The picture above shows four u-shaped burrows (the right arm of a short one overlaps the left arm of another broken one). I am not sure who took this picture but its quality makes me think it might be Jim Wolford. The leftmost and rightmost burrows are complete and easily transcribed. If we look at the left narrow u-shaped burrow, we see that the end of the u dips into some black muck: this is the anoxic layer. In this photograph the anoxic layer is probably 6 cm below the mud surface (the edge of which can be seen 4/5ths the way up the photo).
Professor & student