Hello, can anyone explain what evidence a flood would leave behind in a sedimentary layer?

Thank you.

Wheelspawn wrote:Hello, can anyone explain what evidence a flood would leave behind in a sedimentary layer?

Thank you.

Sediment?

Varangian wrote:

Wheelspawn wrote:Hello, can anyone explain what evidence a flood would leave behind in a sedimentary layer?

Thank you.

Sediment?

You are baffling us with science!

"Flood" is a bit generic term and the literature is overwhelming on this. Anyway a common feature of all sediments deposited in water is the grading (i.e. granular size decreasing towards the top because of decreasing energy of the flow). Lamination of sediments is another common characteristics and depends on the fluid/sediment ratio and local fluid dynamics.
Sediment texture, structure and depositional characters greatly differ from each point of the depositional environment.

The MIT usually has very useful notes that are open access. Here it is the basic sedimentology course:
http://ocw.mit.edu/courses/earth-atmosp ... ure-notes/

trubble76 wrote:

Varangian wrote:

Wheelspawn wrote:Hello, can anyone explain what evidence a flood would leave behind in a sedimentary layer?

Thank you.

Sediment?

You are baffling us with science!

Varangian wrote:
Sediment?

Yes, but sediments are deposited by more than just water, am I right?

I think you need to be a little more explicit in your question.

I had a flood in my kitchen and it left a layer of guck on the floor eg.

Asahfall sediments, pyroclastic flow sediments, wind deposited sediments. A lot more to sedimentation that just water.

RS

Is this question in relation to debunking creationists assertions about "flood geology"

Then "This would have created many hundreds, or thousands of layers that buried lots and lots of dead things" -that's what the creationists usually say.

The problem is that there are many different kinds of flooding and many different types of sedimentary layers that floods could lay down.

The classic floodplain layers being fine sediments (compared to the fluvial channel deposits of their associated riverbed facies) laid down as relatively still flood waters that allow muds and silts to settle out.

Then you have the type of catastophic flood from dams breaking - especially seen in Glacial lake outburst flooding. Which obviously erode and deposit lots of coarse clastic material.

How about the easier question:-
Can anyone explain what evidence a flood would not leave behind in a sedimentary layer?

That might be easier to explain. Especially using facies association models to explain what associated sedimentary layers one should see in the stratigraphic record that would not show up in flood layers.

See some of my own posts regarding this:-

Dune Facies

Alluvial Fan Facies

Neither of which would be found in flood deposits (though I suppose that some alluvial fan deposits could be said to include sediments from flooding events).

So you would not expect to see things like aeolian facies, dessication cracks, major unconformities – the list goes on of things that we do see in the rock record that a flood would not leave behind.

The key point being that it is the association of different sedimentary layers found in the rock record that would indicate the paleoenvironment under which the layers were laid down. So even if you find that there are layers that are compatible with flood deposits in one localised area, without looking at the surrounding strata to find under which context this flooding took place e.g. finding associated river channel deposits indicating a fluvial environment with river and floodplain deposits.
As per the block diagrams below:-

The overbank or floodplain deposits being in green and the figure D showing how all these look in the rock record after deposition.

If it's deposits from Glacial lake outburst flooding you would expect to see evidence of glaciation associated with the flood deposits like drumlins and terminal moraine etc.

I hope that this helps.

Wheelspawn wrote:

Varangian wrote:
Sediment?

Yes, but sediments are deposited by more than just water, am I right?

My sediments exactly.