Sec 3.3 SEDIMENTARY ROCKS

Sediment and sedimentary rock cover about 70% of the earth solid surface (including the ocean floor).

Sedimentary rock layers contain fossils, which are important to studying the past in Geology

Major energy sources such as coal, oil, natural gas, and uranium are derived from sedimentary rocks

Sedimentary rocks are the primary reservoir for ground water

WHY ARE SEDIMENTARY ROCKS IMPORTANT?

1. Weathering – involves the physical disintegration (by wind, water, or organisms) and chemical decomposition of preexisting rock of all types. Solid particles and ions in water are formed

2. Erosion - the incorporation and transportation of sediment by natural forces Dissolved ions carried away by water Solid particles moved by gravity to water sources that carry them away

FORMATION OF SEDIMENTARY ROCK

Deposition – the process of erosion loses energy and sediment begins to accumulate in one place As deposition continues over time, older sediments are buried

and converted to sedimentary rock by compaction and cementation. Lithification - the process by which sediments are transformed

into solid sedimentary rocks Lithos = stone, fic = making

FORMATION OF SEDIMENTARY ROCK

Compaction

Process by which sediments are squeezed together by the weight of overlying rock Sediment grains are pressed

closer together Much of the water is driven out

of the sediments

Cementation

Solidification of sediments by the deposition of dissolved minerals in the tiny spaces between sediment particles. Groundwater carries ions and

minerals into spaces between particles

FORMATION OF SEDIMENTARY ROCK

Clastic Sedimentary Rocks – sedimentary rock made up of weathered bits of rocks and minerals Clastic = Greek for “broken”

Particle size is the primary basis

for distinguishing among various clastic sedimentary rocks Common clastic SR: sandstone,

breccia, shale

CLASSIFICATION OF SEDIMENTARY ROCK

Sorting

Degree of similarity in particle size

Particle Shape

Shape is described in terms of the angularity and sphericity of particles

CLASSIFICATION OF SEDIMENTARY ROCK

Chemical Sedimentary Rock – rock that forms when dissolved ion/minerals precipitate (come out of the water and form a solid). Ions/minerals precipitate when water evaporates or a chemical

reaction occurs Made up of crystals like igneous rock, but easy to distinguish

because they have a different chemical composition. Common chemical SR: limestone, chert, rock salt and gypsum.

CLASSIFICATION OF SEDIMENTARY ROCK

Made up of organic material such as plants, leaves, bark, wood, or fossils.

Coal is a very common and important organic sedimentary rock.

How is coal formed?

ORGANIC SEDIMENTARY ROCK