11 December 2013
On the trail up to Crypt Lake in Waterton Lakes National Park (southernmost Alberta, Canada), there’s a ‘traditional’ hiking trail, and then an intense ledge on a glacial headwall that you must teeter along, including scaling your body up into and through a person-sized tunnel! Right at the transition between the two “phases” of the hike are some boulders of Mesoproterozoic Belt limestones (Helena/Siyeh Formation??) bearing many, many, many stromatolites. I’d like to share some photos of them with you today.
Stromatolites, you’ll no doubt recall, are dome-shaped primary sedimentary structures that are fossilized microbial mats. Photosynthetic cyanobacteria coated the seafloor in slime, trapping carbonate sediment, and growing upward toward the sunlight. They’re a good indicator of shallow conditions, and they also serve as useful geopetal (right-way-up) indicators.
Here’s our first view, a cross-sectional perspective on many individual stromatolitic domes:
After most of these images, I’ll show you an annotated view, with the contrast dialed up and a few representative laminations traced out in white. Here’s the first:
Another, similar exposure, again with the hiking pole for scale:
Zooming in a bit to the good part…
And here’s an annotated version:
Okay, I think you get the idea. Let’s zoom in now, and take a look at some nice examples at close range.
Another example, cut more cleanly in half:
A relatively conical stromatolite shows up in the center of this next shot…
Another cone-shaped example is here:
The next one is more “traditional” in its shape – a broad, blossoming dome…
One more big cross-sectional view, now – to drive home the diversity of forms among these stromatolites:
Some (most) are dome-like, but some are conical, some are horizontal boxy arrangements, and some are broad “tent”-like forms…
Here’s an exposure of the bedding plane – looking down on the ancient seafloor, rather than viewing it in cross-section as in the previous images…
The bumps on the left look like stromatolites, but I wonder about the more linear features at the right – are these ripples? Or simply elongate stromatolites?
Here’s a second, fairly spectacular view of the bedding plane of a very stromatoliferous stratum:
…Contrast dialed up a bit, but no real need to annotate these. They’re pretty stark:
Close-ups of two of these decapitated stromatolites:
What a great place to sit back and catch one’s breath for a few minutes before venturing out onto the ledge, and hence to Crypt Lake itself… Looking forward to returning to this spot in summer 2014.