[meteorite-list] Boris and Natasha write about meteorite crater in ocean

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Tue, 17 Apr 2007 15:18:40 -0500
Message-ID: <040401c7812d$97e3d230$862e4842_at_ATARIENGINE>

Hi, Darren, List,

> structure most likely formed between
> the Cretaceous and Paleogene.
> And then scientists have suddenly
> remembered the hypothesis about
> Earth's collision with a giant meteorite,
> happened some 65 million years ago...

    Article not so good. In KT times, sealevels were not
2 kilometers lower than today but between 500 and 1000
meters HIGHER. Present-day sealevels are lower than
almost all the sealevels of the last half billion years. 65 mya
there was considerable oceanic transgression of the
continents. However, NE Siberia and Beringeria were
land, while southern Siberia was under water because
of changes in continental elevation.
    It's a really complicated problem, because ocean-floor
spreading moves the seabottom toward the subduction
zones. Figuring out where the seabottom that presently
contains the astrobleme was 65 mya (million years ago)
is a nightmare problem. In fact, the location seems to be
perched right on the edge of a subduction zone.
    A 500 meter impactor is about 1/250000th of the
volume of Big Chicxy. If you look at it that way, this
could be a secondary crater. Technically, the term
"secondary crater" means a crater from the impact of
a piece of a larger impactor: "An impact crater produced
by the relatively low-velocity impact of fragments ejected
from a large primary crater. Also known as satellitic crater."
    Enough data about the morphology of this crater should
be able reveal if it is a lower-velocity crater. If a secondary
crater, the impactor might be bigger than the 500 meter
estimate which I'm sure was made on the assumption of
cosmic velocity. A 1000 meter impactor would be only
about 1/30000th of the valume of Chicxulub. A tiny chip
off the big hammer.
    That would be a neat discovery which not even Moose
and Squirrel could spoil.


Sterling K. Webb
---------------------------------------------------------------------
----- Original Message -----
From: "Darren Garrison" <cynapse at charter.net>
To: <Meteorite-list at meteoritecentral.com>
Sent: Tuesday, April 17, 2007 10:09 AM
Subject: [meteorite-list] Boris and Natasha write about meteorite crater
inocean


Article good, English not so good. Much catch Moose and Squirrel for
Fearless
Leader.

http://www.russia-ic.com/education_science/science/breakthrough/450/

Meteorite Traces Deep In The Ocean



A theory suggests a giant meteorite falling on Earth 65 million years ago
and
killing all dinosaurs. Russian scientists have found traces of this
meteorite.
During a marine expedition, organized by the Institute of Marine Geology and
Geophysics (Russian Academy of Sciences) and aimed at ocean studies, the
crew of
the science and research ship "Morskoy Geofizik (Marine Geophysicist)"
discovered an astroblem - a circular structure, which usually forms after a
celestial body falls down from the sky - at the bottom in north-west of the
Pacific. Researchers gave found astroblem the name "Sakhalinka". .

The processes that take place after celestial bodies fall into the ocean are
studied very poorly, because scientists know location of very few underwater
craters on our planet, and the fact that every new astroblem causes a tide
of
scientific interest and curiosity is not surprising at all. The "Sakhalinka"
astroblem is unique, since it is located very deep at the ocean bottom. All
known underwater craters - Chicxulub of Mexico, Mj?lnir impact structure in
the
Barents Sea and Lockne of Sweden are located between 200 and 400 m, whereas
Pacific astroblem lies as deep as 6 thousand meters.


During the expedition discovered crater was investigated by means of CSP
(continuous seismic profiling), thus its exact contours and some other
parameters were detected. Crater's diameter at 5900 m depth is 12 km, and
its
depth in basement topography is 7 hundred meters. Crater's centre has
following
geographic coordinates - 30 degrees and 15 minutes of north latitude and 170
degrees 3 minutes of east longitude.

Scientists have thought over possible conditions, which led to "Sakhalinka"
astroblem formation, and their calculations suggest meteorite's diameter to
reach 500 m. Statistics of meteorite falling claims that such large objects
approach our planet only once in 100 thousand years. When such a meteorite
falls
into the ocean, it generates tsunamis with waves, higher than 10 m, 1
thousand
km away from the epicenter, or the impact point in other words. However, no
matter what a splash a giant celestial body makes, when it falls to the
ocean,
it forms no crater, when the ocean in the point of impact is deeper than 4
thousand meters. Therefore, "Sakhalinka" astroblem appeared at those times,
when
the ocean was much shallower than it is today.


 Russian think-tank has performed a reconstruction of paleooceanologic
environment, which brought researchers to a conclusion that during the
Cretaceous period ocean level was about 2 km lower than its current level.
Sedimentary deposits, filling the astroblem, allow stating possible crater's
age
- the structure most likely formed between the Cretaceous and Paleogene. And
then scientists have suddenly remembered the hypothesis about Earth's
collision
with a giant meteorite, happened some 65 million years ago. Meteorite
rounded
our planet from south-west to north-east and fell to many smaller
meteorites,
thus forming a "crater belt", and finally fell somewhere to the ocean. Last
trace of said celestial body on Earth scientists consider to be Kara
cryptoexplosion structure. Bearing in mind movements of ocean plate in
Cenozoic
era, geologists think that "Sakhalinka" perfectly fits into the Euro-African
crater belt and appeared because of said meteorite or a part of meteoritic
cloud
had fallen to the Earth. Everything indicates that dinosaurs were in fact
killed
by a giant meteorite.
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Received on Tue 17 Apr 2007 04:18:40 PM PDT