SEDIMENTARY ROCK

Earth Science

Chapter 2.3

Objectives:

1. Describe the origin of sedimentary rock.

2. Describe the three main categories of sedimentary rock.

3. Describe three types of sedimentary structure.

Origins of Sedimentary Rock Wind, water, ice, sunlight, and gravity all

cause rock to physically weather into fragments

Through erosion, these rock and mineral fragments, called sediment, are moved from one place to another.

The sediment is deposited in layers, and eventually newer layers cover the older layers.

The most noticeable feature of sedimentary rock is its layers, or strata.

A single, horizontal layer of rock is sometimes visible for many miles.

Composition of Sedimentary rock Sedimentary rock is classified by the way it

forms.

1. Clastic sedimentary rock made of fragments of rocks cemented together

by a mineral such as calcite or quartz. can have coarse-grained, medium-grained, or

fine-grained textures.

Course – grained Fine – grained

ConglomerateSandstone

Shale

Siltstone

2. Chemical sedimentary rock forms from solutions of dissolved mineral and water.

As rainwater slowly makes its way to the ocean, it dissolves some of the rock material it passes through

Some of this dissolved material eventually crystallized and forms the mineral that make up chemical sedimentary rock.

Halite

3. Organic sedimentary rock made up of the skeletons and shells of sea

animals○ These remains collect on the ocean floor and

eventually become cemented together Coal is a type of organic sedimentary rock that is

formed when decomposed plant material is buried beneath sediment and is changed by increasing heat and pressure.

Chalk Coal

Sedimentary Rock Structures

Many features indicate the way sedimentary rock is formedMost important feature is stratification

○ the process in which sedimentary rocks are arranged in layersStrata differ from one another depending on

○ Kind○ Size○ Color

Ripple marksFeatures in which sedimentary rocks sometimes

record the motion of wind and water waves on lakes, oceans, rivers, and sand dunes

Mud cracksStructures that form when fine-grained sediments

at the bottom of a shallow body of water are exposed to the air and dry out.

Even raindrop impressions can be preserved in fine-grained sediments, as small pits with raised rims.