Any one interested in more information can go to
http://www.lpi.usra.edu/meetings/metsoc2001/pdf/5196.pdf
A ~3.4 km-diameter near-circular, slightly polygonal, structure is
found in the Al `Amarah marshes, at 47°4'44.4"E, 31°8'58.2"N, ~17 km
NW of the Tigris-Euphrates confluence, in southern Iraq (Figure 1).
Prior to the militarily-inspired draining of the marshes in 1993 [1],
the structure was filled with a lake enclosed by an elevated rim,
surrounded by a ~500 m-wide dark annulus. After the partial draining
of the marshes, the lake has shrunk, and it now appears as a light
coloured spot, due to salt encrustations following evaporation of the
surface waters.
Geological setting:
The alluvial plains of Iraq occupy a structural trough related to
active orogenic processes in the Zagros mountains [2]. Near the
Tigris-Euphrates confluence, marine sediments of the Miocene-
Pleistocene Dibdibba Fm [2] and Holocene Hammar Fm [3] are overlain
by Recent delta plain and delta front deposits of the Mesopotamian
Plains, in which there are numerous marshes and permanent lakes [2].
The Recent sediments of the Tigris-Euphrates plains were deposited in
the last 5000 years, during which 130-150 km of seaward progradation
has taken place [2].
Formation of the Al Amarah structure:
The strikingly circular shape of the Al `Amarah structure, contrasts
markedly with the highly irregular shapes of the other marsh lakes in
the region. Because of the extremely young nature of the sediments in
the marshlands, an origin of the structure by karst solution, salt
doming, tectonic deformation or igneous intrusion can be ruled out.
The structure predates the Iraq-Iran and Gulf wars of the 1980's to
1991, since it is present on satellite imagery from 1984. It is
postulated that the structure was formed by a Recent bolide impact in
the marshlands of southern Iraq, thus accounting for its geometry,
and the apparent rim and annulus visible in pre-1993 imagery.
Quasi-historical reference?
The formation of such a young impact structure may have had a
catastrophic effect on the people living in the region, and there is
a possible quasi-historical reference to such an event in the account
of the Deluge from the Epic of Gilgamesh, dating from ~2000
BC: "...and the seven judges of hell, the Annunaki, raised their
torches, lighting the land with their livid flame. A stupor of
despair went up to heaven when the god of the storm turned daylight
into darkness, when he smashed the land like a cup. One whole day the
tempest raged, gathering fury as it went, it poured over the people
like the tides of battle" [4]. Could this be a reference to a bolide
impact which triggerred a tsunami?
People of this list may be interested that something similar has been
hypothesised for some time in Northern Syria
http://www.archaeology.org/online/features/godzilla/
Something like Tunguska is now being suggested for northern Syria at
about 2200 B.C.--based on a dust and tephra layer found at Tell
Leilan and elsewhere--by Marie-Agnès Courty of the French Institut
National Agronomique. The layer was first thought to be volcanic
fallout, but now the dust and tephra are said to include not just
volcanic rock fragments, but also limestone and sandstone, and
variety of spherules and vesicular glassy grains. Associated with it
is black carbon, which is said to be too much to be from local fires.
The mixed geological composition of the dust and tephra, plus the
carbon, are claimed to be evidence of the explosion of an "extra-
terrestrial projectile." But hold on! There may be no need to reach
into space for a catastrophe. The volcano may have been thrown out
prematurely. The final paragraph of Courty's 1998 paper on the
subject reads: "Abundantly reported from past geological records, the
presence of spherule-rich layers as possible diagnostic markers of
extra-terrestrial impact has been fiercely debated, but it appears
they are often associated with volcanic events. Therefore,
unambiguous evidence, such as shocked quartz, the presence of
tektites, an iridium anomaly, or the occurrence of silicon carbide
and diamond are generally preferred to recognise impact-induced
ejecta layers. None of these fingerprints has so far been retrieved
from the 4 kyr. B.P. dust layer." ....
Could something similar have been happening in northern Syria?
Perhaps not for individual, huge projects but in aggregate could it
be an alternative to Courty's suggestion that "the occurrence of
multi-site ignition together with black carbon production resulting
from extensive biomass burning, also reported to be caused by
asteroid impacts, provides indirect evidence to support an extra-
terrestrial hypothesis"?
This is interesting stuff.
Regards
John Croft