29 August 2014

Friday fold: Pleistocene glacial folding of Cretaceous sedimentary rock?

It’s Friday! Time for a fold. Here’s one in the Horseshoe Canyon Formation of eastern Alberta, seen on the bluff east of the Red Deer River near Willow Creek (“The Hoodoos”).

fold_badlands_smClick to enlarge

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This is anomalous – it’s unusual to see deformed strata out here, so very far from the mountain front to the west. One possibility is this representative of soft sediment deformation in the sediments; slumping, say, shortly after deposition.

Another possibility is more astonishing — the idea that Pleistocene ice sheets may have plowed into these pre-existing strata of Cretaceous age and crumpled them up as they moved along. (Subsequently, the crumpled uppermost Cretaceous rocks were buried in post-glacial sediments (loess and outwash). Such a thing has in fact been documented in the Great Plains north of here, at about the same distance from the Rockies. And previously on this blog, we’ve examined a similar case of glacially-induced deformation just east of Glacier National Park, Montana.

What do you think? Happy Friday!

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27 August 2014

Dinosaur bone

In July, I found a dinosaur bone in Dinosaur Provincial Park!

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It was lying in a wash coming off a small mesa, and sure enough, when the students and I walked up the little draw, we came to in situ bones poking out of the cliff above.

After showing it to the students, I put it back down exactly where I had found it, of course.

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23 August 2014

An examination of the Horseshoe Canyon Formation in eastern Alberta

One of the delights of this year’s Canadian Rockies regional geology field course was the serendipitous acquisition of an expert in the stratigraphy and sedimentology of the strata of the Great Plains. We started our trip in Drumheller and Dinosaur Provincial Park, spots where Cretaceous strata of the Judith River Group, Bearpaw Shale, and Horseshoe Canyon Formation are exposed through the downcutting action of the Red Deer River. My friend Astrid Arts, who I met through Twitter, joined us in the field for a few days and brought along her friend and colleague Jason Lavigne, who had studied the Horseshoe Canyon as the basis of his master’s thesis at the University of Alberta in Edmonton. Both Astrid and Jason work in the “oil patch” in Calgary. Jason agreed to take over the field instruction for half a day, showing us some key sites that were foundational to his thinking about the depositional setting of the Horseshoe Canyon Formation.

The first stop that Jason took us to was south of Rosedale, along Willow Creek, just south of a spot called “the hoodoos.” There, we looked north across a small valley to see this:

stop3_smClick to enlarge

Note that at the base of the outcrop, the strata are inclined about 5° to 12° relative to horizontal (and the overlying strata). These are point bar deposits, prograding (laterally accreting) out from left to right. They’re older at the left (west), and younger toward the right (east). These strata were deposited by a meandering river.

stop3_sm anno

This river was draining the newly-rising Rocky Mountains to the west, and flowing downhill into the Western Interior Seaway. Portions of it are clearly terrestrial, and portions are clearly marine. It’s a transitional unit.

Here’s a detail from one of Ron Blakey’s excellent paleogeographic maps (Northern Arizona University / Colorado Plateau Geosystems) of the setting:

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Directly overlying the inclined point bar deposits is “coal 0,” the oldest (and stratigraphically deepest) coal layer in these strata. As  you go up in the stratigraphic sequence, each successive coal is numbered 1, 2, 3, 4, etc. Here’s another look at coal 0, exposed east of the road where we parked on the way in:

coal0Click to enlarge

The other thing to notice here is the disconformity up top: the yellowish massive layers overlying the Cretaceous strata are Pleistocene glacial sediments – loess and silty outwash.

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We then stopped in the town of East Coulee, a few short kilometers to the south, to look east at a fine mud-filled channel.

mudchannelClick to enlarge

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This mud layer overlies coal 0. There are clam borings in the top of the coal, and dinoflagellate fossils in the mud-filled channel – indicating a marine incursion. The river probably avulsed to a different course, and this channel became a tidal channel instead of a fluvial channel. The distinctive seismic signature of this mud channel is very easy to image geophysically. It’s about 10 km long and 2 km wide.

So here’s a summary of what we saw at these two sites:

sketch

Jason favors a deltaic interpretation to make sense of these outcrops, but the area shows signatures of all three classic end-members of the Galloway ternary diagram for delta classification: we see evidence of fluvially-dominated portions (point bars), akin to the modern Mississippi “Bird’s foot” delta, and elsewhere there are tidal-dominated portions (our marine mud channel), like the modern Sao Francisco delta in Brazil, and elsewhere (we didn’t see this on our trip) there is hummocky cross-stratification, which is cited as being consistent with storms that periodically rework wave-dominated deltas (like that of the modern Ganges). The Ebro delta in Spain (Flash Earth link) was cited by Jason as the best modern analogue for the depositional system that he thinks best explains the characteristics of the Horseshoe Canyon Formation, because different areas of that single delta are wave, river, and tide dominated.

I was so grateful to have Jason there to explain all this to us – not only is it geographically out of my range of expertise, but the sedimentological details are also unfamiliar to me. The students really appreciated him sharing his time and experience with us on the trip. Thanks, Jason, and thanks for bringing him along, Astrid!

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12 August 2014

More Canadian Rockies student projects

In addition to the projects I linked to last week, here are a few more:

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8 August 2014

Friday fold: Buckle vs. passive folding in the Chancellor Group slates

I reckon it’s time for me to start processing some of the new images I collected this summer, and sharing them here on the blog. I saw some great new rocks over the past month in the Canadian Rockies, and I’m looking forward to sharing them with you. Here’s a really sweet one to start us off…

fold_Chancellor_smClick to enlarge

That’s an excellent example showcasing the differences between buckle folding and passive folding. Buckle folding is the result when you have a relatively stiff layer between two weak layers. Passive folding results when pressure solution decreases the volume of a rock in a systematic way (imparting cleavage) and sedimentary layers passively change shape as both they and their surrounding matrix are shortened through volume loss.

The rock shown here is “slate” of the Chancellor Group, a limy mudrock-dominated package in the western main ranges of the Canadian Rockies. This particular outcrop is in Yoho National Park, on the road to Natural Bridge. It includes a few coarser layers, too, and then the whole package was squeezed intensely during the orogeny that built the Canadian Rockies (what they refer to as the Laramide Orogeny, though that term would carry a different meaning south of the border). The cleavage (orange lines in the annotation below) was imparted during this tectonism.

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Note how the muddy layers are strongly cleaved, implying volume loss through pressure solution. The cleavage is a “spaced” variety, which essentially equates (in my mind) to planar stylolites (i.e., lacking wiggles like classic stylolites). The coarser layer (outlined in purple) exhibits a different sort of strain, however. It’s buckled, implying it was stiffer than the mudrock above and below when it got compressed. Note the cuspate/lobate margins of this unit – this style is typical of buckle folding, as well as the pronounced difference in its cleavage development. Note how the cleavage of the underlying mudrock/slate flares out in the regions marked “A” (below the big synformal lobes of the stiff, coarse bed), and converges inward in the region marked “B” (below the big antiformal cusp below the stiff, coarse bed). Also note the extensional veins that extend up into the stiff, coarse layer. These appear to flare out from the base of the stiff layer’s lobes, in a sort of outer arc extension of the fold.

This was an exquisite outcrop.

I GigaPanned it, too. See if you can find the portion of the outcrop we’ve been discussing in this blog post within the larger context of the outcrop where it’s located (on the road from the Trans-Canada highway west of Field toward Emerald Lake and Natural Bridge):

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There’s a lot of passive folding to be seen there. Buckle folding is less common. If you like bedding / cleavage relationships, this is a great outcrop to visit.

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Here’s a second GigaPan, to show the passive folding of bedding with well-developed cleavage, and weathering along that cleavage plane:

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And, while we’re at it, here’s a nice example of the folding of a sandy layer within the Chancellor that was featured as a previous Friday Fold.

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Here, the advantage is provided by another sandy layer, which exhibits buckle folding (as well as cleavage refraction):

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Enjoy poking around in these virtual outcrops until you find the folds you’re looking for!

Happy Friday.

The new GigaPans in this post were made on an expedition following my Canadian Rockies field course, and supported by NSF grant DUE- 1323283.

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7 August 2014

A selection of “Canadian Rockies” field course final projects

I’ve got some student work to share with you today. Like yesterday’s guest post on deltas growing into Canadian Rockies glacial lakes, my Rockies students are turning in their final projects – digital products that aim to serve the world at large by introducing key places in the Canadian Rockies to a wider audience. The idea is to go from outcrop-scale observations to the larger context, to tell the interpretive story of the Canadian Rockies through the context of key places we visited on the trip.

Marissa D. found the Frank Slide to be an impressive place. She made this Tumblr to delineate its geology.

Zack S. made this Google Earth tour of the Crypt Lake trail. Zack offers the following instructions:

  • Save the KMZ file to your computer.
  • Open Google Earth.
  • Double-click the KMZ file to place the tour folder into Google Earth.
  • Please hide all “layers” except for the “borders and labels” layer.
  • Please hide all other “places” besides the tour folder.
  • Click the “play tour” button below the “places” box.
  • Pause the automated movement of the tour at each stop.
  • Click the alphabetized marker at each stop (each stop has only one associated marker).
  • When you are done with a particular marker, close the pop-up box and un-pause the tour.
  • I have provided an online playlist of ambient music to add to the tour as well. I highly recommend using it, as it adds to the atmosphere of the tour. Just click here, http://8tracks.com/anon-1089753594/tour-ambiance, and hit the “play” button.

Jeffrey R. also focused on Crypt Lake. He made a website to explain it.

Sean B. was entranced by the outcrop of Bison Creek Formation with distinctive tension gashes. So he made this Prezi to explain it.

Davis M. also picked the Bison Creek Formation outcrop, but for him it was one of three examples of places where we observed tension gashes on the trip. Check out his tension-gash-themed website to explore them.

Soo L. looked at the evidence of last year’s flooding in Canmore, with some bonus time up on the lakes west of the Icefields Parkway. She made a Tumblr, too – so start at the bottom.

There will be more to come in the coming days (as feedback and edits are incorporated), but consider this a little taste of some of the most prime-time-ready projects.

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6 August 2014

Guest post: Glaciolacustrine deltas in the Canadian Rockies

[guest post by Maddy Rushing, George Mason University, one of Callan's students this year in Regional Field Geology of the Canadian Rockies]

The Canadian Rockies are well known for their superb glaciated landscapes and active ice fields. Not so well known, are the glaciated landforms that lay beneath the surface. Observing the rock record and numerous outcrops throughout these mountains, one can find a map of the past.

First, we will take a look at modern day glacial deltas to be seen in the Canadian Rockies today. Peyto Lake in Banff National Park, Alberta. The image below from Google Maps depicts Peyto Lake as a glacial-fed lake having its primary inflow from Peyto Creek which drains water from the Caldron Lake and Peyto Glacier and finally flows north, into the Mistaya River.

Map 1

The delta of focus is located at the southern most end of Peyto Lake. This delta is of ice-contact variety for its deposition occurs at the margin of the glacier. The sediment being deposited at this delta accumulates from various locations regarding the glacier. Most of the sediment travels through subglacial rivers or streams, however the glacier itself transports some sediment on its own.

Here is a closer look at the delta: (zoomed in from Google Maps)

Map 2

The GigaPan below (by Callan) shows the delta from a profile view. Looking closely, you can see the dendritic drainage system typical of deltas.

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And as you can see, the location is quite beautiful.

Outcrops can provide a great visual representation for how these deltas form and show what they look like so that geologists may be able to find them in other locations to better understand the geological changes that a certain area has undergone. The following outcrop was found in Kootenay National Park, right outside of Radium Hot Springs.

delta outcrop

These are sediments we interpreted as having been deposited by a prograding glaciolacustrine delta. The delta likely was formed during one of the more recent of numerous glaciation periods in the Canadian Rockies; perhaps the Illinoian? Considering the outcrop has not been dated and assuming it was in fact formed during the Illinoian Glaciation, it is reasonable to infer that the approximate age of this outcrop is 130,000 years. This delta is a coarse grained lacustrine delta as opposed to a marine delta with gentle slopes and fine grained sediment such as the Mississippi Delta. These coarse grained deltas are known as Gilbert Deltas (named after Grove Karl Gilbert of USGS) and are characteristic of rivers or streams coming into contact with freshwater lakes. Gilbert Deltas have three stratigraphic components: a topset, foreset, and a bottomset. The picture below shows the orientation of these beds.

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Topset beds are deposited by streams or distributaries, typically consisting of coarse- grained sediment that leaves a horizontal layer across the top of a delta. Foreset beds are found below the topset beds and are deposited by sediment that was carried down the end of a delta into deeper waters than the topset beds and thus are a bit more fine-grained as well. Foreset beds characteristically have a slight angle that suggests the direction of flow and delta growth. Finally, the horizontal bottomset beds underlie the foreset beds and are deposited in deeper, calmer waters leaving the finest delta sediment. The sequence of these beds provide an exquisite deltaic cross-section such as this one on Kootenay Highway.

The image below is a better look at this outcrop:

outcrop without truck

annotated

Unfortunately, there was not ample enough time to spend at this outcrop to get images of better quality or ones that incorporate scale (here’s a link to GoogleMaps StreetView of the outcrop: Kootenay Hwy Glacial Delta Outcrop). Regardless, the stratigraphic relationship is clearly recognizable. An annotated image of a zoomed in portion of this outcrop is depicted above, showing the relationship between the three stratigraphic components.

Observing this outcrop, allows us to interpret this area as a pervious glaciolacustrine delta similar to the modern day glaciolacustrine delta seen at Peyto Lake. Making these observations is important within the geological field because it allows us to compare and contrast the type(s) of environment(s) a particular area has confronted, ultimately to better understand the geological changes of that area. The Canadian Rockies is a great place to go to make these observations as well as enjoy the area on it’s own.

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1 August 2014

Friday fold: Contorted Rome Formation next to the Max Meadows Fault

My student Mercer Parker shot this one over to me the other day:

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Those are the slim strata of the Rome Formation (a.k.a. Shady*), strongly deformed in the region adjacent to the Max Meadows (“M&M”?) Fault.

Thanks, Mercer!

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* Will the real slim Shady please stand up?

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24 July 2014

Making tracks

I’ve had a great three weeks in the Canadian Rockies, but now I’m heading out.

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It’s been an honor and a privilege to teach in these fine mountains, among amazing rocks with talented colleagues and thoughtful students, and I’ve really enjoyed the past week of GigaPanning with my colleague Aaron Barth.

Yesterday, Aaron and I saw these bear tracks in the mud next to a creek where we were GigaPanning. The Canadian Rockies have imprinted themselves on me in a similar way. I’m leaving with more than 50 new GigaPans and an uncountable number of positive memories.

 

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12 July 2014

Stromatolite from near Crypt Lake

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Greetings from the field… here’s a scene I contemplated yesterday…

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