Transcript Precambrian

Formation of the Great Lakes
Part 2
Precambrian and Paleozoic
History Channel Video
Chapter 2 in Grady
Chapter 2 in Greenberg
Great Lakes Basin in the
Precambrian
 Foundation for Great Lakes Basin (GLB)
was formed over 3 bya in Precambrian
 Canadian Shield
 Igneous rocks
 Exposed in northern and northwestern part of GLB
 Extends below sedimentary rocks deposited in the
southern and eastern parts of GLB during
Paleozoic era
Canadian Shield Rock
Canadian Shield
 Once Shield formed
 Middle of continent stable geologically
 Craton
 Margins of continent very active
 Volcanism creating new land
 Orogenies
Great Lakes basin
 Remnants of the rocks of these three provinces
form the deep basement of the Great Lakes basin.
 Smooth
 Grey to pinkish
 Central Lowlands Province
 Lower midwest USA region of the GLB
 No shield rock is visible at surface
 Region was covered over and over again by shallow sea
 Bedrock here is limestone
 Lots of evidence of ancient life – good fossils
 Basin for lower Great Lakes
 Resources: coal, natural gas, petroleum
Precambrian
 The Precambrian is actually a segment of
time that includes two eras, the
Proterozoic and the Archaean that span
billions of years.
 The oldest rocks on earth formed during
this time, as well as the first continents,
and the earliest, simplest forms of life.
Cambrian
Archean
 3800 to 2500 mya
 The oldest rocks on earth are from this era
 During the Archean, the cratons--the masses of
rock that make up the basic, initial structure of
continents--formed.
 The crustal bodies that formed were smaller
than today's continents and are referred to as
protocontinents.
 Today, Archean-aged rocks are found in areas
such as the Superior Upland and the Rocky
Mountains.
Archean Era
 Major Events:
 The earth was pummeled with meteors.
 Scientists believe that a huge impact tore
away a large chunk of the earth and trapped it
in orbit, forming the moon.
 Seawater and an atmosphere developed.
 The oceans became populated with algae,
bacteria, and colonies of microorganisms
known as stromatolites (first oxygen
deposited in atmosphere).
Precambrian
 Many of the oldest rocks found on earth
today are found in the Superior Upland, a
part of the Canadian Shield, the broad
swath Precambrian rocks that curves
around Hudson Bay.
 These rocks make up the "core" of the
North American continent.
Precambrian
 Other Precambrian rocks are found
throughout the continent, in places such
as the Adirondack Mountains, the Rocky
Mountains, the Llano Uplift, the Black Hills,
the Baraboo Range, and the Grand
Canyon.
Great Lakes Basin in the
Precambrian
 Volcanism and sedimentary deposits were the
source of the rich mineral deposits found in this
region
 Early sedimentary and volcanic rocks were
folded and heated into complex structures.
 These were later eroded and, today, appear as
the gently rolling hills and small mountain
remnants of the Canadian Shield, which forms
the northern and northwestern portions of the
Great Lakes Basin.
Great Lakes Basin in the Late
Precambrian (cont.)
 Central North America experienced
repeated transgressions and regressions
of shallow, tropical seas during Paleozoic
 large areas of tropical coral reefs
 seas deposited layers of materials that
became sedimentary rocks
 limestone, shales, sandstone, gypsum
Two Types of Cells
 Prokaryotes – cells without a nucleus,
simple cell structure
 Bacteria and Archaea
 Eukaryotes – cells have a nucleus which
contains the DNA, also have complex
structure
 Includes protozoa, algae, plants, fungi and
animals (including us)
Life in the Precambrian
 Archaean Era - 3800 to 2500 mya
 Oldest sedimentary rocks (3.8 BYA)
 Few fossils
 First life appears ~3.6 bya
 Chemotrophic, anaerobic, asexual
 Oldest fossils - 3.55 BYA
 Prokaryotes dominate
 Eubacteria and Archaea
 Cyanobacteria form extensive stromatolite systems
 Primitive Eukarya appear
 Photosynthesis appears
How old are they?
 Oldest known fossil bacteria are about 2.8
billion years old
 Look like cyanobacteria suggesting ancient
origin for photosynthesis
 Cyanobacteria fossils from stromatolites date to
2.8 to 2.5 bya (maybe older)
 Filamentous strands of cells resembling modern
species of Oscillatoria or Lyngbya
 Stromatolites still exist as living fossils
Floating
cyanobacterial mat
from a hot spring
Fossilized
cyanobacterial mat
Colonial chroococcalean cyanobacterium from the
Bitter Springs chert of central Australia, a site dating
to the Late Proterozoic, about 850 million years old.
Palaeolyngbya also
from the Bitter
Springs chert.
Living Lyngbya
Lyngbya
Stromatolites
 Layered mounds of calcareous material
between cyanobacterial cells.
 Following slides show fossil stromatolites
 Closest place to find these: Upper Peninsula
of Michigan
FOSSIL
Doing the backstroke among the stromatolites in
a tropical Precambrian sea
Stromatolites Keweenaw Peninsula,
Michigan
Michigan Stromatolites Marquette
County 2.1 to 2.2 bya
Michigan Stromatolites Marquette
County 2.1 to 2.2 bya
Stromatolite Formation
 Many layers were produced as calcium carbonate
precipitated over the growing mat of bacterial filaments.
 Photosynthesis by the cyanobacteria depleted carbon
dioxide in the surrounding water, initiating
precipitation of calcium carbonate.
 The minerals, along with grains of sediment
precipitating from the water, were then trapped within
the sticky layer of mucilage that surrounds the
bacterial colonies, which then continued to grow
upwards through the sediment to form a new layer.
 As this process occured over and over again, the
layers of sediment were created.
Stromatolite Structure
Stromatolite
formation still
occurs today; Shark
Bay in western
Australia is well
known for the
stromatolite "turfs"
rising along its
beaches.
Marine, low latitude,
hypersaline
environment.
Fossil Oscillatoria
Living Oscillatoria
Living Stromatolites Shark Bay, Australia
Proterozoic
 The Proterozoic was a time in which
multicellular algae began to appear.
 The continents grew in size
 Oxygen began to build up in the
atmosphere (from cyanobacteria).
 Today, Proterozoic rocks are found in
features like the Superior Upland, the
Black Hills and the Adirondack Mountains.
Cambrian
Paleoproterozoic
(2500 to 1600 mya)
 Oxygen present in atmosphere so  Metabolism began diversification
 Earliest Proterozoic life was single-celled and
anaerobic – did not use oxygen
 Oxygen was toxic to these organisms – 1st max
extinction event!
 Various ways to breakdown glucose anaerobically
 Later, more complex single-celled aerobic life
evolved which used oxygen
 Use oxygen for the process of respiration
Paleoproterozoic
 Peak of stromatolites
 Cyanobacteria oxygenated the atmosphere
 Oxygen caused “Rusting of the Earth”
 Depletion of oceanic iron
 Combined with oxygen and precipitated as “rust”
 Precipitated iron settled to the ocean floor
 Iron found in Banded Iron Formations
Banded Iron Formations
 Banded Iron Formations (BIFs) are another type
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of stromatolite
1.8 to 2.5 billion years old
Composed of alternating layers of iron-rich
material (commonly magnetite) and silica (chert)
Also found in Northern Michigan
How they were made
 Cyanobacteria provided the source of oxygen for BIF
formation.
FOSSIL
Banded Iron Formations
 How they were made #1
 Large amounts of the soluble form of iron were
released from the Earth's interior into the Archaean
oceans. (reduced ferric iron)
 Oxygen in the oceans would have oxidized (rusted)
this iron to form insoluble (ferrous) iron oxide which
precipitated and formed layers of reddish sediment on
the ocean floor.
 The layers or banding is assumed to result from
cyclic peaks in oxygen production. It is unclear
whether these were seasonal or followed some other
cycle.
sis
Banded Iron-Formation
 Seasonal and/or
biological cycles resulted
in intervening periods
when iron or oxygen
were not as available
 The black layers are
made of chert (microcrystalline quartz) that
was laid down during
these intervening
periods.
Banded Iron Formations
 How they were made #2
 It is also thought that bacteria may have played a role
in the formation of these bands of precipitated iron.
 Certain bacteria can oxidize reduced ferric iron to
insoluble ferrous iron
 Economic significance
 BIF’s are important sources of iron ore (mining)
 Bacteria are capable of precipitating a number of
other minerals including manganese and even gold
 These processes are being adapted to facilitate
mining of these minerals and removal of heavy
metal pollutants from soils
Banded Iron
Formations
Complex Single-celled Life
 Acritarchs
 Acid-resistant, organicwalled, micro-plankton
 Common Proterozoic
eukaryote fossils
 Represent encysted "resting
stage" of organism
 Resting cysts of algae
 Egg cases of small
metazoans
 Others are cysts of
unknown eukaryotes
Late Proterozoic Ice Age
 Occurred from 850 to 635 mya in the late Proterozoic
 Second, and possibly most severe glaciation in earth’s
history
 Glacial deposits are so widespread at this time that
geologists refer to it as “Snowball Earth".
 May have caused extinction of Acritarchs
 It has been suggested that the end of this cold period was
responsible for the subsequent Cambrian Explosion,
However, this theory is still controversial
 Formal name Varangian glaciation
 Named after an area in Norway
Precambrian Animals
650 to 544 mya
Ediacaran Fauna of Australia and
Newfoundland, CA
Soft Bodied Invertebrates
Life in the Late Proterozoic
 In the latest part of the Proterozoic (~ 600 mya), multi
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cellular, complex life is recorded in the fossil record.
Oldest fossils within Kingdom Animalia are Vendian age 650
to 544 mya, and are found at nearly 30 locations around the
world, and are most distinctive.
Fossils are preserved as thin impressions on bedding
surfaces of fine to medium-grained sedimentary rocks.
Organisms were very thin, lacked any minerallized hard
parts or well developed organs or organ systems, and had a
quilt-like outer surface.
Uncertainty about what groups of animals these fossils
might represent, and, if they were ancestral to the animals
that appeared in the late Cambrian.
Avalon Peninsula Newfoundland, CA
Ediacaran Biota
 Appeared immediately after the prolonged
period of global glaciations towards the end of
the Precambrian
 Extraordinary organisms:
 Discs
 Fronds
 Segmented morphologies
•Jellyfish
•Worm Tubes
 Locations
 Flinders Range (Ediacaran Hills), South Australia
 Avalon Zone of Newfoundland
 Nama Group in Namibia
Cyclomedusa
a jellyfish
Charnia masoni - no known
living descendants
Dickinsonia costata – early
relative of earthworms?
f09_27_pg19
f09_28_pg20
Trace fossils of primitive
worms
Precambrian Ocean – Ediacaran Fauna
620 to ~543 mya
Charnia
Cloudinia
Cyclomedusa
Dickinsonia
Parvancorina
Spriggina
Paleozoic Era
 With the coming of the Paleozoic Era,
most of central North America was flooded
again and again by marine seas, which
were inhabited by a multitude of life forms,
including corals, crinoids, brachiopods and
mollusks.
 The seas deposited lime silts, clays, sand and
salts, which eventually consolidated into
limestone, shales, sandstone, halite and
gypsum.
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The Paleozoic Periods
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Cambrian – Cambrian Explosion!
Ordovician
Silurian
Shallow seas covered GLB
Devonian
Carboniferous – coal forests
Permian – ended in mass extinction event
 Largest mass extinction until the one going on now!
 Cause? - maybe glaciation (Snowball Earth);
asteroid?
Paleozoic
 The Paleozoic era witnessed the
proliferation of life in diverse forms across
the planet.
 Animals and plants began to move out of the
water and populate terrestrial environments.
 As the continents shifted around the globe,
they had, by the end of the Paleozoic,
combined to form the supercontinent
Pangaea.
Precambrian
Cambrian
Ordovician
Silurian
Devonian
Carboniferous
Permian
Triassic
Jurassic
Animals Diversify
The Cambrian Explosion
570-505 million years ago