Which Statement is True About Sedimentary Rock Grains?

[SUDOnym]

Hi there

I am a physics teacher but also teach all sciences up to age 13. Have encountered an mcq on rocks (that I am teaching to a class of 11 year olds (year 7))which I cannot answer:

A sedimentary rock has very small grains.
Which statement is true?
A The grains were deposited by fast-flowing water.
B The grains were deposited by a glacier.
C The grains could have been deposited by water or by the wind.
D We cannot say how the grains were
transported.

Please help me out if you know the answer!

Thanks

 

[Borek]

Glacier transports everything, including large boulders.

 

[SUDOnym]

Thanks... are you sure that's the answer here... I was thinking it might be either C or D...

 

[Borek]

I never told B is the answer, I pointed to the fact that should help _find_ the answer.

 

[SUDOnym]

oh right... is it C then?

 

[Borek]

That would be my guess, as good as yours.

 

[Ophiolite]

Grain size, while partly dependent upon source rock and transport medium, is more related to the energy of the environment and the time over which this energy is applied to the grains.

Thus distance from source provides time for grain size to be reduced by impact and abrasion.
Or, as on a beach, repeated reworking of the grains will diminish their size.

Fast flowing water will easily support small grains, so A is wrong.
Glaciers can deposit boulder clay, a very fine grained material, but as Borek has noted they may also deposit boulders.

The grains could have been deposited by water or wind, but as we have seen glaciers could also be implicated, I have to opt for D.

 

[Borek]

Definitely it is not the best question ever asked.

 

[AlephZero]

Definitely it is not the best question ever asked.

I agree. Google for "oolites".