8/2/2019 Abyssal Plains - Handout

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Abyssal plains - vast, flat, sediment-covered areas of 

the deep ocean floor 

- flat seafloor area at an abyssal depth (3,000 to

6,000 m [10,000 to 20,000 feet]), generally adjacent to a

continent, submarine surfaces vary in depth only from 10

to 100 cm per kilometre of horizontal distance.

Irregular in outline but generally elongate along

continental margins

-the lack of features is due to a thick blanket of 

sediment that covers most of the surface

-Seismic profiles (cross sections) of abyssal

plains reveal accumulations of sediment averaging one

kilometre in thickness, deposited on undulating

topography 

-common in the Atlantic, less common in the

Indian Ocean, and even rarer in the Pacific

Location - near the Pelagic zone – open ocean (water is

not at bottom or near the shore), specifically, located in

the Abyssopelagic layer (4,000 – 6,000 m)

-covered with pelagic mud (mud which is not yet

thoroughly known, but contains complex minerals) with

fine sand layers from nearby turbidites (type

of sedimentary rock composed of layered particles that

grade upward from coarser to finer sizes and are thought

to have originated from ancient turbidity currents in the

oceans, integral components of sedimentary deep-sea

fans adjacent to the base of continental slopes, and they

are also found below the major river deltas of the world

where they build features called abyssal cones)

Formation – turbidity current (sediments)

- underwater density current 

of abrasive

sediments, thought to be caused by the slumping of 

sediment that has piled up at the top of the continental 

slope

 -decompression melting (plain itself)

-similar to spreading centers (diverging

plates cause parts of upper mantle to move upward and

solidify by conduction or convection)

-seafloor spreading – new oceanic crust

is formed and gradually moves away

-forms in the Abyssopelagic zone (more common

in the Atlantic)

SEDIMENTARY ROCKS PRESENT

1. Marlstone – freshwater limestone, lime-rich

mudstone

http://www.citizendia.org/Marl

2. Calcilutite – limestone mud

http://search.datapages.com/data/doi/10.1306/74D7

15C3-2B21-11D7-8648000102C1865D

3. Micrite – fine-grained limestone

http://www.fp.sfasu.edu/geology/geologytutorial/Roc

ks/sld032.htm

4. Chert – a form of microcrystalline quartz

http://geology.com/rocks/chert.shtml

5. Turbidite - v

ertical sequence of sediments

deposited by a turbidity current 

http://petrogroupcompany.com/infoCurso.php?

idCurso=27

 

8/2/2019 Abyssal Plains - Handout

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 ANIMALS POSSIBLY PRESENT

1. Rattail fish/Grenadier fish

http://www.allthesea.com/Deep-Sea-Fish-Rattail-

Fish.html

2. Black lizardfish/deep-water greeneye

3. Feeler fish

4.

  Abyssobrotula galatheae – a species of cusk

eel

5. Abyssal spiderfish

-look at http://www.cedamar.dzmb.net/Species-

List for a complete list of abyssal plain animals

(too many, more than 200)

 ABYSSAL PLAINS

http://m.eb.com/assembly/86712

http://elearning.stkc.go.th/lms/html/earth_science/LO

canada6/604/9_en.htm

http://science.howstuffworks.com/environmental/gre

en-science/bury-co2-in-ocean2.htm

Sources

http://www.britannica.com/facts/5/6190

96/abyssal-plain-as-discussed-in-

sedimentary-rock

http://www.universetoday.com/74357/a

byssal-plain/

http://www.britannica.com/EBchecked/t

opic/2483/abyssal-plain