geol exam 3
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whats the difference between weathering & erosin?
- weathering is the breaking down of rock
- erosin is the transportation of that broken material away from it's sources
what r 2 types of weathering
what r 3 types of joints that form in rocks?
- exfoliation joints
- coumnar joints
- planar joints
what are 2 forms of wedging that can happen mechnaical weathering
frost & root wedging
what r 3 main types of reactions in chem weathering
will acid increase or decrease chemical weathering?
what does cO2 in the air combine with to form acid?
what is the terrain the has lots of sinkholes & caves called?
which mineral is more susceptible to weathering: olive or quartz?
which layers are more resisteant to weathering &which layers are less resistant to weathering?
- more resistant to weathering (on top)
- less resistant (bottom of the rock)
what factors influence the rate of weathering?
- rock type
what are the 3 types of mass wasting classified by their movement
whats the slowest flow mass wasting called?
what factors of a slope determine its susceptibility to mass wasting?
- high relief
- thick layers of loose rock, debris & or soil
- presence of water
- lack of vegetation
- seismic activity
what should u not do to prevent slope failure
- over steepen slope
- remove vegetation
- add water
- add additional weight
what are 3 techniques used to prevent rockfalls & rockslides on highways
- remove all rocks that are prone to sliding
- stictch together outcrops
- construct concrete sheds with sloping roofs
how do streams with alot of suspended load appear?
they appear muddy
meandering streams flow faster at which part of the bend
outside the bend
whats teh name of the feature formed when part of river channel becomes abandoned
what feature od formed when sediment deposits at the mouth of river as a result of flow veocity decreasing
the chance of a 50yr flood happening in any goven yr is what?
whar r 3 ways that we can work around flooding that occurs on rivers
- building dam
- not settleing in areas that flood
how far can streams erode down to
their base line
what are 3 ways that stream erosin occurs
- hydraulic action
what 2 things happen during lithofaction?
what common minerals can cement sediment together
whats is the name of the poorly sorted seimentary rock with angular clasts
what mineral is limestone mainly compsed of
whats the name of the single celled plant organisms with shells of silica
what eniorments do evaporates form in
wats is the oxygen content of the water in which plant material that eventually becomes coal is
what fossils tell you about the rock they are found in?
- the depositional enviorment
- the age of rock
whats the name of the deposit of till found on to the side of the glacier?
whats the most common sedimentary structure
whats the name of the cycle hat decribes the movement &interchange of water between sea, air & land
whats the most important geollogic agent in eroding transporting & depositing sediment?
what are the 3 ways sediment can transported by a stream
- bed load
- suspended load
- dissolved load
Upper sandstone and mudstone unit: This unit includes sandstone, mudstone and layers of coal. The upper part of the unit contains sandstone beds with small cross beds. The mudstone has mudcracks and plant fossils. The lowest part of this unit is a little different, and will be the subject of a future question.
The most likely environment of deposition for the majority of the upper sandstone and mudstone unit described above is
In the description of the upper part of the upper sandstone and mudstone unit, it mentions "sandstone beds with small cross beds." How do you interpret these small cross beds?
formed by migrating ripples or dunes on a river bed
In the description of the upper part of the upper sandstone and mudstone unit, it mentions mudcracks. How do you interpret these mudcracks in a way that is consistent with the environment of deposition that you infer for this unit?
formed on the flood plain surrounding a river
How do you interpret the layers of coal within the upper sandstone and mudstone unit?
formed in a swampy environment alongside a river
Now let's turn our attention to the lowest part of the upper sandstone and mudstone unit. This is described as containing "tan sandstone beds with broken marine shells."
What environment of deposition do you infer for these rocks? (Keep in mind that it should be an environment that would normally be found adjacent to the environment that you inferred for the part of this unit).
sandy beach or delta
The next layer down is the medium to dark gray shale. What environment of deposition do you infer for these rocks?
muddy part of ocean
Yes. The description specifies that there are fossils of marine organisms in these rocks, so we must choose one of the marine environments that is listed: sandy beach, coral reef or muddy part of ocean. The fact that most of this unit is made of shale, makes "muddy part of the ocean" the best answer.
The next layer down is yellowish-tan sandstone containing quartz sand with small pieces of marine shells. The very base of the unit is a thin conglomerate that overlies an erosion surface. This lower part locally contains fossils of wood and leaves. What environment of deposition do you infer for these rocks?
sandy beach or delta
Yes. Sandstone can form in many different environments, but the presence of marine shells narrows it down to a marine environment. The fact that the marine shells are only present as "small pieces" would be consistent with shells being broken up by waves crashing on a beach. Also the fossils of wood and leaves in the lower part of this unit must have come from on land, so that further confirms that this unit was deposited near the shoreline (beach or delta) because it contains fossils of both marine and land-dwelling organisms.
The lowest unit includes congomerate at the base with moderately rounded pebbles and coarse sand containing scattered pieces of fossilized wood. The conglomerate is overlain by reddish, maroon and gray shale and mudstone with plant fossils. There are also dinosaur footprints in the mudstone.
The reddish color of this unit, along with the types of fossils present indicate that these rocks were deposited in
an on land enviornment
The red color in rocks often indicates the presense of the iron-oxide mineral, hematite. This most commonly forms in environments that are exposed to oxygen in the atmosphere, and NOT in under-water environnments. Also, all of the fossils listed (plants, wood, dinosaur tracks) are things that would form on land, not in an ocean or lake.
Considering your answer for the previous question, what do you think is the most likely depositional environment for the lowest unit (congomerate and red and gray shale and mudstone)?
The conglomerate could have been deposited in a river channel and the mudstone on the floodplain surrounding the river. It would be natural for wood and plant fossils and dinosaur footprints to be preserved in the muddy floodplain surrounding the river channel. Alternatively, the conglomerate could have been deposited on an alluvial fan, near a steep mountain front (partial credit), but it is harder to explain the shale and mudstone in that environment.
The change of environment from the base of the section up to the thick gray shale indicates
a transition from a non-marine environment early on, followed by a rising of sea level that led to a marine environment during deposition of the gray shale.
The sequence of the three lowest units indicates rising sea level. We start with the conglomerate and red and gray shale and mudstone deposited along a river system, which is above sea level, and thus, non-marine. This is followed by the yellowish-tan sandstone, which formed at a beach or delta, at the shoreline. Then later we have the gray shale, which was deposited in the ocean. This progression indicates that sea level (relative to the continent) was rising over time.
Based on your answer to the previous question, does the change of environment from the base of the section up to the thick gray shale indicate a transgression or regression of the sea?
The three lowest rock units indicate a rise in relative sea level over time, and this is called a transgression. A drop in relative sea level is called regression.
Does the change from the thick gray shale to the overlying sandstone (at the top of the section) indicate a transgression or regression of the sea?
The gray shale was deposited in a marine environment, and after that we have the sandstone and mudstone of the uppermost unit, which was deposited in a river system. This indicates a transition from a marine to a non-marine environment, caused by a drop in relative sea level, which is called a regression.
Which of the following phrases summarizes the history of the entire sequence?
transgression followed by regression
What is the type of joints where one set forms parallel to layering in the rock while the other sets form perpendicular to the layering?
planar joints sets
Which mineral of those listed is least resistant to weathering?
Tilting utility poles and cracked foundations are evidence of what type of mass wasting?
What part of a meandering river moves the slowest?
What are some ways to mitigate flooding?
move houses away, high teefs?, etc
Stream cut terraces show a change in what?
A depositional environment to an erosional environment
What type of drainage pattern resembles the branches of a tree?
Which of the following minerals does not act as a cementing agent during the lithification process?
What is mineral is limestone made mostly of?
What type of rock is formed from deposits on the abyssal plains?
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