Early Paleozoic

Geology

Basic Rules of Geology

• Transgression – rise in sea level

• Regression – lower in sea level

• Convergence leads to orogeny

• Orogeny leads to erosion

Continental Architecture• Craton

• Mobile Belt

• Epeiric Seas

– Stable, immobile part of a continent

– Located along continental margins, receive sediments, and deform during collision

– Widespread shallow seas that transgress and regress over the continent

– i.e., Franklin, Corilleran, Quachita, Appalachian

Phanerozoic Eon

• Phanerozoic – comprises 12% of all geologic time– Paleozoic Era – 6.5% of all geologic

time

Paleozoic Eon Introduction

• 6 major continents were present – as well as several microcontinents and island arcs

– Deposition due to transgressions and regressions– Mountain building (orogeny) due to collision of

continents

Early Paleozoic Cordilleran AppalachianCraton

LatePaleozoic

EarlyPaleozoic

• Major Events of North America– Sauk Sequence

– Tippecanoe Sequence

– Taconic Orogeny

Paleozoic PaleogeographyGlobal History

• Late Cambrian

• Late Ordovician

– H2O circulated freely

• Late Silurian

– Polar regions ice free– Epeiric seas

– Major highlands

– Gondwana moved southward and across the South Pole

Laurentia, Baltica, Siberia, Kazakhstania, China

Gondwana, Siberia

Tillites in Sahara Desert

– Laurentia developed active convergent boundary in eastern margin– Baltica moved NW and collided with Laurentia

Paleozoic – Late Cambrian Sauk Sequence

• First major transgression– Most of N.A. covered by

epeiric seas

• Evidence of shallow-water deposition

– well-sorted, clean sands (ancient shoreline)

– Carbonates (stromatolites & ooids)

– N.A. along equator

• Grand Canyon

Paleozoic – Late Cambrian Sauk Sequence

– Good example of Sauk Sequence

Tapeats Sandstone

Bright Angel Shale

Mauv Limestone

– Transgression – “fining upwards”

– Time transgressive

Paleozoic – Late OrdovicianTippecanoe Sequence

• Sauk Sea regressed

– Produced unconformity

• N.A. in tropical environment

– Limestone and dolostone experienced rapid erosion

Boundary between Sauk and Tippecanoe Sequences

• Major transgression– St. Peter SS at base of

sequence– Followed by widespread reefs and evaporites– Carbonates Carbonate--corals, bryzoans,

dolostone--reefs/evaporites

• Tippecanoe famous for basin rimmed by reefs and evaporites (?)

Paleozoic – Late OrdovicianTippecanoe Sequence

• Modern reef structure– 30º N&S of equator– Warm, shallow H2O– No sedimentation

input– Normal salinity

– Michigan Basin

• Evaporites– Evaporation >

precipitation– High salinity

Paleozoic – Late OrdovicianMichigan Basin

• Contradiction– Pinnacle reef– Evaporites

• Possible Explanation– Rimmed coral basin

– Periodically flooded

– evaporation

Pinnacle reef grew upwards in response to rising sea level

Evaporite formation

• During L. Cambrian & L. Ordovician

(Sauk and Tippecanoe Sequences)

Paleozoic – Late SilurianAppalachian Mobile Belt

• Broad, passive margin along eastern edge of Laurentia

• Deposition of carbonates overlying shallow-marine seds.

Paleozoic – Late SilurianAppalachian Mobile Belt

• Taconic Orogeny

– Baltica collided with Laurentia

– Widening of Iapetus Ocean along divergent boundary

– Iapetus plate subducted beneath Laurentia

– Results in arc volcanism

(mountain-building)

Passive active margin

• Birth of Appalachian Mts

Late Silurian

Passive margin, L. Proterozoic-L.Ordovician

Mid Ordovician Orogeny

Silurian