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Early Paleozoic Events


Marine Transgression The rocks of each facies become younger in a landward direction during a marine ... Vail curves are derived from seismic stratigraphic ... – PowerPoint PPT presentation

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Title: Early Paleozoic Events

Early Paleozoic Events

In the Beginning (of the Paleozoic)
  • Phanerozoic "visible life".
  • Refers to rocks younger than the Precambrian.
    540 m.y. ago to the presentConsists of three
    eras (from oldest to youngest)
  • Paleozoic "ancient life
  • Mesozoic "middle life
  • Cenozoic "recent life"
  • Early Paleozoic Cambrian, Ordovician and
  • Late Paleozoic Devonian, Mississippian,
    Pennsylvanian, and Permian

Figure 3-38 (p. 85)Sedimentary facies
(lithofacies) developed in the sea adjacent to a
land area. The upper surface of the diagram shows
present-day facies, whereas the front face shows
the shifting of facies through time. Notice that
bottom-dwelling organisms also differ in
environments having different bottom sediment and
water depth.
Figure 3-41 (p. 87)An illustration of Walthers
Principle, which states that vertical facies
changes correspond to lateral facies changes.
(After Brice, J. C., Levin, H. L., and Smith, M.
S. 1993. Laboratory Studies in Earth History, 5th
ed., Dubuque, IA William C. Brown.)
Marine Transgression
  • The rocks of each facies become younger
  • in a landward direction during a marine
  • One body of rock with the same attributes
  • (a facies) was deposited gradually at different
  • in different places so it is time transgressive
  • meaning the ages vary from place to place

younger shale
older shale
Marine Regression
  • During a marine regression,
  • sea level falls with respect to the continent
  • and the environments paralleling the shoreline
    migrate seaward

Marine Regression
  • A marine regression
  • is the opposite of a marine transgression
  • It yields a vertical sequence
  • with nearshore facies overlying offshore facies
  • and rock units become younger in the seaward

older shale
younger shale
Sea Level Changes
  • The ancient geographic arrangement of the
    continents is referred to as paleogeography
    ("ancient geography").
  • Reconstructing the ancient arrangement of the
    continents requires paleomagnetic, paleoclimatic,
    geochronologic, tectonic, sedimentologic, and
    biogeographic fossil data.
  • Paleomagnetic evidence provides information on
    the latitude at which the rocks formed. The
    orientation of the continent can be determined
    from the direction to the paleomagnetic pole, as
    recorded by bits of iron in the rock.

  • Longitudes, however, cannot be determined (which
    accounts for some of the differences in the
    paleogeographic reconstructions).
  • Paleoclimatic evidence comes from
    environmentally-sensitive sedimentary rock types
    (glacial deposits, coal swamp deposits, reef
    carbonates, evaporites).

Late Neoproterozoic Paleogeography
  • Global paleogeography during the Late
    Neoproterozoic, about 750 mya. Note that the
    continents are joined, forming the supercontinent
    Rodinia (or Proto-Pangea). Rodinia had begun to
    rift apart. The surrounding ocean is Mirovia.

Late Neoproterozoic Paleogeography
Cambrian Paleogeography
  • continents have moved off the South Pole
  • Iapetus Ocean (sometimes called the
    Proto-Atlantic) formed as Laurentia drifted away
    from South America.
  • Note the Ouachita trough segment (green on the
    map above), which separates off as a
    microcontinent (see Middle Ordovician map), and
    eventually converges with South America (orange).

Cambrian Paleogeography
  • Note that shallow seas cover many of the
    continents. The evaporite deposits are clustered
    within about 30 degrees north and south of the
    equator. This is the latitude at which the great
    deserts of the world occur today.

Figure 8-2 (p. 269)Paleogeographic and tectonic
elements of North America during the Cambrian
Period, showing position of the Cambrian
  • Warm ocean waters
  • The presence of stromatolites and mudcracks in
    these carbonate rocks indicate deposition in
    shallow water.
  • The water deepens toward the edges of the
    continent, where deep water shale is deposited
    (blue-green). Along the edge of the exposed land
    mass (yellow), sand is deposited.

Ordovician Paleogeography
  • Continents distributed along the equator.
  • Note the Ouachita Terrane
  • Also note the Taconic Orogenic Belt between
    Laurentia (North America) and Baltica (Europe and
    western Russia).

Ordovician Paleogeography
  • global sea levels were high. Shallow seas nearly
    cover many of the continents,
  • By the Middle Ordovician, Gondwanaland was moving
    toward the south pole, which led to glaciation in
    Africa at the end of the Ordovician.

Figure 7-9 (p. 248)In its long history, the
Earth has experienced several major episodes of
widespread continental glaciation.
Figure 8-27 (p. 289) Paleogeographic map of
Ordovician North America.
  • In North America during the Ordovician, sea
    levels were high, and the craton was flooded.
  • In the Appalachian area, the Cambrian and early
    Ordovician were dominated by shallow water
    carbonate deposition, as indicated by the
    presence of mudcracks and stromatolites.

Change in Ordovician Depositional Setting
  • The depositional setting changed dramatically
    during the Middle Ordovician. Carbonate
    sedimentation ended. The carbonate platform
    collapsed or was downwarped.
  • This was caused by the narrowing of the Iapetus
    Ocean along a subduction zone. Large volumes of
    black shales with graptolites, and immature
    sandstones spread westward over the carbonate
    rocks. As the Iapetus Ocean narrowed, a volcanic
    island arc approached the North American craton,
    leading to deformation and orogenic activity.

Figure 8-24 (p. 286)Plate tectonic forces that
resulted in the Taconic orogeny. (Adapted from
Rowley, D. B. and Kidd, S. F. 1981. J. Geol. 89
Compare Cambrian paleography to Ordovician
Taconic Orogeny
  • There are two main highlands areas, the higher of
    the two is in the northern Appalachians.
  • Erosion of Taconic mountains created the
    Queenston Delta (or clastic wedge)

Silurian Paleogeography
  • Note that the Iapetus Ocean is beginning to close
    as Laurentia and Baltica converge.

Figure 8-30 (p. 291) Paleogeographic map of
Silurian North America.
Shallow marine deposits formed in the
epicontinental sea, including carbonates with
reefs, and the Michigan basin evaporites. Note
the Silurian Tuscarora Sandstone in the central
Appalachian region.
Early Paleozoic Sedimentary Deposits
  • The Cambrian-Precambrian Boundary
  • The base of the Cambrian was long identified by
    the first-occurrence of shell-bearing organisms
    such as trilobites.
  • In the 1970's, a distinctive group of small
    shelly fossils was found below the first
    trilobites in Siberia and elsewhere, and dated at
    544 my. This small shelly fauna includes sponge
    spicules, brachiopods, molluscs, and possibly

Tiny Early Cambrian fossils with shells from
New classification of the Cambrian base
  • The new classification of Lower Cambrian
    chronostratigraphic units is based on the
    discoveries of the small shelly fauna and a
    variety of trace fossils. The base of the
    Cambrian is now placed at the oldest occurrence
    of feeding burrows of the trace fossil Phycodes
    pedum, and dated radiometrically at 544 my using
    uranium-lead isotope dates from rocks in NE
    Siberia .

Figure 8-7 (p. 271)The trace fossil Phycodes.
(After Crimes, T. P. 1989. Trace Fossils, in The
Cambrian- Precambrian Boundary. Oxford Monographs
on Geology and Geophysics 12. Oxford, England
Clarendon Press.)
Early Paleozoic Sedimentary Sequences
  • Transgressions and regressions of seas occurred
    across North America in the Early Paleozoic as
    the glaciers melted and enlarged. These sequences
    are bounded by (or separated by) unconformities.
  • Lawrence Sloss used the sedimentary record across
    the North American craton to divide the Paleozoic
    rock record into unconformity-bounded sequences,
    sometimes called cratonic sequences or Sloss

Early Pz Cratonic Sequences
  • Two major transgressions occurred in North
    America in the Early Paleozoic, which Sloss
  • Sauk sequence (older - primarily Cambrian)
  • Tippecanoe (Ordovician-Silurian)

Cratonic Sequences
  • Similar sequences are found on other continents,
    suggesting that worldwide (or eustatic) sea level
    change was responsible for the transgressions and
  • These eustatic sea level changes were probably
    related to glaciations and sea floor spreading.
    During times of rapid sea floor spreading, ridge
    formation displaces sea water onto the

Figure 3-42 (p. 88)Sloss sequences correspond
to Vail curves of global sea level change. Vail
curves are derived from seismic stratigraphic
profiles, which permit tracing of unconformities
across the craton and into thick continental
margin sedimentary rocks.
Cambrian Sedimentary Deposits - Sauk Sequence
  • During the Cambrian, there were no vascular
    plants on the land, so the landscape was barren.
    Erosion would have been active and severe without
    plant roots to hold the soil.
  • Transgression of the sea onto the craton followed
    the Neoproterozoic glaciaton.
  • Shoreline (beach) deposition produced a vast
    apron of clean quartz sand.
  • Carbonate deposition occurred farther from land.

Figure 8-9 (p. 274)Upper Cambrian lithofacies
map. (Simplified and adapted from Stratigraphic
Atlas of North America and Central America. Shell
Oil Company, Exploration Department.)
Grand Canyon Region
  • The Lower Cambrian Tapeats Sandstone is an
    example of the sandy beach deposits unconformably
    overlying Precambrian rocks
  • The Tapeats Sandstone is overlain by the Bright
    Angel Shale, an offshore deposit.
  • The Bright Angel Shale is overlain by the Muav
    Limestone, indicating deposition farther from the
  • These rocks form a transgressive sequence.

Cross section of Cambrian strata exposed in the
Grand Canyon. The red lines are trilobite zones,
which approximate time lines. Note that these
sedimentary units are diachronous (cut across
time lines). In each case, the sedimentary units
are older in the west than in the east.
A Marine Transgression in the Grand Canyon
  • Three formations deposited
  • in a widespread marine transgression
  • exposed in the walls of the Grand Canyon, Arizona

Ordovician-Silurian Deposits - Tippecanoe
  • When the Tippecanoe Sea flooded North America, it
    deposited the famous St. Peter Sandstone, an
    unusually pure, well sorted, well rounded quartz
  • The sandstone is overlain by extensive limestone
    deposits, locally replaced by dolomite.
  • In the eastern US, the limestones are overlain by
    and interbedded with shales along the periphery
    of the Queenston delta or clastic wedge. The
    Niagara Falls area is a classic locality where
    these rocks are exposed.

Figure 8-15 (p. 278)Stratigraphic section (A)
and block diagram (B) of Niagara Falls. (Map
after E. T. Raisz.)
Niagara Falls
Tippecanoe Evaporites
  • Near the end of the Tippecanoe sequence,
    landlocked reef-fringed basins developed in the
    Great Lakes area.
  • Michigan Basin.
  • During the Silurian evaporation led to the
    precipitation of immense quantities of rock salt
    and gypsum within the basin, indicating an arid

Figure 8-17 (p. 279) Isopach map showing
thickness and area of evaporite basins during the
late Silurian. Areas of evaporite precipitation
were surrounded by carbonate banks and reefs.
(Adapted from Alling, H. L., and Biggs, L. I.
1961. Bull. Am. Assoc. Petrol. Geol. 45 515-547.)
Figure 8-18 (p. 280)Cross-section illustrating
a model for the deposition of evaporites in a
barred basin.
Sea water flows into the basin over the
partially-submerged barrier. Evaporation produces
dense brines, which sink to the bottom of the
basin and are unable to mix with open sea water.
When the brine becomes sufficiently concentrated,
evaporite minerals are precipitated.
Early Paleozoic Tectonics
  • Plate Tectonic Events (in order)
  • Breakup of Rodinia (Proto-Pangaea)
  • Oceanic closing and orogeny to form Pangaea
  • Taconic orogeny
  • Caledonian orogeny
  • Acadian orogeny
  • Alleghenian orogeny
  • Hercynian orogeny

Taconic Orogeny
  • Taconic orogeny occurred in three phases
  • Appalachian Mountains built in collision with
    part of western Europe
  • compression folded shelf sediments into mountains
    and Logan's thrust formed (48 km displacement)
  • Giant granite batholiths produced by Taconic

Appalachian Mobile Belt
  • Evolution of the Appalachian mobile belt
  • Late Proterozoic opening of Iapetus Ocean
  • with passive continental margins
  • and large carbonate platforms

Appalachian Mobile Belt
  • Middle Ordovician transition to convergence
    resulted in orogenic activity

Early Paleozoic Climate
  • Transgressions generally mild climate
  • Regressions harsher, more diverse climates
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