PRINCIPAL 



INVESTIGATOR(S) JoLynn Carroll 



Geotech, Inc. 



P.O. Box 14000 



Grand Junction, CO 81502 



PROJECT TITLE EXTENSION OF 210 PB GEOCHRONOLOGY WITH INVERSE 



NUMERICAL TECHNIQUES 



AMOUNT OF FUNDING FY 1994: $46 K 



SUMMARY OF GOALS 



The principal goal of this research is to significantly improve on the determination of 

 sediment accumulation rates over conventional techniques. During the first two years of the 

 OMP, the basic modeling procedure was successfully developed and tested. The goal now is to 

 apply the procedure to determine age distributions with sediment depth for radioisotope profiles 

 collected during the field portion of the OMP. 



A) Assessing the Effect of Sediment Mixing on Age Determinations - Mixing caused by 

 biological or physical processes, distorts or erases the signature of radioisotope decay in sediment 

 profiles. Numerous studies have been conducted to understand mixing processes and from these, 

 researchers have developed a variety of mathematical formulations to simulate mixing effects on 

 radioisotope profiles. These models will be applied to a variety of synthetic radioisotope data 

 profiles having known age distributions. The profiles will then be analyzed by the numerical 

 procedure to determine the resultant effects on the age determinations caused by the different 

 mixing models. Profiles will be created to represent a range of variable tracer strengths and 

 variable sediment accumulation rates. These results will allow us to better define the practical 

 limitations of determining sediment ages from disturbed radioisotope distributions. 



B) Determining the Accuracy of Sediment Ages - Applying the procedure to a given 

 radioisotope profile, we are able to determine a distribution of sediment ages at each sediment 

 depth. The incorporation of probability/risk data interpretation techniques will allow us to 

 rigorously define the accuracy limitations of the model determined sediment ages. This 

 information will then be used to evaluate when the expenditure of resources for additional data 

 collection will significantly improve the accuracy of a given age distribution. 



C) Data Sectioning - The determination of accumulation rate distributions with depth in a 

 sediment column exhibiting highly variable radioisotope concentrations is tedious and 

 time-consuming. We must section the data into several pieces and analyze the pieces separately. 



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