Sediment and Sedimentary Rocks

Book questions and slide notes

Quartz is a common mineral in sandstone. Under certain circumstances, feldspar is common in sandstone, even though it normally weathers rapidly to clay. What conditions of climate, weathering rate, and erosion rate could lead to a feldspar-rich sandstone? Explain your answer.

Feldspar-rich sandstone forms in an arid, dry environment.

Describe with sketches how wet mud compacts before it becomes shale.

Mud/clay volume decreases as water is pushed out due to pressure from objects on top. Particles reorient and splitting surfaces in shale form parallel to mineral grains.

What do mud cracks tell us about the environment of deposition of sedimentary rock?

Sediment was exposed above water as water level dropped creating a very fine-grained sediment as it dries.

How does a graded bed form?

A single bed may have gravel at its base and grade upward through sand and silt to fine clay at the top. A graded bed may be deposited by a TURBIDITY CURRENT (Turbidity currents are underwater avalanches and are typically triggered by earthquakes or submarine landslides), which is a turbulently flowing mass of sediment-laden water that is heavier than clear water and therefore flows down-slope along the bottom of the sea or a lake.

List the detrital sediment particles in order of decreasing grain size.

Boulder (256mm)

Cobble (64mm)

Pebble (2-64mm)

Sand (2mm)

Silt (1/16mm)

Clay (1/256mm)

How does a sedimentary breccia differ in appearance and origin from a conglomerate?

Conglomerate can be distinguish from breccia by the definite roundness of its particles.

Describe three different origins for limestone.

Biochemical (from remains of sea animals)

Inorganic (precipitated from solutions)

Recrystallization (new crystals form in rock).

How does dolomite usually form?

Dolomite usually forms from the alteration of limestone by magnesium-rich solutions.

What is the origin of coal?

Origin from plant fossils in coal beds such as leaves, stems, tree trunk, and stumps with roots often extending into the underlying shales, so most coal formed right at the place where plants grew.

Sketch the cementation of sand to form sandstone.

a) Loose sand grains are deposited with open pore space between the grains.

b) The weight of overburden compacts the sand into a tighter arrangement, reducing pore space.

c) Precipitation of cement in the pores by groundwater binds the sand into the rock sandstone, which has a clastic texture.

How do evaporites form? Name two evaporites.

Evaporites form from the evaporation of seawater or a saline lake, such as Great Salt Lake in Utah. 2 types are Rock Gypsum, formed from the mineral gypsum & Rock Salt, composed of mineral called halite,.

Name the three most common sedimentary rocks.

Sandstone, Shale, & Limestone

What is a formation?

A formation is a body of rock of considerable thickness that is large enough to be mappable, and with characteristics that distinguish it from adjacent rock rock units.

Although a formation is usually composed of one or more beds of sedimentary rocks, Units of metamorphic and igneous rock are also called formations.

Explain two ways that cross-bedding can form.

By flow of air and water, sand grains move as migrating ripples and dunes.

Particles of sediment from 1/16 to 2 millimeters in diameter are of what size?

Sand

Rounding is

the grinding away of sharp edges and corners of rock fragments during transportation.

Explain how chemical sedimentary rocks are formed, and give several examples

Form when dissolved mineral salts precipitate from water as it evaporates, a process called chemical precipitation, or when supersaturated water loses chemical components.

Ex: limestone, rock salt/halite, gypsum, chert, and certain types of dolostone. 

What is the origin of oils and gas?

originate from the remains of ancient marine organisms and plants that were buried in sedimentary rocks, such as shale.

Describe what clues a geologist uses to interpret where and how a sedimentary rock formed and why this is important. 

examining its texture (grain size, shape, sorting), composition, and sedimentary structures

Compaction and cementation are two common processes of

lithification

Which is not a chemical or organic sedimentary rock?

shale

The major difference between breccia and conglomerate is

rounding of the grains

Which is not a type of sandstone?

travertine

Shale differs from mudstone in that

shale is visibly layered and fissle; mudstone is massive and blocky.

The chemical element found in dolomite not found in limestone is

Mg (Magnesium)

In a graded bed, the particle size

decreases upward

A body of rock of considerable thickness with characteristic that distinguish it form adjacent rock units is called a/an

formation

If sea level drops or the land rises, what is likely to occur?

a regression

Thick accumulations of graywacke and volcanic sediments can indicate an ancient

convergent boundary

A sedimentary rock made of fragments of preexisting rocks is

detrital.

Clues to the nature of the source area of sediment can be found in

the composition in the sediment.

Why is sedimentary rocks important

widespread, history, reservoirs, economic deposits, soil formation

what does clastic mean

based on particle size

gravel

greater then 2mm, fairly coarse

conglomerate

larger particles, smooth and rounded

breccia

similar sized particles, but larger particles are sharper and angular

sandstone

less than 2mm, clear different colors

quartz

fairly glass, translucent, no cleavage

arkose

vary in grain size, pink peach feldspar

siltstone

gritty, might not see individual particles

shale

composed of clay, layered and soft

What does chemical mean

based on composition

calcite

affected by acid test, softer than harder plate

rock salt

= halte

chert

= smooth like table

Cryptocrystalline

= it is hidden

what is the process to sedimentary rocks

compaction and cementaion

bedding

layered or form of strata

graded bedding

usually in water

cross bedding

in wind or water, sand particles

river cross beds

smaller than cross bedding (about a foot)

ripple marks

surface feature, wind or waters form

mud cracks

surface feature, in mud or clay and in banks of river and lakes

how many surface features and penetrative features

penetrative (4)

Surface(2)

glacial: breccia

poorly sorted, angular

mountain stream: conglomerate

poorly sorted, round

wind dunes: quartz sanstone

well sorted, round

deep lake: dark shale

well sorted, clay to silt size

river channel: sandstone or conglomerate

moderate to poorly sorted, silt to sand sized

what are the sedimentary basin types

Rift basin and passive margin basin

Clues to the nature of the source area of sediment can be found in

the composition of the sediment

A sedimentary rock made of fragments of preexisting rocks is

detrital

Thick accumulations of graywacke and volcanic sediments can indicate an ancient

convergent boundary

If sea level drops or the land rises, what is likely to occur?

a regression

A body or rock of considerable thickness w/ characteristics that distinguish it from adjacent rock units is call a/an

formation

In a graded bed, the particle size

decreases upward

The chemical element found in dolomite not found in limestone is

Mg

Shale differs from mudstone in that

shale is visibly layered and fissile; mudstone is massive and blocky

Which is not a type of sandstone?

travertine

The major difference between breccia and conglomerate is

rounding of the grains

Which is not a chemical or organic sedimentary rock?

sandstone

Compaction and cementation are two common processes of

lithification

Rounding is

the rounding of a grain to a spherical shape

Particles of sediment from 1/16 to 2 millimeters in diameter are of what size?

sand

How does a graded bed form?

A graded bed may be deposited by a turbidity current (are underwater avalanches triggered from earthquakes or underwater landslides) which is a turbulently flowing mass of sediment laden water (heavier than clear water) therefore it flows down to the bottom of the sea or lake floor. 

Sediment

loose (unconsolidated) particles

Detrital sediments

weathering and erosion of per-existing rocks and based on particle size

Chemical sediments

chemical precipitation form solution and secretion by organisms in water

Formation of sedimentary

1) Transportation (water and wind/air)

2) Deposition (water sources)

3) Preservation (under or buried)

4) Lithiation (cementation and compaction)streams

Coarse products (boulders and cobbles) require

fast moving water (mountain streams) are not transported very far from their sources

Intermediate-sized particles

(sand) are transported by rivers and wind and deposited at coasts or in deserts (quartz)

Fine particles

(silt and clay) are carried to regions where the water is still (offshore environments) and feldspars and ferro-magnesium minerals form the bulk of these particles

Dissolved material

(Ca, Na, K, CO3, SO4, Cl) is carried farthest and deposited where the ocean, sea, or lake is evaporated off.

evaporites rocks

1) calcite (CaCO3)
2) gypsum (CaSO4.2H2O)

3) Halite (NaCl)
4) Sylvite (KCl)

Detrital or Clastic

Form from cemented (Lithification) sediment grains that come from pre-existing rocks, the most common

Chemical

• Form by precipitation of minerals from low-temperature solution

• Have crystalline textures, held together by interlocking crystals, no cement

Organic

Consolidation of the carbon-rich remains of plants and animals

Conglomerate

» Rounded gravel
» Coarse-grained
» Short, distance but enough to round gravel

Breccia

» angular gravel
» Coarse-grained
» Landslide deposit
» May not have travel far