Environmental Engineering Reference
In-Depth Information
in detail and are called type sections. Once the chronology of deposition has been firmly
established, a stratigraphic column can be constructed for the entire area being mapped
(USGS 2007).
As shown in Table 2.4, many types of geologic processes are responsible for building the
geologic history of the large urban areas within the United States. We will demonstrate
the process of facies analysis using the stratigraphic columns from Figures 5.2 through 5.4
because they contain a good record of the depositional history of the Rouge watershed.
The stratigraphic columns from each site are presented in Figure 5.10.
The distance separating the three sites and represented by each column shown in
Figure 5.10 is approximately 1.5 km. Each site is perpendicularly aligned (north to south)
to the strike of the geologic units identified at each location (west to east). The lines drawn
between each stratigraphic column connect geologic units appearing in more than one
stratigraphic column such as the Lacustrine Beach Sand Deposit and the Lacustrine Silty
Clay Deposit. The units of Fill Material and the Beach Dune Sand Deposit exhibit converg-
ing lines because they are not present in the other stratigraphic columns within the study
area.
A simple analysis of the facies represented by each depositional unit in Figure 5.10 indi-
cates each site was once part of a former lake, with the beach and associated dunes located
toward the west and the deeper water. The small amount of dip present between columns I
and II (approximately 10 m per km) is also characteristic of these glacial lacustrine features.
The presence of a lake between columns I and III is further confirmed by the absence of
West
Elevation (MSL)
East
235 m
I
Be
a
ch
dune
s
and
deposit
230 m
Lacustrine
beach sand
deposit
II
Fill material
Top soil
III
Lacustrine
beach sand
225 m
Lacustrine
silty clay
Top soil
Lacustrine
silty clay
Lacustrine
silty clay
220 m
Approximately 1 km
215 m
FIGURE 5.10
Example of facies analysis or cross dating using stratigraphic columns from Figures 5.2 through 5.4.
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