Lab_6_2024W
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University of California, Santa Barbara *
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Geology
Date
Apr 3, 2024
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EARTH 2 Your name: ___________ Lab day & time: ______________ TA name: ____________
Lab 6: The Geology of Santa Barbara
Purpose of the lab:
Learn about the Geology of Santa Barbara
Study uplift along the Santa Barbara coast
Apply knowledge learned in lecture and previous labs to geology in the field.
We will meet in PSB-S and walk together to the wooden, beach-access staircase east of Santa Cruz Hall.
PART 1: Beach sands, wave-cut terraces and the Monterey/Sisquoc shales.
At this stop, we will study the modern beach environment and the rocks that make up the white cliffs.
A.
The staircase is supported on pillars that are anchored into the bedrock of a wave-cut terrace—a flat bedrock surface produced by wave erosion—beneath the loose sand. In the winter, storms remove the
sand from the beach and it then returns in the summer. Climb down the stairs and observe the height of the sand on the bottom support pillars and stairs. Draw the top of the sand on the figure.
Given that the cement block that anchors the stairs to the bedrock is 1.5 meters high, how deep is the sand today? _________ m [2]
B.
The white rocks that make up the beach cliffs in Santa Barbara are part of the Monterey and Sisquoc Formation. These shales, which formed off-shore from 18–4 million years ago, are very rich in microscopic silica diatom skeletons and are the source rocks for the oil in the Santa Barbara channel. Based on this description and your observation of the rocks, are these igneous, metamorphic or sedimentary rocks? Justify your answer. [2]
C.What is the grain size of these rocks? Give your answer in mm, fraction of a mm or indicate too small to see. [1]
1
1.5 m
EARTH 2 Your name: ___________ Lab day & time: ______________ TA name: ____________
D.
Have the rocks been deformed (fold, tilted, faulted) since they formed? If so, how have they been deformed? How can you tell? [2]
Recall the principles for interpreting the geologic record from lecture.
E.Walk both ways along the cliff, looking up (if the tide is low enough), and then climb part way back up the stairs to observe the upper part of the cliff face. What material makes up the top of the cliff? Is it the same as the base of the cliffs? [1]
F.What are the small, white pieces along the contact you just identified? You can see them from the beach, but can get a better look from the stairs. What do they imply about the elevation of this contact, relative to sea level, when the overlying sediments were deposited? Explain your answer. [2]
G.On the sketch above, draw a line on the cliff face showing the contact you just identified. [1]
H.
Now, make a sketch of the cliff face directly across from the bottom of the stairs (where the drainage pipe comes out ~2/3 of the way up). Your sketch should go from the beach sand to the top of the cliff and include the contact you identified above and the orientation of layering within the Monterey/Sisquoc Formation rocks. [1]
2
EARTH 2 Your name: ___________ Lab day & time: ______________ TA name: ____________
I. What type of unconformity does the contact represent (angular, nonconformity, disconformity)? Name the unconformity here and label it on your sketch in Question H. [2]
J. The surface of the unconformity is an old terrace that carbon dating indicates was cut by the waves about 45,000 years ago (Gurrola et al., 2014). Since then it has been uplifted to its present height. Using the supplied measuring tapes, measure the current height of the unconformity. (Climb up the stairs to the level of the unconformity, then measure the height straight down to the beach). Current height _________ m [1]
K.The graph above shows how sea level has varied over the past 120,000 years (modified from Gurrola et al., 2014 based on data from Muhs et al., 2012). Using this graph, determine the elevation of sea level relative to modern sea level 45,000 years ago.
Sea level 45,000 years ago: _____________ m [1]
L.
How much has the wave-cut terrace exposed in the beach cliffs been uplifted since it was formed 45,000
years? Be sure to account for both the change in sea level and its current height relative to sea level.
___________________ m [1]
M.
Now calculate the rate of uplift of the Santa Barbara beach cliffs in both m per thousand years (m/ka) and mm per year (mm/yr).
___________________ m/ka [1]
_________________________ mm/yr [1]
3
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EARTH 2 Your name: ___________ Lab day & time: ______________ TA name: ____________
N.
Based on your answer above, how many km of uplift would occur per million years (km/Ma)?
__________________ km/Ma [1]
O.
From your lecture notes, what process is leading to uplift in Santa Barbara? Be sure to include an explanation of why there is uplift in Santa Barbara even though most of California is a transform (strike-slip) boundary [2].
PART 2: Campus Point Beach
A.Study the large boulders along the beach and at the base of the cliffs to the east of the beach.
i.
Are the boulders igneous, metamorphic or sedimentary rocks? [1]
ii.Describe the grain size of the rock and determine the name of this type of rock (e.g., andesite, shale, sandstone, rhyolite, gneiss, etc.)
Grain size: ________________ mm [1]
Rock name: __________________________ [1]
iii.
Are the boulders the same rock type as the beach cliffs you looked at in Part 1? Explain your answer. [1]
4
EARTH 2 Your name: ___________ Lab day & time: ______________ TA name: ____________
iv.
Note the honeycomb weathering on some boulders. This is a very common type of weathering, especially near the ocean. It is caused by salt crystals growing in pore spaces within the rock, causing the rocks to break down (physical weathering!). The formation of pockets with thin walls between them may be related to a combination of the salt weathering and wind blowing over the rock: Initial salt weathering leads to formation of a small pit. This pit changes the aerodynamics of the surface and causes wind to travel more quickly over the pit, leading to enhanced evaporation of salt water within the pit, additional crystallization of salt as the water evaporates, and further breakdown of the rock (Rodriguez-Navarro et al., 1999). Make a small sketch of the honeycomb weathering below (note the scale, 15 cm is slightly longer than an iphone). [2]
v.The boulders were brought in to act as a breakwater and slow erosion of the sea cliffs behind them. Have they been effective? [1]
PART 3. Campus Point A.
Observe the waves breaking on the beach from the top of Campus Point.
i. The wave-cut terraces we discussed in Part 1 form due to wave erosion of the coast. Wave erosion is effective
because it is a continuous process.
Count how many waves hit the beach in one minute:
________waves/min [1]
Now calculate how many waves hit the beach in one year:
________waves/year [2]
Even if each wave only erodes a little bit, over time the constant wave action adds up to a lot of erosion. 5
15 cm
EARTH 2 Your name: ___________ Lab day & time: ______________ TA name: ____________
B.
Regional overview.
In Part 1 (at the stairs), we examined an old, uplifted wave-cut terrace. There are actually a series of uplifted terraces in Santa Barbara, which reflect progressively older marine surfaces that have been uplifted over time. The cartoon below from Gurrola et al. (2014) illustrates a modern terrace/platform, an uplifted, older terrace (E1), and an even older terrace (E2). i.
The terrace that UCSB is built on is a widespread feature in the Santa Barbara area. Observe the terrace surface looking east down the coast and mark it on the sketch of the coast below. [1]
ii.Next look for and label two higher surfaces that might be older, more uplifted terraces that have been rounded by erosion. [1]
6
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