I've been thinking about the idea of weird geology, ever since Dana at En Tequila Es Verdad introduced the topic for Accretionary Wedge #34 — I haven't been thinking about it long and hard, mind you, because I've been busy writing geo things at work, using up both my writing and thinking capabilitites. I wrote a little, thought a bit; then, after thinking some more, I thought I’d finish up this morning at the laundromat, but it tuns out they don’t have wi-fi, which is one thing I find not only entirely weird, but just a little bit irritating.
I have a few thoughts about geological weirdness, the biggest of which is that after all these many years (however long it’s been), I am no longer as surprised by the things rocks can do as when I was first starting to map as part of my job back in the late 1970’s. Back then, I learned an important lesson that has stuck with me over the years, which is: if the rocks are doing something you don’t think is possible or which you have never heard of or read about, look again. Have another geologist come check out your contacts and the nature of whatever weirdness you think you spotted, and brainstorm some ideas. Chances are, you have run across something merely unusual but not impossible. You will have to go with whatever the rocks are telling you that they did on their way to becoming whatever thing they are now.
Volcanic rocks, inside or outside the Huge Caldera settings sometimes known as "Supervolcanoes," can do some particularly unexpected things. When anywhere near them, learn to expect the unexpected and to throw out preconceived notions as soon as it becomes clear that you need to (which isn’t all the time, admittedly). Apply this way of thinking to other, non-volcanic settings. Over the years, expecting the unexpected will serve you well.
Other places to expect particular geologic weirdness are 1) anywhere in the Basin and Range province and 2) any time you are anywhere near a metamorphic core complex or where you suspect that you are in detachment or extreme extension terrane. I’ve found tilted Precambrian rocks above a 50-foot thick, crumbly, weakly mineralized mesobreccia of gneissic rocks, all sitting on top of tilted Tertiary sediments that included soft, punky lake beds. Possibly this unusual tectonic stratigraphy of very-much-older over very-much-younger was not produced by extreme extension, possibly the Precambrian was thrust over the middle to late Tertiary via a thrusting method related to left-lateral strike-slip faulting along the Garlock Fault. Who knows? We never drilled deep enough to find out what lay beneath the tilted Tertiary rocks beneath the tilted Precambrian rocks.
As for weird today, I'll just leave you with these pictures of a giant breccia (breccia in the foreground, breccia in the background). We were driving into the slot-canyon portion of Titus Canyon, a one-way dirt route into Death Valley from just south of Beatty. We drove around a curve in the road, suddenly coming face to face with a megabreccia. I slammed on the brakes (not that I was driving very fast to begin with).
The same angular rock fragments from the first photo can be seen in this second photo, this time without anyone for scale. The breccia extends at least 35 to 40 feet up the wall.
In reading up on this breccia, I found more than one explanation, including more than one kind of sedimentary origin to vaguely cited tectonic causes. Anyone have any ideas?
For a picture with better scale, go here.
Too bad I didn’t get a picture of myself standing in front of this magnificent megabreccia!
Carnival of the Arid #4 is Up! - and Titus Canyon
Things You Find in the Field: Leadfield
UPDATE: Accretionary Wedge #34: Weird Geology is now up at En Tequila Es Verdad.
UPDATE II:The Encore to the #34 Wedge is now up! (The first Wedge to come in two pieces.)