Earth Materials

Sedimentary Rocks

• I. Sedimentary rocks are formed from pieces of other rock; from organic material; or from chemicals out of solution.

• a. Sediments: loose particle from the weathering (breakdown) of pre-existing rocks or organic materials.

• ex. Shells, sand, pebbles, mud

• II. There are 2 main groups of sedimentary rocks:

Clastic rocks (from fragments of rock)

and Non-clastic rocks (from chemical or organic processes)

• 1. Clastic sedimentary rocks.

• a. Classified by size of particles. (clay, silt, sand, etc)

• b. rocks are named according the particle size, and not by the composition.

• c. Clastics have cement to hold the particles together. (such as calcite, iron oxide and silica )

The cement is the youngest part of the rock. The sediments can be a huge assortment of ages.

• d. Lithification is the process of becoming sedimentary rock (loose sediments becoming rock), which involves: – compaction due to pressure or weight of

overlying sediments (clay becomes shale), or

– Cementation by precipitation of minerals in pore spaces from waters carrying ions in solution (siltstone, sandstone, conglomerate)

e. The size of the sediments indicate the environment of formation

• 2. Non-clastic: (chemical/biochemical)

a. Chemical rocks: precipitation of minerals from water in lakes, in the sea, in caves, and in hot springs.

– Evaporites form from the evaporation of water (usually seawater). Rock salt , and

– Precipitates when ions come out of solution in water: ex. limestones

• b. Organic rocks, usually coal (from plants) and various limestones with shell fragments.

• ex. Coquina (fossil shells cemented together;) and Chalk (made of microscopic planktonic organisms; fizzes readily in acid)

• c. Limestones can be chemical, bioclastic or a combination of both.

• II. Sedimentary rocks form a thin veneer on top of the non-sedimentary continental crust,

• 1.Weathering creates sediments that build up.

2. MOST sedimentary rocks form in quiet water, because the particles are carried by rivers and deposit in slow areas of the river, in lakes, deltas and in the ocean.

3. Stratification is the creation of layers.

– occurs because new sediments are deposited on top of older ones in horizontal layers.

4. Fossils are almost only found in sedimentary rock Metamorphism and melting destroy the imprint, bone, and trace fossils.

• New York has different types of salt and gypsum deposits. How did they get here?