papers are:
[ Rich Murray: full abstracts also given ]

1. Lost Impacts

2. High resolution Osmium isotopes in deep-sea
ferromanganese crusts reveal a large meteorite impact
in the Central Pacific at 12.4 ka

3. What Caused the Younger Dryas? An Assessment of
Existing Hypotheses

4. An Independent Evaluation of the Younger Dryas
Extraterrestrial Impact Hypothesis

5. Cosmic impact: What are the odds?

6. Cometary airbursts and atmospheric chemistry:
Tunguska and a candidate Younger Dryas event

7. Problems with the Younger Dryas Boundary ( YDB )
Impact Hypothesis

8. Beringian Megafaunal Extinctions at ~37 ka B.P.:
Do Micrometeorites Embedded in Fossil Tusks and
Skulls Indicate an Extraterrestial Precursor to
the Younger Dryas Event?

9. Airbursts in the Sky with Diamonds? Shock
Limits to a Younger Dryas Impact.

10. The platinum group metals in Younger Dryas
Horizons are terrestrial

11. Putting the Younger Dryas Cold Event into Context

12. Field-Analytical approach of land-sea records
for elucidating the Younger Dryas Boundary syndrome

13 Evidence of four prehistoric supernovae <250
parsecs from Earth during the past 50,000 years

14. Oblique impacts into low impedance layers

15. Cold Climate Related Structural Sinks Accommodate
Unusual Soil Constituents, Pinelands National Reserve,
New Jersey, USA.

16. Positive anomaly in platinum group elements and
the presence of shocked diamonds: Two question marks
at the Younger Dryas

17. Nanodiamonds and Carbon Spherules from Tunguska,
the K/T Boundary, and the Younger Dryas Boundary Layer

18. Are Nanodiamonds Evidence for a Younger Dryas
Impact Event?

19. Rockyhock and Kimbel Carolina Bays: Extraterrestrial
Impact or Terrestrial Genesis?

20. No support from osmium isotopes for an impact event
at the Bolling-Allerod/Younger Dryas transition

21. Climatic Control of Biomass Burning During the Last
Glacial-Interglacial Transition

22. Human Population Decline in North America during
the Younger Dryas

23. Summary of impact markers and potential impact
 mechanisms for the YDB impact event at 12.9 ka

24. Testing Younger Dryas ET Impact ( YDB ) Evidence
at Hall's Cave, Texas

25. Wildfires, Soot and Fullerenes in the 12,900 ka
Younger Dryas boundary layer in North America.

Obviously, the discussion about the Younger Dryas
Impact Hypothesis continues.

Yours, Paul H.
___________________________________________________


http://www.cprm.gov.br/33IGC/1345536.html

HPF-16 Correlation between marine and terrestrial ecosystems
Land-sea correlation elucidating the spatial variability of the
4 kyr B.P. impact event from the submicron to the global level
Marie-Agnes Courty, CNRS (France)
Michel Mermoux, CNRS (France)
David Smith, MNHN (France)
Mark Thiemens, Univ. of California (United States)
Xavier Crosta, CNRS (France)
Nicolas Fedoroff, CNRS (France)
Thierry Ge, INRAP (France)
Fran?ois Guichard, CEA (France)
Kliti Grice, Univ. of Technology (Australia)
Paul Greenwood, Centre for Land Rehabilitation,
School of Earth and Geographical Sciences (Australia)

Land-sea correlation is of major importance to unravelling
impact events that operated at multiple temporalities through
a continuum of spatial scales.
Our multidisciplinary study of marine and terrestrial records has
provided clues to elucidate the conflicting pattern of the 4 kyr BP
impact from the submicron to the global level.
The markers of this impact comprise anomalous micro-facies and
allochthonous debris with organic, mineral and metallic tracers
characterized by petrography, XRD, Raman microspectrometry,
SEM, GC-IR-MS, isotope and noble gas analyses.
Dating on charred plant materials provides C14 radiometric ages
at 4050-3950 + 50 yr BP.
The allochthonous debris comprise intact rock-clasts,
glassy components and crystallised breccia with a wide size range
(a few mm down to a few m).
Lechatelierite, baddeleyite, diaplectic quartz and graphite-derived
diamond in the glassy phases confirm the impact origin.
A micro-faunal-floral assemblage
(foraminifera, diatoms and radiolaria) from subtropical, subpolar
and austral seawaters in intact marine clasts gives a provenance
from austral latitudes.
Tasmanite-like bitumen and sandstone clasts with chromite,
zircon, metal-rich quartz and alumina components supports an
origin from the continental plateau somewhere around
South of Australia.
The proximal emplacement of the impact-ejecta in the
Austral Ocean (Adelie Land and Kerguelen Plateau)
is traced by 7 to 12 m thick anomalous facies.
Evidence of heating of local marine components and their mixing
with the impact debris indicates seawater vaporisation
by a hot debris jet.
The identification of the 4 kyr BP tracers suggests that the
Henbury crater field, the Boxhole crater, intermediate areas with
glass debris, and the Edeowie glass field in South Australia,
together with the Darwin glass field in Tasmania, could relate
to projection of the hot debris jet to the nearby land areas.
Association of the 4 kyr BP tracers to a wild-fire on the
Reunion Island and to a giant tsunami along the north-west
Sumatra coast would respectively express local wildfires by
dispersion of the firery debris and long-distance effects of the
impact shock-wave.
The distal emplacement of the impact-ejecta in the northern
hemisphere is represented by a widely-distributed pattern
of scattered fine debris and an erratic pattern showing great
concentrations of the 4 kyr BP allochthonous debris along a
narrow band locally traced across Syria and France.
They formed splashed deposits of layered pseudo-tektites,
pillow-like slabs, highly-vesiculated glassy materials and breccia
blocks associated with firing evidence.
The spatial pattern of the fire traces indicates micro-scale ignition
produced by fragmentation at the soil surface of blocks yielding a
hot metal-rich carbonaceous melt due to their re-heating while
re-entering the Earth atmosphere.
The fine debris pattern is suggested to trace dispersion of
ejecta blocks fragmented before reaching the Earth's surface.
___________________________________________________








 
Received on Thu 15 Oct 2009 02:27:59 AM PDT