This document summarizes key concepts about sedimentary rocks: 1) Sedimentary rocks form from the compaction and cementation of sediments such as weathered rock fragments, mineral precipitates, and organic remains. 2) Sediments are deposited in layers from wind or water and then lithify to become sedimentary rocks, providing clues about past environments. 3) Sedimentary rocks are classified as either detrital rocks, which form from weathered materials, or chemical rocks, which form from inorganic or organic chemical precipitates.

1. CH. 3 – SEDIMENTARY RX

2. Sediment 1) weathering products (gravel, sand, clay minerals) 2) chemical precipitates 3) organic remains

3. Sedimentary Rocks “ sedimentum” = “settling” Sediment settles out of wind or water - forms layers at the surface

4. Importance of Sedimentary Rx 1) 75% of exposed rx at surface (outcrops) 2) Clues to past environments 3) Fossil record 4) Economic value

5. Sedimentary Rx Classification 1) Detrital = weathering products (mechanical or chemical) 2) Chemical

6. Detrital Sedimentary Rocks Named by particle size Particle Size Name Gravel, pebbles Conglomerate

7. Detrital Sedimentary Rocks Particle Size Name Sand Sandstone (quartz sand) Clay-size Shale (red, green, black)

8. Detrital Rock Process 1) Weathering 2) Erosion (transportation) 3) Deposition (sediment settles) 4) Lithification – turning sediment into rock (“lithos” = rock) (after sediment is buried)

9. Types of Lithification Processes a) Compaction - most effective on fine-grained rx (ex: shale) Exception : St. Peters Sandstone Starved Rock State Park, IL

10. b) Cementation Minerals dissolved in groundwater precipitate around sediment Ex: silica, calcite, hematite Lithification Processes

11. Sedimentary Rx Classification 2) Chemical Named based on composition Ex: calcite = limestone halite = rock salt plant remains = coal

12. Chemical Sedimentary Rocks a) Inorganic – formed by chemical reactions in environment Ex: Evaporites - rock gypsum, (Fig. 3.23) rock salt Ex: Travertine (limestone)

13. Chemical Sedimentary Rx b) Organic (“biochemical”) Plant remains = coal Microscopic sea shells = chalk Broken sea shells = ___________

14. Detective Analogy Geologists are solving a mystery Scene of Clues Mystery the Crime Solved

15. Mystery Solved (Sed. Rx) Depositional environment - any area on surface where sediment accumulates Ex:

16. Principle of Uniformitarianism “ Present is the key to the past” Study modern depositional environments for clues Ex: Coquina limestone

17. Clues 1) Sediment size Distance deposited from source area Large = (closer to, further from) Small = (closer to, further from)

18. Clues (sediment size) High vs. low energy environment Large particles = (high, low) Ex: ___________ Small particles = (high, low) Ex: ___________

19. Clues 2) Sediment shape Distance deposited from source area: close to or far from? angular = ______ rounded = ______

20. Breccia

21. Clues 3) Sedimentary Structures - features produced in sediment BEFORE lithification Ex: mudcracks, ripple marks, trace fossils

22. Mudcracks Environmental conditions: a) b) Ex: river floodplain

23. Ripple Marks Indicates current direction in shallow water

24. Trace Fossils Evidence an organism was in the environment but no physical remains of the organism exist Ex: footprints, coprolites

25. Clues 4) Fossils – evidence of prehistoric life Fossil record is incomplete - shows remarkable pattern of change from simple to complex life forms

26. Steps to becoming a fossil Step 1: Death Step 2: Hard parts – bones, teeth, shells (Who you are!) Step 3: Rapid burial (Where you die!) Step 4: Time (prehistoric)

27. Fossils Fossil record biased towards marine environment - abundant life in oceans - many critters have hard parts - lots of sediment for quick burial

28. Fossils Good evidence for reconstructing past environments Ex: Deep marine shale vs. muddy river shale