Chapter Six
Sedimentation and Sedimentary Rocks
SEDIMENTATION AND SEDIMENTARY ROCKS
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INTRODUCTION
A.DEFINITION OF SEDIMENT: FRAGMENTS OF SOLID MATERIAL (FROM PREEXISTING ROCKS, REMAINS
OF ORGANISMS, PRECIPITATION FROM SOLUTION)
B.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
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
III. CLASSICATION OF SEDIMENTARY ROCKS:
DETRITAL SEDIMENTARY ROCKS:
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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
B. CHEMICAL SEDIMENTARY ROCKS
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INORGANIC CHEMICAL SEDIMENTARY ROCKS
a) LIMESTONE (INORGANIC)
i) FORMATION
ii) OOLITIC LIMESTONE
iii) TUFA
iv) TRAVERTINE
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
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• 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
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% 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