Reference no: EM132801641

Sedimentary rocks and the record of the Paleozoic in Wisconsin

Collaboration:
This assignment needs to reflect your understanding and knowledge of the questions below. While you may discuss these questions generally with your classmates, TAs, and me, the work you submit must be your own. You must reaffirm the honor code on this and all assignments.

Sandstone
The images below are of the Jordan sandstone collected at an outcrop on Guhl Road in Readfield Wisconsin (about 5 miles south of Cactus Rock/New London). The Jordan Formation is from the upper Cambrian (meaning it is from the end of the Cambrian). The sandstone is a yellowish-orange. Particles are well rounded and between 0.5-1.0 mm. The mineralogy is overwhelmingly quartz.

1. What environment was this sandstone deposited in?

2. Describe how the mineralogy, grain size (including the sorting), and grain shape of this sandstone informs us about the depositional environment that this rock records. For each of these four lines of evidence, you should have 2 sentences describing how that feature supports your conclusion about the depositional environment.

• Mineralogy:

• Grain Size:

• Grain Shape:

Oneonta Formation
At the same outcrop in Readfield, just above the Jordan Formation, we see the Oneonta Formation. The rocks of the Oneonta Formation are a dull gray-tan. There are extensive horizontal cracks with abundant, though not as continuous, vertical cracks. The rocks react and effervesce when dropped with hydrochloric acid, however, this reaction only occurs after the rocks have been scratched and the freshly powdered surface is what reacts. The rock unit contains stromatolite fossils. There are also ooids present in the rock.

3. What type of rock is this (Importantly, you should be sure you are confident in your answer to this question before proceeding)? What mineral dominates this rock?

4. What environment does was this rock deposited in?

5. Describe how the mineralogy, ooids, and stromatolites in this dolostone informs us about the depositional environment that this rock records as well as its diagenesis. For each of these three lines of evidence, you should have 2 sentences describing how that feature supports your conclusion about the depositional environment.
• Mineralogy:

• Ooids:

• Stromatolites:

Stratigraphy

The outcrop at Guhl Road shows the Cambrian aged Jordan formation at the base with the Ordovician Oneonta Formation overlying the Jordan. You should use the descriptions of the individual rock units from the previous sections as well as your interpretations, along with the figure below, to interpret what happened to leave this stratigraphy.

6. Use the figure and description above to interpret the depositional environment of this location during the Cambrian and Ordovician. What happened "here" to result in the change in rock type that was being deposited.

7. This sequence of rocks records the end of the Cambrian and the start of the Ordovician. You will write a short paragraph (~5 sentences) summarizing what happened as Earth moved from the Cambrian to the Ordovician.
• Consider the following questions to help craft your paragraph:
i. In general, what marks the end of a geologic period and the start of a new one?
ii. What changes in life in these ancient seas would have happened across this time boundary?
1. What are some organisms that might have been alive at the time the Jordan sandstone was being deposited that disappeared by the time of the Oneonta dolostone?
2. What are some organisms that began to thrive in the Ordovician that weren't alive prior to this time boundary?
iii. What are some of the possible causes of this extinction event?

Proximity and Connections to Cactus Rock:

The outcrop we see at Guhl Road is just a few miles from Cactus Rock. The elevation of Cactus Rock sits just a bit higher than the top of the rocks we see at Guhl Road. Cactus Rock formed 1.7 billion years ago. The sedimentary rocks at Guhl Road were deposited about 500 million years ago (the Cambrian Ordovician boundary is 488 million years ago). What amazes me about these relationships is that the rocks at Guhl Road, which are ~500 MILLION YEARS OLD!, are much closer in time to today than they were to the formation of Cactus Rock! Cactus Rock was already well over a billion years old by the time these rocks were being deposited! However, that doesn't mean that there aren't some connections. For this section, you will want to think about how the rhyolites/granites that were a part of Cactus Rock, relate to the materials deposited at Guhl Road. For these questions, you will want to think about how the weathering of the Cactus Rock helped form these other deposits. You should specifically reference the chemical reactions discussed in the PowerPoint presentations on Moodle as appropriate.

8. How might the weathering and erosion of Cactus Rock have contributed to the Jordan Sandstone?

9. How could the weathering of Cactus Rock have contributed materials needed to form the limestone that is today the Ordovician dolostone?

10. In addition to the sandstone and dolostone that we see at Guhl Road, there are also shale deposits in the area. How might the weathering of Cactus Rock have contributed to the formation of these shales?

Michigan Basin Michigan Basin

In our lab from this unit, you considered the geology of the Michigan Basin, now, you will think about what is going on underground.

1. Sketch a geologic cross section from Door County, WI to southeastern Michigan. Door County sits on the boundary of Silurian and Ordovician rocks. Southeastern Michigan sits approximately on the Devonian - Silurian boundary. The contact of Silurian and Ordovician rocks lies approximately 3,000 meters below the center of Michigan's lower peninsula. Your cross-section should show bedrock from the Ordovician, Silurian, Mississippian, Pennsylvanian, and Jurassic with these units labeled clearly on your sketch.

2. How does the structure of the Michigan Basin that you drew help explain the connection between the geology of local features such as High Cliff State Park and the Door County peninsula and Niagara Falls?

Attachment:- Paleozoic in Wisconsin.rar