Accounting for core shortening in age-dpeth modelling

[Katherine Holt]

Hi All

This is more of a general question than an oxcal one, but I figured this community would be the best place to ask it.

Are there any models available to deal with shortening in lake and peat cores? For example, the corer is driven into the sediments for a full metre, but only 0.9m of sediments is actually captured. I've read lots on observation and explanation of this phenomenon, but nothing on how it can be modelled and corrected for in an age-depth model.

Any help would be most appreciated.

Thanks!

Kat

[Rayfo...@aol.com]

Hi Kat,

 

Now coring is not something I've dealt with, however since there have been no responses so far to your query perhaps this may help:

 

Characteristics of and corrections for core shortening in unconsolidated sediments

Journal of Coastal Research

By:

Robert A. Morton and William A. White

And from their abstract:

" Minor artificial displacement of sediment depths can alter plots of physico-chemical parameters and can significantly influence calculated rates of sedimentation and other depth-dependent statistical relationships. This study (1) demonstrates how plots of interval shortening and cumulative shortening can be used to characterize the distribution of shortening at depth and (2) presents a simple equation for stratigraphic restoration so that core observations and analyses are corrected to their original depths."

 

regards

 

Ray

 

 

 

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[Holt, Katherine]

Hi Ray

Thanks very much for taking the time to send this through.

Much appreciated!

Kat

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[Gold]

Another method that I prefer, is to do nothing about this.  The reason 
is that practically speaking, the core compression and stretching can be 
highly variable, at least in the turbidite lithologies that I work in.  
So I suggest that it is not that likely that it could be modeled in a 
way that would do more than adding noise to the model.  But, this 

variability then becomes changes in sed rate in the model, 
which the models can handle.  So, just as GPS cannot tell you the 
discrete sources of crustal motions, only the result, changes in sed rate and 
core deformation are rolled together as variations in time.  If you 
don't care about the sed rate, but only care about the ages of events in 
the stratigraphy, then this results in a simpler problem not dependent 
on a secondary and potentially ad hoc models.  On the other hand, if you 
care about vertical position in the absolute, or sed rates, then this 
won't work and you'd have to try to model it.

This is discussed a bit in this paper:

http://pubs.usgs.gov/pp/pp1661f/ 

  Dr. Chris Goldfinger
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