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The Rock Cycle – in the Context of Areas of the Lithosphere
Igneous and
Metamorphic
rocks
Sedimentary
rocks
Generalized
Bedrock Geology
of Michigan
In Michigan,
sedimentary
rocks make up the
bedrock in the
eastern northern,
and
southern
peninsulas.
Sedimentary rocks
found in Michigan
include:
Igneous and
Metamorphic
rocks
Sedimentary
rocks
Generalized
Bedrock Geology
of Michigan
sandstone,
shale,
limestone,
rock salt,
and rock gypsum.
In Michigan,
we live on top of
a complex group
of sediments that
were deposited by
the Glaciers.
Generalized Quaternary
Geology of Michigan
What will
these
sediments
become?
As the ice advances
it can scour the bedrock
and move a lot of material.
When the ice retreats,
sediments are deposited
and new set of landforms exist.
Michigan has been sculpted by four major
glacial advances in last 1.8 million years
during the Pleistocene Epoch.
Glacial deposits
are much younger
than the
bedrock on which
they are resting.
Let’s look at the Devonian age
sedimentary rocks in Michigan.
The State Stone the ”Petoskey Stone”
is a fossil coral (Hexagonaria percarinata)
that lived in middle Devonian
age seas some
375 million years
ago. The rocks
that formed
in that
environment
are mostly
limestones.
Some
Devonian
life forms
that existed
were similar,
while others
were very
different
from what
we know
today.
Eddy Discovery Center
This
map of
the globe shows
one possible
interpretation of
the distribution of
land and water
during middle
Devonian time.
Do you know where,
what is now
Michigan, would be?
Middle Devonian Rocks in Michigan
Middle Devonian rocks are made up of many different
sedimentary rock formations. These rocks are shown in blue.
In Michigan,
igneous rocks
make up the
bedrock in the
western northern
peninsula.
Igneous and
Metamorphic
rocks
Sedimentary
rocks
Generalized
Bedrock Geology
of Michigan
In Michigan,
metamorphic
rocks make up the
bedrock in the
western northern
peninsula.
Igneous and
Metamorphic
rocks
Sedimentary
rocks
Generalized
Bedrock Geology
of Michigan
DEQ GSD - The Rock Cycle in Michigan - February 2001
Metamorphic rocks
found in Michigan
include:
iron ore,
schist,
slate,
quartzite,
marble, and
gneiss
Igneous and
Metamorphic
rocks
Sedimentary
rocks
Generalized
Bedrock Geology
of Michigan
DEQ GSD - The Rock Cycle in Michigan - February 2001
Plate Tectonic Theory
Every mountain and valley, ocean and continent, rock outcrop – event climate can
be related to the location of earth’s Tectonic Plates and the nature of their
boundaries.
Plate Tectonics is a powerful idea – like all strong scientific theories it explains
the events of earth history and provides for accurate predictions.
What is some of the evidence for plate tectonics?
What data was used to build the theory?
Alfred Wegner’s hypothesis: continental drift
Modern Reconstruction
– 200 m.y. ago
-based on vast and
wide variety of data
Wegener’s Reconstruction
of1915
-based on fit of continent,
the fossil record, Permian
glacial deposits, geology
of Africa/South America
Wegener’s Evidence
The Fit of the Continents
Noted by others prior to
Wegener
Impressed earth scientists as
crude and questionable
A much better fit was
recognized when the edge of
the continental margins are
matched – science the modern
coastlines are the product of a
dynamic sea level as well as
erosion
The Fossil Record
Identical fossils are found on
both sides of the Atlantic – a
pattern that defies logical
explanation if continents were
always apart.
After the time of separation
fossils are different because of
divergent evolution (i.e., later
species are increasingly
different)
Convincing example:
Mesosaurus, limited to black
shales of the Permian (260
m.y.o.) only found in range
shown
Modern distribution of animals
with common ancestors are
quite diverse due to isolation
Wegener’s
Evidence
Matching Rock Types and Structures
-A fit of MORE than just the shape
“It is just as if we were to refit the
torn pieces of a newspaper by
matching their edges and then check
whether the lines of print run
smoothly across. If they do, there is
nothing left but to conclude the
pieces were in fact join in this way.”
-Mountain belts end at the coast and can
be found continuing across the ocean
-Structures (oriented folds, faults) line up
with consistency.
-Rock types line up with consistency
Wegener’s
Evidence
Ancient Climates
(Paleoclimatology)
-The “fixed continent:” perspective
requires one to explain how
Permian glacial deposits could be
located in India, southern Africa,
Australia and temperate zones of
South America - in addition to the
bewildering distribution of coal
deposits in what is currently
temperate latitude (Pennsylvania,
British Isle)
Note the pole-ward striations in
India
-Continental Drift provides an
explanation.
-Glacial striations help us discern
the location of a south pole
-Places modern temperate zones
near the equator
Wegener’s Evidence