Paleozoic Tectonics

PALEOZOIC TECTONICS - OVERVIEW

• SUMMARY - CONTINENTAL DISPERSION DURING THE EARLY PALEOZOIC & SUBSEQUENT CONVERGENCE DURING THE LATE PALEOZOIC (A WILSON CYCLE)
• INITIALLY - DISRUPTION OF A SUPERCONTINENT (PANGEA I - FORMED IN MIDDLE PROTEROZOIC TIME) IN THE LATE PROTEROZOIC (800 MY) & DISPERSION OF THE SEVERAL RESULTANT CONTINENTS UNTIL THE MIDDLE ORDOVICIAN (475 MY)
  • development of passive continental margins at the edges of the several continents, with accumulation of thick sedimentary sequences
• CONTINENTS REASSEMBLED INTO A SECOND SUPERCONTINENT BY THE END OF LATE PALEOZOIC (275 MY) TIME
  • development of convergent continental margins at the edges of most continents during the Ordovician, culminating with continental collisions & suturing during the Late Paleozoic

PALEOZOIC TECTONICS - DETAILS

• LATE CAMBRIAN (550 TO 540 MY) - CONTINENTS ARE WELL DISPERSED & MOSTLY MOVING APART (LIKE TODAY)
  • 6 major continents
    • LAURENTIA (North America + Scotland)
    • BALTICA (Scandinavia, northern Europe, Russia [west of the Urals])
    • SIBERIA (east of the Urals + Mongolia = Northeast Asia)
    • KAZAKHSTANIA (Central Asia)
    • CHINA (including Southeast Asia)
    • GONDWANA (South America, Africa, Antarctica, Australia, India, southern Europe & Florida!)
  • continents are mostly in low latitudes (no continents at the poles)
    • CLIMATE IS VERY WARM & THICK LIMESTONES DEPOSITED IN SHALLOW SEAS
• MIDDLE ORDOVICIAN (490-475 MY) - CONTINENTS ARE STARTING TO CONVERGE
  • Gondwana (Sahara region) at the South Pole
    • GLACIATION IN the SAHARA
• MIDDLE SILURIAN (435-430 MY) - SIBERIA, BALTICA & LAURENTIA CONVERGING
  • Late Silurian - Gondwana (Chile region) at the South Pole
    • GLACIATION IN SOUTHERN SOUTH AMERICA
• DEVONIAN (~400 MY AGO) - CONVERGENCE WAS DOMINANT & LAURENTIA & BALTICA COLLIDE TO FORM LAURUSSIA
  • Gondwana nearly covers the South Pole, but doesn't result in glaciation
    • GONDWANA TOO BIG - MOISTURE CAN'T GET TO INTERIOR
• LATE CARBONIFEROUS [PENNSYLVANIAN] (~300 MY AGO) - FINAL CONSOLIDATION OF PANGEA II BEGINS WITH COLLISION OF LAURUSSIA & GONDWANA & OF KAZAKHSTANIA & SIBERIA
  • Gondwana moves slightly off South Pole; glaciation results
• PERMIAN (~250 MY AGO) - PANGEA II IS ESSENTIALLY FORMED (CHINA PROBABLY IS NOT ATTACHED TO IT)
  • Gondwana again completely covers South Pole; extensive evaporites

CONTINENTAL FRAMEWORK

• MOBILE BELTS VS. CRATONS
  • mobile belt = elongate zone of intense deformation & igneous activity that generally occurs at the periphery of continent
    • contain THICK (10-15 KM) SEQUENCES OF SEDIMENTS
  • craton = ancient geologically-stable central nucleus of a continents consisting of an exposed Precambrian shield surrounded by a platform of thin (<5km), essentially flat-lying Phanerozoic sedimentary strata
    • craton surfaces are GENTLY WARPED INTO BASINS, DOMES & ARCHES

NORTH AMERICAN MOBILE BELTS

• INITIALLY PASSIVE (DIVERGENT) CONTINENTAL MARGINS WITHIN PLATES DURING EARLY PART OF PALEOZOIC WITH THICK (10-15 KM) SEDIMENTARY SEQUENCES
  • marginal to Iapetus Ocean on the east
• APPALACHIAN MOBILE BELT (INCLUDING THE APPALACHIAN & OUACHITA OROGENS - EAST & GULF COASTS OF NORTH AMERICA)
  • eastern margin of Laurentia rifted during Late Proterozoic
  • island arcs developed far from North America during the Late Proterozoic = PIEDMONT
  • 3 orogenic events - Taconic, Acadian-Caledonian, & Alleghanian-Ouachita-Hercynian
    • TACONIC - Middle Ordovician collision of eastern Laurentia with an island arc (Piedmont)
    • ACADIAN-CALEDONIAN - Devonian collision of Laurentia with Baltica to form Laurussia
    • ALLEGHANIAN-OUACHITA-HERCYNIAN - Carboniferous/Permian collision of Laurussia with Gondwana
  • Clastic Wedges shed onto North American & European cratons from eroding orogenic belts
    • QUEENSTON CLASTIC WEDGE (Taconic Orogeny - North America only)
    • CATSKILL CLASTIC WEDGE /OLD RED SANDSTONE CLASTIC WEDGE (Acadian/Caledonian orogeny) - consists of redbeds & contains lots of land plant & animal material
      • development of widespread black shales (Chattanooga Shale)
    • APPALACHIAN BASIN CLASTIC WEDGE/NEW RED SANDSTONE CLASTIC WEDGE (Alleghenian/Hercynian orogeny) - lots of coal
      • coal in CYCLOTHEMS = repeated deposition of distinct sedimentary sequence of non-marine & marine strata
      • due to delta lobe switching & to Pennsylvanian glacial cycles
• CORDILLERAN MOBILE BELT
  • Late Proterozoic rifting of the western margin of Laurentia
  • island arcs developed immediately off western Laurentia during the Ordovician separated by Back-Arc Basins
  • Only 1 Paleozoic Orogeny & No Clastic Wedges
  • ANTLER OROGENY - Devonian collision of western Laurentia with an island arc (KLAMATH MOUNTAINS)

SEDIMENTARY DEPOSITIONAL SEQUENCES

• RESULT FROM LARGE-SCALE TRANSGRESSIONS & REGRESSIONS ACROSS THE CRATON
  • transgressions begin at craton margins & progress toward the craton interior until most of the continent is covered by a shallow sea
  • during regressions, the continent is again mostly exposed & widespread unconformities develop
• SEQUENCES ARE THICKEST & MOST COMPLETE (SHORTEST UNCONFORMITIES) AT THE CRATON MARGIN & THINNEST & MOST INCOMPLETE (LONGEST UNCONFORMITIES) IN THE CRATON INTERIOR
• SEQUENCES USUALLY HAVE A BASAL TRANSGRESSIVE SS, OVERLAIN BY SHALE, WHICH IN TURN IS OVERLAIN BY CHEMICAL ROCKS (LS, DOLOSTONE, & EVAPORITES)
  • examples:
    • 1) Sauk Sequence - Tapeats SS, Bright Angel Shale & Muav LS;
    • 2) Tippecanoe Sequence - St. Peter SS & Silurian carbonates/ evaporites in Great Lakes region;
    • 3) Kaskaskia Sequence - Oriskany SS, Devonian (Western Canada) & Mississippian carbonates & Devonian/ Mississippian boundary black shale (Chattanooga Shale)
    • 4) Absaroka Sequence - Cyclothems in Pennsylvanian & evaporites in W. Texas basins

Study Questions

1. When did the Late Proterozoic-Paleozoic Wilson Cycle initiate?

2. When did it change from dispersion to convergence?

3. What were the 6 major Early Paleozoic continents & their relationship to modern continents?

4. What were the positions of these continents during the Paleozoic & the effect on climate?

5. What are the general characteristics of cratons & mobile belts in terms of tectonic stability, sediment thickness & position relative to continent interior?

6. What are the general characteristics of sedimentary depositional sequences in terms of sediment thickness & unconformity distribution & their basic cause?

7. What is the basic lithologic sequence within sedimentary depositional sequences?

8. What are some important sedimentary units within the North American Sequences?

9. What are the details of the Taconic, Acadian-Caledonian & Alleghenian-Ouchita-Hercynian Orogenies?

10. What are the details of the Queenston Clastic Wedge, the Catskill Clastic Wedge-Old Red Sandstone & the Appalachian Basin-New Red Sandstone?

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