1. Sedimentary Rocks John Day Fossil Beds Natl. Mon.,Oregon

2. Sedimentary rocks  composed of sediment (particles derived by weathering)

3. Detrital sediments  particles derived by physical weathering Non-detrital sediments  minerals precipitated from solution by inorganic chem. processes or activities of organisms Classification of Sedimentary Particles SizeSediment Name >2 mmgravel 1/16-2 mmsand 1/256-1/16 mmsilt <1/256 mmclay

4. Why Should You Study Sedimentary Rocks? Sediments are the most common Earth materials. Rock Features record environmental conditions at the time sediment was deposited. (impt. in deciphering Earth history) Fossils  knowledge of pre-existent life preserved in sedimentary rocks Some sed. rocks contain resources (i.e. water, petroleum, natural gas, etc.).

5. Transport & Deposition Ice -- carries particles of any size. Wind -- transports sand & smaller particles. Water (most prolific agent) Larger particles require more vigorous current for transport. Depositional environment  geographic area where sediment accumulates

6. Rounding -- abrasion during transport reduces particle size & smoothes sharp corners Sorting -- variety of particle sizes present in sediment or sed. rock (influenced by transport & depositional processes) well-rounded, poor-sorted gravelangular, poor-sorted gravel

7. Processes (Physical, chemical, & biological) operating in the depositional environment impart distinctive charac. to accumulating sediment.

8. How Are Sediments Transformed into Sedimentary Rocks? Compaction –due to weight of overlying sediment –particles pack more closely & pore space is reduced –deposit’s volume reduced Cementation –binds one particle to another by chemical precipitation of minerals in sediment pore space. –{Common cements include quartz, calcite, & hematite.} Lithification –involves compaction & cementation –converts sediments to sedimentary rocks

9. Classification of Detrital Sed. Rocks Based on: Sediment Size Composition Detrital sedimentary rocks comprised of solid particles derived from parent material by phys. weathering

10. Conglomerate = rounded gravel (>2 mm) Breccia = angular gravel B A

11. Sandstone = sand-size (1/16 - 2 mm) particles classified by mineralogy Quartz sandstone  most common Arkose sandstone  25% feldspar

12. Mudrock  any combination of silt & clay Siltstone  silt (1/16 – 1 / 256 mm) Claystone  clay (< 1 / 256 mm) Shale is fissile clay. (splits along many closely spaced planes) Mudrocks = most common sed. rock (quiet-water environ) shale

13. Chemical sedimentary rocks  ions taken into soln by weathering of parent material **crystalline texture (interlocking mineral grains) Biochemical sedimentary rocks  Organisms aid in the precipitation of minerals. Classification of Chemical Sed. Rocks Based on: Mineral composition Texture

14. Evaporites  formed by precipitation of minerals from evaporating water \ Rock salt { halite (NaCl) } (A) & Rock gypsum {gypsum (CaSO 4. 2H 2 O)} (B) are most common. A B

15. contains much pore space Limestones composed of Calcite (CaCO 3 ) Fossiliferous limestone Coquina skeletal fragments of marine invertebrates -- pores filled w/ cement & mud -- Clastic texture  shell fragments

16. Coal crystalline texture carbon (compressed, altered plant remains that occupied swamps & bogs) B Chert crystalline texture silica (layers of microscopic shells of marine organisms) A

17. Sedimentary Facies -- sets of sed. rock w/ distinct attributes imparted by their depositional environment Coastal areas  facies accumulate simultaneously on various areas of seafloor (w/ unique charac.). Strata (beds)  layers differ in color, texture, & comp. from rock layers above & below.

18. Regression (seaward shift in the shoreline) Drop in sea level Nearshore deposits overlie offshore deposits. 1 2 3

19. Transgression (landward shift in shoreline) Rise in sea level Nearshore seds overlie old land surfaces, & offshore seds are stacked on top.

20. Grand Canyon Muav Limestone (offshore) Bright Angel Shale Tapeats Sandstone (onshore) (deposition record of laterally adjacent environ.) Transgression  Sed structures, fossils & ripple marks Determining the Depositional Environment

21. Cross bedding Graded bedding Oscillation ripple marks Current ripple marks Mudcracks - formed by physical processes at the time of deposition Sedimentary Structures

22. Cross bedding  inclined layers w/in a bed  Formed by wind or water  slopes downward in flow direction

23. Graded bedding  upward decrease in grain size w/in a bed {deposits of turbidity currents}

24. Ripple marks -- small ridges separated by intervening troughs Oscillation ripple marks (A) symmetric cross- sections generated by the back-&-forth motion of waves. A B Current ripple marks (B) asymmetric cross- sections record flow in one direction (i.e., streams).

25. Mudcracks  shrinkage (polygonal patterns of intersecting fractures) clay-rich sediment depositional environ.  periodic drying (i.e., a river floodplain, lake shore, or tidal flat)

26. Morphology of organisms reveals info about environment the organisms lived in. 1.Heavy-shelled clams = shallow-water, turbulent 2.Thin, fragile-shelled clams = low-energy 3.Filter-feeding organisms (corals) = clear seawater (suspended sediment clogs their feeding organs.) Fossils are NOT Sedimentary Structures.  remains or traces of ancient organisms

27. Resources in Sedimentary Rocks? Sand & gravel  building & road construction Limestone  cement Gypsum  wallboard/plaster Phosphate-bearing sedimentary rock  fertilizer Sand-sized quartz  glass Carnotite (uranium mineral)  fuels nuclear reactors [assoc w/ plant remains in sandstones formed in ancient stream channels] Hematite & magnetite (banded iron formations)  iron ores