This week's Friday Field Photo is from the Cretaceous of Patagonia and shows off some rather larger sole marks. Sole marks are sedimentary structures at the base of beds, typically best preserved when coarser-grained material is on top of finger-grained. Some sole marks are useful for paleo-environmental reconstruction because they show the direction the ancient flow was oriented. One such paleocurrent indicator is a flute cast, which, in these deep-marine sedimentary rocks, originate from turbulent eddies as the flow erodes into the underlying substrate. This space is then filled with sediment in the flow creating the cast. Flutes are elongate and parallel to the paleo-flow. Textbook flute casts are deepest on their upstream end and shallow (and widen) towards the downstream end. They are not always so perfect, especially when a bunch of them coalesce.
The examples here are nicely displayed on the bottom side of an overhang, which is the base of a conglomeratic turbidite bed. Flute casts in most cases (at least that I've seen) are typically a few to several tens of centimeters long and maybe a few centimeters wide. As you can see above (and in the zoomed in version below) these flute casts are quite a bit larger owing to the power of these turbidity currents.
Happy Friday!
Image: Huge Flute Marks / from my Flickr page
