Sunday, July 27, 2014

Urban Botany, Urban Art and the Instagram Effect

There’s a scrappy little Virginia creeper growing from the crevice below the right rear heel of the giant prairie dog (click on image to view).
I stumbled into urban botany by way of Lucy Corrander’s Street Plant posts (my favorite is this one).  I’ve done a few too -- about dandelions and other plants taking back the streets -- so-called weeds.  But I’ve mostly ignored our urban flora.  Yet every time I read about Lucy’s street plants, I think it would be neat to look at our own.  So finally I did.

I often bike through downtown Laramie, but totally ignore the plants of cracks and crevices.  So I wasn’t sure I would find many suitable subjects.  I needn’t have worried.  We have tough and tenacious plants, and our streets are not that well kept.  In fact, I had to narrow my focus.  I decided to limit myself to plants in artistic habitats.
Virginia creeper, Parthenocissus vitacea, is well-established at the base of a telephone pole.
Syl Arena wrote recently about the therapeutic value of Instagram, the popular online mobile photo-sharing service with distinctive Instamatic-like square images:
“Most of us, who are serious about creating great images, remember a time when making photographs was fun, spontaneous, and easy. Yet, we get all tangled up and photography becomes a stressor rather than a release. ... Now, I reach for my iPhone and take that snap. I try to do this at least once a day–stop my life for a moment and make a photo for the joy of making the photo. ... I find it’s a convenient way to stay connected to the playfulness that brought me into photography way back when.”  Syl Arena in My New Photo Therapist
It sounded appealing -- liberating as well as playful -- so I instagrammed the urban plants.  Actually, I used the square photo setting on my iPad mini, but the experience was the same.  Limited to square photos, with no viewfinder and often bright sunlight, I wasn’t able to obsess over composition.  Pretty soon I was “connected to playfulness”.
Lucy mentions the looks she gets when she’s on the pavement face-to-face with street plants.  I had no such pleasure.  If anyone looked at me odd, I didn’t see it.  I did have to move once for a delivery truck; there wasn’t room in the alley for both of us.
Prairie Dog Town, by Jeff Hubbell and Lindsay Olson.
Among the most common street plants in Laramie is cheatgrass, Bromus tectorum.
Cheatgrass habitat -- a crevice below the Snowy Range.
Close by I found more cheatgrass, with dandelions and kochia (left to right).
Occasionally I strayed from the Instagram format for habitat shots.  From Escape by Meghan Meier.
Kochia with a bit of dock.
Kochia, or summer cypress, is really common in downtown Laramie ... and most other parts of town.  It came to the USA from Eurasia and is one of our tumbleweed species.  We city-dwellers think it’s a weed.  But it’s very good browse for livestock and wildlife, and after I learned that the seeds are high in protein and great feed for birds, I didn’t feel so bad about all the kochia in my yard.  The seeds also have medicinal potential (for humans).  The NRCS has put together an excellent Plant Guide for kochia (PDF).  Kochia is Kochia scoparia to some and Bassia scoparia to others.  It’s a member of the amaranth family.

Here’s a much more robust dock plant, Rumex crispus.  Plants at the base of phone poles seem to do well.  The fence is here because the optical shop burned several months ago and it’s still being repaired.
Parking artifacts often ended up in my photos -- not because I sought them out but because parking is such a big concern in our daily lives.
No Parking, with white yarrow and hollyhock.
Mr. Peanut is ...
... watering the tansies!
Much of Mr. Peanut's garden is in hollyhocks, both real and imaginary, with a healthy population of insects.  This is Hollyhock Haven by Travis Rhett Ivey.
I was shooting one last parking photo when ...
Foxtail, wild aster and yet more kochia, with fallen sign.
... a cottontail popped out of the vegetation (see him below?).
He stayed and watched me take photos.  So I instagrammed him.
My favorite mural is Crossing Sherman Hill -- the famous grade across the mountains between Cheyenne and Laramie.  Here’s Union Pacific steam locomotive No. 4014 -- the Big Boy -- coming down the curving grade into the Laramie Basin.
Up at the summit, the train passes by striking granite rock outcrops -- like Vedauwoo and the Crow Creek tors.
And finally -- the caboose, passing several of the many snow fences along the route.
I took a video of the wonderful half-block-long mural, by Travis Rhett Ivey:
video
While I was sitting on the sidewalk photographing Virginia creeper in a crevice at the base of the Sherman Hill, two people approached me.  But they didn’t look worried, or even puzzled.  In fact, they were taking photos too.  They had come from El Paso, Texas to Wyoming, for the Frontier Days celebration in Cheyenne, and drove over the Sherman Hill to visit Laramie and see the downtown murals.  We chatted for awhile, then they headed off to the newest one, at the Napa auto parts store.  I followed shortly.

I found a small patch of saltgrass.  It’s one of our common prairie grasses, especially where soils are alkaline, but doesn’t seem to be much of a street plant.
Saltgrass, Distichlis spicata.
Saltgrass habitat, from We Built the Dream by Talal Cockar.

The Laramie Mural Project is a collaboration involving the University of Wyoming Art Museum, local artists and downtown business owners.  A brochure is available at the downtown Tourism Office.  On the Project website, you can take an “audio tour” narrated by the artists (click on “Mural Tour”).

Thursday, July 24, 2014

The Great Unconformity is greater here.

The juniper-covered hillside above doesn’t look terribly spectacular, but don't be fooled!  A really long and puzzling story is told by these rocks -- the ones that are present, and especially the ones that aren’t.
Portion of stratigraphic column from Knittel et al. (2004), modified.
This diagram is a stratigraphic column corresponding to the hillside -- a schematic representation of the rock layers with the oldest at the base.  Note the box with nothing but question marks.  This is an unconformity, a hiatus, a missing interval, a gap in the rock record.  And it's huge.

The rock record is often referred to as a book, because rocks tell the story of the Earth if we know how to read them.  Following this analogy, an unconformity means pages are missing ... or in this case, whole chapters.  But were the pages really removed?  Perhaps they were never written.
Unconformity (Geol.): a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous.
Unconformities aren’t rare.  For example there are 14 major unconformities in the Grand Canyon of the Colorado River (USA; source).  One of these gets almost all the attention -- the Great Unconformity, where the Cambrian Tapeats sandstone overlies the Precambrian Vishnu schist, a gap in the rock record spanning more than a billion years.
View into the Grand Canyon from the South Rim.  From the Colorado River (below left of center), the gray Vishnu schist rises steeply to cliffs of brown Tapeats sandstone.  The contact between the two is the Great Unconformity.  Photo courtesy Jack Share of Written in Stone.
The Great Unconformity isn’t unique to the Grand Canyon.  It’s exposed at scattered locations across North America and around the world.  Why is so much of the rock record missing over such a large area?  What does this say about that time on Earth?  This is where the book analogy breaks down.  While there is a missing part to the story -- a really long one, maybe equivalent to several chapters -- the gap isn't silent.  Its existence tells something of what was going on at that time.

The Great Unconformity began back when there was probably just one continent, Rodinia. [If you’re unfamiliar with how continents shift, grow, join, split and jostle each other, see this introduction to plate tectonics by the US Geological Survey.]  Supercontinent Rodinia stood above sea level for a long time, perhaps 350 million years.  Not being underwater, deposition was minimal.  Instead, erosion appears to have reduced Rodinia to a low relatively-flat surface of igneous and metamorphic rocks (not much protective vegetation in those days).
These paleo-reconstructions of Rodinia are teaching slides from SnowballEarth.org.
Then Rodinia began to come apart, as supercontinents do.  Continent-sized and smaller pieces spread far and wide.  One of the biggest ones was Laurentia, or ancestral North America.  As Rodinia broke up, much of Laurentia/North America was covered by shallow advancing seas, and sandy sediments were laid over the ancient rocks, now on the seafloor.  With deposition underway once again, the gap in the rock record was brought to a close and the Great Unconformity ended.

The Great Unconformity in the Inner Gorge of the Grand Canyon (USA) is probably the best known and most visited ...
Geologist Wayne Ranney embraces more than one billion years of Earth history in the Grand Canyon.  Ages are approximate.  Photo courtesy Jack Share of Written in Stone (labels added).
... but the Great Unconformity in south central Wyoming is greater!  That’s because the underlying older rocks are older, and the overlying younger rocks are younger.
The Greater Great Unconformity near Fremont Canyon, Wyoming.  Ages are approximate.
Why are the older rocks older?  Because Laurentia/North America was not uniform in age -- it was an assemblage of older continents and other crustal pieces.  The Wyoming Craton was one of the oldest, with rock ages ranging from 1.7 to 3.6 billion years.  The granite at Fremont Canyon is roughly 2.4 billion years old.  In contrast, the Vishnu schist in the Grand Canyon is “only” about 1.7 billion years old.
Modern-day Wyoming is in one of the oldest parts of North America; source
2.4-billion-year-old granite in Fremont Canyon, cut by the North Platte River.
And why are the younger rocks younger?  That story’s a little more complicated.  After Rodinia broke up during the Cambrian period (roughly 500 million years ago), much of Laurentia was covered by a great shallow sea -- the Sauk Sea.  Lots of sand was deposited, so the Great Unconformity usually consists of Cambrian sandstone atop Precambrian igneous or metamorphic rocks, as in the Grand Canyon.  But this isn’t always the case.

Not all that long ago, the overlying sandstone of the Great Unconformity in south central Wyoming was assumed to be a typical Cambrian sandstone.  Then Sando and Sandberg (1987) went and looked at it.  Not Cambrian, they concluded.  Instead, they recognized a new formation, the Fremont Canyon sandstone, which was younger by a hundred million years or so (late Devonian).  Thus the Great Unconformity in south central Wyoming grew to two billion years.

But their discovery created still more questions.  Where are the Cambrian sands of the great Sauk Sea?  Why are they absent?  Were they removed by erosion?  Perhaps they were never deposited.  Indeed, parts of Laurentia remained above sea level during the Cambrian period -- the Canadian Shield and possibly a Transcontinental Arch.
Paleo-reconstruction of Laurentia during late Cambrian time, with highlands labeled.  Modified from the EarthViewer App, free from the Howard Hughes Medical Institute.
Like others, Sando and Sandberg assumed that this part of Wyoming had been on the Transcontinental Arch and therefore was not submerged during Cambrian time, explaining the "missing" sediments.  But Myrow et al. (2003) looked at a similar situation to the south in Colorado -- also supposedly involving the Transcontinental Arch -- and reached a different conclusion.  They found evidence that Cambrian sediments were deposited, but that subsequent uplift caused complete removal.  They recommended that
“... regional reconstructions of earliest Paleozoic paleogeography along the entire length of the purported Transcontinental Arch should be reevaluated ... paleogeographic reconstructions can be [seriously] biased by the presumption that missing strata represent periods of non-deposition rather than subsequent episodes of erosion”  [as we learned in Geology 101]
So the story told by the Great Unconformity remains incomplete.  At minimum we're missing much of the chapter on south central Wyoming, and probably more.  But scattered pages will continue to be found, and though they may be really hard to read, we'll learn a bit more about Earth's deep past.  How amazing and wonderful, especially for geo-trippers!

The Greater Great Unconformity is exposed southwest of Casper, Wyoming, thanks to uplift during the Laramide Orogeny and erosion by the North Platte River.  It can be conveniently viewed northwest of Natrona County Road 408 about a half mile east of the Fremont Canyon Bridge.  Other viewpoints are described in Knittel et al. (2004), pp 26-27 and 64-69.
Fremont Canyon is in the Heartland of Laramide Tectonics.  Click on image for a better view.

Sources

Jack Share's blog Written in Stone, Seen through my Lens includes very informative posts about the Great Unconformity, available here.

Knittel, P, Van Burgh, Jr., DP, Logue, TJ, Strube, BE, and Jones, RW.  2004.  Field guide for the Alcova area, Natrona County, Wyoming.

Myrow, PM, Taylor, JF, Miller, JF, Ethington, RL, Ripperdan, RL, and Allen, J.  2003.  Fallen arches: Dispelling myths concerning Cambrian and Ordovician paleogeography of the Rocky Mountain region.  Geological Society of America Bulletin 115:695-713.

Sando, WJ and Sandberg, CA.  1987.  New interpretations of Paleozoic stratigraphy and history in the northern Laramie Range and vicinity, Southeast Wyoming.  US Geological Survey Professional Paper 1450, 39pp.

Thursday, July 17, 2014

Folded Land

Google Earth view of the "Heartland of Laramide Tectonics" in south central Wyoming. Red rectangle encloses area of photo below.  Click on images to view details.

Last month I took a short tour of the Heartland of Laramide Tectonics.  I had several geology guidebooks with me, so it was a fascinating trip.  The timing was good too.  If I had gone 75 million years earlier, it would have been really boring.
Traveling across south central Wyoming 75 million years ago.
At that time, the sea that had covered much of Wyoming for so long had retreated, leaving behind scenery of little relief.  But then the land was folded.  Now it’s a much more interesting place to visit.
Traveling across south central Wyoming in 2014.  Bold arrows point to selected attractions.
This folding happened during the Laramide Orogeny -- the period of mountain-building that produced the Rocky Mountains.  Most of Wyoming is dominated by Laramide structures.  They’re distinctive and usually easy to spot (it helps that the climate is semi-arid and vegetation often sparse).
Wyoming, with prominent Laramide mountain ranges in red; adjacent basins aren't labeled.
The creation of Laramide ranges and basins involved moving, tilting, folding and breaking (along faults) broad blocks of continental crust all the way down to basement rocks.  What?!  Is it possible to fold and break the basement of a continent?  Is it safe?
Basement (geology): rocks below a sedimentary platform or cover, or more generally any rock below sedimentary rocks or sedimentary basins that are metamorphic or igneous in origin.
 “Basement” is one of those terms we understand and use, but find difficult to define.  Part of the problem is that usage varies by continent.  In North America "basement" generally refers to igneous and metamorphic rocks of the craton -- the old stable part of the continent that has been around since Precambrian time.  The North American craton underlies much of Wyoming.
Source.
Actually, Wyoming was once on its own craton, before it was sutured to some others to form the North American craton.
Source.
So, as we were saying ... during the Laramide Orogeny “the Rocky Mountain foreland was fractured by deep-rooted reverse and thrust faults that uplifted broad blocks of Precambrian basement rocks, separated by deep basins" (Snoke 1993).  For example rocks from the continental basement are now exposed high in the Wind River Range, uplifted along a steep reverse fault (below).  A short distance west in the northern Green River Basin, these same rocks are 45,000 feet lower -- "staggering structural relief" (Snoke 1993).
Basement rocks form the high peaks of the Wind River Range, east of Pinedale; source.
The Laramide Orogeny was a big event in both time and space.  It lasted roughly 30 million years; start and stop times are debated and varied from north to south.  A large part of western North America was deformed, from Canada south into Mexico.  Actual Laramide-style deformation, involving basement rocks, characterized the tract from southernmost Canada to central New Mexico.
Extent of Laramide-style deformation, showing exposed Precambrian basement rocks (stippled); modified from Snoke 1993 (from Hamilton 1988).  Heartland outlined in red.
The area around the North Platte, Sweetwater and Medicine Bow Rivers in south central Wyoming has been called the Heartland of Laramide Tectonics (Lillegraven and Snoke 1996).  After my trip I asked one of the authors about the Heartland concept.  He attributed it to the other’s propensity for colorful language, but also emphasized that the region is filled with exemplary Laramide structures.

It certainly is a folded land.  My trip crossed multiple folds and faults, passing through scenery made of rocks ranging from Precambrian basement to mid-Tertiary basin fill.  Their stories are fascinating.  It’s so wonderful that by looking at rocks and landforms we can glimpse past worlds ... 30 million, 100 million, even a billion years ago.
Small anticline reveals Triassic redbeds, deposited when much of Wyoming was a muddy coastal plain.
Who walked here 170 million years ago?  Click on image to see tracks in beach sand turned to rock, and tilted to almost vertical.
Then there are the mysteries -- mountains flanked by steeply-tilted rocks on one side and a normal fault on the other, buried mountains, mountains crossed by rivers, and most puzzling, mountains far from any active plate boundary (where mountains usually arise).  How did these things come to be?  Sometimes we have a good idea, sometimes there are multiple theories based on the same incomplete evidence.  And sometimes we just don't know, which is fine.  This mystery adds to my sense of awe, and allows for informed speculation, a favorite pastime.  I love looking at Laramide landscapes and pondering what might have happened.
Water gaps were cut by the now-drowned North Platte River, as it made its way across Laramide folds (second gap visible in distance).
The gap and river before Alcova Dam was built in the 1930s.  From the Collections of American Heritage Center, University of Wyoming, Copy and Reuse Restrictions Apply.
My tour began at Alcova Reservoir, where the North Platte has cut through the Alcova uplift instead of going around it.  Much of the scenery is dominated by Permian and Triassic redbeds, in part because their color is so eye-catching.  My guide was Knittel et al.’s Field guide for the Alcova area (2004), which provides lots of information, including explanations for non-geologists.  The visuals are great -- maps, aerial photos, historical photos, photos with geologic features labeled, and panoramic shots.  There’s even a tour up Fremont Canyon from Alcova Lake, if you have a boat.  The road mileages didn’t match my car’s odometer, but that’s not so unusual and wasn’t a problem.  A virtual guide provides additional labeled photos linked to map locations.
Alcova Reservoir amid tilted redbeds.
From Alcova I drove south to Fremont Canyon.  Here the North Platte has cut through uplifted strata all the way down to basement rocks, revealing an intriguing gap in the rock record of some two billion years.
The Archean granite in Fremont Canyon above Alcova Lake is about 2.4 billion years old.
Pathfinder Dam was named for "The Pathfinder" -- JC Fremont.  His boat capsized nearby.
Next stop was Pathfinder Dam, one of BuRec’s earliest (1905-1909).  Then I crossed miles of Tertiary basin fill with Precambrian granite knobs sticking up through -- perhaps the most mysterious “mountain range” in Wyoming.  I reached the south "flank" of the "range" at the amazing Seminoe Mountains -- steep dark foreboding rocks crossed by both the North Platte River and the county road.  How improbable!  I emerged at Seminoe Reservoir, with views of spectacular Laramide flatirons.  This area is covered in A new look at the Laramide orogeny ... in southeast Wyoming, which includes several road logs (Lillegraven and Snoke 1996).
Above, the Pedro Mountains in the distance are Precambrian basement rocks that were uplifted, down-dropped, buried, and partially exhumed.
Above, approaching the north side of the Seminoe Mountains.  Yes, the county road really does cross here ... so does the North Platte River, a short distance east.  Below, looking north from the crest of the Seminoes down into the drainage of the North Platte.  The river has eroded off enough Tertiary cover to reveal parts of the underlying Pedro Mountains.
My tour of the Heartland of Laramide Tectonics ended on the south side of the Seminoe Mountains, where steeply-tilted sandstone and limestone flatirons made a nice backdrop for a portrait of a ruggedly beautiful limber pine (Pinus flexilis).

Posts about some highlights of the Heartland trip will follow.

Sources

Casper College.  Alcova geological site 2008; Virtual field trip of Alcova Lake, and Fremont Canyon, Natrona County, Wyoming.  Accessed July 2014.

Knittel, P, Van Burgh, Jr., DP, Logue, TJ, Strube, BE, and Jones, RW.  2004.  Field guide for the Alcova area, Natrona County, Wyoming.

Lillegraven, JA and Snoke, AW.  1996.  A new look at the Laramide orogeny in the Seminoe and Shirley mountains, Freezeout Hills, and Hanna Basin, south-central Wyoming.  Wyoming State Geological Survey Public Information Circular No. 36.

Snoke, AW  1993.  Geologic history of Wyoming within the tectonic framework of the North American Cordillera, in Snoke, AW, Steidtmann, JR, and Roberts, SM, eds.  Geology of Wyoming.  Wyoming State Geological Survey Memoir 5:2-56.