Sedimentary Rocks

1. Sedimentary Rocks

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 Size Sediment Name >2 mm gravel 1/16-2 mm sand 1/256-1/16 mm silt <1/256 mm clay

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)

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

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

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)

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 (CaSO4 . 2H2O)} (B) are most common.

15. contains much pore space

16. Coal crystalline texture carbon (compressed, altered plant remains that occupied swamps & bogs)

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.).

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

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

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.

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. Heavy-shelled clams = shallow-water, turbulent Thin, fragile-shelled clams = low-energy Filter-feeding organisms (corals) = clear seawater (suspended sediment clogs their feeding organs.)

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