Chapter Six

Sediments & Sedimentary Rocks

SedimentSediment - loose, solid particles originating from: Weathering and erosion of pre-existing rocksChemical precipitation from solution, including secretion by organisms in waterClassified by particle size Boulder - >256 mmCobble - 64 to 256 mmPebble - 2 to 64 mmSand - 1/16 to 2 mmSilt - 1/256 to 1/16 mmClay -

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