Impact ejecta and Megabreccia

In the broadest sense, the term BRECCIA may in some instances be applied also to impact ejecta and to displaced rock masses within the crater.

The ejecta blanket of the Ries impact structure (Germany) is composed of the so-called Bunte (multicolored) breccia (clast size < 25 m) and allochthonous megablocks (coherent clasts  > 25 m). The distinction has been made for mapping reasons but otherwise is arbitrary. Disregarding this arbitrariness, the Ries crater ejecta as a whole may also be termed a megabreccia.

In the impact literature, extensive breccias containing very large components are generally termed megabreccias, and they have been frequently reported (e.g., for the Wells Creek, Steinheim basin, Gosses Bluff, Sierra Madera and Wetumpka impact structures). Perhaps most impressive ist the Late Devonian Alamo megabreccia (see http://www.mines.edu/students/m/mmorgan/) giving evidence of a giant offshore impact.

Below, we show images of the polymictic Ries crater megabreccia (Bunte breccia ejecta) and of polymictic megabreccias (displaced rock masses)in the Rubielos de la Cérida impact basin (Spain).

More about megabreccias can be seen and read here:

http://www.impact-structures.com/spain/rubie/megabr.html

http://www.impact-structures.com/spain/controversy/megabrecha.htm

Megabreccia: Bunte breccia ejecta, Ries impact structure, Ronheim quarry.

Aspect of the megabreccia near Barrachina, Rubielos de la Cérida impact basin. The polymictic, multicolored breccia has much in common with the Ries crater Bunte breccia.

Bunte breccia of the Ries impact structure. Ronheim quarry.

Aspect of the Barrachina megabreccia, Rubielos de la Cérida impact basin.

Bunte breccia of the Ries crater; Ronheim quarry.

Polymictic megabreccia, southeastern rim of the Rubielos de la Cérida impact basin.

Bunte breccia of the Ries impact structure; Gundelsheim quarry. Height of the wall is about 6 m.