SEDIMENTARY GEOLOGY OVERVIEW

1. SEDIMENTARY GEOLOGY OVERVIEW Andrew S. Madof Orals Review - 2007 January 12, 2007

2. SEDIMENTARY GEOLOGY = Sedimentology (process) + Stratigraphy (response) Sedimentology = study of PROCESSES (i.e. production, composition, transport, and deposition of sediment) Stratigraphy = study of RESPONSES (i.e. inferring the controls on the spatial and temporal changes of strata) → exact processes that created the rocks can’t be know because only the rocks are left, not the processes

3. Sedimentation And Sedimentary Rocks Sedimentary Rocks: • Form 75% of the rocks exposed at the Earth’s Surface • Are the reservoirs for fossil fuels, iron and aluminum ores, and groundwater • Record of Earth’s history

4. Sediment • Sediment = loose, solid particles and can be: • Terrigenous = fragments from silicates (igneous and/or metamorphics) • Biogenic = fossils (carbonate - reefs; silicates - forams) • Chemical = precipates (halite, gypsum, anhydrite, etc…) - note: with chemical sedimentary rocks, evaporation > precipitation and/or supersaturation in closed basins (lakes or oceans) • 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

5. Grain size Grain size (diameter) and grain-shape depend on: • Transport media: rivers (pebbles bounce on river bottom, sand moved in traction, and silt/clay suspended in water column); oceans and lakes (near-shore and deep-water systems); glaciers (sediment moved on glacier bottom); wind (sand dunes) • Distance from parent rock: the longer the distance traveled, generally the smaller and the more well-rounded the grains (due to higher kinetic energy) • Mineral hardness: the harder the parent rock, the longer it will take the sediments to erode (example: silicates are more resistant to weathering and erosion than feldspars, and this is why beaches are often comprised of sand, not feldspar-rich sediments) • Consider: sorting (= range of grain sizes) → winds sort well (meaning grain sizes are very similar); glaciers sort poorly (meaning there is a large spread of grain sizes in glacial deposits)

6. Classification Of Sedimentary Rocks DETRITAL (TERRIGENOUS) SEDIMENTARY ROCKS: • Mudstones • Sandstones • Conglomerates • Breccias DETRITAL SEDIMENTARY ROCKS: • Classification Based On Particle Size a) All detrital rocks are clastic b) Sand and silt are predominantly quartz c) Finer-sized particles of clay minerals

7. 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 CONGLOMERATES AND BRECCIAS: a) Grain diameters larger than 2 mm b) Conglomerates have rounded grains c) Breccias have angular grains

8. Breccia (from fault motion?) Sandstone

9. 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

10. Chemical Sedimentary Rocks Inorganic Chemical Sedimentary Rocks LIMESTONE (inorganic): I) FORMATION II) Oolitic Limestone III) Tufa IV) Travertine

12. Lithification = Turning Sediment Into Sedimentary Rock • Diagenesis = Changes in the sediment due to increased heat, pressure, and circulating groundwater • Lithification = Compaction + Cementation • Compaction = Diagenetic process by which the weight of overlying materials reduces the volume of sedimentary body (decreases porosity)

13. Cementation & Recrystallization • Cementation: Precipitation of dissolved ions in the pore space a) calcium carbonate - CaCO3 b) silica - SiO2 c) iron compounds - Fe+2 and Fe+3 • Texture of Rock: Formed by compaction and cementation of sediment particles • Recrystallization: recrystallization of certain unstable minerals into new, more stable minerals (this happens primarily in carbonates, when you start with carbonate mud [a.k.a. micrite] heat it up, then cool it to form larger grains [a.k.a. sparite])

15. Types of Sediment

18. Common Geological Environments

19. Locations of Subsurface Evaporites

21. Sedimentary Structures • Bedding (stratification): arrangement of sediment particles into distinct layers A) Changes in sediment change bedding B) Changes in transport energy change bedding • Normally graded bedding: sediment layer (formed by a single depositional event) in which particle size varies gradually with the coarsest particles on the bottom (note: inversely graded bed = fines on bottom and coarse grains on top )

23. Cross-bedding and Mudcracks • Cross-bedding: sedimentary layers deposited at an angle to the underlying set of beds • 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

24. Development of Cross-Bedding

25. Asymmetric and Symmetric Ripples tidal currents (bi-directional) river or wind currents (uni-directional)

26. Formation of Coal from Swamp Deposits

27. Formation of Coal from Swamp Deposits

28. Initial Deposits of Flat/Tabular Clay

29. Formation of Ooliths

30. Origin of Mud Cracks

31. Lithification of Sediments

34. Sedimentary Facies Formation

35. Sedimentary Facies Formation

36. Sediment in a Stream

37. Marine sedimentary environment

38. Landward Migration of Shoreline = Regression(regression can either form due to 1) lower sea level or 2) shoreline building basinward [a.k.a. progradation])

39. Graded Bedding = Vertical Decrease of Sediment Size Turbidite = RESPONSE Turbidity Current = PROCESS