Weathering & Sedimentary Rocks

What is a sedimentary rock?

A rock formed from pieces of pre-existing rock or from dissolved/biological material.

What are the 3 types of sedimentary rocks?

Detrital, Chemical, Biochemical

What are detrital sedimentary rocks made of?

Broken pieces (clasts) of pre-existing rocks

Steps to form detrital rocks

Weathering → Erosion → Deposition → Cementation

What is weathering?

Breaking down rock into smaller pieces

What is erosion?

Transport of sediment (water, wind, ice)

What is deposition?

Sediment settles

What is cementation?

Minerals glue sediment together

Chemical weathering

Rock breaks down by chemical reactions (dissolving)

Physical weathering

Rock breaks down without chemical change

Two main types of physical weathering

Freeze/thaw and plant root wedging

How does freeze/thaw work?

Water freezes → expands → cracks rock

Example of chemical weathering

Acid dissolving minerals (like calcium carbonate)

Main transport agents

Water, wind, ice

What happens when transport slows?

Larger particles settle first

What causes well-sorted sediment?

Water or wind slowing down

What causes poorly sorted sediment?

Ice, landslides, fast movement

What rounds sediment?

Water transport

Conglomerate

Detrital, rounded, poorly sorted, mountains/glaciers

Mature sandstone

Detrital, well sorted, quartz, beach/desert

Immature sandstone

Detrital, rivers, less sorted, mixed minerals

Mudstone / shale

Detrital, very fine particles, well sorted, still water (lake, swamp)

How do chemical sedimentary rocks form?

when minerals, dissolved in water, precipitate (crystallize) out of the solution to form solid rock

Example of chemical rock

Rock salt (halite)

How do biochemical rocks form?

Living organisms (like corals, shells, or plants) die, and their remains accumulate in layers, typically on the ocean floor or in swamps

Limestone

Biochemical, calcium carbonate, ocean origin, fizzes with acid

Chert

Silica, biochemical, scratches glass, looks waxy

Conglomerate forms in what environments?

Mountain streams and glaciers

Immature sandstone forms in what environment?

Intermediate rivers

Mature sandstone forms in what environment?

Beaches

Mudstone and shale form in what environments?

Quiet water (lakes, swamps, lagoons)

Sandstone (dunes) forms in what environment?

Deserts

Breccia forms in what environment?

Landslides

Biochemical chert and limestone forms in what environment?

Oceans (marine)

What forms in groundwater environments?

Rock salt, chert (chemical), calcium carbonate (geodes)