Unconformities As + A2

Question 1

Deposition in fluvial basics

Answer 1

Meandering stream
braided stream
Flood plain

Question 2

energy and velocity changes in rivers

Answer 2

energy-
high at source
drops at med
low at mouth
high on outside of bend
low on inside of bend

velocity-
high where steep gradient
lowers where flatter
high on outside of bend
low on inside of bend
low where tributary or lake joins

Question 3

effect of velocity on dep

Answer 3

As velocity decreases deposition increases
e.g. inside of bend

must be very low to dep fine sed e.g. clay

Question 4

meandering stream

Answer 4

high e on outside of bend = erosion
low e on inside of bend = deposition

Question 5

braided stream

Answer 5

semi arid area = lack of rainfall

sudden deposition due to lack of rain or melt water

dep of C material e.g. sand and pebbles leads to blockages that the river braids around

dep at front of blockages

Question 6

Flood plain

Answer 6

flat plain adjacent to body of water

flooded at times of high energy

very low energy, allows for dep of very fine particles e.g. clay

may see dessication cracks if irregularly flooded

good for fossils as low e and fine sed

Question 7

Breccia vs conglomerate

Answer 7

Breccia-
C grain
angular- short transport
poorly sorted- rapid dep
e.g. wadi/alluvial fan

conglomerate-
C grain
rounded- longer transport
poorly sorted- rapid dep
e.g. river/beach

Question 8

Hot desert enviro basics

Answer 8

wadi conglomerate
aeolian sandstone
alluvial fan arkose
playa lake evaporates

Question 9

Wadi conglomerate

Answer 9

wadi- desert stream channel dry except for rainy season (often ravine or valley)

high energy- transports coarse material

lack of rain- rapid dep as water seeps into porous rock = poorly sorted

conglomerate= poorly sorted, subrounded (more rounded as more transport/ Secondary transport e.g. melt water)

red due to iron oxide

Question 10

alluvial fan arkose

Answer 10

water rushes down then spreads out= fan shape (rapid dep)

dep nearer the mountain= coarse then fines out

breccia near mountain

arkose near middle

arkose= sand stone with 25% + feldspar (often from granite upstream)

arkose shows little weathering as quartz and feldspar=hard

Question 11

aeolian sandstone

Answer 11

aeolian = wind

aeolian sandstone= formed from wind

often see large crossbedding/asymmetrical ripples

red due to iron oxide

Very well sorted + rounded and highly spherical

frosted due to attrition

entirely quartz due to weathering away

silica cement

Question 12

Playa lake evaporates

Answer 12

playa= dry lake bed

playa lake= temp lake in arid enviro

h20 evaporates,
dissolved ions become concentrated,
least soluble salts come out of solution on edge of lake,
more soluble salts further in

playa lakes form as streams don’t reach sea due to high evaporation
infiltrate playa lake instead

Question 13

Dep in carbonate environments basics

Answer 13

Shallow-
bioclastic/fossiliferous
reef
oolitic

deep-
chalk
micritic

Question 14

Bioclastic/fossiliferous limestone

Answer 14

Up to 75% fossils

rest= calcareous + og deterial mud

Grey and crumbly
hard and well jointed and massive beds
contains broken segments of crinoids

commonly formed mid jurassic

sometimes whole fossils mostly broken due to transport

Question 15

reef limestone

Answer 15

CO3 secreting algae engluf reef and cement it together

mostly coral

unbedded and has trilobite+ bivalve fossils

form in warm (23-25) shallow(>25m) high e

atoll- coral colonise Island, island sinks, coral ring

Question 16

Oolitic limestone

Answer 16

white/yellow if iron stained

often crossbedding

oolith= nucleus rolled in CO3 mud bu current in tropical climate less the 2m

shallow sea

aragonite to calcite as more stable

common see fossils prev on sea floor- some whole some fragment

Question 17

Chalk

Answer 17

white, hard, massive, well jointed

compound of coccoliths, cancerous disks or oval platelets (from single celled planktonic algae)

May = micofossils of calc foraminifera/ Marco fossils of brachiopods

Low e and deep (<200m)

only if little sed supplied from land

Flint nodules common

Question 18

Micritic

Answer 18

Fine, hard (crystalline) from diagenisis of calcareous mud

calcareous mud produced by precipitate from sea / by CO3 secreting algae

planktonic foraminifera to calcareous ooze buried diagenesis to micritic limestone

buried as O crust moves away from the ridge to greater depth

Question 19

Beach

Answer 19

Includes Lattoral zone

sed dep here by rivers

High e and bilateral flow = sym ripple marks

May have shells + fossils (shelled orgs or trace fossils)

back= large clasts e.g. boulder/pebbles
Mid= gravel to C sand
In H2O= med + fine sand to mud (silt+clay)

clay settles out last as smallest

After mud oft limestone (remains of shelled orgs)

Question 20

Shallow sea

Answer 20

Lowest tide to cont shelf

sed dep here from rivers

lower e than beach + unidirectional flow = assym ripple marks

average H2O depth 130m

transgression = fining up

Regression = fining down

Also great e.g. of Walthers law
lime, Shale and sand

Question 21

What is a delta + description?

Answer 21

Where river flows into sea

Carries sed, meets the sea, loses E, dep sed

Delta= fan shape as load spreads wide

coaser closer to mouth
finer further out

Question 22

Conditions to preserve a delta

Answer 22

Little wave action and low tidal range

Non in Uk

Question 23

What causes distributary channels?

Answer 23

River channels quickly fills with sed as high dep
splits
distributary channels
many routes to sea

Question 24

Different sections of Delta Dep

Answer 24

Delta top- above water

Delta front- where river meets sea

Pro Delta- far Into sea

Question 25

Delta top

Answer 25

Above water
mostly dis channels + swap + flood plains

swap = anaerobic = form peat = diagentic processes = form coal

Trees grow here = form seat earth (sand and clay rich soil

delta switching- channles oft change course
lateral changes in coarse to sea

Sep dep here called TOP SETS
C grained + gravel to Channel sandstone (often crossbedded)

Question 26

Delta Front

Answer 26

River meets sea
C grained dep first to silt last (finer lower down and marine fossils may be found)

front of delta eventually migrates into sea - leads to vert succession (fining down)

Sed dep here called FORE SETS
C sand oft crossbedded

crescent shaped mouth bars form here

E lost as enters sea = very clean sand
as current removes fine sed

Question 27

Pro Delta

Answer 27

Dep at low E in deeper H2O

Dep here called BOTTOM SET
clay and silt

thinly bedded
lacks sed structures

lithify = form Shale
May contain marine fossils

Question 28

Pro Delta

Answer 28

Dep at low E in deeper H2O

Dep here called BOTTOM SET
clay and silt

thinly bedded
lacks sed structures

lithify = form Shale
May contain marine fossils

Question 29

sed sequences in Delta

Answer 29

form as Delta progrades into sea

D top overlays earlier D front

Shale-silt-sandstone-seat earth-coal (upward)

coal and roots give away

Question 30

Formation of disbrutary mouth bars

Answer 30

Cresent shaped mouth bars

silt and sand

where dis channel enters sea

Question 31

Sed transport in rivers

Answer 31

Sorted by size

often sub mature

C nearer source
med downstream e.g. sand
fine at mouth e.g. clay

some rivers end in shallow marine=quick dep

Question 32

Sed transport by wind

Answer 32

Min mature
eroded by attrition and abrasion

calcite sometimes present
usually in sol to dry and arid

texturally mature (W rounded and sorted)

Highest E

Question 33

Sed transported by Glacier

Answer 33

Poor sorted
tillite has large range

angular

Glacial till = dep name

May be transported by melt water = fluvial glacial dep= like river

Question 34

Shallow siliciclastic

Answer 34

sep dep in littoral zone (H to L tide)

High E

also dep on cont shelf

see sorting with distance

Question 35

Types of Conglomerate

Answer 35

Polymicritic = C grained sed rock containing clasts of many diff rock types

Oligomictic = “ few diff rock types

Monomicritic = “ single rock type

Question 36

Dep in shallow siliciclastic enviros basic

Answer 36

Beach and Shallow sea