Areas of

CONCENTRATION

Western Sahara: the Chwichiya region

In hot deserts, there are areas with a higher concentration of meteorites

The grounds in these areas are certainly very old, but have also been preserved from moisture. A weak vegetation of these grounds also favors the discovery of meteorites.

The "dense collection areas" D.C.A

Recently, some places in the world have been divided into zones called DCA, which are places where meteorites accumulate. For example, in the “Al Haggounia” area, the meteorites found and classified in this area will be called successively according to the chronology of discovery, Al Haggounia 001, 002, 003…

This division has been made (sometimes artificially) by the Meteoritical Society which is in charge of validating and referencing the classified meteorites.
All the meteorites listed are classified in an official way with a corresponding gps point.

The nomenclature of meteorites is becoming more consistent. ndeed, before, meteorites of type NWA, meteorites of the Sahara whose exact place of origin was not known, were classified in NWA whereas the GPS point was known.

NWA 7831 EXEMPLE

Northwest Africa 7831 (NWA 7831) 27.307°N, 12.083°W
Saguia el Hamra, Western Sahara

Found : 2013 Mars

Classification : HED achondrite (Diogenite)

History : Found buried in the ground near Chouichiyat on March 3, 2013, and excavated by a team of local people.

Physical characteristics : A single large mass (at least 20 kg) composed of yellow-green crystalline material with pale orange weathering products along numerous fractures. Much of the material disintegrated into fragments upon excavation.

δ17O = 1.677, 1.793, 1.810; δ18O = 3.680, 3.879, 3.875; Δ17O = -0.266, -0.255, -0.236 per mil.

With the new nomenclature NWA 7831 would be called Al Haggounia 00X.
This makes it possible to know which meteorites have been discovered in the same area and also to better identify matched meteorites.

Hasnaa Chennaoui is a Moroccan woman who fights to enhance the scientific heritage of Morocco in the field of meteorites, this requires the determination of the precise location of meteorites on Moroccan soil. Of course, it is necessary that everyone plays the game, from the meteorite hunter to the trader.

What makes this concentration area special is the number of achondrites found within a radius of 6 km2. Achondrites represent only 8% of the meteorites found.

Perhaps the ordinary (metal-rich) chondrites were destroyed by the action of the water that flowed through the area? The fact that the terrain is sedimentary also makes it easier to distinguish the achondrites.

Other areas of concentration

In the hot deserts, it is in Chile, in the Acatama desert that the largest concentration of meteorites in the world has been found.
The Acatama Desert is one of the oldest desert in the world, it has been very arid and stable over several million years.
A concentration zone called San Juan DCA, has been studied by scientists in a partnership with France, Chile, the United States and Brazil (including Jerome Gattecceca). In this area, 26 unpaired meteorites have been discovered, which represents an estimated density of 10 meteorites per km2.

The age of the meteorites has been dated, at least half are less than 20,000 years old.
A flow model of meteorites entering the Earth has been studied:
83 meteorites larger than 10 g would fall per million km2 per year.
In the San Juan area, the number of meteorites found corresponds to a density of 10 meteorites per km2. In 20,000 years, the density of meteorites should be 1.66 meteorites per km2, which does not correspond at all.
There is therefore no coherent explanation to explain such a concentration.
Moreover, if one assumes that there are more meteorites in an area because the terrain is very old, which seems logical, why are there not more achondrites?
Over a long period of time, achondrites are less fragile to be preserved from time than ordinary iron-rich chondrites.

There is another DCA in Chile with an even greater density of meteorites.
his area is the DCA of “El Médano”, it has been studied by an international scientific team (including Jerome Gattacceca), a publication took place in 2016.
191 meteorites were found on a 1.5 km2 area. Removing the matched meteorites, the actual density on the ground is 86 meteorites per km2. The estimated density of fallen meteorites is even higher, because achondrites are difficult to find on this type of terrain, and not all meteorites could be found. A calculation estimates according to these criteria the concentration to : 152 meteorites per km2. This would mean that the terrain where the meteorites were found would be several million years old.

 

The most important accumulation area in the world is in Antarctica, it is called Yamato.
13,716 meteorites have been discovered in this area, about 25 meteorites per square kilometer have been found. But this accumulation is related to a phenomenon of ice movement.

 

Other unproven factors to explain areas of concentration in hot deserts:
According to scientists, the distribution of falls on Earth is homogeneous. But can we not imagine that stones would be concentrated in space and would have the same trajectory of arrival on Earth?

 

  • Benguerir
    Morocco Official Fall 2004 LL6 25000
    g
  • Bensour
    Morocco Official Fall 2002 LL6 45000 g
  • Douar Mghila
    Morocco Official Fall 1932 LL6 1161 g
  • Oued el Hadjar
    Morocco Official Fall 1986 LL6 1215.5 g
    Breja 2010 LL6 16 kg

We can also add Breja, which fell in 2010 between the Moroccan and Algerian border. On 9 falls observed in Morocco in 78 years, 5 are LL6.
Didn’t all these LL6 come from the same parent body that was in space?
It is possible that the same parent body generates two different falls, this has been proven:
By studying the noble gases in two meteorites, scientists have shown that
thesetwo meteorites came from the same parent body:

They are Mt Tazerzait, a chondrite L5 fallen in Niger in 1991 and Baskowka L5, fallen in Poland in 1994.

 

The website of the University of Washington, Department of Earth and Planetary Sciences, presents a map of the location of lunar meteorites matched, yet located in very different areas of Morocco.
The site hypothesizes that all these meteorites are from the same parent body and that the trajectory of meteorites in space would lead to localized falls in Morocco.
But afterverification, all these meteorites were found in the Atlas, in Anoual.
This map is therefore false.


Paired* stones Anoual and Northwest Africa 773, 2700, 2727, 2977, 3160, 3170, 3333, 6950, 7007, 8127, 10656, and 10985

 

Another hypothesis
If the meteorites of the Almahata Sitta fall, which fell in 2008, 50,000 years later, would not have been discovered as a concentration area and not meteorites related to the same fall?
The 660 meteorites of the Almahata Sitta fall were classified: Ureilite, H5/6, LL4, EH4/5,EL6, and EL5/6, EL3, EL6, H5, CH, EH3, EL3-6, EL5, EL3/4, L4-5, rumuritite, and bencubinite. That is a minimum of 17 different classifications.