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9 .8 Option — Oceanography: 7 The type of sediment on the ocean floor varies

Syllabus reference (October 2002 version)
7. The type of sediment that accumulates on the floor of the deep oceans varies according to water depth, supply of nutrients to surface waters, and distance to land masses	Students learn to: outline the origin, characteristics and the distribution of different deep-sea sediments in the Pacific Ocean Basin, including calcareous ooze sediments; siliceous ooze sediments; deep-sea clays; manganese nodules; glacial marine sediments; and continental margin sediments discuss the different circumstances required for the deposition of different deep-sea sediments in the Pacific Ocean Basin	Students: gather data from secondary sources to distinguish the textual and compositional differences between calcareous ooze sediments; siliceous ooze sediments; deep-sea clays; manganese nodules; glacial marine sediments; and continental margin sediments

Extract from Earth and Environmental Science Stage 6 Syllabus (Amended October 2002). © Board of Studies, NSW.

[Edit: 8 August 08]

Prior learning: Science Stages 4 and 5. Outcome 4.9, 4.9.6 d)

Background: Sediments fall into two main types: those that have been washed or blown into the ocean from the continents and those that are organic in nature and have been produced from the remains of skeletons of algae and small animals. The first type is called terrigenous and consists of gravels, sands and silts. These terrigenous sediments are mostly carried by water down rivers but some have blown into the ocean.

gather data from secondary sources to distinguish the textual and compositional differences between calcareous ooze sediments; siliceous ooze sediments; deep-sea clays; manganese nodules; glacial marine sediments; and continental margin sediments

Gather information from different sources such as from Earth and Environmental Science text books, geology text books, electronic and paper encyclopaedias and the Internet. When using the Internet use a search engine such as Google. Although this dot point does not specify Pacific Ocean sediments it will help you for the next dot point if you include information about the Pacific Ocean in your research.
Construct a table like the one below with the different types of sediments in the first column and the differences you are comparing as headings to the other columns.
When your table is complete use it to come to conclusions about the different types of sediments. Some of the boxes have suggested answers.
Some useful websites are listed below.
Terrigenous sediments
Department of Geology, University of Puerto Rico Mayaguez Campus, Puerto Rico

Chapter 4 Marine Sedimentation
Department of Geology and Meteorology, Kean University, New Jersey, USA

Sediment Type	Texture	Composition
Calcareous ooze sediments	Fine grained calcareous ooze	Skeletons of foraminifera, pteropods, calcareous algae (eg coccolithophores), shells, nannofossils, with varying amounts of bioclasts and benthic and planktonic ostracodes,
Siliceous ooze sediments		Skeletons of radiolarians and diatoms, sponge spicules
Deep sea clays
Manganese nodules
Glacial marine sediments	Ranging from fine sediments to gravel	Coarse, poorly-sorted debris and a silt fraction composed of rock flour; typically contain little or no carbonate or biogenic material. Along the inner continental shelf, deposits are subglacial till, gravels, and sands, with some biogenic material.
Continental margin sediments

outline the origin, characteristics and the distribution of different deep-sea sediments in the Pacific Ocean Basin, including calcareous ooze sediments; siliceous ooze sediments; deep-sea clays; manganese nodules; glacial marine sediments; and continental margin sediments

Background information

The term sediment refers to particles that have settled to the bottom of a liquid. Sediments are classified by the processes involved in determining their physical and chemical characteristics. Important distinguishing characteristics of sediments include:

chemistry and mineralogy (reflecting origin of particles)
grain size(s) (determined by the energy of transport, deposition)
degree of compaction and/or cementation (resulting from burial and diagenesis (rock formation).

The source particles can be either preexisting rock (detrital sediments) or precipitates formed in the solution from which they settle (chemical sediments).

Outline indicates you don’t need a lot of detail. The information could be summarised into a table like the one below.

Deep sea sediments in the Pacific Ocean

Sediment	Origin	Characteristics	Distribution
Calcareous ooze sediments	Protozoa (foraminifera) algae (coccolithophores), inorganic calcium carbonate	When they die the calcium carbonate shells and skeletons sink to the bottom of the ocean. They are 36% of Pacific Ocean sediment	Mostly in equatorial regions where upwelling of ocean currents occur, carrying nutrients with them. Not found in really deep waters as much of the calcium dissolves in water deeper than from 500 to 1500 metres in the Pacific Ocean.
Siliceous ooze sediments	Protozoa (radiolarians) and diatoms	Fine-grained deep sea sediment mostly from skeletal remains. 15% of Pacific Ocean sediment	Polar and equatorial bands where nutrients are supplied to surface waters by vertical upwelling. Like calcareous oozes the silica dissolves at particular temperatures and pressures. This is deeper than for calcareous oozes.
Deep sea clays	Erosion of terrestrial material and volcanic ash	They are deposited by settling through the water column. Occur in the deepest oceanic basins and accumulate at a very slow rate. 49% of the Pacific Ocean sediment.	Transported to open oceans by wind and surface currents.
Manganese nodules	Oxides of the metals of manganese and iron with very small quantities of other metals. The source of the metals is not known but they may come from hydrothermal vents at mid ocean ridges.	They occur as nodules and crusts.	Primarily in deepest oceans and near mid ocean ridges.
Glacial marine sediments	These sediments come from glaciers on land in the high latitudes.	The composition of the rock material is relatively unaltered as it is transported by ice and ultimately dropped as the ice melts.	At high latitudes where glaciers meet the ocean. Found in the Bering Sea and off the Antarctic.
Continental margin sediments	These are transported from land to the oceans, carried by rivers and winds. They are formed by physical and chemical weathering of rocks that are exposed on continents. 75% of all sediments.		The thickest accumulation occurs in continental rises but most is in continental margins, river deltas, bays and estuaries. They can be trapped in marginal trenches.

Continental Rise
This is found at the base of the continental slope. Here the slope angle decreases. The continental rise may be hundreds of kilometres wide.

There is a thick accumulation of sediment transported downslope from the continental shelf. At the mouths of submarine canyons, deep-sea fans are present which may be carved by turbidity currents. These bottom-currents carry suspended sediment downslope.

As the currents slow, the suspended sediments begin to settle out; larger and heavier grains settle first.

Graded beds called turbidities are deposited by turbidity currents.

discuss the different circumstances required for the deposition of different deep-sea sediments in the Pacific Ocean Basin

Deep sea sediments could be:
- Red/Brown clays which are the most widespread of all sedimentary deposits on the earth. They are very fine grained and accumulate at a very slow rate.
  
  They are the only thing which can survive the extreme pressure of the deepest basins as other sediments tend to have their minerals dissolve. The closer they are to the land mass the more rapidly they will be deposited and their deposition rate will be greater when there is a drought and bare soil is blown into the sea. They also are composed of volcanic ash so will be thicker when there is a lot of volcanic activity.
- Siliceous ooze tends to concentrate in waters that are colder and deeper than calcareous ooze as the calcium begins to dissolve out at higher temperatures with less pressure. Siliceous particles dissolve more slowly as they sink. They are found where nutrients are carried up from deeper cooler waters near the equator, feeding the radiolaria and diatoms that produce the silica. Siliceous oozes are characteristic of areas of high fertility and are found in ocean margins and polar regions.
- Calcareous ooze is found in shallower, warmer ocean waters in the Pacific Ocean as the calcium dissolves in the range from 500 – 1,500 metres deep. If they haven’t dissolved as they sink through these depths they will slowly dissolve on the ocean floor. This ooze is found where foraminifera and coccoliths are abundant in the warm surface water. It is mostly the skeleton of these organisms that form this ooze.
- Manganese nodules are only found in the deep oceans in the vicinity of mid ocean ridges. They appear to be produced from minerals that are extruded from vents at the ridges.
  
  They precipitate from sea water by chemical reactions.