Transcript Geomorphology

Geomorphology
and
Relative Dating
Basic Terms
• Geomorphology – the study of the
characteristics, development, and origin of
landforms
• Topography – the surface pattern of the
Earth
• Relative dating - A method used to
determine the general age of a rock, rock
formation, or fossil based on a sequence
of events
Dating of Rock Layers
• Scientists use several methods to determine the
ages of layers of rock. These methods include:
– Relative Dating: Finding the relative ages of rocks
based on their position among other rocks.
– Fossil Dating: Using types of fossils to date rocks.
– Radiometric Dating: Using the radioactive decay of
certain elements to date rocks.
• Key term: Strata = Layers of rock.
(Stratum = one layer of rock.)
Relative Dating Rules
• Superposition:
– newest layers are on top/ oldest on bottom
Original Horizontal
– Rock strata are horizontal when they are
formed.
– Later rocks may be tilted by folding or faulting
Lateral Continuity
• layers of sediment extend in all directions when
they become rock
• Later, processes like erosion or faulting may
break continuity.
Intrusions/Cross Cutting
• Intrusions are always younger than the
rocks they invade.
– Pluton – Massive intrusive igneous formation.
– Dike – Intrusion that forms ~ vertically within
breaks in rock strata.
– Sill – Intrusion that forms ~ horizontally within
breaks in rock strata.
Inclusions
• Rock contains a different rock that does
not belong naturally within the rock type.
– Ex. Layer of sandstone with a chunk of
marble in the middle
Unconformity
• Layers show a time of erosion between
periods of depostion.
Folding
• Compression causes the land to deform
and bend
Syncline
Anticline
Faulting
• A break in the crust and movement on at
least one side.
• Types:
– Normal
– Thrust/Reverse
– Transform
Normal
• Results form tension in the crust
• A steep slope occurs on the upthrown
block
Thrust/Reverse
• Produced by compression
• The upthrown block creates an overhang
above the downthrown block
• Landslides usually accompany this fault
Transform
• Movement is completely horizontal
Fault Block Mountains
Horst
• An uplift of a block between two parallel
faults
Graben
• A downthrown block between two parallel
faults
Isostasy
• The Earth’s surface will compress under
extreme pressure and rebound when the
pressure is released.
Using Fossils to Date Rocks
• Fossils contained in rocks can be very
useful in determining relative ages of rocks
throughout the world. Why? Because
organisms change over time; new species
evolve, and others become extinct.
– Fossil Succession: Scientists use a welldefined sequence of the appearance and
disappearance of widespread fossils, mostly
marine organisms, as clues to relative ages of
rocks.
Index Fossils
Radiometric dating
• Uses the half-life of chemical components
in the rock to determine its exact age.
– Works well for igneous as melting and cooling
restarts the “clock”
– Can determine the age of the particles that
make up the sedimentary
Sequencing Practice
• In order, from
oldest to youngest:
–
–
–
–
–
–
–
–
–
Gneiss
(Erosion)
Sandstone (S.S.)
Dike
Shale
Dike II
(Erosion)
Upper Sandstone
(Faulting &
Folding)
– (Erosion)
– Volcanics
– (Erosion)
Sequencing Practice
• In order, from
oldest to youngest:
– G
– A
– K
– B
– Fault I
– E
– (Erosion)
– Z
– F
– T
Sequencing Practice
• In order, from oldest
to youngest:
– E
– G
– L
– C
– Fault H
– Erosion
– Tilting
– M
– D
– J
– A
– Erosion
– N
– K
– B
– More Tilting
– Erosion
– F
– Erosion
Sequencing Practice
• In order, from oldest
to youngest:
– H
– F
– D
– G
– (Erosion)
– I
– (Erosion)
– C
– (Erosion)
– A
– B
– M
– Fault L
– Fault K
– (Erosion)
– Fault J