Chapter SixChapter Six

Sediments & Sedimentary RocksSediments & 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. INTRODUCTION1. 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 

•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:

Grain size

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 • • 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• 

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 

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

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 • 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

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• % of sedimentary rocks in outer 10 miles• Basic classification of sedimentary rocks• Most sedi. Rocks – Chemical or detrital• Definition of sedimentary rocks• Sorting by wind, glaciers (well sorted vs poor sorting)• Degree of sedimentary particle rounding• Bedding plane, sedimentary structure, occurrence• Diagenesis, Lithification, Cementation• Composition of detrital sedimentary rocks• Environment – deposition of shale• Breccia and Conglomerate• Oolitic Limestone• Definition of Sedimentary Facies – Characteristics that distinguish

one from another