Lab 4: Structures and Geologic Maps

Transcription

1 Key Questions: GEOL 1311 Earth Science Lab 4 Structures and Geologic Maps What shapes do rock bodies take in the Earth? How do two-dimensional visualizations of the Earth, such as maps and cross-sections relate to the three-dimensional Earth? At the end of this lab you will be able to: Describe the main types of geologic structures we see on the Earth. Read geologic maps. Be able to predict surface geology based on cross-sections of the Earth and vice-versa. PART I. Working with 3D Geologic Blocks Credits: These exercises are modified from: The Hidden Earth Project, led by Dr. Steven Reynolds, Arizona State University ( Background Information: In this module, you will learn about five major geologic features - layers, folds, faults, intrusions, and unconformities. These five features intersect surfaces in various ways due to geologic events that continually occur below the surface. Throughout the module, you will interact with movies to learn how geologic events such as tilting, deposition, erosion, and faulting change and modify the appearance of these five features on the surfaces of blocks. After interacting with these movies, you will be able to identify and recognize the five main features and reconstruct the geologic history that resulted in the complex pattern of surface features found in these blocks. Directions: Open the file for 3D Geologic Blocks in a web browser as directed by your Teaching Assistant. Follow the directions on the screen and fill out the attached worksheets as appropriate. 1

2 Name Geologic Blocks: 103 Worksheet L-1 Sketch L-2 Sketch L-3 Sketch F-1 Sketch F-2 Sketch F-3 Sketch

3 Name Geologic Blocks: 103 Worksheet Direction of faulting: Visual clues used: Ft-1 Describe Ft-2 Sketch I-1 Describe I-2 List Order of Events (old to young)s (old U-1 Sketch

4 Blocks Module Student Guide In this module, you will learn about five major geologic features - layers, folds, faults, intrusions, and unconformities. These five features intersect surfaces in various ways due to geologic events that continually occur below the surface. Throughout the module, you will interact with movies to learn how geologic events such as tilting, deposition, erosion, and faulting change and modify the appearance of these five features on the surfaces of blocks. After interacting with these movies, you will be able to identify and recognize the five main features and reconstruct the geologic history that resulted in the complex pattern of surface features found in these blocks. The movies included in this module are QuickTime Virtual Reality (QTVR) movies and allow you to click-and-drag the mouse to change features in them. Above each movie, arrows will indicate the direction(s) you can move the mouse and text will indicate what changes will occur as you click and drag the mouse. Most sections begin with rotating movies so you can see the four sides and top of a block. These movies can be rotated by clicking and dragging the mouse from left to right (or right to left). The slower you drag the mouse, the smoother the changes will be. Other movies allow you to change two features at a time. For example, some movies let you rotate a block (clicking and dragging side-to-side) as well as making the block partially transparent so you can see features beneath the surface (by clicking and dragging upand-down). For movies with two changes in them, dragging the mouse diagonally will cause both changes to occur simultaneously. To prevent this, try to drag the mouse horizontally and then vertically (or vertically and then horizontally). Note: You can also use the arrow keys on the keyboard to make these changes occur and have more careful control over the changes. Other movie types in this module allow you to: cut into a block (from the left, from the right, and from the top) so you can see how a process such as erosion would change the surface of a block. offset the fault to observe how layers or folds would appear to change after faulting occurs. You can also simulate erosion by cutting into the blocks, rotate the blocks, and change the amount of transparency. reveal the unconformity to see the boundary between old and young rocks (where there is a large gap in time in which no distinct events occurred). While progressing through this module, you will be asked to complete various activities on worksheets. Questions on the worksheets will ask you to: sketch a missing face of a block; sketch a block after imagining it has been cut into; sketch a face of a block after it has been faulted; describe the differences between types of faults, how they change features, and how they can be recognized in the field; list geologic events in the order they occurred; describe differences in types of intrusions; and draw unconformities. Make sure you have the worksheet for each section before you begin. This module was designed to help you form your own definitions of terms and procedures. For this reason, answers will not always be provided for confirmation. The same is true of the application questions at the end of each section. Try to formulate your own answers on your own or in your group before asking your teacher for help.

5 Use the Quicktime movie that illustrates strike and dip to help you with the following for diagrams. 1. Draw three horizontal layers. 2. Draw three vertical layers. The dip of these layers is º The dip of these layers is º The direction of dip is The direction of dip is 3. Complete this block. 4. Complete this block. a b c d 45º 60º The strike of these layers is The strike of these layers is The dip (direction and angle) of these layers is The dip of these layers is The oldest layer is 5

6 Background Information: PART II. Working with a Geologic Map Geological maps represent 3D geology on a 2D surface similar to regular maps. The different colors on a geologic map show different rock formations. Formations are packages of rocks of the same type and age that are distinct from surrounding rocks. Elements of a Geological Map: Legend Scale Stratigraphic column The following symbols are used to denote geologic periods: Pc Precambrian (4,500 to 543 mya) C -- Cambrian (543 to 490 mya) O Ordovician (490 to 443 mya) S Silurian (443 to 417 mya) D Devonian (417 to 354 mya) M Mississippian (354 to 323 mya) P Pennsylvanian (323 to 290 mya) P Permian (290 to 248 mya) T -- Triassic (248 to 206 mya) J -- Jurassic (206 to 144 mya) K Cretaceous (144 to 65 mya) T Tertiary (65 to 1.8 mya) Q Quaternary (1.8 mya to today) Contacts: Contact lines are heavier, and separate different rock units. On a geologic map, faults are shown as solid lines, and the dip is usually given. Rock units on a map will have one of the preceding letters as the first part of the symbol for the rock unit; the second part will be part of the formation name. For example, Kf means Cretaceous Finlay (limestone), while Qal means Quaternary alluvium. 6

7 Directions: Answer the following questions using the geologic map of Texas. 1. Describe, in words, the color pattern on this map. What do you see? 2. What is the oldest rock unit on the map? Write out its name AND its symbol. 3. What is the youngest rock unit? Write out its name AND its symbol. 4. How are faults shown on this map? Draw some of the symbols. 5. If you follow I-35 from Dallas to San Antonio, you are following the Balcones Escarpment. What is the Balcones Escarpment? HINT: use the cross section on the back labeled U2-U3. 6. What kind of rocks are the TV formations between El Paso and Alpine? 7. As you drive from Fort Worth to Big Spring, do the rocks get older or younger? 7

8 8. As you drive from San Antonio to Corpus Christi do the sediments get older or younger? 9. Look at cross section F-F1. Locate the Live Oak Creek area and look in the pc formation to locate the vertical fault. Estimate the amount of displacement on the fault in the pc. 10. Look at cross sections E-E1. Locate the (green) Cretaceous rocks and follow them with your finger from the Fort Worth Basin to the Louisiana border. How many and what type of geologic structures do you see? 11. Look in the explanations to find the Precambrian rocks; find the pink granites and the brown metamorphic rocks. How many places in Texas are they exposed at the surface? What kinds of rock (igneous, metamorphic, sedimentary) are most exposed in Texas? Preparing for the Lab Quiz Practice with 3D blocks at Given a diagram of any geologic structure, are you able to identify the structure (e. g. anticline, syncline, normal fault, reverse fault, strike-slip fault? For diagrams of faults, can you identify direction of motion with arrows? 8