August 16, 2012
Time to explain our mystery fossil!
Scott is correct – it DOES look kind of like something was coming out of a hole on the left of one of the orange tubes.
These are fossils of burrows – tubes dug by animals on the seafloor. The block we’re looking at in the photo is turned on it’s side, and we’re looking at the underside. The orange color is a coincidence of the sediment type and weathering processes. It nicely highlights the shapes for us.
In healthy ecosystems, marine critters live above, on, and in the sediment at the seafloor. But how to preserve these burrows? It can be difficult, because storm and wave activity can erase the trace that these burrows ever existed. Typically we only record fossils of burrows that were deeper – at least 20-30 cm into the muck.
These burrows in the photo are called, “Thalassinoides”. We name trace fossils independently, because we’re rarely sure of the tracemaker. These kinds of burrows – deep, diverging, with many chambers – are associated with shrimps in the modern ocean. There’s very cool modern work done on these burrowing shrimps – especially by Dr. Wiebke Ziebis at USC.
Burrows are amazing. Once you learn how to see them in rocks, you can’t UN-see them! It was a blast showing off lots of photos of burrows during my talk at the Geological Society of Peru today. Some people there at the meeting – and the geologists I worked with in the field – will now see burrows long overlooked in the past.
Here’s one of my favorite pics of fossil burrows. It’s from a site in Nevada, famous for it’s well-studied sedimentary layers. I talked with a grad student researching there and she, like many other people, hadn’t even realized her site was FULL of burrows!
This is my labmate, Carlie. Behind her, the dark colors highlight the burrows that permeate so much of these sedimentary layers. Burrows – they are all over the place! They tell us a lot about the environment – The diversity and abundance of animals, oxygen levels, all that good stuff. So, after a mass extinction, obviously I’m keeping my eyes out for burrows of sea floor animals.