Don't know quite how tektites would wind up in such massive aggregations. The ones on Earth are scattered fairly widely, I think.

The deposits in these Martian craters are huge.

In a discussion a while ago -- with Dan Spires, I imagine! -- the suggestion was made that the dark deposits were carbon from the asteroids that made the craters (assuming the craters are impact generated). There are asteroids that are apparently almost pure carbon. There's no indication that I'm aware of from any of the orbiting instruments that would confirm the presence of carbon in these areas. A suggestion that the deposits were frozen hydrocarbons -- ie: oil -- was also made. Again, there's no indication that it's true.



But if the instruments can't identify suface carbon because of the carbon dioxide atmosphere, the search for carbon and carbon compounds on the surface of Mars is pretty well doomed for the time being.

On the other hand, if the dark deposits were actually erupted or extruded from the interior, they could be an iron-sulfur compound. Don't know whether orbiters would be able to identify the composition if it were.

The Oxia crater and "wind streak" deposits show some similarities to the Syrtis Major volcanic complex, but I'm not aware of an anomalous composition for Syrtis.

So. Seems it's another mystery.

Here's an example of what the surface of the dark deposit looks like:
http://ida.wr.usgs.gov/fullres/divided/sp2532/sp253203g.jpg

This example is in Trouvelot crater. All the deposits have a similar appearance, with what appear to be flow ridges, heavy pitting, and these very interesting "splash" craters.

The crater with the white object in its center -- that looks something like an upended boat -- is pretty remarkable. Who knows what it is? I believe it is considered to be an outlier of the white stuff deposit to the north of this segment, but I don't know.

See for yourself:
http://ida.wr.usgs.gov/html/sp2532/sp253203.html

Cheers, BFelix