Sole marks

Sole marks are sedimentary structures found at the base of beds, best seen in surface view. They are typically preserved as casts of incisions/depressions created at the top of the underlying bed and filled with sediment of the overlying bed, often with a grainsize contrast between the beds (sand over mud). Sole marks are common in deposits of sediment gravity flows (like turbidites), where turbulence or bedload transport in an energetic flow can erode or leave marks on the underlying substrate in conjunction with active sedimentation. This picture, showing the base of a bed from the Pennsylvanian Minturn Formation, near McCoy (CO, USA), illustrates several kinds of sole marks: a) Flute casts, elongated scours with a wider round concavity at the upstream end, tapering to a pointed termination down current. Flute casts are formed by turbulent eddies in the flow and are excellent paleocurrent indicators; b) Prod marks, small irregular indentations, caused by particles suspended in the flow that occasionally hit the substrate; c) Groove casts, linear features, parallel to the current direction, formed by particles (like pebbles or sticks) dragged with the bedload and eroding the substrate. Prod marks and groove casts are sometimes called "tool marks," because they form as objects in the flow interact with the substrate. See if you are able to identify the three types of marks in the picture. In which direction do you think the flow was moving, towards the top or the bottom of the image? Lens cap for scale has a diameter of 6 cm.

sediment gravity flows sedimentary structures sole marks Pennsylvanian groove casts flute casts prod marks tool marks paleocurrent