Environmental Engineering Reference
In-Depth Information
Area of bioturbation
Ripple marks
DNAG
Carbonaceous
ash layers
CM IN
Erosional contact representing
an unconformity
Coarser grained
sediments
Finer grained sediments
FIGURE 2.36
Late Pleistocene unconsolidated sedimentary deposit in the Rouge River watershed composed of sand (lighter
color) and ash (black). (Photo by Daniel T. Rogers.)
• Chemical disturbance from the migration of water from the surface through the
sedimentary layers; leaving behind a chemical precipitant or dissolving a portion
of the original constituents of the sediments. Given the correct circumstances, this
type of disturbance may lead to a karst topography.
The upper portion of Figure 2.36 shows an example of a disturbance likely originating
from a naturally occurring source because the line separating the disturbed portion
from the non-disturbed portion is not sharp, as would be characteristic of an anthro-
pogenic source. Instead, the boundary is transitional and gradual in most areas, sug-
gesting the disturbance was probably a combination of bioturbation or differential
subsidence.
2.7 Summary and Conclusion
The geology of a watershed literally forms the foundation of where we live. Moreover, the
geology of any urban region shapes the manner in which we live: our lifestyles; food pro-
duction; natural resource availability; economic activity, and ultimately determines our
standard of living and our sustainability. We have explored the different types of geologi-
cal environments where urban developments are located, and discovered that most urban
areas exist in geological settings of sedimentary origin. Along the way, it was also dis-
covered why the geology of urban areas is very complex and changes rapidly. In addition,
we learned every urban area of the United States has a unique set of geologic deposits
formed from more than two—and in some cases up to eight—distinct geologic processes.
A representative sample of the many types of geological environments of urban areas
throughout the United States has been presented. What is abundantly apparent from this
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