Porosity variation in chalk

Vertical porosity variations in chalk are generally assumed to result from either a vaguely defined combination of primary sedimentary and diagenetic processes or solely to diagenetic processes. In this study, image analysis of backscatter electron images of polished samples and geochemical microprobe mapping were applied to measure the porosity variation in a limited number of chalk samples. Microscope data indicate that in all cases the chalk has been subjected to diagenetic processes, but our data suggest that the variations in porosity originate in primary sedimentary differences.