THE EARLY PALEOZOIC
THE CAMBRIAN 544-505 MY
CAMBRIA>>WALES
ADAM SEDGWICK 1835
THE ORDOVICIAN 505-438 MY
ORDOVICE>>WELSH TRIBE
CHARLES LAPWORTH 1879
NEOPROTEROZOIC TO MIDDLE CAMBRIAN STRATIGRAPHIC COLUMN.
PRINCIPLE LIFE FORMS AND STAGES OF THE EARLY CAMBRIAN PLACEMENT OF BOUNDARY AT THE PHYCODES pedum ZONE, TRACE FOSSIL, @ 544 MYTYPE LOCALITY>>BURIN PENINSULA, NEWFOUNDLANDCAMBRIAN DIVISIONS
BASED TRILOBITE ZONES[BIOMERES -INTERVALS OF TIMES BETWEEN TRILOBITE EXTINCTIONS]
PALEOGEOGRAPHY• CAMBRIAN CONTINENTS WITHIN 60O OF
PALEOEQUATOR• GONDWANA
– TIBET, SE ASIA, ARABIA, AFRICA, AUSTRALIA, ANTARCTICA, S. AMERICA
• LAURENTIA> RIFT ZONES>PASSIVE MARGINS
• FLOODING OF INTERIORS DUE TO RIFT SYSTEMS
• IAPETUS OPENED BET N. AMERICA & EUROPE
• SUBDUCTION ZONES DEVELOPED LATER
TECTONIC EVENTS Pan-African Orogeny Caledonian-Hercynian Orogeny
Appalachian, Caledonian, Hercynian, Urals, Ouachita, Samfrau
Overall scenario is coalescence of Pangea during most of the Paleozoic
Taconic Orogeny mid to late Ordovician Caledonian Orogeny late Silurian to early Devonian Acadian Orogeny mid Devonian Alleghenian Orogeny late Penn, Permian Hercynian Orogeny - Ouachita Orogeny
PLATE TECTONIC MOVEMENTS FROM
THE NEOPROTEROZOIC TO THE DEVONIAN (750 MY TO 370MY)
BREAK UP OF RODINIAAVALONIAN OROGENYOPENING OF IAPETUSOPENING OF RHEICTACONIC OROGENY
CLOSING OF IAPETUSACADIAN OROGENY
The Appalachians• Valley and Ridge
– folded & faulted sedimentary rks
• Blue Ridge Province– metamorphosed Precambrian and Paleozoic
Rks
• Inner Piedmont– high grade metamorphic rks intruded by
granites
• Charlotte & Carolina Slate Belt– metamorphosed & folded late Proterozoic &
Cambrian sediments and volcanics
A) Cambro-Ordovician Passive Margin: Sandy Shelf DepositsB) Middle to Late Ordovician Development of Trench Along the Eastern Boundary and Subsequent Closure of the Iapetus OceanC) Collision of Island Arc and other Accreted (exotic) Terranes with North America in the TACONIC OROGENY
CAMBRIAN PALEOGEOGRAPHY:
SHALLOW EPICONTINENTAL
SEAS COVERED THE CENTRAL US
Earliest Paleozoic timeof lowest sea level due toProterozoic glaciationsBy middle Cambrian seahad flooded the continent
LITHOLOGIC FACIES OF THE CAMBRIAN
The transgression of theCambrian is visible in the rocks of the Grand Canyon
NEOPROTEROZOIC TO CENOZOIC
TRANSGRESSIONS AND REGRESSIONS OBSERVED ON THE
CRATON
Variable sea level represented sequences of sediments bounded by unconformities on all of the cratons - e.g. Sauk, Tippecanoe
Early Paleozoic Climates
• Climates overall warmer than today• Continents 600 N & S of equator• Arid to sub arid environments 450 N & S
of equator• Redbeds (alluvial) 300 N & S of equator• Tropical reefs 300 N & S of equator
– Cambrian Archeocyathids; Ordovician Bryozoans
• Glaciation during the late Ordovician in Africa
PALEOZOIC LIFE
• Cambrian Explosion>Break up of Rodinia– radiation of all phyla>Continental Shelves
• Cambrian Reef Systems
• Cambrian extinctions (2nd largest)
• Ordovician radiation
• Global Faunas (Cambrian vs. Paleozoic Faunas)
• Ordovician Reef Systems
• End-Ordovician extinction events
THE TOMMOTIAN FAUNA
Small Shelly Fossils1-2 mmCalcium phosphateCalcium cqarbonateMost phyla represented1 to 2 MY duration
Trilobite Radiation
• Comprise 95% of all Cambrian Fossils
• Most successful arthropod
• Chitinous shell with an underlayer of calcite
• 5 major extinctions during the Cambrian and associated radiations
• Each Cambrian Biomere involved the extinction of 40 to 95% of existing trilobite genera
Archaeocyathids & Stromatoporoid Reefs
•Archeocyathid Reefs begin during the Tommotian Stage in Siberia•Spread rapidly through world•Extinct by Early Cambrian•Stromotoporoid Reefs begin during the Middle Cambrian•They remain a dominant reef builder until the Devonian
Ordovician Life• Terminal Cambrian trilobite extinction
led the way for rapid Ordovician radiations in other groups
• Radiation of molluscs particularly gastropods decreased importance of stromatolites
• Tabulate and Rugose coral reefs
• Graptolites as index fossils
• Emergence of land plants
• First Vertebrates
Ordovician Extinctions
• Blackriver-Trenton– Mid Ordovician, catastrophic regional
extinction– All echinoderms and cephalopods; 90%
trilobites, 83% pelecypods
• Terminal Ordovician Extinction– Major glaciation in Gondwana (sea level drop]– 3rd largest in recorded geologic history; 80%
of all genera
THE MIDDLE PALEOZOIC
THE SILURIAN 438-408 MY
SILURES>> WELSH TRIBE
Roderick Murchison 1835
THE DEVONIAN 408-360 MY
(Old Red Sandstone)
DEVON>> County in SW England
Roderick Murchison
Adam Sedgwick 1839
INTRODUCTION• Silurian
– 30 MY Duration
• Devonian– 48 MY Duration
• Final Collision and Suturing of Baltica and Laurentia
• Caledonian and Arcadian Orogenies• High Stands of Sea Level• Epicontinental seas; marine deposits and thick
sequences of evaporites• Reefs became important
PALEOGEOGRAPHY• Closing of Iapetus Ocean
– Baltica-Laurentia; Mongolia-Siberia
• Closing of Rheic Ocean as Gondwana migrated to west (Laurentia/Baltica-Gondwana)
• Laurentia continued to be a tropical craton• Shallow seas covered the continents during much of
Silurian• Devonian orogenies in Northern Hemisphere
– Caledonian (Scandinavia/Greenland) & Acadian (New England) & Antler (CA-NV)
TECTONIC EVENTS
• Caledonian & Acadian Orogenies– Extension of Late Ordovician Taconic Orogeny
• Mid Devonian Iapetus Ocean closed
• Baltica collided with Laurentia
• Avalonia (Island Arc) sutured to both Baltica and Laurentia
• Norway collided Greenland forming the highlands responsible for the Old Red Sandstone
OrogenicDevelopmentOf the Eastern
US
Acadian Orogeny produced a thick clastic wedge (the Catskill Wedge) of red beds[conglomerates and sandstones]
During the Devonian the rate of sedimentation increased from 7m/MY to 17m/MY to 70m/MY
Chattanooga Shale- Anoxic black shale, marker bed
East-West Cross Section across the Devonian Catskill Wedge
The Appalachians• Valley and Ridge
– folded & faulted sedimentary rks
• Blue Ridge Province– metamorphosed Precambrian and Paleozoic Rks
• Inner Piedmont– high grade metamorphic rks intruded by granites
• Charlotte & Carolina Slate Belt– metamorphosed & folded late Proterozoic &
Cambrian sediments and volcanics
1500 m of carbonates, rock salt and gypsumin 5 major cycles
Cyclic: Dolomite, Anhydrite, Halite
Model Illustrating the Deposition of EvaporitesMichigan Basin
Variable sea level represented sequences of sediments bounded by unconformities on all of the cratons -
Highest Stand of sea Level
NEOPROTEROZOIC TO CENOZOIC TRANSGRESSIONS AND REGRESSIONS OBSERVED ON THE CRATON
The Reef System• Tabulate corals and Stromotoporoid
sponges• Fauna was vertically zoned (tiered by
depth)• Clear ecological succession in reef
building from pioneer community (clumps of twig-like colonies) to platy and domed shaped colonies to binding stage by sponges
• Michigan, Canning Basin (Australia), British Columbia
Mineral Deposits
• Sedimentary copper, lead and zinc sulfides and Iron ores
• Occur in shales and carbonates• Disseminated or interbedded• Tri-state mining district (MO)• Howard’s Pass, Yukon, Canada• Wales• New York to Alabama
Clinton Iron Ore
Silurian Clinton Group near Birmingham, AL
The ore is an oolite of hematite (iron oxide)
Other Economic Deposits
• Silurian Salt, Michigan and upstate New York
• Silurian Petroleum Deposits-OH, OK,TX• Devonian Petroleum Deposits
– Williston Basin- MT and Alberta– First oil well in US 1859 (PA)
• Silica for glass- Devonian Oriskany Sandstone, 95-99.8% pure
Mid-Paleozoic Climates• Gondwana centered over the South Pole
– climates ranged from cold to warm– glacial striations present in South America yet
Red beds and carbonates and evaporites were also present in N. Africa, India and Australia
• Other continents were equatorial– Laurentia, Baltica and Siberia were warm
MID PALEOZOIC LIFE
• The Origin of the Ammonoids– Cephalopods, Devonian– Evolved from straight chambered nautiloids
• Eurypterids and the Origin of Arachnids– Chelicerata (horseshoe crabs and sea
scorpions)– Ferocious predators of the Paleozoic seas
Radiation of Fishes• During Cambrian and Ordovician only 1 order
of fish, jawless, Ostracoderms (Marine)
• Early Silurian 3 more orders of jawless fish and the first jawed fish, acanthodian, appeared and inhabited both marine and fresh water
• By Middle Devonian all classes of jawed fish had appeared
• All restricted to 40o of the equator
• Extinction at end of Devonian, terminated the ostracoderms and the armored placoderms
The Radiation of Land Plants• Earliest Fungi appear in the Early
Silurian
• First Land Plants are Late Ordovician
• First Vascular Plants are Late Silurian
• With the appearance of forests in Late Devonian oxygen levels increased and reached a peak in the Late Paleozoic
• Land erosion rates significantly decreased
The Development of Tiering
• Vertical Separation Between Organisms– Removes competition between organisms of
similar feeding habits
• Different stalk heights in crinoids
• Low herbaceous plants grading into true forest with tall trees
Terrestrial Communities
• By Early Devonian land communities were diverse
• Rhynie Chert (Aberdeen, Scotland)
• Silicified peat bog
• Preserved plants as well as spiders, mites and insects
Mass Extinction• Major marine extinction of the Late Devonian
– Frasnian-Famennian epochs
• 33% marine families became extinct
• Nearshore marine and reef benthic species– corals, stromotoporoids, all but 1 order of
trilobites, many brachiopods and ammonoids
• No corresponding terrestrial extinction
Frasnian-Famennian Extinction• Occurred during a regression
• Associated with low oxygenated water and high metal concentrations
• Sharp drop in temperature (O2-Isotope studies)
• Presence of glass spherules
• All indicate a probable asteroid impact which caused deep anoxic and high metallic content water to poison shoal communities