Sole marks in the Old Red

This outcrop of sandstone and conglomerate is located by the sea in southern Ireland near Bunmahon. These clastic sediments were deposited during the Devonian. Such reddish sedimentary layers are widely known by their name Old Red or Old Red Sandstone. I am used to rocks like this because they are very common in Estonia, although our redbeds are not nearly as strongly cemented as they are in Ireland.

Sedimentary layers are originally horizontal. As you can see, these are clearly not. I assure you that the inkpen on the picture is nearly horizontally placed and the dip of the rock layers is almost vertical. In this case, how can you tell where is the original stratigraphical way up? It is often hard to tell but in this particular instance it is not difficult at all. I took this picture because here we can see a very good example of a sole mark. I am talking about the grooves in the fine-grained sandstone which are filled with coarse sandstone and conglomerate.

I find it very difficult to imagine how on earth can it happen that the conglomerate bed gets deposited first with these sharp and clearly unstable (the lowest one) humps and after that came sandstone that covered them. On the other hand, it seems plausible to assume that sandstone was deposited first, grooves were somehow formed on top of it and they were filled with conglomerate. This is what sole marks seem to be for me — pure logical imagination.