Lab 6- Virtual Pilbara Field trip
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Geology
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Apr 3, 2024
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GEOL 102
History of the Earth
Name: Lab 6: Virtual Field Trip – Pilbara
Purpose
:
In this investigation, you will explore some of the most well preserved Archean rocks using a Virtual Field Trip (VFT) put together by Arizona State University: https://vft.asu.edu/
These sites are all found on the Pilbara Craton
, in Western Australia. This area preserves some of the very best examples of Archean geology anywhere on Earth. It’s also relatively dry and remote, and thus has excellent exposure. Specifically, we’re going to focus on a few concepts:
1.
What rocks are typical of this area from the Archean
2.
What we look for as signs of early life
3.
Become familiar with the Pilbara craton in general, as it’s a crucial place in understanding early Earth history! Have fun!
Part I. Marble Bar (18 points) Enter this field trip here: https://vft.asu.edu/VFTMarbleBar/panos/MarbleBar/MarbleBar.html
Rocks at Marble Bar represent one of the oldest preserved sedimentary sections on Earth. They can give us information about the environments where very early life may have first appeared and evolved. Explore the area to answer the following questions. Main Marble Bar Chert Area: 1.
What is the law of original horizontality? (2 points)
2.
What types of rocks are here? (2 points)
3.
How did the banding in the Marble Bar Chert form? (4 points)
Upper ridge: 4.
What types of banding do you see here? Which types of rocks are preserved here? You’ll need to make observations, there are no videos or pictures here. (2 points) Outcrop area: 5.
What’s a pillow basalt? (2 points) 1
GEOL 102
History of the Earth
6.
What was the depositional environment shown here? How far below the surface of the water were these rocks deposited? (2 points)
General question: 7.
What kind of environment did early life most likely live in, at least in this location? That is, based on the rocks and minerals here, what was the environment like then? (4 points)
Part II. Dresser Formation (14 points)
The Dresser Formation preserves the oldest stromatolites on Earth! You’ll see some samples of these in the in person lab, but stromatolites are sedimentary structures that are likely formed by microbes. Enter this field trip here: https://vft.asu.edu/VFTDresser/panos/Dresser/Dresser.html
Upper Dresser Formation: 8.
What’s the name of the area here? How old is the Dresser formation? (2 points)
9.
What is the evidence that microbes made the stromatolites formed here? (4 points)
Lower Dresser Formation: 10. What type of fossils are preserved here? (2 points)
General question: 11. What does the depositional setting (i.e., water depth) at this site, and how do we know? What does this tell you about the environment in which early life lived? How do we connect the geology of this area to the biology of what was living? (6 points)
Part III. Karijini Gorge (20 points)
Karijini gorge is a national park in Western Australia. It preserves some of the world’s most awesome exposures of Banded Iron Formations.
These are units that were relatively common in the Precambrian (Archean and Proterozoic), but are much rarer in the Phanerozoic. They are comprised of alternating layers of silica and iron oxide, and there has been a lot of research in trying to figure out how they formed! BIFs are often mined as iron ore, and the units in Western Australia are some of the biggest deposits in the world. Iron ore from this area is carried by autonomous trains to a port in Port Hedland, where it is shipped out, mostly to China. We will explore the science behind these deposits in this section of the lab.
2
GEOL 102
History of the Earth
Enter this field trip here: https://vft.asu.edu/VFTKarijiniGorge/panos/karijinigorge/kg.html
First, click the “Close to Rocks” arrow, and watch all the videos in the “Dales Gorge Overview” icon. To answer the questions below, you’ll need the overview videos and all the videos in both the “Dales Gorge Layers” and “Red Rock, Iron, and Chert” icons, which you can get back to by clicking “Close the Falls”.
12. Describe the physical characteristics of these units. Include in your answer the environment of deposition and what minerals are found in the layers here. Please outline evidence for the depositional setting as well. (4 points)
13. Is there a lot or only a little organic carbon found here? (2 points)
14. What “biosignatures” are found in the layers here? (2 points)
15. How much iron is there in these rocks (a lot or a little)? What was the source of the iron? (2 points)
Next, click “Down the Canyon”. Watch the videos in the “BIFs and evidence of oxygen” and “Microbes and rust” icons. Answer the following questions. 16. What is the conventional interpretation of how BIFs formed? (4 points)
17. What lines of evidence do we use to detect the presence of oxygen in the rock record? (2 points)
18. Are there types of microbes that can do photosynthesis but NOT make oxygen? How would these organisms impact the formation of BIFs? (2 points) 19. How does the history of Earth and it’s oxygenation inform our search for life elsewhere? (2 points)
There is one more stop down the canyon if you wish to explore it! Down here are examples of natural asbestos outcrops, that (gulp), used to be mined.
Part IV. Summary (8 points)
Write a couple paragraphs summarizing the paleoenvironments you’ve seen on this set of field trips. Focus on the similarities and differences between the sites, and how they record the environment, activity, and evolution of early life on Earth. Your answer may include textural evidence, geochemical evidence, or a combination of the two as supporting information. 3
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