Sediments sedimentary rocks

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

Chapter Six

Sediments & Sedimentary

Rocks

• 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

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

2 GRAIN SIZE – CONTROLLED BY:

a) NATURE OF PARENT ROCKS

b) NATURE AND ENERGY LEVEL OF TRANSPORT MEDIUM

•3) GRAIN SHAPE - DEPENDS ON:

• a) TRANSPORT MEDIA: SWIFTLY FLOWING RIVERS BOUNCE PEBBLES

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

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

•6.RECRYSTALLIZATION: RECRYSTALLIZATION OF CERTAIN UNSTABLE

Cementation & Recrystallization

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

FOR FOSSIL FUELS AND GROUNDWATER

4.CONGLOMERATES AND BRECCIAS

a) GRAINS LARGER THAN 2 MMb) CONGLOMERATES HAVE ROUNDED GRAINSc) BRECCIAS HAVE ANGULAR GRAINS

B CHEMICAL SEDIMENTARY ROCKS

1 INORGANIC CHEMICAL SEDIMENTARY ROCKS

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

Cross-bedding & mudcracks

Origin of mud cracks

Asymmetric and symmetric ripples

D LITHIFICATION: TURNING SEDIMENT INTO

SEDIMENTARY ROCK

SEDIMENT DUE TO INCRESED HEAT, PRESSURE,

AND CIRCULATING GROUNDWATER

DIAGENESIS

•

THE WEIGHT OF OVERLYING MATERIALS REDUCES THE VOLUME OF SEDIMENTARY BODY

Lithification of sediment

Initial deposits of flat/tabular clay

Formation of ooliths

Locations of subsurface evaporite

Formation of coal from swamp deposits

Formation of coal –contd.

Common geological environment

Geology at a glance

Marine sedimentary environment

Sedimentary facies formation

Sedi Facies formation – contd.

Landword Migration

Chapter Summary

one from another