Midterm 2

Question 1

What happened during the Hadean?

Answer 1

1. An andesitic island arc forms by subduction of oceanic lithosphere and partial melting of basaltic oceanic crust. Partial melting of andesite yields granitic magma.
2. The island arc in step 1 collides with a previously formed island arc, thereby forming a continental core.
3. The process occurs again when the island arc in step 2 collides with the evolving continent thereby forming a craton, the nucleus of the continent

Question 2

What are basic characteristics of the Proterozoic Eon?

Answer 2

– 2.5 billion to 542 million years ago
– Unlike Archean rocks, many Proterozoic rocks
are unmetamorphosed.
– Fossils are uncommon.
– Komatiites become rare in the Proterozoic.
– Fewer greenstone belts and granite-gneiss
complexes.
– Evidence of passive continental margins.
– Banded iron formations
First continental red beds form.
– O2 volume in the atmosphere increases.
– At least two glaciations.
– Multicellular organisms evolve.
– First aerobic organisms.
– First cells with internal, membrane-bounded
nucleus, which are found in plants and
animals

Question 3

How is the proterozoic eon divided?

Answer 3

– Divisions of the Proterozoic Eon are based on
radiometric dates rather than timestratigraphic
units.
– Archean-Proterozoic boundary of 2.5 billion
years ago (Ga) is somewhat arbitrary, but
approximately represents a change in crustal
evolution

Question 4

*What is the Proterozoic History of Laurentia up to the Paleoproterozoic? (exam objective - Outline the Proterozoic history of Laurentia from the assembly of the Archean cratons
through the Neoproterozoic)

Answer 4

• Important events in the evolution of the
continent Laurentia occurred during the
Proterozoic.
• Laurentia included North America, Greenland, parts of Scotland, and perhaps
the Baltic Shield of Scandinavia Archean cratons collided to form the nucleus of Laurentia.
• Eastern and southern Laurentia accreted
during the Proterozoic.

Question 5

*What is the Proterozoic History of Laurentia during the Paleoproterozoic? (exam objective - Outline the Proterozoic history of Laurentia from the assembly of the Archean cratons
through the Neoproterozoic)

Answer 5

– Collisions at 1.8-2.0 bya among Archean
cratons formed several orogens, which are
linear to arcuate deformation belts.
– Metamorphism occurred and batholiths
intruded during the orogens.
– Many banded iron formations and red beds
deposited.
– Thelon orogen occurred 1.92-1.96 Ga when the
Slave and Rae cratons collided in northwest Canada.
– Wopmay orogeny at ~1.9 Ga
– Trans-Hudson orogen of 1.82-1.84 Ga occurred in the US and Canada when the Superior, Hearne, and
Wyoming cratons collided.
– Penokean orogen occurred on the southern margin of Laurentia over tens of millions of years and was most intense about 1.85 bya
– Sedimentary rocks in Wopmay orogen of
northwestern Canada record the opening and
closing of an ocean basin.
• A complete Wilson cycle of sediments is present.
• Sandstone-carbonate-shale assemblage, which
forms on passive continental margins.
• This assemblage also well represented in the
Penokean orogen of the Great Lakes region

Question 6

*What is the Proterozoic History of Laurentia at Mesoproterozoic accretion and Igneous Activity? (exam objective - Outline the Proterozoic history of Laurentia from the assembly of the Archean cratons
through the Neoproterozoic)

Answer 6

– Following a lull of several millions of years,
tectonism and continental accretion resumed
along the southeastern margin of Laurentia.
– The Granite-Rhyolite province formed from about 1.35-1.55 Ga, which included a lot of granitic and anorthosite plutons.
– Surface exposures of the province occur in
eastern Canada, Greenland and the Baltic Shield of Scandinavia
– Origin(s) of the granitic and anorthosite
magmas is uncertain, but may be due to
excessive heating and partial melting of the
mantle under Laurentia.

Question 7

*What is the Proterozoic History of Laurentia at Mesoproterozoic Orogeny and Rifting? (exam objective - Outline the Proterozoic history of Laurentia from the assembly of the Archean cratons
through the Neoproterozoic)

Answer 7

– The Grenville orogeny occurred on the
eastern boundary of Laurentia from 1.0-1.3
Ga.
– Grenville rocks are exposed in the modern
northern Appalachian Mountains, eastern
Canada, Greenland, and Scandinavia.
– The Llano province in Texas is probably a
westward extension of the Grenville belt
– The Grenville belt may have resulted in the
closure of an ocean basin that assembled the
supercontinent Rodina, which persisted into
the Neoproterozoic
– Beginning about 1.1 Ga, tensional forces
opened up the Midcontinent Rift, which
consists of two branches.
– Many geologists think that the rift is a failed
spreading zone.
– The Midcontinent Rift was active for about 20
million years. Had it continued, North
America would have been split.
– The central part of the Midcontinent Rift
contains numerous overlapping basalt flows.
– Along the rift’s margins, conglomerates were
deposited in alluvial fans.
– The conglomerates grade into sandstones
and shales with increasing distance from the
sediment source

Question 8

*What is the Proterozoic History of Laurentia during Meso and Neoproterozoic Sedimentation? (exam objective - Outline the Proterozoic history of Laurentia from the assembly of the Archean cratons
through the Neoproterozoic)

Answer 8

–Sedimentation occurred in the eastern US
and Canada, and the western basins of the
US.
• Exposures in northern Rocky Mountains.
• Grand Canyon Supergroup - fluvial and shallow marine deposits with stromatolites deposited 740 million years ago (Ma) to 1.2 Ga.

Question 9

Explain the Proterozoic Supercontinents

Answer 9

• Continents are not simply land areas
above sea level.
• Continents consist of granitic crust and are
thicker than mafic oceanic crusts.
• Supercontinents consist of two or more
continents that have merged into one.
• Present style of plate tectonics began by
the Paleoproterozoic.
• Ophiolites, which indicates plate
convergence, are found in Neoarchean
rocks in Russia and probably
Paleoproterozoic rocks in China.
• These ophiolites are similar to younger
examples in Finland
• The supercontinent Nuna may have
existed 1.8 Ga.
• The oldest documented supercontinent is
Rodinia, which assembled 1.0-1.3 Ga and
began fragmenting about 750 Ma.
• Separate pieces of Rodinia reassembled
into the supercontinent Pannotia about
650 Ma.
• Pannotia fragmented about 550 Ga

Question 10

*Describe the ancient glaciers and their deposits up to the Proterozoic era (exam objective - Describe the evidence for widespread Neoproterozoic glaciation)

Answer 10

– Pleistocene 11,700 years ago to 2.6 Ma
– Two during the Paleozoic Era
– Two major Proterozoic glaciations:
• Paleoproterozoic
• Neoproterozoic
– Tillites of Bruce Formation of Ontario,
Canada, about 2.7 Ga or Neoarchean

Question 11

*Describe the ancient glaciers and their deposits during the Paleoproterozoic era (exam objective - Describe the evidence for widespread Neoproterozoic glaciation)

Answer 11

– Evidence of Paleoproterozoic Glaciations:
•  Tillites of about the same age
• Michigan, Wyoming and Quebec
• Australia
• South Africa
•  Striated bedrock
– The Paleoproterozoic tillites in different
areas may have formed from several
separate glacial events rather than just
one event.

Question 12

*Describe the ancient glaciers and their deposits during the Neoproterozoic era (exam objective - Describe the evidence for widespread Neoproterozoic glaciation)

Answer 12

– Glaciers of the Neoproterozoic
• Widespread, 600-900 Ma.
• At least 4 separate glacial episodes, but not
all areas in Figure 9.10c were glaciated at the
same time.
• Most extensive glaciations in Earth’s history.
• Glaciers may have been present in near equatorial
regions
• Controversial Snowball Earth Hypothesis,
where the entire Earth may have been covered by
glaciers at one or more times during the
Neoproterozoic.
• The snowball Earth may have been triggered by
the near-equatorial location of all continents.
• Extensive weathering of those continents
absorbed the greenhouse gas CO2 from the
atmosphere.
•The reflection of sunlight by glaciers would
have promoted additional cooling and growth
of glaciers.
• Snowball Earth glaciations would end by
greenhouse CO2 and methane emissions
from volcanoes.
• Life could survive during snowball Earth
glaciations if the ice was thin enough for
photosynthesis and if organisms lived near
active volcanoes or hydrothermal vents.

Question 13

Describe the Snowball Earth hypothesis

Answer 13

• snowball Earth hypothesis proposed that
Earth’s surface became entirely or nearly entirely
frozen (sea ice + ice sheets)
– Mean global temperature -50 oC (albedo effects)
1. Because of exceedingly cold spells earth oceans start to freeze
2. Lowered reflectivity causes further cooling, ending in “snowball earth”
3. CO2 cycle in ocean stops; CO2 outgassed by volcanoes builds up
4. Strong greenhouse effect melts “snowball earth” results in “hothouse earth”
5. CO2 cycle restarts, pulling CO2 back into oceans, reducing greenhouse effect to normal

Question 14

Describe the proterozoic history of Laurentia

Answer 14

1. during the paleoproteozoic, archean cratons were sutured along deformation belts called orogens
2. Laurentia grew along its southeastern margin by accretion of the Yavapai and Mazatzai provinces
3. The last episodes in the Proterozoic accretion of Laurentia involved the origin of the Granite-Rhyolite province and Grenville-Llano provinces

Question 15

What were the Proterozoic supercontinents

Answer 15

1. India
2. Australia
3. East Antarctica
4. Kalahari
5. Congo
6. West Africa
7. Amazonia
8. Baltica
9. Laurentia
10. Siberia

Question 16

*Describe the glaciers of the Neoproterozoic (exam objective - Describe the evidence for widespread Neoproterozoic glaciation)

Answer 16

• The reflection of sunlight by glaciers would
  have promoted additional cooling and growth
  of glaciers.
  – Snowball Earth glaciations would end by
  greenhouse CO2 and methane emissions
  from volcanoes.
  – Life could survive during snowball Earth
  glaciations if the ice was thin enough for
  photosynthesis and if organisms lived near
  active volcanoes or hydrothermal vents

Question 17

*Describe how the atmosphere changed during the Proterozoic (exam objective - Describe the composition of the Proterozoic atmosphere)

Answer 17

• The amount of O2 in the atmosphere at the
  beginning of the Proterozoic was probably
  no more than 1% of the current value.
  • By the end of the Proterozoic, O2
  concentrations may not have exceeded
  10% of current levels.
  • Oxygen-producing stromatolites did not
  become common until about 2.3 Ga
  (possible source of Paleoproterozoic
  snowball earth).
• During the Proterozoic, atmospheric CO2
  decreased as O2 increased.
  • Atmospheric CO2 decreased through
  growth of the biosphere and the precipitation of carbonate minerals,
  especially calcite and dolomite in limestones and dolostones, respectively

Question 18

*Explain banded iron formations (BIFs) and how they impacted the changing atmosphere (exam objective - Describe the origin of Banded Iron formations)

Answer 18

• Alternating millimeter- to centimeter-thick layers of iron-rich minerals and chert.
  – Most deposited in shallow-water shelf environments from 2.0 to 2.5 bya.
  – Iron could originate from weathering of rocks
  and hydrothermal vents.
  – In the absence of O2, (reduced) iron (Fe2+) is
  soluble in water.
• Iron dissolved and accumulated in low O2
  bottom waters of Paleoproterozoic oceans.
  – The iron-rich waters upwelled to the surface
  of the oceans, where they came into contact
  with some O2 and precipitated iron minerals.
  – Modern atmosphere and ocean waters contain too much O2 for the formation of BIFs

Question 19

*Explain continental red beds for the proterozoic and how it impacted the atmosphere (exam objective - Describe the composition of the Proterozoic atmosphere)

Answer 19

• Sandstones and shales covered by iron
  oxides, especially hematite (Fe2O3).
  – First appeared about 1.8 Ga.
  – Their formation coincided with atmospheric O2
  concentrations of only 1-2% of current levels.
  – O2 concentrations of only 1-2% may not be
  enough to oxidize iron and produce red beds.
  However, ultraviolet radiation could convert
  some O2 into elemental O and ozone (O3),
  which are more effective at oxidizing iron

Question 20

What life existed during the proterozoic

Answer 20

• Paleoproterozoic record characterized by
  the same organisms as found in the
  Archean: bacteria and archaea.
  • Stromatolites became more common in
  the Paleoproterozoic.
  • Organisms that produce sexually probably
  evolved by the Mesoproterozoic

Question 21

Describe the characteristics of eukarryotic cells

Answer 21

• Reproduce sexually.
• Larger than prokaryotic cells.
• Many are multi-celled.
• Many are aerobic, which means that they could not
evolve until the atmosphere had sufficient O2.
• Have internal membrane-bounded nucleus that
contains the chromosomes.
• Other internal structures not found in prokaryotic
cells.

Question 22

Describe the five kingdoms that are used to classify organisms

Answer 22

– Five common kingdoms of life forms can be
reduced to three broad groups or domains.
– Two groups (archaea and bacteria) consist of
prokaryotic cells and the others have
members with eukaryotic cells.

Question 23

Describe the monera kingdom and provide examples of organisms in this kingdom

Answer 23

2 subkingdoms
Archaea - prokaryotic cells, single celled, differ from bacteria in genetic and chemistry
e.g methanogens, halophiles, thermophiles
Bacteria - Prokaryotic cells; single-celled, cell wall different from archaea and eukaryotic cells
e.g. cyanobacteria, mycoplasmsas

Question 24

Describe the Protista kingdom and provide examples of organisms in this kingdom

Answer 24

Eukaryotic cells; single-celled, greater internal complexity than bacteria
e.g. algae, diatoms, protozoans

Question 25

Describe the Fungi kingdom and provide examples of organisms in this kingdom

Answer 25

Eukaryotic cells; multi-celled, major decomposers and nutrient recyclers e.g. fungi, yeast, mold

Question 26

Describe the Plantae kingdom and provide examples of organisms in this kingdom

Answer 26

Eukaryotic cells; multi-celled, obtain nutrients by photosynthesis
e.g. trees, grass, plants

Question 27

Describe the Animalia kingdom and provide examples of organisms in this kingdom

Answer 27

Eukaryotic cells; multi-celled, obtain nutrients by ingestion of preformed organic molecules e.g worms. clams, mammals, fish, sponges, reptiles, birds, ampibians

Question 28

*What are the oldest known eukaryotic fossils?(exam objective - Describe the fossil evidence for the evolution of eukaryotic cells)

Answer 28

– The oldest known eukaryote fossils are in 1.2
Ga Mesoproterozoic rocks in Canada
• The tiny organisms, called Bangiomorpha, were
multicelled, probably produced sexually, and
resembled red algae.
• cells larger than 60 microns were
abundant by at least 1.4 Ga.
– The oldest known megafossil (i.e. not a
microfossil) is Grypania, which is found in the
2.1 Ga Negaunee Iron Formation of Michigan.
• Grypania may have been a large single-celled
bacterium or algae.
- Hollow fossils known as acritarchs were
probably cysts of planktonic algae. They
became common during the Meso- and
Neoproterozoic.

Question 29

Explain endosymbiosis and the origin of eukaryotic cells

Answer 29

– Eukaryotic cells probably evolved from prokaryotic cells that formed symbiotic
relationships.
– The organisms became unable to live independently.
– Endosymbiosis - when one symbiotic organism lives within the other.
– Endosymbiosis is seen in living eukaryotic cells that contain internal structures, or organelles, such as mitochondria and
plastids.
– The organelles have their own genetic material and they synthesize proteins just like prokaryotic cells.
– Through organelles, bacteria could have
entered into symbiotic relationships,
eventually giving rise to eukaryotic cells.

Question 30

Explain the existence of multicelled organisms

Answer 30

– In multicelled organisms, cells are specialized to
perform certain functions, such as reproduction
and respiration.
– Multicelled organisms first appeared in the
Neoproterozoic.
– The fossil record does not provide much
information on the origin of multicelled organisms.
– Most information comes from studying modern
organisms.
– Multicelled organisms with as few as four
identical cells are capable of living.
– Cells in colonies could evolve specializations,
such as sponges.
– Carbonaceous impressions of multicelled
Proterozoic algae are known from many
locations.

Question 31

What are advantages of multicelled organisms

Answer 31

• Multicelled organisms live longer than single-celled
organisms.
• Cells can be replaced and new cells produced.
• Cells have increased functional efficiency when
their functions are specialized in organs.

Question 32

*Describe neoproterozoic animals found in the fossil record (exam objective - Describe the characteristics of the Ediacaran fauna and how they relate to modern Phyla)

Answer 32

1. Ediacaran fauna of South Australia
   • Soft body impressions.
   • Algae and several animals unknown today.
   • Fossils of three phyla may be present - jellyfish
   and sea pens (phylum Cnidaria), segmented
   worms (phylum Annelida), and primitive
   members of the phylum Arthropoda (which
   include today’s insects, spiders and crabs).
   • Spriggina could be an ancestor of trilobites.
   • Possible early echinoderms.
   Ediacaran fauna is also a collective term for
   fossil associations similar to those found in
   South Australia
   • Found on all continents except Antarctica.
   • 545 to 600 mya fauna in Namibia, Africa and
   Newfoundland, Canada.
2. Other fossils
   • Jellyfish-like impressions.
   • Burrows probably from worms.
   • Possible 700-900 mya fossil worms from China.
   • Small branching tubes in 590-600 mya rocks from
   China could be early relatives of corals.
   • Neoproterozoic Kimberella, possible mollusk.
   • Several animals with skeletons, or at least partial
   skeletons, existed in the latest Neoproterozoic

Question 33

What mineral resources existed in the proterozoic

Answer 33

• Most of world’s iron comes from Proterozoic banded iron formations,
especially those in Canada and the US.
• Nickel and platinum from Sudbury mine, Canada.
• Platinum and chromium from Bushveld Complex of South Africa.
• Recoverable oil and gas from Proterozoic rocks in China and Russia.
• Some Proterozoic pegmatites contain
gemstones, tin, cesium, rubidium, lithium and beryllium.
• Pegmatites adjacent to Harney Peak Granite in the Black Hills, South Dakota,
are 1.7 Ga. They contain some of the largest crystals in the world and have been
mined for gemstones, tin, lithium and micas.

Question 34

What periods are included in the Early Paleozoic

Answer 34

• Cambrian
• Ordovician
• Silurian

Question 35

What was the architecture of the continents during early paleozoic

Answer 35

• The supercontinent Pannotia (late Neoproterozoic Eon) began to break apart 550 Ma or shortly before the beginning of the Paleozoic Era at 541 Ma.
• By the early Paleozoic, there were six
major continents: Baltica, China, Gondwana, Kazakstania, Laurentia and
Siberia.

Question 36

Describe the characteristics of the continents during early paleozoic

Answer 36

• Each continent consisted of two major
components:
– 1. relatively stable craton over which epeiric
seas transgressed and regressed.
– 2. surrounded by elongated mobile belts in
which mountain building took place.
• North America:
– Franklinian, Cordilleran, Ouachita, and
Appalachian mobile belts.

Question 37

What are paleography maps

Answer 37

• Geologists construct paleogeographic
maps by looking at relevant paleoclimatic,
paleomagnetic, fossil, stratigraphic,
sedimentologic, and tectonic data.
• The maps show land and sea distributions,
possible climatic regimes, mountain
ranges, swamps, and any glaciers.

Question 38

Describe the paleozoic paleogeography

Answer 38

• Paleozoic paleogeographic history is not as precisely known as the histories of the
Mesozoic and Cenozoic Eras.
• The magnetic anomaly patterns in Paleozoic ocean crust were largely
destroyed by subduction during the formation of Pangaea (late Paleozoic).
• Paleozoic paleogeographic
reconstructions are primarily based on
structural relationships, climate-sensitive
sedimentary rocks (such as: red beds,
evaporites, tillites, and coals), and fossil
distributions.

Question 39

Describe the location of the six paleozoic continents

Answer 39

– Baltica - Russia west of the Ural Mountains
and most of northern Europe (Fennoscandia).
– China - also includes Indochina and Malay
Peninsula.
– Gondwana - Africa, Antarctica, Australia,
Florida, India, Madagascar, and parts of the
Middle East and southern Europe.
– Kazakhstania - Kazakhstan in Asia.
– Laurentia - most of North America, Greenland,
northwestern Ireland, and Scotland.
– Siberia - Russia east of the Ural Mountains,
Asia north of Kazakhstan, and south of
Mongolia.

Question 40

What were the paleozoic microcontinents and microplates

Answer 40

– Avalonia - Belgium, northern France, England,
Wales, part of Ireland, Maritime Provinces and
Newfoundland of Canada, and parts of New
England, USA.
– Various (volcanic) island arcs on microplates.

Question 41

Describe the paleogeography during the cambrian period of Paleozoic

Answer 41

• Polar regions mostly ice free.
– Recall: Neoproterozoic snowball earth
• By Late Cambrian epeiric seas (epicontinental
seas) covered parts of the continents.
• Highlands in northeastern Gondwana, eastern
Siberia, and central Kazakhstania.
• Eastern Laurentia is a passive continental margin.

Question 42

*Describe the paleogeography during the ordovician period of Paleozoic (exam objective -
Outline the major orogenies along the eastern margin of Laurentia during the Early
Paleozoic)

Answer 42

• Gondwana moved southward and crossed the
South Pole.
• Ordovician glaciations - tillites found in North
Africa.
• Early Ordovician - Avalonia rifted from Gondwana
and moved northeastward.
• Late Ordovician and Early Silurian - Avalonia
collides with Baltica
• Eastern margin of Laurentia becomes an active
convergent boundary - subduction.
• Taconic orogeny (mountain building) occurred in
New England in the Late Ordovician.

Question 43

*Describe the paleogeography during the silurian period of Paleozoic (exam objective -
Outline the major orogenies along the eastern margin of Laurentia during the Early
Paleozoic)

Answer 43

• Baltica-Avalonia collides with Laurentia, which
closes the northern Iapetus Ocean and begins the
Caledonian orogeny on these continents.
• Southern Iapetus Ocean remains open between
Laurentia and Baltica-Avalonia.
• Siberia and Kazakhstania moved from a southern
tropical position in the Cambrian to a northern
temperate latitude by the end of the Silurian.

Question 44

*What is cratonic sequence? (exam objective - Outline the evidence for the major transgressive and regressive sequences in Laurentia
during the Early Paleozoic)

Answer 44

large-scale (greater
than supergroup) lithostratigraphic unit
representing a major transgressive-regressive
cycle bounded by craton-wide unconformities.
• Sedimentary rock record of North America is divided into six cratonic sequences.

Question 45

*Describe the North American cratonic sequences (exam objective - Outline the evidence for the major transgressive and regressive sequences in Laurentia
during the Early Paleozoic)

Answer 45

• The transgressive phase is usually covered by well-preserved younger
sedimentary rocks.
• The regressive phase ends with an unconformity – due to regional erosion.
• Each of the six unconformities extend
across various sedimentary basins of the North American craton and into mobile belts along the cratonic margin.
• The basic unit of sequence stratigraphy is the sequence, which is a succession of sedimentary rocks bounded by unconformities and equivalent conformable
strata.
• Sequence boundaries result from a drop in
relative sea level.
• Sequence stratigraphy is used for correlation
and mapping in the petroleum industry.

Question 46

*Describe the Sauk sequence (exam objective - Outline the evidence for the major transgressive and regressive sequences in Laurentia during the Early Paleozoic)

Answer 46

• Neoproterozoic – Early Ordovician.
• Sediments of the first major transgression onto the Paleozoic North American continent.
• Deposition of marine sediments limited to passive shelf areas of the Appalachian and
Cordilleran borders of the craton.
• Tropical climate (i.e. HOT) and erosion of the
exposed craton.
– No land plants until Ordovician
• Transgressive phase of the Sauk Sea began in the Middle Cambrian.
• By Late Cambrian, epeiric seas (shallow continental seas) covered most of North
America, leaving only the craton (Canadian Shield) and a few islands of the
Transcontinental Arch above sea level.
• Shallow marine sediments accumulated on both the shelf and craton. Sediments
included carbonates and detrital sands.
• Carbonate deposition was dominant on the craton as the Sauk transgression
continued during the Early Ordovician.
• The advancing Sauk Sea eventually covered the islands of the
Transcontinental Arch.
• The Sauk Sea regressed from the craton of North America during the Early
Ordovician, exposing land to erosion.
• The exposed carbonates experienced extensive erosion in the tropical
environment.
• The resulting unconformity is the boundary between the Sauk and Tippecanoe
sequences.

Question 47

*Explain the Transgressive Facies Model for Cambrian of the Grand Canyon Region (exam objective - Outline the evidence for the major transgressive and regressive sequences in Laurentia
during the Early Paleozoic)

Answer 47

– In a stable marine environment where sea
level remains the same, coarse detrital
materials deposit near shore and fine-grained
carbonates accumulate farthest offshore and
away from the source of detrital sediments.
– Cambrian rocks of the Grand Canyon,
Arizona, provide an excellent model of marine
sediment deposition during a transgression.
– The Grand Canyon represented a passive shelf
on the western margin of the craton during the
time of the Sauk Sequence.
– During the Neoproterozoic and Early Cambrian, the region was mostly above sea level.
– The Tapeats Sandstone represents the basal
transgressive shoreline deposits during the Early
Cambrian.
– As the transgression continued into the Middle
Cambrian, the muds of the Bright Angel Shale
were deposited on top of the Tapeats sands.
– By Late Cambrian, the Sauk Sea transgressed so
far over the craton in the Grand Canyon region
that carbonates of the Muav Limestone were deposited over the muds of the Bright Angel Shale.
– The vertical succession of Tapeats Sandstone to the Muav Limestone forms a typical trangressive sequence and represents a
progressive migration of offshore facies towards the craton over time.
– The Cambrian rocks of the Grand Canyon also illustrate that many formations are timetransgressive; that is, their age is not the same everywhere they are found.
– Predictable succession of facies was deposited laterally at the same time
– The Muav Limestone began to accumulate on
the shelf before the deposition of the Tapeats
Sandstone was completed on the craton.
– The Bright Angel Shale is Early Cambrian in
California and Middle Cambrian at the Grand
Canyon.
– Implication is that formations defined based
on their lithostratigraphy are diachronous
(Greek = through time), deposited at a
different time in different places

Question 48

*Describe the Tippecanoe sequence (exam objective - Outline the evidence for the major transgressive and regressive sequences in Laurentia during the Early Paleozoic)

Answer 48

• Middle Ordovician to Early Devonian
• The Tippecanoe Sequence resulted from the
transgression of the
Tippecanoe Sea onto the
North American craton following the post-Sauk regression.
• The sea deposited clean and well-sorted quartz sands over much of the craton.
• The Tippecanoe basal sandstones were followed by the deposition of carbonates as the transgression proceeded.
• The limestones primarily resulted from growth
of calcium-carbonate secreting organisms, such as corals, brachiopods, stromatoporoids,
and bryozoans.
• (dolostones resulted from magnesium-rich fluids altering buried limestones during diagenesis)
• In the eastern portion of the North American
craton, carbonates grade laterally into shales.
• The shales represent the farthest extent of detrital sediments derived from the
weathering and erosion of the Taconic Highlands.
• The highlands resulted from a tectonic event
occurring in the Appalachian mobile belt (Taconic Orogeny).
• The Tippecanoe Sea gradually regressed from the craton during the Late Silurian.
• Evaporites precipitated in the warm climates of the Appalachian, Ohio, and
Michigan basins.
• Nearly one-half of the sediments in the Michigan Basin are halite and anhydrite (post-depositionally-dehydrated gypsum).
• The End of the Tippecanoe Sequence
– The Tippecanoe Sea retreated to the craton
margin by the Early Devonian.
– Lowland topography was exposed.
– The craton experienced mild deformation
during the Early Devonian, which formed
many domes and arches – uplifted areas on
the craton; and basins – down-dropped areas
on the craton that accumulated sediments.

Question 49

Describe the tippecanoe reefs

Answer 49

– Organic reefs are limestone structures
constructed by living organisms.
– The first skeletal reef builders were the archaeocyathids of the
Cambrian.
– Coral and stromatoporoid reefs became common in the Middle Ordovician.
– Reef and evaporite deposits are abundant in
the Middle Silurian rocks of the modern Great
Lakes region.
– The Michigan Basin is surrounded by large Silurian barrier reefs.

Question 50

*Describe the formation of the tippecanoe evaporites (exam objective - Describe the association between barrier reefs and evaporite basin deposits during the
Early Paleozoic)

Answer 50

– Reef and evaporite deposits are abundant in
the Middle Silurian rocks of the modern Great
Lakes region.
– The Michigan Basin is surrounded by large Silurian barrier reefs.
– The reefs restricted
seawater circulation into
the basin, which allowed for the precipitation of evaporites, including anhydrite (postdepositionally-
dehydrated gypsum) and rock salt (halite).
• In general, evaporite salts precipitate from seawater in a specific order, beginning
with the least water-soluble and ending with the most soluble.
• Calcite (CaCO3) precipitates first, then gypsum (CaSO4•2H2O) and finally halite (NaCl). After burial, gypsum dehydrates to
anhydrite (CaSO4).
• Reef organisms cannot live in highly saline evaporating brines.
• The relationships between the growth of the reefs and the formation of the evaporites in the Michigan Basin are not completely understood.

Question 51

Describe the Appalachian Mobile Belt and the Taconic Orogeny

Answer 51

• Appalachian mobile belt - first Phanerozoic orogeny in North America began in the Middle Ordovician.
• The mountain building from the orogeny affected the climate and sedimentary history of the craton
• From Sauk time (Neoproterozoic to Early
Ordovician), the Appalachian region was a broad passive continental margin.
• The Iapetus Ocean was growing at a divergent
plate boundary.
• The Appalachian mobile belt became “mobile”
once the oceanic Iapetus plate began to subduct under the continental Laurentia plate. The Taconic orogeny occurred beginning with the collision of an island arc with Laurentia.

Question 52

What are the two depositional environments of the Appalachian Mobile belt

Answer 52

1. Shallow water carbonate platform
   • Extended from Newfoundland to Alabama.
   • Formed during the transgression of the Sauk Sea.
   • Carbonate deposition ceased along the east coast
   in the Middle Ordovician.
2. Deep-water deposits
   • Replaced the carbonates.
   • The sediments mark the onset of mountain building and volcanism, the Taconic orogeny.
   • Black shales, sandstones, graywackes, and volcanic
   deposits.
   • Deep-sea lava flows, volcanic ash layers, and intrusive igneous bodies from present-day Georgia to
   Newfoundland during the Middle to Late Ordovician.

Question 53

What is a clastic wedge?

Answer 53

an extensive accumulation of mostly detrital sediments deposited adjacent
to uplifted areas.
– Associated with the Taconic orogeny, called the
Queenston Delta.
– Sediments are thickest and coarsest near the
originating highlands and become thinner and
finer-grained away from the source area.
– Eventually grade into carbonate cratonic facies
(west of the highlands).
• For example the Queenston Delta Clastic Wedge
– More than 600,000 cubic kilometers of rock
weathered and eroded to form the Queenston
Delta sedimentary rocks.
– Based on this volume, the Taconic Highlands were at least 4,000 meters high (similar to Canadian Rockies today).

Question 54

What were the early paleozoic mineral resources

Answer 54

• Sand and gravel can be mined from
Queenston delta sediments (construction)
• Limestone (cement).
• Silica sand from basal sandstones - used in
manufacturing of glass and refractory bricks
and as hydraulic fracturing sands in oil and
gas recovery.
• Gypsum (drywall and plaster).
• Halite (seasoning, de-icing, chemicals).

Question 55

What periods are in the late paleozoic era

Answer 55

• devonian
• carboniferous (Mississippian and Pennsylvian)
• permian

Question 56

Describe the late paleozoic paleogeography

Answer 56

• Coals, evaporites, and tillites indicate a variety of climatic conditions during the Late Paleozoic.
• Major glaciations and warmer interglacial
episodes occurred over much of Gondwana
as the continent continued to move over the
South Pole during the Late Mississippian to
Early Permian.
• Waxing and waning glaciers had profound
effects on sea level and biota.
• Continental collisions produced the supercontinent Pangaea by the end of the Permian and produced high mountains that affected oceanic and atmospheric circulation patterns.

Question 57

*Describe the paleogeography of the Devonian period of the late paleozoic era (exam objective - Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the Late Paleozoic and how they relate to the formation of Pangea)

Answer 57

– Following the Taconic orogeny, the southern
Iapetus Ocean narrowed between Laurasia and
Gondwana.
– Mountain-building continued along the eastern margin of Laurasia from the Acadian orogeny.
– Erosion of the highlands produced vast amounts
of red fluvial sediments in northern Europe (Old
Red Sandstone) and the eastern US (the Catskill
Delta).

Question 58

Describe the paleogeography of the Devonian period of the late paleozoic era

Answer 58

– Gondwana moved over the South Pole, resulting in extensive continental glaciation.
– Advancing and retreating glaciers affected eustatic sea level and sedimentation patterns on the cratons.
– Gondwana began colliding with Laurasia
during the Early Carboniferous, which
resulted in the Hercynian, Appalachian, and
Ouachita mobile belts.
– The Ouachita Mountains of Oklahoma and Arkansas formed last, during the Late
Carboniferous and Early Permian.
– The Carboniferous coal basins of the eastern US,
western Europe, and the Donets Basin of the
Ukraine lay near the equator. The absence of
strong seasonal growth rings in tree fossils
indicate that the climates were warm and wet.

Question 59

Describe the paleogeography of the Permian period of the late paleozoic era

Answer 59

– Pangaea fully assembled.
– Panthalassa was the enormous ocean that
surrounded Pangaea.
– The waters of Panthalassa probably freely circulated, which led to more equable water
temperatures worldwide.
– The large landmass of Pangaea and the high
mountains from the Hercynian (Variscan),
Alleghenian, and Ouachita orogenies resulted in
widespread arid and semiarid climates on the
supercontinent – rain shadow of high mountains.
– Extensive Permian red beds and evaporites
occurred in western North America, central Europe, and parts of Russia.

Question 60

*Explain how the late paleozoic era evolved North America (exam objective - Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the Late Paleozoic and how they relate to the formation of Pangea)

Answer 60

• Late Paleozoic climates of North America
were diverse and included periods that
produced extensive:
– Shallow-marine carbonates.
– Swamps that resulted in coal.
– Dry evaporite-forming conditions.
• Large fluctuations in eustatic sea level
from advancing and retreating glaciers.
• Ordovician Taconic orogeny continued
with the Caledonian, Acadian, Alleghenian
and Ouachita orogenies, which were
associated with the assembly of Pangaea.

Question 61

Describe the Kaskaskia Sequence of the Late Paleozoic era

Answer 61

• Middle Devonian to Late Mississippian
• Boundary with underlying Tippecanoe Sequence is marked by a major unconformity.
• Kaskaskia Sea
transgressed over a low-relief craton.
• Most basal deposits are well-sorted quartz
sandstones (e.g., Oriskany Sandstone of New York and Pennsylvania).
• In the US, the sediment sources of the basal Kaskaskia sandstones were mostly the eroding highlands of the Appalachian mobile belt, exhumed Cambrian and
Ordovician sandstones along the flanks of the Ozark Dome, and
exposures of the
Canadian Shield in the Wisconsin area.
• Other basal rocks of the Kaskaskia Sequence are carbonates.
• Except for widespread Upper Devonian
and Lower Mississippian black shales, the majority of Kaskaskian rocks are
carbonates, including reefs, and associated evaporites.
• Major reef building occurred in many parts of the world during the early Late Devonian.
– After the deposition of the Upper Devonian to
Lower Mississippian black shales, extensive
shallow sea carbonate deposition resumed on
the North American craton for the rest of the
Mississippian period.
– The Mississippian carbonates contain crossbedding, ripple marks, and abundant crinoid
fossils
– Reefs were abundant, but much smaller than the complexes of the earlier Paleozoic.
– During the Late Mississippian, the Kaskaskia
Sea regressed from the North American
craton.
– Detrital clastic sediments, including the petroleum-bearing sandstones of the Illinois Basin, replaced the carbonates.
– Weathering and erosion produced a cratonwide
unconformity, which marked the end of the Kaskaskia Sequence.

Question 62

Describe the development of reefs in Western Canada in the late Paleozoic era

Answer 62

– These Middle and Late Devonian reefs have
large reserves of petroleum.
– Reefs formed as the Kaskaskia Sea transgressed
southward in western Canada.
– By the end of the Middle Devonian, the reefs
coalesced, restricted the flow of seawater and
extensive evaporites precipitated.
– More than 50% of the world’s potash, which is
used in fertilizers, comes from these evaporites.

Question 63

Describe how shale was formed during the late Paleozoic era

Answer 63

– Beginning in the Middle Devonian and continuing into the Late Devonian, the
deposition of shales and coarser detrital rocks
replaced carbonate-evaporite deposition in
parts of North America.
– The detrital deposits originated from the rising
mountains of the Acadian orogeny.
• Black Shales
– By the end of the Devonian, widespread black
shales were forming over much of the North
American craton.
– The Chattanooga Shale in the eastern US.
– Upper Devonian-Lower Mississippian black
shales are typically noncalcareous, thin
bedded, and less than 10 meters thick.
– Fossils are rare. Some Devonian black shales
contain conodonts
– Exact origin of the shales is debated.
– Formed in undisturbed anaerobic bottom waters
in shallow seas.
– High biologic activity in overlying oxygenated
surface waters.
– Organic matter rained down on the seafloor and
depleted the sediment-water interface of
dissolved oxygen.
– Black shales contain uranium and are petroleum
source rocks.

Question 64

Describe the Absaroka sequence

Answer 64

• Pennsylvanian through Early Jurassic
• The unconformity between the Kaskaskia and Absaroka sequences essentially
separate the North American Mississippian
and Pennsylvanian systems and the European Upper and Lower Carboniferous
systems.
• The lower-most sediments of the Absaroka Sequence are largely confined to the margins of the North American craton.
• The deposits were thickest in the east and southeast, near the highlands of the
Appalachian and Ouachita mobile belts.
• The rocks laterally change from nonmarine detrital rocks and coals in the east to largely marine detrital and carbonates in the west.
– Intracratonic basins filled with sediment during
the Late Pennsylvanian.
– Absaroka Sea slowly retreated from the craton.
– In the Early Permian, the sea extended from
Nebraska to west Texas.

Question 65

Describe the cratonic uplift that occurred to form the ancestral rockies

Answer 65

– Severe cratonic deformation in North America during the Pennsylvanian period.
– Greatest deformation in southwest, formed
Ancestral Rocky Mountains.
– Precambrian igneous and metamorphic rocks and overlying Paleozoic
sedimentary rocks
were eroded.
– Red arkosic sandstones and conglomerates
accumulated in surrounding basins.
– The uplift may have resulted from the collision
of Gondwana with Laurasia along the Ouachita mobile belt.
• Mountain building during the Late Paleozoic had profound effects on climate
and sedimentation history, and wasassociated with the formation of Pangaea
during the Permian.

Question 66

*Explain the formation of evaporite deposits and reefs during the Absaroka sequence (exam objective - Define cyclothems and how they relate to deposition of coal during the deposition of
the Absaroka sequence)

Answer 66

– Thick evaporites were deposited in Kansas
and Oklahoma by the Middle Permian.
– By the Middle Permian, the Absaroka Sea had
retreated southward to western Texas and
southern New Mexico.
– During the Middle and Late Permian, lagoons,
massive reefs, and open-shelf environments of the Absaroka Sea existed in western Texas and southern New Mexico.
– During the Middle to Late Permian, limestone,
evaporites, and red bed sandstones accumulated
behind massive reefs in western Texas and
southern New Mexico.
– Important petroleum reserves occur in the
Permian reefs.
– By the end of the Permian period, the Absaroka Sea had retreated off the North American craton.

Question 67

*Describe the formation of the cordilleran mobile belt during the late paleozoic era (Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the
Late Paleozoic and how they relate to the formation of Pangea)

Answer 67

– During the Neoproterozoic and Early Paleozoic, the Cordilleran area of western North America was a passive continental
margin.
– During the Late Devonian and Early Mississippian, the Antler orogeny occurred.
• Subduction? began along the former passive margin, and an eastward moving island arc collided with the western part of the North
American craton to produce a highland area.

Question 68

• Describe the formation of the appalachian mobile belt during the late paleozoic era (exam objective - Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the
  Late Paleozoic and how they relate to the formation of Pangea) (exam objective - Discuss the significance of the Old Red Sandstone and Catskill delta rocks to the Acadian orogeny)

Answer 68

– Caledonian mobile belt in western Baltica (now Scotland, Ireland, and Norway).
– During Middle Ordovician, subduction of oceanic Iapetus plate under Baltica continent.
– Caledonian orogeny - Mountain building along
the western margin of Baltica.
– Clastic deposition - Old Red Sandstone.
– From Newfoundland to Pennsylvania.
– Northern oceanic Iapetus plate subducted under
Laurentia.
– Orogeny occurred when Baltica continent collided with Laurentia continent to form Laurasia.
– Weathering of the highlands produced the
Catskill Delta and Old Red Sandstone clastic
wedges.

Question 69

*Describe the formation of the ouachita mobile belt during the late paleozoic era (exam objective - Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the Late Paleozoic and how they relate to the formation of Pangea)

Answer 69

– The remains of the belt currently extend from the subsurface of Mississippi to the Marathon
region of western Texas.
– During the Neoproterozoic to the Early Mississippian in this region, shallow-water
detrital and carbonate sediments accumulated
on a broad continental shelf.
– Bedded cherts and muds that became shales formed in deeper waters.
– The Ouachita orogeny began in the Mississippian
period as the region changed from a passive
continental margin into an active convergent plate
boundary.
– The orogeny continued through the Pennsylvanian and Early Permian periods as Gondwana collided with Laurasia.
– A large mountain range, including the Ouachita
and Marathon mountains, formed
– Ozarks of Arkansas are all that’s left.
– The mountains largely eroded during the
Mesozoic Era.
– Microplates collided to form part of Central
America.
– The compressive forces of the Ouachita mobile belt also broadly uplifted the
southwestern part of the North American craton.

Question 70

*Explain the impact of the Alleghenian and Ouachita orogenies (Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the Late Paleozoic and how they relate to the formation of Pangea)

Answer 70

– Hercynian mobile belt of Europe and the
Appalachian and Ouachita mobile belts of North America mark where Laurasia collided
with Gondwana.
– Gondwana and southern Laurasia collided in the Ouachita mobile belt during the Pennsylvanian and Permian.
– Eastern Laurasia (Europe and southeastern
North America) collided with Gondwana
(Africa) as part of the Hercynian (Variscan)-
Alleghenian orogeny.
– Hercynian (Variscan) fold belt was in Europe. The Alleghenian tectonic event was in the North America.
– The Hercynian (Variscan)- Alleghenian orogeny
began during the Mississippian and became more intense during the Pennsylvanian and Permian
periods.
– The Hercynian (Variscan), Alleghenian, and Ouachita orogenies represent the joining of Laurasia and Gondwana to form the
supercontinent Pangaea.

Question 71

What role did microplated and terranes play in the formation of Pangaea?

Answer 71

• Numerous microplates and continental terranes existed during the Paleozoic.
• These microplates and terranes contributed to orogenies and the formation
of Pangaea.
• Avalonia microcontinent (Atlantic Canada)
• Iberia-Armorica terrane-microplate - Iberian peninsula and surrounding parts of southwestern Europe.
• Perunica (Bohemia).
• Numerous Alpine fragments (Austria).
• Paleozoic terranes and microplates separated from continents and collided
with other continents.
• Paleozoic terranes and microplates often developed their own unique fossil assemblages (fauna ; flora).

Question 72

What are the late paleozoic era mineral resources?

Answer 72

• Oil and natural gas deposits.
– Devonian rocks of Alberta and the Michigan, Illinois, and Williston (North Dakota and Montana) basins.
– Natural gas in Devonian black shales.
– Permian reefs of western Texas.
• Coal (especially Pennsylvania period).
– Bituminous
– Anthracite (Pennsylvania)
• Salt deposits.
– Permian Delaware Basin of Texas.
– Zechstein deposits of Europe.
– Devonian Elk Point Basin, Canada.
– Michigan Basin.
• Limestone - used in manufacturing of
cement and steel.
• Silica sand - glass manufacturing and
bricks for blast furnaces.
• Tin, copper, gold, and silver in Late Paleozoic rocks.
• Lead and zinc deposits in Mississippian rocks of Missouri.

Question 73

What contribution did Charles D. Walcott contribute to our understanding of the early history of life?

Answer 73

• In 1909, geologist Charles D. Walcott discovered the impressions of numerous Middle Cambrian soft-bodied organisms
in the Burgess Shale of British Columbia,
• The deposition site for the Burgess Shale was the base of a steep submarine
escarpment.
• The animals preserved in the shale lived on mud banks that formed along the top of the escarpment.
• Occasionally, the mud banks would become
unstable and the community would slide
down the slope of the escarpment as a
turbidity current.
• The organisms would be buried and preserved in the deep-water anaerobic
environment.
• The anaerobic water and muds prevented bacteria and scavengers from destroying the soft-bodied organisms. They were
preserved as carbonaceous films.

Question 74

What was the Cambrian explosion?

Answer 74

• Multicelled Ediacaran fauna
presumably had a long Precambrian history, but they lacked hard parts and were not well-preserved in the fossil record.
• The “Cambrian explosion” refers to the appearance of many different skeleton bearing animal fauna in the Early Cambrian.
• The animals evolved over several million years in the Early Cambrian.
• Scientists investigate the Cambrian explosion by:
– Looking for new fossil localities.
– Comparing the molecular sequences of the same gene from different living species to determine their evolutionary history.
– Hox genes Basic body plans evolved by the Early Cambrian.
• The cause(s) of the relatively rapid evolution is still debated.
• More than likely, the explosion was due to
a number of biologic and geologic factors,
perhaps including:
– Glaciations in the Proterozoic followed by
global warming in the Cambrian.
• Other possible geologic and biologic
factors for the Cambrian explosion:
– Possible changes in ocean chemistry could
favor the evolution of mineralized skeletons.
• Possible increases in the calcium concentration of
ocean water from increased volcanism.
– Evolution of predators.
• In response, shells and skeletons would offer
greater protection from predators and survival.

Question 75

Explain how Shelly Fauna emerged in the Paleozoic era

Answer 75

• Earliest known organisms with hard parts were small and calcareous tubes found in the Neoproterozoic Ediacaran faunas.
• These were followed by microscopic skeletonized fossils in the Early Cambrian.
• Endoskeletons, internal.
• Exoskeletons, external, including shells.
• Skeletons would provide organisms with the following advantages:
– Protection against
predators.
– Protection against ultraviolet radiation, which
would allow them to live in shallower water.
– Protects the animal from drying out in an intertidal environment.
– Provides support for muscles to attach, which
allows the sizes of the organisms to increase.
• Early Cambrian
fossil record
indicates that the
evolution of shelly
invertebrates was
a response to the
evolution of new
predators.

Question 76

What characterized the start and the end of the Paleozoic era

Answer 76

• At the beginning of the Paleozoic, abundant animals with skeletons
appeared.
• The end of the Paleozoic witnessed the worst mass extinction in the Earth’s
history.

Question 77

List the different Phylum of invertebrate marine that emerged during the Paleozoic period

Answer 77

1. Protozoans - first animals, unicellular eukaryotes
2. Porifera - sponges, multi-celled, filter feeding animals, first group to branch off from other animals
3. Archaeocyatha - “ancient cups”, multi-celled, filter feeding animals
4. Cnidaria - jelly fish, coral
5. Bryozoa - “moss animals”, filter feeders
6. Barchiopoda - had upper and lower valves vs. left and right in bivalves
7. Mollusca
8. Annelida - segmented worms
9. Arthropoda - trliobites, insects, scorpians, crabs, lobsters
10. Echinodermata - sea urchins, sea cucumbers,
11. Hemichordata - acorn worm, graptolites

Question 78

Explain how invertebrate marine life began in the beginning of the Cambrian period of the Paleozoic era

Answer 78

– Major transgressions on world’s cratons opened up vast shallow seas for inhabitation.
– Plate tectonics not only affected ocean circulation patterns, but also environments and biota.

Question 79

*Explain how the cambrian marine community developed (exam objective- Discuss the origin of animals with skeletons (hard parts) during the Early Paleozoic - probably need to find a more complete answer then from your slides)

Answer 79

– New body plans evolved.
– Animals moved into new ecologic niches.
– High percentage of evolutionary experiments.
– Almost all major invertebrate phyla evolved
during the Cambrian, but some phyla only had a
few species.
– Trilobites, inarticulate brachiopods, and
archaeocyathids were major skeletonized invertebrates.
– Trilobites
• About 50% of total Cambrian fauna.
• Arthropods.
• Benthonic, mobile, sediment feeders.
– Brachiopods
• Inarticulate - Chitinophosphate shells.
• Articulate - teeth and sockets, calcite shells.
• Benthonic, sessile, suspension feeders.
– Archaeocyathids
• Formed reefs
• Extinct by end of Cambrian.
• Benthonic, sessile, possible suspension feeders

Question 80

*Describe invertebrate marine life on the burgess shale biota during the Cambrian period (exam objective - Describe the origin of the Burgess shale and why it preserves such a remarkable record of Cambrian fossils)

Answer 80

– Sauk Sea transgressed the Cordilleran shelf
and onto the western edge of the North American craton.
– Middle Cambrian mud banks formed.
– Many of the soft-bodied organisms are now extinct.
– They have the basic body plans from which all modern invertebrates evolved
– For years, most paleontologists placed the
bulk of the Burgess Shale biota into existing phyla.
– Other paleontologists now think that the biota
represent evolutionary “experiments” involving many phyla that went extinct.
– Debates continue over the classification of the biota.

Question 81

*Describe the Ordovician marine community during the Paleozoic period (exam objective - Outline the importance of conodonts for relative dating of sedimentary rocks - answer explains what conodonts are but NOT their importance in relative dating - need to find) (exam objective - Outline the different types of reef-builders that were active during the Paleozoic)

Answer 81

– Major transgression of the Tippecanoe Sea began in the Middle Ordovician.
– Many new marine habitats were soon filled by a variety of organisms.
– Brachiopods diversified.
– Adaptive radiation of bryozoans
– Increased diversity
and abundance of
acritarchs (organic
walled phytoplankton).
– Bryozoans,
stromatoporoids, and tabulate and rugose corals
became major reef builders in the Middle Ordovician.
– Articulate brachiopods
diversified in shallow marine
environments.
– Graptolites (extinct) -
planktonic animals abundant in Ordovician and Silurian.
- Conodonts (extinct) - microscopic tooth-shaped
feeding apparatus from an eel-like jawless swimming animal.

Question 82

Describe the Ordovician Mass Extinction

Answer 82

– Occurred at the end of the Ordovician.
– More than 100 families of marine invertebrates became extinct.
– In North America, about 50% of brachiopods and bryozoans died out.
– Extinction may have been caused by extensive glaciation at the South Pole on Gondwana
– Sea levels would have decreased, perhaps
limiting available habitat
– Many other hypotheses
• Anoxia, volcanism, gamma ray burst
– Surface waters cooled and would have stressed the phytoplankton acritarchs.
– Impacted the marine food web.

Question 83

*Describe the Silurian and Devonian Marine Communities in the Paleozoic era (exam objective - the different types of reef-builders that were active during the Paleozoic)

Answer 83

– After the Ordovician mass extinction,brachiopods, bryozoans, gastropods,
bivalves, corals, crinoids, and graptolites rediversified at the beginning of the Silurian.
– Major reef building in Silurian and Devonian.
– Stromatoporoids and tabulate and colonial rugose corals dominated the Silurian and Devonian reefs.
– Unlike many marine invertebrates, scorpion-like
eurypterids (Phylum
Arthropoda) also lived in brackish and fresh waters.
– Ammonoids, a subclass of cephalopods, evolved from nautiloids in the Early Devonian and rapidly diversified.
– Their distinctive suture patterns, short stratigraphic ranges, and widespread
distribution make them excellent guide fossils for the Devonian through the
Cretaceous.

Question 84

Explain the Devonian Mass Extinction

Answer 84

– World-wide near-total collapse of reef communities.
– Land-dwelling seedless vascular plants seemingly unaffected .
– Tropical marine groups were most severely affected, whereas higher latitude marine communities were not.
– Global cooling may have been responsible.
– Tropical organisms would have been severely
affected.
– Marine organisms living in cooler water could have migrated closer to the equator and survived.
– The closing of the Iapetus Ocean also reduced the area of shallow shelf environments, where many marine invertebrates lived.

Question 85

Describe the Carboniferous Marine Community during the Paleozoic era

Answer 85

– Brachiopods and ammonoids quickly
recovered after the Late Devonian extinction.
– Lacy bryozoans and crinoids reached their
greatest diversity during the Carboniferous.
– With the decline of stromatoporoids and
tabulate and rugose corals, reefs were smaller patches consisting of crinoids,
blastoids, lacy bryozoans, brachiopods, and calcareous algae.

Question 86

Describe the Permian Marine Community during the Paleozoic era

Answer 86

– Permian marine invertebrate communities
resembled Carboniferous ones.
– Bryozoans, sponges, and various types of calcareous algae were common.
– Permian communities not as widely distributed due to restricted size of shallow
seas on the cratons and less shelf space along the continental margins as Pangaea formed.
– Spiny or productid brachiopods important in
Texas reef complexes.
– Fusulinid foraminifera (microscopic calcite-shelled
organisms) first evolved in the Late Mississippian.
– They greatly diversified during the Pennsylvanian.
– They experienced further diversification during the
Permian.
– Fusulinids are important guide fossils for the
Pennsylvanian and Permian.

Question 87

What evidence first appeared in the Paleozoic era suggesting the existence of vertebrate?

Answer 87

• The discovery of 397-million-year-old (earliest
Middle Devonian) footprints in Poland changed our views of the origin and early evolution of tetrapods.
• Tetrapod means “four foot” and refers to intermediates between fish and the
earliest amphibians.
• The Polish footprints indicate that the
transition from lobe-finned fish to tetrapods occurred earlier than previously realized.
• The early tetrapods lived in coral-reef lagoons rather than streams, lakes, or
swamps as previously thought.
• In the Paleozoic Era, vertebrates and plants moved from water onto land.
• For both groups, the biggest barrier in the
transition to land was the method of reproduction.
• Evolution of seed plants and the amniote egg in animals removed this barrier.

Question 88

*Explain the evolution of vertebrate during the Paleozoic era (exam objective - Describe the characteristics of the ancestor of Phylum Chordata)

Answer 88

• The ancestors and early members of the phylum Chordata were soft-bodied
organisms that left few fossils.
• Chordate (Phylum Chordata) - an animal
that at least during part of its life cycle has:
– a notochord.
– a dorsal hollow nerve cord.
– pharyngeal slits.
• Vertebrates are a subphylum of Chordata.
• Yunnanozoon lividum is one of the oldest known chordates and lived in China 525 Ma - Cambrian
• Embryology suggests that chordates and echinoderms
may have shared a common ancestor.
• In embryos, the cells of chordates and echinoderms
divide by radial cleavage so that they are aligned
directly above each other. In all other invertebrates,
cells undergo spiral cleavage.
• Biochemistry of muscle activity and blood proteins are also similar.
• Fossils and evidence from molecular biology suggest that vertebrates evolved
shortly after their ancestral chordate, which may have resembled Yunnanozoon
lividum.

Question 89

*Explain the evolution of fish during the Paleozoic era (exam objective - Discuss the origin of animals with skeletons (hard parts) during the Early Paleozoic)

Answer 89

• The most primitive vertebrates are fish.
• The earliest known fish remains are Upper
Cambrian.
– Phosphatic scales and plates of Anatolepis, a
primitive marine jawless fish (class Agnatha).
• All known Cambrian and Ordovician fish were marine.
• Earliest freshwater fish from the Silurian.
• Ostracoderms - “bony skin” are the oldest fish in the class Agnatha.
• Ostracoderms were armored, jawless fish
that evolved during the Late Cambrian and became extinct in the Devonian.
• Most ostracoderms lived on the seafloor, including Hemicyclaspis.
• The vertical scales of Hemicyclaspis wiggled
sideways, which allowed the fish to propel itself along the seafloor.
• The eyes on the top of its head allowed it to see predators above.
• The fish probably sucked up bits of food in sediments through its jawless mouth.
• Pteraspis, another ostracoderm, was more
elongated than Hemicyclaspis and probably
an active swimmer.

Question 90

*Explain the evolution of jaws in fish (exam objective - Describe the evolution of jaws in early fish)

Answer 90

– Studies suggest that jaws evolved from the first
two or three anterior gill arches of jawless fish.
– The evolution of the jaw may have been first related to respiration rather than feeding.
– By evolving joints in forward gill arches, fish could open their mouths wider.
– By opening and closing its mouth, more oxygenbearing
water could be pumped by the gills.
– The modification from rigid to hinged forward gill arches let fish increase both their food and oxygen intake.
– The evolution of the jaw as a feeding structure quickly followed.
– The earliest jawed fishes are Early Silurian and are acanthodians (class Acanthodii).

Question 91

What are the different classes of fish in the Paleozoic era

Answer 91

• Agnatha
• Acanthodii
• Placodermii
• Chondricthyes
• Osteichthyes

Question 92

Describe the class Acanthodians of fish

Answer 92

– They had large spines, paired fins, scale coverings over much of their bodies, and reduced body armor.
– They may have been the ancestors of present-day bony and cartilaginous fish
groups.
– Acanthodians were most abundant in the Devonian and became extinct in the

Question 93

Describe the class Placoderms of fish

Answer 93

– Another group of jawed fishes.
– Evolved during the Silurian.
– Heavily armored.
– Lived in both the ocean and freshwater.
– Placoderms showed great diversity and included
bottom dwellers and predators.
– They reached peak abundance and diversity
during the Devonian and became extinct in the
Permian.
– Included the large Late Devonian predator,
Dunkleosteus.
– Dunkleosteus lived in mid-continental North
American epeiric seas.
– Possibly more than 12 metres long.
– Heavily armored head and shoulders.
– Flexible tail.
– Huge jaw with sharp bony teeth.

Question 94

Describe Cartilaginous fish (class Chrondrichthyes) from the Paleozoic era

Answer 94

– Evolved during the Devonian.
– Cartilaginous fish include modern sharks, rays, and skates.
– Cladoselache - primitive Late Devonian shark.

Question 95

Describe Bony fish (class Osteichthyes) from the Paleozoic era

Answer 95

– Bony fish evolved during the Devonian.
– Two groups:
• Ray-finned fish (subclass Actinopterygii)
• Lobe-finned fish (subclass Sarcopterygii)
– Amphibians evolved from lobe-finned fish.
– Ray-finned fish include modern trout, bass,
perch, salmon, and tuna.
• Lobe-finned Bony Fish
– Modern species characterized by muscular
fins.
– Coelacanths (order Coelacanthimorpha)
• Marine.
• Evolved in Devonian.
• Thought extinct in the Cretaceous until discovered
in 1938 off the coast of Madagascar.
– Lungfish (order Dipnoi)
• Fairly abundant in the Devonian.
• Today only three freshwater genera exist.
• “Lung” is a modified swim bladder, mostly used for
buoyancy. Lungfish have gills.
• The lung takes in air and allows the fish to survive
when lakes and streams dry up.
• The fish burrows into sediment to prevent dehydration
and breathes through the lung until water returns to the
lake or stream.
– Crossopterygians (order Crossopterygii) a type of lung fish
• Rhipidistian (suborder Rhipidistia)
crossopterygians were probably the amphibian
ancestral group.
• Rhipidistrians were dominant freshwater predators during the Late Paleozoic.
• Eusthenopteron - a rhipidistrian and transition form between fish and amphibians.
• Eusthenopteron - elongated body for swimming and muscular fins for moving on land.
– Bony fish expanded during the Late Paleozoic.

Question 96

Which fish became extinct during the Paleozoic era

Answer 96

– Ostracoderms, although armored, would have
been easy prey for swifter jawed fish.
– Ostracoderms became extinct at the end of the
Devonian, which coincided with the rapid evolution of jawed fish.
– Placoderms, like acanthodians, greatly decreased in abundance after the Devonian and became extinct in the Permian.

Question 97

*Explain the movement of vertebrate to land during Paleozoic era (exam objective - Describe the circumstances that led to the evolution of amphibians from lobe-finned fish - NOTE - information on slides does not really explain the circusmtances you will need to find this)

Answer 97

• During the Devonian, amphibians were the first vertebrates to live on land.
• Land plants evolved in the Ordovician.
• Insects, spiders, and perhaps snails also became land-living before amphibians.
• To live on land, vertebrates had to overcome several barriers:
– Desiccation (avoid drying out).
– Reproduction (amniote egg).
– Effects of gravity.
– Lungs for respiration.
• Limbs probably originally evolved to help fish move around in streams, lakes, or swamps choked with plants and other debris.
• Fossils of Acanthostega, a tetrapod found in the 360 mya Old Red Sandstone from Greenland, had limbs, but the limbs were too
weak to allow the animal to walk on land.
• Acanthostega had both lungs and gills.
• Ichthyostega, the oldest known amphibian, could walk on land and fossils are found in the Upper Devonian Old Red Sandstone of Greenland.
• In 2006, the “fishapod” Tiktaalik roseae was discovered in Late Devonian rocks on Ellesmere Island, Canada.
• It is an intermediate between lobe-finned fish and Acanthostega.
• Tiktaalik had gills and scales like a fish, but true tetrapod forelimbs, which included functional wrist bones and five digits.
• Late Paleozoic amphibians came in a variety of sizes, shapes, and modes of life, but did not resemble modern frogs, toads, newts, and salamanders.
• Labyrinthodonts.
– Up to 2 meters in length.
– Lived in streams and swamps.
– Ate fish, other amphibians, vegetation, and insects.
– A few species survived into the Triassic.

Question 98

Explain the mass extinctions that occurred during the Paleozoic period

Answer 98

• Tropical organisms tend to be more affected than organisms in temperate or
high latitudes.
• Species in many different phyla are affected, but in most cases the phyla
survive.
• Archaeocyatha is an example of an extinct
phylum.
• During the past 650 million years, the first extinction only affected acritarchs.
• Several extinctions occurred in the Cambrian, but only affected marine
vertebrates, especially trilobites.
• Ordovician mass extinction.
• Devonian mass extinction - reefs and fish.
• Permian mass extinction - worst in Earth’s history.
• Several Mesozoic mass extinctions.
– Late Cretaceous was the worst.
• Dinosaurs, flying reptiles, ammonoids, and marine
plesiosaurs and ichthyosaurs became extinct.
• Perhaps due to an asteroid impact .
• Several Cenozoic mass extinctions.
– Most severe at the end of the Eocene Epoch.
• Probably due to global cooling.
– Extinction at the end of the Pleistocene.
• Mostly affected large mammals.
• Marine mass extinctions may have occurred over hundreds of thousands or
even millions of years.
• Most mass extinctions probably due to climate changes rather than single global catastrophes, such as asteroid impacts.

Question 99

Describe the Permian Mass Extinction

Answer 99

– About 96% of marine invertebrate species
went extinct.
– Fusulinids, rugose and tabulate corals, trilobites, blastoids, and several orders of bryozoans and brachiopods disappeared.
– Extinction of about 70% of terrestrial vertebrate species.
– Nearly 33% of land insects went extinct.
– Cause(s) uncertain.
– Extinctions occurred over several millions of years, so an asteroid impact is unlikely.
– Reduced marine shelf area from the formation of Pangaea is unlikely.
• The supercontinent formed before the extinction.
– Glaciations waned in the Permian and are also eliminated as a cause.
– Deep-sea anoxia and increased CO2 levels in
the oceans are possible causes.
• Very little O2 circulated into deep oceans.
• Stagnant waters would have covered shelf regions.
– Global warming is another possible cause.
• Would have eliminated downwelling of cold, dense,
and oxygenated waters from polar regions into
lower latitudes.
• Resulted in stagnated and stratified oceans rather
than well-mixed and oxygenated waters.
– Widespread volcanism during the Late Permian.
• Massive fissure eruptions in Siberia.
• Released large amounts of greenhouse CO2 into the atmosphere.
• Chlorine and fluorine from the eruptions would have damaged the ozone layer and increased the
exposure of organisms to ultraviolet radiation.

Question 100

*Explain how reptiles evolved during the Paleozoic era (exam objective - Describe the major evolutionary adaptations that allowed reptiles to become the
dominant land animals over amphibians)

Answer 100

• Amphibians were limited in colonizing the land because they had to return to water
to lay their gelatinous eggs.
• The evolution of the amniote egg freed
reptiles from that restraint.
• Amniote egg - the developing embryo is
surrounded by a liquid-filled sac - amnion.
• The egg has a yolk (food sac) and allantois (waste sac).
• Reptiles also differ from amphibians in skull structure, jawbones, ear location, and
limb and vertebrate construction.
• Reptiles probably evolved from labyrinthodont amphibians by the Late
Mississippian.
• Oldest known reptile is Westlothiana from Late Mississippian rocks in Scotland.
• Early reptiles were loosely grouped together as protorothyrids.
• During the Permian, reptiles diversified and replaced amphibians.
• Reptiles were successful because of their eggs, advanced jaws and teeth, tough skin and scales to prevent desiccation, and
their ability to rapidly move on land.
• Pelycosaurs, or finback reptiles, evolved from protorothyrids during the
Pennsylvanian and became the dominant reptile group in the Permian.
– Edaphosaurus - a herbivore.
– Dimetrodon - a carnivore.
• The purpose of the back sail is unknown.
– Possibly to regulate body temperature by
catching the Sun’s rays or cooling with wind.
• Therapsids, mammal-like reptiles, evolved from carnivorous pelycosaurs in the Permian.
• Pelycosaurs became extinct during the Permian.
• Therapsids diversified into herbivores and carnivores.
• 2/3 of all reptiles and amphibians became extinct at the end of the Permian, but therapsids survived into the Triassic.
• Therapsids displayed the beginnings of mammalian features:
– Fewer skull bones.
– Enlarged lower jawbone.
– Differentiation of teeth.
– More vertical legs.
– Possibly covered with fur.
– May have been endothermic - warm blooded.
– They lived in cooler middle and higher
Permian latitudes, and not just low latitudes.

Question 101

Explain plant evolution during the Paleozoic era

Answer 101

• When plants made the transition from water to land, they had to solve many of the same problems as animals:
– Avoiding desiccation.
– Developing support.
– Reproduction.
– Effects of gravity.
• Plants initially evolved in seawater, then
moved into freshwater, and finally onto land.
• Land plants divided into:
– Vascular.
• Majority of modern land plants.
• Tissue system of specialized cells for movement of
water and nutrients.
– Nonvascular.
• Bryophytes (liverworts, hornworts, and mosses).
• No specialized cells.
• Tend to live in moist areas.
• Earliest land plants in Middle to Late
Ordovician.
– Probably nonvascular.
– Fossil plants with spores in Libya.
• Vascular plants evolved well before the Middle Silurian.
• Ancestor of vascular plants probably some type of green alga.
• No fossil transition found.
• Physiology indicates a link between green algae and vascular plants.
• Primitive seedless vascular plants (for example, ferns) resemble green algae in
their pigmentation, important metabolic enzymes, and type of reproductive cycle.
• Green algae are one of the few plant groups to transition from marine to
freshwater.
• Vascular tissues give support for land plants.
• Additional strength comes from lignin and cellulose in the plant walls.
• Cutin, an organic compound found in the
outer walls of land plants, provides protection against desiccation, ultraviolet
radiation, oxidation, and parasites.
• Roots and leaves improved nutrition.

Question 102

*Describe the Silurian and Devonian Floras (exam objectives - Describe how the evolution of gymnosperms enable them to become the dominant
element in the world’s flora)

Answer 102

– Cooksonia:
• Earliest known vascular land plant.
• Middle Silurian of Wales and Ireland.
– Earliest vascular land plants.
• Small, simple, leafless stalks.
• Seedless.
• Spore-producing structures.
• No true roots.
• Rhizome, underground part of the stem, provided
water and anchored the plant.
– Leaves, roots, and other plant structures did not evolve simultaneously, but at different times - mosaic evolution.
– Land plants greatly diversified during the Late
Silurian and Early Devonian.
– By the Late Devonian, forests of large treelike
plants (up to 10 meters tall) existed.
– Seedless vascular plants require moisture for
fertilization.
– The evolution of seeds in the Late Devonian allowed land plants to become independent of moist conditions and spread over the Earth.
– Gymnosperms - flowerless seed plants, have male and female cones.
– Before seed plants evolved, heterospory -
species produced two types of spores. Early
Devonian plant - Chaleuria cirrosa.
– Millions of years after the evolution of heterospory, progymnosperms evolved in the
Middle to Late Devonian.
– Progymnosperms - fern-like reproductive plants
with gymnosperm anatomy.
– Progymnosperms gave rise in the Late Devonian to seed plants.

Question 103

Describe the late carboniferous and permian floras

Answer 103

– Mississippian flora similar to Late Devonian.
– Pennsylvanian (Late Carboniferous) - major
source of world’s coal.
– Coal - altered plant remains that accumulated
in low, swampy areas.
– Seedless vascular plants dominated flora of
Carboniferous coal-forming swamps.
– Gymnosperms also important, especially in
non-swampy areas.
– Seedless vascular plants, the lycopsids and
sphenopsids, most important coal-forming
groups in the Pennsylvanian period.
– Lycopsids were small in the Devonian, but in
the Pennsylvanian, they achieved heights of
30 meters as Lepidodendron and Sigillaria.
– Calamites - 5 to 6 meter-tall sphenopsid.
– Living sphenopsids include the horsetail and
scouring rushes.
– Cordaites - group of tall Pennsylvanian
gymnosperm trees that lived on higher and
drier ground.
– Glossopteris - nonswamp plant that was so
abundant in Gondwana that it became major
evidence of continental drift.
– Pennsylvanian floras generally persisted into
the Permian, but climatic changes caused
them to become less abundant.
• The End of the Paleozoic Era
– Cordaites became extinct at the end of the Permian.
– Lycopsids and sphenopsids reduced in size after the Permian.
– Gymnosperms were better adapted to warmer
and drier climates, and came to dominate the
Permian, Triassic, and Jurassic landscapes

Question 104

*What is the evidence for the breakup of Pangaea (exam objective - Outline the evidence for the breakup of Pangea)

Answer 104

• Magnetic anomalies are well preserved in
the ocean crust associated with the breakup of Pangaea.
• The magnetic anomalies help determine the movement of continents
during the Mesozoic and Cenozoic eras.

Question 105

Describe the breakup of Pangaea during the Triassic period

Answer 105

• The breakup of Pangaea began with the separation of Laurasia from Gondwana
during the Triassic period.
• By the end of the Triassic, the newly formed and expanding Atlantic Ocean
separated North America from Africa.
• The breakup of Pangaea allowed water from the
Tethys Ocean (or Sea) to
flow into the expanding central Atlantic Ocean.
• During the Late Triassic and Early Jurassic, North America separated from South America.
• Waters from the Pacific Ocean flowed into the
newly formed Gulf of Mexico basin.
• Thick evaporites precipitated in the basin.
• Gondwana broke up during the Late Triassic
and Jurassic.

Question 106

Describe the break up of Pangaea during the Jurassic period

Answer 106

• Antarctica and Australia remained sutured together, but separated from Africa, India, and South America.
• India moved northward.
• South America and Africa began separating during the Jurassic with shallow seawater precipitating evaporites in the rift zone.
• The eastern end of the Tethys Ocean began closing to form a narrow Late Jurassic and Early Cretaceous seaway between Africa and Europe, the forerunner of the modern Mediterranean Sea.

Question 107

Describe the break up of Pangaea during the Cretaceous period

Answer 107

• By the end of the Cretaceous:
– Australia and Antarctica had separated.
– India had moved into the low southern latitudes.
– South America and Africa were widely separated by the growing south Atlantic
Ocean.
– Greenland had separated from Europe and North America.
• Seas transgressed the continents in the Cretaceous.
• Higher heat flow and expansion of oceanic
ridges likely explain the rise in global sea level – higher ocean floor = less volume.
• By the Middle Cretaceous, about 1/3 of the continents were covered by epeiric seas
• The final breakup of Pangaea occurred in
the Cenozoic.

Question 108

What was the effect of the breakup of Pangaea on global climates

Answer 108

– Climates result from complex interactions
between wind, ocean currents, and the location
and topography of the continents.
– During the Permian, arid climates occurred over
much of the large interior of Pangaea because:
• The interiors of supercontinents are far from oceanic sources of moisture.
• Mountain ranges also block moisture.
– Sedimentary rocks often provide important clues
about depositional environments.
• Evaporites, extensive red beds (sandstone) and sand
dunes form in deserts.
• Coals - warm or cool moist climates.
– During the Triassic, low and middle latitudes were
often dry with evaporites and red beds. Coals
indicate high latitudes were wetter.
– Seasonal monsoons along the Triassic Tethys Ocean.
– Continents moving northward from the breakup
of Pangaea in Late Triassic caused temperature
decreases in the high latitudes.
– With the breakup of Pangaea, atmospheric circulation patterns greatly accelerated in the Mesozoic
– Relatively equable worldwide climates
persisted through the end of the Cretaceous..

Question 109

What was the effect of the breakup of Pangaea on global climates and ocean circulation patterns

Answer 109

• During the Jurassic and Cretaceous, the middle- and low-latitude oceans were still quite warm.
  – With the breakup of Pangaea, oceanic patterns greatly accelerated in the Mesozoic.

Question 110

Describe the paleogeography changes that occurred during the Mesozoic

Answer 110

• Global sea rise in
Cretaceous.
• Marine deposition over much of North American
Cordilleran.

Question 111

Outline the major orogenies along the western margin of North America during the
Mesozoic

Answer 111

• Volcanic island arc off the west coast of North
American craton sutured onto North America in
the Permian or Triassic
(subduction). This
was the Sonoma
orogeny.

• During the Jurassic, the
Sierra Nevada, Rocky Mountains, and other lesser
mountain ranges formed during the Cordilleran
orogeny.

Question 112

Outline the changes to continental interior of North America during the
Mesozoic

Answer 112

the Paleozoic of North America consisted of a series of marine transgressions and regressions.
• Marine transgressions and regressions were not as important in North America
during the Mesozoic Era
– Deposition in some interior seaways, typically
adjacent to uplifting mountain ranges
– Appalachian mountains continue to erode
• Most of the continental interior of North America was above sea level during the Mesozoic.
• Two sequences in the Mesozoic - the Absaroka Sequence (Late Mississippian to Early Jurassic) and the Zuni Sequence (Early Jurassic to Early Paleocene).

Question 113

Outline the changes to eastern coastal region of North America during the
Mesozoic

Answer 113

• During Early to Middle Triassic, coarse detrital sediments from the eroding
Appalachian Mountains (Alleghenian orogeny) filled surrounding basins.
• The heights of the Appalachian Mountains
were greatly reduced.
• During the Late Triassic, North America began to separate from Africa.
• Fault-block basins formed from Nova Scotia to North Carolina
• Erosion of fault-block mountains produced
the thick and poorly sorted non-marine detrital sediments of the mostly Late Triassic and partially Early Jurassic Newark Group.
• Extensive lava flows occurred on the floors
of the fault-block basins.
• Numerous dikes and sills intruded in the basins, including the Palisades sill
along the Hudson River in the New York-New
Jersey area.
• As the Atlantic Ocean formed and grew, the eastern coast of North America transformed from a rifting zone into a passive continental margin.
• The fault-block mountains of eastern North America eroded during the Jurassic and Early Cretaceous.
• Sediments from the eroding Appalachian
Mountains contributed to the growing continental shelf.
• During the Cretaceous, the Appalachian region was elevated again and shed
additional sediments onto the continental shelf.
• These rocks are currently exposed in a belt from Long Island, New York to Georgia.

Question 114

Outline changes to the gulf coast region of North America during the
Mesozoic

Answer 114

• The Gulf region was above sea level until the Late Triassic.
• North America separated from South America during the Late Triassic and Early
Jurassic, and the Gulf of Mexico began to form.
• Ocean water flowed into the Gulf of Mexico basin.
• Evaporites precipitated in the shallow and restricted basin during the Jurassic.
• Evaporites - more than 1,000 meters thick.
• By Late Jurassic, the Gulf of Mexico was deeper and less restricted.
• Evaporite precipitation ceased and normal marine conditions occurred.
• During the Cretaceous, northward transgressing seas flooded the Gulf Coast
region.
• As part of the transgression, fine-grained
deep-water sediments were deposited over nearshore sands.
• Following a major regression at the end of
the Early Cretaceous, a major transgression created a wide seaway from the Arctic to the Gulf of Mexico
• Reefs were widespread in the Gulf Coast region during the Cretaceous.
• The reefs were mostly composed of rudist bivalves.
• Because of their high porosity and permeability, rudist reefs are excellent
petroleum reservoirs..

Question 115

*Outline the major orogenies along the changes to the western margin of North America during the
Mesozoic (objective on study guide)

Answer 115

• Except for Late Devonian-Early Mississippian Antler orogeny, little tectonism occurred in the Cordilleran
region of western North America during the Paleozoic.
• Island arcs and ocean basins off the west
coast of North America during the Permian.
Sonoma orogeny
– During the Permian-Triassic Sonoma orogeny,
subduction of the Farallon oceanic plate caused the island arc system to collide with the North American craton.
– The island arcs were sutured onto the North
American craton and formed the landmass
Sonomia.
– During the Late Triassic, a steeply dipping
subduction zone developed on the western
margin of North America.
Cordilleran orogeny
– The ocean-continent convergence zone
involving the Farallon oceanic plate and the
western North American continent controlled
Cordilleran tectonics for the rest of the Mesozoic and most of the Cenozoic Era.
– Cordilleran orogeny refers to the mountainbuilding
activity that began in the
Jurassic and continued into the Cenozoic Era.
– Cordilleran orogeny consisted of a series of
mountain-building events that occurred in
different regions at different times, but
overlapped to some extent.
– The events involved the western movement of
the North American continental plate and the
subduction of the Farallon plate.
Nevedan orogeny
- was the first event of the
Cordilleran orogeny.
– Late Jurassic into the Cretaceous.
– Large volumes of granitic magma accumulated.
– Sierra Nevada, Southern California, Idaho, and Coast Range batholiths formed.
– Franciscan Complex
• 7,000 meters thick.
• Chaotic mix of graywackes, volcanic breccias,
siltstones, black shales, chert, pillow basalts.
• Continental shelf, slope, and deep-sea sediments
and volcanic rocks brought into a submarine
trench.
• Blueschist metamorphism from subduction - high
pressure, temperatures relatively cool.
– Great Valley Group - 16,000 meters of
conglomerates, sandstones, siltstones, and
shales that were deposited on the continental
shelf and slope while the Franciscan deposits
were accumulating in the trench.
– Franciscan Complex and Great Valley Group
were squeezed onto the edge of the North
American craton by the subducting Farallon
plate.
– Late Cretaceous
• Thrusting occurred farther east up to the Idaho-
Washington border.
• Most volcanism and plutonic activity migrated
eastward into Nevada and Idaho.
• Eastward migration caused by the subduction of
Farallon plate changing from a high to low-angle.
Sevier Orogeny
– Second event of the Cordilleran orogeny.
– Caused by subducting Farallon plate.
– Mostly Cretaceous.
– Affected western North America from Alaska to Mexico.
– Numerous overlapping low-angle thrust faults.
– Produced generally north-south trending mountains from Montana to western Canada.
Laramide orogeny
– Final episode in the Cordilleran orogeny.
– Late Cretaceous to Early Cenozoic.
– Occurred east of Sevier orogenic belt.
– Rocky Mountains mostly formed in Cenozoic.

Question 116

Describe Mesozoic sedimentation that occurred in the western region

Answer 116

– Early Triassic Cordilleran mobile belt includes
shallow-water sandstones, shales, and limestones.
– During the Middle and Late Triassic, the western shallow sea regressed.
– Red beds formed.
• Lower Triassic Moenkopi Formation of US southwest.
– Lower Triassic Moenkopi Formation
• Mudstones.
• Mud cracks, ripple marks, and amphibians and reptile tracks.
• Depositional environments - streams, floodplains, and freshwater and brackish ponds.
• Halite and gypsum crystal casts indicate arid climates
– Upper Triassic Shinarump
Conglomerate
• Unconformably overlies the Moenkopi Formation.
– Upper Triassic Chinle Formation
• Multicolored shales, siltstones, and sandstones.
• Petrified wood of Petrified Forest National Park,
Arizona.
• Fossils of labyrinthodont amphibians, phytosaurs,
and small dinosaurs.
• Similar pollen to Lower Newark Group of eastern
US - indicates similar ages
– Early Jurassic
• A lot of large cross-bedded, wind-blown
sandstones.
• Wingate Sandstone - desert dune deposits.
• Kayenta Formation - stream and lake deposits.
• Navajo Sandstone - large cross-bedded coastal
dunes..
– Middle Jurassic
• Sundance Sea twice flooded the interior of western North America and
Sundance Formation
deposited.
– Late Jurassic
• Mountains of Nevadan Orogeny shed sediments
eastward.
• Sediments deposited in the Sundance Sea to form
the sandstones, mudstones, shales, and local
conglomerates of the Morrison Formation.
• Morrison Formation rich in Jurassic dinosaur
fossils, which were mostly deposited in streams
during flooding.
• Soils in Morrison Formation indicate a dry climate.
– In the Early Cretaceous, Arctic waters spread
southward over the North American craton to
form a large in-land sea in the Cordilleran
region.
– In the Middle Cretaceous, transgressions occurred on other continents, perhaps from the expansion of very active oceanic
spreading ridges.
– Widespread deposition of black shales occurred in the Middle Cretaceous.
– By Late Cretaceous, the Cretaceous Interior
Seaway extended from the Arctic to the Gulf of Mexico and occupied the areas to the east of the Sevier orogenic belt.
– Sediment deposition was controlled by sealevel
changes, climate, and tectonics.
– The eastern margin of the Cretaceous Interior Seaway received little sediment from the relatively low relief to the east.
– The western shoreline of the seaway shifted back and forth in response to sediment supply from the Sevier orogenic belt to the west.
– Facies relationships in the sediments of the western Cretaceous Interior Seaway show lateral changes from conglomerates and
coarse sandstones adjacent to mountain belts
to finer sandstones, siltstones, shales, and
limestones and chalks in the east.
– During times of especially active mountain
building, clastic wedges of gravels and sands
prograded further east.
– At the end of the Mesozoic Era, the
Cretaceous Interior Seaway withdrew from
the craton.
– Marine waters retreated north and south.
– Marginal marine and continental deposition
resulted in the formation of coal-bearing deposits on the coastal plains.

Question 117

What role did accretion of terranes play in the growth of western north america?

Answer 117

• Terranes are small lithospheric blocks that
originated from elsewhere.
• They include island arcs, oceanic crust, and small fragments of continents, which accreted onto larger continents.
• They differ from each other and continents in fossil content, stratigraphy, structural trends, and paleomagnetic properties.
• Perhaps, more than 25% of the western margin of
North America originated from the accretion of
terranes.

Question 118

Describe the mesozoic mineral resources

Answer 118

• Mesozoic rocks contain a variety of resources, including coal, petroleum,
uranium, gold, and copper.
• Important petroleum reserves formed in the Middle East during the Mesozoic Era.
• The Jurassic Louann Salt formed, which later created important oil and gas traps in the Gulf of Mexico.
• The richest uranium deposits in the US occur as the mineral carnotite in Mesozoic sandstones of the Colorado Plateau of
Colorado and adjoining states of Wyoming, Utah, Arizona, and New Mexico.
• Jurassic “Minette” iron ores of western Europe.
• Some important diamond deposits in South Africa are associated with
Cretaceous volcanic kimberlite pipes.
• Jurassic intrusive rocks in the Sierra Nevada provided gold for the California
“Gold Rush.”
• The world’s largest copper deposits
formed during the Mesozoic and Cenozoic
along the western margins of North and
South America.

Question 119

*Exam objective - Describe the origin of the Great Oxygentation event (topics 8 & 9 Proterozoic Earth and Proterozoic Life)

Answer 119

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Question 120

*Exam objectives - Outline the major orogenies along the eastern margin of Laurentia/Laurasia during the
Late Paleozoic and how they relate to the formation of Pangea (Topic 11 Late Paleozoic earth)

Answer 120

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Question 121

*Exam objective - Outline the evidence for the major transgressive and regressive sequences in
Laurentia/Laurasia during the Late Paleozoic (Topic 11 Late Paleozoic earth)

Answer 121

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Question 122

*Exam objective - Discuss the significance of the Old Red Sandstone and Catskill delta rocks to the Acadian orogeny (Topic 11 Late Paleozoic earth)

Answer 122

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Question 123

*exam objective - Outline the importance of conodonts for relative dating of sedimentary rocks (paleozoic invertebrates - topic 12)

Answer 123

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Question 124

*exam objective - Outline the reasons for sea level changes in North America during the Mesozoic (mesozoic earth - topic 14)

Answer 124

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