Sediment Sedimentary rock Notes 11 Sedimentary Rocks Form

Sediment Sedimentary rock Notes #11

Sedimentary Rocks • Form when sediments (bits and pieces of any other rocks) are compacted and cemented together. **Normally layered**

Sediment • The following processes are necessary for the formation of sediment: 1. Weathering – breaking down of rock material by physical or chemical means 2. Erosion - The transportation of weathered sediment by water, wind, ice, gravity, etc. ** Mountains that have been uplifted are typically the source of weathered and eroded sediments**

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The following processes are necessary for the formation of sedimentary rock: 3. Deposition – dropping off of sediment - Usually occurs in a body of water (oceans). - This happens when the agent of erosion slows down or stops - Burial of each layer beneath

4. Compaction – Squeezing of sediment by the weight of overlying sediment - Results in de-watering 5. Cementation - gluing together of sediment by minerals - Quartz or calcite is dissolved in water, when the water leaves the sediment, the minerals remain gluing the sediment together. ***This process by which sediments get compacted into rock is called lithification.

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Two main classes of sedimentary rocks clastic and chemical • Clastic rocks are made up of pieces of other rocks. • Chemical rocks are made from evaporation of water and/or chemical precipitation

Clastic Rocks • Made of pieces from less than 0. 0004 cm to 1 m or more in size. • Classified based on particle size – Clay, silt, sand, pebbles, cobbles, boulders • Composition does not matter • Made of mostly quartz, feldspar, and clay minerals due to their resistance to weathering

Conglomerate - pebbles

Breccia – angular pebbles

Sandstone – notice the layers

Siltstone – a little finer grained

Shale – usually dark grey or black

Grand Canyon of Arizona

Notice: layers and sediments

Chemical Rocks • May have crystalline texture • Classification based solely on composition - monomineralic • Grain size does not matter • Dissolved minerals precipitate out of salt water solution (ocean water is salty) and are called “evaporites”

Evaporites • Steps for evaporite formation 1. Minerals dissolve in water (weathering) 2. Water evaporates (deposition) 3. Dissolved minerals precipitate out leaving salt minerals behind. (cementation) • Precipitation is the opposite of dissolution

Halite – rock salt - Na. Cl

The Dead Sea in Jordan • 8. 6 X saltier than the ocean • Water is saturated so salt precipitates on everything

The water in the Dead Sea is so dense with salt, that you float much higher than in a lake or the ocean.

• The Great Salt Lake in Utah (ancient lake Bonneville) is another example

Rock Gypsum – Made of gypsum Ca. SO 4

Dolostone – made of dolomite

*Not in ESRT* Made of Si. O 2 – “diatomaceous ooze”

Limestone – crystalline, made of calcite

There is a third sub category called Bioclastic meaning life-pieces • Made mostly of fossils, shells, or organic material Fossiliferous limestone

• Fossils are evidence of past life. Only found in sedimentary rocks • May be shells, teeth, claws, bones, etc. • Typically hard parts

Coquina – broken pieces of shells

Bituminous Coal – fossilized plant remains

Horizontal sorting during deposition • As streams enter a body of water they slow down and drop off their sediment load. • The larger particles fall first and the smaller particles may travel farther into the ocean. Conglomerates and breccias siltstone

Sedimentary Structures • STRATIFICATION - sediment layers are stacked on top of each other. The Grand Canyon in AZ is a perfect example.

Sedimentary Structures • CROSS-BEDDING - It reflects the transport of gravel and sand by changing currents

Sedimentary Structures • RIPPLE MARKS - are produced by flowing water or wave action

Sedimentary Structures • MUD CRACKS - form when a water rich mud dries out

I know it is a sedimentary rock because 1. It has fossils (organic remains) 2. It has pebbles 3. It has clasts 4. It is layered