Types of Sedimentary Rocks and Weathering

Clastic sedimentary rocks

Made of transported and deposited fragments

Biochemical sedimentary rocks

Deposited by living organisms

Organic sedimentary rocks

Dead remnants of living organisms' soft bits

Chemical sedimentary rocks

Precipitated directly out of solution

Physical weathering

Jointing, frost/salt/root wedging, abrasion, thermal expansion

Chemical weathering

Dissolution: dissolve rocks in (acidic) water (rainwater)

Hydrolysis: chemical reaction between rock and water to break them down and form new minerals

Sorting (Clastic Sedimentary Rocks)

Clast size, Angularity, sorting clast composition

Halite

Chemical sedimentary rock

Reef limestone

Biochemical sedimentary rock

Chert

Biochemical sedimentary rock

Oil shale

Organic sedimentary rock

Travertine-limestone

Chemical sedimentary rock

Chalk

Biochemical sedimentary rock

Coal

Organic sedimentary rock

Thicknesses of packets of sedimentary rock

Bed < Unit (aka a member) < Formation < Group

Compaction

Squeezing out fluids and reducing pore space, significantly reducing volume and increasing density of sedimentary rock

Energy depositional environment

Higher energy depositional environment associated with larger class

Quartz

Most resistant to chemical weathering

Mature clastic sediments

Far from the source, rounded clasts, small grains, and good sorting

Sedimentary structures

Bedding: formed by discrete sedimentation periods

Unit: discrete packet of similar rock

Formation: collection of units grouped in time/environment

Group: set of formations connected by time/environment

Processes of clastic sedimentary rocks

1) Weathering breaks down rocks in place

2) Erosion mobilizes particles, carrying them away from their source

3) Particles are transported long distances downhill

4) Deposition is when the particles cannot be transported by the flow any longer

5) Burial as sediment layers accumulate

6) Lithification involves the cementation of sediments into sedimentary rocks

Grade (metamorphism)

Describes pressure/temperature conditions of metamorphism

Facies

Describes assemblages of minerals that indicate conditions of metamorphism

Protolith

The name/type of a rock before it was metamorphosed

Hornfels

Non-foliated metamorphic rock formed in a contact aureole (next to an igneous intrusion)

Blueschist

Metamorphic rock formed in a subduction zone

Gneiss amphibolite

Metamorphic rock formed in a continental collision

Conglomerate

Sedimentary rock with the largest clasts

Asymmetric ripples

Consistent flow direction

Symmetric ripples

Oscillating flow direction (e.g. beach)

Ripples

Same sort of bedform as dunes, but smaller

Frost wedging

Mechanism of physical weathering

Glacial moraine

2-meter-sized to gravel-sized angular clasts, very poor sorting, highly variable clast lithology

Mountain stream

Rounded pebbles and cobbles to sand-sized, poor sorting

Alluvial Fan

Gravels and arkose sand, medium sorting, red/orange color

Beach/Intertidal zone

Grey/yellow, well-sorted sand-sized grains, occasional shells

Lake

Inter-bedded, thin mudstone and siltstone layers

Shallow marine/reef

Biogenic limestone, lots of broken up shells

Turbidites

Repeated underwater landslide deposits

Undeformed

Flat layers, equant grains, or grains aligned by lithification + compaction, jointing

Deformed

Angled layers + folding, faulting, metamorphic foliation + neocrystallization

Brittle deformation

Deformation in cold rocks, sudden stresses cause materials to behave brittlely

Ductile deformation

Deformation in warmer rocks, high pressure, slow stresses can lead to ductile deformation

Composition

Some rock types are softer and more ductile than others