Early Paleozoic: What a Long Strange Trip It's Been
- Overall Physical Features
- Six (6) major continents
- Free ocean circulation
- Ice-free
- Transgression of epeiric seas
- Practically entire N.Am. shield inundated during early Paleozoic
- Moderation of global temperature
- 1st evidence of glaciation in Late Ordovician
- Orogenesis, thick deposition of terrestrial strata, increasing volcanism.
- Sloss Sequences: N.Am. Paleozoic rocks divided into four major Transgressive-Regressive cycles
- Sauk (Camb - Ord)
- Tippecanoe (Ord -Sil)
- Kaskaskia (Dev -Miss)
- Absaroka (Pa - Jr)
- Mesozoic rocks found in the Zuni (Jurassic-Cretaceous)
- Cenozoic rocks found in the Tejas (Tertiary)
- Paleogeographic Position
- Cambrian was equatorial
- Continental axis across the equator
- N-C Mexico to Ellesmere Island.
- Beginnings
- Originally base of Cambrian equal to the appearance of first shelled-fossils
- Trilobites are principal guide fossil.
- 1970's found shelly (calcium phosphate) fauna below the original boundary
- Recognition of the Tommotian stage (570- 543 MY BP [ recent radiometric date])
- Sauk Sequence I
- Early Cambrian sediments confined to continental margins
- Continental shield exposed to high rates of erosion (absence of land plants)
- Transgression (onlap sequence) began over the continent in Neoproterozoic
- Higher-elevation areas without deposition,
- Trans-continental arch (Ontario to Mexico).
- Late Cambrian
- Southern craton (Montana to New York) covered in marine environments.
- Nearshore composed of clean quartz sands.
- Stromatolites, mud cracks, and other intertidal/shallow subtidal deposits
- Newfoundland to Alabama
- Carbonates with a minimal faunal contribution
- Large carbonate platform
- Cordillera Region
- Sands grade westward into fine-clastics and then carbonates
- Passive margin sedimentation in deep ocean basins (e.g., middle Cambrian Burgess Shale)
- Grand Canyon Series
- Carbonates (Muav Ls)
- Fine Clastics (Bright Angel Shale)
- Sandstones (Tapeats Sandstone)
- The End of the Sauk Sequence
- Ordovician characterized by carbonates
- Early Ordovician Regression
- Widespread unconformity separates Sauk & Tippecanoe sequences.
- Ordovician Paleogeography
- Paleoequator from Baja California to Greenland.
- Evidence includes Ordovician evaporites (salt & gypsum) in arctic Canada
- Thick marine carbonate platforms along continental margins.
- Tippecanoe Sequence
- Mid-Ordovician transgression
- Cambro-Ordovician sands reworked into ultramature clean quartz sands
- Extending over 7500 mi2
- St. Peter Sandstone -Corning Glass
- Tippecanoe Carbonates
- Carbonate platforms comprised of a wide diversity of shelled macroinvertebrates developed
over the mature sandstones
- Chemically-precipitated limestones
- Bioclastic limestones
- Organic reefs
- East of the present Mississippi river, shales deposited over the carbonates
- Silurian Reefs
- In northern part of the craton an extensive carbonate platform formed, while in the Silurian
extensive reef and evaporite deposits formed (within 15o) of the Paleozoic equator.
- Late Silurian Restricted Basins
- Large reef complexes in the mid-continent around restricted cratonic basins (i.e., Michigan
Basin)
- Large quantities of salt & gypsum (Salina Group >750 m).
- Cordilleran Tippecanoe Sequence
- Subduction between Pacific & N. Am. plates
- Volcanic island arc with a thick deposits within subduction zone (graywacke &
volcaniclastics)
- Backarc basin deposits to the east include volcanics, siliceous black shales (graptolite facies),
and bedded cherts
- Eastward is a thick carbonates, shales & ss
- Southern Craton
- Flanked by trough-like basin (1500 m) - Ouachita-Marathon (AK to TX) trough
- Early Cambrian (?) deposits are graywackes, quartzites, and cherts
- Middle Cambrian are igneous Intrusives overlain by sandstones and carbonates
- 100 m of sediment deposited in Silurian
- Remainder of 10,000 m deposited during the Late Paleozoic.
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