Located along the shores of the Little Rouge River close to Twyn Rivers Drive is a superb example Ontario bedrock comprised of late Ordovician Whitby Shale, a compacted and lithified mud that formed on the bottom of a deep sea that flooded Ontario during the Ordovician period of the Paleozoic era. While this bedrock type extends from Lake Ontario to Georgian Bay, most of the shale is covered by thick layers of glacial sediments and exposed outcrops are rare, though there are occasional outcrops along Bronte Creek and Sixteen Mile Creek Canyon.
The Whitby Formation that is exposed along the lower Rouge and Little Rouge Rivers shows a fine example of the 450 million year old shale formation that forms the bedrock layer hidden below many layers of glacial deposits that formed during the Paleozoic era
Paleozoic or Palaeozoic Era is the earliest of three geologic eras of the Phanerozoic Eon, (541 to 252 million years ago) and is subdivided into six geologic periods (from oldest to youngest): Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian. The Paleozoic was a time of dramatic geologic, climatic and evolutionary change.
During the Ordovician period which spanned from 485 to 440 million years ago, many species prevalent today evolved including primitive fish, cephalopods and coral. Whitby shale is known for its high content of organic material and fossils of trilobites, snails and shellfish, as well as other pre-historic creatures that once lived in the shallow inland sea that covered much of east central North America during the Ordovician period. More importantly, the first arthropods went ashore to colonize the continent.
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Note: The bedrock surface declines southward from an elevation of 180 metres above sea level beneath the Oak Ridges Moraine (ORM) deposits to approximately 40 metres above sea level at Lake Ontario. Whitby Shale is quarried at the Bowmanville quarry of St. Marys Cement Company to mix with the Lindsay Limestone for the manufacture of portland cement.
To log this earthcache:
Rules:
Park at the parking coordinates along Twyn Rivers Drive and proceed west to the trail head coordinates south of the Little Rouge River. Please stay on the trails and do not attempt to approach this earthcache from the north side of the river.
Follow the trail along the south shore of the river until you reach the secondary trail that will take you to the water’s edge.
All observations can be made from the trail and there is no need to wade into the river.
Please send me your answers within 4 days of posting your found log. If there is more than one cacher in your party, include the names in your group. Only one person needs to send me the group answers. No spoiler photo's please. Found logs posted without proof you visited the site will be deleted.
Questions:
- At the posted coordinates, look towards the northeast bank of the Little Rouge River and you will see an exposed flat section of Whitby Shale. Estimate the length and height of this exposed outcrop.
- What is the elevation above sea level at the posted coordinates?
- What is the colour of the exposed shale? Is the colour consistent throughout the vertical layers? If not, what differences in colour do you observe?
- Depending on the water depth and visibility of the Little Rouge River, can you tell if the shale extends below the waterline of the river, and does it extend to the southwest bank?
- OPTIONAL: Take a photo of you or your GPS along the trail or river. There are a number of nice spots that showcase the valley.
References: Road Rocks ONTARIO - Nick Eyles
Friends of the Rouge Watershed - http://www.frw.ca/rouge.php?ID=105
Paleozoic Geology of Southern Ontario by D.F. Hewitt
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