Tuesday, March 28, 2023

Seeing the Craton

Granite quarry near Milbank, South Dakota, in the southwest part of the Superior Craton.
"Craton" comes from the Greek word κράτος, meaning strength.

Seeing the Craton 

Northeast South Dakota, sculpted by glaciers,
landscapes so young, almost infantile,
ice melted just 12,000 years ago.
Glacial floods scoured a deep oversized
valley for the Minnesota River.
I went there to see the craton.

Craton—aged worn-down but strong
rocks hinting at what they once were:
volcanic, sedimentary, intrusive
2.6, 3.5, maybe even 4 billion years ago.

Older even than plate tectonics—
mad dance of Earth's giant plates
recycling crust and leaving none
older than ca. 2 billion years
except for cratons.

Cratons, why are you still here?!
You reside on every continent
yet we know so little.

Perhaps these elderly cratons
wear exceptionally thick undercoats
donned before tectonic chaos began,
back when mantle was hotter
solidifying into stronger threads.
Will they ever tell us?

"cratons are like great-grandmothers at family gatherings, while younger crust moves excitedly around them, they sit quietly, occasionally remarking on how different things were when they were young." Simon Wellings, Cratons – old and strong

2.6 billion-yr-old Milbank granite: brick red feldspar, gray smoky quartz, black biotite mica.
Milbank granite holds a high gloss polish (note reflections); Dakota Granite offices.
Inside the Milbank Chamber of Commerce building.
Old quarry, now accessible to the public (45.2085101 -96.5168962).


Frost, CD, et al. 2023. Creating Continents: Archean Cratons Tell the Story. GSA Today 33.

Kirk, K. 2023 (March). Dakota Mahogany: Core of the Continent. Natural Stone Institute.

Paul, Jyotirmoy. 2021. Cratons, why are you still here? Eos, 102, 25 March. 

Wellings, S. 2012 (December). Cratons – old and strong Metageologist

Monday, March 13, 2023

Tree Following in March ... almost spring!

Eastern Laramie Plains, Laramie Mountains in distance, my junipers circled.

Mid March is here and spring is approaching, even in Laramie at 7200 ft elevation. It's time to visit the junipers I'm following this year. As usual, we left the trailhead via Trail 1 and soon veered off cross-country on gently-sloping limestone.
This Limber Pine near my junipers has a lot of character! (not all pines aspire to be trees :)
The dog paws in the center of the photo below belong to my field assistant, who found a patch of snow to squirm around on upside down—to scratch her back I guess.
This African hunting dog (50% Basenji) loves snow.
It was a cool but mostly sunny day with just a light breeze. I was able to photograph the junipers in some detail.
My Rocky Mountain Junipers—the many stems seem odd. Other trees in the area are similar.
A closer look at the trunk situation.
Juniper berries were more common on the east (leeward) side—mostly yellow, a few blue. 
The "archeological site" I mentioned last month revealed its age—not old at all! One of the boards was lying atop last year's grass stems. Apparently someone besides me likes this site too.
This time we continued eastward up the limestone slope "to see what we could see". From the not-so-high point I spotted two American Crows squawking from a similar high point nearby. Crows here are used to people and dogs. These two seemed interested in us actually.
Much of the snow that was here last month had melted. But the ground was still moist and contrasted nicely with the lichens that are so common. I was sure I would find this lichen (right?) online, but not. So I posted it to iNaturalist hoping for an identification. If you recognize it, please add a comment.
I hoped to find a few of our earliest wildflowers. And I did ... but not in bloom just yet. Easter Daisies were locally common on sparsely vegetated soil, their favorite habitat. I bet they will be in full flower next month.
Easter Daisies (Townsendia) are common here.
Plants are ca. 2–4 cm across.
Ready to bloom!

This is my contribution to the March gathering of tree followers kindly hosted by the Squirrelbasket (click on link to learn more about what we do). And read more news about our followed trees.