Ocean Basins and Their Origins

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Questions and Answers

What characterizes a continental slope?

An area of shallow waters near land.

A flat expanse of ocean floor.

A region with abundant marine life.

A steep edge where oceanic and continental crust meet. (correct)

What is the primary feature formed at the end of a submarine canyon?

Abyssal fan. (correct)

Ocean basin.

Oceanic trench.

Continental rise.

Which process describes the movement of loose, wet sediments downslope?

Seafloor spreading.

Turbidity currents. (correct)

Continental drift.

Hydrothermal circulation.

How do active continental margins typically differ from passive margins regarding their continental slope?

They generally have a steeper slope. Signup and view all the answers

What geological activity is primarily associated with active continental margins?

Subduction zones. Signup and view all the answers

What is the average depth of ocean basins?

5 km Signup and view all the answers

Which of the following sources contributed to the water found on Earth?

Gases from the initial coalescence Signup and view all the answers

What is the reason for volcanoes continuing to spew water vapor?

Volatiles being recycled with tectonic activity Signup and view all the answers

How does oceanic crust compare to continental crust?

Oceanic crust is denser and thinner Signup and view all the answers

What technique involves using a pipe to collect a mud core from the sea floor?

Coring Signup and view all the answers

What would happen if there were no ocean basins?

Water would be 2 km deep everywhere Signup and view all the answers

Which of the following techniques is NOT used for studying the sea floor?

Soil sampling Signup and view all the answers

What characteristic differentiates oceanic crust from continental crust?

Oceanic crust rides lower isostatically Signup and view all the answers

What technology is primarily used to create maps of seafloor topography?

Echo sounding Signup and view all the answers

Which of the following features is NOT found at mid-ocean ridges?

Volcanic islands Signup and view all the answers

What type of geological activity occurs in rift valleys at mid-ocean ridges?

Normal faults and earthquakes Signup and view all the answers

What process do bacteria use in black-smokers to produce energy?

Chemosynthesis Signup and view all the answers

What is the role of a magnetometer in studying the seafloor?

Recording magnetic fields of rock Signup and view all the answers

What is the approximate length of the mid-ocean ridge system?

80,000 km Signup and view all the answers

Which mechanism is primarily responsible for the formation of new crust at mid-ocean ridges?

Seafloor spreading Signup and view all the answers

What occurs when seawater circulates through hot rocks in the rift zone?

It dissolves metals and sulfur Signup and view all the answers

What type of sediment is primarily eroded and transported from continents to the ocean floor?

Terrigenous sediment Signup and view all the answers

Which of the following characteristics describes pillow basalt?

Has a thickness of 1 to 2 km Signup and view all the answers

What is the depth range of vertical basalt dikes found at the ocean floor?

3 to 5 km thick Signup and view all the answers

Which sediment type consists of a mix of fine clays and debris from organisms?

Pelagic sediment Signup and view all the answers

What feature of passive continental margins is characterized by a shallow, gently sloping surface?

Continental shelf Signup and view all the answers

Carbonate platforms are primarily composed of what type of rock?

Limestone Signup and view all the answers

What misconception was debunked about ocean floor sediments during research in 1947?

Mud is deeper near ocean ridges Signup and view all the answers

Which of the following describes an abyssal plain?

A flat expanse of pelagic sediments Signup and view all the answers

What geological feature is located in the center of the image captured by the MODIS satellite?

Andros Island Signup and view all the answers

Which feature describes the area where oceanic and continental crust meet?

Continental slope Signup and view all the answers

What process contributed to the inundation of the Great Bahama Bank between 10,000 and 2,500 years ago?

Melting of ice-age glaciers Signup and view all the answers

Which of the following best describes a submarine canyon?

A deep valley eroded into the continental shelf Signup and view all the answers

What characteristic of the waters above the Great Bahama Bank is noted?

Does not exceed 6 meters in depth Signup and view all the answers

What term describes the sediment fan often found at the end of a submarine canyon?

Abyssal fan Signup and view all the answers

Which of these aspects defines a continental rise?

A gradual transition to the deep ocean floor Signup and view all the answers

What is the primary composition of the Great Bahama Bank?

Carbonate platform Signup and view all the answers

How does tectonics influence sea-level changes?

Continental movement due to tectonics affects relative sea-level. Signup and view all the answers

What is a trench in the context of oceanic features?

A narrow, often deep depression along a subduction zone. Signup and view all the answers

What is an accreted terrane?

When an island arc becomes part of the continental crust after subduction. Signup and view all the answers

What happens to the elevation of the Mid-Oceanic Ridge as one moves away from its axis?

It gradually decreases. Signup and view all the answers

Which of the following accurately describes a seamount?

An underwater volcano that rises at least 1 km above the sea floor. Signup and view all the answers

What characterizes an atoll?

A circular coral reef surrounding a central lagoon. Signup and view all the answers

Which statement best explains the relationship between spreading rates and sea-level?

Fast spreading elevates the seafloor and reduces water volume. Signup and view all the answers

What distinguishes a guyot from a seamount?

A guyot is a seamount that has risen and eroded, resulting in a flat top. Signup and view all the answers

Study Notes

Ocean Basins

Ocean basins cover 71% of Earth's surface
Oceanic crust is denser than continental crust, and rides lower, isostatically
Oceanic crust is thinner (4-7 km) than continental crust (20-40km)
Ocean basin depths range from 2 to 11 km, averaging approximately 5 km
Earth's oceans contain 1.4 billion km³ of water
Without basins, the average depth of water covering the globe would be 2 km

The Origin of Oceans

Water originated from native volatiles from the molten early Earth
Gases from initial Earth coalescence
Cometary water
The moon-forming impact likely caused a net loss of volatiles
Volatiles are recycled with tectonic activity
The early solar system was full of comets

Studying the Sea Floor

Sampling methods include rock dredges (open-mouth nets), coring (pipes to collect mud cores), sea-floor drilling (similar to oil drilling), and submersibles (manned and robotic)
Remote sensing methods include echo sounding (SONAR for mapping seafloor topography), seismic profilers (higher-energy sonar for penetrating and reflecting data), magnetometers (towed behind ships to record magnetic fields of rock), and microwave radar (for mapping sea surfaces, which can mimic sea-floor topography)

Features of the Seafloor

Mid-ocean ridges are continuous mountain chains about 80,000 km long
They were discovered after World War One and improved mapping technologies after World War Two
Rift valley - a 1-2 km wide split along the ridge's center where new crust forms. Normal faults and earthquakes can occur in this valley
Transform faults - hundreds of fractures crossing perpendicular to the ridge
Black smokers are sulfur-laden jets of hot water near ridges. Chemosynthesis bacteria produce hydrogen sulfide in black smokers
Global sea-level change is affected by continent and basin ratios, and tectonic activity causing continents to shift and change relative height. Fast spreading rates often cause higher seafloors, leading to reduced water volume.
Oceanic trenches and island arcs are narrow, often deep depressions located along subduction zones (Trench associated with descending slabs)
- Trenches can range from 8-11 km in depth
- Marianas Trench is an example
- Island arcs form above the subducting plate boundary.
- Accreted terranes form when an island arc subducts and becomes part of the continental crust
Seamounts, oceanic islands, and atolls
- Seamounts are submarine mountains rising 1 km above the sea floor
- Oceanic islands are seamounts that rise above the sea surface
- Guyots are worn-down, sunken oceanic islands
- Atolls are circular coral reefs that surround a central lagoon

Sediments and Rocks of the Sea Floor

Early beliefs about ocean sediments were that they were uniformly thick
Observations in 1947 showed the thickness of seabed sediments to be thinner near ridges
Ocean floor sediments include:
- Terrigenous sediment (sand, silt, and eroded clay from continents)
- Pelagic sediment (mix of fine clays and biogenic debris)
- Abyssal plains (flat expanses of pelagic sediments)
Basaltic ocean crust
- Pillow basalt – rounded basalt magma structure
- 1-2km thick
- Vertical basalt dikes are 3-5km thick
- Gabbro is also present

Continental Margins

Passive continental margins
- Continental shelf – a shallow, gently sloping surface often laden with sediment. Is often isostatically depressed
- Continental slope - a sharp edge of the shelf where oceanic and continental crust meet
- Continental rise – transition from slope to deep ocean floor
Active continental margins -form at subduction zones.
- Trench is associated with the descending slab -Continental slope is significantly steeper compared to passive margins -Continental shelf-slope-rise complex forms as a result of subduction complex, forearc basin, and sediments.
Submarine canyons are deep valleys eroded into the continental shelf
Abyssal fans are sediment fans often found at the end of submarine canyons
Turbidity currents form with loose, wet sediments tumbling down the slope. Such current often creates submarine landslides.

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Description

Explore the fascinating world of ocean basins and their significance on Earth's surface. Learn about the origin of oceans, the properties of oceanic crust, and methods of studying the sea floor through innovative sampling techniques. This quiz will deepen your understanding of oceanography and tectonic processes.