Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments (silt-sized particles) of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering or bedding less than one centimeter in thickness, called fissility. Mudstones, on the other hand, are similar in composition but do not show the fissility.
The process in the rock cycle which forms shale is called compaction. The fine particles that compose shale can remain suspended in water long after the larger particles of sand have deposited. Shales are typically deposited in very slow moving water and are often found in lakes and lagoonal deposits, in river deltas, on floodplains and offshore from beach sands. They can also be deposited in sedimentary basins and on the continental shelf, in relatively deep, quiet water. This area sat under Lake Agassiz for millions of years and shale has been deposited throughout the region. The creek has exposed the shale and has allowed us to see layer after layer of shale deposits.
As you tour around the rock gorge you may see fossils in the shale. Fossils, animal tracks/burrows and even raindrop impact craters are sometimes preserved on shale bedding surfaces. Shales may also contain concretions consisting of pyrite, apatite, or various carbonate minerals.
There are 2 entrances into the rock gorge
You can climb down into the rock gorge at entrance 1 (N 51° 03.305 W 100° 08.017 ) or entrance 2 (N 51° 03.351 W 100° 07.979). Please be careful climbing in and out as it can get slippery or unsteady at times depending on the weather.
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1. From the top layer of the rock gorge walls estimate the distance until the shale layer starts?
2. What type of shale do you think is located here?
3. Try to spot some fossils in the shale. Describe what kind of fossils you found
