Essay Geology: Sedimentary Rock

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Bedding – formation of parallel layers by particles setting on sea, river, or a land surface

Strata= series of beds
Formation – series of unique strata ~ recognized on reg scale
• Fundemental geologic mapping unit

Sed rocks cover land surface & sea floor
• Found at Earth’s surface
• Thin layer ATOP igneous and metamorphic rock in crust

Occur in upper crust = surface veneer/cover
Igneous rocks = basement of crust

Cover = nonexistent to 20 km thick
Sed rocks = > 80% of E’s surface, < 1% of mass

Supai Group/Hermit Shale/Coconine Sandstone/Toroweap Formation/Kaibad Limestone

Sed rocks = bulk of energy resources
• Coal, petroleum, natural gas, & groundwater

Weathering – break up and corrode solid rocks → Sediment
• Weathering → Dissolved ions

Solids picked up by wind then buried in soil
Dissolved ions carried by streams or groundwater or new minerals in spaces between underground grains

Sed Environments Factors:
1. Geographic location and plate tectonic setting
2. Transport Agent and medium
• Waves, lakes, rivers, ocean currents, wind, ice, tide/tidal currents
3. Climate
4. Organic processes and organisms
Sediments: sand, gravel, dust, calcified orgs, saline precipitates

Tidal Flats Deep Sea Cont’l Shelf Reefs Cont’l Margin
Tidal currents Ocean/turbidity currents Waves & tides Waves & tides Ocean currents & waves
Sand & mud Mud & sand Sand & mud Calcified orgs Mud & sand
Arid – Humid
Org mix sediments Deposit of remains Deposit of remains Carbonate secretion by corals Remains deposits

Sediment: Loose/Unconsolidated
1. Rock frags/ grains of minerals broken down from rocks
2. Mineral crystals precipitate out of water
3. Shells when orgs extract ions out of water

Sedimentary rocks: formed at E’s surface by
• Cement loose rock frags or grains of minerals
• Cement shell frags
• Precipitation of minerals from water solutions

Lithification: transformation of loose sediment into solid rock
• Compaction: grains squeezed together by weight of overlying sediment into a mass denser than the original.
• Cementation: minerals precipitate around deposited particles and bind them together

Cemented and Compacted AFTER BURIAL under sediment layers

Sandstone: Lithification of sand
Limestone: Lithification of shells & Carbonate particles

Sed Rocks Classification
• CLASTIC/DETRITAL: Cemented together detritus, clastic = broken
• Chemical: Minerals that precipitate from water solutions
• Biochemical: Made up of shell of organisms
• Organic: Consist of carbon-rich relicts of plants

Clastic/Detrital Factors:
• Composition (mineral content)
• Grain size
• Grain shape
Coarse forms FIRST. Fine forms LAST.
Finest = Clay
Coarsest = Boulder, Cobble, Pebble

Very coarse: Breccia (angular frags) gravel. Conglomerate (rounded clasts) Gravel & Quartz sand grains.

Medium: Arkose (sand sized quartz & feldspar grains) = Orthoclase Feldspar Sandstone (almost pure quartz sand) Graywacke (mix of different clasts, lithic clasts)

Fine: Siltstone (fine sand) Very Fine: Shale (clay ~ splits into thin sheets) Mudstone (clay, doesn’t split into thin sheets)

Gravel-Sized: grains visible, larger than sand
• Conglomerate & Breccia

Sand-sized: Grains visible like a sandbox

Clay-sized: Grains not visible, smooth, dull luster on broke surface

Mud (Fine) + Pressure → Shale
Sand (Med) + Pressure → Sandstone
Gravel (Coarse) + Pressure → Conglomerate

Sorting: Presence of different sizes
Rounded Grains = Physically mature
Angular Grains = Physically immature
Clay Presence = Chemically mature
Feldspar Presence = Chemically immature
• Chemical Weathering Hyrdolysis: Feldspar → Clay

Least-Most Mature: Alluvial fan, River, Beach
Alluvian Fan + River: Lithic clasts, quartz feldspar, clay flakes
Beach: Quartz

Chemical Sed Rocks: formed by precipitation out of water solutions
• Without life
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