Back to the roots - Chiemgau impact

This is a bit off topic, but since I am in holidays...:
The chiemgau impact is a controversially discussed, postulated meteorite impact, located in the heart of my Bavarian home, the Chiemgau. The change log for the german Wikipedia entry has more than 500 (!) pages and shows the quality of the controversy.
One of the pro arguments was the discovery of some strange, finger-print like looking surfaces on stones collected in the Chiemsee, which were identified as 'regmaglypts' (surface ablation structures produced by partial melting of the meteorite surface when it passes the atmosphere) by the impact advocates.
I found this explanation very unlikely, as regmaglypts are extremely rare, and such ornamented stones are very common in this lake. The carbonate rich waters of the Chiemsee favors calcareous algae such as Charophyta (v) or Cyanobacteria. The bottom river Alz which origins in the Chiemsee is covered near Seebruck by recent calcareous Oncoids (e.g. Rott, 1991, Hägele et. al, 2006). Further, similar structures are quite common and well known at the Bodensee, Attersee and other alpine lakes area where they are known as 'Furchensteine'.
Therefore a biogenic origin of those 'regmaglypts' seems to be more likely, most probably produced by endolithic cyanobacteria. I reported my suspect, and my hint was frankly published on their homepage ... but they didn't really believe.
I currently am visiting my home village and last rainy Tuesday I had the opportunity to visit the lake Chiemsee and could collect and observe a large number of these Furchensteine near Chieming. Here they are really very common, I could count up to 40 of them per square meter.
I found dry specimen at the lake beach as well as some fresh, in-situ exemplars in the lake itself covered by water. Those Furchensteine which are covered by water, show a cauliflower like structure, made up by some kind of organic coating, most probably algae. After scratching off this coating, the typical finger-print structures appear.
For me there is no doubt that these structures are biogenic. If you want to see more pictures, I have uploaded some here.