Geology Reference
In-Depth Information
TABLE 2.1 Explanation for Figure 2.11 (Note: U, Upper; L, Lower; und. Undivided)
Period
Color/Pattern
Symbol
Cretaceous
Light green
K
U Pennsylvanian
Blue
IP
2
L Pennsylvanian
Blue diagonal
IP1
M
t
Mississippian
Light purple diagonal
Devonian (und)
Brown
D
U Devonian
Brown
D
2
L
Devonian
Brownish gray
D1
Silurian
S
Light purple
Ordovician (und, L, U)
Reddish purple
0,0,,0
2
•c
Cambrian
Brownish orange
Era (and rock type)
U Precambrian
Yellowish tan
p-C u
Keweenawan sed rocks
Reddish brown
pCu
2
Keweenawan vole rocks
Light brown
p£u.
Basic Intrusives
Brownish green
p-Cb
Middle Precambrian
Light brown
p-€ m
Granite and Granite Gneiss
Pink
p-ei
Lower Precambrian
Olive green
P-ei
3. Almost all of the Precambrian rocks are metamorphic or
? Precambrian rocks form the basement rock of conti-
nents and are known as "shields" where they outcrop. They
extend under the younger Phanerozic Eon rocks, which in
the map area are sedimentary rocks, and present different
environmental challenges to land use planning.
7. Although this bedrock map shows the distribution of
rocks of different ages (and in the Precambrian some of the
rock types), in most areas of the map these rocks are buried
beneath unconsolidated sediments ranging from a few to
as much as 700 feet thick. Which of the following cities is
underlain by the oldest bedrock? (check one)
Chicago
, Detroit
, Duluth
4. The geologic cross section (Figure 2.11) for the bedrock
geology map of central North America (Figure 2.10) shows
the stratigraphy of part of the Michigan Basin between A,
northwest of Milwaukee, Wisconsin and A', northeast of
London, Ontario, Canada. In the cross section the Silurian
system is labeled (S). Label other geologic units shown.
Note: Geologic maps of larger scale also show details on rock
type that are important in seeking resources (water, metallic
minerals, gravel, stone, etc.) and meeting environmental
challenges.
PART C. AERIAL PHOTOGRAPHS
AND REMOTELY SENSED IMAGES
Aerial Photographs
5. The circular geologic structure centered on the blue area in
the lower peninsula of Michigan is a basin; however, in the
cross section it appears as a (circle one)
anticline
An aerial photograph is a picture taken from a cam-
era position located somewhere above the earth's
surface. Such pictures may be taken obliquely (for
example, see Figure 5.2, which shows oblique pho-
tographs of Mt. St. Helens in Washington). In geol-
ogy, it is common to use aerial photographs that
have been taken vertically looking down to the
ground. These photographs are often overlapped
syncline.
6. If you drilled a hole at the "D" north of Milwaukee, what
geologic systems would you pass through before you
reached the Precambrian igneous or metamorphic basement
rocks? List the sequence of rocks from youngest to oldest.
