GEOL-G 103 Lecture 3: 03 Marine Sediments Outlines (1)

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Published on 10 Nov 2016
Readings Outline Module 4 ͞Marine Sediments͟
(3) Marine Sediments Readings Outlines
Chapter 4 Outline
How Are Marine Sediments Collected and What Historical Events Do They Reveal?
o Collecting Marine Sediments
A bucket like device called a dredge was used to scoop up sediment from the deep ocean
floor for analysis but this process had many limitations. The dredge could come up early
and it only grab a sample later causing gravity corer a hollow steel tube with a heavy
weight on top was to collect the first cores(cylinders of sediments + rocks) now ships do
Rotary drilling collect the cores from the deep ocean.
o Environmental Conditions Revealed by Marine Sediments
Marine sediments provide a wealth of info about past conditions on earth, sediment
accumulate on the ocean floor and preserve the materials and conditions of the
environment that existed in the overlying water column, after sediments are collected and
interpreting earth scientist infer past environmental conditions such as surface temp.,
nutrient supply, abundance of marine life, atmospheric winds, ocean current patterns,
volcanic eruptions, extinction events, change in earth climate, movement of tectonic
o Paleoceanography
Study of how ocean, atmosphere, and land have interacted in past produce changed in
ocean chemistry, circulation, biology, and climate called paleoceanography. Branch of
oceanography that relies on sea floor sediments to gain insight into these past changes.
What Are the Characteristics of Lithogenous Sediment?
Is derived from preexisting rock material that originates on the continents or islands from
erosion volcanic eruptions or blown dust. (Which is also known as terrigenous sediment)
o Origin of Lithogenous Sediment
Lithogenous sediment start as rocks on continents or islands. Over time weathering
agents such as water, temp extremes, chemical effects break the rocks into small pieces.
Smaller rocks are easily eroded (picked up and transported). Eroded materials is the basic
component of which all lithogenous sediment is composed. Eroded material is carried by
ocean streams, wind, glaciers, gravity. Transported sediment can be deposited in many
enviro, like bays, lagoons, deltas by mouths of river, beaches at shoreline, and off shore
o Composition of Lithogenous Sediment
Reflects the material from which it was derived. All rocks are composed of discrete
crystals naturally occurring compounds called minerals. Most abundant, chemically
stable, durable miner is earths crust quartz which is made of silicone, oxygen like
ordinary glass. Quartz is resistant to abrasion can be transported long distance, deposit far
from its source area
o Sediment Texture
Texture and grain size is important. Wentworth scale of grain size shows that particals
can be classified as boulders(largest), cobbles, pebbles, granules, sand, silt, clay
(smallest), sediments size is proportionate to energy needed to lay down a deposite.
-Deposites particles layed down in high level strong wave action (boulders,cobbles)
-fine grained particles layed down in low level and current speed is minimal, fine grain
stick together
The texture also depends on the sorting which is a measure of uniformity of grain and
shows transportation processc
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Readings Outline Module 4 ͞Marine Sediments͟
o Distribution of Lithogenous Sediment
Neritic Deposits ----found on continental shelves and in shallow water near islands and
are coarse grained
Beach Deposits
Composed mostly of quartz-rich sand that is washed down to the coast by
rivers can also be composed of wide variety of sizes and compositions. Material is
transferred by waves that crash against the shoreline also by storms.
Continental Shelf Deposits
Glaciers melted and sea level rised, rivers today drop their sediment in
drowned river mouths rather then carry it onto the continental shelf like in
geologic past.
Turbidite Deposits
Turbidity currents are underwater avalanches that periodically move down
the continental slopes and carve submarine canyons, turbidity carry cast
amounts of neritic material it spreads out as deep sea fans, comprises the
continental rise, thins toward abyssal plains which are called turbidite
Glacial Deposits
Poorly sorted deposites containing particles ranging from boulders to clays
found in high altitude portion of coninetal shelf. Glacial deposits where
laid down during recent ice age by glaciers that covered continental shelf
and eventually melted.
Pelagic Deposits----found in the deep ocean basins nd are typically fine grained
Abyssal Clay
Composed of at least 70%(by weight) fine, clay sized particals from the
continents, far from land, deep abyssal plains contain thick sequences of
abyssal clay deposits composed of particles transported great distance by
winds or ocean currents and deposited on ocean floor.
What Are the Characteristics of Biogenous Sediment?
Derived from the remains of hard parts of once living organisms.
o Origin of Biogenous Sediment
Sediment begins as hard parts(shells, bones, teeth) of living organisms from algae,
protozoans, to fish and whales. When they die their remains settle on the ocean
floor and acumualte as biogenous sediment.
--Can be classified as
Macroscopiclarge enough to see without microscope(shells, bones,
teeth, large organisms)
Microscopicsmall only can see through microscope and produce tiny
shells called tests that sink after it dies and rain down in great numbers. They can
add up and be called ooze which is fine mushy material
o Composition of Biogenous Sediment
Two chemical compounds in biogenous sediments are….
--calcium carbonate- forms from mineral calcite
--Silica- which is combined with water
Most comes from microscopic algae called diatoms and protozoans called
radiolarians. Diatoms photosynthesize and need strong sunlight found on upper
surface of water of ocean. diatoms are free floating and builds a greenhouse out of
silica as a protective covering and lives inside
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