From your question it is not clear to me if your objective is the identification of human caused elevated heavy metal concentrations in sediments out of concern for the environment and human health, or if you are simply working to understand the geology of a region and are concerned with sample contamination.

If you are looking at environmental contamination, then I would say that in many cases neither global nor regional UCC values will be useful.  In one site investigation we were measuring copper and zinc concentrations in roadside sediments that were far above both global and regional UCC values.  The immediate conclusion might have been that the roadway was the source of this copper and zinc, but that would have required very unusual levels of copper and zinc to be produced by the traffic on the roadway.  I collected local bedrock samples and had them analyzed.  The local bedrock was very enriched in copper and zinc (compared to regional values) and was the obvious source for the elevated levels in the roadside sediments.  UCCs are a good starting point, but need to be supplemented with local bedrock information to truly assess human heavy metal concentrations.

Having said this, the geology of some areas of the world will be such that UCCs will give values that closely match all the bedrock in the area. 

Yes Prof. Bivin. I agree with you. If you have any link or papers with the values you mentioned (just for model reference), it would be much appreciated.

From your question it is not clear to me if your objective is the identification of human caused elevated heavy metal concentrations in sediments out of concern for the environment and human health, or if you are simply working to understand the geology of a region and are concerned with sample contamination.

If you are looking at environmental contamination, then I would say that in many cases neither global nor regional UCC values will be useful.  In one site investigation we were measuring copper and zinc concentrations in roadside sediments that were far above both global and regional UCC values.  The immediate conclusion might have been that the roadway was the source of this copper and zinc, but that would have required very unusual levels of copper and zinc to be produced by the traffic on the roadway.  I collected local bedrock samples and had them analyzed.  The local bedrock was very enriched in copper and zinc (compared to regional values) and was the obvious source for the elevated levels in the roadside sediments.  UCCs are a good starting point, but need to be supplemented with local bedrock information to truly assess human heavy metal concentrations.

Having said this, the geology of some areas of the world will be such that UCCs will give values that closely match all the bedrock in the area. 

Can you also analyse material where you are certain there are no contaminants to establish a baseline for the region's soils / geology? Not sure how feasible this might be and it depends on your key research questions. Any ref. material / CRM needs to be from a suitable source and of a relevant material. 

Thanks Prof. Mathew and Simon. As said by prof. Mathew it will be much useful to take the  near by local bed rock metal concentrations as the baseline values. But still , how to measure the contamination of rock samples giving  a baseline?

Secondly, if I am not wrong, shall I take the lowest concentration of a metal among the measured values in my region of study as a baseline value for that metal? Will it be the least value among various local bedrock samples?

Prof. Simon, as you said we could not be assured of regions of no contamination. At the same time rock contamination may not be a rapid one , as the chemical weathering consumes time. Please give your comments

For environmental studies it is recommended  to use a suitable reference material that bear similar mineralogical and chemical composition of your samples. These can be collected from a pristine area where no human impacts. Recently, we are carrying out a research to establish a geochemical reference material for the Red Sea coastal environments because the nature of Red Sea sediments (carbonate dominated) is completely different from other seas. When we tried to apply UCC or average shale composition in environmental assessment, the results were over- to underestimated. In Ghandour et al (2014; J. Envi. Mon. Assess.) we used the average chemical composition of the deepest sediments in the same area (which we expected to be unpolluted). So I prefer to use a local reference material in environmental studies rather than the general ones.

Thanks prof. It might be. Because our local unpolluted state of crust would not be the same with other virgin regions.thank you

In my opinion those global reference materials like UCC and Average Shale, among others, only should be used when the local background is unknown and there is no possibility to determine it; because you can concluded different things in function of the chosen reference material. Moreover, the concentrations of several metals in the UCC vary from author to author (e.g.: Rudnick & Gao (2003) presents a Cr content for the UCC that doubles the concentration of Cr published in Shaw (1967)).

In my PhD I am trying to assess if there is contamination in some estuarine sediments, and for that aim I calculated the local geochemical background from the deepest levels (pre-industrial sediments) of some cores. And in this case, even inside of the same waterbody, the geochemical background in its upper region differs from geochemical background obtained for the lower region.

Thank you prof.sandra

You find an article that I published in 1999, you may be helpful:

https://www.researchgate.net/publication/258848016_Assessment_of_the_state_of_pollution_by_heavy_metals_in_the_surficial_sediments_of_Algiers_Bay#share

Article Assessment of the state of pollution by heavy metals in the ...

Thank you Benamar.

please make your question more clear.The ref concentration are appeared in most clin chem book