The Richat Structure:

[Chronos]

The Richat Structure.

http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/aster

[nikas]

The Richat Structure.

http://earthobservatory.nasa.gov/Newsroom/NewImages/Images/aster

The link doesnt work. I never heard of it before.

[Chronos]

You've never seen the Richat Structure?  Here it is:

[nikas]

I have seen it. I didn’t know that was called that way. What's so artificial about it? Nature can form very easily round circles. The right angle is something difficult!!

[Qoais]

The Richat Structure, a prominent circular feature in the Sahara desert of Mauritania near Ouadane, has attracted attention since the earliest space missions because it forms a conspicuous bull's-eye in the otherwise rather featureless expanse of the desert. Described by some as looking like an outsized ammonite in the desert, the structure, which has a diameter of almost 50 kilometres (30 miles), has become a landmark for space shuttle crews. Initially interpreted as a meteorite impact structure because of its high degree of circularity, it is now thought to be a symmetrical uplift (circular anticline or dome) that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure.

[Qoais]

Department of Earth and Atmospheric Sciences, University of Quebec at Montreal, 201 President Kennedy Avenue, Montreal, Quebec H3C 3P8, Canada, 2. Department of Geological Sciences and Geological Engineering, Queen's University, Kingston, Ontario K7L 3N6, Canada

The Richat structure (Sahara, Mauritania) appears as a large dome at least 40 km in diameter within a Late Proterozoic to Ordovician sequence. Erosion has created circular cuestas represented by three nested rings dipping outward from the structure. The center of the structure consists of a limestone-dolomite shelf that encloses a kilometer-scale siliceous breccia and is intruded by basaltic ring dikes, kimberlitic intrusions, and alkaline volcanic rocks. Several hypotheses have been presented to explain the spectacular Richat structure and breccia, but their origin remains enigmatic. The breccia body is lenticular in shape and irregularly thins at its extremities to only a few meters. The breccia was created during karst dissolution and collapse. Internal sediments fill the centimeter- to meter-scale cavities. Alkaline enrichment and the presence of Cretaceous automorphous neoformed K-feldspar demonstrate the hydrothermal origin of these internal sediments and their contemporaneity with magmatism. A model is proposed in which doming and the production of hydrothermal fluids were instrumental in creating a favorable setting for dissolution. The circular Richat structure and its breccia core thus represent the superficial expression of a Cretaceous alkaline complex with an exceptionally well preserved hydrothermal karst infilling at its summit.

[rockessence]

Nature can just as easily form right angles, even cubes!

[nikas]

Nature can just as easily form right angles, even cubes!

Show me one case!

[rockessence]

Gladly:

Salt: the building block of life!



fluorite:


http://www.italianminerals.com/USA/Fluorite-2.html

Pyrite:

[Jake]

What about the remains of one of its cities (not necessarily the capitol)? Or the remains of another ancestral culture (not necessarily Atlantis)?

Jake