sedimentary rocks Flashcards
what is a sediment?
a collection of loose earth materials
how do sediments form?
when older bigger rocks break into smaller pieces
-when minerals in rock react with air/water to form new minerals
-minerals in rock dissolve in water and reprecipitate elsewhere
-animals extract dissolved mineral ions to build shells
what are minerals precipitated out of water called?
sedimentary minerals,
if loose, sediment
if together, rock
what is precipitation triggered by?
a change in conditions
what is weathering?
the process that creates sediments
what is physical weathering?
the physical breaking of big rocks into small rocks
what is chemical weathering?
alter minerals and rocks as they react with air and water
-produces new minerals and dissolved elements and compounds
what are the types of sediment texture?
crystalline
clastic
what is crystalline texture?
minerals precipitate out of solution
what is clastic texture?
broken pieces of earth material
what are compositions of chemical sediments?
iron bearing crystals/ residues
microcrystalline quartz
dolomite microcrystals
calcite crystals
halite crystals
gypsum crystals
what are biogenic sediment?
produced through biological activity
built out of dissolved minerals extracted from water
types of clastic sediment?
siliciclastic
bioclastic
what is siliciclastic?
consists of quartz and feldspar grain, rock fragments and clay
what is bioclastic?
fragments of transported skeletal material
what does source refer to?
the exposed rocks from which sediment forms
what happens to sediment once it has formed?
it can be picked up and transported through erosion
what are agents of erosion?
air, water, ice, gravity
erosion by gravity?
only solid clast moves
moves large and small clasts at the same time
erosion by air, water, ice?
pick up and move sediment
the more viscous, the more power to move clast
which erosion agent has the lowest viscosity?
air
only move small clasts
which erosion agent has the highest viscosity?
ice
moves small to large clasts
how do clasts move from water and air?
rolling
saltation
traction
suspension if small
how do clasts move in ice?
on top
trapped within
how does speed affect erosion?
the faster it is, the more power it has to move a large range of clasts
how are sediments deposited?
minerals form in situ from reaction with air/water and a rock
-precipitate out of solution when conditions change
-ions extracted from water to build shells/skeletons
when is clastic sediment deposited?
when the agent of erosion loses its power to transport grains
what causes agents of erosion to lose power?
a drop in velocity
a drop in viscosity
what is the hjulstrom diagram?
predicts the critical velocities at which a given grain size can be picked up, moved and deposited by WATER
why is clay so hard to erode?
because clay is platy and layered and it sticks to itself
what are the main depositional environments?
continental
costal
marine
what are features of sedimentary structures?
small
3D
form in sediment during or after deposition
what is primary sedimentary structure?
structures form as sediment is deposited
what is a strata?
most common primary sedimentary structure
horizontal layers of sediment
what are beds?
layers bigger than 1cm
what are laminations?
layers less than 1cm
what is a graded bed?
when grains become more fine
what is cross-bedding?
result of deposition on inclined surfaces, produced by flowing water or wind
what are symmetrical ripples?
ripples with the same angle on both sides caused by bidirectional currents
what are asymmetrical ripples?
ripples with one steep side one shallow side
caused by unidirectional cuurent
what are imbricated pebbles?
overlapping flat pebbles due to flowing water pushing them over
what are sole marks?
grooves or indents that form either from objects dragged across sediment or
back current eddies scour out patches in the sediment
what is secondary sediment structure?
formed after the deposition
how are mudcracks formed?
when water dries up and clay minerals contract
what is bioturbation?
organisms pull up sediment and erase primary structure
what is soft sediment deformation?
sediment is loaded onto waterlogged sediment
compression causes water to squeeze out, deforming the original bedding
two types of lithification?
compaction
cementation
what is lithification
the process that turns sediment to stone
what is compaction
due to burial, reduces pore space by forcing grains together
what is cementation?
precipitation of chemical sediments in-between clasts
characteristics of siliciclastic composition?
distinguished by grain size and shape
how are chemical sedimentary rocks distinguished?
crystal type
how are bioclastic rocks distinguished?
composed of calcite organisms
grain size and shape
grain type
