Circle Ridge, Wyoming

Structures and Landscapes

GLS210 Geomorphology Lab

Dr. Lindley Hanson, Dept. Geological Sciences, Salem State College ()

Erosional landscapes are strongly influence by the lithology and structure of the rocks being consumed. Lithology determines rock competence, while structure influences avenues of erosion and overall grain of the landscape.

Goal: In this lab you will learn to recognize and interpret variations in landscapes attributed to lithology and structure. As with any discipline knowledge of the jargon in required. During lab and lecture we will be building a glossary of terms through Google Doc. You will be expected to be able to know and identify features in the glossary.

Objectives:

Upon completion of this lab you are expected to be able to:

interpret topography and basic structural elements and alpine landscapes from satellite images
correlate rock strength to lithology
identify and define numerous landscape element (see Google Docs glossary)
distinguish between tectonic landforms and landforms created by differential erosion.

Directions: Type your answers in blue. Images must be annotated in powerpoint and placed back into the document. Upon completion submit through webct.

Time requirements:

Lab time: 6 hours. Homework 4 hours

Requirements:

Google Earth, powerpoint and word

kml files: Panoramio (

Prelab preparation:

Before lab research and define at least 10 of the terms listed at the end of this lab.
Read:

Chapter 5 and 12 in Bloom
Chapters 14 and 15 in Jones and Jones

Laboratory Exercise:

This lab contains two sections. Part I is designed to familiarize you with basic structures and how they are manifested in the topography. You will also be introduced to features and landforms associated with different structures. Part II is an interpretive section that requires that you to interpret aspects of a structure based on elements of the landscape.

Before starting activate Panoramio in the Google Earth Layers Pane. Open the StructuresLab.kmz file. However keep all folders and layers unselected until needed. Deselect features you have finished. Too many active layers and folders with slow down Google Earth.

Part I. Tour of structures and landscapes

Tour the following region through Google Earth and answer the questions. Be prepared to discuss your answers in class.

A. Horizontal Sedimentary Rocks

Open and view “Horizontal Rocks” folder. Write down your observation and answer the questions. Double click on the marker to get a description of the area. The examples in this section lie in the arid and semiarid regions of the West, where resistant strata are composed of sandstone or massive limestone, and less resistant strata are either shale or finely-interbedded layers of variable lithologies.

1. Grand Canyon

Activate Terrain mode and fly around the landscape. Note the formation contacts and their lateral continuity and the dominant drainage basin pattern of the region. (Refer to pp. 269-271 in Bloom)

a. Identify the Physiographic Province.

b. What is the evidence that the strata are horizontal and vary in their resistance to weathering and erosion

Describe the landscape. What feature(s) or concepts from your glossary are illustrated here?

2. Canyonlands

a. Describe the landscape. What feature(s) or concepts from your glossary are illustrated here?

b. Note the blocks of White Rim Sandstone on the floor of the canyon. What mass-wasting process is occurring here and why?

c. Note that the jointing is most obvious along the margins of the canyon. Construct a hypothesis to explain this relationship.

3. Monument Valley

a. Describe the landscape and identify the province. What feature(s) or concepts from your glossary are illustrated here?

b. Monument Valley and the Grand Canyon contain similar lithologies and structure. Compare and contrast their landscapes. How are they similar? How are they different?

c. The Monument Valley buttes (image) are composed of the following lithologies in ascending order: The Permian Organ Rock Shale forms the pedestal, the DeChelly sandstone the vertical columns, and the Triassic Moenkopi (sandstone) Formation and the Shinarump Conglomerate form the cap. In the space below redraw Merrick butte from this image. Draw in and label the formation contacts.

d. On what observations did you base your interpretation?

4. Badlands of South Dakota

The typical topography of the Badlands results from a combination of climate and geology. The region receives on average 16 inches of rain a year, temperatures range from an average low of 32 °F during the winter and to 91°F in July, promoting short grass prairies. Rainfall typically occurs as intense summer thunderstorms. The poorly consolidated Eocene-Oligocene rocks of the White River Group lack many of the essential nutrients for plant growth. The combination of poor vegetative cover, easily eroded strata, which is both fine grained and impermeable, heightens the effect of runoff to create this highly dissected landscape.

a. Describe the landscape and identify the province. What feature(s) or concepts from your glossary are illustrated here?

b. In the Grand Canyon and Badlands NP strata are horizontal yet their landscapes are noticeably different. Explain why this is so.

B. Inclined Strata

1. Eastern Flank of the Wind River Uplift (marker 1)

a. Describe the landscape and identify the province. What feature(s) or concepts from your glossary are illustrated here?

b. What is the triangular feature that the place mark is located on? How did it form?

c. The rule of Vs is discussed in on page 287 of your lab manual. View the landscape from 6000 ft. State and explain whether or not the rule of Vs accurately predicts the dip of the strata throughout the view area.

d. What controls the angles of the resequent (or dip slope) and obsequent slopes along the hogbacks?

Identifying Unconformities and other structures

e. Paleozoic strata unconformably overlie highly metamorphosed Precambrian rocks. Move due west of the marker until you locate the unconformity. With the measuring tool determine approximately (to the nearest .5 miles) how far west the unconformity is from the marker. Name the type of unconformity this is.

Answer_ miles

f. What other structures do you see in the metamorphic core of the Wind Rivers?

Signs of Alpine Glaciation

g. Was this mountain range ever covered by alpine glaciers? ____ Cite any evidence if present.
h. Double click on the Wind River Lakes marker, and then on the Wrangell-St Elias Range. Compare these two landscapes and discuss the formation of the elongate lakes formed on the western flank of the Wind River Range.

2. Comb Ridge, Utah

a. Describe the landscape and identify the province. What feature(s) or concepts from your glossary are illustrated here?

b. What evidence is there that the strata west and east of the escarpment are horizontal?

c. From the base up why does the obsequent slope change from gentle to steep?

C. Faults

1. The Garlock Fault is a predominantly strike slip fault that extends from the San Andreas Fault to Death Valley.

a. What geomorphic feature is formed over the fault?

b. Explain why such features form along strike slip faults faults.

2. The Owens Valley Fault is the western-most normal fault of the Basin and Range. The scarp marking the fault line reflects the relative motion between the western and eastern block.

a. Based on the topography and the information given about determine the direction of dip for the fault.

b. In general, can you tell the dip of a fault from the slope of the fault scarp? Explain.

D. Jointed Terrains

1. Zion National Park, Utah

a. Describe the landscape. What feature(s) or concepts from your glossary are illustrated here?

2. Arches National Park, Utah

a. Describe the landscape. What feature(s) or concepts from your glossary are illustrated here?

3. Black Hills, South Dakota

a. Like the Wind River Range in Wyoming the Black Hills is an Laramide uplift. Look closely at the Panoramio images. Is the rock exposed here sedimentary, igneous, or metamorphic? Describe the landscape.

b. Zoom out and look at the overall fold structure of the Black Hills uplift. What is it?

c. Look at the immediate area around the marker. Is there any evidence that this area was affected by alpine glaciation?

E. Folds

1. Southern Iran: Tectonic Landforms

a. Structural and topographic basin: Using the image below placefive strike (one on each side in in the middle) and dip symbols around the structure showing the strike and direction of dip of the beds. Draw the fold axis with arrows indicating directions of plunge. Indicate where the oldest and youngest strata are. Identify the fold and label any other observed geomorphic landforms.

b. Southern Iran: fold 2. On the image complete the following. Draw three strike and dip symbols (flanks and hinge). Indicate the fold axis and locate the oldest and youngest strata. Identify the fold and label any other observed geomorphic landforms.

Part II. Interpretive exercises

A. Grass Valley, Nevada

Describe the landscape. What feature(s) or concepts from your glossary are illustrated here?
Determine whether Grass Valley a full graben or half graben? Discuss how you came to this conclusion.

B. Southern Appalachians – Vicinity of Gate City Kentucky

Study the topography and the Geology of Gate City map overlay. . (Legend)Do not select the Structure-Sections overlay. A description of the geologic formations is given in the Appendix. Complete the following:

1. Describe the landscape and identify the Physiographic Province. What feature(s) and/or concepts from your glossary are visible here?

2. Refer to the features indicated by place marks:

a. Fold AIdentify the obsequent and resequent slopes and determine whether this fold is an anticline or syncline and the direction of plunge and cite your supporting evidence.

b. Fold B Identify the obsequent and resequent slopes and determine whether this fold is an anticline or syncline and the direction of plunge and cite your supporting evidence.

c. Fault (Marker 3) In addition to folds, this region is cut by numerous faults that all dip to the southeast and are contemporaneous with folding. Is this fault a thrust or normal fault? Discuss your evidence. Hint: follow the trace of the fault east and note the age of the beds on both sides.

d. Would you consider the scarp formed along the fault a fault scarp, fault-line scarp, or something else? Does it vary along strike? Explain.

e. Marker 4. Identify the drainage basin pattern of the region around this marker and the structure of the underlying sedimentary rocks? In which Appalachian Province is this located?

f. Describe the topography of the formations listed below. (Do they form lowlands or ridges? Is the topography variable, indicating a variety of interbedded lithologies?)

Clinch Sandstone (Scl):

Sevier Shale (SSv):

Newman Limestone (Cn):

Marysville Limestone (Cambrian m):

Lee Conglomerate (Cls):

Russell Formation (Cambrian rl)

g. Hypothesize the origin of the very prominent ridge indicated by marker 5 and discuss your logic. (Check your answer by activating the structure section.)

h. The Cumberland Gap (Marker 6) is a water gap formed by a stream flowing across the grain of the landscape. List and describe three hypotheses developed to explain the origin of streams that traverse the regional structure.

3. The basins and domes in Iran are considered tectonic landforms, however the ridges and valleys in the Appalachian Province are not. Explain the difference.