Hermann,
The recent surge in salt movement in the Gulf of Mexico can be clearly linked in time and space to an order of magnitude increase in sediment deposition rates in deep water in the last few million years due to the incredibly efficient glacial processes for transporting sediment southwards into the catchment area of the Mississippi River.
As for the broader issue of measuring the rates of geologic processes, there is an entire can-of-worms being opened here that involves a myriad of problems that relate to evaluating geologic time. I think of this family of problems as analogous to the uncertainty principle in physics. The shorter the time period over which you desire to know a rate, the harder it is to measure. Every age determination, regardless of method, has an inherent uncertainty. Any measure of geologic rate involves comparing two determinations of age, each with an inherent uncertainty. These uncertainties can be overcome by looking at rates over long periods of time, such that the total uncertainty is small compared to the time scale being investigated. But when you get interested in shorter-term rates of geologic processes, you are always fighting the signal-to-noise ratio of the measurements themselves. Whenever an examination of short term rates suggests much higher values than the longer-term average values - which is often correct in the case in episodic natural systems - I would highly encourage the application or error analysis to make sure that you are not misinterpreting noise, due solely to the inherent uncertainty in the age determinations, as true signal. For those interested in an extensive discussion of the mathematics of these issues, and how to resolve them, I can recommend some work I was involved with many years ago:
Anders, M.H., S.W. Krueger and P.M. Sadler, 1987, A new look at sedimentation rates and the completion of the stratigraphic record: Journal of Geology, v. 95, no. 1, p. 1-14.
Cheers,
Scot
-----Original Message-----
From: Tectonics & structural geology discussion list [mailto:[log in to unmask]] On Behalf Of Hermann Lebit
Sent: Friday, January 13, 2012 10:41 AM
To: [log in to unmask]
Subject: Re: help - velocity of salt tectonics
Scot,
like Frank Peel, colleagues in other companies have undertaken such efforts in various basins. Unfortunately little is published about the results, but let hope some of them will come forward due to our little discussion here.
In average Neogene/ Paleogene displacement rates are surprisingly similar for delta systems in the South Atlantic basin and the GoM and at a magnitude of mm/a, even for deltas without salt. Interestingly they show for two certain time intervals distinguished spikes with displacement rates increase to >10 mm/a. Since these spikes are not restricted to a particular delta (catchment) system a global factor such as climate is evident. Changing weathering and transport condition increased sediment input during these intervals which in turn causes the accelerated gravitational flow. This scenario is by the way in contrast to a recent paper by Brun & Ford (2011) that favors gravitation-driven gliding mainly due to margin tilt.
Hermann
On 1/12/12 3:31 PM, Krueger, Scot wrote:
> Andrea,
>
> The 0.5 cm/yr number I quoted was from an unpublished analysis I had done, but there are published cross sections from which you can calculate similar numbers. The recently published The Salt Mine (AAPG Memoir 99), by Hudec and Jackson, has an interpreted seismic section on page 7 which shows 11 miles of advance on the Sigsbee Escarpment near Saint Malo, based on subsalt cutoffs, since the Miocene/Pliocene boundary (~5 Ma). Doing the quick math on the back of an envelope (check me Frank!) I get about 3.5 mm/yr of advance. If you are looking for a published reference, that may be about as good as I can come up with on short notice. I invite anyone to chime in if they have other published salt advance rates to share, from the GOM or elsewhere.
>
> Scot Krueger
>
> -----Original Message-----
> From: Tectonics& structural geology discussion list
> [mailto:[log in to unmask]] On Behalf Of Andrea Billi
> Sent: Thursday, January 12, 2012 9:32 AM
> To:[log in to unmask]
> Subject: Re: help - velocity of salt tectonics
>
> Ijaz, Scot,
> thanks a lot for your help.
>
> Scot,
> is there a publication reporting the data you mentioned?
>
> thanks
> Andrea
>
>
>
> "Krueger, Scot"<[log in to unmask]> ha scritto:
>
>> A good example of the rapid end of the spectrum would be the salt
>> "surge" of the Sigsbee salt glacier in the central deepwater Gulf of
>> Mexico, which has advanced by up to 25 km in the last 5 Ma, or an
>> average geologic rate of 2.5 cm/yr. The rates in the GOM for an
>> average location and an average time would almost always be below
>> that rate. And since the local behavior at the front appears to be
>> stick-slip over periods of a few million years, the shorter term slip
>> rate during the slipping phase may be somewhat higher. Hope this
>> helps.
>>
>> Scot Krueger
>>
>> -----Original Message-----
>> From: Tectonics& structural geology discussion list
>> [mailto:[log in to unmask]] On Behalf Of Andrea Billi
>> Sent: Wednesday, January 11, 2012 5:09 AM
>> To:[log in to unmask]
>> Subject: help - velocity of salt tectonics
>>
>> Dear All,
>>
>> I was looking for typical ranges of velocities for sedimentary
>> overburdens sliding over a salt layer along passive margins.
>>
>> In models by Gemmer et alii (Basin Research 2004, 16, 199-218) and
>> Albertz et alii (Tectonics 2010, 29, TC4017,
>> doi:10.1029/2009TC002539) I see velocities between a few millimetres
>> to a few centimeters per year, depending on various boundary
>> conditions.
>>
>> Do you know other natural or experimental data concerning these velocities?
>>
>> Thanks a lot
>>
>> Andrea
>>
>> _________________________________________________
>> Andrea Billi (PhD)
>> Consiglio Nazionale delle Ricerche, IGAG, c.o. Dipartimento Scienze
>> della Terra, Sapienza Università di Roma, P.le A. Moro 5, 00185,
>> Rome, Italy.
>>
>> Phone: +39 06-49914955
>> Skype: a.billi
>> Email:[log in to unmask]
>> Web site:http://www.andreabilli.com
>> _________________________________________________
>>
>> Dalla Costituzione della Repubblica Italiana Art. 9: "La Repubblica
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>> Art. 33: "L'arte e la scienza sono libere e libero ne è l'insegnamento."
>>
>> "Non è grave il clamore chiassoso dei violenti, bensì il silenzio
>> spaventoso delle persone oneste." Martin Luther King
>>
>>
>>
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>
> _________________________________________________
> Andrea Billi (PhD)
> Consiglio Nazionale delle Ricerche, IGAG, c.o. Dipartimento Scienze della Terra, Sapienza Università di Roma, P.le A. Moro 5, 00185, Rome, Italy.
>
> Phone: +39 06-49914955
> Skype: a.billi
> Email:[log in to unmask]
> Web site:http://www.andreabilli.com
> _________________________________________________
>
> Dalla Costituzione della Repubblica Italiana Art. 9: "La Repubblica promuove lo sviluppo della cultura e la ricerca scientifica e tecnica."
> Art. 33: "L'arte e la scienza sono libere e libero ne è l'insegnamento."
>
> "Non è grave il clamore chiassoso dei violenti, bensì il silenzio
> spaventoso delle persone oneste." Martin Luther King
>
>
>
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> This message was sent using IMP, the Internet Messaging Program.
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