Geologic Mapping Techniques

Questions and Answers

What is the primary purpose of geologic mapping?

To find mineral deposits

To measure rock density

To trace and plot contacts between rock units (correct)

To analyze weathering patterns

At which scale is geologic mapping considered most efficient?

1:1,000,000

1:25,000 or 1:50,000 (correct)

1:100,000

1:500,000

How should a sharp, well-exposed contact be represented on a map?

As a series of dots

As a dashed line

As a solid thin line (correct)

As a thick dashed line

What can be used to map contacts when they are not exposed in natural outcrops?

Zigzag courses between outcrops Signup and view all the answers

Which type of rock contacts can be traced using the distribution of quartz grains in soil?

Contacts between quartz-rich and quartz-poor rocks Signup and view all the answers

Which of the following is an example of a rock contact that can be mapped?

Contact between sandstone and shale Signup and view all the answers

What method can be used to trace contacts between many rock units when no large fragments are found?

Analyzing soil composition, color, and texture Signup and view all the answers

Which scenario describes how the upslope contact of a rock unit can be located?

Using the up-slope limit of fragments from a unit Signup and view all the answers

What type of rock contact can be established when downslope creep has mixed the float?

Contact between conglomerate rock and shale Signup and view all the answers

What is the first step to begin mapping rock unit contacts effectively?

Start along a sharp contact between two distinctive rock units Signup and view all the answers

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.

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.