Sedimentary Rocks (L8) Flashcards
What are sedimentary rocks?
rocks that are formed by the accumulation and hardening of sediment
The 3 kinds of sediment and its quick definitions?
Clastic - consists of particles derived from pre-existing rocks (e.g., sand)
Chemical Sediment - Consisting of mineral matter precipitated from a solution (e.g., salt)
Biochemical Sediment - which consists of materials produced by organisms (e.g., shells)
When exposed to earth’s surface, rocks are broken down by ____
processes of weathering (due to physical and/or chemical breakdown)
Mechanical/physical weathering and how is it accomplished in nature?
involves the physical breakup or disintegration of rocks into smaller particles without changes in their composition
by physical agents (e.g, water, wind) but also can be aided by biological factors
Chemical Weathering?
breakdown or decomposition of minerals due to chemical reactions of minerals with water or gases in the air
what does the resistiance to weathering follow?
the same trend as the order of crystalization in Bowen’s Reaction Series
Which temperature minerals are most stable at Earth’s surface and why?
Low-temperature minerals b/c Earth’s surface is a lot cooler than environments in which minerals form from magma
When is Chemical weathering most intense?
in warm and humid climates
What does chemical weathering produce and how?
residual products and free ions
Solid components are left as a residue and the remaining material is dissolved in water, in the form of ions
Residual sedimentary particles can be dislodged and transported away in which 4 ways?
Gravity (mudflows, debris flows etc.)
Water (streams)
Wind
Glaciers
The difference between weathering and erosion?
weathering is the breakdown of material whereas erosion involves the removal of material from the site of weathering
can act hand-in-hand but not same thing
When do sedimentary particles ultimately come to rest?
once the transporting medium can no longer carry them
what is the general rule of sedimentary particles being deposited?
smaller/lighter particles are deposited in less-agitated conditions than larger/heavier particles when transported by wind or water
How do sedimentary particles experience some degree of sorting?
can be due to constant wave action, while the sand-sized particles settle out, finer grained particles are swept away
What kind of transportation method of sedimentary particles results in poor assortment and why?
rapid transportation by events such as debris flows b/c particles aren’t remobilized and redeposited by sorting processes like waves
How can geologists know the method in which the sediment was deposited by just looking at it?
b/c the characteristics of the clastic sedimentary rocks like fossils can provide info on where it was deposited
Ex., Shale is like rock and you can see microscopic clay particles that show fossils
Lithification?
the transformation where once buried, sediment undergoes changes that transform it into rock
How does Lithification work?
as sediment layers are buried to deeper and deeper levels under successive sediment layers, the particles are squeezed together as the spaces between them decrease in size
What are the 3 stages of Lithification?
Deposition - where clasts are dropped or settled out
Compaction - as it gets buried under more sediments, the particles are closer together
Cementation - groundwater moves between the grains and the minerals it leaves behind glues the particles together
How are clastic sedimentary rocks classified?
by grain size (clast size)
Rock equivalent of gravel
Conglomerate (large clasts rounded if larger clasts angular = breccia)
Rock equivalent of sand
sandstone (sand-sized particles, sandpaper feel)
Rock equivalent of mud
Shale - if it breaks easily into small plates
Mudstone - if its more massive without a fine structure
Equivalent of clay and sand?
Silt (particles barely visible under magnification)
What does water on Earth’s surface all contain?
dissolved ions derived from weathered minerals and volcanic gases
Why is the sea salty?
the proportion of positive ions of sodium and negative ions of chloride = halite (our common salt)
What happens in sea water due to evaporation?
dissolved ions become so concentrated that the water cannot hold it so the ions join together and become minerals
Evaporative deposits/minerals ?
when the water highly concentrated in sat cannot escape back to ocean and become further concentrated to the point that they become this
2 common minerals in evaporative deposits are:
gypsum (clacium sulphate) and Halite (sodium chloride)
Rock salt
a rock formed exclusively of halite (spread on our roads as de-icer)
Rock Gypsum
a rock formed exclusively of gypsum (chalkboard chalk)
What is Travertine?
the type of limestone which is a chemical limestone that forms in caves and hot springs (stalactites)
What does biochemical sediment consist of?
materials that are produced by chemical processes associated with bio activity (shells, bones, teeth, etc)
What are 4 common rocks that are formed from biochemical sediment?
fossiliferous limestone
reef limestone
chert
coal
Fossiliferous Limestone
type of biochemical limestone composed entirely of calcite shells (skeletons) of organisms
Chalk
a variety of fossiliferous limestone, made of microscopic skeletons of plantonic algae
Chert
the solidification of the common biochemical sedimentary rock where the silica of an organism’s skeleton dissolves and forms a gel on the seafloor
Why was Chert used for its arrowheads and tools?
due to its hardness and the sharp cutting edge from its conchoidal fractrure
Coal
a special type of biochemical sedimentary rock that is largely composed of organic matter from plants
What is interesting about coal?
it’s one of the few rock types that doesn’t necessarily contain any minerals
Where are sedimentary rocks also widely used in?
Construction of buildings
What is the NSB and GSB made of?
Whirlpool Sandstone (100% quartz sand)
Where does Tyndall Stone get its attractiveness from?
the dark colored mottled shapes against a lighter tan-colored background
What is a Dolostone?
much like limestone but is composed of mineral dolomite instead of calcite
Why is the dolostone “Eramosa Limestone” ideal for flagstones?
b/c its naturally finely laminated and easily splits into flat slabs
