Sedimentary Rocks

1. Sedimentary Rocks

2. Sedimentary Petrology- What is it? • A) Study origin, occurrence, mineral comp. & texture of sed rks. • B) Not dep. environ. nor interp. of sedimentary structure • C) Emphasize sed rocks & classification

3. Why study sedimentary rocks/sediments? Sedimentary rocks make up only 7.9% of the Earth’s crust. rcheel@brocku.ca

4. 66% of the surface of the Earth is covered by sediment or sedimentary rocks. • Humans interact with the Earth largely at or near its surface. rcheel@brocku.ca

5. Grow food on it. Build structures on it. Take resources from it. They….. rcheel@brocku.ca

6. At the same time they….. Hide garbage and other waste material in it. Modify its physical and chemical properties so that it is no longer useable by them. It is important to understand the various properties of the sedimentary cover and have systematic methods for describing these properties. rcheel@brocku.ca

7. More Reasons to Study Sed Rocks • Sedimentary rocks provide best evidence of earth history because: • Often contain fossils, properties to establish environments, and • Often provide geologic age of materials. • Record sedimentological, chemical, fossil; evidence of changing tectonics & paleoceanography • Economic significance Grand Canyon

8. Origin of Sed. Rks A. Weathering 1. Chemical 2. Mechanical 3. Weathering provides raw materials

9. Erosion Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, or movement in response to gravityhttp://www.wordiq.com/ 1. Wind 2. Water 3. Ice

10. Deposition 1. Beaches 2. Lakes 3. Slopes 4. Rivers

11. Cementation/Compaction 1. Sediment may be compacted 2. Cement precipitates in voids

12. Extent Of Sedimentary Rocks • A) Cover 66% cont. surface, much ocean floor • B) Ig & met rocks unstable at surface • Form under dif. TP regimes • Surface= LTLP regime • Form in less O2, CO2, H2O • C) Minerals break down • Form grains & clays • Break down due to weathering

13. Sedimentary RK Types & Lithologies • Clastic/Detrital • Formed of particles derived from pre-existing rks • Chemical precipitates • Precipitate from solution • 95%=S.S, L.S, Mudrock • Sandstone-20-25 % • Form in high energy environment • Some in low energy • Mud < .06mm; sand 2 - 0.06mm

15. Quartz Rich Sandstone

16. Quartz Rich Sandstone Microphotograph

17. Arkose

18. Conglomerate

19. Breccia

20. CO3 rocks • CO3 rocks =10-15% of sed rocks • CaCO3 (Arag/Calcite); CaMg (CO3)2 (Dolomite) • Also Siderite (FeCO3), Magnesite (MgCO3)-rare • Most-hard parts of org. • Deep H2O corrosive • Most CO3=shallow H2O • Transitional rocks • Coquina-SS or CO3 • Marl-CO3 & clay

21. Coquina

22. Mudrocks • Mudrocks 65% • Most abundant-65% of sedimentary rocks • Not well studied • Common due to Ig/met rocks • Composed of 20% qtz & 80% other silicates • Qtz stable others not • Detrital content • Qtz common • Minor felds • With little clay in sandstone • Found low energy environment • Mudstone mostly silt/clay

23. Halite

24. Cementation A. Rks get lithified B. Sed accumulation leads to compaction; porosity reduce C. Most common cements--SiO2, CaCO3, iron-oxide

25. Thickness of Sedimentary rocks • 1.8km-continent., 0.3km-oceanic • Difficult to measure-where does meta begin • 20,000m in some basins

26. Depositional setting-sedimentary basins • Oceanic basins • Garben along cont. margins • Arc-trench systems • Suture belt basins • Intracratonic basin

27. Oceanic Basins • Depo on bathy. highs • Depo on flanks • >4000m-generally no CO3 seds. • Away from flanks -red clays, siliceous shells

28. Rifted Continental Margin • Form when cont. rifted-get extension • e.g S. America rifted from Africa • First get vol & non-marine seds. • Periodic flooding-get evapo. • Then shallow to deep rocks with more rifting

29. Arc Trench Systems- • Trench seds=Turbidites • Transport along axis • Forearc-overlie oceanic or transitional crust • Vol. sed & sed from pluton or uplifted trench/slope break • Great Valley=Forearc basin • Forearc=shelf, deltaic, terrestrial • Intrarc • Turbidites & vol. material from Arc • Retroarc basin=backarc basin

30. Suture belt basin • Form where have cont-cont. collision • Basins form in suture zone • Seds=clastic from erosion of continent.

31. Intracratonic Basins • Origin not well understood • Downbowing next to cont. margin • Aborted cont. rifting • Local cooling of asthenosphere • Get cratonic seds. • Mostly non-marine & shallow marine seds.-well rounded

32. Stop Here

33. III) Clastic/Detrital Components A Clays--sheet-like silicates B Quartz C Feldspars--unstable--fast erosion and deposition D Micas--unstable--fast erosion and deposition

34. IV) Size Distribution A. Know scale B. Provide info about depo. env. C. Greater energy to transport larger particles D. Clays accumulate in quiet water

35. V) Clastic Rk types A. Shale--clay and silt particles 1. Particles are microscopic 2. quiet water, non-turbulent deposition 3. Settle following flocculation 4. Form laminae/massive beds 5. Fissil=shale; non-fissil=mudstone 6. Generally recessive

36. B. Sandstone 1. Made of sand-sized grains 2. Deposited in a variety of environments 3. Sorted to poorly sorted 4. Wind deposits better sorted than water-tranported deposits?

37. B. Sandstone Continued 5. Shape of grains--rounded to angular, related to distance or time of transport 6. Sandstone types i. quartz arenite ii. arkose iii. graywacke iv. lithic sandstone 7. conglomerate/breccias i. good for provenance ii. not transported far

38. VI) Chemical Sed Rks A. Inorganic precipitates B. Biochemical Rks C. LS most abundant chemical sed rk 1. composed of calcite 2. mostly marine 3. Corals= warm water, shallow tropical environment; <30 lat

39. Other Chemical Sed Rks Continued D. Rk types 1. chalk 2. travertine 3. oolitic l.s E. Dolomite 1. calcium magnesium carbonate 2. Rks=dolostone

40. Chemical Sed Rks Continued F. Chert 1. composted of microcxline qtz 2. nodules and layers, biochemical rks G. Evaporites Halite, Gypsum