exam 2 geology

chapter 7

Which of the following are most likely to preserve conditions of ancient environments on the Earth?

sedimentary rocks

Sedimentary rocks are most likely to form

near the Earth’s surface

The majority of the rocks that form at the surface of the Earth are

sedimentary rocks

What is the difference in the formation of chalk versus chert?

They are made of different source materials.

Chemical sedimentary rocks are classified primarily on the basis of

mineral composition

Biochemical limestones are dominated by carbonate mud and fragments of

skeletons of marine invertebrates made of calcite and aragonite.

Which of the following is true regarding biochemical chert?

It is made of cryptocrystalline quartz.

The breakdown of exposed rock into small fragments and dissolved ions is termed

weathering

Compaction and cementation of grains occurs during

lithification

Grains become rounded primarily during

transportation

The primary difference between breccia and conglomerate is that conglomerate

possesses more rounded grains than breccia

The image below shows an outcrop of coarse-grained sedimentary rock. Note the rock hammer for scale. What is the name of this rock type?

conglomerate

If water is the transport mechanism of sediment, the grain size of sedimentary deposits most closely indicates the

velocity of the water at the moment the sediment settled to the bottom.

The sedimentary rocks breccia and conglomerate most commonly form in a ________ environment.

mountain stream

Two major sources of energy, coal and oil shale, are considered ________ sedimentary rocks.

organic

Cemented shells of marine organisms form which kind of sedimentary rock?

biochemical

Geologists call individual layers of sedimentary rocks ________, whereas several of them together are called ________.

beds; strata

Stratification refers to

the development of layering within sedimentary rocks.

When graded beds are observed in a rock outcrop, this tells geologists that a

turbidity current deposited these beds, depositing coarser material first.

The image below shows a series of graded beds. How many graded beds are shown?

3

The image below shows ancient dunes exposed in Zion National Park in Utah. Using the interpreted portion of the image at the left, what was the dominant wind direction that formed these sedimentary structures?

toward the right

Consult the figure below. Here, distinct internal laminations are inclined at an angle to the boundary of the main sedimentary layers. These are termed

cross beds.

Which environment would most likely produce sedimentary deposits characterized by poorly to moderately sorted, angular to subangular grains that consist of feldspar, quartz, and lithics (rock fragments)?

alluvial fan

Which transport medium carries the largest particles?

ice in glaciers

It is unusual for ________ to carry grains larger than sand.

wind

Symmetric ripples form when

water deposits sediment in layers, but the direction of flow periodically changes.

If a geologist found preserved mud cracks, he or she could conclude that the environment in which they formed

was once covered in wet mud.

Large layers of cross-bedded sand can be indicative of a ____________ environment.

desert

Which environment would most likely produce sedimentary deposits characterized by very well-sorted, very well-rounded grains that are nearly pure quartz?

beach

What type of sediment is typically found in lake bottoms?

clay/mud

Topset, foreset, and bottomset beds are indicative of ________ environments.

delta

Which of the following is NOT true? Sediments deposited in a beach environment are typically

composed of angular grains.

Thick accumulations of sediments and fossils in the deep ocean tend to be ___________-sized because of the low amount of energy in the environment.

clay

Limestone is most likely formed in which of the following environments?

shallow-marine carbonate

A well-sorted sandstone with asymmetric ripples was most likely deposited as sand by a

river (far from source).

Because the velocity of sediment settling (deposition) is positively related to grain size for waterborne sediments, fluvial deposits are more likely than glacial deposits to

be well sorted

The image below of Death Valley, CA, shows a road that curves around a(n)

alluvial fan

Diagenesis refers to

physical and chemical alterations, including compaction and cementation, that occur as sediment is transformed into rock.

As compared with metamorphism, diagenesis

takes place at lower temperatures and pressures.

Sea level rises locally, and marine sediments are deposited on top of terrestrial sediments during events termed

transgressions

Which of the following is true about regressions?

They occur when the land is uplifted by tectonic processes.

Death Valley is currently sinking partly due to the weight of continuously accumulating sediment shed from the mountains that border the valley. What phenomenon is this an example of and what depositional environment is created by the sediment deposition?

subsidence and alluvial fans