Use of electrical conductivity to analyze depositional environments: Example of a Holocene delta sequence on the Nobi Plain, central Japan

The usefulness of electrical conductivity (EC) of stirred Holocene deltaic sediments from three cores from the Nobi Plain, Japan, was assessed as a proxy for marine transgression and regression. Lack of correlation of EC with mud content for the sediments with >20% mud suggested that permeability was a negligible factor. Marine deposits showed high EC (>0.9 mS/cm), terrestrial deposits low EC (<0.4 mS/cm), and brackish deposits intermediate. Because it was positively correlated with the percentage of marine diatom species, EC in inner-bay deposits primarily reflected salinity. In the YM core (the youngest of the three cores), EC of the inner-bay deposits was weakly positively correlated with clay content, which controls pore water content. EC of inner-bay clayey deposits was generally higher in YM than in KZN, suggesting that the lower EC in older clayey sediments results from compaction. These findings suggest that the EC values of fine sediments initially record salinity but may decrease gradually over time under the influence of compaction. Thus, to reconstruct the original salinity, the effects of compaction and of grain size distribution-and especially clay content-should be evaluated.