Transcript Plate tectonics_GSA 2011

Plate tectonics of the North
American Continent at the
Cretaceous-Paleogene
Boundary
and Implications For a
Terrestrial Cause in the
Great KP Extinction
Controversy
1
The Great KP Extinction Controversy
During the Cretaceous (K), dinosaurs had
roamed the Earth.
But by the beginning of the Paleocene (P),
65 million years ago (Ma), a mass
extinction had occurred that wiped out
nearly 75% of life on Earth, including the
dinosaurs.
2
• In 1980, Dr.’s Louis and Walter Alvarez
discovered a layer of clay at several sites
along the KP boundary containing high
levels of iridium, as well as other exotic
materials.
• Because iridium is rare on Earth’s surface,
the Alvarez team proposed that the layer
must have been formed by an
Extraterrestrial impact.
(Alvarez, et al, 1980)
• So far, this has been the most widely
accepted hypothesis.
3
• In 1981, however, Dr. Dewey McLean
showed how Deccan Traps volcanism in
India could have increased CO2 levels in
the atmosphere causing a severe global
warming event, thereby causing the
extinctions.
(McLean, 1981)
4
• For decades now, these two hypotheses
have battled for top contender, yet, neither
has been chosen as the champion.
• This presentation will attempt to
show that this is because it was
neither an asteroid nor the
Deccan Traps that caused the
extinctions of 65 million years
ago.
5
• In 1996, Dr. Charles Officer and Jake
Page introduced another hypothesis that
seems to have gone completely unnoticed
in the KP Extinction Debate.
• In their book, The Great Dinosaur
Extinction Controversy, they showed that,
not only were the Deccan Traps occurring
in India, but that massive volcanism was
occurring all over the world at that time.
(Officer and Page, 1996)
6
• Particularly, large
magmatic events were
occurring in North
America that were not
only coeval with the
Extinctions, but also,
with the uplifting of
the Laramide Orogeny
and the disappearance
of the Western Interior
Seaway.
7
• However, as no exact mechanism had been
found to account for the exotic mix of materials
in the KP boundary layer, this hypothesis was
largely dismissed in the KP Extinction Debate.
• So, my original question was: If an asteroid had
struck the earth at the same time that large
magmatic and uplifting events were occurring on
opposite sides of the world, could the asteroid
have caused some sort of disturbance in the
mantle to account for these events?
8
• The answer to that question was clearly NO.
• The Laramide Orogeny began within North America ~80
Ma and lasted until ~50 Ma.
• In India, the KP Boundary layer is found as a separate
layer within the Deccan Traps, and at least one study
shows that the Traps began erupting some 400,000
years before and continued some 400,000 years after
the deposition of the KP boundary layer. (Bhandari, and
Shukla, 1996)
• So the next question to be answered was…what,
exactly, caused the Laramide Orogeny at the KP
Boundary? So I began to study the geology of North
America directly before, during and after the KP
boundary.
9
The Western Interior Seaway
• Before the beginning of the Laramide,
Texas lay at the bottom of a shallow
seaway that stretched across the interior
from the Arctic Ocean to the Gulf of
Mexico. This cold, salty sea is known as
the Western Interior Seaway.
• Before the Laramide, bays and estuaries
covered most of New Mexico (Chronic,
1987); and Arizona lay along the
floodplains of that ancient sea. (Chronic,
1983)
10
• Most of the
fossils found at
the KP boundary
in North America
were animals that
lived within, or
along the shores
of, the Western
Interior Seaway.
North America
in the Age of the
Dinosaurs, 75 Ma.
(National Geographic,
January, 1993)
11
• Officer and Page (1996) showed that the
Western Interior Seaway was mostly gone
by 65 Ma.
• Critical habitats, and indeed, an entire
biosphere, disappeared, before the KP
boundary, mainly caused by the uplifting
of the western half of North America
during the Laramide Orogeny.
12
The Laramide Orogeny
• The Laramide Orogeny began within the
interior of the continent at ~80 Ma and
lasted until ~50 Ma.
• However, many major fold and thrust
events, as well as, magmatic events,
occurred directly at the 65 Ma boundary.
• Officer and Page showed that the
Laramide magmatic trend had been dated
between 69 and 64 Ma (Officer and Page,
1996).
13
TODAY…
In Texas…roughly 2/3 of Texas sits on the
Cretaceous shelf, while the other 1/3 sits
on top of Paleocene and younger
sandstone deposited as the Laramide
uplifted to the west and sediments filled
in the Gulf. (Chronic, 1987)
In Arizona…recent evidence shows that the
Kaibab plateau, which was uplifted along
with the rest of the larger Colorado plateau, had
uplifted as early as 65 Ma. (National Geographic, 2007)
14
And in Denver…In 2008, Dr.’s Doug Nichols and
Kirk Johnson of the Denver Museum of Natural
Science published a book titled Plants at the
KT [P] Boundary, which contended that the
rapid disappearance of plant life at 65 Ma,
followed by a fern spike, was definitive
evidence of an asteroid impact…
However, Dr. Johnson has also collaborated on
another study that this author believes to be
definitive evidence that it was NOT an
asteroid…
15
• In a study done on drill cores from
developments throughout the Denver Basin,
Johnson and others showed that the Pierre
Shale was formed at the bottom of the Western
Interior Seaway, dated at 68 Ma.
• Above the Pierre Shale lies a layer of volcanic
tuff, followed by the KP boundary layer at 65
Ma, containing high levels of iridium.
• By 64 Ma, plant life had not only returned, but
flourished to become a thriving rainforest.
(Raynolds, et al, 2007)
• In other words, the Denver Basin went from the
bottom of a sea to a thriving rainforest in the 4
million years spanning the KP boundary.
• That was not caused by an asteroid, but by the
rapid uplifting of the Laramide.
16
• Salt Lake and the Great Salt Lake Desert of
Utah was once a part of that salty seaway
that was trapped by the rapid uplifting of the
Rockies.
• Utah and Hell’s Creek Montana became the
last refuges of the dinosaurs struggling to
survive at the KP Boundary.
17
So, then, what, exactly, caused
the Laramide Orogeny?
• One study shows that
"Subduction of an oceanic plateau, about 8565 Ma (remnants in the Franciscan), produced
east-vergent tectonic wedging in the Coast
Ranges, possible thrusting along the eastern
Sierra Nevada Batholith margin, and
development of Rocky Mountain Laramide
structures. The ‘Laramide Orogeny’ is herein
redefined to include all Late Cretaceous-early
Tertiary (75-45 Ma) fold thrust structures from
the Pacific Coast to the Rocky Mountains.“
(Moores, Wakabayashi, and Unruh, 2003) ][=‘
18
It is within the
Franciscan
melange that we
find our clues to
what really
happened at the
KP boundary.
On the west coast
of North America,
we can still see the
scar.
(Scripps Institute of
Oceanography)
19
The Coast Range Ophiolite
(#4, green) represents a
Jurassic age oceanic
crust that was uplifted
onto the continent.
The Great Valley Sequence
(#1, yellow) that lay on
top of the Coast Range
Ophiolite represent
sediments that were
deposited on that ocean
floor while it still lay
within the ocean.
USGS Professional Paper 1515,
The San Andreas Fault.
Geologic sketch map of California,
Based on U.S. Geological Survey (1966),
Jennings and others (1970), and Ross
(1984).
20
The Franciscan
melange, (#5, blue)
however, is still
somewhat of an
enigma, as it lay
structurally beneath
the Coast Range
Ophiolite.
It mainly consists of
greywacke,
greenstone, red
radiolarian chert, and,
in some areas,
blueschists and
serpentinite.
21
So, then, what, exactly, is the Franciscan?
One study shows that the sandstone
(greywacke) found within the Franciscan
is volcanic in nature and is made up of
greenstone, similar to the greenstone
found in the Permanente Terrane.
This study also “concluded that these rocks
were deposited on the flanks of an
oceanic rise or plateau….”
(Larue and Sampayo, 1990)
22
• Another study shows that the cherts found
within the Franciscan are manganiferous,
and were formed on the flanks of a midocean ridge. (Crerar, et al., 1982)
• Manganese is known to emanate from
hydrothermal vents along mid-ocean
ridges today.
23
Another study shows
that a Jurassic age
Hydrothermal Vent
Community has been
found within the
Franciscan, similar to
those found around
the Galapagos
Islands today,
complete with tube
worms and other
sulfur-based life
forms.
(Little, Danelian,
Herrington and Haymon,
2004)
24
• The Franciscan, then, would seem to
show all of the evidences of being a midocean ridge AND/OR ocean-island
plateau, similar to today’s Galapagos
Islands.
• But WHEN, exactly, did it attempt to
subduct beneath North America?
25
One study shows that the Calera
limestone formation found within the
Franciscan “…was deposited on top of
an oceanic rise or plateau during the
Late Cretaceous and was subsequently
transported NE until it was accreted to
the North American continental margin
~63 Ma.”
(Tarduno, Irwin, Blake, and Coleman,
1985)
26
One study found in USGS Special Paper 1515
concluded that…
“uplift of the Franciscan Assemblage and
extension of the upper plate, consisting of
Coast Range Ophiolite and Great Valley
Sequence, occurred during the Cretaceous
(or, at the latest, during the early Tertiary”
(Fuis and Mooney, 1990).
Other studies show that major Franciscan uplift
occurred at the same time as graben formation within
the Coast Range Ophiolite at the KP Boundary, ~65
Ma. (Moxon and Grahamm, 1987; Unruh, Dumitru and
Sawyer, 2007)
27
• Vedder and others
showed that thrusting
on the Salinian block
(#9, light pink)
occurred from 65-55
Ma. (Vedder, Howell,
and McLean, 1983)
• Wakabayashi and
Moores, 1988,
showed that the
Salinian had collided
with the Franciscan
and was in place by
~60-50 Ma.
28
• More recent drill cores from SAFOD show
that the sediments on both sides of the
Salinian block are arkosic sandstones
deposited as the Salinian collided with
the Franciscan. Dating shows that these
sandstones were deposited between 70
and 64 Ma. (Springer, et al, Lithosphere,
2009)
29
• Los Angeles,
Santa Barbara
and Ventura all
sit on top of
thick
CretaceousPaleocene
sediments.
(USGS Prof.
Paper 1515)
30
As the Salinian block collided with the
Franciscan, this would have trapped the
MOR/plateau within a backarc basin
between the Salinian block on the west
and the subduction zone/Coast Range
Ophiolite/Sierra Nevada complex on the
east.
As the MOR/hotspot was thrust beneath
the continent, it would move in beneath
the downgoing plate, thereby causing the
flat-slab subduction that moved the
Laramide into the Interior.
31
Pelona-Orocopia Schists
• Jacobson and others show that the
Pelona-Orocopia-Rand Schists that lie
structurally beneath California and Arizona
are remnant pieces of that downgoing
plate that were pushed up beneath the
continent. Protolith and emplacement
ages range from 90 Ma in the northwest to
60 Ma in the southeast, and attributes the
formation of the schists to subduction of
an aseismic ridge.
• (Jacobson, et al., 2011)
32
Yellowstone
Mantle Plume?
This study shows that
the Yellowstone
mantle plume…
was a seamount, in
the Pacific, off the
coast of California,
65 Ma.
But, by 50 Ma, it was
beneath the
continent.
(Oppliger, Murphy,
and Brimhall Jr.,
1997)
33
It is this event that caused the Coast
Range Thrust on the west coast, leading to
the uplifting of the western half of the North
American continent, the large magmatic
provinces within the interior and the
disappearance of the Western Interior
Seaway at the Cretaceous-Paleocene
boundary.
This presentation will suggest that this
event also caused the deposition of the KP
boundary layer, as well as the extinction of
the dinosaurs, 65 Ma.
34
All of the materials being used to describe
the asteroid, can also be explained by the
closing off of this mid-ocean ridge and/or
ocean island hotspot on the west coast of
North America.
Iridium
Glass Spherules
Shocked Quartz
Granite
Oceanic Basalt
35
Asteroid?
• As of today…the only piece of the
“asteroid” ever found is a minute chunk of
iron and nickel containing high levels of
iridium, chromium, and olivine. (Frank
Kyte, 1993)
• However, this bit of rock was not found in
the Gulf, but in 65 million year old
sediments of the North Pacific, due east of
the Hawaiian Islands.
36
Iridium
• One study shows that rare OsIrRu grains have
been found uplifted in the Josephine Ophiolite of
Oregon (Port Orford) and northern California.
And that these grains are found throughout the
Pacific, from the Hawaiian Islands to Asia.
• The authors of this study suggested that the
Iridium was “…transported from the core-mantle
boundary region to the lithosphere as xenoliths
in a mantle plume/convection system.”
(Bird, Meibom, and Frei, and Nagler, 2002)
37
The Josephine
Ophiolite
• The Josephine Ophiolite
(#8) was uplifted along
with the larger Coast
Range Ophiolite at the
Cretaceous-Paleocene
boundary.
• Chromium is also found in
the uplifted Josephine
Ophiolite in Washington.
(Brownfield, et al, USGS,
1994)
38
Glass Spherules
• It has been shown that the glass spherules
found within the KP boundary layer are altered
oceanic basalt, which is why it is believed that
the asteroid struck in an ocean basin.
(Montanari, Hay, Alvarez, Alvarez, Asaro,
Michel, and Smit, 1983)
• These spherules contained high levels of ReOs, also attributed to the asteroid.
39
• Glass spherules can be created by
volcanic processes as magma comes into
contact with water. The ocean floors
surrounding seamounts are often littered
with glass spherules.
• Re-Os is also found in the ultramafic rocks
of the Josephine ophiolite. (Bird, et al.,
2002)
40
“Shocked” quartz
• Shocked quartz can also be created by geologic
processes and is often found in uplifted
ophiolites.
• Charles Officer showed how shocked quartz
was generated in the eruption of Toba. (Carter,
Officer,Chesner and Rose, 1986)
• The greywacke of the Franciscan consists of
abundant angular quartz and deformation
lamellae is present in quartz grains within the
Franciscan. (Schemann, Unruh and Moores,
2008)
41
Other Evidence
• Air bubbles trapped in amber show that oxygen levels
dropped from 35 parts per million at
67 Ma to 27 ppm at 65 Ma. (Dowswell, et al.,
2000)
• Dr. Gerta Keller showed that foraminefera began
disappearing from the record 500,000 years before the
KP boundary. (Keller, 2000 )
• High levels of CO2 cause calcium-bodied plankton to
dissolve at depths of greater than 4500 ft below sea
level.
• This could show that CO2 was increasing in the ocean
waters at the same time that oxygen levels were
decreasing in the atmosphere, before the KP boundary.
42
• Miller and others show that at 67 Ma, sea
levels dropped dramatically, but that by
65 Ma, sea levels had returned to near
normal.
(Miller, et al., 2003)
43
• But here, we have a chicken and egg
problem…As this study was taken in New
Jersey on the east coast of North
America.
• Could the uplifting that was occurring on
the west coast cause the appearance of
lower sea levels on the east coast?
• If sea levels had dropped due to
glaciation, as Miller suggests…wouldn’t
the Seaway have returned once sea levels
returned to normal at 65 Ma?
44
The Real Killer?
• Clues to the real killer in the KP Extinction
Event, however, may be found in dinosaur
eggshells recovered at the KP boundary, as
high levels of Selenium have been recorded in
them (Koch, ).
• Fine particle emissions of the Kilauea eruption
of 1983 showed high levels of Iridium, as well as
high levels of Selenium, Arsenic, and Fluoride.
The authors of this study suggested that the
Iridium could have been released as volatile
Iridium Hexaflouride (IrF6).
(Zoller, 1983)
45
• Iridium is not attacked by water, or hydrochloric
or nitric acids. It is, however, attacked by
molten salts, (NaCl or NaCn). Iridium is also
explosive when in contact with oxygen from the
atmosphere.
• If the Iridium was separated from the
Hexafluoride…Hexafluoride combines with
Selenium to become a poisonous gas.
• Selenium hexafluoride, causes breathing
difficulties and respiratory failure leading to
death.
• A poisonous gas would not show itself in the
bones of dinosaurs, but would be recorded in
eggshells and…in plants.
46
• Dr. Officer showed that high
levels of selenium are still
found in KP boundary soils
throughout North America
today.
• This map shows where
seleniferous plants in North
America are still causing
trouble for cattle and other
wildlife, leading to sickness
and death.
• The USGS also maintains a
Selenium de-contamination
task force in the Great Valley
of California today. (USGS,
Menlo Park, California)
Open dots-50-500 ppm selenium
Black dots-more than 500 ppm
selenium. (Rosenfeld and Beath,
1964, In Officer and Page, 1996.)
47
Before
65 Ma
48
After
65 Ma
49
I will not argue here whether there was
actually an asteroid or not. But, IF an
asteroid did strike the Gulf at 65 Ma, it did
NOT cause:
• the uplifting of the entire ocean floor on the west
coast,
• the uplifting of the western half of the North
American continent;
• the disappearance of the Western Interior
Seaway;
• the change in oxygen/CO2 levels;
• the drop in sea levels;
• the volcanism that was occurring throughout the
world at that time;
• OR the Extinctions that were already occurring
hundreds of thousands of years before it hit.
50
The evidence presented herein will
hopefully show that it was the
subduction of a mid-ocean
ridge
and/or ocean island plateau on
the west coast of North
America, 65 million years ago,
that DID.
51
This presentation will also suggest that the
capture of this ridge on the west coast
COULD cause a disturbance in the
mantle. And, as the westward moving
North American continent collided with the
ridge to the west, a surge of activity along
the Mid-Atlantic ridge COULD have led to
Africa and India’s rapid eastern
progression at the KP boundary, thereby
also leading to the formation of the
Deccan Traps of India.
52
Thank You
Paula Crook
Geography and the
Environment,
University of Texas,
Austin
53