The Mid-Cretaceous Period
Presented by
Rodney Anderson, Kim
Barkewitz,
Ryan Marks, Mark Smyczynski,
and Bettina Vuong
May 1, 2001
What in store
¬Overview of the Cretaceous
Period
¬Recent stages of continental
drift
¬K-T mass extinction
¬Cooling of earth
¬Formation of the Himalayas
¬Rockies and the influence on
climate
¬Final thoughts
The Mid-Cretaceous
Period
¬100 million years ago (ma)
¬Mean global surface
temperature ~ 6 to 8 degrees above today’s
¬Little evidence of ice sheets
of continental scale
¬Subtropical plants and
animals lived far poleward
Geochemical Models
¬Suggest high levels of CO2
¬Translate to high
temperatures
¬Models suggest that
Crustaceous period was very warm and the earth may experience the warm
time
period again
Recent Stages of
Continental Drift
¬Early stages of the
Cretaceous Period marked the breakup of the super-continent, Pangea
K-T Mass
Extinction
¬Background Information
¬ Occurred 65 million years
ago
¬ Second largest mass
extinction event in geological history
¬ The first occurred 250
million years ago, triggered by a collision with a comet or asteroid (90% of
marine species & 70% of land vertebrates were destroyed)
¬ Event in which dinosaurs
went extinct
¬ Marked the end of the
Cretaceous period
¬ 75% of all species on Earth
went extinct
¬ Has generated public
interest in recent times due to controversy in the scientific community over
the cause of the extinction
Four Theories of
Possible Causes
¬ Sudden sea level changes
¬ Sharp temperature
fluctuations
¬ Volcanic eruptions
¬ Meteorite Impact
Sea level change
¬ Until recently, was a widely
accepted theory for explaining mass extinctions
¬ Known drops in seal level
have been linked to extinctions of marine life
¬ These occurred when large
regions of continental shelves were exposed to the atmosphere
¬ In turn, shallow-marine life
lost their habitats
¬ Despite these events, some
of the largest drops in sea level have not caused mass extinctions
¬ It remains unclear as to why
land based organisms would become extinct due to change in sea level
Temperature
Fluctuations
¬Characterized by periods of
extreme warmth
¬Causes stress on marine
life, especially in the tropics
¬In the tropics,
temperature-sensitive organisms die off, causing losses in biodiversity of the
oceans
Volcanic Eruptions
¬ Short term effects: Volcanic
activity would increase the amount of sulfuric acid aerosol in the atmosphere,
cooling the climate
¬ Long term effects: CO2 released into the atmosphere
by volcanic activity would lead to global warming
¬ Stresses such as ash,
debris, and excess CO2 in the atmosphere would hinder many
organisms’ abilities to adapt to the new environment
¬ Evidence of extensive
volcanic activity at the time of the K-T extinction found in sediment layers in
the Deccan Traps of India and Pakistan
Meteorite Impact
¬Most widely favored
explanation by scientists to describe K-T extinction
¬Astronomical theory: Earth
was hit by a supernova that destroyed the ozone layer, leaving the surface
exposed to high levels of ultraviolet radiation
¬However, this theory lacked
substantiation
¬Chicxulub crater theory
Chicxulub Crater
¬ (sheek’-soo-loob)
¬ An asteroid 4-9 miles in
diameter hit the Earth
¬ Created the Chicxulub Crater
at the tip of the Yucatan Peninsula in Mexico
¬ Penetrated the Earth’s
crust, caused scattering of dust and debris into the atmosphere
¬ Scattering of dust and
debris in turn caused: wildfires,
tsunamis, severe storms with high winds, acid rain, seismic activity, possible
volcanic activity
¬ Temperatures lowered due to
the blockage of the sun by dust and sebris, stopping photosynthesis from
occurring
Evidence for
Meteor Impact
¬Found a layer of sediment
from the same time as the K-T extinction containing unusually high
concentrations of iridium
¬Traces in the sediment were
found in 1979
¬Iridium is a rare element
found in the center of the Earth and in extraterrestrial meteors and comets
Theory of
Environmental Consequences of K-T
¬ Impact would be sudden
¬ As meteorites passed through
the atmosphere, the ozone layer would be destroyed, allowing UV rays to reach
the surface
¬ Shockwaves of high intensity
would occur at the site of impact
¬ Temperatures of materials
hitting the Earth would ignite fires
¬ Ash would reduce the amount
of sunlight reaching the Earth
¬ There would be a cooling of
the Earth due to the presence of debris clouds and aerosol layers in the
atmosphere, drastically reducing the amount of incoming solar radiation
Theory of
Environmental Consequences of K-T
¬ Photosynthesis would not occur, killing plant life and
removing food for most life on Earth
¬ Within months, the effects of the impact would lessen,
however most life on Earth would have been destroyed
¬ Plate tectonics, fluctuations in temperature,
volcanism, and sea level changes prior to the extinction were deteriorating the
environment
¬ The impact of the meteorites accelerated this process
of deterioration
Cooling of Earth
¬During the middle parts of
the Cenozoic Period (roughly eighty million years ago) planet earth
began to cool at an exponential rate.
¬Vast majority of the facts
point to declining levels of CO2 in the atmosphere thus reducing the natural
greenhouse effect.
What May Have Caused A Decline in Atmospheric CO2?
¬Decline in Ocean Tectonic
movement
– Fewer ocean upwellings
¬Increased Chemical
Weathering
–
Development of the Himalayas
– Development of Tibetan
Plateau, increased seasonal rainfall
Evidence of
Decreased Levels of Atmospheric CO2
¬ Large differences between
the levels of 12C and 13C
– the greater the difference
between 12C and 13C the less Atmospheric CO2
Other Possible
Explanations for Planetary Cooling
¬ Increased Solar
Luminosity
– K-T impact may have
increased polar ice caps so greatly that solar radiation was being absorbed at
a fraction of what it used to
Formation of
Himalayas
¬ creation of Himalayas took millions of years
¬ Himalayas are a young mountain range
¬ Himalayas are good example of strike-slip faulting
¬ 225 million yrs ago India was an island off the
Australian coast
¬ began moving northward at 9 meters a century
¬ 80 million yrs ago India was located south of the
Asian continent
¬ 40-50 million yrs ago Indian plate subducted and hit
Asian plate, northward advancement slowed by half
Formation of
Himalayas
¬ dramatic example of continental convergence and
collision,landmasses about the same rock density, one could not subduct under the
other, both were forced up
¬ tectonic movement best characterized as a Duplex
System
¬ system where a series of thrusts branch from a lower
to an upper detachment
¬ before collision an earthquake lifted ocean floor
13,000ft
Stages of the
Himalayas
¬ timeline consists of five stages
¬ 1st- India hit Asia
¬ 2nd- 65 million yrs ago Tethys bed driven
high to cause retreat of the sea. Sedimentary deposits elevated into high
mountain ranges & deposited into large basins and valleys, Upper Eocene Era
¬ 3rd- 25 million yrs ago, Middle Miocene
Era, major structure of mountain range created
Stages of the
Himalayas
¬ 4th- 2 million yrs ago, Pliocene Era,
further uplifting, plus some shear and stress forces occurred
¬ compression squeezed and pushed thrust sheets to the
south, folding of the Siwaliks(range in the Himalayas)
¬ 5th- 600,000 yrs ago,late Pleistocene Era,
determined present day form of the Himalayan system
¬ biggest consequence was lifting of the deep valleys,
large amount of debris due to large uplifting of the frontal range
Climate
¬ Himalayan Mountains form a barrier between two
different climate zones
¬ in turn each region developed a specific flora
¬ southern slopes, moisture-drenched clouds from
lowlands are drenched by monsoon rains
¬ northern slopes, bare, dry and cold
¬ every valley has its own micro-climate due to dry
north and humid southern slopes, and between eastern and western climate variations
Climate(Continued)
¬ barrier obstructs the passage of cold continental air
from the north into India in the winter
¬ plus, forces southwestern monsoonal winds to give up
most of its moisture before crossing the range northward
¬ average annual rainfall on the south side slopes
varies from 60”(1,530mm) at Shimla to 120”(3048mm) in the western slopes near
Mussourie
¬ north places such as Skardu, Gilgit and Leh get only
3-6”(76.2-152.4mm)
Climate(Continued)
¬ eastern Himalayans are at a lower altitude than
western Himalayans so in turn are warmer
¬ lowest temp recorded at Shimla is 130F(-250C)
¬ average temp at altitude of 6,380’ is 520F(110C)
¬ average temp at altitude of 16,500’ is 170F(-80C)
¬ average temp at altitude of 19,500’ is -80F(-220C)
¬ lowest temp recorded is -210F(-290C)
¬ winds can blow at excess of 100mph
Climate(Continued)
¬ two periods of rainfall
¬ winter rains and the rains brought by southwestern
monsoon winds
¬ winter rains results from the low-pressure system
advancing into India from the west, heavy snowfall
¬ January in the west on 3”(76.2mm) of rainfall, to the
east less than an inch(>25.4mm) rainfall.
¬ end of May conditions are reversed
¬ rains cease in September, after which the best weather
occurs until the beginning of winter in December
Rockies and the Influence
on Temperature
¬Formed 60 million years ago
¬Due to compressional forces
in the earth, aided by plutonic and volcanic action on the West Coast—Laramide
orogeny, a series of mountain building events
The North American
Rockies
Geography of the
Rockies
¬100 separate ranges that
dominate North America
¬Four broad groups: Canadian Rockies, Northern Rockies, Middle
Rockies, Southern Rockies
¬Physical attributes: High elevations, considerable mineral
wealth, common trends in climate
Climate in the
Rockies
¬Precipitation increases from
North to South
¬North receives ~3 times as
much rain, mostly from Pacific cyclonic storms
¬South tends to be dry, most
precipitation falls as snow in winter
Climate continued…
¬Cool temperate—cold winters
and cool summers
¬Occurs at ~7,000 – 10,000 ft
¬Higher elevations—severe
cold winters and short, cold summers
¬Short growing seasons
¬Susceptible to frost in the
summer
Factors affecting
climate
¬Altitude
¬Proximity to large
lakes—moderating effect due to large lakes
¬Wind flows through the
valley
¬Rain shadow affect on high
mountains
The Rain Shadow
Affect
Final Thoughts
¬Last of the Age of the
Dinosaurs
¬K-T Mass extinction
¬Breakup of the world
continent of Pangea
¬Formation of the Himalayas
and Rockies
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