Sediments and Sedimentary Rocks

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Feb 22, 2014 (3 years and 8 months ago)

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Chapter 8:

Sediments and Sedimentary Rocks




Lecture Slides prepared by

Peter Copeland • Bill Dupré


Copyright © 2004 by W. H. Freeman & Company

Understanding Earth

Frank Press • Raymond Siever • John Grotzinger • Thomas H. Jordan

Fourth Edition

Sedimentary

R
ocks



a rock resulting from the
consolidation of loose sediment
that has been derived from
previously existing rocks and
accumulated in layers. (clastic,
detrital, or terrigenous)


a rock formed by the precipitation
of minerals from solution by either
organic or inorganic processes
(chemical)

Sedimentary Stages of

the Rock Cycle

Weathering

Erosion

Transportation

Deposition (sedimentation)

Burial

Diagenesis

Fig. 8.1

Transport and Deposition

of Clastic Sediments


Movement of sediment by wind,
ice or water


The mode of transport will
produce distinctive deposits

Transport will effect the

sediment in several ways

Sorting
:

a measure of the variation in the
range of grain sizes in a rock or sediment


Well
-
sorted sediments have been
subjected to prolonged water or wind
action.


Poorly
-
sorted sediments are either not
far
-
removed from their source or
deposited by glaciers.

Sorting

Fig 8.2

Physical Effects of Transport Will Effect
the Sediment in Several Ways

Roundness
:
measure of the angularity of
particles; the less angular, the more
roundness it is said to possess

Sphericity
:
how circular and round a
particle is

sorting, roundness, and sphericity all
increase with amount of transport


Fig. 8.3

Sedimentary Environments

Fig. Story 8.4

Fig. Story 8.4

Sedimentary Structures

Stratification = Bedding = Layering

This layering that produces
sedimentary structures is due to:


Particle size


Types (s) of particles

Sedimentary Layering

Other Examples of Sedimentary Structures


Cross
-
beds


Ripple marks


Mudcracks


Raindrop impressions


Fossils (some may have been
preserved in growth position)

Cross
-
bedded sandstone

Fig. 8.5

Fig. 8.6


Ripples on a beach

Fig. 8.7

Ripples Preserved in Sandstone

Fig. 8.7

Fig. 8.8

Fig. 8.8

Fig
.
8.9

From Sediment to Sedimentary Sock

(lithification)

Compaction
:
reduces pore space.


clays and muds are up to 60 % water; 10%
after compaction

Cementation
:
chemical precipitation of
mineral material between grains (SiO
2
,
CaCO
3
, Fe
2
O
3
) binds sediment into hard
rock.

Recrystallization
:
Pressure and
Temperature increase with burial (30
°
C/km or
1
°
C/33 m).

2

Lithification

Fig. 8.11

Turbidity Currents

Suspension of water sand, and mud that
moves downslope (often very rapidly)
due to its greater density that the
surrounding water (often triggered by
earthquakes).

The speed of turbidity currents was first
appreciated in 1920 when a current broke lines
in the Atlantic. This event also demonstrated just
how far a single deposit could travel.

Fig. 8.11

Fig. 8.11

Fig.

8.11

Fig. 8.11

Fig. 8.12

Fig. 8.13

Types of Detrital Rocks


Classification is primarily based on the
size of the constituent particles


conglomerate

breccia

sandstone

(quartzite, arkose,
greywacke)

shale

mudstone

siltstone

Clastic Sedimentary Rocks:

Conglomerate

Fig. 8.14

Clastic Sedimentary Rocks:

Sandstone

Fig. 8.14

Clastic Sedimentary Rocks:

Shale

Fig. 8.14

Fig. 8.15

Composition of

Sedimentary Rocks



limestone

CaCO
3

chert

SiO
2

salt

NaCl, KCl, K
2
SO
4


gypsum

CaSO
4

• 2H
2
O

coal

altered organic debris

Chemical Environments:

Carbonates

clear water



away from big rivers
(or volcanoes)

warm water



subtropical to tropical

shallow water
, two reasons:


organic
: sunlight only penetrates


to about 100 m

inorganic
: CCD (dissolution of



CaCO
3
dependant on
P
)

Carbonates Promote Shallow Water by
Two Mechanisms


Organic:

organisms that secrete their
skeletons to form carbonate deposits
need to live in the sunlight.


Inorganic:

calcium carbonate dissolves
at high pressure.


e.g., the higher the pressure, the greater
the depth

Chemical Environments:

Evaporites


Found only in restricted environments
(Mediterranean Sea, Texas Coast)


Minerals precipitate according to solubility


gypsum





halite

50% evaporation


90% evaporation

CaSO
4

•2H
2
O



NaCl

Coral Reefs and Atolls

Box 8.1

Coral Reefs and Atolls

Box 8.1

Coral Reefs and Atolls

Box 8.1

Coral Reefs and Atolls

Box 8.1

Coral Reefs and Atolls

Box 8.1

Chemical Sedimentary Rocks:

Limestone

Fig. 8.17a

Chemical Sedimentary Rocks:

Gypsum

Fig. 8.17b

Chemical Sedimentary Rocks:

Halite

Fig. 8.17c

Chemical Sedimentary Rocks:

Chert

Fig. 8.17d

Reefal Limestone

Fig. 8.18

Evolution of
a

Rift Zone

Fig. 8.20

Tectonics and Sedimentary Basins:

Rift Basins

Fig. 8.21