FOLDS: ANTICLINES, SYNCLINES, MONOCLINES

“Living on a layer cake
Way down under the ground
Living on a layer cake
Take a slice and look around.”

                  (Chris Rawlings)

Growing up in Kansas I was quite used to term “layer cake geology”—the rocks are relatively flat, at least on the surface, and it is fairly easy to predict the ages of outcrops.  After stripping off the glacial debris in the northeastern one-fifth of the state, one finds the youngest rocks in the west and the oldest in the eastern part of the state. As an example, in driving I-70 from the Colorado-Kansas line east to Kansas City the traveler would traverse rocks ranging from the Pleistocene/Holocene sediments and late Cenozoic Ogallala Formation through a nice section of Cretaceous rocks, to fantastic exposures of fossiliferous Permian (the Flint Hills) and Pennsylvanian rocks (Osage Cuestas).  Triassic and Jurassic strata are missing (on the surface) and the oldest rocks cropping out in Kansas are of Mississippian age in the extreme southeastern corner.  One must look in the subsurface to locate older rocks.  The traveler also will not notice any appreciable tilting of the beds---layer cake geology at its best; however, erosion by streams has produced fine exposures.  

 

Generalized geologic map of Kansas showing outcrops of Cenozoic (C), Cretaceous (K), Permian (Pm), Pennsylvanian (P), Mississippian (M), glacial (G).  Map courtesy of Kansas Geological Survey. 

You can imagine my surprise, then, on my first trip to Colorado (in grade school) when I noticed that some rock layers were not flat but were actually “standing up”!  How in the world did that happen?  In the pre-internet days the only possibility for an answer was waiting until school started in the fall and then consulting an ancient set of “encyclopedias”. 

In the meantime, I continued to collect rocks and minerals with the most interesting specimens being those from local sand and gravel quarries.  Little did I realize that “those most interesting” minerals (mostly jasper, chert, and quartz) had a source area near the “standing up rocks”.  At any rate, I was hooked on geology.

TWO roads diverged in a yellow wood,

And sorry I could not travel both

And be one traveler, long I stood

And looked down one as far as I could

To where it bent in the undergrowth;

Then took the other, as just as fair,

And having perhaps the better claim,

Because it was grassy and wanted wear;

Though as for that the passing there

Had worn them really about the same,... Today (August 2015) I thought about this early Colorado trip in relationship to an NPR story about Robert Frost and his most famous poem—The Road Not Taken.  I don’t know about schools today but virtually every kid in my time studied the poem in English class(es).  The poem reminded me of, not two roads diverging, but two layers of rocks diverging--one being flat the other bending.  I know, strange analogy, but that is the way my mind works!  What I did find in the “encyclopedia” was that mountain building, and igneous rock events, pushing up from below, had tilted and bent the overlying sedimentary rocks.  Of course, in the days before our understanding of plate tectonics the “encyclopedias” really did not explain how these mountains formed.  As I grew older, and with an additional understanding of geology, I became fascinated with the bending and folding of rock layers, especially those that formed topographic or geographic features.  Colorado and the Mountain West are fortunate to have a wide variety of folded rocks that are described by Matthews and others (2003) as “metamorphic folds, basement cored folds, salt-cored folds, monoclines, syn-depositional folds, anticlines, synclines, domes, basins, refolded folds, evaporate-flowage folds, collapse folds, disharmonic folds, and forced folds”.  This small article will focus on some of the larger geographic features that readers might locate.     Cartoon sketch of an anticline (with oldest rocks in the center and beds dipping away from the axis) and a syncline with youngest rocks in the center).  Public Domain sketch courtesy of Pearson Scott Foresman.  Anticlines are folds where the limbs dip away from the axis (convex-up) and where the oldest rocks are in the center of the fold.  The cartoon above shows a nice symmetrical fold while in reality most anticlines are asymmetrical, plunging, or even overturned.  In addition, erosion often planes off the top of the structure so that the fold does not form a topographic high and one must examine geologic maps and/or aerial photos to determine size and extent.  A structural high (anticline) does not always produce a topographic high (hill/mountain).  At other times the structure is quite visible as resistant rocks in the limbs form an impressive outline of the fold.  Most anticlines in Colorado are the result of compression associated with the Laramide Orogeny (building of Rocky Mountains).  Imagine piling several carpets, of different colors, on top of each other and then pushing them against a wall.  The carpets would “bulge up” into several “anticlines” due to the compressive forces. Many of the larger mountain ranges in Colorado, such as the Front Range, are actually large anticlines where steeply dipping sedimentary rocks are exposed along the flanks and Precambrian basement rocks crop out in the center of the fold.  The original extent of the sedimentary rocks was “over” the Precambrian rocks; however, with uplift the sedimentary rocks were eroded off the top.  Geologists often term this type of large fold as a “basement-cored anticline”.  The Black Hills of South Dakota represent a miniature version of a Laramide basement-cored anticline and one that is easy to see and understand.  Here in South Dakota vertical movement has produced a topographic high corresponding with a structural high.  In the Black Hills, at the center of the anticline (sometime referred to as a dome), are rocks of Precambrian age.  As one moves out from the center the sedimentary rocks of Paleozoic and Mesozoic age grow progressively younger.  What makes the Black Hills nice to study is the lack of large faults that often complicate the geological understanding of Colorado’s mountain ranges.   Sketch of the Black Hills showing the Precambrian-cored center of the anticline (Strahler and Strahler 1978).  Smaller anticlines (non-basement-cored), also due to compression and folding, are often found off the flanks of the mountain folds.  One of my favorite vest pocket anticline is Split Mountain at Dinosaur National Monument along the CO-UT state line, a fold associated with the much larger Uinta Mountain Range. At Split Mountain the Green River cuts a fantastic canyon right through the heart of the anticline and a raft ride takes the paddler through both limbs and the core of the fold.  Aerial photograph of Split Mountain Anticline at Dinosaur National Monument.  Resistant beds nicely outline the nose of the fold; all beds dip away from the core.  Photo from mapcard.com.   Dipping rocks (Weber Formation) on the flank of Split Mountain Anticline with Green River in foreground. Some subsurface anticlines are commercially important as they serve as traps for petroleum (oil and gas).  The Raven Park Anticline (aka Rangely Anticline), the major petroleum trap at the giant Rangely Field in northwestern Colorado, was discovered in 1901 and has produced between 800-900 million barrels of oil, mostly from the Weber Sandstone at subsurface depths of ~6400 feet.  Secondary Recovery (water injection) started in 1957 while Tertiary Recovery (injection of  CO2) commenced in 1986 and the anticline is still producing. It is interesting to note that the Weber is subsurface at Rangely but is well exposed and surficial at Dinosaur National Monument, a mere ~30 miles away.     Gently dipping limbs of the Cub Creek or Jensen Syncline (Dinosaur National Monument).  Foreground rocks are the Jurassic Morrison Formation.  Red rocks in distance (showing the fold) are Triassic and Jurassic in age. Synclines are the opposite of anticlines with the limbs dipping toward the center of the axis, convex-down, and where the youngest rocks are in the center of the fold.  Most synclines associated with the Colorado mountains are small in stature and rarely form topographic features.  The Cub Creek Syncline at Dinosaur National Monument is an easy fold to observe. Large scale basins are the opposite of the basement-cored anticlines and include Laramide features such as the Denver-Julesburg Basin east of the Front Range (70,000sq. mi.) and the Piceance Basin in northwest Colorado.  Both of these are structural basins (large synclines) and do not form topographic lows and therefore do not show up as “landscape features”.  There is a formation elevation change (in the subsurface) of about 9000 feet from the edge of the Denver-Julesburg Basin to the center.   Blue Mountain at Dinosaur National Monument.  Notice the horizontal beds on top of the mountain which then bend and dip steeply down the flank.  The massive sandstone is the Weber Formation which reappears in the subsurface (-6400 feet) at the Rangely Oil Field approximately 30 miles to the southeast. The last type of the major folding structures is the monocline, often described as “half an anticline”—there is only one dipping limb coming off flat or horizontal layers.  The Colorado Plateau has some of the most impressive monoclines in the world with the “bend” commonly associated with subsurface faulting in the underlying Precambrian rocks.  Monoclines at Colorado National Monument and Dinosaur National Monument are especially impressive.    The great monocline at Colorado National Monument.  The lower gray rocks are Precambrian in age, the slope forming unit is the Chinle Formation (Triassic) while the upper massive sandstone is the Wingate Formation (Jurassic). This small article cannot begin to cover all of the standing, contorted, disturbed, folded, and bent rocks in Colorado.  Virtually any of the rocks in the western one-half of the state are folded and faulted and a drive on most of the roads leading west will reveal some of the magic.  Purchase a geologic map from the State Survey and take a road trip! As for my circuitous route from Kansas to Colorado—I came here from the city, a thousand miles away; Now I sing a mountain song of the night wind in the pines; I've seen the quiet splendor of a field of columbine (The Mountain Song; John Denver). REFERENCES CITED Matthews,V., K. KellerLynn, and B. Fox.  2003. Messages in Stone. Denver: Colorado Geological Survey. Strahler, A. N., and A. H. Strahler. 1978. Modern Physical Geography. New York: John Wiley & Sons.

WHY A GEOLOGIST?

One of the important books in the middle part of my life was entitled All I Really Need to Know I learned in Kindergarten (Robert Fulghum).  I have read it several times and learned much with each perusal.  In fact, one of his truisms sort of guided my life, especially in my youth: It wasn’t in books. It wasn’t in a church. What I needed to know was out there in the world.  So, from a very young age I was out in the world looking, engaging and learning. 

Growing up in a small town in Kansas in the 1950’s was a pretty amazing experience---there I said it.  Most readers probably now believe that senility has really fogged my mind, but let me explain.  Television was almost non-existent, one or two black and white channels came later, and the closest things to video games were the pin ball machines in the local pool hall.  However, machines cost 5 cents per play and who wanted to waste a nickel?  So, kids needed to invent projects and games and pick up rocks and collect leaves and study insects and therefore my fascination for science and nature began-- What I needed to know was out there in the world.

I grew up in a very non-wealthy family---certainly poor by today’s standards but not unlike 95% of the other families in town (400 people maybe counting some dogs).  Therefore, my purchased toys were often of the least expensive variety.  For example, I wanted a metal “erector set” but received wooden “tinkertoys.”  I never did receive an electric train that ran circles on a small track nor a “chemistry set.”  Therefore I went out into the world and improvised.  One of my favorite “toys” was the generator/magneto secured from the old crank telephones.  Today these old wooden phones are found in antique shops and are fairly expensive.  “Back then” I simply looked behind the telephone office and pulled out a generator/magneto from a discarded phone.  

Western Electric Five Bar Magneto.  Photo courtesy of  the Old Phone Man who has an absolutely wonderful web site located at www.oldphoneman.com.

These generator/magnetos had a permanent set of horseshoe magnets (usually 2-5) and produced alternating (AC) current when the crank was rotated.  The faster I cranked, the higher the volts produced.  One could get a hundred volts or so by really “cranking her up”! 

In the actual telephones the hand cranked generators/magnetos caused the bell to ring.  With the addition of fairly large zinc-carbon batteries a signal was transmitted to the local telephone office (Central) and an operator answered and then connected you, via switchboard, to another number.  I still remember our home phone number—119—and my father’s place of business—33.  So, I cranked the phone and Bertha the operator answered “Central.”  I said “Bertha, what is the temperature today?”  She imparts that information and then I stated, “Give me 33 please” and I am connected to my father’s phone.

But, there were other kid uses for the generator/magnetos.  These gadgets were powerful little things and could impart a painful shock so one had to be careful.  My favorite use was attaching wires to the positive and negative terminals and then clamping these wires to slender steel rods.  I inserted the rods into a damp area of soil a few feet apart and gave her a crank.  Like magic, earthworms (fishing worms) appeared on the surface available for scooping up and using for bait.

Another exercise involved using the same device to fish for denizens residing in the local Saline River.  By tossing the rods into the water and cranking up a shock the fish were stunned and came to the surface and one could net them.  Now, this was not a legal means of obtaining fish in Kansas and I am not claiming responsibility.

I also used the generator/magnetos to power a small light bulb.  This was nothing spectacular but when sticking the light bulb next to a neighbor’s window and cranking away, nifty results were often achieved---and we ran like crap for home.  Once I attached the wires to fences around the local baseball field and waited for unsuspecting victims---but only gently cranking for a mild shock.  It was a great way to learn about electricity “on the cheap” and certainly whetted my curiosity for science.

I also loved to fool around with DC power and collected the old zinc-carbon batteries from telephones and from lanterns used, and discarded, by the local railroad work crew.  These batteries still had some juice left and were used for a couple of projects.  One was simple and involved powering flashlight bulbs in small wooden houses we built to make a Christmas Village.  OK, not as fancy as the commercial villages available today but never-the-less an entertaining and a learning project.  I also constructed a variety of electromagnets by wrapping copper wire around a nail or an iron core and attaching the opposite ends to the positive and negative battery terminals.  A lesson in physics at its finest.

I also recycled the zinc-carbon batteries by tearing them apart and extracting the zinc shell.  I really don’t know how I learned the shell was zinc or that inserting the zinc into sulfuric acid produced hydrogen—it was just learning out in the world!  Anyway, I went down to my father’s gasoline station, found some discarded car batteries and extracted the sulfuric acid---without my father’s knowledge.  Then it was out to the back yard with the acid, some dish soap, the zinc and a “firecracker punk.”  

Later in life I learned about the chemical equation: Zn + H₂SO₄ --> ZnSO₄ + H_2.  So, hydrogen is a very flammable gas and effervesces from the solution and produces bubbles (the dish soap) that can explode when touched with a lit punk!  I also learned that one could eliminate the dish soap, put the solution and zinc into a soda bottle, quickly cap the bottle with a weak balloon so that the hydrogen gas offered inflation, tie off the full balloon and carefully remove it to another location.  One then attached the punk to a “long” stick (ten feet or so) and popped the balloon with a loud explosion and a fireball.  An even larger explosion would occur if you used your breath to further inflate the balloon as a mixture of oxygen and hydrogen is very explosive.  Wow, that is a real chemistry lesson.

  

For my experiment in geology I went meteorite and gold mining with my electromagnets.  Somewhere I learned that iron minerals were often associated with gold flakes and the trick was to locate iron minerals.  So, off I went to the sand pits and outcrops of the Dakota Formation with my magnets.  I only located a few small particles of magnetite and my magnifying glass did not locate gold.  Then it was off to look for iron meteorites.  Those finds turned out to be pieces of metallic slag used for ballast along the railroad tracks.  But it was a learning experience.

The second geology project involved making a compass although I did not have the slightest idea of how to transport it to the deep woods.  But I took one of my mother’s sewing needles and magnetized it on my handy-dandy electromagnet by running it back and forth across the coils maybe 50 times.  I had a small cork floating in an old plastic pan and gently laid the magnetized needle on the floating cork and watched it slowly turn and point North. Well actually it was magnetic north but at that point in life I knew nothing about magnetic declination.

All of these little projects whetted my longing for “real” science courses where I would be exposed to a variety of laboratory experiments.  However, I learned very quickly that Imagination is more important than information. Einstein said that, and he should know (Robert Fulghum).  I was very slow in physics classes since my skills with a slide rule were lacking—cross off that college major.  In third semester chemistry the breakage of numerous titration burets broke my budget---scratch off that major.  But wait, all was saved with a course in Physical Geology and I never looked back.  If the dream is held close to the heart, and imagination is applied to what there is close at hand. Everything is still possible (Robert Fulghum)!