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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

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Chapter Six

Sediments & Sedimentary Rocks


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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


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SEDIMENTATION AND SEDIMENTARY ROCKS

  • 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


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TYPES OFSEDIMENT


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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


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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


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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:



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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







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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


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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


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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


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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


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B. CHEMICAL SEDIMENTARY ROCKS

INORGANIC CHEMICAL SEDIMENTARY ROCKS

a) LIMESTONE (INORGANIC)

i) FORMATION

ii) OOLITIC LIMESTONE

iii) TUFA

iv) TRAVERTINE


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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




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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














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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


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