Exam 3 Flashcards
(65 cards)
1
Q
Percentage of earths history the Precambrian represents
A
86%
2
Q
First crustal record
A
3.8-4.4 BY ago
3
Q
Precambrian outcrops
A
1) Cores of mountain ranges
2) Deep Gorges (Grand Canyon)
3) Shield Areas
4
Q
Shield Area
A
- The shield is the core of a continent
- Precambrian continental core is exposed in a convex-shaped layer on the earths surface
- Overlain by the platform
5
Q
Platform
A
Flat strata that initially overlays the shield
6
Q
Craton
A
Shield + Platform
7
Q
Dating methods that can’t be used for the precambrian
A
Biostratigraphy can’t be used as there is no record of precambrian life
8
Q
Cambrian vs. Precambrian
A
Separated by the existence of Trilobites (Olenellus)
9
Q
Canadian Shield
A
North America, contains records of key Precambrian eras and events
10
Q
Paleoarchaean Volcanics
A
~3.5 BY ago pillow lava was present, indicating that oceans were present
11
Q
Mesoarchean
A
< 3.0 BY ago Quartz (SiO2) and pebbles of Granite are present, indicating that continental crust had to be differentiated by this point
12
Q
Siderian
A
- < 2.5 BY ago the first Stromatolites were recorded, which were formed by Cyanobacteria
- ~2.2-2.5 BY ago the Gowganda Formation in Canada indicates glacial deposition
13
Q
Stenian
A
~1.2 BY ago the North American Rift began
- Keweenawan Rift complex
14
Q
Cryogenian
A
~700 MY ago the ice-house Snowball Earth was recorded by an abundance of glacial till
15
Q
Earliest Evidence of Precambrian Life
A
- 3.4-3.5 BY ago
- Warrawoona Grove (NW Australia)
- Onverwatched and Fig Tree Groups (South Africa)
- Prokaryotic Cyanobacteria
16
Q
Great Oxygenation Event
A
1.8-2.0 BY ago the Ozone layer formed
17
Q
Eukaryotic Cells
A
1.2-1.75 BY ago Acritarchs with a differentiated nucleus were present
18
Q
First Metazoans
A
- 600 MY ago more complex life with differentiated functional cellular material were present
- Rawnsly Quartzite within the Ediacaran Hill of Southern Australia
- Ediacaran Assemblage
19
Q
Vendian (Ediacaran) History
A
- Techtonic Framework: Rifting
- Aulacogens
- Timing of rifting (~500-600 mya)
20
Q
Aulacogens
A
- Rifting occurs in rift triple-junctions
- Aulacogens are failed rifts
21
Q
Cambrian History
A
- North America and craton structure
- Transcontinental Arch
22
Q
Arches and Basins
A
- Form through the stress of moving the crust
- Basins are where most of earths sediment accumulates
23
Q
Transcontinental Arch
A
- Extended from Great Lakes to Northeastern Arizona
- Most of the sedimentary record is to the flanks of the arch
24
Q
Cratonic Sequences
A
Large-scale stratagraphic unit representing a major transgressive-regressive episode and bounded by craton-wide unconformities
25
Sloss' 1963 Cratonic Sequences
- Tejas = upper Cretaceous to upper Quaternary
- Zuni = lower Jurassic to upper Cretaceous
- Absaroka = upper Mississippian to lower Jurassic
- Kaskaskia = lower Devonian to upper Mississippian
- Tippecanoe - lower Ordovician to lower Devonian
- Sauk = Cambrian to lower Ordovician
26
Sauk Cratonic Sequence
- Mature quartz sandstone
- Base of well rounded quartz topped with limestone
- Transition to carbonate deposition
27
Cambrian Paleoclimate
Tropical as indicated by the presence of limestones
28
PC vs Cambrian
- Presence of Trilobite
- Diversity of life
29
First fish
Cambrian
30
Dominant Cambrian Life
- Trilobites – arthropods that account for 55% of the fossil record
- Brachiopods (inarticulate) – 35% of the fossil record
- Archeocyathids
- Molluscs
- Echinoderms
31
Organisms missing from the Cambrian
- Burrowing organisms
- Range of filter-feeding organisms
- Large predators
32
The Great Experiment (Burgess Shale)
- 15-20 specimen of cambrian fossils discovered that represented phylums that didn't exist
- Marine shale in British Columbia
33
Ordovician History in North America
- Middle Ordovician Regression
- Later Ordovician epeiric sea
- Shaley deposits in the later Ordovician
34
Middle Ordovician Regression
- Tippacanoe / Sauk
- St. Peter Sandstone at the bottom of the Tippacanoe was deposited by sand
- Almost 100% quartz
35
Later Ordovician Epeiric Sea
- Extensive limestones, indicating tropical climate
- Virtually all of North America is under water
- Burrowing creatures
36
Shaley Deposits of the Later Ordovician
Shale is finely grained particles of silt and sand that accumulate in deep water, as opposed to limestones
37
Evidence of Ordovician Mountain Building (Taconic Orogeny)
1) Conglomerate debris inside the shales in the eastern portion of North America
2) Volcanic ash that indicates an adjacent volcanic arc complex
3) Red-beds formed by transport of iron rich minerals via rivers and streams
4) Intrusive granite and ultramafic indicate subducting oceanic crust
5) Unconformities and thrust faults
38
Modern Analog for the Taconic Orogeny
Australia's border with Indonesia is an arc complex and the Great Barrier Reef has limestone
39
Ordovician Plate Techtonic Interpretation
1) Early Paleozoic: passive margin
2) Mid-Ordovician: continental collision
3) Late-Ordovician: coastal plain and red-beds
40
Ordovician Life (Less phyla, more families)
- Articulate Brachiopods
- Bryozoans
- Crinoids (sea lillies) -> Echinoderms
- First true coral reefs
-> Rugosids
-> Tabulates
---> Halysites (chain coral)
---> Favosites (honeycomb coral)
- Stromatoporoids
- Recaptaculites (sunflower coral) -> algae
- Ostracodes
- Vertabrates (jawless fish)
41
Ordovician Predators
- Nautiloids
- Starfish
42
Ordovician Scavengers
- Trilobites
- Gastropods (snails)
43
Ordovician Index Fossil
Graptolites (cordata)
44
Ordovician Extinction
- Second largest in history
- Climate shift to cold climate, killing off creatures only suited for warm, tropical environments
- More than 100 marine families die out
- 50% of North American Brachiopods and Bryozoans died
- Extensive glaciation at the South Pole
45
Characteristics of the Silurian
- Poorly represented across North America in the rock record
- Incredible reef complexes
- Immense evaporite deposits
- Outcrop exposure beneath Niagara Falls
46
Major Silurian Basins
Michigan Basin, Ohio Basin, Appalachian Basin
47
Barrier Reefs
Grow parallel to the shoreline on the ledge of a deep basin
48
Pinnacle Reefs
Form in carbonate banks and on adjacent slopes where shallow and deep marine systems meet
49
Silurian Evaporite Formation
- Sea level drops
- Reefs grow to sea level
- Not enough water is supplied, so water becomes supersaturated and minerals evaporate out
50
Silurian Paleoclimate
Warm and dry as indicated by the presence of limestones and evaporite minerals
51
Sequence of Precipitation for Evaporites
Calcite, Gypsum, Halite, Potash (Kcarbonate)
52
New Life in the Silurian
- Eurypterids (sea scorpions)
- Vascular land plants (Lycopsids)
- First air breathers (Arthropods)
- Fish
--> Jawless fish (ostracoderms)
--> Jawed fish (acanthodians)
53
Devonian Physiographic Development
Acadian and Antler Orogenies
54
Acadian Oregeny
Occurred in the Devonian on the East side of North America. Europe and North America collided to form the Acadian mountains, with the Catskill delta to the west and the old red sandstone to the east
55
Antler Orogeny
Occurred in the Devonian on the West side of North America. Formed the Antler mountains
56
Transition from Tippacanoe to Kaskaskia
At the end of the Silurian, there was a major regression that caused an early Devonian unconformity called Oriskany Sandstone. Then, there was a subsequent marine transgression
57
Devonian Cratonic Basin Deposition
The Tippacanoe regression left an unconformity surface with old red sandstone, and the basins were filled by the Kaskasia transgression
58
Michigan Basin in the Devonian
Basin is growing, filling with evaporites and enhanced barrier reefs
59
Reef Development in West Canada
Alberta-Williston basin accumulated massive amounts of Potash. Canada accounts for most of the words Potash
60
Black Shales (Chatanooga Shale)
Formed during the Devonian where there was algae, low oxygen, and low energy
61
Devonian Paleoclimate
Tropical/Subtropical based on terrestrial vegetation and marine deposits of limestones
62
New Devonian Life
- Fish
- First amphibians (Ichthyostega)
- Land Plants
- First ammonites
- Wingless insects and spiders
63
Devonian fish
- First true sharks
- Placoderms (Dunkleosteus)
- Lobe-finned fish
--> Lungfish
--> Coelacanths
--> Crossopterygians (ancestor to amphibians)
64
Devonian Land Plants
- Sphenopsids (horsetails)
- Spore-bearing ferns
- Seed ferns
- Evergreen trees
- Scale trees
65
Late Devonian Extinction
- 70-75% of marine invertebrates die out
- Only 15% of brachiopods survive
- Ammonites are devastated
- Tabulate-rugoes-stromatoporoid reef communities decimated and temporarily replaced by the glass sponge Hydroceras
- Marine invertebrate survivors are cold water forms
