Randall Carlson | SCABLANDS TOUR - Ice Age Mega Scale Floods | Ancient...

Discover the Origin of a Beautiful Rock Formation

The Grand Canyon Explained | How the Earth Was Made (S2, E1) | Full Docu...

How Ancient Floods Have Shaped Our Landscape | Earthshocks: Megaflood | ...

Hike with a Geologist & Learn How Erosion Forms Beautiful Landscapes

The Power of Volcanoes Pt. 2: In the Shade of burning Mountains | Full D...

The Power of Volcanoes Pt. 1: Years without Summer | Full Documentary

A Visit to an Exhumed Permian Landscape

 Not by me, but by Wayne Ranney's Earthly Musings blog.

His visit was to southwestern Oklahoma, of the Fort Sill and Wichita Mountains area, visiting sites related to U.S. History and Geology on the same journey.  The first "half" of his post is related to the latter-19th Century history of this U.S. Army fort.  Interesting and thought-provoking.   [BTW, my Dad's artillery unit spent part of its WWII training in early- to mid-1943 at Fort Sill.]

The Wichita Mountains are composed of Precambrian to Eocambrian igneous rocks (of which the Mount Scott Intrusive Suite forms a significant part) and Cambrian and Ordovician sedimentary rocks (north of the Meers Fault) (Price, 2014).  

The igneous rocks are associated with magmatism during the formation of the "Southern Oklahoma Aulacogen" (SOA), late-Proterozoic to earliest-Paleozoic failed continental rifting of the supercontinent "Pannotia" (Price, 2014).   

The "Basement-Cored Uplifts" associated with the Wichita Mountains (trending NW to SE) include the Arbuckle Mountains to the east and westward extend as far as the Uncompahgre Uplift in Colorado and Utah and is associated with the Ancestral Rocky Mountains.  Essentially parallel to the north in Oklahoma and the Texas Panhandle is the Anadarko Basin.

Wayne's second "half" of the post is about the Wichita Mountains area as an "Exhumed Permian Landscape", i.e., what we see now is what was exposed, eroded, and then covered by Mesozoic and Cenozoic sedimentary rocks.  And then exposed again by post-Cenozoic erosion. 

In other words, in this setting, we are looking at late-Paleozoic landforms, adorned with numerous plants that have appeared in the fossil record and evolved during the Mesozoic and Cenozoic Eras.  Quite thought-provoking.

[In William D. Thornbury's classic "Principles of Geomorphology" (1968), Fundamental Concept 7 is: "Little of the Earth's topography is older than Tertiary and most of it no older than Pleistocene."  From Thornbury (1968): "Ashley (1931) has made a strong case for the youthfulness of our topography.  He believed that 'most of the world's scenery, its mountains, valleys, shores, lakes, rivers, waterfalls, cliffs, and canyons are post-Miocene ... "

Fundamental Concept 8 is: "Proper interpretations of present-day landscapes is impossible without a full appreciation of the manifold influences of the geologic and climatic changes during the Pleistocene."  Without going into too much detail, just consider the effects of glaciation and inter-glaciation related changes in the Ultimate Base Level.]

[Please spend time on the above-linked Earthly Musings post.]

For more interesting reading, please visit Wayne Ranney's personal blog, "All in a Days Karma". 

Figure 1.  Saddle Mountain, north of Wichita Mountains Wilderness.  Public Domain image.  Eocambrian Saddle Mountain Granite, Wichita Granite Group.

For a personal aside, I have my own perceived "Exhumed Landscape" story, on the Georgia Coastal Plain.  [When the post is completed, it will be linked here.] 

More on Exhumed Landscapes are here, here, and here.  [Haven't read these, yet.]

Additional References:

Ashley, G.H., 1931  Our youthful scenery, Bulletin Geological Society of America, vol. 42, pp. 537 - 546.

Price, J.D., 2014  The Mount Scott Intrusive Suite, Wichita Mountains, Oklahoma, in Igneous and Tectonic History of the Southern Oklahoma Aulacogen, Oklahoma Geological Survey Guidebook 38, pp. 299 - 318.

Suneson, N.H., 2019  Roadside Geology of Oklahoma, Mountain Press

Down Memory Lane, Lurching I Go, Again - Part 4

 [While doing "series posts" (consisting of Part 1, Part 2, ... ), I have been guilty of posting a Part 1 and then getting distracted and not completing planned subsequent related posts.  As for the prior parts of this thread, please scroll down.]

As previously mentioned, despite the regrets of not having finished this project and failing to inform myself of what my cohorts learned, over the years I have used some of my scanned slides (and memories) as Educational Resources, as seen with the labeled images (Figure 1) and suggested discussions below.

In an attempt to resurrect my portion of the project and to spend some "really quiet time" with only the sound of the wind and my thoughts, I visited the Eagle Mountains either in the Fall of 1979 (or was it 1980?), by myself.

As usual, I checked in at the ranch house to verify it was still OK (it was).  While chatting with the caretaker, he mentioned that the remnants of a hurricane had "wandered up the Rio Grande Valley" from the Gulf Coast and that it "sat" over the Eagle Mts. for a weekend, during which time they got 22 inches of rain (courtesy of "Orographic Lifting" - my conclusion).  [Usable in Weather and Climate discussions.]

(I suppose by examining Gulf of Mexico weather records could help estimate the date, but it doesn't matter.)  He advised me of this as "some of the roads didn't exist - in a usable manner - anymore" and he didn't have the proper equipment to fix them.  [I guess the owner in Houston was trying to decide if fixing them was worth it.]

 Figure 1A.

The text box (in the above image) obscures the roadway we used in 1978 in the NE quadrant.  This was a normal arroyo (dry canyon) crossing, down-gradient from a canyon draining part of the "highlands".  Though this wasn't part of my 1978 field area, I had wanted to explore the more-accessible parts of the NE and SE quadrants and so some more photography.

The image below shows the "roadus interruptus" within an "inner montane valley".  It illustrates the poorly-sorted nature of valley alluvium, deposited by "normal" seasonal flooding versus the 4 feet (+/-) of rapid down-cutting from a single catastrophic flash flood.  At the base of the vertical cut, you can see a small "apron" (talus cone) starting to form, as part of nature's re-establishment of a "natural angle-of-repose" for this range of clast sizes.  

[These considerations are usable in discussions of "Cycles of Erosion and Deposition"; "Changes in Flood Velocity and Capacity" due to "Gradient Variations" and degree of "Valley Confinement"; as well as "Soil-Moisture Retention" due to this being on the east side of the mountains.  Suitable for Physical Geology, Hydrology, Weather and Climate, Environmental Science, and Ecology.] 

 Figure 1B.

At the time I was taking this above photo, I wasn't thinking of educational resources or scholarly discussions, I was thinking "Well damn, I will not be doing much exploration in this area of the NE quadrant".  With that, after exploring what I could, I returned to the comfort of the "home base" at East Mill.  (This autumn photo below was probably taken at that time.)

Figure 2.  (Looking approximately Northeast.)

[Please forgive the dust spots on the sky portion of the photo.]

East Mill is a special place for me, even after not having visited it in 40+ years.  Other than a distant train passing miles away, across Eagle Flat, and random airplanes (some to be discussed below), all you could hear was the wind.  So calming as to be spooky at night, when alone.

A weather-related memory stands out amongst the East Mill events of the summer of 1978.

Within the Desert Southwest, usually in early-July, the summer heating of the continental U.S. landmass triggers a "quasi-Monsoon Effect", drawing in moist air from the Gulf of Mexico and the Gulf of California.  We welcomed the appearance of clouds over the mountains (Orographic Effect), as they brought us some shade.  But often that shade was followed by thunderstorms that forced us back to East Mill.

One afternoon, with active clouds in the area, we had "knocked off" and eaten dinner early, as we expected storms.  

[In the view shown in Figure 2, directly behind us, in the Red Light Bolson was the Rio Grande, cutting across at a NW-to-SE angle.  In Mexico, the term "Rio Grande" is not used until downstream of the confluence of the "Rio Conchos" with the "Rio Bravo" ("Rio Grande" of American usage).] 

With an hour and a half of daylight left, a small but intense thunderstorm, that probably began in Mexico, crossed over the ridge west of East Mill, and for about 10 minutes we were treated to heavy rain and lightning strikes within a quarter-mile.  We both piled into my truck and backed up-slope for maybe a 200 yards, to get a little further away from the windmill.

After the storm was "finished" with us, we returned the truck to its normal position.  We stepped out and enjoyed the cool, freshly-washed air.  As the storm trundled across Eagle Flat, then the Carrizo Mts., and across I-10 towards the Beach Mts. (NW of Van Horn), something happened.  It seemed to stop moving.  After a few minutes, it became apparent to me that the storm had reversed direction (by 180 degrees) and was coming back for another noisy visit.

I said "It's coming back.", to which Dan replied, "That's impossible!".  We argued briefly, then I decided to shut up and let the storm do the talking.  A few minutes later, Dan had to admit, "The storm is coming back ... "  

Sure enough, the damn storm drifted about 10 - 15 miles northeast, before the winds changed and pushed it back for Round 2.  We again backed the truck up the hill and watched as the storm repeated its performance, after which it traveled back over the ridge and returned to Mexico.  And with that, our Meteorology lesson in "the Movement of Convection Thunderstorms" was over.

I regret having lost touch with Dan.  If memory serves me correctly, he may have been from upstate New York.  He had a rather laidback attitude about things for a northerner.  I only heard him cuss twice, both times during our being set upon in the Eagle Mts. - at different times - by plagues of gnats and then wasps.  No fellow grad students had ever mentioned being besieged by either.  

When the gnats were at their peak, it seemed that they were desperate for moisture to the point of getting it from your eyes, nose, and mouth, driving Dan to cussing and stating that he was "ready to quit Geology and go sell insurance".  Oh, the heresy!  During the plague, we discovered that the gnats were victimizing other mammals as well.  One day, Dan managed to quietly walk to within 6 feet of a rabbit, because it was rubbing its front paws over its nose and eyes in search of relief.  It finally noticed him and hopped off.  It wasn't until we got a good rain that the gnats subsided.

Sometime later, we gradually started seeing a growing number of reddish-orange wasps flying about.  As they flew closely around us, their behavior seemed more about curiosity than aggression, perhaps they were asking "Well, did you bring us something to eat?".  As luck would have it, we had forgotten to bring any wasp treats.  Dan's second episode of cussing followed one of the curious wasps crawling into his backpack and when he reached in for something, the wasp demonstrated that it COULD sting if it needed to. 

[Sorry, still compiling the list of References.]

What a Geologist Sees - Part 9

  Figure 1.

The photo at top is of an embankment of saprolite, which is literally (and colloquially called) "rotten rock". This embankment was exposed during a short period of local construction. Saprolite is the term used to describe exposures that display some original rock structures, but because of intense chemical weathering, the internal structures of most of the minerals have been broken down to the point where the "rock" can be crumbled in your hand - thus the term "rotten rock". The processes that yield saprolite are what produce the inorganic components of soils.

If the exposure has been reduced to a structureless clay, e.g., the famous Georgia red clay, we call this "residuum".

The lower photo is of the original "country rock", a fresh, hard biotite gneiss, a metamorphic rock that is similar to granite. This particular gneiss (silent "g", rhymes with "rice"), probably part of the widespread Lithonia Gneiss, is composed of potassium (orthoclase) feldspar, plagioclase feldspar, quartz, biotite mica and probably muscovite mica, along with some accessory and trace minerals.

     Figure 2.

The progression from gneiss to saprolite takes place through chemical reactions involving water and natural acids over long periods of time. In the process of hydrolysis, hydrogen cations replace the metallic ions (K, Na, Ca) that occur in the mineral structures of feldspars, micas, and other silicate minerals. The removed metallic ions then become part of the dissolved minerals in groundwater (and surface waters) and are flushed out of the system. Any iron-bearing minerals, including silicates, are altered by oxidation, in addition to hydrolysis. There are other chemical weathering processes, but these two are probably most prevalent.

At or near the surface, quartz is generally fairly stable, so probably most of the original quartz remains, while the feldspars and micas have broken down into various clays.

In addition to the chemical weathering, whereby the actual chemistry of the minerals change, there is also physical weathering, where the rock is broken into smaller pieces by natural processes, yielding more surface area upon which the chemical processes can occur, i.e., both types can occur simultaneously and tend to enhance one another.

It is a little unusual, in this area, to see the fresh parent rock and the resulting saprolite in the small area of a stand-alone drug store.

On a side issue, if there is enough quartz present (as opposed to clays) and there is enough porosity and permeability (hydraulic conductivity), saprolites can sustain small, residential drinking water wells, in this area.

What a Geologist Sees - Part 19

Glacier National Park is one of the "Bucket List" places that I hope to visit, someday.

[For the moment, a photo taken by a friend will have to suffice until I can get there to take my own.]

The feature pictured at right is Chief Mountain, which consists of Proterozoic limestones sitting atop Cretaceous shale and sandstones. This is totally "out-of-whack" with "what should be". Under normal conditions, the Concept of Superposition applies, wherein in a series of layered rocks (usually sedimentary, but could apply to some volcanics), the oldest layers are at the bottom and the youngest are at the top. The Proterozoic is much older than the Cretaceous.

The presence of a "thrust fault" is the reason for the existing condition. During periods of tectonic deformation, where there is lateral compression, sometimes sheets of rock will break loose and get "shoved on top of" younger layers. The lateral breakage is usually along a shale layer. In this case, the thrust fault is referred to as the Lewis Thrust Fault or the Lewis Overthrust. Erosion after the period of faulting isolated Chief Mt. from the remainder of the thrust sheet, thus we call Chief Mt. a "klippe", which is a type of "erosional outlier", i.e., it is laterally separated from similar rocks.

The mesas and buttes of Monument Valley are also erosional outliers, but they have no underlying thrust fault, so they are not klippes.

There are plenty of thrust faults in the Appalachians, including the Georgia Piedmont, though they are obscured by soil and vegetation cover. There is a thrust fault (name forgotten) exposed in an outcrop on the west side of I-285, north of the intersection with I-20 and near the Chattahoochee River, but the traffic makes it difficult to pull over and get a good photo.

There is a Georgia Piedmont Thrust Fault, shown in Figure 9, of this post.