Sunday, July 24, 2011

Hoodoos and Satin Spar - geologic niceties in Palo Duro Canyon

Palo Duro Canyon, noted for the great beauty of its multi-hued strata, also hides several surprising geologic treasures. Georgia O'Keeffe wrote of the canyon, "It is a seething cauldron, filled with dramatic light and color." I couldn't agree more. Two of my favorites among all the wonders of the park are hoodoos and satin spar gypsum.

 The hoodoos I speak of are not related to voodoo nor are they any type of Halloween decoration!  They are a beautiful geologic structure created by differential erosion. You've most likely seen pictures of them at Bryce Canyon National Park in Utah, the strikingly sculpted towers of sandstone that look like fairy tale castle spires. Palo Duro too has hoodoos (this is soo much fun typing all these oos), although not in the number or complexity of structure seen in Bryce. The most famous hoodoo in Palo Duro, at the end of a hot and shadeless 6 mile (round trip) hike is the "Lighthouse," seen in the adjacent picture.  Ok, maybe hiking this in over 100 degrees wasn't the smartest thing to do, but you can't stop me from going to see rock! This beautiful 310 ft high hoodoo is actually a national natural landmark.  The top of the Lighthouse is part of the Triassic Trujillo Formation (see the last blog notes). It's a tough sandstone, resistant to weathering.  The older Triassic variegated Tecovas Formation forms the main part of the hoodoo and the rocks that use to surround it. These surrounding softer mudstones eroded much faster than her sandstone cap, leaving the lone beauty standing there for all to see. 

The red- and white-striped Spanish Skirts of the Permian Quartermaster Formation show lovely details when one climbs close enough to look.  Glittering white stripes of satin spar gypsum decorate the red sandstone beds.  Here in Texas, the shallow marine sea rose and fell.  During cycles of evaporation, gypsum, an evaporite mineral, formed on the edges of the sea. You can see the same process at Lake Meade in Arizona and Nevada. Evaporite minerals form the white line marking the older height of the reservoir. Gypsum precipitates first when the water evaporates, followed by the more familiar halite or salt. The satin spar form of gypsum grows as aggregates of fibrous crystals. Tiny vertical needles shine in the layers. Here's a picture of a single layer I saw sparkling in the ruffled red sandstone skirts in Palo Duro Canyon.  The obligatory scale coin gives you an idea of the size of this layer.  It's just one of the many jewels making Palo Duro one of the most beautiful places to visit in Texas.

Next up:     Bats in my Belfry: Carlsbad Caverns National Park

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