Mariner 10

1
Mariner 10 Mercury Discovery Rupes (Discovery
scarp) Thrust faults formed as the planets
interior cooled and shrank, causing compression
in the crust
2
Offset in a stream along the San Andreas Fault,
CA. This photo is part of the classic collection
of John Sheltons book Geology Illustrated,
considered to be one of the most influential
popular scientific works of the 20th Century.

• Tectonism When forces build up on rocks in the
  earth, the rocks eventually slip or break
  releasing the stored up energy in a sudden
  earthquake. Faults (planar offsets in rocks and
  landscape) are the features that form when the
  earth slips and moves.

3

• Tectonism Graben are tectonic valleys (not
  erosional) formed in areas that are being pulled
  apart (extensional). A normal fault forms on
  each side of the valley and the middle drops
  down. These Graben valleys are in Canyonlands,
  Utah.

4

• Tectonism Normal faulting on a grand scale
  The Teton Mountains in Wyoming are on the up side
  of the fault, Jackson Hole and other areas east
  of the mountains are on the down side.

5

• Tectonism A reverse fault forms under
  compressional forces. Notice the overlap in the
  layers indicating shortening that results from
  compression. (Montana)

6

• Tectonism If rocks are very hot and under high
  pressure at the time of compression, they will
  fold (deform plastically) rather than break.
  These metamorphic rocks in Eastern Connecticut
  must have been deformed deep within the Earth and
  brought to the surface by erosion much later.

7

• Tectonism
• Syncline in a Washington County Maryland roadcut.
  
• Notice that this picture also dispels any notion
  that a syncline must be in a valley!

8
Plunging syncline

• Tectonism Plunging syncline just north of Half
  Moon Bay, CA. The word plunge indicates that the
  entire fold has been tilted, in this case
  downward in the direction away from the airplane.

9
Sequence of events 1) deposition of sediments
that become rocks, 2) rocks are buried, 3) rocks
are folded deep in the roots of a mt range, 4)
mts erode away and the folded rocks are exposed
with a river flowing over them, 5) new tectonism
begins to uplift new mountains and the river
erodes across them.

• Tectonism This Space Shuttle picture reveals
  not only 300mya folding in the Macdonnel mountain
  range in Australia (with compression in a
  north-south direction), but an amazing sequence
  of events Because its not likely that the
  river ever flowed up over the mountains, the
  river must have been there before the mountains,
  and eroded through the mountains at the same rate
  the mountains were rising up.

10
Stone Mountain, GA above
Weathering and Erosion. Mechanical Weathering
results from unloading (causing exfoliation
parallel to the surface), freezing and thawing of
water (causing cracking in rocks and shattering
along joints), heating and cooling (which causes
rocks to expand and contract, breaking them
apart), and other factors.
11
Weathering and Erosion. Oxidation of iron
combined with leaching of soluble elements
produces the red soils characteristic of humid,
warm climates. Less-extensively weathered
bedrock is seen in the lower part of the image.
12
Weathering and Erosion. Gravity is one of the
primary erosional forces. Mass Wasting occurs
when rocks move downward under the force of
gravity. Despite the warning sign and flag, not
all tourists in Kefalonia Greece understand the
risk!
13
Weathering and Erosion. Soil moves downward
under the force of gravity in a process called
creep. The trees on the Wasatch Plateau in Utah
chart the movement of the soil by always turning
to grow upward as the rotation of the soil tries
to tilt them over.
14
Weathering and Erosion. Gravity and rain
conspire to create many unusual features. Here
resistant boulders provide a protective cap for
cone-shaped Hoodoos.
15
Weathering and Erosion. Spectacular arches in
Arches NP, Utah are produced by a combination of
mechanical weathering by wind blown sand,
chemical and mechanical weathering by water,
presence of a resistant cap rock, vertical
fractures in the original rock layer (now long
gone), and gravity.
16
Weathering and Erosion. Rainwater runoff has
carved the castles and spires of Bryce Canyon NP,
Utah. Exposed roots of the small pine tree
reveal the rate at which sediment is eroding from
the upper rim of the erosional amphitheater.
17
Weathering and Erosion. Dendritic (tree-like)
drainage patterns form from surface rivers
flowing over areas of high rainfall and uniform
underlying rock. Eastern flank of Andes in
Argentina. Space Shuttle image.
18
Weathering and Erosion. Classic work of river
erosion, Grand Canyon as seen from the south rim.
More resistant layers form cliffs, less
resistant layers form slopes.
19
Weathering and Erosion. Sometimes after a river
has reached its base level and a meandering
channel is established, tectonic events cause the
region to be uplifted, and downward erosion is
renewed. The result is entrenched meanders, such
as these along the San Juan River in Utah.
20
Weathering and Erosion. As a region erodes down
to base level, a broad plain develops, often
containing a few remnant buttes or hills. Imagine
the now-eroded layer of sandstone that must have
once stretched between the buttes. Mitten
Buttes, Arizona, Cutler Formation.
21
Weathering and Erosion. Energy from wind-driven
waves (not just tides) can cause significant
coastal erosion. Clockwise from Upper left
Ocean Beach San Francisco, Great lakes, Oregon
Coast.
22
Weathering and Erosion. One of the clues that
convinced early geologists in the 1800s that the
Earth had to be very old was the presence of
erosion surfaces underneath other rock. The
feature shown here (from Portugal), tells the
story first of sediments that were deposited and
turned
to rock (the lower in-place rocks). Then, these
rocks were folded deep in the Earths crust by
powerful compressional forces that must have
built mountains. Then the overlying rocks and
mountains were eroded away (producing the
erosional surface). New sediments were deposited
on top of the erosional surface and turned to
rock, and finally, erosion exposed the whole
sequence. This feature is called an Angular
Unconformity.
23
Deposition and Stratigraphy. Animation of angular
unconformity generation.
24
Deposition and Stratigraphy. Alternating
episodes of deposition and erosion are necessary
to explain the presence of unconformities such
as this angular unconformity at Shepherd Point,
Utah. In general, erosion occurs where rock is
uplifted and gravity, wind, water, or ice carries
weathered sediment away. Deposition occurs
either where water/air movement slows, allowing
particulate matter to settle out, or where
conditions are right for sediments to crystallize
from solution.
25
Deposition and Stratigraphy. The V shaped
canyon in Death Valley CA reveals erosion in the
upland. The alluvial fan forms where sediment is
deposited in the lower-energy environment that
occurs where slope decreases.
Classic John Shelton photo
26
Deposition and Stratigraphy. The
currently-active part of the Mississippi Delta as
seen with the ASTER imager of the Terra
Satellite. Sediment is deposited by branching
distributary channels where the river water stops
flowing upon encountering the sea. With less
water movement, the sediment settles out.
Sufficient sediment is carried by the river to
extend the delta by about 300 feet each year.
27
Former Location of Harbor
Deposition and Stratigraphy. In the days when
Paul the Apostle spent two years preaching in
Ephesus on the western coast of Asia Minor, the
region of the Great Theater looked out on a
beautiful bay much like that at modern Izmir.
The walkway led from the theater to the harbor.
Years later, sediment carried by the river silted
up the bay and the site is now landlocked.
Agricultural practices in the region probably
speeded up the erosion and deposition process.
28
Deposition and Stratigraphy. A high energy
environment, such as a beach subject to severe
storms, will wash away small particles and
deposit larger particles. At left is a modern
high energy beach on the North Shore of Lake
Superior. Above is a conglomerate (Schunemuck
Mountain Conglomerate) deposited on an ancient
Devonian high energy beach (much later exposed
and polished by glacial erosion).
29
Deposition and Stratigraphy. Low-energy
environments of deposition include a swamp (left)
and a lagoon (below on left, protected from open
ocean waves by a barrier island). Sediments in
the swamp and lagoon will be muddy and
organic-rich. Sediments along the higher-energy
foreshore and dunes will be sandy.
Above Cypress swamp near Albany Georgia.
Right Barrier island and marsh lagoon, Plum
Island Massachusetts.
30
Deposition and Stratigraphy. MISR image of the
Great Barrier Reef, Australia. Deposition of
CaCO3 sediment from solution in sea water to make
limestone usually occurs where the supply of
particulate sediment is low. Deposition of
chemical sediments doesnt depend on the energy
in the environment of deposition, since there are
no particles to settle out.
31
Deposition and Stratigraphy. Coral reefs often
form in warm climates where water temperatures
and salinities are very stable. The stability
results in great diversity of life. Great
Barrier Reef, Australia
32
Deposition and Stratigraphy. Coral reefs often
form in areas with lots of sunlight and food,
resulting in a great abundance of life GBR
33
Deposition and Stratigraphy. A common, if
somewhat simplified, sequence of sediments on a
continental shelf (going from the beach out to
sea) is sandstone (where moderate energy waves
wash finer sediment away), mud (both silt and
clay deposited in deeper water where there is
less water movement), and carbonate sediments
(CaCO3-based sediments deposited where little
particulate sediment reaches). These sediments
become the rock types sandstone, shale, and
limestone. A concept called Walthers Law
suggests that sediments that occur adjacent to
each other in modern environments may have become
stacked on top of each other in the past due to
migration of environments through time.
34
Deposition and Stratigraphy. Many layers are
stacked on each other in the Grand Canyon AZ.
Notice three layers in the lower right TS
Tapeats sandstone, BAS Bright Angel Shale, and
ML Mauve Limestone. Notice that they are in
the same sequence typical of shorelines, but
stacked on top of each other instead of side by
side.
35
Deposition and Stratigraphy. The sequence
(upward) of sandstone, shale, limestone can occur
in a stacked sequence if an ocean advances over
an area slowly, depositing sandstone first, then
as the water deepens, shale and limestone later
(and thus on top of the sandstone). Therefore,
this sequence at the Grand Canyon is the record
of an ocean advancing over this area during the
Cambrian time period.
36
Deposition and Stratigraphy. When the sea
transgressed over the region of the Grand Canyon,
it advanced over a pre-existing erosional
surface. Rocks exposed at that ancient surface
included metamorphic Schist, Igneous Granite, and
tilted PreCambrian sedimentary layers. The
surface beneath the Tapeats Sandstone (labeled
with a 2) is called the Great Unconformity.
The surface labeled 1 is an even more ancient
unconformity.
37
Deposition and Stratigraphy. Tilted Precambrian
rocks lie below the Great Unconformity in the
lower half of the image. Above the unconformity
is, in sequence, the Tapeats Sandstone (making a
cliff), Bright Angel Shale (making a slope), and
the Mauve Limestone (making a short cliff below
the more prominent cliff-former at the top of the
butte). This tells the following story 1)
ancient deposition, 2) tilting of rocks, 3)
erosion of rocks, 4) advance of an ocean that
deposited new rocks, and finally 5) recent
erosion of the canyon that has exposed it all.
38

• Life Processes
• Tree roots cause both physical and chemical
  weathering. Physical weathering is due to the
  outward pressure provided by turgor pressure in
  the cells that can force cracks wider. Chemical
  weathering is due to acids produced by the tree
  and ion exchanges of the rootlets.

39

• Life Processes Humans are one of the most
  significant erosional forces on Earth, moving
  more rock and sediment per year than almost any
  other single process. This is the Kennecoff Mine
  in Utah, an open pit mine producing copper,
  molybdenum, gold and silver.

40

• Life Processes Almost all species that have
  ever lived are now extinct, and the creatures
  alive today did not exist just a geological
  moment ago (that is, we do not find fossils of
  those creatures in rocks from the geological
  past). Therefore, we reasonably conclude that
  life is a dynamic and changing part of Earth.

41

• Life Processes Example life from the Mesozoic,
  the Age of Reptiles. Percent of Mesozoic
  species extinct gt 99. Clockwise from u-left,
  Tricerotops (a ceratopsian), Chasmosaur Belli (a
  ceratopsian), Tyrannosaurus (a therapod), and
  Lambeosaurus (an ornithopod), all dinosaurs.

42
The following slides are a preview of plate
tectonics for our next section
43

• Tectonism
• Illustration of the main types of Tectonic Plate
  boundaries and their features (including mountain
  belts, volcanic chains, isolated volcanoes,
  trenches, and high plateaus. Earth is the only
  planet known with this style of Plate Tectonics.

44
Space Station Earth Volcanoes in Mexico form
chains running parallel to the plate tectonic
convergent boundary.
45

• Tectonism Compressional forces at convergent
  plate boundaries can thicken the crust in those
  areas, producing mountains. French Alps.

46
Space Shuttle Topographic Map of East Africa
Rift.
47
Gemini 11 (right), Apollo 17 (above) Plate
tectonic rift, opening of the Red Sea and Gulf of
Aden between Arabian Peninsula and Horn of Africa
48

• Tectonism Illustration of plate motions, plate
  boundaries, and changes in continents from the
  end of the Precambrian until today NAM North
  America, BALBaltic 1 sec 10 million years.
  after PGISMac by Malcolm Ross and Christ
  Scotese and Paleomap Project by Chris Scotese.