Science Discovery Series

Olympus High School

Jeff Taylor

Science Instructor

Get Your High School Diploma Online

Episode 1Sand Dunes and Sedimentary Rocks

How They Form

Paria Canyon, AZ

Sandstone• Sandstone are layers of sand-sized particles

that are cemented together.

• The cement determines the strength of the sandstone.

• Sandstone can form from sand dunes, river or lake bottoms, or former beaches.

Grand Staircase-Escalante NM, UT

Sand Dunes• Sand Dunes form where sand particles are blown in the

wind and then pile up in a place where the wind slows.

• Rain trickles down to the bottom of the dunes.• Minerals that dissolve in water cement the sand and

solidifies the base.

Great Sand Dunes NP, CO

Lithification

• These sand dunes have lithified when water seeped in and cemented the sand grains.

• Later, winds blew away the loose sand above.

Maui, HI

Sandstone

• Fossilized sand dunes can be determined by their cross-bedding.

• Cross-bedding are alternating layers that are tilted against each other.

Navajo Sandstone, Big Water, UT

Navajo Sandstone

They formed in an ancient Sahara-like Desert some 75 million years ago

The Dive, Grand Staircase-Escalante, UT

PlayasEvaporite Basins

• Salts dissolve from rocks into rainwater• Water gathers at the valley floor to form shallow lakes• Hot summer evaporate the water, leaving just a flat salt layer• This salt can be sodium chloride or a variety of alkaline

substances like gypsum, calcite, or soda.

Carrizo Plain NM, CA

Gypsum Dunes

• When evaporites from a dry lake are broken into small pieces and blown in the wind, they can pile up into dunes.

• At White Sands, NM the “sand” will dissolve in your mouth!

White Sands NM, NM

Lake or Ocean Sandstones

• Sandstone layers that are completely horizontal are usually formed at the bottom of lakes or the ocean.

Vermillion Cliffs Wilderness, UT

Lake and Ocean Settling

• When sediment flowing down a river meet a lake, they drop out and settle to the bottom to form a flat layer.

Lake Sediments• Here, changing lake levels leave horizontal

beds of sediments.

When buried, they will compact into stone.

River Deposited Sandstones

Ripple Marks

• Ripple marks are a sign on an ancient stream or lake shore

Conglomerates

• Conglomerates are a mixture of rock sizes that form in rivers.

• Large rocks are cemented together with sand, mud, and salts.

Conglomerates forming today• This stream bed is making a conglomerate

layer for future aliens to discover

Mudcracks and Silt Layers

Red Sandstones

• Stained by iron oxide (rust) minerals

Soft Sandstones

• Some sandstones are so weakly cemented, that they “melt” when it rains and fall apart in your hands.

Blue Sandstones Stained by Copper

Various Minerals in the Rock

Siltstones

• Siltstones are similar to sandstone, but the grains are much finer.

• They form at the bottom of the ocean and lakes where very small particles settle to the bottom.

Clays and Mudstones• In the ocean or lake bottoms where

microscopic particles settle, mud and clays cement together for form layered rock.

• Mudstones are strong and well cemented.• Clays tend to be weaker and easily crumble.

HoodoosConglomerate Capping Sandstone

Hoodoo’s form where strong rock protects weaker rock underneath

Volcanic Ash• Volcanic ash can settle onto the ground or into lakes to

form sediments.

Bentonite Clays• Bentonite clays form when volcanic ash

from eruptions lands in water.• This ash mixes with the mud and organic

matter for form a weak, puffy layer, that is extremely sticky when wet.

More Bentonite Clay

Evaporites• When lakes or shallow ocean areas

evaporate, they leave their salts behind.

• These salts form layers of crystals.

Tufa• When springs in a soda lake emerge, they

deposit their minerals in large pillars.

Evaporite Basin• Water drains down into the basin.• The water evaporates, leaving salts behind

Coal, Oil, and Natural Gas• When organic matter such as dead plants get

buried in mud it can be preserved as layers of coal.

• Oil and Natural gas pockets can also form under these layers, typically with the help of heat underground.

Petrified Wood and Fossils

• Hard organic remains such as tree trunks, bones, and teeth can be fossilized as their natural minerals get replaced by other minerals.

Fossils• The calcium and carbon of

Petrified wood and fossil bones are often replaced by quartz or magnesium.

Limestone

• When the shells of clams, snails, or coral reefs are preserved in the ocean sediments, limestone forms.

• Limestone is made of Calcium Carbonate.• Limestone is a sure sign that an area was

tropical once.

Travertine

• Limestone dissolves in water.• Where water trickles down into the layers,

it eats away at the rock forming caves and sinkholes.

• When the water drips in the caves and evaporates, it leaves the limestone behind again forming Stalactites.

Limestone Continued…

• Since limestone dissolves in water, it forms steep and interesting landscapes due to erosion.

More Limestone features

More Limestone Features

Limestone

• Since Limestone is weak, it was often carved into for ancient tombs

Glacial Till

• Glaciers carve and pulverize rock into silt.• This silt is transported by ice and melt

water to the edge of the glacier.• Here it forms layers that are easily broken.

Erosion

• Rivers and rain carve deep canyons into sedimentary rock.

Zion Canyon

• 2000 feet deep sand dunes cut by the river

Sandstone Canyons

Grand Canyon

• 5000 ft deep with alternating layers of limestone, sandstone, siltstones, and fossils going back over 1 billion years.

Slot Canyons• Occasional torrents of water from flash

floods can carve deep narrow canyons into sandstone.

• Some storms will flood this canyon with water 80 feet high!

From Rock to Rock

• Rivers deposit the sand from erosion in new locations to become new sandstone layers for future Geologists!

Erosion

• Rain, Ice, and Wind can combine to form some strange erosional features!

Arches

• Wind erosion is primarily responsible for natural arches.

• Ice and rain also play a role in weakening lower layers of rock.

Quiz – How did this form?

• Devil’s Golf Course

Tilting

• Plate movements can cause the layers be be thrust upwards, downwards, or twisted.