7: Soil and Loess

Question 1

What is the main problem with using soils as global paleoclimate archives?

Answer 1

Not very well preserved usually

Question 2

What are the two main special situations of high accumulation rates which can preserve soil in the paleoclimate record?

Answer 2

Floodplains, windblown dust (loess)

Question 3

What is the primary location of paleoclimatic archives of soil, and why is this location timeless?

Answer 3

South of the furthest reach of glacial ice sheets, thus band across asia – glaciers do not reach to erode archive

Question 4

Where is loess most often formed?

Answer 4

Periglacial regions – marginal to ice cover

Question 5

When is loess most readily formed in periglacial conditions?

Answer 5

Cold periods

Question 6

Besides periglacial sources of loess, what would be the other potential source?

Answer 6

Desert derived

Question 7

What are the two factors of loess grains?

Answer 7

Usually silt sized, tend to be the same size – well sorted

Question 8

What colour dust does goethite produce?

Answer 8

Orange

Question 9

What colour dust does haematite produce?

Answer 9

Red

Question 10

What mineral produces red dust?

Answer 10

Haematite

Question 11

What mineral produces orangey dust?

Answer 11

Goethite

Question 12

What are the most common magnetic minerals in loess?

Answer 12

Haematite/goethite, yet still not very common

Question 13

What are the three main factors of loess source areas?

Answer 13

Extensive, Seasonally dry, Non-vegetated

Question 14

Pedogenisis is a function of what 5 main things?

Answer 14

Time, Climate, Parent material, Organic activity, Relief

Question 15

For the Chinese case study, soil formed from loess after how many years?

Answer 15

~100 years (quick for soil formation)

Question 16

What are the three factors that make loess such a good paleoclimate archive?

Answer 16

Similar grain size, Well mixed by transport, Good for magnetic measurements

Question 17

Why is well mixed loess advantageous for paleoclimate archives?

Answer 17

Reduces the variability of a major source

Question 18

What is the most common domain sized magnetite grains found, and what proxy confirms this?

Answer 18

SD, Xarm

Question 19

What are the seven soil condition controls which effect magnetic content?

Answer 19

(1) Soil moisture
(2) Temperature
(3) Organic matter input and consumption
(4) Bioturbation
(5) Oxygen availability
(6) Soil age
(7) Burning of vegetation

Question 20

For the Russian Steppes example, the highest susceptibility (most magnetic) was found to have the highest ____.

Answer 20

Rainfall

Question 21

Too much rainfall (>____mm) results in soil being too __ or __ for magnetic mineral formation

Answer 21

2000mm, acidic or wet

Question 22

Insufficient drainage/too ___ rich (acidic) results in what?

Answer 22

Organic, Fe in solution (ferrous ions)

Question 23

Too dry/insufficient ___ results in what?

Answer 23

Organic matter, Fe oxidized (haematite)

Question 24

In alkaline and slightly reducing conditions, what occurs in soils?

Answer 24

Fe as magnetite (pedogenic enhancement)

Question 25

What is the term for when a soil is too wet/organic rich?

Answer 25

Gleyed

Question 26

Rainfall generally has a rough link with what parameter, however crude, and why?

Answer 26

Susceptibility, soil moisture

Question 27

Pedogenic magnetite is generally produced during what intervals, associated with what?

Answer 27

Wetter intervals (interglacials)

Question 28

Besides SD magnetite and haematite/goethite, what else enhances X in soils?

Answer 28

SP magnetite content

Question 29

How can we determine rough estimates of rainfall of the past?

Answer 29

Using susceptibility of todays soil as a marker/proxy

Question 30

In China during an interglacial, when does the most rainfall occur and why?

Answer 30

Summer – monsoon

Question 31

In China during a glacial period, when does the most rainfall occur and why?

Answer 31

Winter – monsoon

Question 32

Where does most of the loess come from in China during a glacial period?

Answer 32

Siberia/Mongolia

Question 33

With the low susceptibility during loess deposition, what is expected of grain size and what does this show?

Answer 33

Larger grain sizes – stronger winds able to carry larger grains

Question 34

What could be a magnetic effect of natural fires or burning crops?

Answer 34

Thermal transformation of weakly magnetic minerals in presence of organic matter

Question 35

How was the dating sequence of Chinese loess deposits determined?

Answer 35

Magnetic reversals and the identification of chrons and sub-chrons

Question 36

In Poland, there is examples of a ___ soil region sandwiched by loess layers, where susceptibility is lower than the loess.

Answer 36

gleyed