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I came across this question in my text book: "During a visit to a mountainous area, students noticed a high mountain consists of 3 different parts: The top of the mountain consists of fossiliferous limestone. The middle of the mountain consists of fine grained rocks. The foot of the mountain consists of thick layers of boulder, gravel and tree trunks.

Which of those parts belongs to a marine environment? And which belongs to an aerobic environment? And which belongs to a river environment?"

My attempt at a solution is this:

The top (fossiliferous limestone) -----> marine environment.

The middle (fine grained rocks) -----> aerobic environment.

The base (boulder, gravel and tree trunks -----> River environment.

I wanted to know if my answer was correct or not, because the answer to the question in the book was:

the top---> marine environment.

the middle---> river environment.

the base --> aerobic environment.

Could someone please clarify it for me?

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    $\begingroup$ Unless there is more information, I think you are right and the book is wrong. But it's not a very clear example. The fossiliferous limestone is certainly marine. If 'fine grained rocks' is shale, it's formed at the seafloor, often aerobic. Bolulder and gravel suggests high energy as in a river, but however if the there are coal seems as in the tree trunks, that could also suggest an aerobic environment. $\endgroup$ – Tactopoda Apr 7 '17 at 0:57
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    $\begingroup$ @Tbb, No, actually there was no more info. And it said that the base of the mountain contains both gravel and tree trunks, which made me confused. $\endgroup$ – Asmaa Apr 7 '17 at 2:37
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    $\begingroup$ Regarding which layer is from a river environment, it may also depend on which section of an ancient river has been preserved - head waters, the tail end of the river or somewhere in between. The further down river, generally, the small the grain size of the sediments in the river. Having a layer composed of boulders & gravel suggests there may not have been time for gravitational segregation of materials & that it may not be from a river . $\endgroup$ – Fred Apr 7 '17 at 9:35
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Because the top layer is marine, you're being asked to think of the sequence being "coastal" in origin, where there is ocean, coastal plain, and inland mountains. In this scenario, two things are happening in tandem: the mountains are eroding and sea level is rising.

As the mountain erodes, boulders and cobbles (eroded from steep slopes) bury trees and form coarse conglomerates and source material for the coastal plain deposits, which are the middle unit of your sequence. As sea level rises due to local subsidence or a global sea level rise, the marine environment marches steadily inland depositing sands and then limestones.

Assuming no unconformities, yours is a textbook example of a continuous depositional sequence!

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    $\begingroup$ But in your answer, you didn't mention anything about a river environment. And still, I don't know which answer is correct? Mine or the textbook's? $\endgroup$ – Asmaa Apr 13 '17 at 11:47
  • $\begingroup$ The book is correct for the answer I gave above: "As the mountain erodes, boulders and cobbles (eroded from steep slopes) bury trees and form coarse conglomerates and source material for the coastal plain deposits, which are the middle unit of your sequence. As sea level rises due to local subsidence or a global sea level rise, the marine environment marches steadily inland depositing sands and then limestones." $\endgroup$ – Knob Scratcher Apr 17 '17 at 3:08

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