Chapter 10: The Seafloor and Continental Margins

Which areas shown on the map have the shallowest seafloor depth?

(P) passive continental margins

Match the technique that geologists use to study the seafloor with its characteristics of being either a direct or remote method of study.

----Direct---- Drilling into the seafloor Visiting with manned subs ----Remote----- Observing with satellites Mapping with sonar

Put the following phrases in the correct order to describe the formation of the salt deposits underlying the Gulf of Mexico. Put the first step on top.

1. Salt was deposited during the Mesozoic era 2. Salt was buried causing it to flow upward and sideways 3. The moving salt created folds and domes in the overlying rocks 4. Oil and gas were trapped in the folded sedimentary rocks

The Indian Ocean began to form about ________ million years ago.

120

In the diagram, match the letter with the name of the feature present on the continental margin.

A (lower ocean floor) Continental rise B (underwater slot canyon) Submarine canyon C (upper ocean floor) Continental shelf D Continental slope

What happens to the crust behind a migrating island arc as it moves along with a subducting slab?

A back-arc basin forms. A spreading center develops. The crust thins and a rift forms.

Order the steps in the formation of seamount form the first event at the top to the last event at the bottom.

A conical basaltic volcano forms an island. The volcanic mountain cools and subsides. The top of the volcano flattened by wave erosion and continues to subside. The flat-topped volcano is buried by sediment.

Order the steps in atoll formation from first on top to last on bottom.

A volcanic island forms, establishing a shoreline for the construction of a fringing reef. An island subsides, forming a barrier reef some distance from the shoreline. A central, shallow lagoon forms surrounded by a ring of coral and other carbonate material.

Using the map determine where the sediment cover is the thickest on the seafloor.

Along the continental margins. Near river mouths

Match the name of the reef type with its correct setting.

Atoll Curved reef surrounding a shallow lagoon. Barrier reef Forms at the edge of a continent. Fringing reef Surrounds and/or may be attached to an island. Carbonate platform Forms a broad, shallow platform.

What is the source of energy for giant tube worms and clams that live at hydrothermal vents?

Bacteria that break down H2S

The ________ Sea was formed by the enlargement of a river valley that was scoured by glaciers and then filled in by the sea. The ________ Sea was isolated from a larger sea, was reduced in size, and was flooded during sea-level rise.

Baltic Black

Put the processes that first occur when oceanic plates spread apart at the mid-ocean ridge in order.

Basaltic lava erupts from the rift. Blocks of oceanic crust are downdropped in normal faults. Sediment settles onto new basalt. Oceanic crust has a smooth surface covered by layered sediment.

The ______ ____ was isolated from the ocean and became a lake until the Ice Age ended and the Mediterranean Sea flooded, returning it to a small sea.

Black Sea

Which sea was a lake prior to being flooded by the ocean at the end of the Ice Age?

Black Sea

The CCD, or _______ compensation depth, is the depth at which calcite disappears in the ocean.

Carbonate

Match the location on the map with the plate-tectonic boundary that occurs there.

Cayman Trough - Transform Boundary Lesser Antilles - Subduction of the North American plate. Central America - Subduction of Cocos plate

Match the part of the Atlantic Ocean with the continents that split to form it.

Central Atlantic Ocean North America and Africa South Atlantic Ocean Africa and South America North Atlantic Ocean North America and Europe

Place the formation of each section of the Atlantic Ocean in order.

Central Atlantic Ocean (first) South Atlantic Ocean North Atlantic Ocean (last)

Which conditions promote the growth of coral reefs?

Clear water Shallow water Warm water

Why are reefs located between 30 degrees north and 30 degrees south of the equator?

Clear water is present in this zone. Warm water is present in this zone.

A submarine landslide commonly forms ________.

Distinctive lumps on the seafloor. A ragged scar on the slope above.

The seafloor east of Papua New Guinea has small basins, trenches, and island arcs. True/False: This area is considered one of the least complex areas of oceanic crust.

False

Which of the following statements describes black smokers?

Form mineral deposits rich in copper and zinc. Form sulfide-rich chimneys. Form along mid-ocean ridges.

Which describe how marine salt deposits form?

From restricted water flow in a marine basin. From evaporation of seawater.

Turbidity currents can erode rock underwater and deposit ____

Graded Beds Submarine fans

The largest organic buildup on Earth is the ______ ______ Reef in eastern Australia. The corals in the reef have grown upward in response to sea-level rise following the last Ice Age.

Great Barrier

About 120 million years ago, the _____ Ocean began to form, as India separated from Australia and Antartica.

Indian

The volcanic rocks on oceanic islands are ______ to intermediate in composition.

Mafic

Match the spreading ridge with its characteristic shape.

Mid-Alantic Ridge Well-defined central rift valley. East Pacific Rise Broad and lacking a central rift.

Order the location of the seafloor regions by elevation with highest at the top and the lowest at the bottom

Mid-ocean Ridge Abyssal Plain Oceanic trench

Which can be extracted from drill cores to determine the numeric age of the sediment on the seafloor?

Minerals from volcanic units Fossils

Island arcs have a curved shape because there is ______ surface area on the outside of the plate than at depth.

More

What process thins the continental crust before it meets the oceanic crust at the continental slope

Normal Faulting

Order the events in the history of the Carribean Basin beginning with the oldest event at the top and the most current event at the bottom.

North America split from Africa and South America through continental rifting. Seafloor spreading moved North America farther from Africa and South America. An island arc and oceanic plateau collided with Florida near Cuba.

Match the name of the sea with the process that formed it.

North Sea Rifting and normal faulting. Baltic Sea Enlarged river valley scoured by glaciers, then filled by the sea. Red Sea Seafloor spreading at a divergent boundary. Black Sea Isolated from a larger sea, reduced in size, and flooded during sea-level rise.

The __________ Plateau and the __________ Plateau are oceanic plateaus that formed over 100 million years ago.

Ontong Java Kerguelen

The modern continents originated from a supercontinent called ________ and all modern oceans from one large ocean that existed about 200 million years ago.

Pangaea

The continental collision of the Eurasian and Arabian plates formed the __________.

Persian Gulf

Which locations contain modern coral reefs?

Phillipines Bahamas Polynesia

Salt is a weak rock that can flow; therefore it forms _____.

Salt glaciers Domes A slip plane for thrust faults

Salt is a weak rock that can flow; therefore, it forms _______. (all that apply)

Salt glaciers Domes A slip plane for thrust faults

What were the key methodologies used to gain an understanding of the undersea geology of the Gulf of Mexico and the Carribean, in order to reconstruct the region's history?

Seafloor mapping and geophysical surveys conducted for petroleum exploration.

Use the map to determine what types of plate motion are occurring in the Gulf of California today.

Seafloor spreading Transform faulting

Match the seafloor feature with the description of its formation.

Seamount Submarine volcanic eruptions. Trench Downwarping of an oceanic plate as it plunges beneath another plate. Mid-ocean ridge Well-defined rift found at divergent boundaries.

Match the seafloor with its descriptions

Seamount - Isolated mountain Abyssal plain Deep seafloor with smooth topography Oceanic trench- Deepest part of the ocean

Match the seafloor feature with its description:

Seamount: Isolated mountain Abyssal Plain: Deep seafloor with smooth typography Oceanic Trench: Deepest part of the ocean.

Rock units beneath the sea floor can be imaged with sound waves using a method called ______.

Seismic-Reflection Profiling

What method produces images of the materials beneath the seafloor using waves?

Seismic-reflection profiling

On the map shown, R has the youngest oceanic crust because it is at a ____

Spreading center

Island arcs form in association with what type of tectonic setting?

Subduction zones

Which statements correctly explain why the Atlantic Ocean is presently growing in size, whereas the Pacific Ocean is shrinking?

The Atlantic Ocean does not have major subduction. The Atlantic Ocean has a spreading center.

Which are true statements describing the near geologic future of the Atlantic and Pacific Oceans?

The Atlantic Ocean will grow in size. The Pacific Ocean will continue to shrink.

Order the processes that formed Monterey Canyon along its length from onshore to the deep sea, with the first event at the top and the last event at the bottom.

The canyon was carved by rivers above sea level The canyon was cut below sea level by turbidity currents Sediment deposits built up a submarine fan

what do the island chains of Hawaii, Tahiti, and Tristan da Cunha have in common?

The formed from hot spots.

What information can be determined directly by analyzing seafloor drill cores?

The type of sediment on the seafloor. The type of rock on the seafloor. The rate of sediment deposition.

Why are island arcs curved?

They form next to trenches on a spherical Earth.

What do the areas shown in red on the map have in common?

They formed adjacent to deep trenches. They are all island arcs.

The yellow areas on the map indicate that the process of __________ is occurring in the Gulf of California, in addition to seafloor spreading.

Transform faulting

Most oceanic measurements made from satellites are of ocean surface properties rather than deep-ocean properties.

True

What are the characteristics of natural salt deposits?

Very soluble in water Can flow to form domes Deposited in layers

In the Phillipine Sea, seafloor spreading is forming a __________, and one can observe submerged ridges indicating that different episodes of spreading have occurred.

back-arc basin

_____ reefs protect the coastline from waves and storms because they occur just offshore from the mainland, whereas _____ reefs are attached to a shoreline or are just offshore, surrounding an island.

barrier, fringing

Magma that erupts at mid-ocean ridges forms pillow ____________. These are pushed away from the ridge crest covered with clay-rich ___________.

basalt sediment

The hot water emitted by _____ at mid-ocean ridges is actually recycled seawater that flows into the subsurface and is heated by a magma source.

black smokers

Magmas that are intermediate in composition form island arcs with explosive _______ volcanoes made of andesite.

composite

The shallower, eastern part of the Bering Sea is underlain by _________ crust, whereas the deeper, western part is underlain by ________ crust.

continental oceanic

The abrupt change from thinned, faulted continental crust to oceanic crust occurs at the _________.

continental slope

Geologists can learn about past environments and climates by collecting cylinder-shaped drill _______ from the seafloor.

cores

In most cases, salts are concentrated by _______ in marine basins or on land to form salt deposits.

evaporation

The sequence shown here with alternating coarser and finer sediment formed by successive turbidity currents is called ________ ________.

graded beds

Oceanic plateaus form from basaltic volcanism originating from ___________.

hot spots

How water, metals, and sulfur discharge from ___________ vents (also known as black smoker) at mid-ocean ridges.

hydrothermal

The Pacific plate is subducting around its edges, forming the _____ _____ showing in red on the map.

island arcs

The direct source of heat for the water emitted by black smokers at mid-ocean ridges comes from _______.

magma

Baseball-sized spheres that precipitate out of seawater and fall to the seafloor are called manganese

nodules

The Sea of Japan formed as a deep basin between Asia and Japan because ___________.

of back-arc seafloor spreading

Coral _____ form in shallow, tropical seas with clear water.

reefs

Submarine canyons transport sediment from the continental shelf to the continental ______.

rise

Movement of the trench away from the island arc is called trench ___________.

rollback

A(n) _____ forms from hot spot volcanism, as a submarine volcano is created and rises above sea level but then eventually is eroded and subsides beneath the sea.

seamount

Manganese nodules form on the deep seafloor as manganese and other metals precipitate from _________.

seawater

Monterey Canyon is a _________ canyon in the continental slope eroded by turbidity currents.

submarine

A fan-shaped sediment deposit on the continental rise formed by turbidity currents is called a ________ ________.

submarine fan

Hot spots form linear island chains because _______.

the plate moves relative to the underlying hot spot.

The bumps and pits on the seafloor in the Gulf of Mexico, shown in the diagram, are cause by __________.

the subsurface flow of salt

Sediments in a submarine farm have graded beds because they are deposited by _____ currents

turbidity

A dense mixture of water and sediment that flows downslope underwater is called a __________.

turbidity current

Hot spots, indicated by the red dots on the map, coincide with _________.

volcanically active island chains