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Chapter Six
Sediments & Sedimentary Rocks
SEDIMENTATION AND SEDIMENTARY ROCKS INTRODUCTIONIMPORTANCE OF SEDIMENTARY ROCKS: i) 75% OF ROCKS EXPOSED AT THE EARTHS SURFACE ii)SOURCE OF FOSSIL FUELS, IRON AND ALUMINUM ORES, ALUMINUM ORES, AND GROUNDWATER iii) RECORD OF EARTHS 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 LATERB. 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 ROCKSb) 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 LAYERSa) CHANGES IN SEDIMENT: b) CHANGES IN TRANSPORT ENERGY2. 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 SPACEa) CALCIUM CARBONATE b) SILICA c) IRON COMPOUNDS5.CLASTIC TEXTURE: FORMED BY COMPACTION AND CEMENTATION OF SEDIMENT PARTICLES HAS CLASTIC TEXTURE6.RECRYSTALLIZATION: RECRYSTALLIZATION OF CERTAIN UNSTABLE
MINERALS INTO NEW, MORE STABLE MINERALS
Cementation & Recrystallization
III. CLASSICATION OF SEDIMENTARY ROCKS: DETRITAL SEDIMENTARY ROCKS:
MUDSTONESSANDSTONESCONGLOMERATESBRECCIAS
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 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 BEDS4. 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 DIAGENESIS3. 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 milesBasic classification of sedimentary rocksMost sedi. Rocks Chemical or detritalDefinition of sedimentary rocksSorting by wind, glaciers (well sorted vs poor sorting)Degree of sedimentary particle roundingBedding plane, sedimentary structure, occurrenceDiagenesis, Lithification, CementationComposition of detrital sedimentary rocksEnvironment deposition of shaleBreccia and ConglomerateOolitic LimestoneDefinition of Sedimentary Facies Characteristics that distinguish one from another