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382: Environmental Magnetism > 7: Soil and Loess > Flashcards

7: Soil and Loess Flashcards

1
Q

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

A

Not very well preserved usually

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2
Q

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

A

Floodplains, windblown dust (loess)

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3
Q

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

A

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

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4
Q

Where is loess most often formed?

A

Periglacial regions – marginal to ice cover

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5
Q

When is loess most readily formed in periglacial conditions?

A

Cold periods

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6
Q

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

A

Desert derived

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7
Q

What are the two factors of loess grains?

A

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

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8
Q

What colour dust does goethite produce?

A

Orange

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9
Q

What colour dust does haematite produce?

A

Red

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10
Q

What mineral produces red dust?

A

Haematite

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11
Q

What mineral produces orangey dust?

A

Goethite

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12
Q

What are the most common magnetic minerals in loess?

A

Haematite/goethite, yet still not very common

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13
Q

What are the three main factors of loess source areas?

A

Extensive, Seasonally dry, Non-vegetated

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14
Q

Pedogenisis is a function of what 5 main things?

A

Time, Climate, Parent material, Organic activity, Relief

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15
Q

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

A

~100 years (quick for soil formation)

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16
Q

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

A

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

17
Q

Why is well mixed loess advantageous for paleoclimate archives?

A

Reduces the variability of a major source

18
Q

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

A

SD, Xarm

19
Q

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

A

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

20
Q

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

A

Rainfall

21
Q

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

A

2000mm, acidic or wet

22
Q

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

A

Organic, Fe in solution (ferrous ions)

23
Q

Too dry/insufficient ___ results in what?

A

Organic matter, Fe oxidized (haematite)

24
Q

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

A

Fe as magnetite (pedogenic enhancement)

25
Q

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

A

Gleyed

26
Q

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

A

Susceptibility, soil moisture

27
Q

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

A

Wetter intervals (interglacials)

28
Q

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

A

SP magnetite content

29
Q

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

A

Using susceptibility of todays soil as a marker/proxy

30
Q

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

A

Summer – monsoon

31
Q

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

A

Winter – monsoon

32
Q

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

A

Siberia/Mongolia

33
Q

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

A

Larger grain sizes – stronger winds able to carry larger grains

34
Q

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

A

Thermal transformation of weakly magnetic minerals in presence of organic matter

35
Q

How was the dating sequence of Chinese loess deposits determined?

A

Magnetic reversals and the identification of chrons and sub-chrons

36
Q

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

A

gleyed

382: Environmental Magnetism (7 decks)

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