Transcript The Ocean Bottom

The Ocean Bottom
Marine Science
Pg 23 in Notebook
Review
 3 layers of earth
 Core
 Mantle
 Crust
 Rock Cycle
 Igneous Rock
 Sedimentary Rock
 Metamorphic Rock
 Continental Drift
 Plate tectonics
 Sea floor Spreading
HMS Challenger: 1872-1876
The beginning of systemtic observations of the ocean & ocean floor
HMS Challenger: 1872-1876
The beginning of systemtic observations of the ocean & ocean floor
Sir John Murray (1841-1914)
gave detailed account of
deep sea sediments
recovered during the HMS
Challenger expedition.
Sediments and Sedimentary
Rock
 Make up
 8% of the Earths crust
 75% of the Earths surface
Types of Sediments
 Terrigenic sediment
produced by the break down of rocks on land
 Biogenic sediment
produced by organisms
 Authigenic sediment
produced in place by chemical reactions in seawater or within
the upper sediment
 Volcanogenic sediment
produced from the eject of volcanic eruptions
 Cosmogenic sediments
produced from cosmic debris that constantly bombards the
Earth
Terrigenic Sediment
 Terrigenic sediment is the
sand, silt, and clay you
normally think of as
sediment.
 Quartz (SiO2 crystall, “Silica”)
is the dominant mineral in
terrigenic sediment.
Terrigenic Sediment
Types of Sediments
 Terrigenic sediment
produced by the break down of rocks on land
 Biogenic sediment
produced by organisms
 Authigenic sediment
produced in place by chemical reactions in seawater or within
the upper sediment
 Volcanogenic sediment
produced from the eject of volcanic eruptions
 Cosmogenic sediments
produced from cosmic debris that constantly bombards the
Earth
Biogenic Sediment
 macroscopic:
 bones, teeth, shells of larger organisms
rare
 microscopic:
 shells and skeletons of planktonic organisms
 chief producers are
 algae (plants, photosynthesizing)
 protozoans
abundant
CaCO3 producers: Coccolithophores
20 mm
20 mm
CaCO3 producers: Foraminifera
50 mm
~400 mm
Types of Sediments
 Terrigenic sediment
produced by the break down of rocks on land
 Biogenic sediment
produced by organisms
 Authigenic sediment
produced in place by chemical reactions in seawater or within
the upper sediment
 Volcanogenic sediment
produced from the eject of volcanic eruptions
 Cosmogenic sediments
produced from cosmic debris that constantly bombards the
Earth
Authigenic Sediments
 derived from dissolved material in sea
water
•
•
•
•
•
Manganese Nodules
Evaporites
Phosphates
Carbonates
Metal Sulfides
Types of Sediments
 Terrigenic sediment
produced by the break down of rocks on land
 Biogenic sediment
produced by organisms
 Authigenic sediment
produced in place by chemical reactions in seawater or within
the upper sediment
 Volcanogenic sediment
produced from the ejections of volcanic eruptions
 Cosmogenic sediments
produced from cosmic debris that constantly bombards the
Earth
Cosmogenic Sediments
• derived from extraterrestrial sources
• macroscopic:
• meteor debris
• rare
• microscopic:
• space dust (spherules,
tektites)
• constantly raining
on Earth
Spherule
Distribution of Sediments
 Ten times more terrigenic than biogenic sediment arrives
at the seafloor each year.
 If this sediment was distributed evenly, then terrigenic
sediment would dominate the sediment cover of the
seafloor.
 This is not the case because of most of the terrigenic
material is trapped along continental margins.
© The Open University
© The Open University
Importance of Sediments
 Economic Value
 Oil, fossil fuels
 Salt & Phosphorus deposits
 Determine shape & structure of Ocean
bottom
 Strongly affect distribution of Benthic
Organisms
 Chronological record of Earth’s history
 Tectonic history
 Climate history
 Evolutionary history
Sediment Thickness
500
20 000
Continental Shelf/ Slope
CLCS/11, Fig. 8.1
Law of Superposition
Younger sediments over Old sediments
YOUNG
---------------------OLD
Sediment Classification
 By Grain Size
 By Origin
Sediment Classification
 Grain Size
 Clay
 Silt
 Sand
 Gravel
<4 μm
4-62 μm
62-2000 μm
>2000 μm
Table 3.1
Sediment Classification based on size
Sediments are often mixtures
of various grain sizes !
Ternary diagram with gravel
Seamount
 Ocean bottom mountains
Oceanic trenches