I found these beautiful and mysterious sculptures in Goblin Valley State Park in southeast Utah, on the opposite side of the main ridge from the goblins.
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View from parking lot. Goblins (technically hoodoos) eroded out of the Entrada sandstone – actually a mix of sandstone, siltstone and shale (cliffs in background).
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Mid-Jurassic Entrada sandstones, siltstones and shales – once tidal flats and coastal dunes. Pale-colored layer above is the Curtis Formation, also Jurassic.
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I took the Goblin’s Lair Trail around to the east side of the ridge (photo above). In a large alcove, I found walls of Entrada sandstone covered with what looked like mud that had run down from above.
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My camera had color issues in the shady alcove.
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For reasons now forgotten, I took no photos of the entire alcove. Here’s a Google Earth view instead. The “mud sculptures” were on north- and northwest-facing walls.
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Click on image to view details.
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Back at the car, I checked accounts of Goblin Valley State Park in two geology guidebooks. They described depositional and erosional features in the park, both ancient and modern: tidal cross-bedding, remnants of tidal channels, dune cross-bedding, ripple marks, talus, stream-bed ripples, gilgai (popcorn-textured soil), microbiotic crust, intermittent stream channels, and of course hoodoos/goblins. But neither book mentioned mud sculptures on alcove walls.
What are they? Are they depositional, erosional, both? All attempts at clever googling have failed. Can you help? If so, please Comment. I seek enlightenment.
Hollis--
ReplyDeleteVery interesting! They have a slickenside-y look about them. My guess: this is the site of a frozen waterfall. Ice builds up in snowy/wet winters (clearly, from your photos, this is not one of them), forming a frozen column of ice. When it melts in the spring, the rotting ice creeps and slides down the face, creating the grooved/polished look in the muddy cliff face. The fact that it's on north and northwest-facing surfaces is consistent with this idea. And of course, after it's melted away there's no evidence left but the "sculpture".
--Howard
Thanks the the comment, Howard. A role for freezing never occurred to me but now I can see all kinds of possibilities ... build up of frozen ice as you say, or maybe half-frozen muddy runoff. I believe it gets cold enough there in mid-winter. It would be great to check it out after a rain or snow. Unfortunately it's ten hours away. But I will stop again ...
DeleteLike all good hypotheses, these are testable. When you do stop again, take along a small bottle of acid (10% HCl--well sealed!; or bring home a representative chip). Tufa, being limestone, will fizz. I agree the formation is reminiscent of some tufa deposits. But the setting, as you’ve described it, doesn’t strike me as typical for hosting a tufa deposit, which form in areas of groundwater discharge--i.e. relatively low-lying areas. Looking at Google Earth, your “alcove” is on the side of a small erosional outlier (isolated, relatively high ground), of--as you’ve described it--sandstone, siltstone and shale. It seems unlikely that carbonate-laden groundwater would be discharging from the top of such a feature. On the other hand, if some of that rock (perhaps the pale-coloured upper unit?) has a carbonate grain cement, it’s possible that this could be leached by rainwater and redeposited as a tufa on the cliff face. Again, the acid bottle would reveal the truth. I love your blog, BTW!
DeleteCheers--Howard
There are several things I need to check at that site ... now that I know more. I may get there in mid April. I will take a bottle of 10% HCl, thanks for the tip. That "ridge" is indeed an erosional outlier. Zooming in on Google Earth, I thought there might be a little gully that runs down to the alcove. I favor the runoff hypothesis ... and near or below freezing temps could provide some viscosity to explain what looks like flowed goo!
DeleteThanks, again, Howard. I appreciate your feedback.
Great observation - look forward to checking it out next time I am down there.
ReplyDeleteThanks, Dan. I'd love to hear your take on it!
DeleteLooks a bit like tufa to me (not be confused with tuff). i.e. carbonate deposits that typically form on cliff-faces. Some of your pictures look like figure 9 in this USGS post. http://pubs.usgs.gov/fs/2004/3044/
ReplyDeletethanks! another idea new to me. So far 2 votes for carbonate (via twitter)
DeleteSounds like you found your answer--good. And we all learned a little more about sandstone and hoodoos from your post. It's been a while since I've been out west--too long. Time for a road trip.
ReplyDelete