Chapter 6 Flashcards
sediment
loose mineral grains such as clasts, shells and shell fragments, plant debris, and or mineral crystals precipitated from bodies of water
clasts
fragments or grains produced by weathering of a rock - boulders, pebbles, sand, silt
Sedimentary rock
forms at or near the Earth’s surface by the cementation and compaction of accumulated layers of different kinds of sediments
Weathering
the chemical and/or physical breakdown of preexisting rock
Weathering produces both
clasts and dissolved ions
dissolved ions
charged atoms or molecules in a water solution
cement
when ions precipitate from ground-water in the spaces between clasts forming cement which holds the clasts together
Physical weathering
breaks the rock into fragments but does not change the minerals that make up the rock
Chemical weathering
process which rock chemically reacts with air, water, and acidic solutions
involves chemical reactions
Generally reduces the number of minerals in sediments over time
chemical reactions
the breaking and forming of chemical bonds
can produce new minerals
unstable or nonresistant minreals
minerals that are easily weathered
stable or resistant minerals
those that can survive weathering
mineralogically immature
sediments that contain minerals which are susceptible to chemical weathering (unstable)
mineralogically mature
stable
sediments that contain minerals which are resistant to weathering
classes of rocks
clasts
chemical
biochemical
organic
Clastic sedimentary rocks
formed from clasts
texture in which discrete grains are held together by a chemical cement or very fined-grained clastic matrix
majority are silicate rocks
weathering of clasts
reduces bedrock into a pile of loose (separate mineral) grains or loose clasts also known as detritus
Erosion of clasts
water, air, glaciers
lithification of clasts
loose sediment into solid rock through compaction and cementation
compaction
when weight of an overlaying sediment squeezes out air or water pressing the clasts closer together
diagenesis
application of pressure and the circulation of fluids overtime gradually change characteristics of sediments and sedimentary rock
Chemical sedimentary rocks
form when water ions become oversaturated and excess ions bond together to form solid mineral grains
cryptocrystalline rocks
grains are so small they look like porcelain
Evaporites
chemical sedimentary rocks in thick deposits composed of crystals formed when salt water evaporates
Travertine
rocks composed of crystalline calcium carbonate formed from groundwater from hot or cold water springs or caves
Biochemical sedimentary rocks
consist primarily of the remains of once-living organisms
Organic sedimentary rocks
contain significant qualities of of the organic material from the soft, carbon rich parts of those organisms
sorting
measure of the uniformity of grain size
subrounded
smooth edges and corners
sediment maturity
degree to which a sediment has evolved from a crushed-up version of the original rock into a sediment that has lost its easily weathered minerals and become well sorted and rounded
beds
layers of sediments
graded beds
layers in which the grain size decreases progressively from the bottom to the top
asymmetric ripple marks
current that flowed from the gentle side toward the steep side
symmetric ripple marks
have steep slopes on both sides from oscillating currents
