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Chapter Six

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  1. Chapter Six Sediments & Sedimentary Rocks

  2. 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

  3. 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

  4. TYPES OFSEDIMENT

  5. 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

  6. 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

  7. 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:

  8. Sediment in a Stream

  9. 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

  10. Development of a bedding plane

  11. Develop. Bedding plane-contd.

  12. Develop. Bedding plane contd.

  13. Graded bedding of sediment

  14. Development of cross-bedding

  15. 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

  16. 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

  17. 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

  18. 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

  19. B. CHEMICAL SEDIMENTARY ROCKS INORGANIC CHEMICAL SEDIMENTARY ROCKS a) LIMESTONE (INORGANIC) i) FORMATION ii) OOLITIC LIMESTONE iii) TUFA iv) TRAVERTINE

  20. 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

  21. Origin of mud cracks

  22. Asymmetric and symmetric ripples

  23. 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

  24. Lithification of sediment

  25. Initial deposits of flat/tabular clay

  26. Formation of ooliths

  27. Locations of subsurface evaporite

  28. Formation of coal from swamp deposits

  29. Formation of coal –contd.

  30. Common geological environment

  31. Geology at a glance

  32. Marine sedimentary environment

  33. Sedimentary facies formation

  34. Sedi. Facies formation – contd.

  35. Landword Migration

  36. 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