Chapter 4 - Haiku

choppedspleenΜηχανική

21 Φεβ 2014 (πριν από 3 χρόνια και 8 μήνες)

101 εμφανίσεις

© 2006 Jones and Bartlett Publishers

Chapter 4

Marine Sedimentation

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


biogenous sediments


hydrogenous sediments


volcanogous sediments


cosmogenous sediments


4
-
1 Sediment in the Sea

Figure B4
-
3 Sediment Cores


Factors that control sedimentation include:


particle size


the turbulence of the depositional environment



Terrigenous sediments strongly reflect their source.


They 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.

4
-
1 Sediment in the Sea


Hjulstr
ö
m’s Diagram graphs the relationship
between particle size and energy for


erosion



transportation


deposition

4
-
1 Sediment in the Sea

Figure 4
-
1 Hjulstr
ö
m’s Diagram


Based upon water depth, the ocean
environment can be divided into:



the shelf


shallow and near a terrigenous source


the deep ocean basin


deep and far from a terrigenous source

4
-
2 Sedimentation in the Ocean

Review


Shelf sedimentation is strongly controlled by:


Tides


Waves


Currents


Their influence decreases with water depth.



Shoreline turbulence prevents small particles
from settling in the shallow water.



Particle size decreases seaward for recent
sediments.


4
-
2 Sedimentation in the Ocean

Shelf Sedimentation

4
-
2 Sedimentation in the Ocean

Figure 4
-
2a Model Prediction of Shelf Sediments

Past fluctuations of sea level have stranded coarse (relict)
sediment across the shelf.


This includes most areas where only fine sediments are
deposited today.

Figure 4
-
2 Shelf Sedimentation

Sea Level Fluctuation and Coastlines

Shelf Sedimentation

Figure 4
-
3b Relict Sediment

4
-
2 Sedimentation in the Ocean


Worldwide distribution of recent shelf sediments
by composition is strongly related to
latitude

and
climate
.



Calcareous biogenous sediments dominate tropical
shelves.



River
-
supplied sands and muds dominate
temperate shelves.



Glacial till and ice
-
rafted sediments dominate
polar shelves.

4
-
2 Sedimentation in the Ocean

Shelf Sedimentation Model

4
-
2 Sedimentation in the Ocean

Figure 4
-
4a Shelf Sedimentation Model

Distribution of Shelf Deposits

4
-
2 Sedimentation in the Ocean

Figure 4
-
4b Relative Amounts of Shelf Sediments


Geologic controls of continental shelf sedimentation
must be considered in terms of a
time frame
.



For a time frame up to:



1000 years,
waves, currents and tides

control
sedimentation.



1,000,000 years,
sea level

lowered by glaciation controls
sedimentation and cause rivers to deposit their sediments at
the shelf edge and onto the upper continental slope.



100,000,000 years,
plate tectonics

determines the type of
margin that develops and controls sedimentation.

4
-
2 Sedimentation in the Ocean

Paleogeography of North America

4
-
2 Sedimentation in the Ocean

Figure 4
-
5a North American Paleogeography 100 MYBP

Figure 4
-
5b Pangaea 100 MYBP

4
-
2 Sedimentation in the Ocean

Figure 4
-
5c Western North American
Tectonic Margin (Active Margin)

Figure 4
-
5d Eastern North
American Nontectonic
Margin (Passive Margin)

Development of a Passive Atlantic
-
type Margin

Figure 4
-
6a Initial Rifting (Triassic Period: 200 MYBP)

Figure 4
-
6b Jurassic Margin (150 MYBP)

4
-
2 Sedimentation in the Ocean

Figure 4
-
6c Present
-
Day Margin Southeast of Cape Cod

4
-
2 Sedimentation in the Ocean

Subduction Tectonics and Sedimentation

Figure 4
-
7a Volcanic Arc
-
Trench System

4
-
2 Sedimentation in the Ocean

Figure 4
-
7b Accretionary Prism

4
-
2 Sedimentation in the Ocean

If influx of terrigenous sediment is low and the
water is warm,
carbonate
sediments and reefs
will dominate.

4
-
2 Sedimentation in the Ocean

Figure 4
-
8 Distribution of Carbonate Shelves


Deep
-
sea Sedimentation has two main
sources of sediment:



External



terrigenous material from the land



Internal



biogenous and hydrogenous from
the sea.

4
-
2 Sedimentation in the Ocean

Deep
-
Sea Sedimentation

4
-
2 Sedimentation in the Ocean

Figure 4
-
9a Sedimentation in the Deep Sea

Figure 4
-
9b River Input of Silt to Oceans

4
-
2 Sedimentation in the Ocean


Major sedimentary processes in the deep sea include:


Bulk emplacement


Debris flows


Turbidity currents

4
-
2 Sedimentation in the Ocean

Figure 4
-
10a Seismic
-
Reflection Profile

Bulk Emplacement of Sediment to the Deep Sea

4
-
2 Sedimentation in the Ocean

Figure 4
-
10b Turbidity Current

Figure 4
-
10c Margin
-
Sedimentation Model

4
-
2 Sedimentation in the Ocean

Figure 4
-
10c Turbidite Beds

Major pelagic sediments
in the ocean are red clay
and
biogenic oozes
.

4
-
2 Sedimentation in the Ocean

Figure 4
-
14b Foraminifera

Figure 4
-
14e Diatoms


Hydrogenous deposits are chemical and biochemical
precipitates that form on the sea floor. They include:


ferromanganese nodules


phosphorite

Figure 4
-
15b Global Distribution of Ferromanganese Nodules

4
-
2 Sedimentation in the Ocean


The distribution of sediments in the

deep
ocean reflects:


Latitude


distance from landmasses


the calcium carbonate compensation depth



Glacial marine sediments occur in the high
latitudes.



Pelagic clays occur far from land and in the
deepest water.

4
-
2 Sedimentation in the Ocean

The Formation of Glacial
-
Marine Sediments

Figure 4
-
12a Ice Rafting

4
-
2 Sedimentation in the Ocean

The Formation of Glacial
-
Marine Sediments

Figure 4
-
12b Deep
-
Sea Deposits Around Antarctica

4
-
2 Sedimentation in the Ocean


Calcareous oozes occur above the calcium carbonate
composition depth.




4
-
2 Sedimentation in the Ocean

The depth at which surface production of CaCO
3

equals dissolution is called the calcium
carbonate compensation depth (CCD
)
Figure 8.17

. Above this depth, carbonate oozes can
accumulate, below the CCD only
terrigenous

sediments, oceanic clays, or siliceous oozes
can accumulate. The calcium carbonate compensation depth beneath the temperate and
tropical Atlantic is approximately 5,000 m deep, while in the Pacific, it is shallower, about
4,200
-
4,500 m, except beneath the equatorial upwelling zone, where the CCD is about
5,000 m. The CCD in the Indian Ocean is intermediate between the Atlantic and the Pacific.
The CCD is relatively shallow in high latitudes.




The rate of sedimentation depends on the type of sediment
in deep sea.


4
-
2 Sedimentation in the Ocean

Figure 4
-
13 Clays in Deep
-
Sea Muds

Global Deep
-
Sea Deposits

Figure 4
-
16a Deep
-
Sea Sediment Distribution

4
-
2 Sedimentation in the Ocean

Global Deep
-
Sea Deposits

Figure 4
-
16b Sedimentation Rates

4
-
2 Sedimentation in the Ocean


Deep
-
sea stratigraphy

refers to the broad
-
scale layering of sediments that cover the
basaltic crust.



The stratigraphy of the deep sea is strongly
influenced by sea
-
floor spreading.


4
-
2 Sedimentation in the Ocean


The Atlantic basin contains a “two
-
layer
-
cake”
stratigraphy


a thick basal layer of carbonate
ooze overlain by a layer of mud.

Figure 4
-
17 Stratigraphy of the Atlantic Basin

4
-
2 Sedimentation in the Ocean


The Pacific basin contains a “four
-
layer
-
cake” stratigraphy.


It crosses the equator where the CCD is lowered to the
ocean bottom.

Figure 4
-
18a Pacific Ocean

4
-
2 Sedimentation in the Ocean

Stratigraphy of the Pacific Basin

Figure 4
-
18b Stratigraphy of the Pacific Basin

4
-
2 Sedimentation in the Ocean

Figure 4
-
18c Model to Account for Pacific Stratigraphy

4
-
2 Sedimentation in the Ocean


The Mediterranean basin is located where plates are
colliding as Africa moves northward relative to
Europe.



Anhydrite and stromatolites of Miocene age indicate
that the Mediterranean sea “dried” out between 5 and
25 million years ago.



Two models have been suggested to account for this
emptying of the Mediterranean Sea of its water.


The “Uplift” Model


The “Drying
-
Out” Model



After drying out, seawater from the Atlantic Ocean
cascaded down the face of the Gibraltar Sill, refilling
it in about 100 years.

4
-
2 Sedimentation in the Ocean

The Drying Up of the Mediterranean Sea

The “Uplift” Model

The “Drying
-
Out” Model