ERTH209 Midterm 3

Where do sedimentary rocks occur?

In the uppermost part of the crust

Clastic rocks

Looser rock fragments cemented together

Biochemical

Cemented shells of organisms

Organic rocks

Carbon-rich remains of once-living organisms

Chemical rocks

Minerals that crystallize directly from water

How are clastic rocks created?

Weathering, erosion, transportation, deposition, lithification

Lithification

Transforms loose sediment into solid rock

What do minerals precipitate from?

Groundwater

As transport distance […], grain size […]

As transport distance increases, grain size decreases

Angularity

The degree of edge or corner smoothness

Sphericity

The degree to which the shape of a clast approaches that of a sphere

Sorting

A measure of the uniformity of grain sizes

Degree of sorting […] with transport distance

Degree of sorting increases with transport distance

Breccia

Coarse, angular, rock fragments

Conglomerate

Rounded rock clasts

Arkose

Sand and gravel with abundant feldspar

Sandstone

Clastic rock made of sand-sized particles

What are fine clastics composed of?

Silt and clay

Silt-sized sediments are lithified to form […]

Silt-sized sediments are lithified to form siltstone

What do clay particles form from?

Mudstone or shale

What are biochemical sedimentary rocks made of?

Sediments derived from the shells of once living organisms

Limestone

Rock made almost entirely of calcite or aragonite

Where does biochemical limestone form?

Warm, tropical, shallow, clear, O2 rich marine water

Chert

Rock made of cryptocrystalline quartz derived from opaline silica

Organic sedimentary rocks

Made of organic carbon: coal, altered vegetation, shale

What are chemical sedimentary rocks comprised of?

Precipitated water solution

What texture do chemical rocks have?

Crystalline

Evaporite minerals

Formed from evaporation of large volumes of sea or lake water: halite, and gypsum

Travertine

CaCO3 precipitated from groundwater where it reaches the surface

Replacement chert

Differs from biogenic in that it doesn't originate from living organisms - flint, jasper, petrified wood, agate

What are 2 prominent features of sedimentary rocks?

Bedding and stratification

Bedding plane

The boundary between 2 horizontal beds

What forms bedding?

Changing conditions during deposition

Formations

Rock units so unique that they can be recognized and mapped

Sediments

Loose fragments of rocks or mnerals, shells and shell fragments, or mineral crystals that precipitate out of water

How is sediment produced?

Weathering

What can bedrock transform into?

Soil

Physical/mechanical weathering

Breaks rocks into unconnected clasts of variable size

Joints

Natural cracks formed in rocks due to the expansion of a rock or cooling and contraction

Frost wedging

Water expands about 9% when frozen, exerting a force on the surrounding rocks

Root wedging

As roots grow, they exert a force on the surrounding rock

Salt wedging

Occurs in arid climates and coastal areas when salt dissolved in water precipitates and exerts a force on the surrounding rock

Dissolution

Minerals dissolve into water, nostly affects carbonate rocks and salts

Oxidation

Reactions during which an element loses electrons, common in iron-bearing materials

Physical and chemical weathering work together to:

Increase surface area, dissolve minerals and cements, alter hard materials into soft materials

Weathering occurs faster:

At edges and corners of a block

Sawtooth weathering

Develop in sequences of alternating strong and weak layers

Substrate

Mineral composition and resistance to weathering are important

Slope steepness

Regolith easily washes from steeper slopes, wetter soils contain more organic material, flat soils tend to hold more moisture

Time

Soils require time to develop. Younger soils tend to be thinner

Bedforms

Water flowing over loose seidment

Ripples

Ridges and troughs that develop perpendicular to flow in sandy sediments

Sand dunes

Big ripples

Cross beds

Created by rpple and dune migration where sediment is carried and drops to one side

Turbidity currents

Forms in deep basins that recieve periodic pulses of turbid water

Mud cracks

Indicates alternate wet and dry terrestrial conditions

Scours

Form when debris is dragged along the bottom of a river

Depositional environments

Locations where sediment accumulates

What kind of rocks are characteristic of mountain streams?

Coarse conglomerate

Alluvial fans

Cone-shaped wedges of sediments that pile up where a rapid drop in stream velocity occurs at a mountain front

Where do sand-dune environments form?

Where there is an abundance of wind-blown, well-sorted sand

River environments

Sand and gravel fill concave-up channels that often scour into previously deposited floodplain sediments

Lake environments

Gravels and sands are trapped near shore, well sorted muds are deposited in depper water

Marine delta

Sediment accumulates where river velocity drops upon entering the sea

Shallow water carbonate environments

Develop in tropical, warm, clear, shallow, normal salinity, marine water

Deep marine deposits

Accumulate fines that settle out far from land

Rift basins

Form at divergent boundaries

Passive margins

edges of continents that are not tectonic plate boundaries

Intracontinental basins

Form in the interior of the craton, far from continental margins or tectonic plate boundaries

Foreland basins

Form on craton side of collisional mountain belt

Transgression

Sea level rising

Regression

Sea level falling

Foliation

Planar fabric that cuts through the rock

Recrystallization

Minerals change size and shape through dissolution and growth of crystals

Neocrystallization

Formation of new crystals from old

Pressure solution

Mineral grains partially dissolve where their surfaces press together, reprecipitate in areas where pressure is low

Plastic deformation

Mineral grains soften and deform when rock is squeezed or sheared at elevated temperature and pressure

What does shale metamorphose to?

Slate

Slate metamorphose to:

Schist

Schist to:

Gneiss

Gneiss to:

Migmatite

Migmatite to:

Hornfels

Polymorphs of Al2SiO5

Andalusite, kyanite, sillimanite

Differential stress

Stress that is greater in one direction

Normal stress

Operates perpendicular to a surface

Compression

Push together normal stress

Tension

Pull apart normal stress

Shear

Acts parallel to a surface - like kneading dough

Grain alignment

Compression and shear combined with elevated T and P cause minerals and rocks to change shape without breaking

Hydrothermal fluid

Speed up chemical reactions and add or subtract elements

Metasomatism

Hydrothermal alteration

Slate

Fine grained, low grade metamorphic shale, has foliation called slaty cleavage

Phyllite

Finme grained mica rich rock that forms by metamorphic alteration of slate

Metaconglomerate

Metamorphosed conglomerate

Schist

Fine to coarsely crystalline rock with larger micas indicating medium to high grade metamorphism

Gneiss

Has distinct bands of mafic and felsic minerals

Compositional banding

Can develop by extensive high T shearing

Migmatite

Partially melted gneiss

Quartzite

Nonfoliated metamorphic rock

Quartz

Metamorphic quartz sandstone