Lab objectives:

• understanding strike and dip, trend and plunge, fold and fault symbology.
• recognition of stratigraphic vs. unconformity vs. intrusive vs. fault contacts.
• distinguish effect of topography versus effect of structure on map pattern.
• recognition of structural trends and patterns (e.g. fold patterns).
• development of basic geologic history of area from map.
• critical review of geologic maps.

General motivation for the lab: Reading and compiling geologic maps is a basic skill in geoscience, and this lab is designed to start developing your geologic map reading skills.

Image to right: Geologic map of California. What can you learn about the geology of California from reading such a map? If you try to capture the explicit and implicit information in this map in words it would be a lengthy document. Maps are very efficient communication devices. Image source: http://education.usgs.gov/california/maps/california_geology1.htm.

Review of map components: map scale, topographic contour interval, magnetic declination, projection, coordinate system (latitude-longitude, UTM), legend.

What types of geologic units might be shown on a geologic map?

What types of geologic contacts might be shown on a map?

• how to distinguish between these types?
• the importance of solid vs. dashed vs. dotted lines.

Topography, structure, and map pattern: We will learn about these relationships in much more detail in next week's lab.

• what is the relationship between a geologic contact and topographic contours if the contact is horizontal?
• what is the relationship between a geologic contact and topographic contour if the contact is vertical?
• law of Vs for a geologic contact tracing across a valley.
• for a geologic unit with a slab geometry and vertically oriented what will be the relationship between the unit (slab) thickness, and the thickness on a map.
• for a geologic unit with a slab geometry and horizontally oriented what will be the relationship between the unit (slab) thickness and the topographic contours.
• structural scale vs. topographic scale and the influence of topography on the map pattern.

Definition of and map symbol for strike and dip:

• strike line: horizontal line in plane of interest.
• strike angle: angle in degrees between N and strike line.
• dip line: line in plant of interest that is perpendicular to the strike line.
• dip angle: angle in degrees between dip line and horizontal line vertically above (also the maximum inclination).
• dip direction: vector (line w direction) perpendicular to strike line and pointing down-dip.
• quadrant convention: strike angle measured either clockwise or counterclockwise of N as designated by cardinal direction attached to the strike number, and cardinal direction of down dip attached to amount (e.g. N30E - 60SE, which would be the same as S30W - 60 SE)
• azimuth convention: angle measured clockwise from N (o to 360) plus the dip amount and the down dip cardinal direction (120 - 45NE, which would be the same as 300 - 45 NE)
• azimuth convention plus right hand rule: azimuth strike angle that is counterclockwise of the dip direction (e.g. 300-45, which would not be the same as 120 - 45, which would acutally be dipping to the SW). In this case the dip direction determines which of the two possible azimuth angles you use, and the dip is always clockwise from the given strike azimuth (hence the term right hand rules)
• Schematic block diagram to right of two planes and the various strike and dip components for those two planes using the azimuth convention.

Definition of and map symbol for trend and plunge:

• trend line: a horizontal vector directly above the linear feature of interest in the down plunge direction.
• trend angle: angle from N of the trend line.
• plunge angle: angle between the trend line and linear feature of interest (as measured in vertical plane).
• quadrant convention: trend angle measured either clockwise or counterclockwise of N or S as designated by an attached cardinal direction (e.g. S65W - 30).
• azimuth convention: trend angle measured clockwise of N to vector end (no need for quadrants to be designated - e.g. 245 - 30)

Map symbols for simple faults and folds.

Small part of Grand Canyon geologic map taken from http://geomaps.wr.usgs.gov/parks/grcaproj/grcaproj.html. It displays many of the type of map relationships described above (sub-horizontal contacts sub-vertical contacts, a major unconformity).

Some additional interesting sites related to geologic maps:

• USGS site that discusses geologic map symbols in some detail. This one is worth the perusal.
• USGS collection of electronic map resources.
• USGS site about geologic maps in general. This one is worth further perusal.
• Description of different types of maps USGS produces.

Part 1 (9 pts.)

Use the provided map (hard copy) of a small part of Spitsbergen (Sørkapp = south cape) to answer the following questions (converse with each other about possible answers, but when drafting your answers you must work on your own). A colored version of the map is available to help (link to color version of map), as is the relevant portion of the map legend (link to legend). Your first should be to familiarize yourself with the map (the topography, scale, geologic units and age relationships, geologic symbols. After having done this complete the following below.

1) Trace with a red pencil the major unconformity shown on the map. Be careful to trace it throughout the map area wherever it exists.

2) What type of unconformity is it (disconformity, angular unconformity or nonconformity)?

3) What is the approximate stratigraphic thickness of unit 13 (contour intervals are 50 meters)?

4) Trace with blue the fold axial surface of the major antiform and synform in the older rock sequence on the map.

5) What direction are the folds in the basement rocks plunging (if you were to follow the hinge zone of a folded surface, the point of maximum curvature, which direction does it go down into the ground)?

6) Are the normal faults steeply dipping or shallowly dipping? What is the map evidence for your answer?

7) Trace the normal fault with the likely largest offset (look carefully) with green.

8) What direction is the structural grain in this area?

9) Draw a north-south cross section sketch from Listefjellet to the coast showing the nature of the major geologic units. First, draw a rough topographic profile sketch. "fjellet" means mountain in Norwegian (as can be seen by the topographic contours also).

Part 2 (11 pts.)

You will each either chose or be assigned a map to work with. Please analyze it as fully as possible for the structural information it contains. Two products should be generated. You are encouraged to help each other with this.

• A 200 word abstract (no more) that summarizes the structural character and geologic history inferable from the map (8 pts.).
• A 5 minute presentation to the rest of the class on this area (3 pts.) to be given next week.

Here are some questions that you can ponder and which may help you analyze the map. The ones in bold should be specifically addressed in your presentation, but you should also address the other questions if they are pertinent.

• What age and types of rocks are involved?
• What might be considered basement and what might be considered cover?
• What cross-cutting relationships do you see? What are older and what are younger structures?
• Are there any unconformities, and if so what type and age are they?
• Are there common orientations (sets) of structures, and what are they?
• What types of faults exist?
• What orientation data is present?
• Do folds exist and if so what is their general trend?
• Are there intrusives, and if so what age are they, and are they deformed?
• How much of the map pattern is due to topography versus how much due to structure?
• What does a cross section view look like? (Can be very useful to generate some cross section sketches of your own).
• Where might the map be open to reinterpretation?

By answering these and similar questions you should have the understanding necessary to assemble an initial idea of the structural architecture and history of the area.

It is traditional and useful to organize your results into a history from earliest to latest events.

Your presentation should focus on three or so major points about the geologic history that can be drawn from the map. You might put them in historical order. You also need to point out on the map the evidence for your assertions. Five minutes is not much time, and so you should definitely carefully organize your presentation. The objective of your presentation is to educate the other students about the structural geology and history of your assigned map area.