1	Sediments, Sedimentary Processes, and Sedimentary Rocks
2	Definitions to get straight…
3	Sediment Classification Sediment is classified by SIZE: Boulder >256mm Cobble 64 mm to ~256mm Pebble 2 mm to ~64 mm Sand 1/16th to ~2mm Silt 1/256th to 1/16th mm Clay, Dust less than 1/256th mm Biological particles- any size
4	Soils-how do they fit in? Soil: loose, unconsolidated material that is composed of bedrock fragments, clay minerals and organic matter Soil Horizons-layers that appear in soils as they mature
5	Sedimentary Processes
6	Rocks are Weathered Physical Weathering Agents: frost-wedging, abrasion, release of confining pressure, thermal expansion/contraction, plants, burrowing animals, lichens Chemical Weathering Agents: Acid! Produced by hydrolysis, carbonation, oxidation, volcanic fumes Climate influences rate & extent!
7	Physical Weathering Frost-action: freezing water on rocks expands and pries rock apart, called frost wedging Pressure release: removal of large rock and pressure can cause rock to crack as it expands After pressure is released, rock expands and may flake off rock layers, called exfoliation Expansion/contraction through extreme temperature changes from the sun or forest fires Plants: roots growing in cracks of rocks Lichens: organisms that grow on basalt-cause weathering
8	Chemical Weathering Hydrolysis: when water molecules break the bonds between mineral’s atomic structures Carbonation: carbon dioxide in the atmosphere or soil combines with water to form acid Oxidation: iron and oxygen. Iron rich, or mafic minerals weather fastest (such as olivine, pyroxene and amphibole) Volcanic fumes: sulfuric acid and hydrofluoric acid dissolves rock
9	Factors Controlling Weathering Mineral solubility Calcite weathers easily Quartz weathers slowly Rainfall Heavy rainfall = faster weathering rate Temperature Hot temperatures = faster weathering rate Vegetation, plants, animals Lush vegetation and life = faster weathering rate Soil cover Thick soil cover = faster weathering rate Time The longer a rock is exposed, the more weathered it becomes
10	Rocks are Eroded Process of stripping sediments off of parent rock, following weathering Agents: wind, water Erosion sculpted Columbia Plateau landscape
11	Sediments are Transported Agents: wind, water, glaciers Sorting occurs during transportation By size, weight & sometimes shape Angular vs. Rounded Well vs. Poor Further sediment is transported, more rounded & sorted grains become
12	Sediment is buried then Lithified Lithification-process of hardening & preserving sediment, by: Cementation- grains bound together with mineral cement Compaction-Compression due to weight of overlying sediment
13	Sedimentary Rocks 3 General Categories Detrital or Clastic- sediments of any size (from weathering and erosion), cemented together Shale Siltstone Sandstone Breccia conglomerate
14	Sedimentary Rocks Chemical- precipitate from solution Evaporites: rocks formed when crystals precipitate due to evaporation Rock salt Micrite oolitic limestone dolomite
15	Sedimentary Rocks Organic- derived from pieces of living organisms Fossiliferous limestone Coquina chalk
16	Sedimentary Rocks in the Field Bedding- horizontal layering of rock Formation- distinctive, continuous body of rock Group- 2 or more Formations
17	Sedimentary Bedding Structures- preserve conditions present as sediment was being deposited 2. Mud cracks Indicate drying on surface
18	Sedimentary Bedding Structures Graded Bedding- Each layer displays gradual change in grain size, from coarse (bottom) to fine (top) indicates changing energy of water
19	Fossils Fossil- Any remains, trace or imprint of a plant or animal preserved in rock Dinosaur, coal, oil, natural gas Primarily in sedimentary rock, rarely in metamorphic rock, never igneous rock Fossilization- process involving rapid burial of animals with hard parts, and lithification Fossils help geologists reconstruct environment of deposition!
20	Depositional Environments Deposition: when the transported sediment comes to rest Followed by accumulation of the chemical or organic sediments Environment of deposition: geographic location that deposition occurs Deep-sea floor, desert valley, river channel, coral reef, lake bottom, beach, sand dune, etc. Each environment has different physical, chemical and biological conditions Results in different types and arrangements of sediments
21	Depositional Environments-Continental Continental depositional environments Strongly influenced by climate Rivers and flood plains Coarse material in the channel Fine-grained material in flood plains Example: conglomerates and sandstones
22	Depositional Environments-Continental Lakes Dominantly fine grained material settles out Example: shale Beaches and deltas may also be present
23	Depositional Environments-Continental Glacial Poorly sorted mixtures of clay to boulder size material
24	Depositional Environments-Continental Alluvial fans Deposited where steep mountain stream meet valley floor Examples: sandstones and conglomerates (with cross-bedding)
25	Depositional Environments-Continental Eolian (wind-deposited) Sand dunes and dune fields
26	Depositional Environment-Transitional Transitional Environment: Transition between continental and marine environments Delta Where the river enters ocean or lake Velocity drops sharply Examples: siltstone and shale
27	Depositional Environment-Transitional Beach, coastal dunes and barrier islands Wind, waves, and currents control formation Dominantly well-sorted quartz sand
28	Depositional Environment-Transitional Lagoons Quiet areas behind barrier islands and reefs Fine-grained sediments Examples: dark shale, coarse sand containing marine organisms, limestones
29	Depositional Environment-Marine Shallow marine shelves Receive lots of sediment from adjacent continental areas Marine evaporites form where shallow sea becomes isolated and dries up Examples: sandstone, siltstone, shale Reefs Form where water is warm and land-derived sediment is scarce Examples: limestone (often containing fossil fragments)
30	Depositional Environment-Marine Deep sea environments Most receives fine particles settling out Deep sea areas offshore from rivers/deltas often receive large quantities of continental material Examples: shale and graywacke sandstones
31	Depositional Environments