Table 1: Interpreting the Sedimentary History from a Stratigraphic Section Using
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Question
Table 1: Interpreting the Sedimentary History from a Stratigraphic Section Using both your text & lecture notes to determine the environment of deposition and list supporting evidence for that environment. Then, answer the questions below this table Rock Unit Environment of osition and Observations to Su Your Chosen Environment Upper sandstone and mudstone unit Dark gray shale Yellowish-tan sandstone Lower basal conglomerate Question 1: What is the oldest environment represented by this rock sequence? Question 2: Does the change of environment from the base of the section up to the thick gray shale indicate an advance (transgression) or retreat (regression) of the sea? Explain the reasons for your answer. Question 3: Does the change from the thick gray shale to the overlying sandstone indicate a transgression or a regression? Explain your answer Question 4: Which of the following phrases summarizes the history of the entire sequence: (a) a transgression, (b) a regression, (c) a transgression following by a regression, or (d) a regression followed by a transgression? (circle your answer)Explanation / Answer
a)
Ans: River system
sand stone is made of sand grains (0.05-2mm)
cemented together. It is formed from sediment deposited by rivers,
mud stone made up of fine-grained clay particles (<0.05mm) compressed together. Mudstones form where clay has settled out in calm water - in lakes, lagoons, or deep sea.
Ans: muddy part of ocean
there are fossils of marine organisms in these rocks, and most of this unit is made of shale.
Ans: sandy beach or delta
this unit was deposited near the shoreline (beach or delta) because it contains fossils of both marine and land-dwelling organisms. (tan or yellow color--from a blend of the clear quartz with the dark amber feldspar content of the sand)
Ans: river system
The conglomerate could have been deposited in a river channel
Q1) lower basal conglomerate.
this is the lowest unit in a stratigraphic section.
Q2)Transgression
In this case we will have deeper sea sediments, shales being deposited on top of continentally-derived beach sediments (sand).A maximum transgression occurs where the finest sediments reach the farthest landward.
Q3) Marine Transgression
it is a geologic event during which sea level rises relative to the land and the shoreline moves toward higher ground, resulting in flooding and we will have deeper sea sediments, shale deposited on top of continentally-derived beach sediments (sand).
Q4) a regression followed by a transgression
Ans: River system
sand stone is made of sand grains (0.05-2mm)
cemented together. It is formed from sediment deposited by rivers,
mud stone made up of fine-grained clay particles (<0.05mm) compressed together. Mudstones form where clay has settled out in calm water - in lakes, lagoons, or deep sea.
Dark grey shaleAns: muddy part of ocean
there are fossils of marine organisms in these rocks, and most of this unit is made of shale.
yellowish tan sandstoneAns: sandy beach or delta
this unit was deposited near the shoreline (beach or delta) because it contains fossils of both marine and land-dwelling organisms. (tan or yellow color--from a blend of the clear quartz with the dark amber feldspar content of the sand)
lower basal conglomerateAns: river system
The conglomerate could have been deposited in a river channel
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