geoloy of ontario Flashcards
1
Q
how many layers does ontario have
A
- 4 layers:
- layer 1 basement: the canadian shield
-layer 2 paleozoic cover - layer 3 glacial deposits
- layer 4 the built landscape
2
Q
when have the layers formed/been established`
A
- 1: 1-3 billion years
- 2: 600-350 million years
- 3: 2.5 million years to present
- 4: past 300 years
- there is uncomforities between layers and big gaps in record
3
Q
what is layer 1: basement and how did it form
A
- candin shield rocks
- granite and gneisses
- geology varies across the shield; it is made of pieces of small continetns joined together by plate tectonic processes
- the shield formed 1 billion years ago
- there are suture zones (orogenic belts) which are places of weakness
- orogenic belts have been eroded- folded and deformed rocks of the shield remain
4
Q
why is information about the shield/orogenic belts important to us
A
- hamilton lies close to old suture zone in shield: Central metasedimetary belt boundary zone
- this is a weakness in the crust and a potetial site for earthquake activity
- the n. american plate is moving westwated (2.7 cm/year) which generates stress
5
Q
layer 2: paleozoic sedimentary rock
A
- shield covered by younger sedimentary rocks in southern ontario
- depositied 600-350 million years ago
- there are fossils present but not dinosaurs. lots of bentic (bottom dwellers). corals and other sedimentary rocks
- paleozoic sedimentary rocks are exposed along the niagara escarpment
- made of limestones, dolostones, sandstones, and shales
- 400-500 million years old
- relatively flat-lying sedimentary rocks, slight dip to south
- only really see up to thorold formation in Hamilton
6
Q
how did the rocks in layer 2 form
A
- warm tropical oceans
- limestones and dolostones form in shallow, clear water
- no sediment input
7
Q
limestones and dolostones in layer 2
A
- limestone: calcium carbonate (CaCO3)
- dolostone: calcium magnesium carbonate (CaMg(CO3))
8
Q
how are vugs produced
A
- when limestone chnages to dolostone there is a volume reduction
- 2 CaCO3 (calcite) + Mg2+ –> CaMg(CO3)2 (dolomite) + Ca2+
- since calcium is bigger than magnesium, when the reaction occurs, the volume is reduced
- this is one type of diagenesis (phyical and chemical change of sedimentary rock)
- this produces vugs
9
Q
clastic sedimentary rock
A
- mudstones and shales which form in quiet water; often deep marine environment
- sandstones indicate higer energy conditions; beach or storms
- sedimetns deposited on sea floor then lififed (made into rock)
10
Q
where did sediment come from
A
- large deltas formed by river draining the taconic
- shales and sandstones
11
Q
how did taconic mountains form
A
- collision of continent with east coast of n. america
- creation of mountain belt (taconic mountains)
- about 440 million years ago
12
Q
layer 3: glacial deposits
A
- climate cooled and ice shee grow about 2 million years ago
- about 20,000 years ago Sounthern ontario covered by ice >2km thick
- glacial deposits include tills, sands, gravels, lacustrine muds (glaciofluvial enviornment)
- the ice retrated abut 12,000 years ago; ice blocked the st. lawernece; large deep lakes found
- areas arounf lake ontario flooded (toronto and hamilton)
- eroded steep shorbluff, beach deposits formed
- layer 3 sediments also conrol the flow of groundwater wich is important for water supply, contamination
13
Q
formation of niagra escarpment
A
- 400-500 million year old rocks
- escarptment as a landform is young
- formed by glacial and fluvial erosion (eg. niagar falls today)
- about 10k of erosion over 12,500 years
- has a resistance ‘cap rock” (lockport dolostone)
- more easily eroded ocks below (rochester shale)
- undercutting causes retreat of the falls/escaprtment
- dolostone and shale have different erosional rates which is why undercutting occurs
- similar processes have produced waterfalls and valleys in hamilton area (ex. tiffany falls)
14
Q
layer 4: the built landscape
A
- urban areas often construtec on ‘fill’ material in hamilton which may be contaiminatedwha
