Carbonate grain-size distribution in hemipelagic sediments from a laser particle sizer

Laser grain-sizer instruments provide the opportunity to study the grain si ze distribution of sediments across a wide size range in a short time. Auto matic measurements can therefore be made, on a routine basis, for a great n umber of samples. Oceanic studies have proved the utility of these methods in characterizing both climatic changes and changes in sediment provenances . In addition, carbonate content is estimated either directly by CaCO3 meas urement, by visual observations, or by proxies such as sediment color refle ctance. Nevertheless, the grain size distribution of the carbonate fraction is still a matter of speculation, and only optical observations can distin guish the nature of each carbonate fraction. Here we present the improvemen ts on a method to study rapidly, with a high resolution, the grain size dis tribution of the carbonate fraction by use of a laser grain-sizer. We descr ibe the basic methodology and apply it to an example from the Pleistocene o f the Northern Atlantic Ocean.