I appreciate you saving that linked subject for me, MPJ. I notice there was a video link on the written text in the article about the Iron utilizing microbes. The fact that the dark streaks are concentrated at the mid-range elevation of the polar ice scarps, near the ice and water saturated solids mixture Lower Unit upper limit, may be very suggestive of action either chemical or biological in progress. The action bringing material to the front limit of the dark streaks is consistent over time, and exceeds the movement of the surrounding exposures which are not streaking. As many still hold that the area cannot sustain very cold liquids for a motivating force, and no chemistry processes causing horizontal movement has been discussed to explain this dark streaking, I am left to think about the obvious biological possibilities.
There is the possibility of a dark layer at a past major climatic shift during a deposition period, but that period would have to have been very short term, very rapid in full shift, and a deposition which was singular only. A KT boundary type layer event possibly?
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In your second link, of the volcanic area, I could see very shallow medium sized craters or circular domains which are crossed by these dark streaks. The circular features are viewable both in the light toned surface areas, and in the parts covered by the dark streaks. This would reduce the chances that the dark streaks are based upon removal of a dust cover.
