[meteorite-list] Terrestrial Impact Craters in Unconsolidated Sediment

From: Bernd Pauli HD <bernd.pauli_at_meteoritecentral.com>
Date: Thu Apr 22 09:52:10 2004
Message-ID: <3D562AE8.71F9560E_at_lehrer.uni-karlsruhe.de>

Keith wrote:

> Is there any example of an impact crater greater than 0.5 km
> in size that has been formed in unconsolidated sediments like
> those underlying quaternary terraces, alluvial plain, deltaic,
> or coastal plain? What would such an impact crater in uncon-
> solidated sand look like?

> Has anyone published anything either about such an impact
> crater or what type of feature an impact would produce in
> unconsolidated sediment?

Tracy responded:

> I think that any crater in loose sediments would likely be filled in
> rapidly by the same mechanisms that deposited the sediment in the first
> place. You might, for a while, be able to track the crater by deformation
> in the surrounding sedimentary layers, but eventually it would all even
> out, leaving barely a ruffle in the geologic record.


Hello Everybody,

Wouldn't the recently discovered and almost authenticated Silverpit
structure in the North Sea neatly fit your descriptions?

Excerpt from the article by Dr Chris Riley (BBC Science)

UK's first impact crater (Thursday, 1 August, 2002):

"The geologists say the crater has been uniquely "fossilised", by
sediments settling into the depression, and is unlike any other impact
crater so far found on Earth. "Other craters on Earth we know about were
created in hard rocks, whereas Silverpit would have been formed in
s o f t underwater s e d i m e n t s - creating a very different
shape of crater," explains Stewart. A tall conical central peak is
buried inside a three-kilometre- (two-mile-) diameter crater that
is itself surrounded by a series of concentric rings which extend
out a further eight kilometres (five miles) in each direction.
"Unparalleled 3D mapping of these concentric features down to a
resolution of tens of metres shows that the outer ripples are
caused by concentric faults in chalk on the sea floor around the
central crater that were probably triggered by the impact," says
Stewart. Its shape and size stand Silverpit apart from other craters
in the inner Solar System and its closest relative appears to be the
Valhalla impact structure on Jupiter's moon Callisto."


Best Sunday regards,

Bernd
Received on Sun 11 Aug 2002 05:14:16 AM PDT