Friday, October 28, 2011

Armored Mudballs!

"Quiet water conditions" is the depositional mechanism most often evoked to explain the presence of fine-grained mud in the rock record.  Mud, generally made up of clay minerals, is defined on the Udden-Wentworth grain size scale as particles smaller than ~0.00015 inches, or around 0.003 mm.  That's pretty small, and any amount of turbulence or motion in a water column will keep particles of that size suspended for quite a while.  However, as I've discussed before, there are some hints that a fair portion of mudrock in the stratigraphic record records higher energy conditions; one of the nifty qualities of clay minerals is that they're weakly charged, and can aggregate together into larger "chunks" that behave as hydrodynamically heavier clasts.  Sometimes, the features that would record this sort of aggregate/flocculate behavior of mudclasts is subtle or cryptic, especially once muddy sediment gets compacted and flattened out.  Sometimes, however, the evidence for muddy clasts is obvious!

The picture below is from the Eocene Cathedral Bluffs Member in SW Wyoming/NW Colorado, a pretty thick succession of fluvial/alluvial sediments that form some fairly picturesque vistas in that area.  The channelform sandstones around here are pretty coarse - usually upper Medium at the small end, and sometimes even getting into coarse and very coarse sands (we're pretty near their source area!).  Anyway, in among the fluvial sandstones, are things like this:

That's a gravel-sized clast, maybe 50 mm across or so, made up entirely of clay, and coated on the outside by a nice armor of sandy grains glommed onto the outside!  In a moment of refreshing clarity, the official science word for these things is the surprisingly restrained term "armored mudball".  Nifty, huh?  Here's another shot:

You can see that these muddy clasts are floating in a coarse sandy matrix.  Because these mudballs are so large, they form a nice erosional lag at the base of the channels.

Here's a close up of some of the gravel-sized mudballs:

The shot below shows the muddy interior of these little fellows:

Neat, huh?  Like almost all things in sedimentary geology, mud is a lot more fun once it starts gettin' pushed around by turbulence!

Tuesday, October 25, 2011

#Occupy Earth

Man, if you aren't reading Matt Taibbi, then you need to get with the program!  He's a writer for Rolling Stone, sometimes on the Olbermann show, and he's just about my favorite writer/journalist/truth-speaker out there.  Taibbi hit it out of the park this week, though, with a completely insightful, totally cogent, takes-no-prisoners explanation of the Occupy Wall Street movement.  READ IT NOW.  It's great, and is the best thing you could give to some of the vote-against-their-own-interest dumbasses out there chortling over all the dirty hippies on the TeeVee.  It's a long piece, but well worth the few minutes it takes to read it.  Then, afterwards, we can get back to the good ol' Class Warfare!  Eat the Rich!

Monday, October 17, 2011

Red Rocks of the Cathedral Bluffs Member

Just a quick post, to get my bloggin' legs back after fall field work/GSA madness!  Here's photographic PROOF that not all red rocks in Wyoming are from the triassic; these are from the Eocene strata of the alluvial/fluvial Cathedral Bluffs, in SW Wyoming.  Behold!

Take a look at the variably expressed soil forming processes preserved in the stratigraphic record, as well as the subtle channelform!  Nifty, huh!?!

Saturday, October 15, 2011

Whale-Fall Puppet Theater

Radiolab, a completely slick science-and-culture type of show on NPR, recently discussed a Whale Fall in one of their episodes.  Whale carcasses represent pretty rich food sources in the oceans, and whole communities of organisms spring up when some poor cetacean kicks the bucket and drifts down to the seafloor.  Anyway, a former intern of the show apparently was able to wrangle some very talented folks into making a completely awesome video illustrating the whale fall!  The best part - it's all done using paper cut-outs!  Cute little paper polychaetes, munching on a dead whale!  What more can you ask for!  Anyway, here's the video, yanked from the radiolab site:

Whale Fall (after life of a whale) from Sharon Shattuck on Vimeo.