Monday, February 25, 2008


Or, as those of us who don’t speak German would say, Trace Fossils.

Trace fossils are a truly unique source of sedimentological and stratigraphic data, providing us with all sorts of nitty-gritty detail about salinity, turbidity, and time relationships along surfaces and within deposits. Marine traces provide us with nifty zonation schemes that can differentiate sub-environments based on wave and current energy, provide sequence stratigraphic info, and even have important ramifications for petroleum geology.

As a field geologists, traces can be a big help in deciphering depositional environments. For folks who work in core, however, they may be even more important; when all you’ve got is 3 inches, spotting a Skolithos or Zoophycus is much easier than nabbing a hummock, for instance.

Anyway, I thought I’d share a few pictures of traces I’ve run across in the field. In future posts, I think I’ll discuss ichnofacies models, petroleum geology applications, and maybe delve into the controversy of nonmarine ichnofacies.

As always, click on the pictures to make em bigger

This first picture is from the Albian Blackleaf Formation in Southwest Montana, and shows some meandering Planolites winding there way along a the contact between a mudrock below and a sandstone above (the sandstone shows some Micro-HCS, which I may talk about later...)

This second image shows a surface chewed up by a whole bunch of little guys; Planolites, maybe some Skolithos. I suppose this is why we have experts in this stuff; takes a trained eye to pick out all the different morphs! This image is from the Book Cliffs, Utah.

This image shows Ophiomorpha; this is a dwelling trace for a shrimp-like fellow, who stuck fecal pellets to the side wall in order to support the tube-structure, implying that the sediment was fairly loose and shifty when the little guy decided to live there. This is a Book Cliffs trace, too.

Finally, shallowing somewhat, here's a picture of a Psilonichnus, a branching, y-shaped tube. These guys can go pretty far into the substrate, and are dwelling tubes for little crab-like critters living in the foreshore. The animals would have to burrow down deep to hit the water table, allowing them to live above wave base.

1 comment:

Jeannette said...

Nice. I look forward to future posts about trace fossils. I especially like the Ophiomorpha photo - - the trace almost appears 'chambered'.

"When all you have is core..."
Ah, yes, core, sweet core.