Sedimentary Rocks

Bits and Pieces

Sedimentary rocks form as sediment is:

Deposited

Buried

Compacted

Cemented

Sedimentary rocks fall into 3 groups:

Clastic/inorganicOrganicChemical

Physical Weathering

Clastic sediments are produced when rock physically weathers, which means it breaks apart.

Big rocks break into smaller rocks.

Weathering is an extremely slow process.

There are 6 sizes of clastic sediments. Boulders Cobbles Pebbles Sand Silt Clay

Particles are collected and transported by running water.

http://www.youtube.com/watch?v=fATA1SOLICo

Abrasion Sediments

become smoothed and rounded as they bounce along the bottom of the stream and hit against each other.

Deposition and Sorting

A stream loses velocity when entering quiet waters so its ability to transport sediment decreases. Particles drop to the bottom. This is deposition.

Large particles settle first. Other particles settle according to size. Smallest particles last. This is sorting.

Burial and Compaction

As more sediments accumulate, the bottom ones are buried.

This increased weight of the top sediments physically squeezes the lower sediments together which compacts them.

Heavy Weight

OUCH!

Cementation

All the waters of the Earth contain dissolved minerals. These dissolved minerals and sometimes clay fill up spaces between the rock fragments and bind them together. This is cementation.

Stratification

Sedimentary rocks often form in horizontal layers called strata.

Fossils

These layers or strata often contain fossils.

Only sedimentary rocks contain fossils.

Fossil Structures

Mud cracks and ripple marks give evidence of environment at formation.

Organic(Bioclastic)Sediments

The remains of plants and animals. The two most common are shells and plant material.

Chemical Sediments

Chemical sediments form when water evaporates and the materials dissolved in the water precipitate (settle).

Bonneville Salt Flats

Home of the land speed record.

Thrust SSC – 763 mph

http://www.youtube.com/watch?v=LKQ-xj5C2m8

Yucca Mountain

Nuclear waste depository

http://www.youtube.com/watch?v=tbq9a2oyMAo

http://www.youtube.com/watch?v=Q41vzLjwZqM

Characteristics of Sedimentary Rocks Sedimentary rocks are the most common

type of rocks on Earth’s surface. Sedimentary rocks usually form underwater. Sedimentary rocks may contain fossils. Sedimentary rocks often form in layers or

strata. Sedimentary rocks are our keys to the past.

Nature’s Palette

Antelope Canyon

Bryce Canyon

Mexican Hat

Clastic Sedimentary Rocks

Breccia – angular Conglomerate -

rounded

Clastic Sedimentary Rocks

Sandstone – can be various size grains.

Clastic Sedimentary Rocks

Siltstone

Clastic Sedimentary Rocks

Shale – breaks along bedded planes.

Bioclastic Sedimentary Rocks Bituminous coal – plant remains = carbon

Bioclastic Sedimentary Rocks Limestone – cemented

shell fragments or precipitates of biologic origin = calcite

Chemical Sedimentary Rocks Rock salt - Crystalline

texture composed of halite.

Chemical Sedimentary Rocks Dolostone –

Crystalline texture composed of dolomite.

Fossil

Chemical Sedimentary Rocks Rock Gypsum –

Crystalline texture composed of gypsum.