Wednesday, June 9, 2010

Today's Hike: Trees, Wildflowers, Stratigraphy, and Faults

We went on a hike today, and for the first time in several months, I hiked beyond my usual rocky-flowery point (here, first set of photos) to this bonzai-like piƱon tree, and beyond that all the way up the hill.
We saw a fair number of different kinds of wildflowers. This is a broomrape, Orobanche L, possibly this one. It's parasitic on other plants and shrubs, just like Indian paintbrush.
Walking up the hill, I pondered the geology. Here, looking south toward Ward Mountain, you can see some variably dipping limestone and shale formations, which I knew to be cut by the low-angle Chainman Fault, which usually places the Ely Limestone on top of the Chainman Shale (younger on older).
After getting back, I stitched several photos together and did some more pondering (click all to enlarge if desired).
I started drawing lines and stratigraphic map symbols. The section starts with a little bit of Permian Riepe Spring Limestone (Prs), above Pennsylvanian Ely Limestone (doublePe), above Mississippian Chainman Shale (Mc), above Mississippian Joana Limestone (Mj), above Devonian-Mississippian Pilot Shale (MDp), above the Devonian Guilmette Formation (Dg). These are fairly widespread and common units in eastern to east-central Nevada, with the cyclothemic Ely Limestone and the two shale formations sandwiching the Joana Limestone being good place markers for figuring out where one is in the section.
Then I went nuts and added teeth to the two low-angle faults, which have been mapped as thrust faults on the two quadrangle maps of the area. To my surprise, I found that the maps show not only the Chainman Fault, which I already knew about, but they also show a low-angle fault between the Joana Limestone and underlying Pilot Shale. I had concluded on this walk that there had to be a fault there, at least on the east side of my photo-drawing, where the Guilmette is rudely cut off by the Joana.

This section and these faults can be seen on the south side of Highway 50 just west of Ely, although the view will be somewhat obscurred by roadcuts and steep hills.
On the way down, I found this rock specimen of a microfault in Devonian or Silurian limestone or dolomite. All in all, it was a good hike.


Gaelyn said...

Damn but you're good. I really like the microfault sample.

Mihaela said...

Awesome, eclectic post. Great mix - flowers, trees, faults, stratigraphy...

Silver Fox said...

Thanks, both of you!