Sedimentation and Sedimentary Rocks

1. Sedimentation and Sedimentary Rocks GLY 2010 - Summer 2014 - Lecture 10

2. Sediment • Unconsolidated material that accumulates at the earth’s surface • Minerals and organic remains of plants and animals are the major components of soil

3. Sedimentary Rock • As sediment accumulates, pressure, and often temperature, increases • Changes occur which convert the sediment from unconsolidated form to a consolidated form, sedimentary rock • Sedimentary rock makes up 5% of the crust of the earth, but accounts for 75% of the rock exposed at the surface

4. Importance of Sedimentary Rock • Provide clues to the earth’s past – examples: • Including erosion of mountain ranges • Transgressions of the sea over the land

5. Fossils • Often contain fossils, which provide clues to: • Types of life living in the past • The environment they lived in

6. Types of Sediment • Detrital • Chemical • Biogenic

7. Sediment Transport • Water, glaciers, or wind moves the sediment from high elevations to lower elevations, where it may accumulate • Annual transport of detrital sediments to the oceans is about 10 billion tons • During transportation, sediment size is often reduced

8. Transport of Sediment By rivers By glaciers

9. Formation of Detrital Rock • Deposition • Sorting • Shape

10. Clastic Rock and Matrix

11. Lithification • Literally means creation of stone • Involves three possible processes • Compaction • Cementation • Recrystallization

12. Compaction • Fragments will be compacted by the weight of accumulating sediment • Air and water are expelled from spaces between grains

13. Cementation • Dissolved substances in water may precipitate solids which act as cements

14. Recrystallization • Unstable minerals may reorganize due to heat, pressure, and fluid interaction into more stable minerals • Process must occur at low temperatures • Ex: Aragonite  Calcite

15. Sedimentary Structures • Bedding - sediments are ordinarily deposited in horizontal units called beds • Graded bedding • Cross-bedding

16. Graded Bedding

17. Graded Bedding Animation

18. Cross Bedding Animation

19. Cross-bedding, Zion National Park Photos: Duncan Heron

20. Principle of Original Horizontality • Most sediments settle through bodies of water • They will be deposited in horizontal, or very nearly horizontal, layers • Beds which are not horizontal have often had their position changed by post-depositional processes

21. Right Side Up • Beds may occasionally be completely overturned, so we need ways to tell if beds are right side up • Selected indicators: • Ripple Marks • Mudcracks • Raindrop impressions • Salt crystals

22. Aeolian Ripple Marks • Aeolian (wind) ripples at White Sands, New Mexico (Photo Yamato Sato)

23. Fossilized Ripple Marks • Parallel ripple marks preserved on a slab of sandstone • The rocks contain the fossilized remains of marine animals - these ripples were formed in shallow sea water by gentle currents • Fossilized ripple marks. Capitol Reef National Park, Utah

24. Mudcracks

25. Mudcracks Mudcracks form by desiccation of mud or clay

26. Raindrop Impressions

27. Salt Crystals • If the deposition occurs in the ocean, and the water is quite saline, salt crystals may precipitate and settle on the sediment

28. Size Range of Detrital Particles • Clay < 0.004 millimeters • Silt 0.004 to 0.063 millimeters • Sand 0.063 to 2 millimeters • Granule 2 to 4 millimeters • Pebble 4 to 64 millimeters • Cobble 64 to 256 millimeters • Boulder >256 millimeters

29. Sediment Types • Mud is composed of clay or silt • Sand is composed exclusively of sand sized particles • Gravel includes granules, pebbles, cobbles, and boulders

30. Detrital Rock Types

31. Shale

32. Siltstone

33. Sandstone with Silica Cement

34. Sandstone with Hematite Cement

35. Conglomerate

36. Quartz Pebble Conglomerate

37. Breccia

38. Formation of Chemical Sedimentary Rocks • Precipitation is the process of converting materials dissolved in a fluid (water or air) to another form • Water dissolved in the atmosphere may precipitate as rain, or as some solid form such as snow, sleet, hail, etc • Solids dissolved in water precipitate as solids

39. Saturated Solution • In order for precipitation to occur, the fluid must be saturated • A saturated solution holds as much as it can of a particular substance • A fluid may be saturated with respect to one substance (e.g. lime) and undersaturated with respect to another substance (e.g. halite)

40. Chemical Precipitation • Solutions which are saturated, or slightly supersaturated, may spontaneously form crystals, which settle in the solution

41. Biochemical Precipitation • Some organisms have the ability to concentrate an unsaturated solution internally to the point where precipitation occurs This fossiliferous limestone contains carbonate shells, produced by biochemical precipitation

42. Evaporites • When saline solutions (sea-water) evaporate, a series of substances precipitate in a definite sequence, from the least to the most soluble • Sequence is: • Lime – a carbonate • Gypsum, a sulfate, precipitates second • Halite, common table salt, is next • Potassium and magnesium salts are last

43. Bonneville Salt Flats

44. Layered Gypsum

45. Evaporite Nodules

46. Chemical Sedimentary Rocks • Limestone is composed of calcium carbonate, CaCO3 • Dolostone is composed of dolomite, CaMg(CO3)2

47. Oolitic Limestone • In warm, saturated, and highly energetic environments, lime may precipitate around tiny bits of suspended matter • They stick together to form an oolitic limestone, such as the Miami oolite formation

48. Oolitic Limestone

49. Biochemical Sedimentary Rock • Coral reefs • Coquina

50. Ancient Marine Reef • El Capitan reef, Guadalupe Mountains National Park, formed as part of a very large reef complex during the Permian period