The posted coordinates bring you to the scenic beach at Bartlett’s Point Park, in the west end of Corner Brook, on the Humber Arm. There is parking just past the Yacht Club, at the noted coordinates. Please take time to look around the little park, it is a hidden gem.
Many Earthcaches throw a lot of complex geological terminology at us as laymen geocachers, and to be honest, probably not much of this is typically understood, or stays in our minds. So in this Earthcache, we will try to use simple language to the extent possible, and define a few unfamiliar geological terms that we can learn and hopefully remember together. So, with that preface, on to the Earthcache!
Geologically-speaking, western Newfoundland lies within the northeast Canadian Appalachians - an old mountain range that extends for more than 3,000 km along the eastern margin of North America from Alabama in the south, all the way north to Newfoundland’s Long-Range Mountains. The area has been created by several “orogenic” events. To clarify, orogeny is the primary mechanism by which mountains are built on continents. An orogenic belt develops when a continental plate crumples and is pushed upwards to form one or more mountain ranges.
The earliest Appalachian sediments were deposited near the start of the Cambrian Period (542 million years ago) on the shores of the opening Iapetus Ocean. The Iapetus Ocean existed in the late Neoproterozoic and early Paleozoic eras of the geologic timescale (between 600 and 400 million years ago). It was situated in the southern hemisphere, between the “paleocontinents” of Laurentia, Baltica and Avalonia (evolving land masses that combined to form the continents that we know today). “Subduction” of the Iapetus Ocean eventually led to its destruction and the collision of different continental blocks and island arcs. Subduction is where one tectonic plate moves under another and is forced to sink due to gravity into the earth’s mantle.
Geological Formations in the Humber Arm Area
The Canadian Appalachians have been subdivided into five tectono-stratigraphic domains. The one we are interested in includes western Newfoundland and the northern Gaspé Peninsula in Québec. The Humber zone, in geological terms, is considered to be an “allochthon”. An allochthon is a large block of rock which has been moved from its original site of formation, usually by low angle thrust faulting (tectonic forces, that is). An allochthon which is isolated from the rock that pushed it into position is called a klippe.
So, back to our Earthcache location at Bartlett’s Point! Specifically, we are talking about a part of the Irishtown Formation, within the “Curling Group” (which has nothing to do with brooms, but a lot to do with rocks and ice) of the Humber Allochthon.
Structurally, the area presents challenges to geologists, because in large parts of the allochthon, stratigraphic successions (i.e. rock layers) are disrupted at a variety of scales into blocks of rock types surrounded by a matrix of sheared shale. In addition, rocks characteristic of several different formations are found mixed at outcrop scale. These two phenomena (fragmentation and mixing) combine to produce rock units termed ‘mélange’.
And this is precisely why this specific location rocks (pun intended)! If you walk along the shoreline here and look at the exposed and weather-beaten outcrop, you will see layers of sedimentary limestone and sandstone, folded in unique patterns when the tectonic collisions closed the Iapetus Ocean and formed the Appalachian Mountains hundreds of millions of years ago. If you look closely (ignoring the graffiti) you will see “dikes” (or dykes) in the rock face – a dike is a sheet of rock that is formed in a fracture in a pre-existing rock body – it basically looks like a stripe of rock of a different colour and texture. Dikes can be formed either by magma (lava) filling in a crack, or in this case by sediment flowing in.
In the exposed area nearby you will also see very interesting beds of loose and crumbling shale. Shale is a fine-grained sedimentary rock that forms from the compaction of silt and clay-size mineral particles that we commonly call "mud"! This composition places shale in a category of sedimentary rocks known as "mudstones."
Your task for this Earthcache is to make some observations of the amazing geology of this area. Please send your answers using the “Message this owner” link and do not include your answers in your online log. You may log the Earthcache as “found” immediately, and if there are any issues with your answers, you will be contacted. ALL Earthcache responses will be read and acknowledged.
- Who was in your group, and what time of day did you visit the site?
- Please describe the rock face on the headland at the shoreline. Find the largest dike and describe what colour it is and what direction it runs in.
- Take a look at the shale – describe the size, texture and appearance of the pieces of shale. You can pick up a handful and examine the fragments.
- Photos of your visit are much appreciated, although not mandatory.
Credits:
Geology of the Humber Arm area, West Newfoundland. Stevens, Robert K. Master’s Thesis. 1965.
Lithostratigraphy and Structure of the Humber Arm Allochthon in the Type Area, Bay of Islands, Newfoundland. Newfoundland Department of Mines and Energy Geological Survey, Report 2000-1.
Wikipedia
| I have earned GSA's highest level: |
 |