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Author Topic:   Geology Question Re Turbidites
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 1 of 9 (509256)
05-19-2009 7:11 PM


Just a quick question for the geologists here --- has anyone ever actually directly observed a turbidite sediment being deposed by a turbidity current, or does the proposed origin of these sediments rest on inference alone?
If the latter, what do you see as the best evidence that turbidite sediments are, in fact, turbidite sediments?

Replies to this message:
 Message 3 by pandion, posted 05-20-2009 12:37 AM Dr Adequate has replied
 Message 5 by petrophysics1, posted 05-20-2009 1:49 PM Dr Adequate has replied

  
AdminNosy
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Message 2 of 9 (509259)
05-19-2009 7:56 PM


Thread moved here from the Proposed New Topics forum.

  
pandion
Member (Idle past 3000 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 3 of 9 (509274)
05-20-2009 12:37 AM
Reply to: Message 1 by Dr Adequate
05-19-2009 7:11 PM


I'm not sure of your specific intent, but my answer is yes, trubidite sediment formation has been observed. Examples are pyroclastic flows and avalanches. In fact, a 1929 earthquake in the Grand Banks produced such sediments. They are noteworthy because they broke transatlantic cables.

This message is a reply to:
 Message 1 by Dr Adequate, posted 05-19-2009 7:11 PM Dr Adequate has replied

Replies to this message:
 Message 4 by Dr Adequate, posted 05-20-2009 2:10 AM pandion has not replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 4 of 9 (509277)
05-20-2009 2:10 AM
Reply to: Message 3 by pandion
05-20-2009 12:37 AM


I'm not sure of your specific intent, but my answer is yes, trubidite sediment formation has been observed. Examples are pyroclastic flows and avalanches.
I don't see how you make that out. Gravity currents, yes. In any case I'm thinking of marine turbidity currents caused by slope failure.
In fact, a 1929 earthquake in the Grand Banks produced such sediments. They are noteworthy because they broke transatlantic cables.
I'm aware of the Grand Banks incident, but the attribution of the breaking of the cables to a turbidity current is based on inference: no-one checked directly that whatever broke the cables also deposed turbidite sediments, did they? Let alone being down there with a submarine to actually observe the deposition, which I guess is what I'm asking.

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petrophysics1
Inactive Member


Message 5 of 9 (509329)
05-20-2009 1:49 PM
Reply to: Message 1 by Dr Adequate
05-19-2009 7:11 PM


Dr. A writes:
Just a quick question for the geologists here --- has anyone ever actually directly observed a turbidite sediment being deposed by a turbidity current, or does the proposed origin of these sediments rest on inference alone?
If the latter, what do you see as the best evidence that turbidite sediments are, in fact, turbidite sediments?
I doubt someone was actually underwater when a slope failure event occured. However there are lots of sidescan sonar pictures and siesmic of this deposition along with core data.
After the delta front work was completed, Jim served as co-chief scientist with Dr. Arnold Bouma on the 1988 Deep Sea Drilling Project, Leg 96 in the Gulf of Mexico. This project focused on drilling of the latest lobe of the Mississippi Fan. Results from this project provided the first ground truth of the sedimentology and stratigraphy of the Gulf’s fan deposits below the thin blanketing hemipelagic sediments that cover the entire fan. Coarse facies found in the channels and distal fan lobes changed our model of fan deposition and supported the thrust by petroleum companies to explore for oil and gas in deep water fan deposits.
from : Doris Malkin Curtis Medal
In the early 80's I had the opportunity to fly around the Mississippi delta in a chopper with Jim Coleman looking at and landing at various different depositional areas in the delta. Phillips Petroleum spared no expense to keep their exploration geologists current. I made a lot of money for PPCo. and later myself off of what I learned from Jim. He had recently done the first sidescan sonar imagery of the delta slope and I got to see that as well. No problem seeing the turbidite channels and deposition but it wouldn't be for several years before the stuff was cored and it was seen just how coarse grained it was and the actual sedimentary sequence.
Lots of interest in this because if you put an oil platform in the wrong place it can end up dissapearing on you.
Here are a few free links.
http://kai.er.usgs.gov/...mex/centgulf/lcs/aapg97/index.html
Abteilung Oberflchengewsser - Eawag
http://jsedres.sepmonline.org/cgi/reprint/70/3/504.pdf
Abstract: Bryant Canyon/Fan and Rio Grande Fan Turbidite Systems: Shelf to Basin Modern Analogues for Productive Tertiary Mini-Basin Systems, by John E. Damuth, C. Hans Nelson, and Hilary Clement Olson; #90078 (2008)
http://www.springerlink.com/content/k17r387t7310tqj6/
Martin

This message is a reply to:
 Message 1 by Dr Adequate, posted 05-19-2009 7:11 PM Dr Adequate has replied

Replies to this message:
 Message 6 by Dr Adequate, posted 05-20-2009 4:28 PM petrophysics1 has replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 6 of 9 (509343)
05-20-2009 4:28 PM
Reply to: Message 5 by petrophysics1
05-20-2009 1:49 PM


Thanks for your post.
I doubt someone was actually underwater when a slope failure event occured.
As a matter of fact, I have found a small amount of footage of slope failure and turbidity currents, at the start of this video:
Such footage might be easier to get than you'd think, since I gather that a submarine can trigger slope failure.
But watching deposition is another matter: you'd have to be lucky enough to be there when a turbidite current went by, watch it depose sediment, and then immediately take a core to look for a Bouma sequence.
---
The 1996 Lake Brienz incident is nice, isn't it?
---
The reason I want to know is that I want to write about turbidite formation, and I should feel a proper Charlie explaining the inferences by which we know that turbidite sediments are deposed by turbidity currents if in fact we know this from direct observation.
---
Phillips Petroleum spared no expense to keep their exploration geologists current.
I bet they never spend a cent on teaching you about Noah's Flood though. Imagine how much more money you could have made if you'd based your work on God's Own Geology instead of wicked atheist lies, eh?

This message is a reply to:
 Message 5 by petrophysics1, posted 05-20-2009 1:49 PM petrophysics1 has replied

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petrophysics1
Inactive Member


Message 7 of 9 (509351)
05-20-2009 5:30 PM
Reply to: Message 6 by Dr Adequate
05-20-2009 4:28 PM


Dr.A writes:
I bet they never spend a cent on teaching you about Noah's Flood though. Imagine how much more money you could have made if you'd based your work on God's Own Geology instead of wicked atheist lies, eh?
What is funny about this is the only geologist I've ever known who is an atheist has a degree in theology from Oral Roberts University where he met John Morris and the rest of the ICR crew. His dream was to prove Noah's flood so he got a BS in geology from OK U and his masters from CU in Boulder. Even wrote some papers for ICR under an alias.
Bring the subject up and he will get instantly pissed about all religion in general.
Edited by Adminnemooseus, : Off-topic banner.

This message is a reply to:
 Message 6 by Dr Adequate, posted 05-20-2009 4:28 PM Dr Adequate has not replied

Replies to this message:
 Message 8 by pandion, posted 05-22-2009 12:09 AM petrophysics1 has not replied

  
pandion
Member (Idle past 3000 days)
Posts: 166
From: Houston
Joined: 04-06-2009


Message 8 of 9 (509465)
05-22-2009 12:09 AM
Reply to: Message 7 by petrophysics1
05-20-2009 5:30 PM


"
Way off-topic content hidden - Adminnemooseus"
Mindless censorship!
Edited by Adminnemooseus, : See above.
Edited by pandion, : No reason given.

This message is a reply to:
 Message 7 by petrophysics1, posted 05-20-2009 5:30 PM petrophysics1 has not replied

  
Dr Adequate
Member (Idle past 284 days)
Posts: 16113
Joined: 07-20-2006


Message 9 of 9 (509480)
05-22-2009 2:19 AM


So, here's what I wrote on the subject. Any criticisms and suggestions will be gratefully received.
In order to see turbidite sediments being deposited, you would have to be in the right place at the right time, where the right place would be in a submarine and the right time would be when a turbidity current happens to go past. And then you would need to take a core sample to confirm that what it deposited had the patterns of sediment that are postulated to be the results of deposition by turbidity currents.
We have not been able to find that any such observation has been made. Some reasoning is therefore required.
Note first of all that turbidity currents themselves are not hypothetical. They can be produced in the laboratory, as seen in the video
[i.e. the video in message #6 of this thread]. Slope failures are also not hypothetical, and can also be seen in the video, as can turbid flow. Furthermore, laboratory experiments confirm that the waning of a turbidity current does indeed result in graded sediments, as we would expect.
We know that whatever process forms these deposits must be happening in the present, because we can see freshly deposited turbidite sediments in the present day. But we also know that the process must be intermittent, partly because we can't see any continuous process forming these deposits on the sea floor, and partly because the grading from gravel up to mud would require a strong current, to transport the gravel, which must then wane (or the mud wouldn't settle). We know also that the initiation of the process must be fairly violent, to produce an impetus which will transport coarse sediments over distances of hundreds of kilometers. These events must also happen reasonably often, to judge by the number of turbidite deposits to be found on the ocean floor. The turbidity currents generated by slope failure would fit this bill.
Moreover, we know of no other cause that could transport such large clasts so far out to sea. This may seem like a mere argument from ignorance, but it gains force when combined with the following argument. We know that there are failures of the continental slope which are by the nature of their origin turbid. Therefore, these currents must transport sediment and deposit it in some form. If it is not deposited in the form of turbidity sediments, in what form is it deposited and where is it?
One frequently cited observation is the aftermath of the Grand Banks earthquake of 1929. In the hours following this, a number of transatlantic cables were severed. Their position was known, as were the exact times when they were cut. It is therefore possible to say that something capable of severing cables moved from near the epicenter of the earthquake at a speed of approximately 100 kilometers per hour.
Perhaps the closest anyone has got to direct observation of turbidite formation is the events in Lake Brienz in 1996. The lake showed distinct signs of an underwater landslip, including a sudden increase in the turbidity of the lake waters, a small (half-meter high) tsunami wave, and the release of a 200-year old corpse from the lake bed. Taking sediment cores from the lake revealed that an abnormal layer of sediment, 90cm thick at its thickest part, had been laid down concurrent with this event: the sediment graded vertically upwards from sand through silt to clay: that is, it looked just like turbidite sediment should. Further investigation suggested that the 1996 event was caused by accumulated sediment sliding down the slope of the Aare delta.
Edited by Dr Adequate, : No reason given.

  
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