CHAPTER 6-3 SEDIMENTARY ROCKS

What is sediment? Loose fragments of rock, minerals, and organic material that result from natural processes (including the breakdown of rock)

Characteristics of sedimentary rocks are determined by: The source of the sediment The way the sediment was moved The conditions under which the sediment was deposited

Processes Compaction- the process in which sediment is squeezed and the size of the pore space between the sediment particles (porosity) is decreased by the weight and pressure of overlying layers Cementation- the process in which sediments are glued together by minerals that are deposited in water.

Chemical Sedimentary Rocks Minerals made up of ions such as Ca, K, and Cl can dissolve in water. This type of rock forms when dissolved minerals precipitate out of water Minerals precipitate due to evaporation (when water evaporates, the minerals that were dissolved in the water are left behind increasing the concentration of the minerals) The minerals left behind form rocks called EVAPORITES. Examples are halite (or rock salt) and gypsum.

Organic Sedimentary Rock Rock that forms from the remains of living things Examples are coal, coquina and fossiliferous limestone INTERESTING NOTE: Chalk is made up of the shells of tiny one celled marine organisms that settle to the ocean floor.

Clastic Sedimentary Rock Made up of fragments of rock that are carried away from their source by water, wind, or ice Over time these fragments become cemented or compacted into solid rock They are classified by the size of their sediments

Clastic continued Conglomerate- rock composed of round fragments from 2 mm to boulders in size Breccia- rock composed of sharp angular fragments Sandstone- rock composed of sand grain size sediment cemented together Shale- rock composed of clay sized particles cemented and compacted together.

Sediments are transported by: Water Wind Ice Effects of gravity

Sorting The tendency for currents of air or water to separate sediments according to size Well sorted- all grains are roughly the same size and shape Poorly sorted- consists of grains that are many different sizes.

Angularity As sediment is transported from its source to where it is deposited, it collides with other sediments and other objects. These collisions cause the sediment to change size and shape. When particles first break they are angular and uneven….. As they travel farther from source they become rounded and smooth. The farther it travels the finer the sediment becomes.

Examples are rivers, deltas, beaches, and oceans The place in which setting is deposited is called the DEPOSITIONAL ENVIRONMENT Examples are rivers, deltas, beaches, and oceans

Characteristics of CLASTIC sediments Stratification- layering of sedimentary rock This occurs when the conditions of sediment deposition change Beds- stratified layers Massive beds- beds that have no internal structures Cross-beds- sedimentary rock characterized by slanting layers Graded bedding- when various sizes and shapes of sediment settle to different layers. (largest on bottom; smallest grain on top) Reverse grading- smallest grains on bottom; largest on top.

RIPPLE MARKS Caused by the action of wind or water on sand. Shows that the sediment was once part of a beach or river bed.

Mud Cracks Form when muddy deposits dry and shrink

FOSSILS The remains or traces of plants and animals may be preserved in sedimentary rock

CONCRETIONS Lumps of rocks on sedimentary rocks that have a composition different than that of the main rock body.

GEODES Groundwater sometimes deposits dissolved minerals inside cavities of sedimentary rock where they crystallize.