Exam 6 - Ocean Basins

Question 1

bathymetry

Answer 1

Bathymetry is the measure of depth of water in oceans, seas, lakes, and rivers. Bathymetry data is used to create maps (called charts) of the seamounts. Bathymetric charts are the equivalent of topographic maps on land.

Question 2

continental margins

Answer 2

these are regions that extend from the coastlines across shallow submarine shelf regions to just beyond the edge of continents where the seafloor descends into deep water

Question 3

deep ocean basins

Answer 3

This includes parts of the oceans where deep water prevails. Deep ocean basins cover the greatest portion of the Earth’s surface.

Question 4

oceanic ridges or mid ocean ridges

Answer 4

nearly 12,000 miles of mountain belts run through ocean basins and are associated with divergent plate boundaries (spreading centers)

Question 5

continental margins

Answer 5

border continental landmasses are submarine geographic regions located between the shoreline and deep ocean. They are the submerged edge of continents. Continental margins include subregions and submarine geographic features:

• continental shelf
• continental slope
• continental rise
• submarine canyons

Question 6

active continental margin

Answer 6

An active continental margin is a coastal region that is characterized by mountain-building activity including earthquakes, volcanic activity, and tectonic motion resulting from movement of tectonic plates. Characteristics of active continental margins include:
• They are located mostly along convergent plate boundaries.
• In most places along active margins, the continental slopes descend abruptly into a deep-ocean trench (there may be no continental rise), or they may be rugged regions associated with large fault systems.
• Most are located primarily around the margins of the Pacific Ocean (the Ring of Fire)

Active continental margins are characterized by rugged coastlines with narrow beaches and steep sea cliffs. The West Coast of the United States is an active continental margin

Question 7

Passive continental margins

Answer 7

Passive continental margins occur where the transition between oceanic and continental crust which is not an active plate boundary. Examples of passive margins are the Atlantic and Gulf coastal regions which represent setting where thick accumulations of sedimentary materials have buried ancient rifted continental boundaries formed by the opening of the Atlantic Ocean basin.

Passive continental margins are characterized by wide beaches, barrier islands, broad coastal plains. The Atlantic Coast of the United States is a passive continental margin

Question 8

continental shelf

Answer 8

A continental shelf is a submerged nearshore border of a continent that slopes gradually and extends to a point of steeper descent to the ocean bottom. Continental shelves are submerged extension of the continent.

Continental shelves typically have low relief: they usually have less than 1 degree of slope. Average is about one tenth of one degree.

Continental shelves are influenced by a variety of geologic processes, particularly associated with the erosion and deposition of sediments on beaches, deltas, and carbonates (coral reefs). Shallow water coastal and shelf environments are particularly influenced by the impact of large storms.

Question 9

Continental resources

Answer 9

Continental resources are areas with important natural resources, particularly fisheries, but also oil and gas, and sand and gravel.

Question 10

shelf break

Answer 10

A shelf break is a general linear trend that marks the boundary between the relatively flat continental shelf and the drop off into deeper water on the continental slope. The shelf break generally follows the ancient shorelines that existed at the peak of the continental glaciation periods of the ice age when sea level was as much at 400 feet (120 meters) lower that present sea level.

Question 11

continental slope

Answer 11

A continental slope is the slope between the outer edge of the continental shelf and the deep ocean floor. The continental slope is cut by submarine canyons in many locations. The continental slope marks the seaward edge of the continental shelf.

Continental slopes typically follow the boundary between continental crust and oceanic crust (Figure 15-12).
Continental slope range in steepness from 1 to 25 degrees, average is 4 degrees.
• Pacific (active margin) average >5 degrees.
• Atlantic (passive margin) average about 3 degrees

Question 12

continental rise

Answer 12

A continental rise is a wide, gentle incline from a deep ocean plain (abyssal plain) to a continental slope

A continental rise consists mainly of silts, mud, and sand, deposited by turbidity flows, and can extend for several hundreds of miles away from continental margins. Although it usually has a smooth surface, it is sometimes crosscut by submarine canyons extending seaward of continental slope regions.

The continental rise is generally absent in regions where deep-sea trenches exist where subduction zones are active.

Question 13

Submarine canyon

Answer 13

Submarine canyons are similar to river gorges carved in mountainous regions on land, however they tend to be both much larger and deeper (Figure 15-14). Characteristics of submarine canyons include:
• They generally form perpendicular to coastline.
• They are commonly associated with zones of weakness such as a fault or a drowned river valley (flooded by sea-level rise).
• They start on continental shelf and cut into (erode) shelf and upper slope, commonly near the mouth of a bay or river.
• They are carved by undersea erosion processes associated with turbidity currents. Turbidity currents transport sediment into deep ocean basins via submarine canyons.

Question 14

Deep-ocean basins

Answer 14

Deep-ocean basins cover the greatest portion of the Earth’s surface. Geographic features associated with deep-ocean basins include trenches, abyssal plains, ocean ridges and rises, and submarine mountainous region

Question 15

abyssal plain

Answer 15

An abyssal plain is an underwater plain on the deep ocean floor, usually found at depths between 4500 and 6000 meters that extends from the continental rise (continental lithogenous sediments accumulate along continental margins) to the distant deep ocean basin where continental-derived sediment deposition is not significant.

Abyssal plains are large horizontal seafloor regions - typically some of the flattest places on the Earth’s surface (on the seafloor, Figure 15-15). Abyssal plains are the largest physiographic regions on the planet, covering millions of square miles in ocean basins.

Question 16

oceanic trenches

Answer 16

Trenches are long, relatively narrow canyon-like features that run parallel to continental margins.
They are the deepest parts of ocean basins. Most trenches are located in the Pacific Ocean - the deepest is the Marianas Trench—10,994 meters (36,070 feet)

Trenches occur where mobile lithospheric plates plunge into the mantle (subduction zones). Ocean crust is in contact with cold ocean water. Over time ocean crust cool and shrinks, increasing in density. Along zones where crustal plates are colliding, the old, cold oceanic crust sinks back into the mantle. Along the way, it heats up, and water and gases trapped in the rock escapes and works its way back to the surface, helping to melt rocks along the way. As a result, volcanic island arcs associated with trenches are are locations of intense volcanic activity above the descending side of the subducting plate sinking back into the mantle. Subduction zone faults are associated with trenches and produce most of the most powerful earthquakes on the planet.

Question 17

origin of oceanic lithosphere

Answer 17

At mid-ocean ridges (spreading centers), newly forming lithospheric plates move apart. This creates space for magma to flow upward into the fractures forming along rift zones. Over time, more and more fractures form, they fill with magma, and then cool and fracture making pathways for more magma to flow upward and the process is repeated. This process generates new oceanic lithosphere (ocean crust). In some locations around the world, large mountain-sized blocks of old ocean crust has been pushed up along faults and exposed on land—where they are exposed, they are called an ophiolite sequence because they consist of unique varieties of rocks that formed in a sequential order

Question 18

formation of oceanic lithosphere

Answer 18

Zones of active rifting along mid-ocean ridges (spreading centers) are typically 20 to 30 km wide. In some locations, the very hot, fluid lava migrating upward from the asthenosphere (upper mantle) reaches the surface of the seafloor resulting in formation of undersea volcanoes. These undersea eruptions produce pillow basalts - pillow-shaped pods of basalt rock formed where the hot lava cools rapidly when exposed to seawater.

As new lithosphere forms, older ocean crust gradually moves away from the mid-ocean ridge crest beyond the zone of active rifting and volcanism. Over time, the cooling-shrinking crust increases in density and isostatically sinks lower because it is floating on the asthenosphere. Marine sediments gradually blanket the aging oceanic crust as it moves away from the spreading center. The layer of sediment grows thicker and thicker as aging ocean crust moves away from a mid-ocean ridge.

Question 19

ophiolite sequence

Answer 19

• Layer 4: represents rocks derived from the upper mantle or rocks formed from the crystallization of magma derived from the mantle. Rocks preserved in Layer 4 deposits are typically a gabbro of ultramafic composition: pyroxenite and peridotite (rocks rich in olivine and other ultramafic minerals) Over time, exposure to seawater and changes in pressure and temperature, the convert to the metamorphic rock, serpentinite.
• Layer 3: Magma injected into parallel fractures above magma chambers along spreading centers create a sheeted dike complex composed of igneous rocks of ultramafic to mafic composition (gabbro and basalt)
• Layer 2: Pillow basalts form from basaltic lava erupting on the seafloor that is flash-cooled by cold seawater into pillow-shaped pods that stack on the seafloor
• Layer 1: When volcanism ends, marine sediments begin to accumulate on top of the pillow basalts.

Question 20

Cosmogenous sediments

Answer 20

Cosmogenous sediments: material that falls to the Earth surface from outer space.

Cosmogenous sediments originated from outer space. Scientists have used satellites to estimate how much material enters the Earth’s atmosphere. Current estimates from satellite data suggesting about 100 to 300 tons (mostly cosmic dust) hits earth each day.

Question 21

Hydrogenous sediments

Answer 21

Hydrogenous sediments: material precipitated directly seawater.

Examples include rocks called evaporites formed by the evaporation of salt bearing water (seawater or briny freshwater). Although salts are a major component of seawater, comparatively little of it gets deposited excepted along the shores of shallow, restricted bays along coastlines and in continental interior basins in arid regions of the world.

Question 22

Lithogenous sediment

Answer 22

Lithogenous sediment: material derived from erosion of other rocks, typically from continental sources

Lithogenous sediments are:
• Mostly small pieces of broken rock transported to ocean from the land (wind, rivers, glaciers, coastal erosion, etc.)
• Generally form deposits rapidly (such as sand on a beach or a river delta)
• Can form in high energy environments and have coarse grain sizes (coarse sand, gravel, cobbles, and boulders).
• Beach sand is mostly composed of the quartz (SiO2), a mineral which very resistant to weathering.
• Most lithogenous sediments eventually are deposited along the margins of ocean basins.
• Some is deposited into the deep ocean by currents and underwater landslides near continents, and far offshore, lithogenous sediment of fine silt and clays, some as desert dust, forest-fire ash, or volcanic ash blown in by the wind.

Question 23

Biogenous sediments

Answer 23

Biogenous: material formed from the accumulation of remains of living organism

Biogenous sediments are mostly composed of the remains of organisms—including skeletal remains of microplankton (both plants and animals), plant remains (algae, wood, roots, and leaves) and remains of larger animals including shells of invertebrates, such as shells, coral fragments, and fish and other vertebrate teeth, bone, and scales, and fecal material left behind by any type of organism. Biogenous sediments can form in both terrestrial and marine environments. Biogenous sediments may be partly mixed with lithogenous sediments (continental-derived sediments) in coastal regions, particularly where streams and rivers contribute sediments.

Question 24

evaporite

Answer 24

An evaporite is a rock composed of salt minerals left behind by the evaporation of salty water. Examples include rock salt (NaCl) and gypsum (CaSO4 • x H2O).

Question 25

rock salt

Answer 25

a rock dominantly composed of sodium chloride (NaCl - the mineral halite; Figure 15-45). Rock salt is an evaporite formed in restricted basins with an inflow of seawater located in an arid environmental setting.

Question 26

Gypsum and anhydrite

Answer 26

Gypsum and anhydrite—gypsum is a mineral composed of hydrous calcium sulfate (CaSO4-2H2O); an evaporite mineral used in the manufacture of plaster and fertilizers. Gypsum is deposited by concentrated seawater and by evaporation of freshwater in arid regions. Crystals of gypsum are common in soils in arid regions. If gypsum looses its water content, it is becomes a mineral called anhydrite

Question 27

Abyssal clays

Answer 27

Abyssal clays are very fine-grained sediments, mostly clay minerals and iron-rich mineral dust that are blow in by the wind from distant terrestrial sources. Much of the abyssal clay components are derived from dust storms in the world’s desert regions and from explosive volcanic eruptions that can blow fine particles high into the atmosphere. Abyssal clays are also fine-grained material carried and redistributed by ocean currents such as tail end of far-turbidity currents that can travel hundreds to even thousands of miles away from continental margins.

Question 28

coral reefs

Answer 28

A reef is a general name for a ridge of jagged rock, coral, or sand just above or below the surface of the sea. A carbonate reef is one that is made of skeletal material composed of coral, coralline algae, and other carbonate skeletal material. Carbonate reefs are commonly called coral reefs, but not all organisms that look like corals are actually corals—other organisms that create solid structure (branching or not) include coralline algae, bryozoans, sponges, stromatoporoids, and many other types of invertebrates).

Question 29

Ooze

Answer 29

Ooze is slimy mud sediment (soft and mushy) on the bottom of an ocean or lake bed formed from the accumulation of skeletal and organic remains of microscopic organisms: phytoplankton (plants) and zooplankton (animals).

• Oozes can be dominantly calcareous or siliceous in composition.
• To be considered an ooze sediment must consist of grater than 30% biogenous material (Figure 15-64).
• Oozes form slowly - accumulating at a rate of 1/2 to 2 1/2 inch per 1000 yrs.

• Oozes form in low energy environments and are very fine grained (clay sized particles).

Question 30

Calcareous oozes

Answer 30

Calcareous oozes are sediments dominantly composed dominantly of calcium carbonate (CaCO3). Two dominant groups of microorganisms that contribute carbonate remains: Coccolithopores (phytoplankton) and Foraminifera (zooplankton)