Environmental Engineering Reference
In-Depth Information
When constructing a cross section, the amount of geologic interpretation between strati-
graphic sections depends upon the
• Number of stratigraphic sections
• Distribution of stratigraphic sections
• Number of data gaps requiring interpretation
• Complexity of each stratigraphic section
Selecting the line or slice direction is perhaps the most important operation when con-
structing a cross section. Usually, several cross sections are constructed to create a more
complete picture of the vertical dimension and depositional sequence. Generally, the cross
section containing the most significant information is one constructed as a perpendicu-
lar slice to the strike or trend of the geologic units being evaluated. These types of cross
sections are most effective because more geologic units are usually represented, and the
relationship, structure, and depositional history are more easily revealed and understood.
This is especially relevant to urban watershed restoration efforts because the majority of
the deposits existing below urban areas are sedimentary in nature.
An example cross section constructed perpendicular to the strike is shown for the Rouge
River watershed in southeastern Michigan in Figure 5.11 (Rogers 1996, 1997; Kaufman
et al. 2005). This cross section includes several types of sedimentary deposits of glacial,
lacustrine, and fluvial origin commonly found in most urban areas of the United States.
Figure 5.12 is a three-dimensional representation of several intersecting cross sections
East
A'
West
A
Plymouth
Livonia
Redford
Detroit
800
Defiance moraine deposit (Qwm
2
)
(inner ridge)
Depth in
meters above
MSL
Sandy clay
Qla
Recent river sediments
Qaa
Sandy or silty clay
Qll
Sand
Qls
700
Sandy or sllty clay
Qll
Qwm
2
230
Sand
Qls
Sandy or silty clay
Qll
Ms
Mbd
Da
Ground moraine
(lower clay unit)
600
195
Sand, gravel,
and cobbles
Qaa
Qwm
2
Da
Upper clay
Qlc
Qfa
Qfa
Dt
Dt
Dd
500
ft.
Qwm
3
160
Dd
Ddr
Interglacial fluvial
deposits
Glacial lacustrine deposits
Glacial deposits
0
4 km
Approximate
vertical exaggeration: 50
Sandy clay
(Qla)
Sand
(Qls)
Sandy or
silty clay
(Qll)
Upper
clay unit
(Qlc)
Defiance moraine
(inner ridge)
(Qwm
1
)
Lower clay unit
(ground moraine)
(Qwm
2
)
Calcareous clay
earlier Wisconsin
substage in age
(Qwm
3
)
Sand, gravel, and cobbles
(undifferentiated)
(Qfa)
Michigan
Recent fluvial
deposits
Bedrock formations
Unconformity
Inferred unconformity
Lower
Mississippian
(Ms)
Lower
Mississippian
(Mbd)
Upper
Devonian
(Da)
Mississippian
Middle
Devonian
(Dd)
Middle
Devonian
(Ddr)
Recent river
and/or Devonian
(Qaa)
Study area
and/or Devonian
(Dt)
FIGURE 5.11
Detailed cross section of Rouge River watershed in southeastern Michigan.
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