Eighth Edition
by Harold L. Levin

Chapter 10 - page 1

Early Paleozoic Events

The Phanerozoic Eon

Phanerozoic = "visible life."

542 million years ago to the present

Consists of three eras (from oldest to youngest):

1. Paleozoic = "ancient life" (542-251 million years ago)
2. Mesozoic = "middle life" (251-65.5 million years ago)
3. Cenozoic = "recent life" (65.5 million years ago to the present)

The Paleozoic Era

The Paleozoic Era can be divided into:

• Early Paleozoic = Cambrian, Ordovician and Silurian
  
• Late Paleozoic= Devonian, Mississippian, Pennsylvanian, and Permian

The Paleozoic is characterized by long periods of sedimentation punctuated by mountain building.

Across the continental interior, Paleozoic strata are relatively flat-lying to gently dipping, and warped into basins, domes, arches, and broad synclines.

Orogenic belts are present along the edges of the continent, where the strata are intensely deformed, with folding, faulting, and igneous intrusions. Deformation occurred as a result of continental collision.

The three mountain-building events (or orogenies) in North America during the Paleozoic are:

1. Taconic orogeny
2. Acadian orogeny
3. Alleghanian orogeny

Major events of the Paleozoic Era.

Paleogeography

Paleogeography = "ancient geography." The ancient geographic arrangement of the continents.

Reconstructing the paleogeography requires paleomagnetic, paleoclimatic, geochronologic, tectonic, sedimentologic, and biogeographic fossil data.

Paleomagnetic evidence provides information on the latitude at which the rocks formed. The orientation of the continent can be determined from the direction to the paleomagnetic pole, as recorded by bits of iron in the rock.

Longitudes, however, cannot be determined (which accounts for some of the differences in the paleogeographic reconstructions).

Paleoclimatic evidence comes from environmentally-sensitive sedimentary rock types (glacial deposits, coal swamp deposits, reef carbonates, evaporites).

The early Paleozoic climate was affected by several factors:

1. The Earth spun faster and had shorter days.
2. Tidal effects were stronger because the Moon was closer to Earth.
3. No vascular plants were present on the land.

Late Neoproterozoic (Late Precambrian) Paleogeography

Just before the Paleozoic began, the Precambrian supercontinent, Rodinia, rifted apart to form six large continents and several smaller continents (microcontinents).

The continents were:

• Laurentia (North America, including parts of Greenland, Ireland, and Scotland)
• Baltica (Most of northern Europe and western Russia)
• Kazakhstania (Between the Caspian Sea and China)
• Siberia (Russia east of the Ural Mtns and north of Mongolia)
• China (China, Indochina, and the Malay peninsula)
• Gondwana (The southern continents, Africa, South America, India, Australia, Antarctica)

Global paleogeography during the Late Neoproterozoic, about 750 mya. Note that the continents are joined, forming the supercontinent Rodinia. Rodinia had begun to rift apart. The surrounding ocean is Mirovia.

Note that nearly all of the continents are located in the southern hemisphere, roughly clustered around the South Pole. When a continental mass is located on a pole, if conditions are right, glaciers will form. This was the time of the Neoproterozoic Varangian glaciation. During glaciations, sea level is lowered worldwide because the water is tied up in the ice sheets. We would not expect to see many shallow epicontinental seas at this time.

Compare the positions of the continents through time. Look to see whether the continents are located in tropical areas or in polar areas. Look to see whether the continents are moving apart (divergent motion; rifting or seafloor spreading), or moving together/colliding (convergent motion, which causes orogenies or mountain-building events.)

At the end of the Paleozoic, these continents collided again to form the supercontinent, Pangea.

Paleogeography during the Early Paleozoic.
A = Late Cambrian
B = Middle Ordovician
C = Middle Silurian