Geology of Banff

Just been to a lovely talk and walk with Jim Oliver geologist and director of hospitality here at Banff. The earth as a cauldron of bubbling soup goes along way to understanding the relationship of igneous, sedimentary and metamorphic rocks, and why the tops of the mountains here are older than the bottoms (I've always thought of the Canadian rockies as teeth, with the middle ones being the ancient ones, the edges soft milk teeth). As I've loved geology since being tiny, but still don't remember much specific info, I took some notes, one finger tapping on my phone. Here's my aide memoir:

The Banff centre sits on the side of tunnel mountain, between two of three long valleys that run for over 100 km. There's no igneous rocks here, but sedimentary rocks made through erosion and brought up by the  plates colliding over to the west with the continental divide.

So sedimentary rocks here are caused by erosion such as water flow in rivers and lakes, and glacial erosion with freezing and thawing cycles causing pressure that breaks up the rock. Particles get carried out and deposited on the sea bottom. Lines visible in the sandstone and siltstone are most probably caused by spring floods, with larger particles carried in the water.

Limestone is what's left from living creatures in a shallow ocean being very slowly compressed and hence very hard rock. The Burgess Shale, probably from the first creatures at the 'beginning of life' in water is found near here. Limestone, also sedimentary, takes about 100 times as long to 'build' as sand and siltstone do.

Metamorphic rocks have basically changed form through the heat of compression. Erosion and sediment fill dips in the floor of the ocean which subsides, creating more dips, more filling, more compression, more subsidence. The pressure causes heat which causes change of for, eg from limestone to marble, or sandstone to slate.

Here's something I'd never thought about before.. the effects of the tides that the moon causes, create heat!

Iceland is the only country where the mid ocean ridge rises to the surface driven by upwelling magma. Expansion there (and other ridges) means contraction elsewhere. In the USA Rockies the (oceanic) plate gets subsumed and lifts up the overlaying rocks to form the mountains. Here in Canada the (oceanic) plate gets pushed up and over the land. The collision between plates is such where 30km depth of sediment on the ocean floor means that limestone doesn't mash up but instead gets lifted very slowly. 5 layers of rocks lift up, and most have been eroded away again, with the oldest Cambrian remaining. Hence the old (520 million year old) rocks sit atop the new (80million year old yung'ns). The sand and siltstone erode most easily, or crumble producing nutrient rich scree slopes that support vegetation and hold the snow. The harder limestone is left as sheer cliff faces, bare of snow. Over a mile has come off the top of the mountains that we now see, creating the prairies, to the East.

Slow motion... another kind of space for thought!

The pressure causes strains that create a corrugated effect, the three valleys. Within each of these are faults. Banff centre sits between the Rundle Thrust Fault and the Sulphur Mountain Thrust Fault - the mountains literally moving rock up and to the East! The uplift  of the Rockies started 120 m. yrs ago, 60 m yrs ago here in this part, and came to a pause around 30 to 40 m yrs ago. - Movements change!
The sulphur ramp hot springs do just that - water filters down through the rock, hits the ramp of the fault, gets heated up, escapes upwards under pressure.

You can see the fault lines of the ramp, the horizontal and diagonal strata and movement particularly well with this much snow highlighting the forms and changes of rocks. Wow!
And there are fossils galore in the limestone, with coral reefs up 5 miles above sea level near the mountain tops. No wonder this is an amazing place to be !

This picture is of a rock just near the pool building with two rings of silica. Jim's theory is that this was probably calcium from stromato porii, bluegreen algae, the first pollutants of earth introducing oxygen into the atmosphere. As water passed through the rock calcium turned to silica.

I asked Jim about Rocky mountain lithophones and rocks that ring... but he hadn't heard of any, so no clues yet, but I'll keep asking around and maybe I should carry a beater (and zoom) with me when I go out walking, just in case!