Wednesday, 11 January 2012

Geological Evidence Against the Flood - Part 1

I've decided, now that all coursework is handed in and I only have to focus on exams, that I will start a series of blog posts on geological arguments against a global flood. I'm not going to simply recycle commonly used arguments, though some of them might be well known, as I intend for these to be quite personal. By personal I mean things which I have observed in the field or things which have cropped up repeatedly in my studies.

Number 1 - Turbidites

Turbidites are not unknown to creationists who have done a fair bit of research, as they sometimes see them as supporting their own flood position. Turbidites are geological structures which are formed rapidly by turbidity currents, a form of underwater landslides. Sometimes they are easy to recognise, as they often consist of alternating layers of mud and sand, with some distinct structures often on the bottom of the sandstone (sole structures such as flute casts or groove casts). The nice, undisturbed deep sea floor steadily accumulates mud, until it is disturbed by a sudden flow of coarser material which is rapidly deposited on top. The coarser material often drags debris over the mud, creating scoops and scours which are filled by sand.

The image below shows some of those sole structures. Sadly not a good picture, as it was hastily taken of the ones I have on top of my freezer (a common depositional environment). What you can see is the bottom of the sandstone, as these grooves were formed in the underlying mud and infilled with sand carried by the turbidity current.


Turbidites come in a variety of forms, often depending on how close to the turbidity current the deposit occurs. If it is close to the current, then these things can be large and with a lot going on. If they are distant from the original current, then they can be tiny and with little going on. They also occur on a variety of scales, so simply being small does not mean that the turbidity current started far away. Turbidites are classified based on the Bouma Sequence, the ideal of which looks something like this:


So why is this a problem for flood geology? On first glance, it really does not seem like an issue, after all, creationists love examples of rapid deposition and these occur in deep water, so it is easy to understand how one could miss that they do no favours for the flood model. In order to explain why I see this as a problem for flood geology, we need to take a little trip to Wales...

At the start of June last year, I found myself in Penstrowed Quarry, looking at some turbidite deposits (from Early-Mid Wenlock, Silurian, if anyone is interested). It was a sunny day, with minor cloud cover, and we had to do a sedimentary log of parts of the sequence. This involved getting right up to the rock face, taking measurements of bed thicknesses, how large the grains were (if visible), whether there were any changes in the individual beds, whether there were any distinctive features, and so on. Below is a picture of me doing just that...


I only managed to record data for seven of the beds, as I attempted to measure the eighth only to have the scree below me give way, causing me to tumble several metres on shale and sandstone. I only suffered a couple of cuts, though the log I was drawing was ruined. 

What I recorded (in my notebook) shows the typical alternation of sandstones with shales found in a turbidite. The sands were obviously deposited quite rapidly and sole structures were common, but the muds are a different matter, especially as many were hemipelagites. The Oxford Dictionary of Earth Sciences defines a hemipelagite as "A deep-sea, muddy sediment formed close to continental margins by the settling of fine particles, in which biogenic material comprises 5–75% of the total volume and more than 40% of the terrigenous material is silt." The muds were not homogeneous, showing changes in deposition, though they did all settle out of suspension slowly, unlike the rapidly deposited sandstones. 

So what we see is a normally quiescent environmental setting, where muds settle out of suspension slowly, containing biogenic material (likely planktic). This environment was intermittently interrupted by turbidity currents which deposited a large amount of coarser sediment. At this point we could ask some interesting questions, to which I do not know the answers. Does the hemipelagite fauna change through the sequence? Do the turbidites become increasingly proximal or distal? 

Below you can see this sequence more clearly and can make out the distinct alternation between the two rock types. A global flood may be able to produce turbidite deposits on a small scale, but it would be a stretch, considering the large amount of shale in this deposit in particular. 


But if you are observant, you might have noticed that there are a lot of beds here and that they are not horizontal. There are hundreds of alternations between slow deposited muds and rapidly deposited sandstones, formed in the deep sea. These were buried deeper and deeper, undergoing the diagenetic processes which turn them into the rock we see today. These were later thrust up to ground level in mid-Wales and tilted eighty degrees. These are not rapid processes, but exceptionally slow. If a global flood explains the turbidites, then what explains the processes of uplift and tilting which followed their deposition? If the flood explains the later tectonic processes, how are the depositional events explained?

This is not small scale stuff, just look at the picture below. 


Tens of metres were exposed in this small part of the quarry (if not hundreds). It is easy to think of the quarry as an isolated occurrence, but context is always key. These deposits extend for tens of kilometres through the Welsh countryside. There were literally thousands (if not millions) of alternating depositional conditions, between slow mud deposition and rapid sand deposition, going on in that region of the deep sea. These many thousands of turbidites were slowly thrust up into the Welsh countryside and tilted. As they are at eighty degrees, one can follow them along in the direction of the bedding, using the law of superposition, and follow the beds into younger or older strata (to the right in the images for younger strata) and again, changes in environment are found. 

Simply learning about something like turbidites is not always enough, actually seeing them in the field shows just how much was going on in our deep past. These deposits are not unique and turbidites also come in a wide variety of forms. Although I believe turbidite deposits, especially those in Penstrowed Quarry, are strong evidence that a global flood cannot explain the rock record, they should still not be taken in isolation. I will be presenting other arguments against the global flood, which, when taken with evidence such as turbidites, makes one wonder how anyone with any geological knowledge could take flood geology seriously. Stay tuned for more. 

10 comments:

Stripe said...

Undersea landslides cannot travel the distances required to deposit tubidites.

Anonymous said...

http://www.icr.org/article/submarine-flow-catastrophic-flood/

*

http://static.icr.org/i/pdf/technical/Tight-Fold-and-Clastic-Dikes-Rapid-Deposition-Deformation.pdf

The Palaeobabbler said...

Stripe:

Can you give a bit more information? Some data to support your claim and a better explanation that what was presented perhaps? (To be honest, my explanations of turbidity currents was ridiculously oversimplified.)

Anonymous:

Your first link is a good example of what I mentioned - creationists do not address turbidites properly. I will have to look into the second link, as it is not really relevant to this post and I have never heard of the locality in question.

The Palaeobabbler said...

It appears my ability to use correct grammar has failed me too...

Stripe:

I can't help but add (seeing as you are taking me on apparently) that the main thrust of my argument in my blog post only requires one thing with regards to turbidites - that the sandstones are deposited rapidly. Their exact mode of deposition is unlikely to be relevant to my main points.

Stripe said...

Greetings - apologies for the seeming hit and run nature of my first post. :)

The problem with turbidite explanations is they are unreasonable. A reasonable explanation requires a large scale, wide area and repeating phenomenon. And the layers we see leave no significant time between layers to conclude anything but that the layers were all made together.

The mechanism for generating turbidites needs to be reasonable and the only reasonable mechanisms point to a global flood.

The Palaeobabbler said...

No worries about the gap in posting, I am a bit too busy lately to even notice.

"The problem with turbidite explanations is they are unreasonable. A reasonable explanation requires a large scale, wide area and repeating phenomenon."

I'm not sure I see your point, as turbidites can be wide-scale and repeated. If I were saying that this is how all strata was laid down, then your point would make sense to me, but I am not. I am saying that turbidite deposits (even very localised ones) cannot be explained using flood geology.

"And the layers we see leave no significant time between layers to conclude anything but that the layers were all made together."

Time between layers? The layers we do see show significant time. As the post mentioned, the muds were deposited slowly and show changes within them (those reflect environmental changes). If the layers were all deposited at the same time, we would not see an alternation of sands and muds and we would not see muds with lamination. Instead we would see the coarser sand at the bottom, fining upwards into the muds.

"The mechanism for generating turbidites needs to be reasonable and the only reasonable mechanisms point to a global flood."

What is unreasonable about current models for turbidite generation? The flood would not cause repeated turbidites on such a massive repeated scale.

Grant Dexter said...

Turbidite deposiition models are based around undersea landslides and background deposition. It's this model that is unworkable. I favour a model that sorts deposits to the same degree over the entire deposition environment. Landslides are controlled by two things, gravity and friction. On land, they only travel very short distances from the point of failure. these distances should be even shorter under water.

A much more reasonable mechanism for wide-area sorting is tsunami. In a situation where lots of sediment is provided and lots of tsunami pass over, the layers we see will be formed quickly.

The Palaeobabbler said...

Grant:

"Turbidite deposiition models are based around undersea landslides and background deposition. It's this model that is unworkable"

You don't actually seem to be saying why.

"I favour a model that sorts deposits to the same degree over the entire deposition environment. "

But that is not what we find in turbidite deposits. A distal turbidite is recognisably different to a proximal turbidite. This image might be helpful. http://www.sepmstrata.org/thinsections/images/fig31.jpg

"Landslides are controlled by two things, gravity and friction. On land, they only travel very short distances from the point of failure. these distances should be even shorter under water."

How are we meant to verify your claim without figures? What is a short distance to you?

"A much more reasonable mechanism for wide-area sorting is tsunami. In a situation where lots of sediment is provided and lots of tsunami pass over, the layers we see will be formed quickly."

Considering that I keep putting emphasis on the quiescent conditions required for the deposition of mud, I am baffled as to why you have ignored that point. It is key to this discussion. Tsunamis deposit sediment on land, but these are deep marine deposits. Just do a quick Google search for tsunami deposits and you will find images which do not match turbidite deposits (not even close) such as these: http://walrus.wr.usgs.gov/tsunami/images/ITST_images/Fig4rev.jpg
http://walrus.wr.usgs.gov/peru2/images/amecosupe2.jpg

Out of curiosity, are you and Stripe the same person?

I'd like to see your data with regards to the extend to which turbidity currents can deposit sediment, otherwise your claims appear to have been pulled from nowhere.

Grant Dexter said...

I find the undersea landslides and background deposition model unworkable because we have wide areas of turbidite deposits that remain even and do not show the transitions you point out. Not that there aren't different zones.

"Short distance" for landslide flow away from the point of failure to me is less than the associated vertical drop. If you can show a landslide whose final mass distribution is, on average, farther from the base of its original position than it was from the top, I'll buy you a big mac combo. :)

Tsunami move through the entire body of water they travel through (unlike wind generated waves) assuming they haven't moved into deeper water. They should indeed affect the sea-floor.

Stripe and I have never been seen in the same room together. ;)

Yes, we are one and the same.

Thanks for your time.

Grant Dexter said...

What is the lateral extent of the strata you are looking at in your photos? I guess it is very extensive - though maybe difficult to track to other locations. And I guarantee each layer in it is a slightly thicker or thinner version of the previous one. No difference in depositional style.