ABSTRACT

Grain size fractions as small as 0.5µ can be isolated by sedimentation in a beaker, provided the experimental conditions are rigidly controlled. This method can be used in any geochemical laboratory because very simple apparatus is required. Important genetic conclusions may be demonstrated from the distribution of boron in different size fractions of sediments.

The finest size fractions, which can be shown by X-ray diffraction analysis to consist essentially of illite, are rich inboron. A small part of the boron in sediments is contributed by tourmalne, but this is absent from the finest size fractions. Previous workers have shown that the concentration of boron in illite is closely related to the inferred salinity at the time of deposition and results of this investigation substantiate these conclusions. Preliminary studies in the Lower Carboniferous rocks of northern England indicate that boron concentration may be a sufficiently sensitive salinity index to detect very small changes in a marine basin. It is demonstrated that boron concentration may also be controlled by the grain size of illite.