Transcript Sedimentary rocks

A Dynamic System
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View from Apollo
What can you make
out?
It’s our Biome!
Nature’s splendor
How old is old?
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The oldest meteorites and moon rocks found
on earth are 4.6 billion years old.
The oldest earth rocks found are zircon
grains from a sandstone in western Australia,
dated 4.1 - 4.2 billion years old.
What happened on Earth during this long
period of time?
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Many natural events:
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Meteorite impacts
Volcanic eruptions & lava flows
Mountain building
Earthquakes
Erosion
Slow movement of continents
Formation and destruction of ocean basins
Glaciations
Climatic changes
All of these natural events are still going on today
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Some events that occurred in the past, and
left a record in the rocks, ARE NOT
OCCURRING TODAY, or haven’t occurred in
the span of human existence:
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Huge meteorite impacts
Large glacial ice sheets
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Other events occur so slowly that they are
difficult to measure:
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Plate tectonics: sea floor spreading; continental
drift
Erosion of mountain ranges
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Still other events are short lived but very
catastrophic:
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Volcanic eruptions
Earthquakes
Floods
Landslides, mudflows, avalanches, etc.
Layers of the Earth
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The Earth is divided into 3 basic
layers
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Crust (composed of…)
 O and Si
Mantle (composed of…)
 Fe and Mg
Core (composed of…)
 Fe and Ni
 very hot
The Crust
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Continental crust
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About 35 km thick; 60 km thick in mountain ranges
Granitic composition (granite rock, basic)
Oceanic crust
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About 5 – 12 km thick
Thin layer of unconsolidated sediment covers layered igneous
rock
Layered structure
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Pillow basalts (basaltic rock that erupted below water)
“sheeted dikes” (interconnected basaltic ridges)
Gabbro (course grained equivalent of basalt, which cooled slowly)
The Mantle
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Lithosphere = the outer mantle + the crust
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Asthenosphere = the inner mantle
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Roughly the outermost 100 km of Earth
Divided into tectonic or lithospheric plates that cover the
surface of the Earth
Depth of 100 – 250 km
Seismic wave velocity decreases (less dense)
Rocks at or near melting point
Plastic behavior; solids that flow (magmas)
Convection in this layer moves the tectonic plates
The lithospheric plates “ride” on the convection
currents of the asthenosphere
The Core
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Outer core
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Molten iron, Fe, (85%) with some nickel, Ni
Inner core
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Solid iron (85%) with some nickel
Also contains lighter elements such as silicon (Si),
sulfur (S), carbon (C), &/or oxygen (O)
Rocks vs. Minerals
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What are rocks?
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Aggregates of one or more minerals
What are minerals?
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Naturally occurring
Inorganic
Solids
Definite chemical composition
Characteristic internal crystal structure
How Do Rocks Form?
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By cooling, hardening, and crystallizing from hot,
molten lava
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By the alteration of pre-existing igneous or sedimentary
rocks by heat and pressure
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= Sedimentary rocks (terrigenous, clastic, or detrital)
By forming from the precipitation of dissolved chemicals
in water
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= Metamorphic rocks
By forming from the compaction and cementation of
sediments
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= Igneous rocks
Sedimentary rocks (chemical and biochemical)
By forming from accumulated organic matter
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Sedimentary rocks (organic; e.g. coal)
THE ROCK CYCLE
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Rocks are constantly “on the move” and
cycling throughout the Earth
Just like T-rex walked on but they have
broken down and reformed time and time
again
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Ripples in beach sand,
such as those in the
upper photograph (A)
may someday become
a rock like the
sandstone in the lower
photograph (B).
This sandstone was
part of a beach over
200 million years ago in
the Triassic period.
Breccia & Sandstone with fossil (remains & imprints)
Igneous Rocks
– sometimes referred to as “fire rocks”
Granite, Pumice, & Obsidian Rocks
- which are these samples? intrusive or extrusive?
foliated vs. non-foliated metamorphic rocks
- gneiss, marble, & slate illustrated
Fundamental Principles of Geology
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Most sedimentary rocks occur in the form of
layers called beds or strata. Each layer is the
result of the deposition of sediment during some
natural event.
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Principle of Superposition
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Principle of Original Horizontality
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Oldest rocks are on the bottom
Younger rocks are on the top
Sediments are deposited in flat layers
Principle of Original Lateral Continuity
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Sediments are deposited over a large area in a continuous
sheet
Other types of Unconformity
1) Angular
unconformities
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Implies tectonic
deformation and
erosion of
underlying strata.
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Grand Canyon,
Arizona
Other types of Unconformity
Nonconformity
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Sedimentary strata
overlying igneous or
metamorphic rocks
(in an erosional - not
intrusive- contact)
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Grand Canyon,
Arizona
Other types of Unconformity
Disconformity
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An irregular
surface of erosion
betwen two units
of parallel strata.
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Death Valley,
California
Other types of Unconformity
Paraconformity
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A planar surface
between two
parallel units of
sedimentary rock,
representing a
period of nondeposition, but no
erosion.
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Grand Canyon,
Arizona