The following questions refer to the geological map of the Mt. Polley area in ce

ID: 304781 • Letter: T

Question

The following questions refer to the geological map of the Mt. Polley area in central British Columbia, and are based on information in the map legend, the map symbols, the cross sections, and on the map itself.

Click on the link below to open the map:

http://www.empr.gov.bc.ca/Mining/Geoscience/PublicationsCatalogue/Maps/GeoscienceMaps/Documents/GM2007-01_Mount_Polley.pdf

1.What is the approximate age range (in years) of the youngest deposits in the map area?

2. Provide the rock-type names (and unit codes) and ages of any three of the layered units that are entirely sedimentary in origin.

3. Based on the map and cross-section A-A’, how would you describe the relationship between the Unnamed Cretaceous Conglomerate and the rocks underneath it? (You may need to refer to the “Symbols” explanations on the map.) Why is this rock called “polymictic”?

4. The oldest unit shown on the map is primarily made up of metamorphic rocks. What are the main rock types, and in what type of metamorphic environment did they form? Where on the map can you find this rock type?

5. The intrusive rock north of Gavin Lake has been isotopically dated. What dating technique was used? What is the numerical date, and to what geological period does this date correspond?

6. The Gavin Lake area intrusion is depicted in Cross Section B. Describe its age relationship with the rock into which it has intruded.

Explanation / Answer

Name of the Formation

Rock types

Age

Dragon Mountain Formation (MJ dcg)

Polymictic conglomerate, sandstone, graded siltstone

Middle Jurassic

Kamloops Group (E Ks)

Mudstone, Siltstone, shale, fine clastic sedimentary formations

Eocene

Unnamed EJr sn

Brown gray siltstone, sandstone, calcareous conglomerate

Sinemurian to Pliensbachian (Early Jurassic)