Interlude B: A surface veneer: Sediments and soils
B.1 Introduction
Sediment: broadly defiedd oinsinstns of loonse fragmeitns of ra kns or miieralns brokei of of bedro kd
miieral rynstalns that pre ipitate dire tly out of waterd aid nshellns or nshell fragmeitns. Produ ed by
weathering: the phynsi al aid hemi al breakdowi of pre-exinstig ro k at or iear the Earth’ns nsurfa e.
Sedimeit formns a nsurfa e veieerd or overd oi bedro k. Cai go from 0 km to 20 km ii thi kiensns
where deepd nsedimeit-flled deprensnsioins alled sedimentary basins have developed. Iitera toi with
water aid orgaiinsmns may modify nsedimeit over tme aid trainsform it ii soil, ai ensnseital material
for life.
B.2 Weathering: forming sediment
Whei you ut ii bedro k you’ll fid ro k with the nsame miieralns aid texture ans whei it frnst formed:
alled frensh ro k. Be aunse of iitera toi with hydronsphere aid atmonsphere it doensi’t nstay frensh
forever. They uidergo weathering: ombiiatoi of pro ensnsens that break up aid orrode nsolid ro k
aid may eveitually trainsform it iito loonse debrins. Regolith: layer of debrins/detrituns.
Physical weathering
Physical or mechanical weathering: breakns ro k iito ui oiie ted clasts (graiins or hui kns) Ea h nsize
raige hans a iame.
Jointing
Exhumaton: ro k deep ii the Earth are uider a lot of prensnsure aid are warmer thai ro kns by the
nsurfa e. Over loig periodns of tme the nsurfa e of the Earth nsurfa e griid away aid remove
overburdeid nso ro k formerly at depth rinsens lonser to the nsurfa e thins pro ensns ins alled Exhumaton.
Prensnsure from depth de reansens. Chaige ii prensnsure aid temperature makens the ro k haige. Su h
haigens ai geierate for ens nsuf ieit to break ro k apart. Natural ra kns that form ii ro kns due to
removal of overburdei or due to ooliig are kiowi ans joints.
Exfoliaton: joiitns are parallel to the grouid nsurfa ed nso ro k peelns of like layerns of ai oiioi.
Formatoi of joiitns turins formerly iita t bedro k iito nseparate blo kns. Gravity thai pullns them dowi.
May olle t ii ai aproi of talus, the ro k bubble at the banse of a nslope.
Frost wedging
Whei water trapped ii a joiit freezensd it for ens the joiit to opei aid may aunse the joiit to grow.
Helpns break blo kns free from iita t bedro k.
Root wedging
Ans rootns grow the apply for e oi their nsurrouidiigns. Whei they grow ii joiitnsd the ai punsh them
opei.
Salt wedging
Dinsnsolved nsalt ii grouidwater pre ipitatens aid growns ans rynstalns ii opei pore nspa ens (arid limate).
Weakeins the ro k. Alnso ii out rop fa ens ii oanstal areansd were nsalt nspray per olatens iito ro k aid
thei driens.
Thermal expansion
High heatd outer layer ro k expaidns. Oi ooliig the layer oitra tns. Thins haige breakns the ro k iito
nsheetlike pie ens.
B.1 Introduction
Sediment: broadly defiedd oinsinstns of loonse fragmeitns of ra kns or miieralns brokei of of bedro kd
miieral rynstalns that pre ipitate dire tly out of waterd aid nshellns or nshell fragmeitns. Produ ed by
weathering: the phynsi al aid hemi al breakdowi of pre-exinstig ro k at or iear the Earth’ns nsurfa e.
Sedimeit formns a nsurfa e veieerd or overd oi bedro k. Cai go from 0 km to 20 km ii thi kiensns
where deepd nsedimeit-flled deprensnsioins alled sedimentary basins have developed. Iitera toi with
water aid orgaiinsmns may modify nsedimeit over tme aid trainsform it ii soil, ai ensnseital material
for life.
B.2 Weathering: forming sediment
Whei you ut ii bedro k you’ll fid ro k with the nsame miieralns aid texture ans whei it frnst formed:
alled frensh ro k. Be aunse of iitera toi with hydronsphere aid atmonsphere it doensi’t nstay frensh
forever. They uidergo weathering: ombiiatoi of pro ensnsens that break up aid orrode nsolid ro k
aid may eveitually trainsform it iito loonse debrins. Regolith: layer of debrins/detrituns.
Physical weathering
Physical or mechanical weathering: breakns ro k iito ui oiie ted clasts (graiins or hui kns) Ea h nsize
raige hans a iame.
Jointing
Exhumaton: ro k deep ii the Earth are uider a lot of prensnsure aid are warmer thai ro kns by the
nsurfa e. Over loig periodns of tme the nsurfa e of the Earth nsurfa e griid away aid remove
overburdeid nso ro k formerly at depth rinsens lonser to the nsurfa e thins pro ensns ins alled Exhumaton.
Prensnsure from depth de reansens. Chaige ii prensnsure aid temperature makens the ro k haige. Su h
haigens ai geierate for ens nsuf ieit to break ro k apart. Natural ra kns that form ii ro kns due to
removal of overburdei or due to ooliig are kiowi ans joints.
Exfoliaton: joiitns are parallel to the grouid nsurfa ed nso ro k peelns of like layerns of ai oiioi.
Formatoi of joiitns turins formerly iita t bedro k iito nseparate blo kns. Gravity thai pullns them dowi.
May olle t ii ai aproi of talus, the ro k bubble at the banse of a nslope.
Frost wedging
Whei water trapped ii a joiit freezensd it for ens the joiit to opei aid may aunse the joiit to grow.
Helpns break blo kns free from iita t bedro k.
Root wedging
Ans rootns grow the apply for e oi their nsurrouidiigns. Whei they grow ii joiitnsd the ai punsh them
opei.
Salt wedging
Dinsnsolved nsalt ii grouidwater pre ipitatens aid growns ans rynstalns ii opei pore nspa ens (arid limate).
Weakeins the ro k. Alnso ii out rop fa ens ii oanstal areansd were nsalt nspray per olatens iito ro k aid
thei driens.
Thermal expansion
High heatd outer layer ro k expaidns. Oi ooliig the layer oitra tns. Thins haige breakns the ro k iito
nsheetlike pie ens.
