Sediments sedimentary rocks

Chapter Six
Sediments & Sedimentary
Rocks


Sediment
• Sediment - loose, solid particles originating from:
– Weathering and erosion of pre-existing rocks
– Chemical precipitation from solution, including
secretion by organisms in water

• Classified by particle size
–
–
–
–
–
–

Boulder - >256 mm
Cobble - 64 to 256 mm
Pebble - 2 to 64 mm
Sand - 1/16 to 2 mm
Silt - 1/256 to 1/16 mm
Clay - <1/256 mm


SEDIMENTATION AND SEDIMENTARY ROCKS
I. INTRODUCTION
IMPORTANCE OF SEDIMENTARY ROCKS:
i) 75% OF ROCKS EXPOSED AT THE EARTH’S SURFACE

ii) SOURCE OF FOSSIL FUELS, IRON AND ALUMINUM
ORES, ALUMINUM ORES, AND GROUNDWATER
iii) RECORD OF EARTH’S HISTORY


TYPES OF SEDIMENT


II ORIGIN OF SEDIMENTARY ROCKS:
A. INTRODUCTION
1. REVIEW OF WEATHERING PROCESSES:
2. CLASSIFICATION OF SEDIMENTS
a) DETRITAL SEDIMENT: PREEXISTING FRAGMENTS OF
PREEXISTING IGNEOUS, SEDIMENTARY AND METAMORPHIC ROCKS
b) CHEMICAL SEDIMENT: PRECIPITATED FROM WATER OR
EXTRACTED BY ORGANISMS AND DEPOSITED LATER
B. SEDIMENT TRANSPORT AND TEXTURE
1. INTRODUCTION
i) TRANSPORTATION AND DEPOSITION OF CHEMICAL
SEDIMENTS
ii) TRANSPORTATION AND DEPOSITION OF DETRITAL
SEDIMENTS


2. GRAIN SIZE – CONTROLLED BY:

a) NATURE OF PARENT ROCKS
b) NATURE AND ENERGY LEVEL OF TRANSPORT MEDIUM

•

1) SORTING
WELL-SORTED: WIND MOST SELECTIVE
POORLY-SORTED: GLACIERS AND FLOODING
RIVERS SORT
POORLY
2) CURRENT VELOCITY


Grain size
•3) GRAIN

SHAPE - DEPENDS ON:

• a) TRANSPORT MEDIA: SWIFTLY FLOWING RIVERS
BOUNCE PEBBLES
•
•
AND SAND GRAINS AROUND VIGOROUSLY
•
• b) DISTANCE FROM PARENT ROCK (AT THE BASE IF A
GLACIER MAY
•
•
BE GROUND TO A ROCKY POWDER)
•
• c)MINERAL HARDNESS:


Sediment in a Stream

C. SEDIMENTARY STRUCTURES:
1. BEDDING (STRATIFICATION): ARRANGMENT OF SEDIMENT
PARTICLES INTO DISTINCT LAYERS
a) CHANGES IN SEDIMENT:
b) CHANGES IN TRANSPORT ENERGY
2. GRADED BEDDINGS: SEDIMENT LAYER (FORMED BY A SINGLE
DEPOSITONAL EVENT) IN WHICH PARTICLE SIZE VARIES
GRADUALLY WITH THE COARSEST PARTICLES ON THE
BOTTOM


Development of a bedding plane


Develop. Bedding plane-contd.


Develop. Bedding plane contd.


Graded bedding of sediment


Development of cross-bedding


Cementation & Recrystallization
•4. CEMENTATION: PRECIPITATION OF DISSOLVED IONS IN THE PORE

•
• SPACE
•
a) CALCIUM CARBONATE
•
•
b) SILICA
•
•
c) IRON COMPOUNDS
•
•5.CLASTIC TEXTURE: FORMED BY COMPACTION AND CEMENTATION
OF
•
• SEDIMENT PARTICLES HAS CLASTIC TEXTURE
•
•6.RECRYSTALLIZATION: RECRYSTALLIZATION OF CERTAIN UNSTABLE
• MINERALS INTO NEW, MORE STABLE MINERALS
•


III. CLASSICATION OF SEDIMENTARY ROCKS:
DETRITAL SEDIMENTARY ROCKS:
•
•
•
•

MUDSTONES
SANDSTONES

CONGLOMERATES
BRECCIAS

A. DETRITAL SEDIMENTARY ROCKS:
1. INTRODUCTION: CLASSIFICATION BASED ON
PARTICLE SIZE
a) ALL DETRITAL ROCKS ARE CLASTIC
b) SAND AND SILT PREDOMINANTLY QUARTZ
c) FINER-SIZED PARTICLES OF CLAY MINERALS


2. MUDSTONES
a) MORE THAN HALF OF ALL SEDIMENTARY ROCKS
b) CONTAIN THE SMALLEST PARTICLES (0.004 mm IN DIAMETER)
c) ENVIRONMENTS OF DEPOSITION: LAKES, LAGOONS, DEEP OCEAN
BASINS, RIVER FLOODPLAINS
d) COLOR VARIETY OF SHALE REPRESENTS MINERAL COMPOSITION
e) PRACTICAL USES OF SHALE: BRICKS, CERAMICS, CEMENT, AND OIL
SHALE


3.SANDSTONES:
a) 25% OF ALL SEDIMENTARY ROCKS
b) SANDSTONE PARTICLES (1/16-2 MM IN DIAMETER)
c) PRACTICAL USES OF SANDSTONES: BUILDINGS AND
RESERVOIR
FOR FOSSIL FUELS AND GROUNDWATER
4.CONGLOMERATES AND BRECCIAS
a) GRAINS LARGER THAN 2 MM
b) CONGLOMERATES HAVE ROUNDED GRAINS

c) BRECCIAS HAVE ANGULAR GRAINS


B. CHEMICAL SEDIMENTARY ROCKS

1.

INORGANIC CHEMICAL SEDIMENTARY ROCKS

a) LIMESTONE (INORGANIC)
i) FORMATION
ii) OOLITIC LIMESTONE
iii) TUFA
iv) TRAVERTINE


Cross-bedding & mudcracks
3. CROSS-BEDDING: SEDIMENTARY LAYERS DEPOSITED AT AN
ANGLE TO THE UNDERLYING SET OF BEDS
4. SURFACE SEDIMENTARY FEATURES
a) RIPPLE MARKS: SMALL SURFACE RIDGES PRODUCED WHEN
WATER OR WIND FLOWS OVER SEDIMENT AFTER IT IS
DEPOSITED
b) MUDCRACKS: OCCUR ON THE TOP OF A SEDIMENT LAYER
WHEN MUDDY SEDIMENT DRIES AND CONTRACTS


Origin of mud cracks

Asymmetric and symmetric ripples


D. LITHIFICATION: TURNING SEDIMENT INTO
SEDIMENTARY ROCK
• 1. DEFINITION OF DIAGENESIS: CHANGES IN THE
SEDIMENT DUE TO INCRESED HEAT, PRESSURE,
AND CIRCULATING GROUNDWATER
• 2. DEFINITION OF LITHIFICATION: END RESULT OF
DIAGENESIS
•
• 3. COMPACTION: DIAGENETIC PROCESS BY WHICH
THE WEIGHT OF OVERLYING MATERIALS REDUCES
THE VOLUME OF SEDIMENTARY BODY


Lithification of sediment


Initial deposits of flat/tabular clay