Sediment Sediment Sediment Sediment 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: Weathering – breaking down of rock material by physical or chemical means 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

- Results in de-watering 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 - NaCl

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 CaSO4

Dolostone – made of dolomite

Made of SiO2 – “diatomaceous ooze” *Not in ESRT* Made of SiO2 – “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 It has fossils (organic remains) 2. It has pebbles 3. It has clasts 4. It is layered