Sedimentary rocks

Question 1

weathering definition

Answer 1

the in situ chemical alteration + mech and bio breakdown of rocks by exposure to atmosphere, water and organic matter

Question 2

types of weathering

Answer 2

chem
bio
mechanical

Question 3

chem weathering

Answer 3

chemicals in water making changes to rocks

carbonation- CO2 + H20—-> carbonic acid
ground water = more acidic than rainwater
limestone susceptible, dissolves to clay particles

hydrolysis- water reacts with silicate minerals e.g. feldspar
left over often clay
speed up with carbonic acid

Question 4

mechanical weathering

Answer 4

crumbling due to rain, wind ect

exfoliation- outer layers breakdown first, day and night temps cause expansion and contraction
outer layers most effected so break first

Frost shattering-
water enters cracks/ joints and bedding planes
expands by 9%
creates pressure
causes cracks and fractures
creating scree

pressure release-
rocks under pressure
buried
pressure reduces due to weathering of overlays
expands in direction of pressure

Question 5

Bio weathering

Answer 5

weakening and disintegration of rocks by plants, animals and microbes

root action-
grow along bedding planes, joints amd cracks
force rock apart widening/ causing fractures
more susceptible to carbonation and hydrolysis
trees swing I’m wind and prise apart fractures

burrowing-
bring rocks to surface
more easy to weather
more carbonation + hydrolysis
and more atmospheric gases in contact with rock

Question 6

Examples of weathering in diff environments

Answer 6

Arctic = mostly frost shattering

temperate = everything

warm arrid = exfoliation

humid tropical = burrowing and root and chemical

Question 7

Types of sed transport

Answer 7

Attrition- carried by water and broken down by hitting eachother repeatedly, frequent collisions

abrasion- grinding and wearing down of material by dragging and hurling

solution-when dissolved material is carried by a river- transport of ions dissolved in water

erosion- transport of rocks/fragments by rivers, wind, sea, gravity and ice

saltation- the bouncing of sand grains as they are picked up carried along and dropped repeatedly by water

traction- rolling/ sliding of large grains along river bed/shore

suspension- very fine sed transported without touching Earth’s surface

Question 8

grain shape/ roundness

Answer 8

spherictity- measure of how close to spherical something is

grains have a higher or lower spherictity

they are also either
very angular, angular, sub angular, sub rounded, rounded or well rounded

this describes the smoothness

Question 9

Grain size

Answer 9

Phi scale
logarithmic - used for large ranges

phi decreases size increases

diameter phi example
> 2 -2–8 gravel
2 -1 very coarse sand
1 0 coarse sand
0.5 1 med sand
0.25 2 fine sand
0.125 3 very fine sand
0.0625 4 silt
0.0039 8 clay

Question 10

Sorting of sed

Answer 10

very well sorted (all same size) , well sorted, mod sorted, poorly, very poorly (all diff sizes)

Question 11

grain size analysis

Answer 11

1. Weigh sed
   2.arrange sieve stack largest at top to smallest with solid pan at bottom
   3.place dry sed sample in top pan
   4.agitate sieve stack for 1min
   5.seperate sieves and weigh mass of sed in each
2. use data to produce graphs/ cumulative freq curves to determine degree of sorting

Bar graphs: y axis- relative mass (g)
x axis- sieve size (phi)
poorly sorted would be evenly spread
Well would be mostly 1 bar

Cumulative frequency graphs: calc to relative percentage mass of each sieve

calc cumulative percentage mass by adding up % as you go down table

Y axis - cumulative mass (%)
X axis- sieve size (phi)
draw curve

calc coefficient of sorting
(84phi - 16phi)/2

<0.5 well
0.5-1 mod
>1 poorly

Question 12

characteristics of sed transported by wind

Answer 12

Wind-
higher energy

small+ med grains

mostly quartz as min mature

Well rounded+ high spherictity

very well sorted

Question 13

characteristics of sed transported by ice

Answer 13

low energy

large range of grain sizes

mineralogically immature

angular

poorly sorted

Question 14

characteristics of sed transported by rivers

Answer 14

high energy

large range of grain sizes
finer further down

mostly quartz- more mature down stream

angular to rounded downstream

progressively more sorted

Question 15

Characteristics of sed transported at beach

Answer 15

high energy

majority coarse
some fine/med

quartz- shell fragments and pebbles

sub rounded - rounded

poorly sorted

Question 16

characteristics ofbsed transported by gravity

Answer 16

low energy

large range of grain sizes

minerals varied- whatever in og rock

angular

poorly sorted

Question 17

Process of diagenisis

Answer 17

all the changes that take place in sed at low temp and pressure, at or near to Earth’s surface

Compaction-
layers of sed acculate one on top of another

mass produces pressure- deeply buried

causes Compaction

pressure dissolution (points of grains resting on eachother dissolve away in pressure solution) and crystallisation occur

grains become closely packed and porosity decreases

mud can be Compacted by 80% as flat platy minerals align
sand only 40% as grains have to bend and fracture as more equi

cementation-
High permeability (sandstone and limestone)

groundwater containing minerals I’m solution flows through pore spaces

minerals are precipitated

form cement binding grains together
sandstone- quarz/silicate cement
limestone- calcite cement

mineralogical changes-
limestone made of unstable aragonite

changes to become more stable calcite during diagenesis (often seen in fossils(

Question 18

what happens to plants in diagensis

Answer 18

plants decay anaerobically form peat

if peat is buried and pressure increases it expels water and other volatiles

reduces volume and increases proportion of carbon

as diagenisi continues gradual becomes coal