Friday, December 2, 2011

Ophiomorpha in core

Trace fossils are, as I've said before, pretty rad.  As a sed/strat type, I mostly appreciate them for their utility in paleoenvironmental reconstructions, their ability to help us constrain substrate conditions, and the help they can give us in interrogating rates and processes of sedimentation.  And, of course, there's all sorts of biological and ecological info to be gleaned from the paleoichnological record as well.

Trace fossils are particularly valuable when all you've got is 3 inch-wide cores to work with!  I'm mostly a field guy, but sadly, some strata remain inaccessibly trapped below the surface of the earth, removed from the joyous and perfect cycle of erosion and redeposition that is the true destiny of all rocks everywhere.  When we want to investigate these strata, we're forced to yank a plug of rock out of a well somewhere, and just hope for the best.  It's not ideal, but you gotta work with what you've got...

Anyway, below are a few pictures of some Ophiomorpha traces I found in core from the Paleocene-Eocene Wilcox fluvial/alluvial/deltaic sediments of the Gulf Coast.  Ophiomorpha is such a neat little trace fossil; a little shrimpy bastard digs his way into some shifting sediment, and in order to keep his little dwelling tunnel safe from collapse, he rolls his own shit into little balls, and sticks it into the walls of the burrow.  Ah, The Grandeur of Nature at Work!

In the picture above, we've got a pretty nice cross-section in a massive, medium-grained sandstone.  You can see pretty clearly the nice fecal ball lining surrounding the inner (and, in the animal's lifetime, what would have been hollow) chamber.

Here's a cut along the length of an Ophiomorpha, truncated by an erosion surface and subsequent plow-and-fill sediment, which was itself burrowed into by yet more Ophiomorpha-producin' shrimp.

And, finally, here's an oblique cross-section of another little tube (maybe a bit squashed, as well?).  Trace fossils are handy things to have around, especially when all you've got is core!

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