Summary of Eastern North America Geology:

Parts of 3 Wilson Cycles in Kentucky and Region
 (A) Rift    (B) Drift   (C) Subduction   (D) Collision

a)  Precambrian Basement - Collision Phase (ID)

b)  Late Precambrian to Cambrian Continental Breakup - Rift Phase (IIA)

c)  Early Paleozoic Passive Margin - Drift Phase (IIB)

d)  Early Paleozoic Active Margin - Subduction and Convergence (IIC)

e)  Late Paleozoic Tectonism - Collision - Formation of Pangaea (IID)

f)  Mesozoic Rifting and Drifting - Breakup of Pangaea  (IIIA, B)

a)  Precambrian Basement
- Collision Phase (ID) 1000-750 Ma.
- deep beneath us (about 1-2 km) is the top of a
- thick sequence of Precambrian metamorphic rocks known as the Grenville.
- represent regional metamorphism associated with an old supercontinent called Rodinia
- we were attached to Brazil right here.
-
 
 
 
 
 

b)  Latest Precambrian Continental Breakup
- Rift Phase (IIA)  750-550 Ma.
- rifting all around North America related to breakup of the supercontinent
- Reelfoot Rift (Lower Cambrian) and Rome Trough (Middle Cambrian) are extensional tectonic features related to this
-
 
 
 
 

 c)  Early Paleozoic Passive Margin
- Drift Phase (IIB)   650-475 Ma.
- gradual sea floor spreading (east coast of Iapetus)
- Kentucky part of a broad inland seaway
- extensive limestone deposition
-
 
 
 
 
 
 

d)  Early - Middle Paleozoic Active Margin
- Subduction and Convergence (IIC) 475-350 Ma.
- Next 125 Ma represent accretion of Suspect Terranes and numerous episodes of Deformation
- Lexington Limestone contains Ash Beds from Volcanic Eruptions
-
 
 
 
 
 

e)  Late Paleozoic Tectonism - Collision - Formation of Pangaea (IID) 325-230 Ma.
- Devonian black shales - erosion from collision with Europe
- Carboniferous sandstones, shales - erosion from collision with Africa
- Carboniferous coals, shallow limestones - filling in the basin formed by collision
- Pine Mountain - thrust fault related to collision - innermost thrust deformation
-
 
 
 
 
 

f)  Mesozoic - Cenozoic Rifting and Drifting
- Breakup of Pangaea (IIIA, B)  230 Ma to present.
- Rifting of eastern North America produced normal faulting and Triassic Basins all around
- Reelfoot Rift reactivated as the Mississippi Embayment in Jurassic with opening of Gulf of Mexico
- Drift phase allowed marine sediments and deltas to fill Mississippi Embayment through Eocene
-
 
 
 
 

A Paleozoic History of Laurentia:
Cambrian through Lower Ordovician
- Basal quartzose sandstone over most areas
- Thin shales
- Broad carbonate platform, extended far inland.
 
 
 
 
 
 
 
 
 
 
 

a.  Why this succession?
b.  Where would you expect younger sandstones?
c.  Why such clean sandstone with so little shale

- Mid-Ordovician Unconformity - widespread:
was it - sea level drop.... or ....
- initiation of convergence along SE Laurentia?
How could you tell?
 
 

 Mid Ordovician to Late Ordovician
- St. Peter Sandstone - transgressive sands at the base
- eastward thickening: thin carbonates to thick detritals (sh & ss & cgl)
- Many ash beds (bentonites), but few igneous rocks.
 
 
 
 
 
 

- Eastern Laurentia: foreland basin, possibly with accretionary wedge preserved to the east (PA - Hamburg area): EAST-DIPPING SUBDUCTION
- Taconic Orogeny - closure of a back arc basin in the northern Appalachians, possible collision with an volcanic island arc in the central Appalachians.
-  unsure of subduction direction !?
 
 

 Silurian: Quiescence?
- plutonics in New England - continental volcanic arc.
- clastics in the eastern foreland basin
- carbonates and evaporites in Michigan and Appalachians
- craton was in low latitude, arid, lots of evaporites.
- draw Michigan basin and neat pinnacle reefs
- Silled Basin (reflux) model or the evaporative drawdown model (Mediterranean)
 
 
 
 
 

 Early Devonian - big unconformity:
 was it:  sea level drop? - early Acadian Orogeny?

Middle to Late Devonian
- Sandstones and Black Shales (and a few limestones
- Collision with Avalon Terrane (a suspect terrane: in northern Appalachians)
- Collision with Baltica (Europe)
- Catskill Delta - clastic wedge - many sandstones and shales, carbonates way inland
- Old Red Sandstone of Britain is the counterpart of the Catskill Clastic Wedge on the European side of the Caledonian Orogenic Belt.
- Black Shales across Laurentia (buried organic matter) - anoxic waters in the foreland basin, lots of buried carbon, now oil-producing!
 
 
 
 

 Mississippian to Pennsylvanian - Begin Suturing of Supercontinent #2
- Collision of Laurentia-Baltica with Gondwana
 - This is the Alleghanian Orogeny, creating the Appalachian Mountains
- Ancestral Rocky Mountains formed from Texas to Wyoming
 - includes Red Rocks Amphitheatre of Denver
 - block uplifts in the Pennsylvanian, coarse clastics shed off flanks
- Permian - Final suturing of Pangea
 - Now including Siberia and China
 
 
 
 
 

 Creatures of the Paleozoic
Plants - invasion of land
- Marine:  decline of the Stromatolites, rise of the calcareous green algae
- Terrestrial:
- Silurian: earliest known land plants - "Cooksonia": small, spore bearing, simple thingies.
- Early Devonian invasion by first VASCULAR plants: psilophytes (rhizomes beneath surface with short stems holding spore sacs)
- Late Devonian Woody plants, still spore bearing
- Carboniferous seed bearing plants, like Glossopteris (a Seed Fern) - no flowers!
 

Animals - Diversification
Extinct by the end of the Paleozoic:
 - Trilobites (three lobed arthropods)
 - eurypterids (big, scorpion-like, 1-3m long)
 - rugose corals, blastoids (round starfish)

Survived the Paleozoic:
 - Fishes (Devonian - Age of Fishes)
 - crinoids - sea lilies
 - clams and brachiopods
 - cephalopods
 - Sponges
 

Burgess Shale (Middle Cambrian)  - a soft bodied fauna from Alberta, Canada
- Many strange creatures, including Hallucigenia, Peytoia, Anomalocaris
- Few fit into current categories (Phyla)

Burgess Shale Organisms - show some other oddballs and mixed up interpretations, like Hallucigenia upside down and Anomalocaris mouth as a jellyfish
- Steven Jay Gould suggests:  "Diversification followed by Decimation"
     Not Phyletic Gradualism (the Cone of Increasing Diversity).