2. 4-1
Sediment in the Sea
Classification of marine sediments
can be based upon size or origin.
• Size classification divides sediment by grain
size into gravel, sand, silt and clay.
– Mud is a mixture of silt and clay.
• Origin classification divides sediment into
five categories: terrigenous sediments,
biogenic sediments, authigenic sediments,
volcanogenic sediments and cosmogenic
sediments.
3. Pathways for Sediment to Reach the Ocean:
1) Fluvial Inputs--Rivers Discharge Sediment
into the Ocean
2) Aeolian Inputs--Winds carry sediments from
the continents into the ocean.
3) Biological Inputs--Marine organisms die and
sink to the bottom.
4) Authigenic Inputs--Sediments that are
formed in the oceans. Mainly metal rich
materials near hydrothermal vents.
5. Factors that control sedimentation
include particle size and the
turbulence of the depositional
• Terrigenous sediments strongly reflect their
environment.
4-1
Sediment in the Sea
source and are transported to the sea by
wind, rivers and glaciers.
• Rate of erosion is important in determining
nature of sediments.
• Average grain size reflects the energy of the
depositional environment.
6. Summary:
General Distribution of Sediments in the Deep Sea
1) Near continental margins (500-1000 km), sediments
tend to be dominated by terrigenous (lithogenic)
material from the margins (turbidity currents and river
derived material).
2) Away from margins and < 4000m, carbonate oozes
dominate.
3) Away from margins and > 4000m, clays dominate
(dominated by wind transport).
4) Away from margins, but under upwelling regions (high
biological productivity), siliceous oozes dominate.
5) Near active mid-ocean spreading centers, metal rich
sediment dominate.
9. 1. Terrigenous sediments
• most abundant
• originate on the continents or islands
• come from erosion, volcanic eruptions,
and blown dust
• the largest terrigenous deposits are near
continental margins
10. 2. Biogenous sediments
• cover the greatest area of seabed
• but their total volume is less than that of
terrigenous sediments.
• originate from the activity of animals and
plants
• over millions of years, can form oil and
natural gas
11. 3. Hydrogenous sediments
• minerals that precipitate directly from water
manganese nodules
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12. Hydrogenous (authigenic) Sediments:
Hydrogenous sediments
precipitate directly from
seawater.
Their formation is poorly
understood, but it is thought to
be associated with
hydrothermal vent systems and
mid-ocean ridge systems.
Most common hydrogenous
sediments are manganese
nodules.
Include evaporites and oolites.
13. Manganese Nodules:
Formed on concentric layers of manganese
and iron oxides.
Form very slowly (1-10 mm per million years).
Found on large areas of the Pacific ocean.
Recent interest in economic development.
18. Sediment grading usually reflects changes in the depositional
environment with time.
lower energy
Higher energy
“fining-upward’
event
Each bed represents an individual depositional event.
19. Marine sediments are usually combinations
of terrigenous and biogenous deposits.
Sediment patterns and composition can tell
us about conditions in the overlying ocean
• they preserve a record of past and present
conditions
22. Key Points
1. Sediments vary greatly in appearance.
2. Sediments can be classified by particle size.
3. Sediments can be classified by source.
4. Neritic sediments overlie continental margins.
5. Pelagic sediments vary in composition and
thickness.
6. Scientists use sensitive tools to study ocean
sediments.
7. Marine sediments are economically important.
