1. The Cambrian Period
542 to 488 Million Years Ago

2. Cambrian Period Geography
Late Precambrian
The break up of Rodinia, reformation into Pannotia, and subsequent break up.
Lower sea levels.
Deposition was limited to the passive shelf margins.
North America was located near the equator. Because plants did not yet exist, erosion was dominant.
Early Cambrian
Six major continents were present in the Cambrian including: Baltica, China, Gondwana, Kazakhstania, Laurentia, Siberia.
Higher sea levels, period of transgression.
Late Precambrian
The break up of Pannotia
Low sea levels.
Deposition was limited to the passive shelf margins.
North America was located near the equator. Because plants did not yet exist, erosion was dominant.
Early Cambrian
Break up of the super continent caused sea levels to rise, creating transgression onto the continents.
Six major continents were present. Each continent can be divided into a craton and one or more mobile belts.
Figure 1. Precambrian 600 Ma
Figure Ma Cambrian

3. North American Craton
The North American Craton was made up of the Canadian Shield and the Cordilleran mobile belt on the west and the Appalachian mobile belt on the east coast.
The Sauk sequence, a period of deposition, took place during the Cambrian.
Sauk, was the first major transgression. Shallow seas covered most of North America.
Deposition during this time formed from shallow marine environments.
Craton is the stable immobile portion of the continent, which forms the foundation on which sediments are deposited. Craton is made up of the shield and the platform.
Figure 3. Middle to Late Cambrian Sedimentation Map

4. Rise In Sea Level Caused by the break up of the super continent.
Cooling and subsidence the of continents.
Uplift at the sites of sea floor spreading.
Proterozoic ice age ended. Water levels rose as ice caps melted.
Figure 4. Early Cambrian passive margin in transgressing sea levels.

5. Grand Canyon- During the Cambrian
The stratigraphy of the Cambrian is representative of a transgressive sequence on a passive margin.
The Tapeats Sandstone was deposited in a shoreline beach environment.
As sea levels continued to transgress, the Bright Angle Shale was deposited in an off shore environment.
The last layer to be deposited during the Cambrian was the Muav Limestone, representative of a shallow marine reef environment.
Picture from:
Figure 5. Transgressive facies.

6. Atmosphere & Climate Atmosphere
Increased temperature, oxygen, and CO2 levels.
Climate
Began very cool at the close of glaciation in the Precambrian.
Continually warmed. North America was located at the equator. Warm shallow inland seas predominated.
Figure 6. The changes of oxygen, carbon dioxide, and temperature throughout geologic time.

7. The Cambrian Explosion
For a long time it was thought that life suddenly appeared during the Cambrian.
Now it is know, life started in the Precambrian, though most were simple and lacked the hard parts required to be well preserved in the fossil record.
Figure 7. Explosion of life.
All but one invertebrate phyla found today, evolved during the Cambrian. The first fossil evidence for phylum Bryozoa is found in the early Ordivician.

8. Cambrian Phyla Figure 8. Phyla diagram.

9. What caused the explosion?
This is still a cause for debate. There was probably not any one single reason, but multiple reasons, both geological and biological, simultaneously working together to create an evolutionary spring board.
The oceanic shelf may have reached climax stage in succession. Thereby, limiting the biodiversity in the ecosystem. The rising sea levels created a shallow marine reefs where new niche’s could be established.
Transgressions onto the continents eroded into the basement rocks creating chemical reactions that released ions of calcium, iron, potassium, and silica which increased the mineralization of the sea water. Organisms with hard shells made up of calcium carbonate and calcium phosphate appeared shortly after.
Prior to the Cambrian, Earth was glaciated. During the Cambrian global temperature increased.
Increased oxygenation in the oceans due to a reduction in anaerobic bacteria and an increase in photosynthetic organisms.

10. Cambrian Life
Though almost all invertebrate life is documented in the Cambrian, three main groups dominate the fossil record.
Trilobites
Inarticulate brachiopods
Archaeocyathids
The first organisms with a backbone like structure occurred during the Cambrian. Possible the ancestor for all invertebrate life.
Picture:
Figure 9. Representation of Cambrian Life.

11. Cambrian Life Trilobites Most prevalent in the Cambrian fossil record.
The majority were bottom feeders.
Inarticulate brachiopods
Inarticulate brachiopods do not have tooth and socket hinges, articulate brachiopods were also present but, in lesser quantities in the Cambrian.
Trilobite photo:
Inarticulate Brachiopods:
Figure 10. Trilobite Species
Figure 11. Inarticulate brachiopods

12. Cambrian Life Archaeocyathids
Cambrian sponge like organisms. Presumably suspension feeders. Became extinct at the close of the Cambrian.
Pikia
Thought to be a primitive chordate. Fossil evidence shows showing a primitive spinal column.
Archaeocyathids photo:
Pikia:
Figure 12. Archaeocyathids.
Figure 13. Pikia

13. Most Unusual Cambrian Organisms
Herpetogaster
Banffia
Odontogriphus
Herpetogaster may be related to living starfish and acorn worms
Banffia is baffling; it’s not clear yet what its closest living relatives are. Copyright Quade Paul
Odontogriphus had a circular mouth ringed with teeth. Copyright Quade Paul
Wiwaxia may have been related to today’s mollusks. Copyright Quade Paul
Diania had spiked, segmented legs that show some similarities to those of insects and other arthropods. Some scientists see that as a sign of close kinship. Copyright Quade Paul
Orthozanclus, a relative of mollusks. Copyright Quade Paul
Pictures and notes from:
Wiwaxia
Diania
Orthozanclus
Figures 14-19, Creatures of the Cambrian Period

14. Video Representation of the Cambrian Period

15. Mass extinction- The close of the Cambrian Period
A mass extinction event of invertebrate organisms occurred at the end of Cambrian period.
Glacial evidence has been found that correlates to the end of the Cambrian.
Glacial ice would have created cooler temperatures, lowered sea levels, and reduced oxygen levels.
This period marks the extinction of the Trilobites and other invertebrates, but opened the way for others to evolve and take their place.

16. PowerPoint prepared by Christina Tinsley
THE END
PowerPoint prepared by
Christina Tinsley