Geo Lab Quiz 1: Sedimentary Rocks

Outcrop

Where bedrock sticks out so we can access it (visually see the layers)

Weathering

How we break down rocks naturally

Physical Weathering

Break down actual rocks but don’t change the composition

Chemical Weathering

Changes the composition of the rock

Dark rocks

Iron rich. Chemically weather. Beaches near source rock have darker grains

Light rocks

Silicon rich. dont weather easily. beaches far from source rock will have light grains

Clastic sedimentary rocks

solid fragments of existing rock. Types: Conglomerates, Sandstone, Siltstone, Shale and Mudstone

Deposition

More energy the river/transporter has, the larger particles it can carry (plus everything smaller). Particles deposited when transporter looses energy. Farther from the source= smaller, rounder, better sorted.

Conglomerates

*clastic sedimentary rock

grain size: pebble or larger

Location: braided streams

Sandstone

*clastic sedimentary rock

grain size: sand

Location: beaches and deserts

Siltstone

*clastic sedimentary rock

grain size: silt

location: floodplains

Shale and Mudstone

*clastic sedimentary rock

Grain size: clay

location: lakes, marshes, deeper oceans

Organic Sedimentary rocks

minerals extracted by organisms or organic remains

Organic limestone

-made up of calcite, fossilifourous limestone

-in shallow, warm waters (coral reefs)

Types: coquina (high energy- beaches) and chalk (deep ocean)

Non-Limestone Organic Sedimentary rocks

low energy, warm/wet (marshes and swamps)

• peat —> coal

Chemical Sedimentary Rocks

Minerals dissolved in water solution which can precipitate due to changes in water temp, pressure, pH

• Evaporirtes: dry, hot basin (halite and gypsum)

Graded Bedding

• largest particles go to bottom

• ha flashfloods and underwater landslides

Ripple Marks

• Asymmetric—> current (wind or water)

  • Meandering river, sand dune

• Symmetric—> waves (one direction)

  • lake or beach

Cross Beds

Wind direction creates ripples. When there is no energy, sediments are dropped

Ex: sand dunes

Varves

Layers of silt and sand

• seasonal variation in energy with an alternating ice cover

• cold/seasonal

Mudcracks

Silt and Clay

Caused by changes in climate from wet to dry

Glacial Striations

Carved out land by glaciers

Fossils

Terrestial vs. Marine