Podcast
Questions and Answers
What is the primary purpose of geologic mapping?
What is the primary purpose of geologic mapping?
At which scale is geologic mapping considered most efficient?
At which scale is geologic mapping considered most efficient?
How should a sharp, well-exposed contact be represented on a map?
How should a sharp, well-exposed contact be represented on a map?
What can be used to map contacts when they are not exposed in natural outcrops?
What can be used to map contacts when they are not exposed in natural outcrops?
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Which type of rock contacts can be traced using the distribution of quartz grains in soil?
Which type of rock contacts can be traced using the distribution of quartz grains in soil?
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Which of the following is an example of a rock contact that can be mapped?
Which of the following is an example of a rock contact that can be mapped?
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What method can be used to trace contacts between many rock units when no large fragments are found?
What method can be used to trace contacts between many rock units when no large fragments are found?
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Which scenario describes how the upslope contact of a rock unit can be located?
Which scenario describes how the upslope contact of a rock unit can be located?
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What type of rock contact can be established when downslope creep has mixed the float?
What type of rock contact can be established when downslope creep has mixed the float?
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What is the first step to begin mapping rock unit contacts effectively?
What is the first step to begin mapping rock unit contacts effectively?
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Study Notes
Geologic Mapping Principles
- Geologic mapping involves tracing and plotting contacts between rock units.
- Most effective at small to intermediate scales (e.g., 1:25,000 or 1:50,000).
Mapping Contacts
- Start mapping along sharp contacts between distinctive rock units.
- Walk along the trace of the contact, plotting visible or inferred points.
- Accuracy of recorded points depends on the contact's irregularity.
Contact Visualization
- A well-defined, sharp contact is represented as a solid thin line on maps.
- Many contacts may only be visible in limited locations or not at all in natural outcrops.
- For non-visible contacts, use a zigzag walking pattern between outcrops of adjacent rock units.
Rock Unit Compositions and Contacts
- Quartz-rich and quartz-poor contacts can be identified by quartz grain abundance in soil.
- Examples of contacts:
- Sandstone and shale
- Sandstone and limestone
- Granite and gabbro
Soil Analysis for Mapping
- When large fragments are absent, soil composition, color, and texture help trace contacts.
- In cases of downslope creep, the upslope limit of fragments indicates the contact of that unit.
- This method can establish contacts between conglomerate rock and shale.
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Description
This quiz explores the fundamental procedures of geologic mapping, focusing on tracing and plotting contacts between rock units. Learn how to efficiently map units at small and intermediate scales and understand the importance of precise contact identification. Test your knowledge on the best practices and methods involved in geologic mapping.
