Advanced petrology ( tectonic and sedimentation).pptx How the sedimentation where taken and the kind of transportation process is going on? The role of plate tectonic settings in sedimentation.

1. WELCOME

2. ADVANCED PETROLOGY
TECTONICS AND SEDIMENTATION
PRESENTED BY: VASUDEVAN. M
M.SC.,GEOLOGY (INT)
ANNAMALAI UNIVERSITY

3. CONTENT
1. Introduction to sedimentation
1.1 Methods of transportation
1.2 Processes of sedimentation
2. Plate tectonic and sedimentation
2.1 Geosynclines
2.2 Plate boundaries and sedimentation
3. Summary
4. Reference

4. 1. INTRODUCTION TO SEDIMENTATION
• Sedimentation is the final stage of a process that begins with
erosion and transportation of eroded materials to sites of deposition.
• Physical sedimentation is the deposition of such materials in the
lowest places to which air and water currents can transport them.
• Chemical sedimentation is mainly the process by which seawater
keeps a constant composition by depositing precipitates to balance
the dissolved weathering products brought in by rivers

5.  Calcium carbonate makes up the largest volume of chemical sediment,
much of it extracted from seawater by invertebrates and secreted as shells.
 Silica-rich sediments are also largely produced by organisms, mainly the
diatoms. Bacteria play an important role in sulfide sedimentation in
environments lacking oxygen.
 Gypsum and salt form from the evaporation of seawater in isolated basins.
 Depositional patterns of sediments are strongly affected by the geomorphic
environments in which they were deposited.
 Tectonism controls both subsidence in the depositional area and
weathering at the source of the erosional debris. Chemical and physical
changes after deposition convert soft sediment to rock and cause many
other alterations of composition and texture.

6. 1.1 METHODS OF TRANSPORTATION
Water-in streams and below glaciers, underground, and in ocean
currents-is the principal means of transporting material from one place to
another.
 In a stream the coarsest material is carried along the bed of the stream
by rolling and sliding;
The medium sized material is carried partially within the flowing water,
at times falling to the bottom only to bounce back up into the curren
and the finer material is carried suspended within the flowing water.

7.  The material dissolved from the
weathering of minerals is carried by
the stream in solution and
ultimately adds to the salinity of the
ocean into which it finally empties.
 Landslides and other movements
induced by gravity also play a role,
as does the wind.

8. 1.2 PROCESSES OF SEDIMENTATION
• Detrital material is deposited when its agent of transportation no longer has
sufficient energy to move it farther. For example, a stream flowing along at a
certain velocity possesses energy to move particles up to a certain maximum
size.
• If the stream loses velocity, it also loses energy, and it is no longer able to
transport all the material that it has been carrying at the higher velocity.
• The solid particles, beginning with the heaviest, start to settle to the bottom.
The effect is much the same when a wind that has been driving sand across a
desert suddenly dies-a loss of energy accompanies the loss in velocity.

9. • Material that has been carried in solution is deposited in a different way, that
is, by precipitation, a chemical process by which dissolved material is
converted into a solid and separated from the liquid solvent. As already noted,
precipitation may be caused by chemical interaction and evaporation
concentration
• Although at first glance the whole process of sedimentation seems quite
simple, it is actually as complex as nature itself. Many factors are involved,
and they can interact in a variety of ways.
• Consequently the manner in which sedimentation takes place and the
sediments that result from it differ greatly from one situation to another. Think,
for instance, of the different ways which materials settle out of water. A swift,
narrow mountain stream may deposit coarse to medium particles along its
bed, but farther downstream, as the valley widens, the same stream may
overflow its banks and spread fine particles including mud, over the
surrounding country.

10. 2. PLATE TECTONIC AND SEDIMENTATION
• The crustal motions of the colossal portions of the lithosphere known as
plates.
• Areas exist on the Earth's crust where sediments accumulate to great
thicknesses. Many of these regions are ultimately pushed up into
mountains, developing most commonly along the margins of the plates.

11. • Thick accumulations of sediments may occur
either where there is a deep hole into which the
sediments are dumped or where the crust
subsides as more and more sediments are
deposited in relatively shallow water.
• We have evidence of both in the geologic record,
but the overwhelming bulk of sedimentary rocks
found in mountain ranges apparently formed
originally as shallow water sediments, as proved
by such indicators as certain kinds of ripple
marks, mad cracks, and shallow-water organisms

12. 2.1 GEOSYNCLINES
• Following the work of James Hall, a nineteenth-century pioneer in
American geology, Marshall Kay, and other twentieth-century
proponents of the idea, the concept of geosynclines developed into a
dominant theme in the interpretation of many mountain belts.
• The concept held that folded rocks in mountain ranges of the world
apparently developed from thick deposits of sediments that
accumulated in these geosynclines-literally, "earth syncline." or large-
scale down warp in the sedimentary rocks found in the Earth's crust. A
geosyncline is thus a large sediment-filled elongate basin.

13. • Parallel adjacent belts characterize geosynclines. These have been
called miogeosyncline (or simply miogeocline by Robert Dietz and
others) where sediments are deposited on continental basement and
where volcanic rocks and deeper water sediments are lacking;
 and eugeosyncline ( or eugeocline) where sediments are deposited
on noncontinental basement and where there is an abundance of
interstratified volcanic rocks and deeper-water sediments.
• The concept of geosynclines is no longer very widely held, as little
evidence can be found for support and no present-day examples seem
to fit it very well It is presented here merely for historical purposes and
because there a still some references to geosynclines in current
literature.

14. FIGURE 1.1
ACCRETION OF THE
SOUTHERN PART
OF THE NORTH
AMERICAN
CONTINENT
North America collected a series
of successive volcanic island arc
chains and steadily
accumulated eugeosynclinal,
miogeosynclinal, and platform
sedimentary deposits.

15. Figure 1.2. Phanerozoic orogens of North
America
Within the Cordilleran, Appalachian, and
Innuitian orogens, the rocks can be divided
into three categories
(Fig. 1.2): eugeosynclinal deposits (EG;
geosynclinal rocks deposited on oceanic
crust), miogeosynclinal deposits (MG;
geosynclinal rocks deposited on continental
crust), and platform deposits (PF).

16. 2.2 PLATE BOUNDARIES AND SEDIMENTATION
• As discussed, there are three basic types of plate boundaries:
 convergent, where old lithosphere is carried downward along
subduction zones and magma rises to form volcanic regions, as the
west coast of South America or the Aleutians;
divergent, where old lithosphere pulls apart and new lithosphere forms
along midoceanic spreading centers, as the Atlantic ridge;
 and transform, or parallel, where two plates slide past one another
with no new lithosphere forming and no old lithosphere being
destroyed, as along the San Andreas fault.

17. • In relating sedimentation to plate tectonic theory, those holding to the
geosynclinal concept might interpret the miogeosynclines as representing
thick sediment wedges forming on divergent continental margins and the
eugeosynclines as representing sediments deposited farther offshore or in
areas marked by volcanic island arcs, perhaps at a converge plate boundary.
• Transform margins are marked by numerous basins that are later filled with
thick sequences of sediments similar to those found along the San Andreas
fault zone.
• The relative motion of the plates on or between which the sediments have
accumulated will determine the ultimate structure of the mountain systems
that later form from these sediments and sedimentary rocks.

18. 3. SUMMARY
• Sedimentation is closely related to plate boundaries, with thick
accumulations along some margins
Miogeoclines are thick accumulations of strata on margins of
continental blocks.
Eugeoclines represent rocks developed farther offshore or in
areas marked by volcanic island arcs.
Geosynclines are large-scale downwarps in the earth's crust
in which large accumulations of sediments occur

19. 4. REFERENCE
Earth, 4th edition 1985, by Frank press and Raymond siever, W. H.
Freemen and company,new York.
Physical geology 1987, by Sheldon Judson, Marvin E. Kauffman and
L. Don Leet, Englewood Cliffs Prentice-Hall
UNIT 7 GEOL 319 : Case Study of the North American
Cordillera, Athabasca University

20. Thank you