Paleozoic Geology
Learning Objectives
Overview:
The Paleozoic is a time of great inland seas and orogenies in the Eastern portion of North America.
At the end of the Proterozoic Protopangea was clustered somewhat in the southern hemisphere. The North American Shield (Laurentia) was lying sideways on the equator.
During the Early Paleozoic Protopangea will separate from each other but by the end of the Paleozoic had come back together again to form Pangea.
Gondwanaland (African, South American, Antarctic, Indian and Australian shields) was closer to the South Pole during the Paleozoic.
The arrangement of the continents relative to one another allowed for free circulation of water between continents and from pole to pole. This leads to more even heat distribution globally which provides uniform living conditions for life in the oceans. Also the arrangement of the continents allowed for free migration of marine animals in the oceans.
The Paleozoic: 544-250 million years
Seven Periods:
Cambrian: 544-505
Ordovician: 505-438
Silurian: 438-408
Devonian: 408-360
Mississippian: 360-320 Carboniferous is a name used in Europe
Pennsylvanian: 320-286 for the Mississippian and Pennsylvanian combined
Permian: 286-250
The
Early Paleozoic: Cambrian, Ordovician, Silurian
The
Late Paleozoic: Devonian, Mississippian, Pennsylvanian, Permian
Early Paleozoic
I) Shield:
During the Early Paleozoic the shield weathers and erodes building up sediment on the platform.
Two major transgression/regression events occur:
Sauk: Cambrian - Early Ordovician, this event lasted 50-60 million years. Extensive layers of classic transgression/regression sequences laid down some extending for hundreds of miles.
A large unconformity subsequently erases some of this deposition.
Tippecanoe: Middle Ordovician through Silurian to Early Devonian. Thick evaporite sequences and extensive carbonate deposition occurs.
II) Eastern Margin:
At the beginning of the Paleozoic the Eastern Margin is covered by open ocean (Iapetus Sea).
Taconic Orogeny:
During the Middle and Late Ordovician. A subduction zone forms and the Iapetus Sea begins to close. An ocean-continent plate boundary produces volcanic island arc. Taconic highlands form, consist of deformed and uplifted shallow marine sediments and volcanic arc material.
It has been estimated that the Taconic highlands reached a height of 13,000 ft. The Queenston Clastic Wedge is composed of sediments eroded off of these highlands.
Caldonian Orogeny:
A subduction zone forms to the north of the Taconic highlands. This causes closing of the Iapetus Sea in the north. As subduction continues deformation and uplift occurs. This orogeny culminates in the Devonian as collision between Baltica (England, Greenland, Norway) and the Canadian Shield.
III) Southern Margin:
This area was covered by shallow seas during the Early Paleozoic.
IV) Western Margin:
At the end of the Proterozoic a rift opens through today's Idaho, Montana and British Columbia. Transgression covers most of the western margins with shallow seas. During the Ordovician and the Silurian a subduction zone forms between the western ocean and the western margin. Volcanic island arcs form as a result.
Other:
Gondwanaland continues to move south towards the pole.
Late Paleozoic:
I) Shield:
Kaskaskian Sea: from the Devonian to the Mississippian an extensive transgression occurs. Transgression sequences and basin deposition occurs.
Absaroka Sea: A very long transgression regression event lasting from Pennsylvanian through Permian and into the Mesozoic.
Uplift in the eastern margin caused the location and extent of the Late Paleozoic seas to move westward.
Cyclothems: During the Late Paleozoic the shorelines of epeiric seas were in delicate balance and sediments deposited alternate between marine and nonmarine. Cyclothems represent a fluctuating shoreline and are extensive along the eastern edge of the Craton.
II) Eastern Margin:
The most intense period of orogenic activity in the eastern margin occurred during the Late Paleozoic.
Acadian Orogeny: A sliver of continent broken off from Baltica (Avalon) collides with North America beginning in the Devonian. This orogeny is a continuation of the Caldonian which is scissoring southward narrowing the Iapetus Sea. The Acadian orogeny is marked by intense metamorphism, granitic intrusions and extensive deformation. Erosion from this mountain complex (Catskill Clastic Wedge) washes into the Absaroka Sea to the west forming vast swamp and lowland environments. (These eventually become the coal beds of western Appalachia).
Alleghenian Orogeny: During the Late Pennsylvanian and Permian, as Pangea forms, intense deformation and metamorphism occurs along the Eastern Margin. Folds and thrust faults form the Valley and Ridge Province and granitic batholiths become emplaced in the Blue Ridge and Piedmont. The formation of Pangea results in the final closing of the Iapetus Sea.
III) Southern Margin:
Sedimentation increases dramatically in this area during the Late Paleozoic. Gondwanaland moves northward toward North America and a subduction zone and eventual collision take place.
Ouachita Orogeny: deformation and uplift caused by formation of Pangea. Late Mississippian through Pennsylvanian.
IV) Western Margin:
The ancestral Rockies form along the southwestern edge of the craton as crustal stress causes faulting and uplift resulting in a basin and range structure.
Antler Orogeny: an eastward moving island arc collides with the western edge of the craton during Late Devonian to Early Mississippian. The Antler Orogeny was not as intense as those in the east.
Other:
At the end of the Paleozoic Pangea had formed. This landmass stretched lengthwise down the globe and open ocean (Panthalassa Sea) covered 300 degrees of longitude. The north pole was in open ocean, the south pole was located in Africa. There was one large embayment in Pangea, otherwise there was little ocean/land interaction except along the shores of this vast landmass. Climate dried and became colder as a result.
