Lab_6_2024W

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University of California, Santa Barbara *

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2

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Geology

Date

Apr 3, 2024

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docx

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6

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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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