GY 111: Physical Geology

Lecture 27: Folds

Instructor: Dr. Douglas W. Haywick

UNIVERSITY OF SOUTH ALABAMA

Last Time

Web notes 26 Lab Manual Chapter 5

A) Types of Geological Maps B) Stratigraphic principles C) Beds in 3D space; the problem of orientation D) Strike and Dip E) Geological maps 1: horizontal and inclined bedding

Geology maps

Show the geology at the surface of the Earth

http://www.geo.ua.edu/Documentation/jpgs/GeoMap.jpg

Geology maps

1) Age of rocks Use single (capital) letters to represent period often followed by subscripts (rock names)

Quaternary

Q

T

K

J

TR

P IP M D S O C PC

http://www.winona.edu/geology/MRW/mrwimages/geological_time.gif

Tertiary

Geology maps

2) Types of rocks Use standardized symbols and/or colors

http://www.rockware.com/rockworks/revisions/litho_plan_02.png

Geology maps

2) Types of rocks

Use standardized symbols and/or colors

http://dept.kent.edu/geology/edlab/structure/GeoMapSymbols.gif

Geology maps

3) Structural Features 4) Bedding Attitude

Use standardized symbols…

… more on this shortly

http://dept.kent.edu/geology/edlab/structure/GeoMapSymbols.gif

Beds in 3D Space

Horizontal bedding is easy to describe…. …. But what if the bedding is inclined

Beds in 3D Space

Horizontal bedding is easy to describe…. …. But what if the bedding is inclined

Beds in 3D Space

Inclined bedding can be oriented any amount in any direction,

And this is a problem to describe

Chalk board

Beds in 3D Space

Strike: The orientation of the inclined bed (0 to 360º) Dip: The inclination of the inclined bed (0 to 90º)

Geological Maps 1

Horizontal bedding leads to fairly simple geological maps (unless you have a lot of erosion (e.g., the Grand Canyon)

Geological Maps 1

Inclined bedding leads to more complex geological maps (but they are still interpretable if you know the rules… which you will get in GY 111L exercises)

Today’s Agenda

Web notes 27 Lab Manual Chapter 6

A) Types of folds B) Anatomy of a fold (terminology) Last Call for Mac and Cheese Bonus

Mechanical Behavior of Rocks Near-surface rocks that are under low T-P conditions behave as brittle material:

– Fault fracture (slippage) – Joint fracture (no slippage)

Deep rocks under elevated T-P conditions behave as ductile material:

– Folding

Folds

http://www.geosci.unc.edu/faculty/glazner/Images/Structure/Folds.html

Folds

http://www.parstimes.com/spaceimages/zagros_anticlines.jpg

Folds

http://www.geology.wisc.edu/~maher/air/130-27v.jpg

Folds

Anticlines: Open downwards Synclines: Open upwards

Folds

Folds

Please note: Folds are 3-dimensional structures

Folds

Folds are simply bent planes and as such, can be described using strike and dip connotation

Folds

Folds are simply bent planes and as such, can be described using strike and dip connotation

Fold axes on maps are indicated with the following symbols:

Anticline Syncline

Folds

A simple geological map of an anticline

Folds

At the point(s) of maximum curvature, the dip of the fold is 0º

Folds

Folds can be horizontal or plunging

Plunging Folds

Asymmetrical Folds

Folds on Maps Some of you will interpret these in an upcoming lab exercise

Oblique View Geological Map (no scale implied)

Anticline

Folds on Maps

Oblique View Geological Map (no scale implied)

Syncline

Some of you will interpret these in an upcoming lab exercise

Folds on Maps As well as more complex structures

Today’s Homework 1. Study! Why wait for the day before the final?

2. Assignment 4 (folds on maps) next Thursday 3. Wednesday lab students: Metamorphic rock exam

4. Go up to a total stranger and give them a hug (then run away very fast)

Next Time Faults

GY 302 Poster Session. Tuesday Nov 22 12:00-2:00PM (Bonus) Rock and Gem Show Thanksgiving weekend (Bonus)

proof of attendance required for both bonuses

GY 111: Physical Geology

Lecture 27: Folds

Instructor: Dr. Doug Haywick

dhaywick@southalabama.edu

This is a free open access lecture, but not for commercial purposes. For personal use only.